Short and Ultra-Short Implants [1 ed.] 2018013422, 2018014232, 9780867157864, 9780867157857

Table of contents :
Short and Ultra-Short Implants Edited by Douglas Deporter
Frontmatter
Library of Congress Cataloging-in-Publication Data
CONTENTS
FOREWORD
PREFACE
ACKNOWLEDGMENTS
CONTRIBUTORS
AUTHOR’S NOTE
Chapter 1: Why Avoid Using Short Implants?
Success Rates
Implant Stress Distribution and C/I Ratio
Risk of Bone Loss and Peri-implantitis
Implant Length and Human Factors
Conclusions
References
Chapter 2: The Performance of Short and Ultra-Short Implants
Implant Macro Design
Surface Features
Crown-to-Implant Ratio
Implant Splinting versus Single-Crown Implants
Modified Surgical Procedures
Keratinized Gingiva
Success Rates of Short and Ultra-Short Implants
Conclusion
References
Chapter 3: A Single Practitioner’s 20-Year Experience with Short Implants
Long-Term Private Practice Study
Results
Risk Factors Related to Short Implant Failure
Guidelines For Using Short STL Implants
Conclusion
References
Chapter 4: Using Short Implants for Overdenture Support
Literature Review
Guidelines for Using Short Implants in the Resorbed Anterior Mandible
Case Study
Conclusion
Acknowledgments
References
Chapter 5: Threaded Implants in the Posterior Maxilla
Sinus Elevation Procedures
Short Implants
Clinical Examples Using Short and Ultra-Short MRTIs
Conclusion
Acknowledgments
References
Deporter_CH06
Chapter 6: Threaded Implants in the Atrophic Posterior Mandible
Limitations with Vertical Alveolar Ridge Augmentation
Short Implants
Patient Selection and Recommended Treatment Guidelines
Conclusion
References
Chapter 7: Press-Fit Sintered Porous-Surfaced Implants
SPSI Macro Design and Surface Features
Clinical Scenarios for Successful SPSI Placement
Challenges with SPSIs
BAOSFE Technique
Challenges with BAOSFE
Case Study
Guidelines for Successful Outcomes with SPSIs
Conclusion
References
Chapter 8: Plateau Root Form Implants
PRF Implants in the Posterior Maxilla
C/I Ratio and Force with PRF Implants
Short PRF Implants in the Mandible
Tight Interdental Spaces
Case Study: Ultra-Short, Narrow-Diameter PRF Implant
Guidelines for the Successful Use of PRF Implants
Conclusion
References
Chapter 9: Ultra-Wide Threaded Implants for Molar Replacement
Considerations in Using Single Molar Implants
Outcome with Short Versus Standard-Length Implants
The Short and Wide Implant Combination
Treatment Protocols with Sample Cases
Conclusion
References
Chapter 10: The Way Forward
References
Deporter_Index

Citation preview

Short and Ultra-Short Implants

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SHORT and ULTRA-SHORT

IMPLANTS Edited by

Douglas Deporter, dds, phd Professor

Faculty of Dentistry University of Toronto Toronto, Ontario

Berlin, Barcelona, Chicago, Istanbul, London, Milan, Moscow, New Delhi, Paris, Prague, São Paulo, Seoul, Singapore, Tokyo, Warsaw

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To my sister, Patti Jane, who died as a child 56 years ago and is always in my thoughts.

Library of Congress Cataloging-in-Publication Data Names: Deporter, Douglas, editor. Title: Short and ultra-short implants / [edited by] Douglas Deporter. Description: Hanover Park, IL : Quintessence Publishing Co Inc, [2018] | Includes bibliographical references and index. Identifiers: LCCN 2018013422 (print) | LCCN 2018014232 (ebook) | ISBN 9780867157864 (ebook) | ISBN 9780867157857 (softcover) Subjects: | MESH: Dental Implantation--methods | Dental Implants | Dental Prosthesis Design Classification: LCC RK667.I45 (ebook) | LCC RK667.I45 (print) | NLM WU 640 | DDC 617.6/93--dc23 LC record available at https://lccn.loc.gov/2018013422

97% © 2018 Quintessence Publishing Co, Inc Quintessence Publishing Co Inc 411 N Raddant Road Batavia, IL 60510 www.quintpub.com 5 4 3 2 1 All rights reserved. This book or any part thereof may not be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, or otherwise, without prior written permission of the publisher. Editor: Marieke Zaffron Design: Sue Zubek Cover Design and Production: Angelina Schmelter Printed in China

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CONTENTS Foreword  vi Preface  vii Acknowledgments  ix Contributors  x

1

Why Avoid Using Short Implants?  1

2

The Performance of Short and Ultra-Short Implants  7

3

A Single Practitioner’s 20-Year Experience with Short Implants  31

4

Using Short Implants for Overdenture Support  43

5

Threaded Implants in the Posterior Maxilla  59

6

Threaded Implants in the Atrophic Posterior Mandible  75

7

Press-Fit Sintered Porous-Surfaced Implants  91

8

Plateau Root Form Implants  113

9

Ultra-Wide Threaded Implants for Molar Replacement  125

10

The Way Forward  149 Index  152

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CHAPTER # | Chapter Title

FOREWORD In many clinical situations, placing what have been considered standard-length dental implants can be difficult or impossible due to anatomical limitations such as proximity of the mandibular canal, pneumatization of the maxillary sinus, and alveolar ridge deficiencies. The health, age, and willingness of the patient to undertake invasive treatments can all be additional barriers. Of course, there are a number of surgical procedures available to facilitate future implant placement in patients with advanced alveolar ridge resorption. More complex approaches include the use of autogenous inlay or onlay bone grafts harvested intra- or extraorally, distraction osteogenesis, zygomatic arch implants, transposition of the inferior alveolar nerve, guided bone regeneration, and various maxillary sinus cavity manipulations. However, these approaches are case sensitive, technically demanding, time consuming, and stressful, not to mention that they increase postoperative morbidity as well as the total cost and duration of the therapy. The use of short and ultra-short implants is currently able to offer the best and least costly option in many situations, but some clinicians still refuse to accept their suitability. This book is the most comprehensive presentation to date on the use of short and ultra-short

implants, and it will give dentists a better understanding of their appropriate application in solving clinical situations from restoring a single tooth to fully edentulous cases. An evidence-based approach in the early chapters of the book sheds light on the long-term performance of various short and ultra-short implant designs, attempting to address concerns of more conservative clinicians who—from personal experience or the opinions of others—feel that such implants are more likely to fail than implants of standard lengths. I foresee that going forward, this book will offer the scientific community a further chance to debate and finally embrace this modern implant treatment approach, and I would like to thank the authors and congratulate them. I feel confident that this text will make a significant contribution to improving our patients’ health and quality of life—goals that all clinicians aim to achieve.

Tiziano Testori, md, dds Founder and Scientific Director Lake Como Institute Como, Italy

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Running A Head Goes Here

PREFACE My first encounter with Prof P-I Brånemark was during a site visit that my colleagues and I made to Göteborg in the fall of 1979. The purpose of this visit was to determine whether it would be appropriate for our faculty at the University of Toronto to replicate a prospective clinical investigation of the Brånemark-type machineturned threaded implant prior to its formal introduction to North America. The team leader was Prof George Zarb, our head of prosthodontics at the time. And while I ultimately did not participate in this study, I left Göteborg with a definite interest in the field that was soon to flourish—implant dentistry. Following the onset of the so-called Toronto Study,1 the concept of osseointegration was introduced to select academic oral surgeons and prosthodontists at a meeting in Toronto in 1982, after which began the quest to more fully understand bone-to-implant fixation and how best to achieve it.2 Thousands—if not tens of thousands—of basic animal and human clinical studies have since been published, and yet there continues to be much more to learn in the field. As it happened, around the time of the Toronto meeting, our faculty was serendipitously joined by none other than Prof Bob Pilliar, the biomaterials scientist and engineer who had invented the cementless hip implant a decade before.3 The cementless hip implant consisted of a solid metal implant core onto which a porous surface multilayer of spherical metal beads of defined size range was secured using a high-temperature, carefully controlled sintering process. This surface topography promoted bone ingrowth into the porous regions, leading to a threedimensional micromechanical interlocking (or interdigitation) of bone with the porous implant surface. Up until that time, most contemporary hip implants had been secured at placement using bone cement, an acrylic grout material (polymethyl methacrylate) introduced

from the dentistry field. The problem, however, was that with time in function the cement was prone to breaking down. This was due primarily to relative micromovements at the cement-to-implant or cement-to-bone interface, resulting in release of fine wear debris that resulted in endosteolysis, bone loss at the interface, and implant loosening. This was inevitably followed by the need for replacement implant surgery. (Interestingly, when orthopedic surgeons were presented with a cemented hip implant that had become loose, they referred to it as being in need of “revision”— thereby avoiding the unpleasant term failure. If only we as dentists could also have this advantage of never having failures!) Prof Pilliar and I attended the Toronto meeting in 1982 with others in our faculty and afterward started to think about alternative designs for endosseous dental implants. Specifically, we began wondering if the sintered porous-surfaced concept could be translated from orthopedics to dentistry and whether this would offer any advantages over a machine-turned threaded implant. We set out immediately to write grant proposals, and in 1983, we were fortunate to gain generous funding from a Canadian federal research agency (Medical Research Council of Canada) to pursue this idea. We undertook studies first in animals and later (starting in 1989) in human clinical trial investigations. What we soon came to realize was that the sintered surface feature of the dental implant that we had conceived provided a much stronger bone-to-implant interface than a threaded implant with a machine-turned surface (ie, resistant to shear, tensile, and compressive interface forces).4 From that point began our premise that sintered porous-surfaced dental implants (SPSIs) could function well in short lengths (as short as 5-mm designed

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intrabony length).5 By the early 1990s, the United States Food and Drug Administration had reviewed and given approval for SPSIs to be tested in the United States by a small group of dentists who were already highly experienced in implant dentistry. However, the catch was that based on their previous experiences with other dental implant designs, these clinicians felt that longer implant lengths would be needed to improve the likelihood of success in their own patients. So the company licensed by the University of Toronto to produce the SPSI created a 12-mm-long version—that being the longest one possible given that the design included a 5-degree taper angle. However, ongoing human clinical trials have confirmed that the original shorter lengths worked as well, if not better, than that 12-mm length.6 It is now well over 25 years since my colleagues and I began reporting that short dental implants (≤ 8 mm) predictably perform well in both edentulous and partially edentulous patients. Finally, the floodgates have opened and many well-respected clinical investigators have begun to report good outcomes with short moderately rough threaded implants both with and without calcium phosphate nanocoatings. Even ultrashort implants (< 6 mm) are coming into use, and as they do, we will continue to unravel the tale of two lengths (standard versus short and ultra-short).7 The authors who I selected to participate in this book all have considerable experience with short and ultrashort implants and continue to challenge the false tenet that they are used with greater risk than much longer ones. However, it is unwise for beginners in the use of short and ultra-short endosseous implants to assume

that they are in any way less difficult than those of more traditional lengths because they most certainly are not. Nevertheless, it is my hope that we have presented the topic effectively and in sufficient detail for clinicians to consider short implants as a viable treatment option for their patients and have an increased probability of success when they choose this approach.

References 1. Zarb GA, Schmitt A. The longitudinal clinical effectiveness of osseointegrated dental implants: The Toronto study. Part I: Surgical results. J Prosthet Dent 1990;63:451–457. 2. Zarb GA. Proceedings of the Toronto Conference on Osseointegration in Clinical Dentistry. St Louis: Mosby, 1983. 3. Pilliar RM. Porous-surfaced metallic implants for orthopedic applications. J Biomed Mater Res 1987;21(A1 suppl):1–33. 4. Deporter D, Watson PA, Pilliar RM, Chipman ML, Valiquette N. A histological comparison in the dog of porous-coated vs. threaded dental implants. J Dent Res 1990;69:1138–1145. 5. Renouard F, Nisand D. Impact of implant length and diameter on survival rates. Clin Oral Implants Res 2006;17(suppl 2):35–51. 6. Deporter D, Todescan R, Riley N. Porous-surfaced dental implants in the partially edentulous maxilla: Assessment for subclinical mobility. Int J Periodontics Restorative Dent 2002;22:184–192. 7. Neugebauer J, Nickenig HJ, Zöller JE; Department of Cranio-maxillofacial and Plastic Surgery and Interdisciplinary Department for Oral Surgery and Implantology; Centre for Dentistry and Oral and Maxillofacial Surgery, University of Cologne. Update on short, angulated and diameterreduced implants. Presented at the 11th European Consensus Conference, Cologne, 6 Feb 2016.

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ACKNOWLEDGMENTS First, I of course wish to thank the contributors to this book who were equally excited as I to share their experiences and knowledge on the previously controversial topic of short and ultra-short dental implants. Their generosity and enthusiasm helped to keep me focused on the project whenever I found it to be daunting. I would also like to thank my colleague Howard Tenenbaum who, as former Head of Periodontics in our faculty, encouraged me to continue my work at a time when others nearby were so heavily critical. I need to acknowledge Dr Daniel Cullum who invited me several years ago to coedit a book with him on minimally invasive dental implant surgery. Working on and helping to complete that earlier book gave me the incentive and courage to undertake the present endeavor as sole editor. Many thanks are due to Jeff Comber, the senior photographer in the Faculty of Dentistry at the University of Toronto, for his tireless efforts to provide and scrutinize many of the images presented in the book. I also wish to thank the welcoming and helpful staff at Quintessence for their assistance in making the project as stress-free as possible.

When I first undertook patient trials of a short dental implant with my coinvestigator Philip Watson in 1989, I had no previous clinical experience in implant dentistry and no idea what to expect. The consensus among “experts” at the time was that implants less than 10 to 13 mm in length were at very high risk of failure, and I was reminded of this for many years by widespread skepticism whenever I presented the results of our work. Robert Summers’s innovation of transcrestal sinus elevation in the mid 1990s boosted my enthusiasm. Using his approach to sinus grafting, I soon learned that short and ultra-short implants could be as successful in the resorbed posterior maxilla as in the resorbed posterior mandible. It is of great satisfaction to me that, after almost 30 years of trying to convince the dental community that implants need not be long to be successful, the time has come for short and ultra-short implants to take their place in routine clinical practice. The contributors to this book have made and will continue to make this achievement a reality. And, by the way, they were all a pleasure to work with.

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CONTRIBUTORS Murray Arlin, dds

Private Practice Limited to Periodontics and Implantology Toronto, Ontario

Pierluigi Balice, dds, mdsc Resident Department of Periodontology School of Dental Medicine University of Connecticut Farmington, Connecticut

Carlo Barausse, dds

Doctoral Student Department of Biomedical Science and Neuromotor Sciences University of Bologna Bologna, Italy

Hugo De Bruyn, dds, msc, phd

Professor Department of Periodontology, Oral Implantology, Removable and Implant Prosthetics Faculty of Medicine and Health Sciences Ghent University Ghent, Belgium

Douglas Deporter, dds, phd Professor Faculty of Dentistry University of Toronto Toronto, Ontario

Pietro Felice, md, dds, phd

Researcher Department of Biomedical Science and Neuromotor Sciences University of Bologna Bologna, Italy

André Hattingh, bchd, mchd

Private Practice Limited to Periodontics and Implantology Sevenoaks, Kent United Kingdom PhD Student Department of Periodontology, Oral Implantology, Removable and Implant Prosthetics Faculty of Medicine and Health Sciences Ghent University Ghent, Belgium

Henny J. A. Meijer, dds, phd

Professor Department of Dentistry, Oral Surgery, and Medicine Faculty of Medical Sciences University of Groningen Groningen, The Netherlands

Vittoria Perrotti, dds, phd

Research Fellow Department of Medical, Oral and Biotechnological Sciences School of Medicine and Health Sciences University of Chieti-Pescara Chieti, Italy

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Adriano Piattelli, md, dds

Professor of Oral Pathology and Medicine Department of Medical, Oral and Biotechnological Sciences School of Medicine and Health Sciences University of Chieti-Pescara Chieti, Italy Professor and Chair of Biomaterials Engineering Catholic University San Antonio de Murcia Murcia, Spain

Roberto Pistilli, md

Resident Department of Oral and Maxillofacial Surgery San Camillo Hospital Rome, Italy

Gerry M. Raghoebar, dds, md, phd

Professor Department of Oral Disorders, Oral Surgery, and Special Dentistry Faculty of Medical Sciences University of Groningen Groningen, The Netherlands

Franck Renouard, dds

Antonio Scarano, dds, md

Associate Professor of Oral Surgery Department of Medical, Oral and Biotechnological Sciences School of Medicine and Health Sciences University of Chieti-Pescara Chieti, Italy

Kees Stellingsma, dds, phd

Assistant Professor Department of Oral Disorders, Oral Surgery, and Special Dentistry Faculty of Medical Sciences University of Groningen Groningen, The Netherlands

Rainier A. Urdaneta, dmd

Private Practice Limited to Prosthodontics Worcester, Massachusetts

Stefan Vandeweghe, dds, phd

Associate Professor Department of Periodontology, Oral Implantology, Removable and Implant Prosthetics Faculty of Medicine and Health Sciences Ghent University Ghent, Belgium

Private Practice Limited to Oral and Implant Surgery Paris, France

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AUTHOR’S NOTE

There has been discussion over the years on exactly what constitutes a short or ultra-short implant. The classification used in this book is based not on total implant length but on the designed intrabony length (DIL). This is the part of the implant responsible for osseointegration and does not include collars or transgingival segments that are not meant to fixate to bone. A standard-length implant is defined as one with a DIL greater than 8 mm. Implants with a DIL between 6 and 8 mm are considered short, while those with a DIL less than 6 mm are considered ultra-short. Please also note that all implant dimensions in this book are given as length × width.

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1

Why Avoid Using Short Implants? Franck Renouard, DDS

I

t has been more than 50 years since the first successfully osseointegrated implant procedure was performed by Dr Per-Ingvar Brånemark, and yet controversy remains regarding the optimal shape and size of solid endosseous root-form dental implants. There are few medical fields with this degree of uncertainty despite the wealth of relevant scientific data. The recommended lengths of dental implants are a striking example. A quick search on PubMed in December 2016 identified 5,400 articles mentioning short implants, but the majority of articles focused on more complex solutions, relegating short implants to the rank of emergency fallback solutions only. Consequently, the mindset persists that the longer the implant, the more successful it will be both in the short and long term. Advanced, costly, and technique-sensitive collateral procedures often need to be performed to be able to use standard-length implants, such as autogenous (and other) bone block grafting, vertical alveolar ridge augmentation, mandibular nerve repositioning, and open sinus grafting. Interestingly, however, the first implants developed and tested successfully by Brånemark in the 1960s were all under 8 mm in length, and some were even shorter than 5 mm. The reluctance of clinicians to use short implants derives largely from their reading of statistical assessments of implant failure while neglecting other considerations like the patient’s sex, the size of the patient’s mouth, the risk of complications with more complex procedures, and the feasibility of such procedures being undertaken by nonspecialists in a private practice setting. If the intention is to provide the simplest, least invasive, least complicated, and least stressful procedure, it is worth asking: why should we avoid using short implants? Arguments commonly put forward include the following:

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CHAPTER 1 | Why Avoid Using Short Implants?

• Their success rate may be lower compared with standard-length implants. • Stress distribution with loading of short implants may result in increased biomechanical risk due to the poor crown-to-implant (C/I) ratio. • There may be a greater risk of failure if crestal bone loss occurs due to mechanical overload or inflammation and infection (eg, mucositis or peri-implantitis). • It is difficult to move away from more familiar ways of doing things. This chapter addresses these concerns.

Success Rates Are the success rates for short implants worse than those of procedures that use standard-length implants? The poor reputation of short implants is—for the most part—based on early implant literature using the original Brånemarktype implant: A commercially pure titanium threaded screw with a machine-turned (ie, minimally rough) surface finish.1–4 In each of these reports, the authors stated in their abstracts and/or conclusions that failure of short (ie, ≤ 10 mm) implants was higher than that of longer ones. This was enough to establish a dogma that was not easily challenged. However, a closer reading of these articles reveals that although the failure rates with short implants were higher, the difference compared with longer implants was less significant than the authors implied. For example, in the report by Friberg et al2 examining 4,641 implants, the failure rate of short maxillary implants covering everything from single crowns to full-arch reconstructions in fully edentulous patients was only 7%. Looking only at the results for partially edentulous patients in this study, the failure rate of short implants plummeted to 1.3%. Moreover, the authors stated that most of the failures were early—once short implants had been fully integrated in bone, they behaved just like longer implants. In 1991, these clinicians were not only using cylindric, machined-surface implants; they were also following a standard and identical

drilling protocol for both short and longer implants and regardless of the bone density encountered. Likewise, a closer look at the report by Lekholm et al4 shows the failure rate for short implants as not significantly different from that of procedures using longer implants. In the study by van Steenberghe et al,1 short implants were separated into those with lengths of 7 mm and 10 mm, and the 7-mm implants had a higher success rate than those with lengths of 10 mm. The adaptation of these findings to comply with the general consensus at the time (ie, that implants shorter than 10 mm fail more often despite contrary objective data) is termed confirmation bias. This type of bias is a very common cognitive behavior: Once a decision has been made or a “fact” learned, the human brain will always look for data that corroborate the preconceived notion in question and dismiss data challenging these notions. It is an unfortunate but frequent occurrence in many scientific fields.5 As implant research continued, the influences of length and diameter on implant survival and success have been studied using a more objective approach to scientific publications: reviewing the facts prior to drawing conclusions. For instance, Renouard and Nisand6 published a systematic review of articles published between 1990 and 2005. Using Medline resources, papers were initially selected if implants were placed in healed sites in human subjects and if the studies provided (1) relevant data on implant lengths and diameters, (2) implant survival rates that were either clearly stated or calculable, and (3) clearly defined criteria for implant failure. A total of 34 studies fulfilled these inclusion criteria, and of these, 13 were devoted to short implants. The investigators in these 13 studies were able to report outcomes for a total of 3,173 implants in 2,072 patients. Implants from a number of manufacturers were included, and the mean implant length was 7.9 mm. Observation periods ranged from 0 to 168 months with a median period of 47.1 months. A total of 9.5% of the study patients were reported as having dropped out, leading to a mean implant survival rate

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Implant Stress Distribution and C/I Ratio

of 95.9%, which is more or less the same as for longer implants of the time. However, some authors reported noticeably lower success rates than this mean, and readers need to understand why. In 2005, Hermann et al7 analyzed a large number of failed implant procedures and reported that short implants had usually been used in sites with low bone volume and density, whereas longer implants were nearly always placed in denser bone. This observation challenges implant length as the cause of failure. For example, did an implant in the posterior maxilla fail because of its length, or was the result caused by low bone density and the clinician’s failure to appropriately modify osteotomy preparation? If a short implant is to be eliminated as a treatment choice, the clinician and patient need to be aware of the likely risks, complications, and possibility of implant failure if longer implants are to be used in conjunction with maxillary sinus grafting or a vertical ridge augmentation procedure. Recent research addressed some of these issues using randomized controlled clinical trials in humans comparing short implants alone with longer implants placed in previously grafted bone. Unlike a lot of the early work with short implants, the investigators employed moderately rough (eg, particleblasted or acid-treated) rather than machine-surfaced implants.8 In resorbed posterior mandibles, Esposito et al9 provided a 3-year report on the use of 6.3-mm-long implants versus 9.3-mm-long implants placed in sites where earlier vertical ridge augmentation had been done using interpositional block xenografts. Each patient received two or three implants that were allowed submerged healing and ultimately restored with splinted fixed prostheses. Two short implants failed and three standard-length implants failed, all in different patients. However, there were significantly more complications in the augmented patients with standard-length implants (22 complications in 20 augmented patients) than those with short implants (5 complications in 5 patients). In a similar vein, Pieri et al10 compared 6- to 8-mm implants with 11-mm implants placed in conjunction

with a lateral window sinus grafting procedure. After a mean functional time greater than 3 years, the implant survival rates were similar, but again there were significantly more surgical complications with the sinus group (10 complications in 9 patients with standard-length implants compared with 1 complication in the short implant group). Choosing not to use short implants because of their supposed inferior performance then appears not to be a wise decision. Indeed, it seems clear that short implants should be the treatment of first choice in sites with low bone volume unless there are other considerations (eg, esthetics) that would contraindicate short implant use.

