By Richard M. Sullivan, DDS
Only 20 years ago, the term "osseointegration" was virtually unknown within the United States. The use of endosseous implants to replace dentition, although not unheard of in 1980, fell outside the American dental mainstream in general practice. This article reviews some of the key developments that have ensued since then. Special attention is paid to the concept of osseointegration as it applies to dental general practitioners.
Tooth loss is a traumatic, even devastating, occurrence; and this has doubtless been true throughout human history. It is not surprising, then, that humans for millennia have sought to replace their lost dentition.1 The Etruscans are believed to have created bridgework fashioned from oxen bones some 2,500 years ago. Likewise, the notion of dental implants has its roots in antiquity. Archeologists have found evidence that occupants of what is now Honduras as long as 1,000 years ago developed a way to use tooth-shaped stones as dental implants.
In Europe, the earliest reference to an implant in modern literature appeared in a French work published in 1809; and by the late 1800s, dentists on both sides of the Atlantic were experimenting with implants made of such things as extracted teeth (human and animal) and lead. As the first half of the 20th century unfolded, dental innovators continued to search for materials and designs that would survive for more than a brief period after implantation. One breakthrough came in 1941, when a Swedish doctor named Gustav Dahl placed a metal structure below the periosteum; vertical extensions protruded through the gingiva. Impressed by this work, two dentists from Providence, R.I., Aaron Gershkoff and Norman Goldberg, brought the technique for placing subperiosteal implants to the United States, an achievement that attracted attention from other American dental practitioners. In 1951, 30 dentists met in St. Louis to form the American Academy of Implant Dentures (later known as the American Academy of Implant Dentistry).2
Another advance came with the work of Leonard I. Linkow of New York, who in 1964 introduced a self-tapping titanium implant. For cases in which bone was limited, Linkow later created a blade implant that eventually became the most widely used implant design in the 1970s.3
By 1978, a National Institutes of Health-Harvard University consensus conference was held to examine the implant modalities predominant at that time: subperiosteal, blade, vitreous carbon, and staple. This conference identified benefits and risks of implants, and a panel made specific recommendations for patient informed consent. As a historical note, Dr. Isaih Lew, then associate clinical professor of implant dentistry at New York University, had wanted screw-shaped implants to be included in the conference. Because they were not "current technology" in the United States at the time and the conference organizers were unaware of European developments, the program excluded them.4
v European Efforts
By the time the first Harvard consensus conference was held, a number of crucial developments were already under way in Europe. In Switzerland, Dr. Andre Schroeder, chairman of the University of Berne, was working to develop a dental implant system for clinical use. This work was done in conjunction with the Institute Straumann, a pioneer in the use of metal products in orthopedic surgery. Dr. Schroeder's experiments, first reported in 1976 in the German-language Swiss Dental Journal, histologically demonstrated the in-growth of bone into titanium plasma-sprayed hollow endosseous implants.5
At the same time, Professor Willi Schulte of the University of Tübingen in Germany was reporting success with immediate placement of vitreous carbon implants after dental extraction.6 Work with this design would eventually lead to the Frialit-2 implant.
v Brånemark's Contribution
In Sweden, similar research was to have an even more profound impact on dentistry. It
had its genesis in an accidental discovery made in the 1950s by a Swedish physician named
Per-Ingvar Brånemark. An anatomical and experimental biologist, Brånemark was
interested in studying bone healing response and regeneration. To observe the functioning
of bone marrow in vivo, a process known as vital microscopy, he adapted an experimental
chamber that had been used in England for insertion into rabbit ears. Unable to obtain
tantalum (the material used in the original design), he instead used titanium to make a
chamber that could be inserted into rabbit legs to allow
microscopic visualization of vital processes. After a months-long series of investigations, he sought to retrieve the chamber for reuse and found to his annoyance that it could not be removed from the rabbit bone.6
Brånemark reportedly was not struck by the significance of this turn of events until
some time after 1960, when he accepted a professorship in the Department of Anatomy at
Gothenburg University. There, using an adaptation of the titanium chamber placed in the
upper arms of human "volunteers" (also known as graduate students), he and his
team investigated the workings and structure of human blood cells under a number of
conditions, including response to cigarette smoking. This work yielded a great deal of
information about the nature of blood, and it showed the researchers that the titanium
serving as lens casings appeared uniquely compatible with the human soft tissue and skin,
provoking no adverse immunological reactions. At this point, Brånemark began to
contemplate using titanium for medical applications (Figures 1 through 4).