Implant Stress Distribution and C/I Ratio In the 1990s, articles began to appear on the impact and patterns of mechanical stress distribution with functioning dental implants. Using finite element analyses, as early as 1992 Meijer et al11 predicted that when dental implants are subjected to lateral (ie, off-axis) loading, stress will be chiefly concentrated in crestal bone surrounding the neck regions of implants. It was concluded that changing implant length had no significant impact on stresses being received by peri-implant crestal bone. Similar conclusions were later drawn by Pierrisnard et al.12 In line with basic mechanical principles, the greater the angle at which a force is received, the greater the stress concentration at the implant neck, with this stress diminishing toward the implant apex. The ratio of crown length to tooth root length (C/R) has long been considered a key factor in designing traditional, tooth-supported prostheses. Having a C/R ratio greater than 1 was considered a risk factor for failure, and this precept was initially thought to apply to dental implant performance as well. With the anticipated implant C/I ratio significantly greater than 1, many clinicians preferred to use collateral surgical techniques to allow for the placement of longer implants.

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CHAPTER 1 | Why Avoid Using Short Implants?

In the posterior mandible, for example, some clinicians have gone as far as to recommend lateralization of the mandibular nerve to enable longer implants to be placed—even though no prospective trials have been reported comparing this risky procedure with short implants. However, numerous authors have now shown that C/I ratio is not an issue for the most part, meaning that once again short implants may be the treatment of first choice.13–15 This is not to say that there are no upper limits for C/I ratio because there certainly may be; however, whether an implant is 5 mm long or 15 mm long, it will ultimately experience the same stress patterns and minimize the importance of C/I ratio on biologic complications. Nevertheless, a long implant-abutment complex will increase the length of the lever arm (measured to the implant neck) and therefore increase the risk of prosthesis overload. This means that selection of the number of short implants used and the use of splinting are important considerations.

Risk of Bone Loss and Peri-implantitis The long-standing Albrektsson criteria16 for dental implant success continue to be used in clinical practice, including the recommendation that bone loss should not be greater than 1.2 mm during the first year of implant function and not greater than 0.2 mm annually thereafter. The majority of successful implants, however, do not show progressive bone loss with time in function, but rather reach a steady state after which no detectable bone loss will occur. Therefore, the Albrektsson criteria have helped create the misconception that in the space of a few years, there could be sufficient bone loss around a short implant for it to lose integration. A number of investigators have demonstrated that the pattern of bone loss with time with short implants appears similar to that experienced by longer ones.17 In contrast, Naert et al18 and Rokni et al15 determined that bone loss was greater with standard-length implants than with short

ones. This is assuming of course that the short implants were placed using appropriate surgical protocols and with attention to the fact that final buccal bone needs to be of sufficient thickness (ie, greater than 2 mm) to minimize its postoperative resorption with exposure of rough implant surfaces.19 Should such exposure occur, there is always the risk of bacteria-induced inflammatory bone loss (ie, peri-implantitis). This condition is an inflammatory process that generally leads to further and often progressive bone loss around the implant. This latter bone loss can be stabilized by remedial procedures in some cases, but a short implant in this condition would certainly be at greater risk of loss of integration than a longer one.

Implant Length and Human Factors Placing an implant is a stressful procedure for most practitioners, especially if it is done infrequently. The more complex the surgical procedure the practitioner has to undertake, the more stress-inducing both before and during the procedure. Studies in the field of general surgery have demonstrated that more complex procedures result in a greater likelihood of complications arising from human error.20 Complex procedures magnify the impact of human factors. As far as is possible, it is wise to use the simplest and least invasive procedures possible to reduce the likelihood of human error, also called nontechnical errors. Performing a lateral window sinus floor elevation or grafting procedure to be able to place a long implant can create a stress level significant enough to impair the clinician’s ability to concentrate on what matters most for implant placement: that the implant is correctly positioned. Studies from the field of aviation offer indisputable evidence that human mental resources are finite regardless of the action being performed. The greater the stress, the harder it is to stay focused for any length of time on what really matters.21,22 Physiologic changes linked to stress prevent the surgeon from holding to

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References

a line of thinking or respecting a protocol that he or she would adopt or implement without question in less stressful scenarios. Opting for simpler courses of action will make it easier to remain focused on the key task at hand. Susceptibility to stress varies between individuals, but electing to use short implants could help reduce stress and assist the clinician in making intraoperative decisions.

Conclusions Short implants are not necessarily inferior to long implants, but nor are they necessarily more infallible than long implants. The objective is not to always choose short implants but to always include them for consideration when making a decision about which approach to take. Short implants should be seen as a reliable alternative with a low risk of complications. They are suitable in many circumstances and offer a workable, reliable solution.

References 1. van Steenberghe D, Lekholm U, Bolender C, et al. Applicability of osseointegrated oral implants in the rehabilitation of partial edentulism: A prospective multicenter study on 558 fixtures. Int J Oral Maxillofac Implants 1990;5: 272–281. 2. Friberg B, Jemt T, Lekholm U. Early failures in 4,641 consecutively placed Brånemark dental implants: A study from stage 1 surgery to the connection of completed prostheses. Int J Oral Maxillofac Implants 1991;6:142–146. 3. Jemt T, Lekholm U. Implant treatment in edentulous maxillae: A 5-year follow-up report on patients with different degrees of jaw resorption. Int J Oral Maxillofac Implants 1995;10:303–311. 4. Lekholm U, Gunne J, Henry P, et al. Survival of the Brånemark implant in partially edentulous jaws: A 10-year prospective multicenter study. Int J Oral Maxillofac Implants 1999;14:639–645.

5. Kapur N, Parand A, Soukup T, Reader T, Sevdalis N. Aviation and healthcare: A comparative review with implications for patient safety. JRSM Open 2015;7:2054270415616548. 6. Renouard F, Nisand D. Impact of implant length and diameter on survival rates. Clin Oral Implants Res 2006;17(suppl 2):35–51. 7. Herrmann I, Lekholm U, Holm S, Kultje C. Evaluation of patient and implant characteristics as potential prognostic factors for oral implant failures. Int J Oral Maxillofac Implants 2005;20:220–230. 8. Albrektsson T, Wennerberg A. Oral implant surfaces: Part 1—Review focusing on topographic and chemical properties of different surfaces and in vivo responses to them. Int J Prosthodont 2004;17:536–543. 9. Esposito M, Cannizarro G, Soardi E, Pellegrino G, Pistilli R, Felice P. A 3-year post-loading report of a randomised controlled trial on the rehabilitation of posterior atrophic mandibles: Short implants or longer implants in vertically augmented bone? Eur J Oral Implantol 2011;4:301–311. 10. Pieri F, Caselli E, Forlivesi C, Corinaldesi G. Rehabilitation of the atrophic posterior maxilla using splinted short implants or sinus augmentation with standard-length implants: A retrospective cohort study. Int J Oral Maxillofac Implants 2016;31:1179–1188. 11. Meijer HJ, Kuiper JH, Starmans FJ, Bosman F. Stress distribution around dental implants: Influence of superstructure, length of implants, and height of mandible. J Prosthet Dent 1992;68:96–102. 12. Pierrisnard L, Renouard F, Renault P, Barquins M. Influence of implant length and bicortical anchorage on implant stress distribution. Clin Implant Dent Relat Res 2003;5: 254–262. 13. Blanes RJ, Bernard JP, Blanes ZM, Belser UC. A 10-year prospective study of ITI dental implants placed in the posterior region. II: Influence of the crown-to-implant ratio and different prosthetic treatment modalities on crestal bone loss. Clin Oral Implants Res 2007;18:707–714. 14. Tawil G, Aboujaoude N, Younan R. Influence of prosthetic parameters on the survival and complication rates of short implants. Int J Oral Maxillofac Implants 2006;21: 275–282. 15. Rokni S, Todescan R, Watson P, Pharoah M, Adegbembo AO, Deporter D. An assessment of crown-to-root ratios with short sintered porous-surfaced implants supporting prostheses in partially edentulous patients. Int J Oral Maxillofac Implants 2005;20:69–76. 16. Albrektsson T, Dahl E, Enbom L, et al. Osseointegrated oral implants. A Swedish multicenter study of 8139 consecutively inserted Nobelpharma implants. J Periodontol 1988;59:287–296.

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17. Renouard F, Nisand D. Short implants in the severely resorbed maxilla: A 2-year retrospective clinical study. Clin Implant Dent Relat Res 2005;7(suppl 1):S104–S110. 18. Naert I, Duyck J, Hosny M, Jacobs R, Quirynen M, van Steenberghe D. Evaluation of factors influencing the marginal bone stability around implants in the treatment of partial edentulism. Clin Implant Dent Relat Res 2001;3:30–38. 19. Spray JR, Black CG, Morris HF, Ochi S. The influence of bone thickness on facial marginal bone response: Stage 1 placement through stage 2 uncovering. Ann Periodontol 2000;5:119–128.

20. Barach P, Johnson JK, Ahmad A, et al. A prospective observational study of human factors, adverse events, and patient outcomes in surgery for pediatric cardiac disease. J Thorac Cardiovasc Surg 2008;136:1422–1428. 21. Wetzel CM, Kneebone RL, Woloshynowych M, et al. The effects of stress on surgical performance. Am J Surg 2006;191:5–10. 22. Weigl M, Stefan P, Abhari K, et al. Intra-operative disruptions, surgeon’s mental workload, and technical performance in a full-scale simulated procedure. Surg Endosc 2016;30:559–566.

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2

The Performance of Short and Ultra-Short Implants Douglas Deporter, dds, phd

I

n 1981, osseointegrated dental implants were first introduced to a worldwide audience by Dr Brånemark and his Swedish colleagues.1 The original Brånemark-type implant had a machine-turned or minimally rough surface finish, and many early users maintained from the outset that the short implant had a high failure rate (eg, 25% with 7-mm lengths), especially in the posterior maxilla.2–5 Despite decades of progress in implant design and technique and the revelation that shortening implant lengths has no significant impact on their stability, many clinicians still believe that short implants are more likely to fail.6,7 The Periotest device (Medizintechnik Gulden) and resonance frequency testing have shown that failure is not increased with shorter implants, and resonance frequency testing has even demonstrated that increasing implant length may actually reduce implant primary stability.8,9 However, since more successful research has been carried out and minimally invasive implant procedures have become the preferred treatment, short implants have become trendier.10–12 Most implant manufacturers now market them—although not all with adequate premarket clinical testing. The current definition of short implant is one with a designed intrabony length (DIL) of 6 to 8 mm, while an ultra-short implant has a DIL of less than 6 mm.13,14 (Note that the DIL refers to the length meant to be responsible for implant fixation to bone, not the total implant length.) The most common location for short implant use is the resorbed posterior mandible (Fig 2-1), but they can also be appropriate in the resorbed anterior mandible15–18 (Figs 2-2 and 2-3). In a posterior maxilla with resorption or a pneumatized sinus (Figs 2-4 and 2-5), some short implant designs have proven to be a legitimate substitute for longer implants used in conjunction with a dedicated open sinus floor elevation

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FIG 2-1  |  This prosthesis is supported by two 8-mm-long Strau- FIG 2-2  |  A radiograph of three 7 × 3.75–mm MRTIs that were used mann Tissue Level moderately rough threaded implants (MRTIs). The implant diameters are 4.1 mm (mesial implant) and 4.8 mm (distal implant). Crestal bone remodeling primarily affects the machined collar segments with some signs of increased crestal bone density on the mesial of the more anterior implant. (Restoration courtesy of Dr Simon Yeh, Toronto, Ontario.)

a

to support a fixed mandibular prosthesis. This radiograph was taken after 5 years in function. The opposing dentition was a fixed, implantsupported prosthesis. (Courtesy of Dr Pietro Felice, University of Bologna, Italy.)

b

c

FIG 2-3  |  (a) This patient participated in a clinical trial in 1990 and received three freestanding, short, and sintered porous-surfaced implants (SPSIs) to retain a complete mandibular overdenture.18 The photographs were taken after 20 years in function. (b) The overall length of the implants was 8 mm, but the DIL was only 6 mm because there was a 2-mm machined transgingival collar segment.13 Note that the implants are encircled by healthy keratinized gingival tissue. (c) A radiograph corresponding to the short SPSIs.

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a

b

FIG 2-4  |  (a) A preoperative radiograph shows a hopeless maxillary left first molar. The tooth was extracted with socket preservation using a xenograft and a dense polytetrafluoroethylene barrier material (Regentex, Osteogenics Biomedical). (b) This SPSI was placed in the first molar site in 2001 using transcrestal sinus floor elevation (ie, bone-added osteotome sinus floor elevation) of 2 mm.19 The original sinus floor can no longer be seen in this radiograph taken in 2017 after the implant had functioned with its original restoration for over 16 years. The implant was 7 × 5 mm with a 2-mm machined collar, making the DIL only 5 mm. (Restoration courtesy of Dr Reynaldo Todescan, Toronto, Ontario.)

and grafting procedure.10,19–21 Using short or ultra-short implants in this last situation greatly reduces the associated risks, patient morbidity and anxiety, and cost. One recent investigator22 actually concluded that there is little justification for open lateral window sinus grafting where 5 mm of subantral bone remains preoperatively because a short implant with or without minimal indirect sinus floor elevation (eg, using hand osteotomes) will often work equally well.19,23 Using short or ultrashort implants can also simplify treatment in sites with alveolar ridge undercuts that would otherwise lead to apical bone fenestrations with longer implants (Fig 2-6). The advantages of short implants include less risk of neurovascular damage in the posterior mandible, less risk of sinus damage or infection in the posterior maxilla, simpler and less invasive surgical procedures, shorter treatment times, and less costly procedures. All of these advantages can especially benefit geriatric patients who now live longer than ever before and often have complex medical issues. However, there have been and continue to be numerous problems that have to be overcome to achieve predictable clinical success with short and ultra-short threaded implants, leaving one recent reviewer to conclude that “clinicians need to be aware that short (threaded) implants with lengths

FIG 2-5  |  This splinted maxillary prosthesis is supported by three 5 × 5–mm MRTIs. The radiograph was obtained after the restoration had been in function for 3 years. (Courtesy of Dr Pietro Felice, University of Bologna, Italy.)

less than 8 mm present greater risk of failures.”24,25 Certainly, these implants should not be perceived as a simplified approach for use by clinicians who are inexperienced in implant surgery. Recognizing this reality, this chapter focuses on literature-based, tested solutions in which short and ultra-short implants are thought to be the best treatment option. Topics include implant macro designs and surface features, modified surgical procedures, crown-to-implant (C/I) ratios, splinting and nonsplinting, and relevance of keratinized periimplant soft tissues. Little is known, however, about the impact of patient health and lifestyle factors on long-term performance of short and ultra-short implants. As with standard-length implants, both patients who smoke and those with a history of severe periodontitis may have sufficient peri-implant crestal bone loss to have a negative biomechanical impact on short and ultra-short implants.26 A patient with both of these confounding factors and who continues to smoke after receiving implant treatment could have up to 2.4 times more peri-implant bone loss than periodontally healthy nonsmokers after comparable implant function times.27 Loss of this much bone with a 5- or 6-mm-long implant could certainly be expected to affect long-term performance.

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a

b

c

d

FIG 2-6  |  (a) This patient received two 5-mm-long SPSIs (DIL: 4 mm) and a 7-mm-long SPSI (DIL: 6 mm).13 All im-

plants had diameters of 4.1 mm and were used to support a hybrid fixed maxillary anterior prosthesis. Such short implants were chosen to avoid creating labial dehiscences given that the ridge had a marked labial undercut. The implants opposed natural mandibular teeth. (b) The 7 × 4.1–mm SPSI was placed in the canine site where there was no ridge undercut. (c) A clinical photograph of the hybrid prosthesis with lips retracted. (Courtesy of Dr Ester Canton, Toronto, Ontario.) (d) The hybrid prosthesis with normal lip posture.

Implant Macro Design Shape Dental implants are primarily threaded (ie, screwshaped) devices with either cylindric or tapered shapes. There are also two currently used tapered, press-fit designs: one with horizontal plateaus or fins (also termed plateau root form [PRF]; see chapter 8) and the other with a sintered porous-surfaced geometry and topography instead of threads (see chapter 7).11,28,29 Both of these latter designs have a long history of successful use in short lengths. With all current threaded implant

macro designs, moderately textured osteoconductive surfaces (eg, particle blasted or acid etched) are used to accelerate osteogenesis and increase bone-to-implant contact. This makes them more likely than machineturned implants to be successful in shorter lengths (Fig 2-7; see also Fig 2-1). Thread design with screw-shaped implants varies substantially between manufacturers and even between various product lines from the same manufacturer. The shape, depth, thickness, face angle, and pitch of threads (ie, the distance between two consecutive threads on the same side of the implant axis) all will affect the degree of bone contact, initial stability, and

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Implant Macro Design

a

FIG 2-7  |  An 8.5 × 4–mm MRTI is shown here after more than 5 years

in function. Note the increased bone density that has developed at the mesial surface that might be related to the implant angulation and the resulting compressive forces that are generated.

function under occlusal loading, particularly in cancellous bone.30 The thread shape, defined by the combination of thread thickness and face angle, may have a V-shape, square, buttress, or reverse buttress design31 (Fig 2-8). The greater the number of threads (ie, the smaller the pitch) and the greater the depth of the threads, the greater will be the surface area available for bone contact and the ability of the implant to dissipate peak stresses—although optimal pitch and depth will vary with thread shape. One recent finite element analysis (FEA) study led the investigators to conclude that triangular (ie, V-shaped) threads may be the best for 10-mm-long implants, particularly in the cancellous posterior maxilla.32 However, no particular thread design has been shown to work best with short and ultra-short threaded implants, and most manufacturers have a similar thread design for short, ultra-short, and standard-length models.

Torque Coelho and Jimbo33 recently reviewed threaded implant designs and the contributions of their various attributes. Their literature searches disclosed that far less

b

c

d

FIG 2-8  |  Typical thread designs used with dental implants. (a) Stan-

dard V-thread. (b) Square thread. (c) Buttress thread. (d) Reverse buttress thread.

work had been published on implant thread geometry than had been documented for implant surface microand nanotopographies.2 Thread geometry will impact both initial osseointegration and subsequent transfer of occlusal stresses to bone during functional implant loading. Regarding initial integration, great emphasis has been and is still placed on using threaded implant macro designs and surgical protocols that will result in high torquing forces being required for implant seating. To this end, current surgical protocols for some short and ultra-short threaded implants include using a final implant drill somewhat smaller in diameter than the implant’s outer thread tips—depending of course on the bone density encountered during site drilling. However, there are limits on how undersized the osteotomy can be without overwhelming the natural elasticity of cortical bone.34 If torquing force is excessive either because the bone was dense or the final bur diameter used was too small despite good initial implant stability (ie, avoidance of early micromovements), there may be strain-related microfractures and compression necrosis in the peri-implant cortical bone.33,35 As a result, before new cortical bone can be formed around implants placed in this fashion, a resorptive phase will

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be needed to remove the damaged bone. Depending on implant shape and surface topography, this may be accompanied by a temporary reduction in implant stability that could result in micromovements sufficient to delay or even inhibit osteogenesis and lead to early implant failures.36 This has led to the suggestion by some investigators that a lesser torque (eg, 25 Ncm) is preferable and that adequate implant stability may be better verified with resonance frequency testing (ie, axial stability) than by achieving high initial torque values (ie, rotational stability).37 However, the ideal combination of factors needed to ensure adequate primary stability with uninhibited new bone formation yielding osseointegration has yet to be revealed.34 Assessment of short implant stability after initial healing is supposedly complete can be made using resonance frequency before commencing prosthodontic procedures.36 If at this point the resonance frequency value (RFV) is less than 60, a further period of unloaded healing and retesting should be considered for short and ultra-short implants intended for restoration with single crowns. Alternatively, if the implant is intended for use in a splinted prosthesis, the use of a transitional splinted prosthesis will allow for a period of progressive loading after which further RFV testing can be used to verify that the affected implants are well integrated and ready for definitive restoration. If the implant has a topography or texture that favors osteoconduction, insult to cancellous bone during osteotomy site drilling will result in bleeding, platelet activation, and rapid fibrin attachment to the implant surface.2,29 With adequate implant stability, cancellous bone formation onto this surface will then commence directly (ie, without a significant resorptive phase) both by contact osteogenesis (ie, on the implant surface) and distance osteogenesis (ie, on the osteotomy walls).38

Taper Currently used implant shapes are either cylindric or tapered, although some hybrid designs have segments

with both shapes. Advantages of tapered shapes include the fact that they more closely resemble tooth roots, they have a reduced risk of creating bone fenestrations apically or damaging adjacent teeth, and they may achieve higher initial stability.39,40 Consequently, the majority of implant designs in the marketplace today have some degree of taper. Press-fit sintered poroussurfaced implants (SPSIs) have a 5-degree taper, while PRF implants have a 3-degree taper.41 The degree of taper can affect both initial implant stability and stress transfer during functional loading. Atieh et al42 used FEA methods to study the impact of taper on immediate loading of threaded mandibular molar implants, concluding that small taper angles (ie, 2 to 5 degrees) placed less local strain on crestal bone during implant loading than higher taper angles (ie, up to 14 degrees).

Other considerations Other macro design considerations for short and ultrashort implants include implant diameter, collar design, prosthetic abutment connection type, and platform switching, all of which may impact crestal bone strains and crestal bone loss.43–47 Many implant manufacturers now include a platform-switch feature (ie, the diameter of the prosthetic abutment is smaller than the implant prosthetic table) in their offerings with the intent of reducing crestal stresses.48 Regarding diameter, some investigators maintain that larger diameters will benefit short implant performance because increases in implant width appear more important than increases in length when it comes to improving stress transfer during off-axis loading.49,50 Clinically stable implants do experience regular, more or less constant microscale off-axis movements and will tend to bend away from the causative stress. This is inevitable with moderately rough threaded implants (MRTIs) because unlike SPSIs, they have little tensile (ie, pulling) resistance capability on their upstream surfaces.51 Consequently, most of the load is received on the surfaces downstream from the force (ie, compressive surfaces) (Fig 2-9).52 Wider

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Implant Macro Design

FIG 2-9  |  Functioning implants experience combinations of vertical, rotational, and transverse (ie, off-axis) forces at any angle. Threaded implants, even those with roughened surfaces, have low resistance to off-axis tensile forces and will therefore experience bending away from the force vector, resulting in primarily compressive bone loading on the downstream crestal bone and diagonally opposite periapical bone. The impact on bone is independent of implant length but lessened by increases in implant diameter. (Reprinted with permission from Hagi et al.52)

implants will likely experience less bending and therefore lead to lower compressive forces on the affected crestal bone.8 The width issue, however, is clouded by observations in one recent literature analysis that short threaded implants had increased failure rates as diameter increased beyond 4.5 mm.53 This may have been partly due to the necessity for excessive insertion torque to seat wider implants.54 Implant collar design (and whether the implant has a platform-switch feature) will affect the degree of crestal bone loss required to establish biologic width—the peri-implant cuff of gingival epithelial and connective tissue that seals off the underlying bone. Biologic width is known to require around 2 mm of surface contact (ie, 1 mm of epithelium and 1 mm of gingival or mucosal connective tissue), and the implant collar needs to accommodate this sealing tissue to avoid loss of crestal bone, soft tissue recession, and unwanted exposure of implant surfaces.55,56 Early collar designs had polished, machined surfaces, and these remain the simplest and likely the safest. However, if a machined collar is too long (ie, greater than 1 mm), bone loss can result from too little stress on crestal bone because of its inability to maintain direct contact with the machine-turned surface (ie, stress-shielding leading to disuse atrophy).41 If the collar has a textured surface, the implant is likely best submerged 1 mm or greater as is recommended with short and ultra-short PRF implants to minimize

Transverse force component

the risk of its exposure and contamination of the textured surface by microorganisms.28 In one recent animal investigation, three different transmucosal collar designs for MRTIs were studied, including typical cylindric machined (0.7-mm height), concave-machined, and concave-roughened surface designs.57 Implants were placed so that the apical border of each collar was positioned level with the alveolar crest. The least crestal bone loss was found with the concave-machined design. This might be because the curved machined surface, similar to a platform-switch feature, increased the length of collar available for accommodation of the connective tissue portion of biologic width. This sort of collar design could be of benefit in the future with short and ultra-short implants in clinical situations that require the least bone loss possible. Both external and internal implant prosthetic abutment connections are in use, although the majority of manufacturers have moved toward internal abutment connections, the most common of which is the Morse taper arrangement. Arguments in favor of internal connections are (1) they reduce micromovements at the implant-abutment interface and loosening of retention screws; (2) they reduce stress on crestal bone, leading to less resorption; and (3) they can reduce the likelihood of bacterial colonies becoming established at and within the so-called microgap level of the implant.58,59

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FIG 2-10  |  This SPSI had been in function for 18 years at the FIG 2-11  |  This patient has had three freestanding SPSIs in

time that the radiograph was taken. It is 7 × 4.1 mm with a 1-mm function for over 17 years. The most mesial implant is 7 mm machined collar (DIL: 6 mm). Noticeable densification of the long (DIL: 5 mm) with a 4.1-mm diameter, while the other two peri-implant cancellous bone can be seen. implants are 7 × 5 mm (DIL: 6 mm). The prosthodontist decided to splint these latter implants.

Biology and implant design While short and ultra-short implants are most helpful in resorbed posterior jaw sites, these same sites are often highly cancellous (ie, bone types 3 and 4), particularly in the maxilla.60 Type 4 bone has traditionally been considered to be of poor quality or to have insufficient bone density to support short or even standard-length threaded implants. However, this conclusion was again largely based on observations with the original machineturned Brånemark-type implant (Nobel Biocare) and surgical protocol.3 Davies38 maintains that cancellous bone has good qualities for implant placement because if it is well-vascularized (ie, rather than being fatty marrow), it heals faster and remodels more readily than cortical bone in response to loading. Following placement of moderately textured (eg, particle blasted and/or acid treated) threaded implants into cancellous bone, highly cellular and vascular trabecular woven bone will form first. The bone will later transform into lamellar bone with extensive Haversian systems, making it highly reactive to functional strains.2 Indeed, this reactivity is necessary to develop and remodel or maintain

a stable interface between cancellous bone trabeculae and the implant surface. The implant surface and cancellous bone must maintain interconnectivity in an orientation and thickness that favors effective stress distribution under occlusal loading.61 This adaptive remodeling can often be seen as increased radiographic density due to increased bone mineralization (Figs 2-10 and 2-11; see also Fig 2-7). Nevertheless, short and ultra-short threaded implants may extend minimally into cancellous bone, and if so, they will need to rely more than standard-length implants on available cortical bone. This bone will ideally thicken by osteoblast activity in response to loading and greatly reduce the risk of becoming overstressed.62 Short and ultra-short press-fit SPSIs rely heavily on cancellous bone for their long-term stability.63 With time in function, they often show peri-implant cancellous bone densification in the cervical third and along the bone-to-implant interface, sometimes giving the appearance of a lamina dura and confirming effective stress transfer.29 Whether short and ultra-short implants with diameters greater than 4.5 mm can be employed successfully will depend on existing buccolingual or buccopalatal

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a

b

d

c

e

FIG 2-12  |  (a) This mandibular first molar was designated for extraction with immediate implant placement. (b) Difficulty was encountered in

following the manufacturer’s instruction to place this ultra-wide (7 × 8–mm) implant 2 mm subcrestally, as seen in this immediate postoperative radiograph. (c) A cone beam computed tomography (CBCT) scan taken of the implant site after more than 5 years in function shows the optimal placement buccolingually. (d) A series of mid-implant, mesiodistal CBCT slices shows moderate crestal bone loss resulting from insufficient initial implant submergence. (e) The clinical photograph shows the gray shadow of metal through the soft tissues, resulting from the failure to position the implant 2 mm subcrestally as recommended by the manufacturer.

alveolar ridge width. For example, some clinicians insist on having the uncommon buccolingual or palatal width of 8 mm to accommodate a 5-mm-diameter short or ultra-short implant.64 Their rationale for this is that the buccal bone wall needs to be at least 2 mm thick near the crest after osteotomy preparation to avoid resorption with exposure of the DIL (ie, implant surfaces meant to remain buried in bone).65,66 An exception to this rule may be when using implants with an inwardly sloped or ball-shaped collar region where with proper protocol new bone formation will thicken the crest67 (see also chapters 6 and 8). However, most implant designs do not have these features, so they may need to be overseated to a depth that correlates with the necessary critical buccal wall thickness.68,69 In one

recent dog experiment, investigators compared sub­­ crestal and equicrestal placements of tapered implants that had internal prosthetic connections. Subcrestal placement resulted in significantly less crestal bone loss following a 4-month period of function.70 One manufacturer offers a short implant with diameters as large as 9 mm and meant for immediate molar replacement (see chapter 9). Their protocol recommends sub­­ crestal implant placement buccally by 2 mm to avoid unwanted crestal bone loss, but depending on bone density this may be difficult to achieve, particularly in posterior mandibles71 (Fig 2-12). Buccal overgrafting under the periosteum at the time of implant placement may sometimes be useful in augmenting deficient buccal bone thickness.72

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a

b

c

FIG 2-13  |  (a) Scanning electron microscope (SEM) of a particle-blasted, acid-treated MRTI surface2 (original magnification ×2000). (b) SEM of

an SPSI surface29 (original magnification ×200). (c) SEM of an SPSI surface after pull-out from a healed implanted site in a rabbit femur. Extensive bone ingrowth can be seen at the sheared bone-to-implant interface surface81 (original magnification ×300).

Surface Features The original Brånemark-type pure titanium (Ti) screw implant had a machine-turned, minimally rough surface finish, thereby providing a relatively weak, primarily frictional bone-to-implant interface following integration.2,29 This resulted in limited resistance to tensile force components with off-axis loading (see Fig 2-9). The associated risk of loss of integration under functional loading was thought to be counteracted by using long implants to provide a greater surface area for bone contact. For example, it was recommended that implant lengths of 13 mm or more were needed to achieve success in the maxilla.5 However, it was soon learned that altering machine-turned implant surfaces to make them moderately rough or textured by methods such as particle blasting or acid washing (Fig 2-13a) was a more effective way to increase bone-to-implant surface contact.2 This surface treatment also improves osteoconduction and contact osteogenesis, thereby achieving faster integration.38,73 Interestingly, it has also been reported that MRTIs made from the alloy Ti-6Al-4V show significantly greater torque-out resistance compared with commercially pure Ti (cpTi) despite the fact that

bone-to-implant surface contact values were similar.74 As a result, virtually all currently available threaded dental implants are moderately rough, and many have nanotexture (ie, submicron topographic features) modifications such as calcium phosphate (CaP) applications. This promotes rapid protein adhesion and subsequent osteoprogenitor cell attachment, proliferation, differentiation, and spreading.75,76 Early results on survival rates with short MRTIs varied widely, demonstrating that success was highly dependent on clinical skills, technique, and experience.77 In a systematic literature review of results with 8-mm-long MRTIs in studies published between 1992 and 2009, Neldam and Pinholt78 reported failure rates of 0% to 22.9%, while another reviewer reported only 6% failure with the same implant type in only 6-mm lengths.79 In the mid 1980s, others introduced the press-fit SPSI using technology developed earlier in orthopedics.41 The DIL of these implants had a 0.3-mm-thick layer of spherical particles of Ti-4Al-6V (the alloy being stronger than cpTi) (Fig 2-13b). The range of particle diameter sizes resulted in an interconnected, interparticle porosity of 50 to 200 µm, favoring vascular and bone tissue ingrowth and resulting in implant

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Surface Features

▼

TABLE 2-1 | Strengths of implant surface textures SURFACE TYPE

ESTIMATED TENSILE STRENGTH (N/MM2)

Machine turned

8 mm) with sinus lifting in atrophic posterior maxilla: A meta-analysis of RCTs. Clin Implant Dent Relat Res 2017;19:207–215. 4. Sanz M, Donos N, Alcoforado G, et al. Therapeutic concepts and methods for improving dental implant outcomes. Summary and consensus statements. The 4th EAO Consensus Conference 2015. Clin Oral Implants Res 2015;26(suppl 11):202–206. 5. Lemos CA, Ferro-Alves ML, Okamoto R, Mendonça MR, Pellizzer EP. Short dental implants versus standard dental implants placed in the posterior jaws: A systematic review and meta-analysis. J Dent 2016;47:8–17. 6. Esfahrood ZR, Ahmadi L, Karami E, Asghari S. Short dental implants in the posterior maxilla: A review of the literature. J Korean Assoc Oral Maxillofac Surg 2017;43:70–76. 7. Jain N, Gulati M, Garg M, Pathak C. Short implants: New horizon in implant dentistry. J Clin Diagn Res 2016;10: ZE14–ZE17. 8. Thoma DS, Zeltner M, Hüsler J, Hämmerle CH, Jung RE. EAO Supplement Working Group 4 - EAO CC 2015 short implants versus sinus lifting with longer implants to restore the posterior maxilla: A systematic review. Clin Oral Implants Res 2015;26(suppl 11):154–169. 9. Lundgren S, Cricchio G, Hallman M, Jungner M, Rasmusson L, Sennerby L. Sinus floor elevation procedures to enable implant placement and integration: Techniques, biological aspects and clinical outcomes. Periodontol 2000 2017;73:103–120.

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10. Bernard JP, Szmukler-Moncler S, Pessotto S, Vazquez L, Belser UC. The anchorage of Brånemark and ITI implants of different lengths. I. An experimental study in the canine mandible. Clin Oral Implants Res 2003;14:593–600. 11. Tan WC, Lang NP, Zwahlen M, Pjetursson BE. A systematic review of the success of sinus floor elevation and survival of implants inserted in combination with sinus floor elevation. Part II: Transalveolar technique. J Clin Periodontol 2008;35(8 suppl):241–254. 12. Wallace SS, Froum SJ. Effect of maxillary sinus augmentation on the survival of endosseous dental implants. A systematic review. Ann Periodontol 2003;8:328–343. 13. Pjetursson BE, Rast C, Brägger U, Schmidlin K, Zwahlen M, Lang NP. Maxillary sinus floor elevation using the (trans­­ alveolar) osteotome technique with or without grafting material. Part I: Implant survival and patients’ perception. Clin Oral Implants Res 2009;20:667–676. 14. Tetsch J, Tetsch P, Lysek DA. Long-term results after lateral and osteotome technique sinus floor elevation: A retrospective analysis of 2190 implants over a time period of 15 years. Clin Oral Implants Res 2010;21:497–503. 15. Summers RB. The osteotome technique: Part 3—Less invasive methods of elevating the sinus floor. Compendium 1994;15:698–700. 16. Kim YK, Cho YS, Yun PY. Assessment of dentists’ subjective satisfaction with a newly developed device for maxillary sinus membrane elevation by the crestal approach. J Periodontal Implant Sci 2013;43:308–314. 17. Kim JM, Sohn DS, Heo JU, et al. Minimally invasive sinus augmentation using ultrasonic piezoelectric vibration and hydraulic pressure: A multicenter retrospective study. Implant Dent 2012;21:536–542. 18. Ahn SH, Park EJ, Kim ES. Reamer-mediated transalveolar sinus floor elevation without osteotome and simultaneous implant placement in the maxillary molar area: Clinical outcomes of 391 implants in 380 patients. Clin Oral Implants Res 2012;23:866–872. 19. Zill A, Precht C, Beck-Broichsitter B, et al. Implants inserted with graftless osteotome sinus floor elevation—A 5-year post-loading retrospective study. Eur J Oral Implantol 2016;9:277–289. 20. Engelke W, Deckwer I. Endoscopically controlled sinus floor augmentation. A preliminary report. Clin Oral Implants Res 1997;8:527–531. 21. Kim YK, Hwang JY, Yun PY. Relationship between prognosis of dental implants and maxillary sinusitis associated with the sinus elevation procedure. Int J Oral Maxillofac Implants 2013;28:178–183. 22. Zijderveld SA, van den Bergh JP, Schulten EA, ten Bruggenkate CM. Anatomical and surgical findings and complications in 100 consecutive maxillary sinus floor elevation procedures. J Oral Maxillofac Surg 2008;66: 1426–1438.

23. Kim MJ, Jung UW, Kim CS, et al. Maxillary sinus septa: Prevalence, height, location, and morphology. A reformatted computed tomography scan analysis. J Periodontol 2006;77:903–908. 24. Neugebauer J, Ritter L, Mischkowski RA, et al. Evaluation of maxillary sinus anatomy by cone-beam CT prior to sinus floor elevation. Int J Oral Maxillofac Implants 2010; 25:258–265. 25. Schwartz-Arad D, Herzberg R, Dolev E. The prevalence of surgical complications of the sinus graft procedure and their impact on implant survival. J Periodontol 2004;75: 511–516. 26. Aimetti M, Massei G, Morra M, Cardesi E, Romano F. Correlation between gingival phenotype and Schneiderian membrane thickness. Int J Oral Maxillofac Implants 2008;23:1128–1132. 27. Cho SC, Wallace SS, Froum SJ, Tarnow DP. Influence of anatomy on Schneiderian membrane perforations during sinus elevation surgery: Three-dimensional analysis. Pract Proced Aesthet Dent 2001;13:160–163. 28. Froum SJ, Khouly I, Favero G, Cho SC. Effect of maxillary sinus membrane perforation on vital bone formation and implant survival: A retrospective study. J Periodontol 2013;84:1094–1099. 29. Tarnow DP, Wallace SS, Froum SJ, Rohrer MD, Cho SC. Histologic and clinical comparison of bilateral sinus floor elevations with and without barrier membrane placement in 12 patients: Part 3 of an ongoing prospective study. Int J Periodontics Restorative Dent 2000;20:117–125. 30. Testori T, Wallace SS, Del Fabbro M, et al. Repair of large sinus membrane perforations using stabilized collagen barrier membranes: Surgical techniques with histologic and radiographic evidence of success. Int J Periodontics Restorative Dent 2008;28:9–17. 31. Kim JM, Sohn DS, Bae MS, Moon JW, Lee JH, Park IS. Flapless transcrestal sinus augmentation using hydrodynamic piezoelectric internal sinus elevation with autologous concentrated growth factors alone. Implant Dent 2014;23: 168–174. 32. Taschieri S, Del Fabbro M. Postextraction osteotome sinus floor elevation technique using plasma-rich growth factors. Implant Dent 2011;20:418–424. 33. Del Fabbro M, Corbella S, Ceresoli V, Ceci C, Taschieri S. Plasma rich in growth factors improves patients’ postoperative quality of life in maxillary sinus floor augmentation: Preliminary results of a randomized clinical study. Clin Implant Dent Relat Res 2015;17:708–716. 34. Rosano G, Taschieri S, Gaudy JF, Weinstein T, Del Fabbro M. Maxillary sinus vascular anatomy and its relation to sinus lift surgery. Clin Oral Implants Res 2011;22: 711–715.

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References

35. Woo I, Le BT. Maxillary sinus floor elevation: Review of anatomy and two techniques. Implant Dent 2004;13: 28–32. 36. Katranji A, Fotek P, Wang HL. Sinus augmentation complications: Etiology and treatment. Implant Dent 2008;17: 339–349. 37. Davó R, Malevez C, Rojas J, Rodríguez J, Regolf J. Clinical outcome of 42 patients treated with 81 immediately loaded zygomatic implants: A 12- to 42-month retrospective study. Eur J Oral Implantol 2008;9(suppl 1):141–150. 38. Bedrossian E. Rehabilitation of the edentulous maxilla with the zygoma concept: A 7-year prospective study. Int J Oral Maxillofac Implants 2010;25:1213–1221. 39. Jemt T, Lekholm U. Implant treatment in edentulous maxillae: A 5-year follow-up report on patients with different degrees of jaw resorption. Int J Oral Maxillofac Implants 1995;10:303–311. 40. Hagi D, Deporter DA, Pilliar RM, Arenovich T. A targeted review of study outcomes with short (< or = 7 mm) endosseous dental implants placed in partially edentulous patients. J Periodontol 2004;75:798–804. 41. Renouard F, Nisand D. Short implants in the severely resorbed maxilla: A 2-year retrospective clinical study. Clin Implant Dent Relat Res 2005;7(suppl 1):S104–S110. 42. Smeets R, Stadlinger B, Schwarz F, et al. Impact of dental implant surface modifications on osseointegration. Biomed Res Int 2016;2016:6285620. 43. Kennedy KS, Jones EM, Kim DG, McGlumphy EA, Clelland NL. A prospective clinical study to evaluate early success of short implants. Int J Oral Maxillofac Implants 2013;28:170–177. 44. Felice P, Checchi L, Barausse C, et al. Posterior jaws rehabilitated with partial prostheses supported by 4.0 × 4.0 mm or by longer implants: One-year post-loading results from a multicenter randomised controlled trial. Eur J Oral Implantol 2016;9:35–45. 45. Srinivasan M, Vazquez L, Rieder P, Moraguez O, Bernard JP, Belser UC. Survival rates of short (6 mm) micro-rough surface implants: A review of literature and meta-analysis. Clin Oral Implants Res 2014;25:539–545. 46. Menchero-Cantalejo E, Barona-Dorado C, CanteroÁlvarez M, Fernández-Cáliz F, Martínez-González JM. Meta-analysis on the survival of short implants. Med Oral Patol Oral Cir Bucal 2011;16:e546–e551. 47. Telleman G, Raghoebar GM, Vissink A, den Hartog L, Huddleston Slater JJ, Meijer HJ. A systematic review of the prognosis of short ( 0.2 mm) peri-implant marginal bone resorption than short or ultra-short (5 or 7 mm) implants. This finding seemed odd at the time, but in fact others have reported a similar inverse relationship between crestal bone loss and C/I ratio for threaded dental implants with either machine-turned or moderately rough surfaces.23,24 Likewise, Urdaneta et al25 reported no impact of C/I ratios (mean: 1.6) with press-fit plateau root form implants on crestal bone loss, implant failure, prosthetic failure, or crown fractures. In a recent study, bone density and mineralization were found to be significantly higher around short (6 mm) implants compared with similar but longer (10 mm) implants.26 This adaptation to occlusal load could be interpreted to indicate effective stress transfer despite short implant length. However, caution still needs to be exercised because there may be critical limits to how high C/I ratios can be without causing problems. In the authors’ experience to date, short and ultra-short MRTIs appear to deal well with large C/I ratios (see

Figs 6-10 and 6-12). It must be mentioned, however, that a loss of 1 or 2 mm of crestal bone supporting an ultra-short implant may have a greater clinical impact on the long-term prognosis of a fixed implantsupported prosthesis than the same amount of bone loss with a standard-length implant. For example, 1 mm of loss with a 4-mm-long implant would represent a 25% loss in peri-implant bone height. Peri-implant bone thicknesses Regardless of implant type and length, all stresses experienced by dental implants are concentrated in the crestal region, making the buccal thickness of crestal cortical bone after osteotomy preparation a particularly important variable.27 Thus, to minimize the risk of unfavorable buccal cortical bone loss, its thickness following implant placement should be 2 mm or greater.20 The challenge here is that to place a 5-mm-diameter ultra-short implant, the preoperative buccolingual alveolar ridge width would need to be around 8 mm. In sites with less than this width, buccal grafting would be needed to avoid complications—unless a 4-mmdiameter implant would perform well (Table 6-1).

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CHAPTER 6 | Threaded Implants in the Atrophic Posterior Mandible

▼

TABLE 6-1 | Clinical indications in the treatment of different degrees of posterior vertical mandibular atrophy RESIDUAL VERTICAL BONE HEIGHT ABOVE THE MANDIBULAR CANAL

TREATMENT SOLUTION

7 mm

6-mm-long implants

6 mm

5-mm-long implants

5 mm

4-mm ultra-short implants

4 mm

Inlay technique

< 4 mm

GBR

Peri-implant soft tissue Likewise, having a thick keratinized gingival biotype covering cortical bone at sites intended for placement of short or ultra-short implants is important. Linkevicius28 reported that a peri-implant soft tissue thickness greater than 2 mm is needed as a protective cover to minimize marginal bone loss. Moreover, the presence of thick keratinized gingiva enables comfortable home brushing and oral hygiene habits, which reduce the risk of plaque-induced peri-implant inflammation and crestal bone loss.29 Ideally, if the keratinized gingival tissue is judged to be inadequate, soft tissue grafting should be undertaken before implant placement.

Patient Selection and Recommended Treatment Guidelines Short and ultra-short threaded implants can usually be placed in atrophic posterior mandibles as long as there is a minimal residual alveolar ridge height of 5 mm, including a safety zone of at least 1 mm above the mandibular neurovascular canal to avoid violation of this vital structure during osteotomy preparation and implant placement. They are contraindicated in patients with high esthetic demands who

are unlikely to be satisfied by the required unnaturally long prosthetic crowns and designs needed to optimize oral hygiene. Preoperative cone beam computed tomography scans are essential to reduce intraoperative risks. Nevertheless, using only subperiosteal infiltration of local anesthetic rather than a mandibular block will provide extra insurance against accidental nerve damage. A successful outcome with short and ultra-short implants will also depend on the following factors: • The use of slightly undersized osteotomies is preferred. • Implant insertion is begun with a motorized handpiece but usually completed with a manual torque wrench to achieve and verify adequate initial implant stability (ideally ≥ 35 Ncm). • A minimal submerged healing interval of 4 months is suggested for most situations before prosthetic loading. • No removable provisional prostheses should be worn during the implant healing interval. • A provisional loading period of about 4 months using a splinted transitional acrylic prosthesis will allow for progressive implant loading. • The use of at least two ultra-short MRTIs is required because the implants must be loaded with splinted prostheses. • Screw-retained prostheses are strongly recommended to avoid the risk of peri-implantitis-driven marginal bone resorption caused by undetectable cement remnants inside the peri-implant sulcus. • The prosthesis should be designed to be as accessible as possible for oral hygiene (Fig 6-14). • The prosthesis should be biomechanically adjusted to the implant position to have axial force distribution parallel to the implant long axis and adapted to individual characteristics of each patient. Regarding occlusion, a balanced group guide should be made to ensure very gentle dynamic movements.