 |
| Figures 1 through 4. Brånemark first used a lens encased in titanium to be installed in the bones of living rabbits. This method of observation is called vital microscopy. This was followed by titanium-sheathed lenses placed in graduate students' upper arms. These experiments in vital microscopy established both the bone and soft tissue compatibility of titanium as an accidental finding. |
In the years that followed, Brånemark and his team pursued this vision along a number of fronts. They designed titanium screws and inserted them into the jaws of beagle dogs, studying the conditions needed to achieve a solid bond between the bone and the metal (Figures 5 through 7). They studied the biomolecular processes that occur when titanium is placed in living tissue. As this understanding advanced, Brånemark believed it necessary to coin a new term to refer to the in-growth of the bone into the threads and crevices of titanium. He finally settled upon "osseointegration," derived from the Latin words os (bone) and integro (to renew).
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| Figures 5 through 7. Functioning implants supporting fixed bridges in dogs and the eventual analysis of the implants provided understanding of the mechanisms to achieve this state of osseointegration before the first humans were operated on. |
By 1965, the Swedish team felt ready to apply its findings to human patients. Although they had originally planned to work with knee and hip joint surgeries, they instead selected as their first human subject a 34-year-old man who had been born with a deformed chin and jaw. Brånemark inserted four titanium fixtures into the man's mandible, and several months later he used the fixtures as the foundation for a fixed set of false teeth. The fixtures survived, the patient's life was transformed, and Brånemark resolved to develop more techniques for dealing with dental rehabilitation.
By 1975, Brånemark's findings and techniques had won approval from an independent
team of three professors who reported to the Swedish National Health and Welfare
Board that "treatment with a jawbone-anchored bridge construction can and should be
used as a complement to conventional prosthetics." A year later, in April of 1976,
the Brånemark method became fully covered by the Swedish national health insurance
system, and Brånemark began training the first Swedish dental experts in his techniques
in October 1977.
Almost five more years would pass, however, before Brånemark's findings would explode like a bombshell upon the consciousness of North American dentists. George Zarb, a dentistry professor from Toronto University who had trained under Brånemark in Sweden and then replicated his results independently, orchestrated this development. In May of 1982, Zarb organized the Toronto Conference on Osseointegration in Clinical Dentistry. The well-respected Zarb personally invited all the leading researchers in American and Canadian dentistry to the conference, and representatives from more than 70 universities responded. At this forum, Brånemark presented the results of his 15 years of meticulous human and animal research.
The weight of the scientific evidence, combined with Brånemark's charismatic personality, convinced a substantial percentage of the Toronto attendees that dental implants should at last be taken seriously. Shortly after the conference, researchers from the Mayo Clinic and Mayo Medical School obtained training in Brånemark's methods in Sweden; and the following year, the Mayo Clinic became one of five academic institutions in North America designated to train dental specialists (oral surgeons and, later, periodontists) in the surgical techniques. Under Brånemark's initial policy, restoration was to be carried out by prosthodontic specialists (with general dentists to follow).
Another consequence of the 1982 Toronto conference was the formation of a study club by a group of dental clinicians from the greater New York area. Their intent was to share research and information about osseointegration, and they eventually formed a national organization to foster education and advancement in the field of implant dentistry. In April of 1986, the first annual meeting of the Academy of Osseointegration was held in Chicago. It was at this point that a differentiation between implant-delivery formats became apparent in the United States. In a general sense, "multimodal implant dentistry" encompasses a wide range of formats, including blade or plate-form implants, subperiosteal, ramus frame, and cylindrical endosseous implants. These implants may rest on or be encapsulated within the bone. Today, when people use the term "osseointegration" they generally imply the installation of cylindrical implants in a manner to ensure rigid fixation of the implant without an intervening fibrous or soft-tissue layer. The osseointegration approach as the foundation for tooth replacement by far predominates other methods, but other implant modalities continue to have adherents.