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Conclusion

a

b

c

d

FIG 6-14  |  (a) Treatment for this patient began with a vertical bone augmentation procedure. This procedure was unsuccessful, so the plan was changed to use three ultra-short 4 × 4–mm self-tapping MRTIs. (b) A definitive prosthesis on its master cast. Note the accuracy and the polishing of the metal substructure to discourage dental plaque accumulation. (Courtesy of Dr Fabio Colombelli, Milan, Italy.) (c) A radiograph of the definitive prosthesis in place. (d) The clinical design of the definitive prosthesis showing optimal access for oral hygiene.

Conclusion

• Expected long-term implant survival rates

The treatment of severe vertical bone atrophy in the posterior mandible involves two major clinical approaches for the achievement of a fixed implantsupported rehabilitation: bone reconstruction or regeneration to permit the placement of standard-length implants, or the placement of short or ultra-short implants taking advantage of the patient’s residual native bone. The factors that determine which treatment is best include:

Based on the literature partially reviewed in this chapter and the authors’ ongoing experiences, implants as short as 4 mm can now be used to treat vertical atrophy of the mandible, assuming that there is at least 5 mm of residual bone height remaining. In cases where there remains only 4 mm of bone height, the interpositional inlay grafting technique seems the best option, while GBR may be attempted in compliant patients with less than 4 mm. This chapter has reviewed experiences with several different short and ultra-short implant designs, each with design features that may have been important in achieving treatment successes. These factors include:

• • • •

Length of surgery Cost of surgery Invasiveness of surgery Postoperative morbidity

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• Implant neck design with recessed, concave necks possibly offering an advantage • Platform switching to moderate crestal bone stresses • Calcium nanocoatings that may allow more intimate bone-to-implant surface contact • Self-tapping implants • Tapered implant shape The relative contributions of these factors need further investigation before an ideal short or ultra-short MRTI design can be achieved for use in the posterior mandible. Further study is also needed to determine if there is an optimal implant macrogeometry (eg, thread design) and whether this differs from that used for standardlength MRTIs.

References 1. van Steenberghe D, Lekholm U, Bolender C, et al. Applicability of osseointegrated oral implants in the rehabilitation of partial edentulism: A prospective multicenter study on 558 fixtures. Int J Oral Maxillofac Implants 1990;5: 272–281. 2. Esposito M, Grusovin MG, Felice P, Karatzopoulos G, Worthington HV, Coulthard P. The efficacy of horizontal and vertical bone augmentation procedures for dental implants—A Cochrane systematic review. Eur J Oral Implantol 2009;2:167–184. 3. Seibert JS. Reconstruction of deformed, partially edentulous ridges, using full thickness onlay grafts. Part I. Technique and wound healing. Compend Contin Educ Dent 1983;4:437–453. 4. Felice P, Lizio G, Checchi L. Alveolar distraction osteogenesis in posterior atrophic mandible: A case report on a new technical approach. Implant Dent 2013;22:332–338. 5. Felice P, Pistilli R, Lizio G, Pellegrino G, Nisii A, Marchetti C. Inlay versus onlay iliac bone grafting in atrophic posterior mandible: A prospective controlled clinical trial for the comparison of two techniques. Clin Implant Dent Relat Res 2009;11(suppl 1):e69–e82. 6. Simion M, Jovanovic SA, Tinti C, Benfenati SP. Long-term evaluation of osseointegrated implants inserted at the time or after vertical ridge augmentation. A retrospective study on 123 implants with 1-5 year follow-up. Clin Oral Implants Res 2001;12:35–45.

7. Felice P, Barausse C, Barone A, et al. Interpositional augmentation technique in the treatment of posterior mandibular atrophies: A retrospective study comparing 129 autogenous and heterologous bone blocks with 2 to 7 years follow-up. Int J Periodontics Restorative Dent 2017;37: 469–480. 8. Chiapasco M, Casentini P, Zaniboni M. Bone augmentation procedures in implant dentistry. Int J Oral Maxillofac Implants 2009;24(suppl):237–259. 9. De Bruyn H, Bouvry P, Collaert B, De Clercq C, Persson GR, Cosyn J. Long-term clinical, microbiological, and radiographic outcomes of Brånemark implants installed in augmented maxillary bone for fixed full-arch rehabilitation. Clin Implant Dent Relat Res 2013;15:73–82. 10. Fontana F, Maschera E, Rocchietta I, Simion M. Clinical classification of complications in guided bone regeneration procedures by means of a nonresorbable membrane. Int J Periodontics Restorative Dent 2011;31:265–273. 11. Renouard F, Nisand D. Impact of implant length and diameter on survival rates. Clin Oral Implants Res 2006;17(suppl 2):35–51. 12. Neugebauer J, Nickenig HJ, Zöller JE; Department of Cranio-maxillofacial and Plastic Surgery and Interdisciplinary Department for Oral Surgery and Implantology; Centre for Dentistry and Oral and Maxillofacial Surgery. Update on short, angulated and diameter-reduced implants. Presented at the 11th European Consensus Conference, Cologne, 6 Feb 2016. 13. Deporter D, Ogiso B, Sohn DS, Ruljancich K, Pharoah M. Ultrashort sintered porous-surfaced dental implants used to replace posterior teeth. J Periodontol 2008;79: 1280–1286. 14. Deporter DA, Kermalli J, Todescan R, Atenafu E. Performance of sintered, porous-surfaced, press-fit implants after 10 years of function in the partially edentulous posterior mandible. Int J Periodontics Restorative Dent 2012; 32:563–570. 15. Nisand D, Picard N, Rocchietta I. Short implants compared to implants in vertically augmented bone: A systematic review. Clin Oral Implants Res 2015;26(suppl 11): 170–179. 16. Felice P, Cannizzaro G, Barausse C, Pistilli R, Esposito M. Short implants versus longer implants in vertically augmented posterior mandibles: A randomised controlled trial with 5-year after loading follow-up. Eur J Oral Implantol 2014;7:359–369. 17. Pistilli R, Felice P, Piattelli M, et al. Posterior atrophic jaws rehabilitated with prostheses supported by 5 × 5 mm implants with a novel nanostructured calcium-incorporated titanium surface or by longer implants in augmented bone. One-year results from a randomised controlled trial. Eur J Oral Implantol 2013;6:343–357.

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18. Tabata LF, Rocha EP, Barão VA, Assunção WG. Platform switching: Biomechanical evaluation using threedimensional finite element analysis. Int J Oral Maxillofac Implants 2011;26:482–491. 19. Esposito M, Pistilli R, Barausse C, Felice P. Three-year results from a randomised controlled trial comparing prostheses supported by 5-mm long implants or by longer implants in augmented bone in posterior atrophic edentulous jaws. Eur J Oral Implantol 2014;7:383–395. 20. Spray JR, Black CG, Morris HF, Ochi S. The influence of bone thickness on facial marginal bone response: Stage 1 placement through stage 2 uncovering. Ann Periodontol 2000;5:119–128. 21. Bolle C, Gustin MP, Fau D, Exbrayat P, Boivin G, Grosgogeat B. Early periimplant tissue healing on 1-piece implants with a concave transmucosal design: A histomorphometric study in dogs. Implant Dent 2015;24:598–606. 22. Rokni S, Todescan R, Watson P, Pharoah M, Adegbembo AO, Deporter D. An assessment of crown-to-root ratios with short sintered porous-surfaced implants supporting prostheses in partially edentulous patients. Int J Oral Maxillofac Implants 2005;20:69–76. 23. Naert I, Duyck J, Hosny M, Jacobs R, Quirynen M, van Steenberghe D. Evaluation of factors influencing the marginal bone stability around implants in the treatment of partial edentulism. Clin Implant Dent Relat Res 2001;3:30–38.

24. Nunes M, Almeida RF, Felino AC, Malo P, de Araújo Nobre M. The influence of crown-to-implant ratio on short implant marginal bone loss. Int J Oral Maxillofac Implants 2016;31:1156–1163. 25. Urdaneta RA, Rodriguez S, McNeil DC, Weed M, Chuang SK. The effect of increased crown-to-implant ratio on single-tooth locking-taper implants. Int J Oral Maxillofac Implants 2010;25:729–743. 26. Sahrmann P, Schoen P, Naenni N, Jung R, Attin T, Schmidlin PR. Peri-implant bone density around implants of different lengths: A 3-year follow-up of a randomized clinical trial. J Clin Periodontol 2017;44:762–768. 27. Pierrisnard L, Renouard F, Renault P, Barquins M. Influence of implant length and bicortical anchorage on implant stress distribution. Clin Implant Dent Relat Res 2003;5: 254–262. 28. Linkevicius T, Apse P, Grybauskas S, Puisys A. The influence of soft tissue thickness on crestal bone changes around implants: A 1-year prospective controlled clinical trial. Int J Oral Maxillofac Implants 2009;24:712–719. 29. Souza AB, Tormena M, Matarazzo F, Araújo MG. The influence of peri-implant keratinized mucosa on brushing discomfort and peri-implant tissue health. Clin Oral Implants Res 2016;27:650–655.

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7

Press-Fit Sintered Porous-Surfaced Implants Douglas Deporter, dds, phd

SPSI Macro Design and Surface Features The technology for press-fit sintered porous-surfaced implants (SPSIs) was first developed in the late 1960s in the field of orthopedics. The motivation was to improve the design of artificial hip implants, which at the time were inserted and secured with bone cement. This made for a fairly weak bone-to-implant interface connection with the risk of cement deterioration and late implant failure, particularly in recipients with active lifestyles. The SPS design revolutionized this field. 1,2 SPS prostheses were made with a multilayered surface of spherical metal particles connected to each other and to the machined solid implant core structure via “sinter neck” regions created by hightemperature, time-monitored, solid state diffusion. By controlling the particle diameter size and sintering conditions, the final product was a three-dimensional (3D) interconnected surface porosity favoring vascular and bone tissue ingrowth with prosthesis fixation by 3D mechanical interlocking3 (Fig 7-1). The same technology was subsequently used to develop a titanium alloy (Ti-6Al-4V) dental implant design with a stronger connection to bone than the original Brånemark-type implant (Nobel Biocare).4 The latter with its machine-turned finish had poor resistance to off-axis tensile loads, creating downstream compressive stress concentration localized to the coronal first few threads regardless of implant length5 (see Fig 2-9). The result was early crestal bone loss of up to 1 mm in year 1, after which a steady state generally developed with successful implants. In contrast, SPSIs experience transverse tensile and compressive loads of equal magnitudes with no localized high stress-driven crestal bone loss6 (Fig 7-2).

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Transverse force component

FIG 7-1  |  A scanning electron microscopic image of an SPSI that had been placed in a rabbit femur. Ti-6Al-4V metal powders with diameters 50 to 150 µm result in a surface layer with 35% to 40% porosity. Bone tissue can be seen to have grown extensively into the porosity, in some sites having reached the solid implant core (arrows) (original magnification ×100).

a

b

FIG 7-2  |  (a) Unlike threaded implant designs (see Fig 2-9), SPSIs do not develop high compressive stresses on the downstream side in reaction to transverse (off-axis) loads. Stress concentration (ie, the red-yellow halo around the implant) is uniform about the implant periphery due to effective resistance to tensile (upstream) loads. (b) Sometimes it is possible to see a lamina dura–like densification of bone at the SPSI surface (arrow). This example is of a 7-mm-long (6-mm designed intrabony length) implant (OT-F3, OT Medical) after 4 years in function. The prosthetic connection allowed for platform switching. Crestal bone remains stable with any resorption limited to the 1-mm machined transgingival collar segment.

From the outset, SPSIs were made for use in short lengths. One of the first human clinical trials used lengths of 7, 8, 9, and 10 mm, all of which had 2-mm machined coronal regions, making their respective designed intrabony lengths (DIL) only 5, 6, 7, and 8 mm, respectively.7 All of these lengths fit the current definitions of either short or ultra-short dental implants.8 In this first trial investigation, implants were used to retain complete mandibular overdentures in individuals with advanced alveolar ridge resorption. After 20 years of continuous function, the implant with the shortest length (5-mm DIL) had performed best with an absolute survival rate of 90%9 (Fig 7-3). However, when the product was first introduced commercially, experts of the day refused to accept that an implant so short could be predictably successful, clinging to the dogma that long implants were always the safest choice.

This negative attitude was due in many instances to a misunderstanding of how the implant affixes to bone. With SPSIs, this has been termed osseoconsolidation as opposed to the osseointegration (ie, primarily frictional grip) achieved with most other implant designs. Consolidation is the process of uniting, and indeed SPSIs become united and interlocked with bone by 3D bone ingrowth. SPSIs need good local vascularity, so they are not suitable for use in type 1 bone; sites with bone types 2 to 4 make better candidates10,11 (Fig 7-4). If an SPSI must be placed in type 1 bone, the site should be prepared by creating an osteotomy, placing platelet-rich autogenous blood clots, allowing the site to heal, and then undertaking delayed SPSI placement. It is also possible to place SPSIs in anterior sites provided that the osteotomy bleeds well during preparation (Fig 7-5).

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Clinical Scenarios for Successful SPSI Placement

FIG 7-3  |  An early 7-mm-long SPSI (Endopore, Innova Life Sciences) with healing cap (arrow). The DIL was only 5 mm because there was a 2-mm machine-turned collar segment. This size implant had a 20year absolute survival rate of 90% when used to retain mandibular complete overdentures.9

FIG 7-4  |  Three contiguous 7-mm-long (6-mm DIL) SPSIs (Endopore) were restored with nonsplinted crowns and are shown here after 12 years in function. Crestal bone loss is limited to the 1-mm-long machined-surface implant collar. FIG 7-5  |  (a) A 7-mm-long (6-mm DIL) SPSI (Endopore) was used in type 2 bone to replace this maxillary left central incisor and is seen here after 17 years of continuous function. The crown-to-implant (C/I) ratio is 2.7, and the patient had been told numerous times over the years by various dentists that the implant was too short and could not possibly succeed. (b) The implant crown on the maxillary central incisor SPSI is shown after 17 years of continuous function. (Restoration provided by Dr Reynaldo Todescan, Toronto, Ontario.)

a

Clinical Scenarios for Successful SPSI Placement Unlike Brånemark-type implants, SPSIs were soon shown to perform well in the low-density cancellous bone (types 3 and 4) encountered often in the posterior maxilla and sometimes in the posterior mandible.10 Short and ultra-short SPSIs can reduce the need for sinus floor augmentation or succeed with minor indirect bone-added osteotome-mediated sinus floor elevation (BAOSFE).12 Deporter et al13 assessed SPSI stability in anterior versus posterior maxillary sites in

b

50 nonsmoking, partially edentulous patients using the Periotest electronic percussion device (Medizintechnik Gulden). (Resonance frequency testing was not available at the time.) Periotest values (PTVs) are always expressed as negative values, and the greater the negativity the greater the implant stability.14,15 After 2 years of function, SPSIs in the posterior maxilla (ie, primarily cancellous bone with good vascularity) had significantly lower PTVs and therefore greater stability than SPSIs in the anterior maxilla (–2.87 versus –0.67). The same patient group and device were used to investigate the impact of implant length (7 to 12 mm), implant diameter (3.5, 4.1, or 5.0 mm), and splinting on SPSI

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FIG 7-6  |  This 7-mm-long Endopore SPSI (1-mm machined collar; 6-mm DIL) was placed in less than 5 mm of subantral bone with a minor BAOSFE. Despite the very large C/I ratio (> 3), it has been functioning for over 19 years against a mandibular free-end removable partial denture. Bone loss remains limited to the 1-mm machine-turned collar. (Restoration provided by Dr Reynaldo Todescan, Toronto, Ontario.)

stability. Implant length made no difference, suggesting that an SPSI longer than 7 mm (with a DIL of 5 mm) was not needed. On the other hand, increases in implant diameter decreased PTV values (ie, readings became more negative), again indicating increased implant stability. Splinting SPSIs also had an impact. In the 50 patients with 151 maxillary SPSIs, approximately half of the implants were splinted while the rest were restored with single individual crowns (even if this meant placing separate crowns on two or more neighboring implants). At each follow-up examination (6 months, 1 year, and 2 years), after disconnecting and removing the restorations and testing for implant stability using a standardized protocol, the implants that had been splinted displayed significantly higher (ie, less negative) PTVs, indicating less stability. For example, after 2 years in function, splinted implants had a mean PTV of –1.27 while implants that had been supporting single individual crowns showed a mean PTV of –3.09. This finding was interpreted to mean that the single implants were receiving greater but still physiologic levels of stress and that their supporting bone was responding appropriately. SPSIs were among the first implant designs found to be more or less unaffected by large crown-to-implant

FIG 7-7  |  This patient received two nonsplinted

SPSIs (Endopore) in the left posterior mandible. They were both 7 mm long with 2-mm machined collars (5mm DIL). The mesial freestanding implant also supported a single-tooth premolar pontic. (Restoration provided by Dr Simon Yeh, Toronto, Ontario.)

(C/I) ratios (Fig 7-6). More than a decade ago, Rokni et al16 reported that C/I ratio with SPSIs had no apparent impact on either implant failure or peri-implant crestal bone loss. More recently, however, Malchiodi et al11 studied the effects of two different calculations of C/I ratio on SPSI performance. Rokni et al16 had reported data only for the anatomical C/I ratio (AC/I ratio, ie, assuming the fulcrum to be at the implantabutment interface), but Malchiodi et al11 also calculated the clinical C/I ratio (CC/I ratio, ie, using the most coronal bone-to-implant contact point as the fulcrum) and concluded the latter to be the more relevant ratio. They suggested that both AC/I and CC/I ratios may have upper limits after which there may be increased risk with SPSI failure, as also appears to be the case with threaded implants.17 The critical upper limits for SPSIs were suggested to be an AC/I ratio of 3.1 and a CC/I ratio of 3.4. Short and ultra-short SPSIs also appear to be unaffected by carrying limited cantilever pontics (Figs 7-7 and 7-8). Occasionally, a large CC/I ratio can cause problems with loosening of retention screws, particularly with single implant restorations. SPSIs were among the first short and ultra-short implants found to be able to support nonsplinted molar crowns. Deporter et al18 reported data from a group of

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a

c

b

d

FIG 7-8  |  (a) This patient received two short SPSIs (Endopore) restored with a distal cantilever. The mesial implant was 9 mm long (8-mm DIL),

while the distal implant was 7 mm long (6-mm DIL), and both were 4.1 mm in diameter. At the 5-year recall, the facing on the cantilever had fractured, creating an esthetic issue. With the advent of the BAOSFE, it was decided to replace the partial denture with three single crowns, which required placement of a third implant (Endopore). The planned first molar site implant required approximately 3 mm of sinus floor elevation using xenograft material. (b) The molar implant was placed in highly cancellous bone; it ended up being overseated and ultimately supported mostly by new bone formed in the sinus. The radiograph was taken after the two mesial implants had been in function for 22 years, while the molar implant (7 × 4.1 mm, DIL 5 mm) had been functioning for 17 years. (c) A clinical photograph of the restorations. (d) A cone beam computed tomography (CBCT) scan of the maxillary left first molar implant site after 17 years in function. (Restorations provided by Dr Reynaldo Todescan, Toronto, Ontario.)

partially edentulous patients who received short posterior mandibular SPSIs (> 60% molars) restored primarily with single crowns (65%). Implants used were either 7 or 9 mm in length and had machine-turned collars of either 1 or 2 mm. After all patients had passed 10 years in function with these restorations, the survival and success rates based on stable crestal bone levels were both greater than 95% with three implant failures linked to surgical errors. Crestal bone loss with all implants was limited to the machine-turned collars and varied depending on whether a 1- or 2-mm collar had been used (Fig 7-9). Bone loss was always less for the 1-mm-collar model and

was due to a combination of biologic width accommodation and “stress-shielding” of bone adjacent to the collar surface.19 Deporter et al20 also reported 100% survival and success for ultra-short (5 mm long with 4-mm DIL) SPSIs in the posterior mandible (Figs 7-10 and 7-11) after 1 to 8 years in function, while Sohn et al21 reported 100% survival of 7-mm SPSIs in the posterior mandible after up to 9 years. More recently, Malchiodi et al22 reported 3-year survival of greater than 98% for 5- and 7-mm-long SPSIs placed in either the posterior mandible or maxilla (Fig 7-12). Again, almost 60% of the implants replaced molars.

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FIG 7-9  |  This patient received two 7 × 4.1–mm implants (Endopore) that have been functioning against two maxillary SPSIs for over 22 years. The more distal implant has a 1-mm machine-turned collar while the other has a 2-mm collar. The 2-mm collar has lost more bone due to coronal “stress-shielding.” (Restorations provided by Dr Reynaldo Todescan, Toronto, Ontario.)

a

FIG 7-10  |  An ultra-short (5 mm long, 4-mm DIL) SPSI (Endopore) replaced a mandibular first molar (with a restoration including platform switching) and has been in function for over 10 years. (Restoration by Dr Simon Yeh, Toronto, Ontario.)

b

FIG 7-11  |  (a) This patient received two SPSIs (Endopore) to restore her resorbed left posterior mandible with a three-unit fixed prosthesis. The more distal implant was 5 × 5 mm (4-mm DIL), while the more mesial implant was 7 × 4.1 mm (5-mm DIL). The radiograph shows the status after 8 years in function. (b) The clinical appearance at 8 years in function. (Restoration by Dr Simon Yeh, Toronto, Ontario.)

a

b

FIG 7-12  |  (a) Two single SPSIs were used to replace the maxillary right first premolar and first molar. The premolar site has a 7 × 4.1–mm (6-mm DIL) implant, while a 5 × 5–mm (4-mm DIL) implant was chosen for the molar site to avoid the need for a dedicated indirect sinus floor elevation procedure. Both implants (OT-F3) have an incorporated platform-switch feature. (b) Single anatomically correct metalceramic crowns were used for the two implants. (Restorations provided by Dr Ester Canton, Toronto, Ontario.)

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Challenges with SPSIs

a

b

d

c

e

FIG 7-13  |  (a) Two SPSIs (Endopore) were placed in the posterior maxilla. Despite the more or less ideal ridge width, operator error resulted in

the mesial implant being placed too far buccally. An inappropriately thin plate of buccal bone resulted. No augmentation grafting was included. (b) After 6 years in function, the improperly placed implant showed advanced peri-implant bone loss. Note that this second premolar implant was 12 mm long (coronal diameter: 4.1 mm), while the molar implant was 7 mm long (coronal diameter: 5 mm). (c) At 6 years, the buccal gingiva overlying the second premolar implant was discolored and showed deep probing depths. (d) Elevation of a mucoperiosteal flap exposed a large crater-like defect with extensive exposure of the sintered implant surface. The implant was removed, and the resulting defect was grafted with xenograft covered by dense polytetrafluoroethylene barrier.27 (e) After healing at the grafted site, a 7 × 4.1–mm (5-mm DIL) replacement implant (Endopore) was placed and later restored with a new single crown. This radiograph was taken after the new implant had been functioning for 10 years while the molar implant had been in continuous function for 18 years. (Restorations by Dr Reynaldo Todescan, Toronto, Ontario.)

Challenges with SPSIs Unfortunately, not all researchers investigating short and ultra-short SPSI performance had these stellar outcomes, which stresses the importance of careful patient selection and operator adherence to defined protocols. Perelli et al23,24 reported failure rates after 5 years for teeth restored using short or ultra-short SPSIs as 16% in the posterior mandible and 10% in the resorbed posterior maxilla. The majority of failures were late (ie, after prosthetic loading) and involved peri-implant infection. Because sintered surfaces are easily contaminated with bacterial plaque, every

effort needs to be taken to ensure that all surfaces are fully submerged in bone at placement, including the machined collar segment.25 These implants are not appropriate for smokers (especially when used in the posterior maxilla) because of the impact of smoking on crestal bone loss.26 Precise osteotomy preparation without bur chatter is essential to ensure a super-tight initial press-fit seating. In addition, if the final buccal crestal bone thickness is less than 2 mm, there is a risk of crestal bone loss sufficient to expose the sintered surface with potentially disastrous consequences27 (Fig 7-13). If there is any concern regarding this bone thickness, it is wise to include buccal overgrafting with

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a

b

FIG 7-14  |  (a) This freestanding 7-mm-long SPSI (DIL: 6 mm) has functioned against the two mandibular implants

shown in b for over 17 years. The implant was placed in type 4 bone using BAOSFE and ended up overseated and ultimately supported primarily by new bone formed under the tented sinus membrane. Some proximal crestal bone cratering is seen, but resorption has not progressed beyond the junction of the machined collar and the sintered surface. The premolar pontic was part of an existing fixed tooth-supported partial denture that originally used the first molar as the distal abutment. This pontic was left in situ as part of the treatment plan and is still in the patient’s mouth. (b) The two SPSIs have currently been the antagonists of the maxillary implant in a for 17 years. (Restorations by Dr Reynaldo Todescan, Toronto, Ontario.)

FIG 7-15  |  A 7 × 5–mm (5-mm DIL) SPSI (Endopore) was intentionally overseated using BAOSFE because of loss of buccal bone height during extraction site healing. The restoration employed platform switching and is shown after 10 years in function. (Restoration by Dr Richard Cameron, Toronto, Ontario.)

a slowly resorbing material such as a xenograft. The grafting will also improve the prosthetic emergence profile and counter any vestibular pooling of food particles by reducing or eliminating anatomical buccal ridge depressions. If all of these protocol steps are observed, crestal bone loss will be minimal and should remain localized to the machined transgingival implant collar.28 A further key point in SPSI placement is to recognize that the implants are tapered, so they need to be driven into place with a surgical mallet to achieve a tight initial contact with bone. Should insufficient force be used

at this malleting step, the implant will not fully seat and could fail to achieve fixation to bone. Ensuring adequate stability using resonance frequency testing (implant stability quotient > 60) will help to reduce this risk. In highly cancellous bone, the necessary malleting force may result in unintended oversubmergence of the implant (Figs 7-14 and 7-15). However, this should not present a problem as long as an appropriately lengthened healing abutment can be immediately connected to the implant. This will prevent the implant from being totally buried in bone, making reentry unnecessarily difficult and traumatic.

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a

b

FIG 7-16  |  (a) A 7 × 4.1–mm (5-mm DIL) SPSI (Endopore) was intentionally overseated to accommodate the

buccal crest that was much lower than the other bone wall heights. A straight-sided 4-mm-long healing abutment was immediately connected to the seated implant, and single-stage initial healing was allowed. (b) After osseoconsolidation healing, a single crown was used with platform switching for this implant. The radiograph was taken after 10 years in function and shows crestal bone remodeling adjacent to the 2-mm machined implant collar only. (Restoration by Dr Richard Cameron, Toronto, Ontario.)

a

b

FIG 7-17  |  (a) The immediate postoperative radiograph for these three SPSIs (Endopore) showed that the most mesial one was not adequately seated on its distal aspect. It was removed the following day and replaced with another implant seated to the appropriate depth. (b) This radiograph shows the three implants after 19 years in function. Note the increased cortical bone density toward the crest. (Restoration by Dr Reynaldo Todescan, Toronto, Ontario.)

Intentional overseating of the implant may be needed in situations where the buccal crestal bone ends up being significantly lower than the other aspects because of previous alveolar ridge remodeling (Fig 7-16). Inadequate implant seating with the sintered surface left supracrestally is a prescription for disaster. If it becomes clear in the immediate postoperative

period that an SPSI has not been fully seated (including the machined collar segment), the implant must be removed and discarded. This will be followed by further site development and placement of another implant—either immediately if feasible or in a delayed fashion (Fig 7-17).

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a

b

FIG 7-18  |  (a) In 1997, this patient requested replacement of her maxillary right second premolar and first molar, maxillary left first molar, and

mandibular left first molar with implant-supported restorations. A computed tomography (CT) scan showed there to be about 4 mm of subantral bone at the maxillary right molar site. The mandibular left molar implant had been intentionally overseated to compensate for a low buccal crest height. (b) The patient received two SPSIs to replace her maxillary right second premolar (7 × 4.1 mm, DIL: 6 mm) and first molar (7 × 5 mm, DIL: 6 mm). She was participating in a prospective clinical trial and was designated to receive a splinted prosthesis. The premolar implant was inserted without disturbing the sinus floor, while the molar site was managed with BAOSFE using osteotomes and xenograft particles.

BAOSFE Technique A major advantage with short and ultra-short SPSIs is that they can often allow the surgeon to minimize or even entirely avoid sinus floor manipulation in the resorbed posterior maxilla (Fig 7-18; see Fig 7-12). Deporter et al29 investigated the use of 7-mm-long SPSIs placed in the posterior maxilla using the Summers BAOSFE technique.12 Even in sites with 4 mm or less of remaining preoperative subantral alveolar bone height, the implant failure rate was less than 2% after a mean functional time of 3.1 years.30 At the time, this outcome was far better than outcomes with threaded implants placed with either open lateral window sinus grafting (OSG; 8.3% failure) or BAOSFE (up to 26.7% failure).31–33 Corrente et al34 reported SPSI outcomes similar to those of Deporter in the resorbed posterior maxilla: 2% failure after 3 years. Since the BAOSFE technique was first introduced in 1994, it has continued to gain acceptance by investigators and clinicians worldwide given that it is much less invasive than the traditional OSG approach.12 As originally described, BAOSFE involved osteotomy development primarily using handheld end-cutting osteotomes and gentle hammering with a surgical mallet. Rather

than removing bone from the site, the slow, incremental advancements of the osteotome tips with incrementally increasing diameters resulted in bone compression toward the sinus floor as well as subtle lateral ridge expansion. Ultimately, an osteotome was used to upfracture the ceiling of cortical sinus floor bone locally at the osteotomy apex, and in so doing it lifted the sinus membrane passively and circumferentially away from the sinus floor bone surfaces. This created a tented chamber into which the implant apex could ultimately be inserted (Fig 7-19). Originally, the majority of investigators added a bone substitute material (most commonly xenograft) to provide additional support for the membrane in its new position and provide a scaffold for new bone formation by cells arising from perivascular tissue and sinus periosteum. Later, it was discovered that implants could be placed without adding exogenous graft particles in many situations and instead rely on the implant apex itself to tent up the elevated membrane. Provided that no membrane damage occurred during the procedure, the tented chamber would fill with blood and lead to the desired new bone formation surrounding the implant apex. For the placement of a threaded implant using this approach, it has generally been recommended that there be at least 5 mm of remaining subantral bone height.35

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BAOSFE Technique

a

FIG 7-19  |  A handheld end-cutting osteotome

advanced incrementally with a surgical mallet can be used to compress native bone and added graft material apically to breach the sinus floor, elevating the sinus membrane locally.

a

b

FIG 7-20  |  (a) An ultra-short 5 × 4.1–mm (4-mm DIL) SPSI (Endopore) was placed in 3 mm of subantral bone using BAOSFE. A major portion of the implant length sits in new bone that formed following the sinus grafting. (b) A CBCT scan of the implant after 6 months of submerged healing prior to reentry and restoration. The majority of the implant is surrounded by new bone at this time. (Restoration by Dr Jeffrey Reynolds, Toronto, Ontario.)

b

c

FIG 7-21  |  (a) A 7 × 5–mm (6-mm DIL) SPSI (Endopore) was planned for this recently extracted but healed first molar socket using BAOSFE and xenograft particles. (b) The baseline radiograph following restoration of the implant still shows a large area of graft particles at the implant apex (arrows). (c) This radiograph shows considerable graft shrinkage at the implant apex after 5 years in function. Crestal bone loss is limited to the 1-mm machined collar segment of the implant. (Restoration by Dr Reynaldo Todescan, Toronto, Ontario.)

However, without the added graft material, greater shrinkage (compared with sites augmented with graft particles) of the new bone can be expected, and not infrequently the implant apex ends up being covered only by the sinus membrane, not by bone.36 If less than 5 mm of subantral bone exists, however, there should not be an issue with placing a 5-mm-long SPSI as long as there remains enough native bone thickness to stabilize the implant (ie, 2 to 3 mm) (Fig 7-20). With so little bone remaining, however, it may be better to add a graft material, either xenograft or ideally several autogenous platelet-rich fibrin clots

(PRP-F).37 (See chapter 8 for an example of BAOSFE with PRP-F.) This will ensure that the maximal amount of new bone is formed around the segment of implant protruding beyond the original sinus floor.38 Irrespective of the amount of graft placed, some shrinkage can be expected with time (Fig 7-21). Using panoramic radiographs, Kopecka et al39 measured subantral bone heights in the posterior maxillae of almost 600 patients and found that the heights were less than 5 mm in 31.6% of second premolar, 73.1% of first molar, and 54.2% of second molar sites. Indeed, 50% of edentulous maxillary molar

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1.5 mm

1 mm

a

b

c

FIG 7-22  |  (a) The preoperative sagittal CT section for this patient showed there to

be minimal subantral bone height. (b and c) The coronal CT section of the first molar site showed 1 to 1.5 mm of subantral bone height. (d) Three SPSIs (Endopore) were placed using hand osteotomes and xenograft using BAOSFE. They were restored with separate crowns and are shown here after 14 years in function. The BAOSFE procedure helped to produce substantial new bone around the implant apices. (Restoration by Dr Richard Cameron, Toronto, Ontario.)

d

sites have less than 4 mm of subantral bone remaining, making management with SPSIs an attractive treatment option.40 However, the option of placing SPSIs using BAOSFE should not be offered to patients who smoke because of the substantially increased risk of failure.41 Systematic literature reviews and direct comparison studies investigating BAOSFE have shown it to be a predictably successful procedure provided that certain guidelines are followed. In most situations, the membrane can be elevated up to 5 mm using osteotomes without resulting in membrane tears.42,43 Zill et al44 recently reported 5-year retrospective results in a group of 113 patients who had received a total of 233 moderately rough threaded implants (MRTIs) in the posterior maxilla. The mean pretreatment subantral bone height was 5.9 ± 1.7 mm, and all implants were placed using transcrestal sinus floor elevation but without the addition of graft particles. The authors suggested that given the risks and cost, there may

be little justification for using an OSG approach to place an MRTI if the original subantral bone height is greater than 5 mm. Further support for this conclusion was provided in a retrospective report with threaded implants by Tetsch et al.45 Both BAOSFE and OSG achieved 97% survival for intervals as long as 14 years; however, the data showed that the two techniques were selected based on different prerequisites. Long (mean length: 11.5 mm) threaded implants were used in all cases. Sites chosen for BAOSFE were those requiring a mean sinus floor elevation of only 3.3 mm, while sites chosen for OSG needed a mean sinus floor elevation of 6.5 mm. As already stressed, SPSIs need not be used in lengths greater than 7 mm; if there is 5 mm of original subantral bone, using a 5-mm-long SPSI will avoid involving the sinus (see Fig 7-12). Otherwise, as long as 2 to 3 mm of bone remains, a 5- or 7-mm-long SPSI can be placed with little to no risk of membrane damage because of the minimal elevation required (Fig 7-22).

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a

b

FIG 7-23  |  (a) A small sinus membrane tear occurred at this BAOSFE site. (b) If BAOSFE is performed correctly, there should

always be a visible ceiling of autogenous bone or added graft particles. (Courtesy of Dr Michael Toffler, New York City, New York.)

Challenges with BAOSFE One problem with the original Summers approach is that patients may be alarmed by the idea of hammering with a mallet. To minimize associated patient anxiety, it is wise to administer mild hypnotic sedation (eg, 5 mg triazolam) by mouth up to 1 hour before surgery. Even so, bone density in posterior maxillary sites and certainly the density of the sinus cortical floor itself can vary widely.46 If the bone is other than types 3 or 4, there is always the risk of too much force being needed to advance the osteotome, resulting in postoperative vertigo of variable duration. To overcome this, it is possible to initiate the osteotomy with pilot burs to a depth short of the sinus floor by approximately 1 mm using the cone beam computed tomography (CBCT) scan measurements for guidance and bur stops to avoid drilling too deep. Thereafter, if the osteotome still will not advance at least 0.5 mm per tap with the mallet, implant-specific burs can be employed to widen the osteotomy, again using bur stops. Following this step, an osteotome tip will be more likely to advance through the last 1 mm of subantral bone, compressing and freeing it from the remainder of the sinus floor. Should the osteotome still not advance easily, specialized rotary instruments are available to drill through the sinus floor with only a small risk of perforating or tearing the sinus membrane. Examples include the Crestal Approach Sinus Kit (Hiossen

Dental) and the more recently developed Densah burs (Versah Dental). The latter are run counterclockwise and will push collected autogenous bone apically. While many BAOSFE sites can be executed successfully with only a panoramic radiograph as documentation, preoperative CBCT scans have now become routine because they provide far more relevant information and help to reduce risks.47,48 CBCT scans allow accurate assessment of the residual alveolar bone height and buccopalatal ridge width, the highly important buccal wall thickness, the thickness of the sinus membrane, and the presence and location of septa and major vessels. They can also reveal pathologic thickening of sinus mucosa and the presence of a blocked ostium, both of which could be risks for sinus infection following BAOSFE.40 With these latter findings, patients should be sent for an ear, nose, and throat assessment before implant treatment. Another risk is the possibility of sinus membrane tears during the procedure (Fig 7-23a). The greater the elevation attempted, the greater the risk of sinus membrane damage.49 Tears can be avoided by ensuring that there is always an intact osteotomy ceiling of compacted bone or graft particles after each surgical step (Fig 7-23b). Suspected membrane tears can be confirmed with a “plugged nose blow” test. If they are small, tears are usually easily sealed with a collagen plug (eg, Heliplug, Integra LifeSciences) followed by a second plugged nose blow50 (Fig 7-24). An even

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a

b

c

FIG 7-24  |  (a) During BAOSFE osteotomy preparation at this first molar site, a small sinus perforation was caused by the initial osteotome. The perforation was immediately sealed with a collagen sponge, and the procedure continued using wider osteotomes to shave autogenous bone from the osteotomy walls and compact it against the collagen plug. No other graft material was employed. (b) Submerged healing of the site was uneventful, and after 6 months, treatment proceeded with reentry surgery and restoration using a single crown. In this radiograph taken after 5 years in function, new bone can be seen surrounding the apex of the 7 × 5–mm (5-mm DIL) SPSI. Crestal bone remodeling occurred in a predictable fashion, being limited to the 2-mm machined collar segment of the implant. (c) A CBCT scan taken of the implant at 5 years confirmed that extensive new bone had formed around the segment of implant placed beyond the original sinus floor. (Courtesy of Dr Michele Perelli, Torino, Italy.)

more appropriate management protocol would be to insert at least one autogenous PRP-F clot into the site to seal the tear.51 These clots have antibacterial and anti-inflammatory properties and of course will promote the desired new bone formation.52 However, if it is not possible to draw the patient’s blood to prepare PRP-F clots, the procedure can continue with the addition of particulate xenograft material if the tear has been effectively sealed with a collagen plug.12 If a few particles escape into the sinus cavity proper, they will quickly be removed by the ciliary action of sinuslining epithelial cells and expelled through the ostium as long as they are smaller than 1 mm. However, graft particles larger than 1 mm could potentially block the ostium and result in a sinus infection if they were to pass through a membrane tear. Advise the patient that a small amount of clotted blood and a few small whitish graft particles may exit through the nostrils in the first 24 to 72 hours. Using short and ultra-short SPSIs in posterior maxillary sites with 3 mm or less of subantral bone remaining may at first seem daunting. However, the 5-degree taper angle ensures that there is little to no risk of the implant disappearing into the sinus cavity even if it is a bit overseated

provided that the osteotomy is precisely shaped to fit the chosen implant diameter (3.8, 4.1, or 5.0 mm). The exception could be a type 4 bone site with a very thin cortical sinus floor, but this situation is unlikely. As a precaution, however, care should be taken in such situations with using the mallet to seat the implant. Tapping with the mallet should begin gently to verify that the implant is stable and therefore not likely to disappear into the sinus. Once a dull sound from the impact of the mallet can be heard, the implant will be secure enough to integrate.

Case Study For the most part, using the transcrestal approach with SPSIs is highly predictable, but failures can occur. The patient shown in Fig 7-25 presented with failure of a long-standing fixed tooth-supported partial denture in the left posterior maxilla. The molar abutment tooth and partial denture pontic were removed, and a single SPSI was placed transcrestally without added graft material. The patient returned approximately 7 months later for reentry surgery. Considerable new bone appeared to have formed around the implant DIL, and the implant was

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Case Study

a

b

c

d

FIG 7-25  |  (a) This patient presented with a failed three-unit tooth-supported fixed prosthesis and wished to have it re-

placed with dental implants. While ridge width was adequate, there was very little subantral bone height remaining. The patient opted to have treatment with BAOSFE and a short SPSI. (b) The maxillary left molar abutment tooth was extracted, and a single SPSI was placed in the first molar location using the transcrestal approach without any added graft material. The implant was 7 × 5 mm (5-mm DIL) and was stabilized only by contact between the remaining subantral bone and the machinesurfaced implant collar. The tapered implant shape prevented loss of the implant into the sinus cavity. It is shown here at the time of reentry surgery. (c) The implant was restored using a single anatomically correct molar crown that functioned well for 6 months before requiring removal because of discomfort. (d) Ultimately, the patient needed an OSG procedure and was restored with two short SPSIs and one standard-length, narrow-diameter MRTI, all of which are shown in this radiograph after 7 years in function. (Restoration by Dr Reynaldo Todescan, Toronto, Ontario.)

subsequently restored with a single molar crown. After 6 months, the patient complained of discomfort from the flare-up of a long-standing chronic left-sided sinusitis for which he needed to use steroidal nasal sprays. Clinical assessment determined that the implant had failed with slight mobility and discomfort. As a result, the implant was removed, and the patient underwent an OSG procedure elsewhere. After this apparently successful procedure, the patient returned for further SPSI treatment. He commented that he was now able to breathe better than he had in years.

Meanwhile, the second premolar became symptomatic, and the treatment recommended was two implants and a three-unit fixed prosthesis. However, the patient preferred to have three implants all with single crowns. Three SPSIs were placed, one each in the second premolar, first molar, and second molar sites. Subsequent to this, the first molar implant again failed to integrate and was removed. At this point, it was decided to attempt a long MRTI, and the bone volume available required one with a narrow diameter. This was successful, and the final rehabilitation with three separate implant crowns is shown in Fig 7-25.

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Guidelines for Successful Outcomes with SPSIs Because SPSIs are generally used in edentulous posterior sites with reduced bone height, it is wise to obtain pretreatment CBCT scans to provide as much information as possible regarding existing alveolar ridge height and width, proximity to vital structures, buccal and lingual or palatal cortical bone thickness, and bone density. Ensuring that planned sites have suitably wide (≥ 2 mm) and thick keratinized tissue is also important. If not, soft tissue grafting is recommended either before or during the implant procedure. In addition, minimizing the risk of nerve damage in the highly resorbed posterior mandible can be achieved by using only infiltration anesthesia. Further guidelines are as follows: • SPSI treatment should not be provided for smokers, particularly in the posterior maxilla. • In the posterior mandible, the alveolar ridge height needs to be at least 6 mm to receive a 5-mm-long implant. • In the posterior maxilla, the subantral bone height can be as little as 2 mm if the operator is experienced with BAOSFE. • Flap reflection should be minimal unless it is anticipated that there will be a need to augment the buccal bone to ensure adequate final thickness (≥ 2 mm). The following steps should be completed to place SPSIs: 1. Each osteotomy is initiated using a sharp pointed narrow cortical penetrating bur followed by a straight-sided pilot bur that should reach the anticipated final required depth (or slightly deeper if feasible) of the osteotomy. (Sites requiring BAOSFE are an exception.) Failing to achieve proper osteotomy depth by this point is a common reason for later implant failure (see Fig 7-17a).

2. Following verification of adequate osteotomy depth, the tapered osteotomy-shaping burs of appropriate length (5 or 7 mm) and diameter (3.8, 4.1, or 5.0 mm) are used in sequence starting with the smallest diameter to increase the osteotomy width in small increments (Figs 7-26a and 7-26b). Note that these burs will not increase osteotomy depth. 3. With all of the shaped burs, care must be taken to avoid bur chatter, which could unfavorably alter the precise osteotomy dimensions needed for implant fixation to bone. 4. The last step before placing the implant will be to insert a trial-fit gauge into the osteotomy to ensure that it fits precisely with no movement possible using digital manipulation (Fig 7-26c). 5. The chosen implant can then be inserted with care being given not to contaminate the sterile sintered porous surface. 6. Without delay, the implant carrier is then detached, and the appropriately color-coded implant driver tip and surgical mallet are used to drive the implant to its full depth; both the sintered porous surface and the coronal machined collar segment should be buried in bone. 7. Finally, a hex-driver tip is used with firm digital force to insert the healing cap, sealing the internal prosthetic connection of the implant. If the procedure has been performed correctly, the operator should find the implant highly secure without movement when using this driver. There are additional factors to consider with SPSIs placed in the posterior maxilla: • In posterior maxillary sites displaying types 3 or 4 bone and after using the initial pointed cortical penetrating bur, the operator can move directly to hand osteotomes to retain and compress all of the bone in the osteotomy site.10 Alternatively, densification burs with depth indicators can be used to avoid using a surgical mallet with its patient irritation factor.

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Guidelines for Successful Outcomes with SPSIs

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FIG 7-26  |  (a) The smallest diameter (3.8 mm) tapered implant bur is used after the pilot bur to begin shaping the osteotomy. (b) The 4.1-mm-diameter implant bur of appropriate length is used next to enlarge the osteotomy. Should a 5.0-mm-diameter implant be planned, the 4.1-mm-diameter bur would be followed by the corresponding 5.0-mm-diameter implant bur. (c) The trial-fit gauge corresponding to the length and diameter of the chosen implant is inserted with firm digital force to confirm that the osteotomy is of the required dimensions to allow full seating of the implant.

a

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FIG 7-27  |  (a) In the posterior maxilla, a shaped pilot bur can be used to initialize the osteotomy, staying short of the sinus floor. The shortest of these burs is 3 mm in length. (b) The trial-fit gauge corresponding to the chosen implant can be used with a surgical mallet to upfracture the sinus floor. Its blunt tip will minimize the risk of membrane penetration. (c) If needed, an end-cutting hand osteotome can be employed to upfracture the sinus floor. (d) When placed properly, the full length of the implant including the machined collar segment should be submerged in bone. d

• Should the bone be too dense to use osteotomes (ie, the operator is unable to advance the tip at least 0.5 mm per mallet application), the appropriate size of tapered pilot bur can be used to approach but not breach the sinus floor (based on pretreatment imaging). These burs are provided in lengths as short as 3 mm (Fig 7-27a).