In the early 1980s, recognizing the need for research to substantiate patient safety for dental implants based on research, an American Dental Association council adopted a resolution that permitted dental implants to be submitted for review. In 1985, Nobelpharma, the company manufacturing Brånemark’s implants for commercial use, submitted the first application, with approval coming the following year.
Since 1985, the American Dental Association's initial use of the word "approval" has given way to the term "acceptance." Eleven implant systems have received the ADA Seal of Acceptance (Table 1). In addition, two implant systems have received provisional acceptance: Astra Tech Implants for partially edentulous indications (Astra Tech, Inc.) and MicroVent Dental Implants (Sulzer Dental, Inc.).
Figure 8. "Osseointegration" implies rigid adaptation of
the implant in the host bone site, with no intervening soft tissue layer visible at the
light microscope level.
During the past 20 years, the field of osseointegration has witnessed a number of significant developments in the United States. One of the most notable is the expansion of the treatment indications. Treatment indications are a method of segmenting the field of osseointegration for discussion purposes; historically, dental restorations supported by osseointegrated implants evolved in this order:
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The fully edentulous lower jaw (Figures 9 through 15); |
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The fully edentulous upper jaw; |
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The short-span edentulous segment; and |
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The missing single tooth. |
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| Figure 10. | Figure 11. |
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| Figure 12. | Figure 13. |
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| Figure 14. | Figure 15. |
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| Figure 10. | Figure 11. |
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| Figure 12. | Figure 13. |
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| Figure 14. | Figure 15. |
| Figures10 through 15. Osseointegrated dental implants were first applied to the fully edentulous jaws. The rigid functional stability they provided was superior to previous augmentation methods. In Sweden, there was an emphasis on fixed restorations in both jaws. Other parts of the world, including the United States, have developed overdenture alternatives utilizing dental implants. | |
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| Figures 16 and 17. Soon after rehabilitation of the fully edentulous patient was introduced, American dentists started applying these principles to the missing single tooth and short-span segmental restoration. |
Treatment indications are important in any discussion of osseointegrated dental implants because not all concepts apply to all indications. The subjective symptoms of the patient seeking treatment, the patient's expectations regarding treatment outcome, anatomical limitations, and the components used all may vary widely, depending upon the treatment indication.
When Brånemark presented his findings at the 1982 Toronto conference, dental implants up to that point had only been utilized for fully edentulous jaws (upper or lower), and the treatment was only recommended for individuals in this category. That might appear to defy logic, since placement of implants for a fully edentulous arch may appear more complex than replacing only one tooth or using implants to support a short-span bridge.
However, the context of Brånemark's early research explains why the field developed as it did. Anxious to avoid the possibility of making any patient's condition worse, Brånemark selected for his early research subjects only individuals whom he classified as "dental cripples." These were people suffering from catastrophic dental failures, for whom traditional treatments were no longer an option. For such people, any success with dental implants would be an improvement.
Soon after the first Americans were trained in Brånemark's method in Sweden, they began to adapt and apply these methods for other treatment indications, specifically single-tooth and short-span fixed partial dentures. In one sense, this was a logical thing to do. If Brånemark demonstrated that a full arch of teeth could be successfully restored on four or five implants, it seemed an obvious extrapolation that a three-unit bridge could be done on two implants (Figures 16 and 17).
| Table 1. Implant Systems With Acceptance | |
| Manufacturer | Implant System |
| Astra Tech, Inc | Astra Tech Implant |
| Nobel Biocare USA Inc. | Brånemark System Dental Implants |
| IMZ 4.0mm Implant System | |
| Steri-Oss HA-Coated Titanium | |
| Screw Type Dental Implants | |
| Steri-Oss Titanium Screw Type Dental Implants |
|
| Straumann Co. | |
| ITI Dental Implants | |
| Sulzer Dental, Inc. | Integral Endosseous Implant System |
| Integral Omniloc Endosseous Implant System | |
| Omniloc Dental Implant System With Interface Ring | |
| Spline HA-Coated Cylinder Dental Implant System | |
However, while the early adopters experienced many successes with the expanded utilization, unanticipated complications and failures also resulted. The first studies demonstrating the efficacy of implants for single-tooth and short edentulous span indications began appearing in the early 1990s. As they have accumulated, understanding has grown of the unique biomechanical factors that must be considered for each treatment indication. Dentists and their patients can benefit from the experiences gained during these developmental years.