• Having used the appropriate tapered pilot bur to a point just short of the sinus floor, the clinician can then upfracture the sinus floor and lift it incrementally while shaping the tapered osteotomy walls using the blunt-ended trial-fit gauges or end-cutting osteotomes and surgical mallet (Figs 7-27b to 7-27d).

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CHAPTER 7 | Press-Fit Sintered Porous-Surfaced Implants

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FIG 7-28  |  (a) The CBCT imaging for a patient wishing to have the maxillary left first molar replaced by a single implant. There was approximately 3 mm of subantral bone remaining but adequate buccolingual ridge width to receive a 5-mm-diameter SPSI. (b) An osteotomy was developed with hand osteotomes using BAOSFE to raise the sinus floor by approximately 2 mm. Considerable but well-contained graft material can be seen in this postoperative radiograph. (c) By 1 year in function, the implant was performing well with major graft shrinkage noted. The original sinus floor can just barely be seen (line and arrows). Minimal crestal bone loss has occurred. (Implant type: OT-F3; courtesy of Dr Andreas Lindemann, Bremen, Germany.)

• Because SPSIs are so short, it is recommended to use a graft material with BAOSFE before inserting the implant, and the best option now appears to be two or more autogenous PRP-F clots. These can be inserted just before implant placement using the blunt end of the appropriate trial-fit gauge and hand pressure only. Additionally, the implant surface can be coated with autogenous growth factors by

dripping any available fluid that can be compressed from the fibrin clots. The clots inserted under the elevated sinus floor will ensure that adequate new bone forms at the implant apex and seal any small membrane tears that may or may not have been detected during the procedure. A recent sample case using a 5 × 5–mm SPSI is shown in Fig 7-28.

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References

Conclusion Press-fit SPSIs have been in clinical use for over 20 years and have proven to be predictably successful in short and ultra-short lengths. They are particularly effective in resorbed posterior jaw sites, preferring all bone types except type 1, which is insufficiently vascular to achieve osseoconsolidation (ie, 3D vascular tissue and bone ingrowth into the implant’s porous surface layer). Unlike short and ultra-short MRTIs, SPSIs do not require splinting to other implants and can be restored for the most part with anatomically correct crowns. Placement requires precision during osteotomy preparation to ensure a tight initial press fit of the implant to the osteotomy. Great care needs to be taken that the whole implant—including the machined collar segment—is submerged in bone and that the buccal and lingual or palatal cortical osteotomy walls remain of a thickness that will discourage crestal bone resorption (ie, ≥ 2 mm). If the osteotomy walls are not thick enough, appropriate hard tissue grafting should be undertaken concurrently.

References 1. Bobyn JD, Pilliar RM, Binnington AG, Szivek JA. The effect of proximally and fully porous-coated canine hip stem design on bone modeling. J Orthop Res 1987;5:393–408. 2. Pilliar RM. Porous-surfaced metallic implants for orthopedic applications. J Biomed Mater Res 1987;21(A1 suppl):1–33. 3. Pilliar RM. Overview of surface variability of metallic endosseous dental implants: Textured and porous surface-structured designs. Implant Dent 1998;7: 305–314. 4. Deporter DA, Watson PA, Pilliar RM, Chipman ML, Valiquette N. A histological comparison in the dog of porous-coated vs. threaded dental implants. J Dent Res 1990;69:1138–1145. 5. Pierrisnard L, Renouard F, Renault P, Barquins M. Influence of implant length and bicortical anchorage on implant stress distribution. Clin Implant Dent Relat Res 2003;5: 254–262.

6. Pilliar RM, Sagals G, Meguid SA, Oyonarte R, Deporter DA. Threaded versus porous-surfaced implants as anchorage units for orthodontic treatment: Three-dimensional finite element analysis of peri-implant bone tissue stresses. Int J Oral Maxillofac Implants 2006;21:879–889. 7. Renouard F, Nisand D. Impact of implant length and diameter on survival rates. Clin Oral Implants Res 2006;17(suppl 2):35–51. 8. Neugebauer J, Nickenig HJ, Zöller JE; Department of Cranio-maxillofacial and Plastic Surgery and Interdisciplinary Department for Oral Surgery and Implantology; Centre for Dentistry and Oral and Maxillofacial Surgery. Update on short, angulated and diameter-reduced implants. [Proceedings of the 11th European Consensus Conference (EuCC), 6 Feb 2016, Cologne, Germany]. Bonn, Germany: BDIZ EDI, 2016. 9. Deporter DA, Pharoah M, Yeh S, Todescan R, Atenafu EG. Performance of titanium alloy sintered porous-surfaced (SPS) implants supporting mandibular overdentures during a 20-year prospective study. Clin Oral Implants Res 2014;25:e189–e195. 10. Lekholm U, Zarb GA. Patient selection and preparation. In: Brånemark PI, Zarb GA, Albrektsson T (eds). TissueIntegrated Prostheses: Osseointegration in Clinical Dentistry. Chicago: Quintessence, 1985:199–209. 11. Malchiodi L, Cucchi A, Ghensi P, Consonni D, Nocini PF. Influence of crown-implant ratio on implant success rates and crestal bone levels: A 36-month follow-up prospective study. Clin Oral Implants Res 2014;25:240–251. 12. Summers RB. The osteotome technique: Part 3—Less invasive methods of elevating the sinus floor. Compendium 1994;15:698–700. 13. Deporter D, Todescan R, Riley N. Porous-surfaced dental implants in the partially edentulous maxilla: Assessment for subclinical mobility. Int J Periodontics Restorative Dent 2002;22:184–192. 14. Olivé J, Aparicio C. Periotest method as a measure of osseointegrated oral implant stability. Int J Oral Maxillofac Implants 1990;5:390–400. 15. Teerlinck J, Quirynen M, Darius P, van Steenberghe D. Periotest: An objective clinical diagnosis of bone apposition toward implants. Int J Oral Maxillofac Implants 1991;6: 55–61. 16. Rokni S, Todescan R, Watson P, Pharoah M, Adegbembo AO, Deporter D. An assessment of crown-to-root ratios with short sintered porous-surfaced implants supporting prostheses in partially edentulous patients. Int J Oral Maxillofac Implants 2005;20:69–76.

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17. Anitua E, Alkhraist MH, Piñas L, Begoña L, Orive G. Implant survival and crestal bone loss around extra-short implants supporting a fixed denture: The effect of crown height space, crown-to-implant ratio, and offset placement of the prosthesis. Int J Oral Maxillofac Implants 2014;29: 682–689. 18. Deporter DA, Kermalli J, Todescan R, Atenafu E. Performance of sintered, porous-surfaced, press-fit implants after 10 years of function in the partially edentulous posterior mandible. Int J Periodontics Restorative Dent 2012;32: 563–570. 19. Deporter DA, Al-Sayyed A, Pilliar RM, Valiquette N. “Biologic width” and crestal bone remodeling with sintered porous-surfaced dental implants: A study in dogs. Int J Oral Maxillofac Implants 2008;23:544–550. 20. Deporter DA, Ogiso B, Sohn DS, Ruljancich K, Pharoah M. Ultrashort sintered porous-surfaced dental implants used to replace posterior teeth. J Periodontol 2008;79: 1280–1286. 21. Sohn DS, Kim WS, Lee WH, Jung HS, Shin IH. A retrospective study of sintered porous-surfaced dental implants in restoring the edentulous posterior mandible: Up to 9 years of functioning. Implant Dent 2010;19:409–418. 22. Malchiodi L, Ghensi P, Cucchi A, Pieroni S, Bertossi D. Peri-implant conditions around sintered porous-surfaced (SPS) implants. A 36-month prospective cohort study. Clin Oral Implants Res 2015;26:212–219. 23. Perelli M, Abundo R, Corrente G, Saccone C. Short (5 and 7 mm long) porous implant in the posterior atrophic mandible: A 5-year report of a prospective study. Eur J Oral Implantol 2011;4:363–368. 24. Perelli M, Abundo R, Corrente G, Saccone C. Short (5 and 7 mm long) porous implants in the posterior atrophic maxilla: A 5-year report of a prospective single-cohort study. Eur J Oral Implantol 2012;5:265–272. 25. Deporter DA, Watson PA, Pilliar RM, Howley TP, Winslow J. A histological evaluation of a functional endosseous, porous-surfaced, titanium alloy dental implant system in the dog. J Dent Res 1988;67:1190–1195. 26. Bain CA, Moy PK. The association between the failure of dental implants and cigarette smoking. Int J Oral Maxillofac Implants 1993;8:609–615. 27. Bartee BK. The use of high-density polytetrafluoroethylene membrane to treat osseous defects: Clinical reports. Implant Dent 1995;4:21–26. 28. Pilliar RM, Deporter DA, Watson PA, Valiquette N. Dental implant design—Effect on bone remodeling. J Biomed Mater Res 1991;25:467–483. 29. Deporter DA, Todescan R, Caudry S. Simplifying management of the posterior maxilla using short, porous-surfaced dental implants and simultaneous indirect sinus elevation. Int J Periodontics Restorative Dent 2000;20:476–485.

30. Deporter DA, Caudry S, Kermalli J, Adegbembo A. Further data on the predictability of the indirect sinus elevation procedure used with short, sintered, porous-surfaced dental implants. Int J Periodontics Restorative Dent 2005;25: 585–593. 31. Geurs NC, Wang IC, Shulman LB, Jeffcoat MK. Retrospective radiographic analysis of sinus graft and implant placement procedures from the Academy of Osseointegration Consensus Conference on Sinus Grafts. Int J Periodontics Restorative Dent 2001;21:517–523. 32. Rosen PS, Summers RB, Mellado JR, et al. The bone-added osteotome sinus floor elevation technique: Multicenter retrospective report of consecutively treated patients. Int J Oral Maxillofac Implants 1999;14:853–858. 33. Toffler M. Osteotome-mediated sinus floor elevation: A clinical report. Int J Oral Maxillofac Implants 2004;19: 266–273. 34. Corrente G, Abundo R, des Ambrois AB, Savio L, Perelli M. Short porous implants in the posterior maxilla: A 3-year report of a prospective study. Int J Periodontics Restorative Dent 2009;29:23–29. 35. Si MS, Shou YW, Shi YT, Yang GL, Wang HM, He FM. Long-term outcomes of osteotome sinus floor elevation without bone grafts: A clinical retrospective study of 4-9 years. Clin Oral Implants Res 2016;27:1392–1400. 36. Lundgren S, Cricchio G, Hallman M, Jungner M, Rasmusson L, Sennerby L. Sinus floor elevation procedures to enable implant placement and integration: Techniques, biological aspects and clinical outcomes. Periodontol 2000 2017;73:103–120. 37. Toffler M, Toscano N, Holtzclaw D. Osteotome-mediated sinus floor elevation using only platelet-rich fibrin: An early report on 110 patients. Implant Dent 2010;19:447–456. 38. Rahmani M, Shimada E, Rokni S, et al. Osteotome sinus elevation and simultaneous placement of porous-surfaced dental implants: A morphometric study in rabbits. Clin Oral Implants Res 2005;16:692–699. 39. Kopecka D, Simunek A, Brazda T, Rota M, Slezak R, Capek L. Relationship between subsinus bone height and bone volume requirements for dental implants: A human radiographic study. Int J Oral Maxillofac Implants 2012;27: 48–54. 40. Shanbhag S, Karnik P, Shirke P, Shanbhag V. Cone-beam computed tomographic analysis of sinus membrane thickness, ostium patency, and residual ridge heights in the posterior maxilla: Implications for sinus floor elevation. Clin Oral Implants Res 2014;25:755–760. 41. Lin TH, Chen L, Cha J, et al. The effect of cigarette smoking and native bone height on dental implants placed immediately in sinuses grafted by hydraulic condensation. Int J Periodontics Restorative Dent 2012;32:255–261.

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42. Wallace SS, Froum SJ. Effect of maxillary sinus augmentation on the survival of endosseous dental implants. A systematic review. Ann Periodontol 2003;8:328–343. 43. Del Fabbro M, Corbella S, Weinstein T, Ceresoli V, Taschieri S. Implant survival rates after osteotome-mediated maxillary sinus augmentation: A systematic review. Clin Implant Dent Relat Res 2012;14(suppl 1):e159–e168. 44. Zill A, Precht C, Beck-Broichsitter B, et al. Implants inserted with graftless osteotome sinus floor elevation—A 5-year post-loading retrospective study. Eur J Oral Implantol 2016;9:277–289. 45. Tetsch J, Tetsch P, Lysek DA. Long-term results after lateral and osteotome technique sinus floor elevation: A retrospective analysis of 2190 implants over a time period of 15 years. Clin Oral Implants Res 2010;21:497–503. 46. Choucroun G, Mourlaas J, Kamar Affendi NH, Froum SJ, Cho SC. Sinus floor cortication: Classification and prevalence. Clin Implant Dent Relat Res 2017;19:69–73. 47. Temmerman A, Hertelé S, Teughels W, Dekeyser C, Jacobs R, Quirynen M. Are panoramic images reliable in planning sinus augmentation procedures? Clin Oral Implants Res 2011;22:189–194.

48. Temple KE, Schoolfield J, Noujeim ME, Huynh-Ba G, Lasho DJ, Mealey BL. A cone beam computed tomography (CBCT) study of buccal plate thickness of the maxillary and mandibular posterior dentition. Clin Oral Implants Res 2016;27:1072–1078. 49. Reiser GM, Rabinovitz Z, Bruno J, Damoulis PD, Griffin TJ. Evaluation of maxillary sinus membrane response following elevation with the crestal osteotome technique in human cadavers. Int J Oral Maxillofac Implants 2001;16: 833–840. 50. Zhen F, Fang W, Jing S, Zuolin W. The use of a piezoelectric ultrasonic osteotome for internal sinus elevation: A retrospective analysis of clinical results. Int J Oral Maxillofac Implants 2012;27:920–926. 51. Toffler M, Rosen PS. Complications with transcrestal sinus floor elevation: Etiology, prevention, and treatment. In: Froum S (ed). Dental Implant Complications: Etiology, Prevention, and Treatment, ed 2. Hoboken, NJ: Wiley, 2016: 427–456. 52. Kim JM, Sohn DS, Bae MS, Moon JW, Lee JH, Park IS. Flapless transcrestal sinus augmentation using hydrodynamic piezoelectric internal sinus elevation with autologous concentrated growth factors alone. Implant Dent 2014; 23:168–174.

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8

Plateau Root Form Implants Rainier A. Urdaneta, dmd

I

t is well known that mechanical stimuli are critical for bone maintenance and remodeling throughout the body and that maintaining bone mass requires continuous loadrelated osteoregulatory stimuli.1–3 In the case of the dentate maxilla and mandible, the mechanical stimuli are created by the forces of mastication and transmitted to bone through the teeth and periodontal ligament. However, when teeth are lost, alveolar bone quickly undergoes resorption due to lack of stimulation.4 With regard to dental implants, both the implant and the prosthetic abutment work as a unit in transferring occlusal loads to bone. These loads are primarily localized to peri-implant crestal bone, so shorter implants will result in larger loads transmitted to bone.5,6 If these loads remain within physiologic limits (ie, they do not cause crestal bone microfractures or disruption of the bone-toimplant interface), it can be hypothesized that the shorter the implant, the greater will be the potential for beneficial osteoregulation of peri-implant crestal bone. With conventional endosseous root-form threaded dental implants and conventional cylindric prosthetic abutments, off-axis loads are received as compressive forces to the crestal bone on the downstream side of the implant (see also chapter 2). Even if the implant has a moderately rough particle blasted/acid-washed surface texture, the upstream side of the implant (ie, the side from which the force originates) has minimal tensile resistance. As a result, the implant will flex away from the force and deliver compressive stresses to the affected first three to five implant threads. With most threaded implant designs, the bone coronal to the first implant thread remains unloaded and as a result is commonly lost due to disuse atrophy.7,8 In contrast, plateau root form (PRF) implants were designed to load, retain, and even stimulate vertical growth of

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a

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FIG 8-1  |  Bone coronal to a PRF implant is prepared to match the shape of the prosthetic abutment before its insertion. (a) This is directed by a guide pin inserted into the implant. (b) Bone is prepared using a sulcus reamer secured by the guide pin. (c) An abutment matching the size of the reamer is inserted to contact its surrounding bone. (Reprinted with permission from Morgan.9)

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FIG 8-2  |  (a) A radiograph of a PRF implant at crown placement. (b) A radiograph taken at the 13-year follow-up.

The mineralization seen under the spherical abutment base suggests favorable stress transfer to crestal bone via the base of the abutment.

peri-implant crestal bone by means of the convex bulb shape of the prosthetic abutment as it emerges from the implant root9 (Figs 8-1 and 8-2). Additionally, the coronal-most aspect of the implant neck has an inwardly sloping, machined-turned surface, which narrows the implant diameter as it approaches

the level of the implant-abutment connection. The abutment has a smaller diameter (ie, standard platform switching) as it connects to the implant neck but thereafter widens gently to form a convex bulb shape. PRF implants are intentionally submerged 1 to 2 mm subcrestally so that once restored, the bulb-shaped

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PRF Implants in the Posterior Maxilla

14.6 mm

4.2 mm

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FIG 8-3  |  (a) The preoperative CT scan revealed limited subantral bone in the maxillary left first molar site (approximately 4 mm). However, there was more than 10 mm buccopalatal ridge width. (b) A 6.0 × 4.5–mm PRF implant was placed immediately after extraction using a crestal sinus elevation procedure and autogenous plateletrich fibrin clots as graft material.

abutment will be more or less at the crestal level and deliver some functional stress to crestal bone, helping to maintain it. This type of implant-abutment configuration has been referred to as bone-loading or load-bearing platform switching because if the implant is appropriately placed subcrestally, the convex shape of the abutment will provide some loading of the surrounding bone.8,10 PRF implants have horizontal, moderately rough– surface fins or plateaus and are designed to be pressfitted into a carefully and precisely prepared osteotomy rather than being torqued with a handpiece or manual torque wrench (as is the case with threaded implants). With regard to force distribution, the shaped base of the abutment is considered as the first thread or plateau (ie, the most coronal area where compressive forces are transferred to bone). Vertical bone growth toward the shaped base of the abutment has been reported in several clinical investigations.8,11–13 In this way, subcrestally placed short or ultra-short PRF implants appear to have a biomechanical advantage over crestally or supracrestally placed conventional threaded implants. However, the minimal bone height needed to place a short or ultra-short PRF implant subcrestally will be greater than that needed to place a threaded implant of similar length conventionally at or above the alveolar crest. This chapter summarizes the author’s clinical experiences with short and ultrashort PRF implants over the past 15 years.

PRF Implants in the Posterior Maxilla When restoring posterior maxillary cases with less than 5 mm of remaining subantral bone height, the standard and still widely used protocol is to perform an open lateral window sinus grafting (OSG) procedure in preparation for either delayed or immediate placement of standard-length (≥ 10 mm) implants. However, investigations have clearly demonstrated that the use of long implants and large sinus grafts is associated with a significantly higher rate of surgical complications and higher treatment costs when compared with the use of short implants with or without transcrestal sinus grafting.14–16 In fact, it has been proposed that for these types of cases, shorter implants represent the preferred treatment alternative.17 The most common response by clinicians inexperienced in the use of short or ultra-short implants in the posterior maxilla is that the implant is too short and will not last. However, this is a misconception that practice and clinical research will disprove. Use of OSG can often be abandoned in favor of short or ultra-short implants, and if an indirect transcrestal sinus augmentation is needed, autogenous leukocyte- and platelet-rich fibrin clots can be used as a graft material18 (Fig 8-3). These clots have the advantages of being anti-inflammatory and antibacterial and are still rich in vascular- and bone-stimulating growth factors.19

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LPRF Bone

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FIG 8-3 (cont)  |  (c) The postoperative radiograph of the implant in situ. (d) After more than 4 months of healing, the inserted fibrin clots had been replaced with bone, and the implant was ready to be restored. (e) The definitive restoration (lithium disilicate crown cemented on a prefabricated abutment) was placed 1 month later. (f) A periapical view taken 1 year after loading; note the noticeable increase in bone density in the grafted area.

C/I Ratio and Force with PRF Implants Placing a crown on a short or ultra-short implant brings a whole new set of clinical issues into play. One of those issues is the potential negative impact of an unfavorable crown-to-implant (C/I) ratio. The greater the crown height, the greater the moment of force or lever arm will be with off-axis loading. Forces may increase by 20% for every 1 mm of increase in crown height.20–22 In the early 2000s, it was still believed that these increased forces arising from high C/I ratio would induce micromovements and additional stress concentration in the peri-implant

crestal bone, possibly causing bone microfractures and crestal bone loss.22 Clinical research on the impact of C/I ratio on splinted threaded implant restorations later demonstrated that increased C/I ratio did not have an impact on crestal bone levels or favor implant failure.23 Indeed, some investigators studying threaded or pressfit sintered porous-surfaced implants (SPSIs) reported an inverse relationship: As C/I ratio increased, crestal bone loss decreased.24,25 However, with both of these implant types, upper limits may exist where very high C/I ratio values may have a negative impact. Regarding PRF implant performance, results from a retrospective study reported by Urdaneta et al11 indicated that C/I ratio values as high as 4.95 were not associated

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C/I Ratio and Force with PRF Implants

a

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FIG 8-4  |  (a) A periapical radiograph of two mandibular PRF implants on the day of crown placement. (b) This radiograph was taken 1 year later; note the peri-implant bone gain since the time of crown placement. (Reprinted with permission from Urdaneta et al.11)

a

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FIG 8-5  |  (a) Periapical radiograph of an 8 × 5–mm implant in the posterior left mandible restored with a metal-

ceramic crown cemented on a prefabricated titanium abutment. (b) This radiograph was taken 8 years later. Note that the bone has grown coronal to the implant-abutment interface and toward the spherical base of the abutment.

with crestal bone loss or failure of single-tooth PRF implants. In the same study, researchers also reported crestal bone mineralization­­—not crestal bone loss as anticipated (Fig 8-4). The finding of increased density of crestal bone surrounding short implants (Figs 8-5 and 8-6) led the investigators into a study assessing 90 variables that might affect this outcome. They reported that there were five factors favorably impacting crestal bone surrounding PRF single-tooth implants: 1. The daily intake of nonsteroidal anti-inflammatory drugs (NSAIDs) 2. The type of opposing dentition 3. An abutment with a spherical titanium base

4. A hydroxyapatite surface coating on the implant 5. Implant size (8 × 5 mm) The finding that short, wide implants were significantly less likely to lose bone than longer (ie, 11 mm) implants of similar width suggested that there may be an ideal length for implants of different widths. In the case of 5-mm-wide implants, shorter implants appear to favor bone retention and mineralization more favorably than longer implants. The clinical success with these short implants and the number of patients needing even shorter implants due to anatomical limitations led the clinicians to the use of ultra-short implants (5 and 6 mm long) (Figs 8-7 to 8-9). Other research published

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a

b

c

d

FIG 8-6  |  (a) The preoperative radiograph showing minimal subantral bone height. (b) Two 6 × 5–mm PRF im-

plants were placed in the posterior left maxilla using a transcrestal sinus elevation procedure with β-tricalcium phosphate as graft. (c) A radiograph taken at the time of crown placement. (d) A radiograph taken at the 4-year recall. Note the significant crestal bone gain observed on the mesial side of the implant in the second premolar site.

at about the same time was encouraging as well; for example, a retrospective study with short and ultra-short SPSIs also concluded that C/I ratio had no significant effect on crestal bone loss or implant failure24 (see chapter 7). In 2012, Urdaneta et al12 published results of a study in which the survival rates of implants 5 to 8 mm long were compared, and all had 5-mm diameters. The work compared the survival of 211 ultra-short (5 and 6 mm long) implants with that of 199 short (8 mm) implants and found that the survival rates were similar. Another group reported the performance of short and ultra-short PRF implants in partially edentulous posterior maxilla sites with sufficient subantral native bone height to allow placement of implants 8 mm or shorter.26 Implants that required indirect sinus grafting at placement were excluded. Implants were submerged up to 3 mm below the bone crest and allowed to heal for 4 to 6 months before reentry surgery. To be included in this retrospective study, a patient needed to have at

least one 5-, 6-, or 8-mm-long PRF implant restored with a single crown that had been in function for at least 3 years. A total of 65 patients were included with 139 implants, broken down as follows: • 5-mm-long implants: 41 • 6-mm-long implants: 46 • 8-mm-long implants: 52 Most of the patients (75.38%) were nonsmokers and did not use NSAIDs on a regular basis. Most of the implant sites were molar sites, and all crowns were porcelain-fused-to-metal crowns. The results showed an overall probability of success for short and ultrashort implants to be 96.24% and 94.39%, respectively. Further assessment of the data indicated that for implants with a C/I ratio greater than 2.0, the probability of success for short and ultra-short implants was 95.64% and 93.51%, respectively.

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C/I Ratio and Force with PRF Implants

a

b

FIG 8-7  |  (a) Three ultra-short 6 × 5–mm implants

were placed in the left mandible. Note the proximity of the mandibular canal. (b) Single crowns were used to restore the three implants shown here at the time of crown placement. (c) At the recall visit after 1 year in function, the crestal bone appears to have grown vertically.

c

a

b

FIG 8-8  |  (a) Treatment included one short and one ultrashort PRF implant (8.0 × 4.5 mm and 5.0 × 5.0 mm, respectively). (b) This radiograph was taken at the time of crown placement for the ultra-short implant. (c) The radiograph depicts the status of the two implants at the 2-year follow-up. (Reprinted with permission from Morgan.9)

c

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a

b

FIG 8-9  |  (a) An ultra-short implant was placed with the intention of restoring a mandibular right first molar with a single implant-supported crown. (b) The radiograph shows the implant on the day of crown placement. (c) Note the crestal bone stability and further bone mineralization 14 months after crown placement.

c

Short PRF Implants in the Mandible Reconstruction of the atrophic posterior mandible is a challenge because of the risk of interference with the inferior alveolar nerve (see also chapter 6). Surgical techniques to augment the posterior mandible include onlay grafting, ridge expansion by ridge-splitting, osteodistraction, simultaneous onlay grafting and osteodistraction with and without osteotomy at the recipient site, angulated posterior implants connected to neighboring teeth, and nerve displacement surgery. Most of these techniques require highly talented surgeons and come with increased healing times, a high risk of complications, and significant morbidity as well as high costs. The risks and benefits of these treatment alternatives should be carefully considered when there is sufficient bone to support an ultra-short implant without grafting (Fig 8-10).

Tight Interdental Spaces The literature has reported inconsistent results with regard to how close an implant may be placed to an adjacent tooth without causing damage to it. Esposito et al27 evaluated implants with matching implantabutment platforms and reported increased bone loss at adjacent teeth as the horizontal tooth-to-implant distance decreased. In contrast, Vela et al28 reported no significant correlations between implant proximity and resorption on the bony crest of the adjacent tooth and suggested that the differing results may be explained by platform switching. Urdaneta et al8 evaluated the effect of proximity of short and ultra-short PRF implants on adjacent teeth, implant survival, and peri-implant bone levels. The investigators retrospectively evaluated 206 subjects who received 235 implants that had been placed adjacent to at least one natural tooth and followed for an average

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Tight Interdental Spaces

a

b

c

d

e

FIG 8-10  |  (a) Two ultra-short PRF implants were placed in the right posterior mandible. (b) Reentry surgery was performed after 3 months of

submerged healing. (c) The crown placement date was 3 months after reentry surgery. (d) A radiograph taken at the 1-year postloading visit. (e) The clinical view 1 year postloading.

a

b

c

d

FIG 8-11  |  (a) A PRF implant that was placed in the site of the mandibular right central incisor ended up close to one of the contiguous teeth. (b) At crown placement, the crestal bone on the problem side appears not to have been resorbed as a result of the slope of the implant collar. (c) At the 1-year recall, the crestal bone remains stable and can be seen to have mineralized further. (d) The clinical status of the implant crown and surrounding soft tissues at 1 year. Interestingly, the side with the greater interdental space had less satisfactory papilla reformation than the side that was cause for concern.

of 42 months. To assess possible damage to the adjacent teeth, they recorded complications on adjacent teeth such as lesions of endodontic origin, subsequent need for extraction, pain, presence of root resorption, and bone loss, concluding that the placement of short or ultra-short PRF implants in close proximity to an adjacent tooth

did not cause damage to that tooth or lead to bone loss or the failure of the implant. As shown in Fig 8-11, the sloping shoulder on PRF implants allows for increased space for bone and soft tissues. Despite the proximity of the implant to the distal adjacent root, the crestal bone was stable after 1 year of loading (see Fig 8-11c).

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a

c

b

FIG 8-12  |  (a) Periapical radiograph of two narrowdiameter (4 mm) PRF implants placed in the right posterior mandible with limited bone height. A 6 × 4–mm implant was placed in the first molar site while a 5 × 4–mm implant was used at the second molar site. (b) The two implants were not splinted together, and the ultra-short implant failed after 8 months in function. (c) The failed implant was replaced with a wider and longer implant (6 × 5 mm). When using ultra-short PRF implants that are also narrow (≤ 4 mm) to restore missing posterior teeth, splinting to adjacent implants is recommended.

Case Study: Ultra-Short, Narrow-Diameter PRF Implant

Guidelines for the Successful Use of PRF Implants

The author’s clinical experiences with ultra-short implants indicate that a 5 × 5–mm implant restored with a single crown can support a maxillary or mandibular molar independently without losing integration. However, reducing the implant width by 1 mm can lead to a completely different outcome. In the case presented in Fig 8-12, a 6 × 4–mm implant was used to support a mandibular second premolar, while a 5 × 4–mm implant was used to replace the first molar. As shown in Fig 8-12b, the implant supporting the first molar failed in the first year of loading. This outcome could have been prevented by splinting or using a wider implant. A wider and longer implant (6 × 5 mm) was used to replace the failing implant, and the definitive restoration will be splinted.

For the placement of a PRF implant, a traditional pilot drill (1,100 rpm) is used to initiate the osteotomy, which needs to be 1 to 2 mm deeper than the actual intended implant length. Thereafter, a series of latch-type cylindrical reamers of increasing diameter (in 0.5-mm increments) is used with a handpiece at low speeds (≤ 50 rpm) without saline—or in some situations manually— to minimize trauma and harvest autogenous bone for grafting. The reamers range in diameter from 2.5 to 6.0 mm, and the final reamer will have the same diameter as the planned implant. The implant has a 3-degree taper angle and is tapped into place with a driving tip and surgical mallet like an SPSI to achieve an initial press-fit stability. Rather than a titanium healing cap, a modifiable plastic healing plug is trimmed and used to seal the implant prosthetic receptor well and prevent

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References

the osteotomy from being overgrown with crestal bone. As a last step, the autogenous bone material that was collected with the reamers is applied over the surgical sites. Initial site healing should be submerged to minimize the risk of micromovements during the integration phase. Other helpful tips include the following: • PRF implants should be inserted at least 1 mm below the lowest level of the surrounding crestal bone. • Ultra-short PRF implants intended for restoration with single crowns should have diameters 4.5 mm or wider. If the diameter is smaller, they should be splinted, especially when used in posterior jaw sites. • To avoid abutment loosening, only PRF implants with 2.5-mm-deep prosthetic receptor wells should be chosen. • When choosing PRF implants to be placed in sites with limited interproximal space, only handheld reamers should be used for osteotomy preparation, and caution needs to be taken not to contact the roots of adjacent teeth. • Short and ultra-short PRF implants should never be immediately loaded.

Conclusion Similar to SPSIs, PRF implants have documented longterm evidence of successful use in short and ultra-short lengths. Also like SPSIs, osteotomies need to be precise in their preparation because the implant relies on a tight press-fit placement for initial stability. In ultrashort lengths, PRF implants should be of diameters 4.5 mm or greater and splinted to other implants if possible. Provided that PRF implants are adequately submerged below the alveolar crest, their unique, bulbshaped prosthetic abutments will provide physiologic, load-related osteoregulatory stimuli that will minimize crestal bone loss and even allow for vertical crestal bone growth after the onset of function.

References 1. Wolff J. The Law of Bone Remodelling. Maquet P, Furlong R (trans). Berlin: Springer-Verlag, 1986. 2. Frost HM. The mechanostat: A proposed pathogenic mechanism of osteoporoses and the bone mass effects of mechanical and nonmechanical agents. Bone Miner 1987;2:73–85. 3. Hassler CR, Rybicki EF, Cummings KD, Clark LC. Quantification of bone stresses during remodeling. J Biomech 1980;13:185–190. 4. Schropp L, Wenzel A, Kostopoulos L, Karring T. Bone healing and soft tissue contour changes following singletooth extraction: A clinical and radiographic 12-month prospective study. Int J Periodontics Restorative Dent 2003;23:313–323. 5. Pierrisnard L, Renouard F, Renault P, Barquins M. Influence of implant length and bicortical anchorage on implant stress distribution. Clin Implant Dent Relat Res 2003;5: 254–262. 6. Sahrmann P, Schoen P, Naenni N, Jung R, Attin T, Schmidlin PR. Peri-implant bone density around implants of different lengths: A 3-year follow-up of a randomized clinical trial. J Clin Periodontol 2017;44:762–768. 7. Pilliar RM, Deporter DA, Watson PA, Valiquette N. Dental implant design—Effect on bone remodeling. J Biomed Mater Res 1991;25:467–483. 8. Urdaneta RA, Seemann R, Dragan IF, Lubelski W, Leary J, Chuang SK. A retrospective radiographic study on the effect of natural tooth-implant proximity and an introduction to the concept of a bone-loading platform switch. Int J Oral Maxillofac Implants 2014;29:1412–1424. 9. Morgan VJ. The Bicon Short Implant: A Thirty-Year Perspective, ed 2. Chicago: Quintessence, 2018. 10. Chou HY, Müftü S, Bozkaya D. Combined effects of implant insertion depth and alveolar bone quality on periimplant bone strain induced by a wide-diameter, short implant and a narrow-diameter, long implant. J Prosthet Dent 2010;104:293–300. 11. Urdaneta RA, Daher S, Lery J, Emanuel K, Chuang SK. Factors associated with crestal bone gain on single-tooth locking-taper implants: The effect of nonsteroidal antiinflammatory drugs. Int J Oral Maxillofac Implants 2011;26:1063–1078. 12. Urdaneta RA, Daher S, Leary J, Emanuel KM, Chuang SK. The survival of ultrashort locking-taper implants. Int J Oral Maxillofac Implants 2012;27:644–654. 13. Urdaneta RA, Rodriguez S, McNeil DC, Weed M, Chuang SK. The effect of increased crown-to-implant ratio on single-tooth locking-taper implants. Int J Oral Maxillofac Implants 2010;25:729–743.

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14. Lemos CA, Ferro-Alves ML, Okamoto R, Mendonça MR, Pellizzer EP. Short dental implants versus standard dental implants placed in the posterior jaws: A systematic review and meta-analysis. J Dent 2016;47:8–17. 15. Fan T, Li Y, Deng WW, Wu T, Zhang W. Short implants (5 to 8 mm) versus longer implants (>8 mm) with sinus lifting in atrophic posterior maxilla: A meta-analysis of RCTs. Clin Implant Dent Relat Res 2017;19:207–215. 16. Nisand D, Picard N, Rocchietta I. Short implants compared to implants in vertically augmented bone: A systematic review. Clin Oral Implants Res 2015;26(suppl 11):170–179. 17. Thoma DS, Zeltner M, Hüsler J, Hämmerle CH, Jung RE. EAO Supplement Working Group 4—EAO CC 2015 short implants versus sinus lifting with longer implants to restore the posterior maxilla: A systematic review. Clin Oral Implants Res 2015;26(suppl 11):154–169. 18. Toffler M, Toscano N, Holtzclaw D. Osteotome-mediated sinus floor elevation using only platelet-rich fibrin: An early report on 110 patients. Implant Dent 2010;19:447–456. 19. Del Fabbro M, Corbella S, Ceresoli V, Ceci C, Taschieri S. Plasma rich in growth factors improves patients’ postoperative quality of life in maxillary sinus floor augmentation: Preliminary results of a randomized clinical study. Clin Implant Dent Relat Res 2015;17:708–716. 20. Bidez MW, Misch CE. Force transfer in implant dentistry: Basic concepts and principles. J Oral Implantol 1992;18: 264–274. 21. Bidez MW, Misch CE. Issues in bone mechanics related to oral implants. Implant Dent 1992;1:289–294.

22. Bidez MW, Misch CE. Clinical Biomechanics in Implant Dentistry. St. Louis: Mosby, 2008. 23. Tawil G, Aboujaoude N, Younan R. Influence of prosthetic parameters on the survival and complication rates of short implants. Int J Oral Maxillofac Implants 2006;21: 275–282. 24. Rokni S, Todescan R, Watson P, Pharoah M, Adegbembo AO, Deporter DA. An assessment of crown-to-root ratios with short sintered porous-surfaced implants supporting prostheses in partially edentulous patients. Int J Oral Maxillofac Implants 2005;20:69–76. 25. Nunes M, Almeida RF, Felino AC, Malo P, de Araújo Nobre M. The influence of crown-to-implant ratio on short implant marginal bone loss. Int J Oral Maxillofac Implants 2016;31:1156–1163. 26. Lombardo G, Pighi J, Marincola M, Corrocher G, Simancas-Pallares M, Nocini PF. Cumulative success rate of short and ultrashort implants supporting single crowns in the posterior maxilla: A 3-year retrospective study. Int J Dent 2017;2017:8434281. 27. Esposito M, Ekestubbe A, Gröndahl K. Radiological evaluation of marginal bone loss at tooth surfaces facing single Brånemark implants. Clin Oral Implants Res 1993;4: 151–157. 28. Vela X, Méndez V, Rodríguez X, Segalá M, Tarnow DP. Crestal bone changes on platform-switched implants and adjacent teeth when the tooth-implant distance is less than 1.5 mm. Int J Periodontics Restorative Dent 2012;32: 149–155.

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9

Ultra-Wide Threaded Implants for Molar Replacement André Hattingh, bchd, mchd Hugo De Bruyn, dds, msc, phd Stefan Vandeweghe, dds, phd

D

ental implants are widely used to restore function, esthetics, and quality of life for patients with one or more missing teeth. More than 50 years of development and scientific research have led to improvements in implant design and surface topographies (see chapter 2) as well as to a better understanding of bone and soft tissue biology. Assuming appropriate case selection, treatment planning, and protocols are used, successful implant treatment can be predictable regardless of implant length or diameter, bone quality, or bone volume. This evolution has increased the indications for implant treatment and continues to alter and improve therapeutic approaches such as immediate molar implant placement and even immediate molar implant function—under carefully defined conditions. These latter procedures can be facilitated with the assistance of cone beam computed tomography (CBCT) imaging and the use of interactive computer software programs to allow virtual planning and a more prosthetic-driven approach with optimal occlusion and loading. The use of CBCT scans has also changed the earlier surgical model of extensive tissue exposure to have a better view of the surgical field. Thus, flapless implant surgery with or without immediate loading has become more approachable and predictable. The original two-stage surgical approach of Brånemark et al1 with submerged initial healing is no longer required for successful implant fixation to bone. A better understanding of bone and soft tissue biology now allows immediate placement of implants in extraction sockets and predictable regeneration of lost or insufficient tissues; this has resulted in improved esthetics and patient satisfaction. However, unfortunately not all clinicians are sufficiently trained, skilled, self-disciplined, emotionally capable, or technically equipped

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to implement highly demanding surgical or restorative procedures such as immediate molar implant placement (see chapter 1). It is also questionable whether all patients require the technologically advanced approaches of computer-assisted treatment. Furthermore, in contrast to what is expected in free-market economies, the cost of implant dentistry has risen continuously despite a growing implant market. This has developed to a point where affordability becomes a burden and barrier for many patients and clinicians. Cost increases relate to the use of complicated surgical protocols, individualized prosthetic treatment protocols, and higher technical expenses. Economic and individual patient personality issues force clinicians to be creative in lowering these treatment barriers while still providing timely, predictable, and profitable treatment. This requires a pragmatic approach with regard to the selection of cases, implants, prostheses, and surgical procedures (eg, simplified or straightforward).

Considerations in Using Single Molar Implants Single implant treatment in anterior jaw sites has been reported as highly predictable in terms of implant survival and hard tissue remodeling.2 Outcomes with this treatment appear to be minimally affected by the timing of implant placement relative to tooth extraction (ie, delayed vs immediate placement) or variations in either surgical (ie, flap vs flapless) or restorative procedures such as the use of immediate provisional crowns.3–5 Esthetic issues are generally limited, although midfacial gingival recession and incomplete papilla fill inevitably occur without proper case selection and appropriate hard or soft tissue grafting at the time of implant placement.6,7 Single implant treatment in molar sites, however, often presents anatomical constraints related to reduced bone quality as well as the location of the mandibular neurovascular bundle or a pneumatized maxillary sinus

with limited remaining alveolar ridge height. This is especially true when socket preservation grafting was not used at the time of tooth extraction or if the tooth has been missing for longer than 6 months.8,9 Furthermore, occlusal forces are twice as high in posterior sites than anterior sites, and this may create biomechanical issues. While deficiencies in buccolingual ridge width can often be managed with ridge-splitting techniques at the time of implant placement, deficiencies in ridge height require far more difficult preparatory regenerative procedures (especially in the posterior mandible), which are notorious for being unpredictable and unstable in the long term10,11 (see also chapter 6). These interventions also add significant morbidity and cost and come with increased risk for failures. A popular approach to overcome the problem of the pneumatized maxillary sinus is sinus floor elevation and augmentation using a variety of graft materials including biomaterials.12 If successful, this protocol allows placement of standard-length (> 8 mm) dental implants in molar sites either concomitantly or after an initial healing interval of 4 months or longer. Depending on the pretreatment and residual subantral bone height, sinus elevation and augmentation can be performed through a lateral window opened surgically in the sinus wall or transcrestally through the prepared implant site using hand osteotomes or specialized bur sets. If there is 5 to 8 mm of residual bone height, the trans­crestal/ transalveolar technique can be performed with simultaneous implant placement even immediately following extraction.13,14 However, if less than 5 mm of subantral bone height is available (particularly with threaded implant designs), the lateral window approach is preferred by most investigators. In this case, the timing of implant placement will depend on the ability of the surgeon to achieve primary stability in whatever bone remains.15 With proper case selection, both sinus grafting approaches have been reported to be more or less equally successful.16 A systematic literature review of studies reporting results with the lateral window approach indicated an

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Outcome with Short Versus Standard-Length Implants

estimated annual implant failure rate of 3.48%, resulting in a cumulative survival rate of 90.1% after 3 years.17 Unfortunately, open window sinus elevation procedures can be accompanied by complications with perforations of the sinus membrane, which occurs in almost 10% of cases.18 In smokers, the number of implant failures and complications—particularly wound dehiscence and infection—are even higher.19,20 Although a grafting material is still generally used with the lateral approach, the use of these grafts does not seem to affect the outcome with the transalveolar technique in terms of implant survival or crestal bone loss.21 This is because as long as the implant is initially sufficiently stable and the sinus membrane has been elevated locally without damage, the tented space created by the membrane around the implant apex will fill with blood and later with new bone. Results from another systematic literature review indicated the annual implant failure rate for the transalveolar approach to be not significantly different from that in posterior maxillary sites that had not required open window sinus elevation for implant placement.22 This study reported the 3-year survival rate as 92.8%.22 Another approach to increase bone volume at resorbed posterior sites is the use of autogenous onlay block bone grafts with donor tissue usually harvested from the hip or calvarium. However, these procedures are often not acceptable to potential patients. Depending on the grafting technique used, implants later placed in the consolidated graft sites have shown survival rates ranging from 89.5% up to 100%, but the main problem with these bone block grafts is postsurgical shrinkage in volume.23 According to Dreiseidler,24 a 15% decrease in volume can be expected in the first 4 months. Nevertheless, successful rehabilitation can be achieved with implant survival rates of 96% in the maxilla and 92% in the mandible after a mean follow-up period of 5 years.25 However, because of continued graft resorption following these procedures, almost 25% of the implants placed in bone block–grafted sites demonstrate continued and ultimately advanced peri-implant bone loss, at least with machine-turned implants.26

In the resorbed posterior mandible, transposition of the mandibular nerve may also be an option. However, despite the fact that implant survival is high with this approach (95.7% after 49 months), complications and unfavorable side effects are common.27 For example, it is reported that 99.5% of patients treated this way experience temporary neurosensory disturbances for at least the first 6 months, and for 0.53% of the patients, the disturbances become permanent.28 When given the choice, patients generally prefer a less risky, minimally invasive treatment alternative whenever possible.29 Therefore, as with the posterior maxilla, investigators have focused more recently on using short dental implants in the resorbed posterior mandible to simplify treatment and reduce risks.

Outcome with Short Versus Standard-Length Implants During the developmental stages of modern endosseous implant dentistry, clinicians generally preferred to use standard-length implants (ie, > 10 mm in the mandible and > 13 mm in the maxilla).30 This preference arose because early types of short root-form endosseous implants had unacceptably high failure rates. These initial designs had either machine-turned (ie, minimally rough) surfaces or titanium or hydroxyapatite plasma-sprayed (ie, extremely rough) surfaces, and they failed at rates as high as 25% or greater in lengths less than 8 mm.31–33 However, the later development of moderately rough (MR) implant surfaces (eg, particle-blasted/acid-treated) with or without incorporated nanotechnologic features, has made the use of shorter implants more applicable.34 These types of surfaces alter and accelerate the osseointegration process and increase the extent of bone anchorage, resulting in higher torque removal values for short MR implants compared with longer minimally rough (ie, machine-turned) implants.35 Improving initial stability with modified surgical drilling protocols has also contributed to improved success with short MR implants (see also chapter 2).