A second important development has been the gradual shift in attention to the creation of esthetic restorations. In the mid-1980s, implant practitioners were focusing on functional rehabilitation of the fully edentulous patient. Esthetic results were secondary to the profound impact on patients' life quality that resulted from having a truly fixed restoration after functioning with denture adhesives for 30 years or more. But as dentists sought to offer osseointegrated dental implants on a more routine and elective basis, demand for esthetic results that were at least comparable to other forms of dentistry grew.
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| Figure 24 | |
| Figures 18 through 24. The transition from functional full arch to esthetic single tooth replacement has entailed a deeper understanding of the implications of soft tissue on the esthetic result. Advances in components, such as this ceramic abutment, allow cemented restorations analogous to everyday restorative procedures in general practice. In this instance, the osseointegration approach prevents the preparation of an unrestored canine tooth, and also prevents the remaking of a crown that would require a midline shade match. | |
Implant dentistry in the1990s experienced a transition from functional rehabilitation to esthetics, with esthetic results improving throughout the decade. One aspect of this transition has been the development of components specifically designed for the single-tooth restoration or segmental bridge (Figures 18 through 24).
What has also emerged is a more detailed understanding of the relationship between residual bone volume and papilla height, along with treatment planning to correct soft-tissue deficits either surgically or prosthetically. It has become apparent that changes in the soft-tissue contours in the post-tooth-loss resorptive process have the greatest impact upon the final restorative esthetic result. During the past two decades, the focus on bone and implants has been joined with an equal focus on ceramics and soft tissue (Figure 25).3
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| Figure 25. The physiologic health of the living bone, periimplant tissue, and functioning restoration help determine long-term success. |
Another significant change has come in the manner in which osseointegrated dental implant restorations are delivered. In the 1980s, dental implant restorations were not only primarily of a full-arch nature, but they were also screw-retained. That is, the dental restoration was attached to the implant or implant abutments with the use of small set screws. From a research perspective, especially with unknown outcomes at the outset, this was very practical. It made the restoration retrievable by the dentist so it could be modified or the status of the individual implants could be experimentally assessed. During the 1990s, however, as more general dentists and dental laboratory technicians have entered the field, a rapid changeover to cemented restorations has occurred. These implant restorations more closely resemble their natural tooth counterparts and do not require the same intricacies in fabrication as a screw-retained restoration. Long-term provisional cements seek to retain the retrievability of cemented restorations. Today, virtually any restoration can be done in either a screw-retained or cemented fashion, provided this preference is accounted for in the treatment-planning process.
Today, approximately 450,000 osseointegrated implants are being placed every year. The fastest-growing treatment indication is the single-tooth replacement. At one time, a dental implant was thought to be an aggressive treatment of last resort. Today, replacing a missing single tooth with an implant-supported crown has a reasonable expectation of a 95 percent success rate. Compared to the preparation of healthy, vital natural abutment teeth, many dentists realize and embrace the idea that the single-tooth implant is actually a more conservative treatment for the patient in the long term (Figures 26 through 36).
Despite all the successes, a couple of factors have impeded still wider acceptance of implants as a treatment modality. For one thing, dental insurance continues to lag behind the technology. Academic training in implant techniques has also developed slowly. For the most part, implant dentistry still is not being taught at the undergraduate level. Dentists must acquire their knowledge about treatment planning, implant placement, and hands-on restorative procedures as a postgraduate pursuit, either from residencies or approved continuing education courses. Ongoing study-club participation supports development in a group-learning context and provides the opportunity for mentorship.