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Regarding the ability of short implants to function without loss of integration associated with excessive occlusal forces, results from a recent radiographic study showed higher bone density and mineralization around short (6 mm) MR implants compared with similar but longer (10 mm) implants.36 While some authors have speculated that this increased density might impair normal remodeling of the affected bone and lead to a loss of osseointegration under functional loading, it could equally be argued that increased bone density around the short implants provides evidence for effective stress transfer to bone by the MR implant surface topography and successful physiologic adaptation to the larger crown-toimplant (C/I) ratio.37 The early definition of short implant was one with a length of less than 10 mm, but this was later more clearly defined as an implant with 8 mm or less of designed intrabony length.38 These shorter lengths could clearly be more appropriate for replacing molars in sites where vertical bone height is limited. Indeed, Rossi et al39 recently reported a 5-year survival rate of 95% with early-loaded 6-mm-long MR threaded implants placed in posterior jaw sites and restored with single crowns. However, success is clearly operator-dependent because an earlier systematic literature review had shown an increase in implant survival from 93% to nearly 99% as implant lengths increased from 5.0 mm to 9.5 mm.40 Using short implants as an alternative to sinus elevation, vertical bone grafting, or nerve transpositioning is clearly desirable because it can reduce treatment cost, treatment duration, the number of surgical procedures needed, and patient morbidity. A Cochrane systematic literature review demonstrated that short implant outcomes in sites with subantral bone heights of 4 to 9 mm appear to be similar to those with longer implants placed in conjunction with sinus elevation.41 This challenged the concept that a sinus elevation procedure should be the treatment of first choice rather than using shorter implants in native bone at posterior jaw sites. Success rates have been similar when short MR implants without sinus elevation have been directly compared with longer MR implants with

sinus floor augmentation.42,43 Even in extreme cases where 4-mm-long ultra-short MR implants were used in resorbed posterior mandibles, 1-year outcomes were comparable to those with similar 10-mm-long implants. The ultra-short implants showed similar resonance frequency stability measurements and no greater crestal bone loss.44 While short implants may be the preferred choice, they do result in possible unfavorable C/I ratios following restoration. However, there is limited evidence to suggest that this situation will be associated with more bone loss or implant failure.45,46 On the other hand, more technical and prosthetic complications are reported when C/I ratio is increased because of increased functional stress on the prosthetic components, in particular with single freestanding crowns.47 Approaches to help decrease the risk of prosthetic mechanical overload include achieving canine guidance, splinting the implants, avoiding cantilevers, and placing a greater quantity of short implants.48,49 Another possibility is to use wider-diameter implants to reduce the bending moments during function and therefore reduce stress on crestal bone as well as provide the mechanical advantage of a wider prosthetic table at the crown-to-implant interface. Using a short and wide implant could then provide a minimally invasive approach for the replacement of molars.

The Short and Wide Implant Combination Using normal-diameter implants (defined here as ranging from 3.5 to 4.5 mm) in molar sites poses a number of difficulties. If more than one molar (or one molar with missing premolars) is to be replaced, multiple normaldiameter implants (as many as one per missing tooth) and a splinted prosthesis can function well. However, if a single molar is replaced with a normal-diameter implant, technical complications can occur due to nonaxial loading, emergence profile, and long-term biomechanical overloading. The use of ultra-wide tapered implants with

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The Short and Wide Implant Combination

a

FIG 9-1  |  The MAX implant (Southern Implants) is a tapered implant with an ultra-wide body. The diameter ranges from 6 to 9 mm. It is provided with a variety of different prosthetic connections and allows for platform switching.

b

FIG 9-2  |  (a) The mandibular right first molar had to be

extracted due to secondary caries. (b) The tooth was removed, and a 7-mm-diameter MAX implant was placed immediately. (c) This radiograph was taken after loading for 1 year and shows stable bone levels with little to no bone loss.

c

a diameter of 6 to 9 mm and the associated wide prosthetic table can overcome these concerns because the loading capability is high even under immediate function conditions (Fig 9-1). Wider implants enhance primary implant stability, increase the surface available for contact with bone, and reduce peri-implant crestal bone stresses and resorption. The wider coronal implant diameter also allows for a more favorable restorative emergence profile and the opportunity to incorporate platform switching, which has been shown to have additional benefits in preserving crestal bone.50 Based on a systematic literature review and meta-analysis, ultra-wide dental implants demonstrate

an estimated 5-year survival rate of 92.7% in retrospective studies and 97.8% in prospective studies with stricter inclusion criteria.51 Vandeweghe et al52 retrospectively scrutinized 93 MAX implants (Southern Implants), which are tapered with an ultra-wide body (Fig 9-2). The implants were moderately rough and were employed in lengths of 7 to 13 mm and widths of 8 or 9 mm. More than half of the implants were placed in the maxilla (63% or 59 implants). Most implants were placed immediately (74.2%), the remainder being placed in healed extraction sites. Immediate functional loading (within 72 hours after surgery) was applied with 29 of the implants (31.2%). The overall implant survival

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a

b

c

d

FIG 9-3  |  (a to d) CBCT images show an adequate volume of bone in the anterior maxilla but limited bone height posteriorly; substantial buccolingual alveolar ridge width in the molar sites allowed for the placement of short, ultra-wide (7 × 7 mm) implants using a single-stage approach without the need for a dedicated sinus elevation procedure.

was 95.7% after a mean functional time of 14 months irrespective of implant length. The success rate based on the amount of crestal bone loss, however, was somewhat lower at 91.4%. The bone-loss-based success rates for immediate placement (89.9%) and immediate loading (86.2%) were lower than for delayed placement (95.8%) and delayed loading (93.5%), although not statistically significantly different. Thus, the innovative protocol of immediate molar implant placement with immediate loading offers promise but clearly requires great care to achieve predictable success.

The ultra-wide implant with its large surface area for bone contact offers high initial stability and superior frictional grip (ie, osseointegration) under functional loading, which can allow the implant to be used in short (7 mm) lengths if need be (Fig 9-3). The very high insertion torque values needed to seat these implants makes their placement challenging, especially in the posterior mandible, but has not been reported to create compression-driven crestal bone necrosis as might have been predicted. In support of this observation, recent studies by others failed to demonstrate a significant

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The Short and Wide Implant Combination

e

f

g

h

FIG 9-3 (cont)  |  (e and f) These radiographs were taken immediately after implant placement, and despite the limited subantral bone height, the ultra-wide-body implants required an initial insertion torque of 60 Ncm. (g and h) These radiographs were taken 3 years after placement surgery and show stable crestal bone levels as well as sinus floor bone remodeling with new bone formation.

difference in marginal bone loss or implant failure rate when high or low insertion forces were compared.53 Because compression forces occurring during seating of these ultra-wide implants are dispersed over a large contact surface, their impact on the surrounding bone appears to be limited. Vandeweghe et al54 evaluated the use of 8- or 9-mm-wide tapered implants in the posterior maxilla to avoid sinus elevation procedures, although follow-up was limited to 15 months. A delayed loading protocol

was followed, but immediate placement into extraction sockets resulted in 100% survival, whereas survival after delayed placement in previously healed bone was only 95.2%. The chosen implants were longer than the available crestal bone height, meaning that the sinus membrane was slightly elevated as the implant was inserted, and no graft material was added. A clinical case displayed in Fig 9-4 at the 7-year follow-up demonstrates radiographic proof of new bone growth over the implant apex.

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2.5 mm

a

b

c

d

FIG 9-4  |  (a) The preoperative radiograph shows bone height limited to about 2.5 mm. (b) This radiograph was taken immediately after placement of a 7 × 8–mm MAX implant, and care had been taken using hand osteotomes to elevate the sinus floor bone and to not perforate the sinus membrane. (c) This radiograph was taken at crown placement and shows bone growth around the implant apex despite the fact that no graft material was used. (d) This radiograph was taken after 7 years and confirms that the bone level appears stable, as does the bone formed around the implant apex.

Immediate placement of wide-body implants It is generally acknowledged that where feasible teeth should be replaced with dental implants as soon as possible after tooth extraction to avoid unwanted alveolar bone resorption and allow straightforward implant placement without the increased morbidity associated with later additional graft augmentation procedures. Immediate placement of shorter but wider-diameter implants can overcome the disadvantage of reduced alveolar bone height, particularly in maxillary molar sites. This approach will enhance the initial stability by increasing the extent that the existing tooth socket

walls are engaged by the implant periphery. There is a growing body of evidence including systematic literature reviews that immediate molar replacement with implants can yield implant survival rates similar to those with implants placed in healed molar sites (up to 97%), suggesting that the immediate protocol can be recommended for more widespread use.55 Nevertheless, experience, learning curve, proper case selection, and accurate treatment execution remain paramount for successful outcomes. The following section of this chapter offers clinical protocols and guidelines for a predictable outcome when using short ultra-wide-body implants for immediate molar replacement.

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Treatment Protocols with Sample Cases

a

b

c

d

e

f

FIG 9-5  |  (a to n) Immediate molar implant placement simulated in the posterior maxilla. Note that as is often the case, the mesial interdental bone of the first molar site is greater in quantity (and often greater in density) and could lead to distal bur drift during site preparation.

Treatment Protocols with Sample Cases Simulated surgical protocols for maxillary and mandibular immediate molar implant placement are depicted in Figs 9-5 and 9-6, respectively. For maxillary molars, preferred sites should have a minimum of 4 to 5 mm of remaining subantral bone, and if so, a 7-mm-long implant is planned. Ideally, the extraction and implant placement will both be done without raising a mucoperiosteal flap. To avoid tooth fractures or damage to surrounding bone, it is advocated to not perform a conventional molar extraction using forceps. Instead,

the crown should be removed using a high-speed bur at the level of the cementoenamel junction (Figs 9-5a and 9-5b). This will allow proper inspection of the furcation and root anatomy. Before tooth root removal, a sharp harpoon-type drill can be used to establish the ideal implant position mesiodistally and buccolingually or palatally generally by drilling through the furcation area (Fig 9-5c). Thereafter, the implant osteotomy site is further prepared to its full depth using twist drills (Figs 9-5d to 9-5f) unless there is a risk of perforating the sinus floor, keeping in mind that this depth must allow the implant to be seated 2 mm subcrestally for optimal results. If need be, traditional hand osteotomes like those of Summers13 can be used to upfracture the sinus

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g

h

i

j

k

l

m

n

FIG 9-5 (cont) 

cortical bone floor before finalization of the osteotomy using burs. This will help to avoid sinus membrane damage and is particularly necessary when preparing a healed extraction socket to receive a MAX implant. Before further site preparation, the tooth root fragments remaining are removed atraumatically (Figs 9-5g and 9-5h). Remnants of the periodontal ligament are left so

that their vascular complex can provide a benefit during site healing. Further site development should continue with the use of a 5-mm-diameter tapered implant bur and then the appropriate dedicated MAX drills, again alternately with hand osteotomes if needed to avoid sinus membrane damage. A depth indicator is used (Figs 9-5i and 9-5j) to determine the correct position

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Treatment Protocols with Sample Cases

a

b

c

d

FIG 9-6  |  Immediate placement simulated in the posterior mandible. (a to c) The tooth is first decoronized, and a sharp drill is used to mark the implant position in accordance with the tooth anatomy. (d and e) After the final depth is reached, the implant site is widened using tapered drills.

e

of the implant (ie, 2 mm below the bony crest and 2 to 3 mm away from the buccal wall). Before the implant is placed, a dedicated tap can be used with a manual torque wrench to allow a smooth finalization of the osteotomy site (Fig 9-5k). The implant can then be placed without making contact with the buccal bony wall but still with high primary stability (Figs 9-5l to 9-5n). If the sinus membrane is perforated during these final steps, it will be effectively sealed by the implant. The procedure for placing a MAX implant in the posterior mandible is depicted in Fig 9-6. The socket anatomy will dictate the length of implant chosen. Some drilling of the apical bone will likely be needed to stabilize the implant, and this usually results in an

osteotomy too deep to receive a 7-mm-long MAX implant. In the posterior mandible, 9- or 11-mm-long MAX implants will generally be needed to achieve sufficient stability, assuming of course that there is sufficient bone to provide at least 2 mm of bone height apically after osteotomy preparation to avoid damaging the mandibular nerve.56 For added safety, mandibular block anesthesia should not be used.

Ultra-wide implant placement guidelines Vandeweghe et al57 evaluated 98 immediately placed ultra-wide-body implants placed using the protocols described in Figs 9-5 and 9-6. After a mean follow-up

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f

g

h

i

j

k

l

m

FIG 9-6 (cont)  |  (f to i) Additional cuts are made to separate the roots for extraction. (j and k) The dedicated MAX drill prepares the implant bed to its final dimension. (l and m) Care is taken to place the implant 2 to 3 mm away from the buccal wall and 2 mm below the crest to compensate for postextraction bone remodeling.

of 20 months, the implant success rate was 97.9% and mean bone loss was limited to 0.38 mm (Figs 9-7 and 9-8). However, to be successful, the protocols must be followed precisely. To further assist new users, the

following 12 simple guidelines have been created to simplify case selection and placement of ultra-wide diameter implants.

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n

o

p

FIG 9-6 (cont)  |  (n) Due to the wide diameter of the implant, tapping of the osteotomy is recommended, preferably using a manual torque wrench, to allow for smooth and accurate implant positioning during insertion. (o to q) Finally, the implant is positioned with high primary stability, not touching the buccal wall and 2 mm below the crest.

q

a

b

c

d

FIG 9-7  |  (a) Due to periapical infection and extensive restoration, it was necessary to extract this mandibular

left first molar. (b) Immediately after tooth extraction, an ultra-wide implant (9 × 7 mm) was placed in a singlestage approach. (c) After 3 months, the implant was loaded with a metal-ceramic crown. (d) This radiograph was taken 4 years after implant placement. Bone levels have stabilized.

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a

b

c

d

FIG 9-8  |  (a) This maxillary right first molar was lost due to a longitudinal root fracture. (b) An ultra-wide implant

(9 × 8 mm) was immediately placed into the fresh socket. (c) Four months after implant placement, the definitive metal-ceramic crown was screw-retained to the implant. (d) This radiograph was obtained 3 years after implant placement and shows stable peri-implant bone levels.

1. Ultra-wide implants are meant for immediate placement into molar extraction sockets, and this should remain the primary application. 2. It is essential to note the periodontal biotype of the patient when considering ultra-wide-diameter implants. Thin biotypes should be avoided unless they are surgically augmented in advance, while thick and medium-thickness biotypes are considered suitable. Optimally, the existing keratinized tissue should be at least 2 mm thick and 2 mm wide. 3. Consideration should be given to avoiding block anesthesia in the mandible to avoid damaging the mandibular nerve during drilling.

4. Flapless surgery is preferred. 5. Great care should be taken in removal of the molar to avoid damaging the surrounding bony foundation. A conventional forceps extraction is contraindicated, especially for molars with divergent roots. If they are used at all, forceps should only be used to assist with initial mobilization of the tooth. Decoronization with a high-speed bur is essential, followed by careful separation of the molar roots. No bone should be sacrificed in removing the individual separated roots. 6. Osteotomy preparation should be performed incrementally. Starting with a sharp, harpoon-type drill to initiate the osteotomy, narrow-diameter pilot drills

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can thereafter be used in a sequenced manner to establish the final osteotomy depth. This also allows for gradual widening of the site until it is suitable to accommodate the tapered implant drills. Site finalization should be completed with the appropriate dedicated surgical taps either in an implant handpiece or manually if need be (eg, in soft maxillary bone or very dense mandibular bone). The additional benefit of using a dedicated tap is to have feedback on what sort of torquing force will be needed to seat the implant. 7. Once seated, the implant must never be in contact with the buccal bony wall of the osteotomy. This will lead to bone loss and exposure of buccal implant threads with catastrophic consequences. (This is the same rule that is universally accepted for immediate implant placement in any tooth position.) 8. The implant must be placed at the correct depth. This is one of the most common errors made with the placement of ultra-wide implants. The best way to prevent this mistake is to plan the depth of preparation from the outset using a CBCT scan. If the planned depth is accurately reached from the beginning, the rest of the osteotomy process is merely a widening exercise, and the correct implant placement depth is easily achieved. Note that it is not possible to adjust the osteotomy depth at the end of the preparation. 9. It is recommended that the planned implant position be verified both clinically and radiographically using the corresponding implant depth indicator immediately prior to implant placement in situ (see Figs 9-5i, 9-5j, and 9-6l) or bone tap. A periodontal probe should be used at this stage to ensure that there is at least a clear 2-mm horizontal gap between the

inner aspect of the buccal osteotomy wall and the implant. The vertical depth of the future implant must be verified with the same probe to ensure that the implant will seat so that its restorative platform will end up 2 mm subcrestally to the lowest point of the buccal bony wall. 10. The operator should expect seating of a MAX implant to require a significantly higher insertion force than a standard-diameter implant. This is inevitable due to the wide implant diameter. A final seating force of 70 Ncm is entirely acceptable and safe. Higher forces can occasionally be encountered, but if site preparation rules were carefully and meticulously followed, higher insertion forces should not be needed. 11. Soft tissue positioning and peri-implant void management are essential for trouble-free healing and the reestablishment of optimal bone levels around the implant fixture. Wide healing abutments greatly assist with the management of the socket entrance so that a simple sling suture at the mesial and distal aspects of the healing abutment should ensure adequately tight soft tissue adaptation (Fig 9-9). A horizontal mattress suture will also help by providing a “drawstring” force on these tissues around the healing abutment. Any remaining voids can then be plugged with moldable collagen such as a collagen plug, but only at the healing abutment level. 12. Single implants in molar extraction sites should be allowed to integrate for 4 months before being loaded. However, if ultra-wide implants are being used as part of a full-arch construction and are supported by additional implants, immediate loading should be as predictable as anywhere else in the mouth.

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a

b

d

c

e

FIG 9-9  |  (a) The maxillary left first molar needed extraction due to caries. (b) An ultra-wide-body implant (9 × 8 mm) was placed immediately and loaded after 4 months. (c) At 1 year, the bone levels have barely changed compared with baseline (surgery). (d) A wide healing abutment and some simple mattress sutures in combination with hemostatic collagen (only at the abutment level) had been used at the time of implant placement to assist with soft tissue adaptation and void closure. (e) Soft tissue healing as seen at the 2-week postsurgery visit.

a

b

FIG 9-10  |  (a) This terminal maxillary left first molar required removal due to root canal complications. (b) An ultra-

wide-body implant (7 × 8 mm) was successfully used to immediately replace the tooth and is shown here 8 years later.

Case presentations Further typically successful cases performed using these guidelines are shown in Figs 9-10 to 9-15.

If deviations from the dictated guidelines occur, complications will arise. For example, placing the implant too close to buccal bone can result in unwanted crestal bone loss (Fig 9-16). An extreme complication is shown

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a

b

c

d

FIG 9-11  |  (a and b) The maxillary right first molar in this patient was replaced using an immediate molar pro-

tocol while the left implant was placed at the previously healed first molar extraction site. (c and d) Both implants were ultra-wide (7 × 8 mm) implants, and these follow-up radiographs were taken 2 years postoperatively.

a

b

FIG 9-12  |  (a) This fractured maxillary left first molar needed extraction. (b) The clinical view of the fracture line. (c) An ultra-wide (7 × 8 mm) implant was immediately placed. This is the view 5 years after surgery.

c

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a

b

FIG 9-13  |  (a) Limited bone volume was available to replace this nonrestorable maxillary left first molar. (b) An

ultra-wide (7 × 8 mm) implant was placed at the time of extraction and is shown here after 9 years. The adjacent premolar was replaced with a standard-diameter implant several years after the molar implant was placed.

a

b

FIG 9-14  |  (a) A fractured maxillary right first molar needed replacement. (b) An ultra-wide (7 × 8 mm) implant was immediately placed and is shown here 5 years after placement. The adjacent premolar was replaced several years after the molar.

a

b

FIG 9-15  |  (a) A maxillary right first molar needed extraction following endodontic complications. (b) Immediate placement of an ultra-wide (7 × 7 mm) implant was undertaken and is shown here 3 years after surgery.

in Fig 9-17. Fig 9-18 displays a case where an 11 × 9–mm MAX implant was placed in a healed mandibular right first molar site. The operator failed to submerge the implant shoulder 2 mm below the lowest position

of the buccal crest, and the outcome was rapid loss of crestal bone already seen at the time of crown placement. The faulty implant seating also resulted in insufficient space to develop an anatomically correct crown.

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a

b

FIG 9-16  |  (a) A mandibular right first molar was no longer restorable. (b) An ultra-wide-body implant (7 × 8 mm) was immediately placed but positioned too far buccally. As seen in this radiograph taken 3 years after placement, unwanted crestal bone loss occurred.

a

b

c

d

FIG 9-17  |  (a) The maxillary right first molar developed endodontic complications. (b) The tooth was removed, and an ultra-wide (11 × 9 mm) implant was immediately placed. (c) The implant was not sufficiently submerged distally and lost significant bone height at the distal aspect by 4 months. (d) The implant was still restored, but further bone and soft tissue loss had exposed the majority of the implant threads buccally and distally during the first year. (e) A clinical view of the failing implant. e

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a

b

c

d

e

FIG 9-18  |  (a) The healed mandibular right first molar site received an 11 × 9–mm implant, but the operator failed

to submerge the implant shoulder 2 mm below the lowest position of the buccal crest. (b) Loss of bone was already evident at the time of crown placement; note the compromised crown form due to the improper implant seating. (c) Further reduction in bone height was seen after 1 year. (d) The implant shoulder became exposed clinically even before restoration. (e) After restoration, chronic inflammation became an issue with the buccal soft tissues.

The buccal bone loss then led to gingival recession and exposure of the coronal-most implant threads clinically. Ultimately, the buccal soft tissues became chronically inflamed. A final example of faulty surgical technique is shown in Fig 9-19. In this case, the initial osteotomy should have been started more mesially to prevent distal drifting of the implant burs. The mesial interproximal

bone volume and density were far greater than that of the distal interproximal bone, which is a frequent finding with maxillary molar sites (see Figs 9-5f to 9-5h) and requires the operator to start the pilot hole intentionally toward the mesial so that the inevitable bur drift will not lead to the implant being too close to a distal molar if present.

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References

a

b

FIG 9-19  |  (a) The maxillary left first molar had a fractured root. (b) A short ultra-wide implant was immediately placed but ended up too far distally due to bur drift; the implant was immediately removed, and treatment was delayed until the extraction site had fully healed.

Conclusion The immediate replacement of molars with dental implants is a desirable treatment approach because it greatly reduces treatment time and cost. A short ultrawide tapered MR threaded implant specifically for use in molar extraction sockets is an important addition to the implant dentist’s armamentarium. Its ultra-wide prosthetic table allows the fabrication of an anatomically correct molar implant crown. However, the surgical protocols recommended by the manufacturer must be strictly followed. First, there must be an intact buccal alveolar socket wall after the molar extraction. Second, the implant diameter chosen must be one that following placement will leave a distance of at least 2 mm between the buccal aspect of the implant prosthetic table and the buccal cortical plate of bone. A pretreatment CBCT scan can help with this decision. Next, the implant must be submerged 2 mm below the lowest point in the buccal cortical plate to avoid buccal crestal bone loss and allow enough space to allow replication of a true molar crown. Finally, care must be taken not to allow the implant burs to drift too far distally because this can compromise both the implant and the adjacent molar.

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