Even with the obstacle of dental implant proficiency being a post-graduate pursuit, implant-supported dental restorations are definitely on an upswing in the United States. More patients are choosing to have their teeth replaced without having their adjacent teeth ground. They are understanding the long-term benefits and decreased risk of complications by avoiding preparation of abutment teeth.
Dentists are recognizing that implant-supported restorations are often the most conservative and predictable approach to tooth replacement. Offering patients this alternative represents the standard of care in informed consent. The author's position is that every restorative dentist in the United States should at least be providing cemented single-tooth and short-span segmental restorations on dental implants, and lower overdentures on ball attachments.
The historical perspective of osseointegration demonstrates that these developments are now part of the mainstream armamentarium for routine treatment planning for the replacement of missing teeth. Dental patients can experience routine benefits with minimum risks and complications based on the careful developmental footsteps established by the foresight of the early innovators.
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| Figure 26. Figure 27. |
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Figure 28. Figure 29. |
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Figure 30. Figure 31. |
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| Figure 32. Figure 33. |
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| Figures 26 through 36. Dental implants have evolved to the point of becoming the more conservative treatment to replace a missing single tooth. Placement of two implants in a one-stage surgical procedure provide the foundation for customized titanium abutments and all-ceramic crowns to be cemented without preparation of unrestored and vital potential abutment teeth. |
Author
Richard M. Sullivan, DDS, is the clinical director of Nobel Biocare USA, Inc.
References
Legends
Figures 1 through 4. Brånemark first used a lens encased in titanium to be installed in the bones of living rabbits. This method of observation is called vital microscopy. This was followed by titanium-sheathed lenses placed in graduate students' upper arms. These experiments in vital microscopy established both the bone and soft tissue compatibility of titanium as an accidental finding.
Figures 5 through 7. Functioning implants supporting fixed bridges in dogs and the eventual analysis of the implants provided understanding of the mechanisms to achieve this state of osseointegration before the first humans were operated on.
Figure 8. "Osseointegration" implies rigid adaptation of the implant in the host bone site, with no intervening soft tissue layer visible at the light microscope level.
Figures 9 through 15. Osseointegrated dental implants were first applied to the fully edentulous jaws. The rigid functional stability they provided was superior to previous augmentation methods. In Sweden, there was an emphasis on fixed restorations in both jaws. Other parts of the world, including the United States, have developed overdenture alternatives utilizing dental implants.
Figures 16 and 17. Soon after rehabilitation of the fully edentulous patient was introduced, American dentists started applying these principles to the missing single tooth and short-span segmental restoration.
Figures 18 through 24. The transition from function full arch to esthetic single tooth replacement has entailed a deeper understanding of the implications of soft tissue on the esthetic result. Advances in components, such as this ceramic abutment, allow cemented restorations analogous to everyday restorative procedures in general practice. In this instance, the osseointegration approach prevents the preparation of an unrestored canine tooth, and also prevents the remaking of a crown that would require a midline shade match.
Figure 25. The physiologic health of the living bone, peri-implant tissue, and functioning restoration help determine long term success.
Figures 26 through 36. Dental implants have evolved to the point of becoming the more conservative treatment to replace a missing single tooth. Placement of two implants in a one-stage surgical procedure provide the foundation for customized titanium abutments and all-ceramic crowns to be cemented without preparation of unrestored and vital potential abutment teeth.
Copyright 2001 Journal of the California Dental Association. Vol. 29, No. 11, Nov. 2001
Reprinted with permission.
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In an effort to resolve some of the existing controversies and to deal with the gaps in knowledge in dental implantology, the NIDR in conjunction with the National Institutes of Health (NIH) Office of Medical Applications of Research and the Food and Drug Administration convened a consensus development conference on June 13-15, 1988. It also is evident that the tremendous interest in this field as well as many clinical case series studies also are responsible for the NIH convening this second Consensus Development Conference on Dental Implants within a 10-year period. A group of distinguished speakers presented current data on many aspects of implantology. The audience of approximately 750 included an illustrious group of clinicians, researchers, and educators, many of whom were responsible for the development and advancement of the field of dental implantology. Following 1-1/2 days of presentations by experts in the relevant fields and presentations by professional organizations involved in dental implantology, a consensus panel consisting of representatives from the fields of dental implantology, oral surgery, anatomy, bone biology, periodontology, materials and engineering, epidemiology, statistics, behavioral science, and the public considered the evidence and formulated a consensus statement responding to the following questions:
The use of dental implants to provide support for replacement of missing teeth is becoming an important component of modern dentistry. As a result of advances in research on implant design, materials, and techniques the use of these devices has increased dramatically in the past few years and is expected to expand further in the future. Many types of implants are now available for application to different clinical cases, and an increasing number of dentists have become involved in this form of treatment. It has been estimated that the overall number of dental implants inserted in the United States increased fourfold from 1983 to 1987, and during that same period the number of practitioners who perform implant therapy increased tenfold. It is estimated that as many as 300,000 dental implants will be used in the United States by 1992. Growth in dental implant utilization also is evident in Europe and Japan.
The magnitude of the missing tooth problem (edentulism) in the United States adult population remains considerable. Although there has been a tremendous reduction in coronal dental caries during the past several decades, this improvement is evident mainly in the younger segments of the population, with individuals over 35 years of age still showing a significant prevalence of full or partial edentulism. According to the 1985-1986 National Institute of Dental Research's (NIDR) national survey of oral health conducted on U.S. employed adults and seniors attending multipurpose senior centers, approximately 42 percent of Americans over 65 years of age and 4 percent of those 35 to 64 years of age are totally edentulous. Moreover, those over 65 years with teeth have lost an average of more than 10 of 28 teeth, and employed dentate persons ages 55 to 64 have lost an average of 9 of 28 teeth. Thus, there are many individuals in this country who could conceivably benefit from dental implant therapy.
Many individuals with edentulism can be treated with partial or complete traditional removable dentures or fixed bridges. However, these prostheses are not satisfactory for a significant number of individuals who have lost the tooth-bearing portions of the bone and simply cannot manage removable prostheses, or are medically compromised and cannot properly masticate food. Moreover, there is a strong suggestion that a substantial number of patients prefer implant-supported prostheses over soft tissue supported prostheses.
Research advances in dental implantology have led to the development of several different types of implants, and it is anticipated that continued research will lead to improved devices. At present, continued evaluation is necessary to determine that appropriate implant devices are available to meet the therapeutic demands of the different portions of the jawbones and the unique needs of patients.
Criteria of success vary with different implant systems. Therefore, it is difficult to compare certain types of implants for which success criteria and indications may be different. Furthermore, for implants that are comparable, proper research designs for comparison (randomized, controlled trials) have not been used. Thus, the panel could only conclude that there is evidence from a number of case series studies that when specific types of dental implants are inserted by clinicians experienced with the respective techniques, a large proportion of implants remains in place for periods of 10 years or more.
However, it is difficult to make definitive statements on the long-term effectiveness of dental implants from these case series studies because of unreported information and the lack of uniform application of proper research designs. Although the ideal research design for documenting the effectiveness of new treatment techniques should be a randomized, controlled clinical trial, case series studies are capable of providing limited evidence when proper methods are used. Future case series studies should conform to the following principles:
The case series studies available generally did not follow these principles. In addition, little data were available on traditional treatment outcome measures such as patient satisfaction, esthetics, comfort, lack of physical and psychological symptoms, phonetics, and masticatory efficiency.
The evidence that dental implants are effective in providing total support for restorations is based on several case series studies with a duration of 10 years or more and several others that lasted for more than 5 years. The evidence that implants are effective in the long term in partially tooth-supported restorations is based on fewer studies that have been conducted for periods of up to 10 years. Because of the lack of randomized trials to compare different implant systems and the lack of uniformity in defining success, it is not possible to make judgments on the comparative merits of different implant systems. Additional knowledge about the biology of hard and soft tissues coupled with technological advances in the construction and insertion of various implants will likely result in a trend toward improved long-term success rates. This expectation is evident in the historical learning curve apparent when survival rates of specific implant systems are monitored. For example, in the case of endosseous implants, available long-term data are derived from studies in which many factors now known to affect implant survival were not properly appreciated when the longitudinal studies were begun. Included among these factors were bone preparation procedures that failed to stay within certain thermal limits now known to be critical for bone cell survival. Furthermore, the insertion of implants in a one-stage procedure may not have ensured absence of functional forces during the critical early stages of wound healing. These techniques may explain in part the early failure of some implants and the frequent fibrous adaptation of bone to some implants. Although it is not clear that the fibrous tissue interface compromises the long-term success rate of endosseous blade implants, the best reported long-term survival rates for root-form implants have been achieved with systems that have bone at the interface.
No reliable data are available on the effect of variations in restorative techniques on the long-term success rate of implants nor are data available on the long-term use of implants in edentulous children.
Dental implants may be classified by type as endosseous, subperiosteal, transosteal, intramucosal, endodontic, and bone substitutes. The data that were presented at this conference were confined to the first three types. These are the only ones for which indications and contraindications have been promulgated in this statement. These implant types are subdivided as follows:
Endosseous:
| Root form.
| Blade (plate) form.
| Ramus frame. | |
n Subperiosteal:
| • Complete.
| • Unilateral.
| • Circumferential. | |
n Transosteal:
| • Staple.
| • Single pin.
| • Multiple pin
| |
For long-term successful performance of all dental implant types the following general factors should be considered:
| Biomaterials.| • Biomechanics. | • Dental evaluation. | • Medical evaluation. | • Surgical requirements. | • Healing processes. | • Prosthodontics. | • Postinsertion maintenance.
| |
All practitioners involved in patient care should be knowledgeable regarding these
factors and their interrelationships. Standards of dental practice would suggest the
following general contraindications for the above three categories of dental implants:
| • Debilitating or uncontrolled disease. |
| • Pregnancy. |
| • Lack of adequate training of practitioner. |
| • Conditions, diseases, or treatment that severely compromise healing,
e.g., including radiation therapy. |
| • Poor patient motivation. |
| • Psychiatric disorders that interfere with patient understanding and
compliance with necessary procedures. |
| • Unrealistic patient expectations. |
| • Unattainable prosthodontic reconstruction.| • Inability of patient to manage oral hygiene. | • Patient hypersensitivity to specific components of the implant.
| |
With regard to indications for a specific implant type, the bone available to support the implant is the primary factor after prosthodontic diagnosis and treatment plan. This bone is measured in width, height, length, anatomical contour, and density. These physiological and anatomical factors may be altered by either osteoplasty or augmentation of the bone. In addition, other factors affecting indications for implant type are the degree and location of the edentulism of the patient. Indications for each implant type are specified below:
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ENDOSSEOUS, root form: |
| Adequate bone to support the implant with width and height being the primary
dimensions of concern.
| • Maxillary and mandibular arch locations.
| • Completely or partially edentulous patients.
| |
n ENDOSSEOUS, blade (plate) form:
n ENDOSSEOUS, ramus frame:
n SUBPERIOSTEAL, complete, unilateral, circumferential:
n TRANSOSTEAL, staple, single pin, multiple pin:
Implant treatment is delivered in several ways: (1) by multidisciplinary teams of dentists in which an oral surgeon or periodontist performs the surgical component of the implant and a prosthodontist performs the prosthetic component; (2) by individual implan-tologists with extensive training in both the surgical and prosthetic components who perform all aspects of the procedure; and (3) by general dentists who may perform both components or the prosthetic component only and whose training in implant techniques may vary widely.
Unfortunately, there are no data available to the panel that address the surgical, restorative, and periodontal requirements for the individuals managing the implant patient.
Minimal training has not been precisely defined, but the panel recommends that the individual that assumes the surgical treatment phase be well prepared in accepted surgical methodologies. In as much as the restorative procedures employed in implantology differ from those in traditional restorative dentistry procedures, the panel recommends instruction in the restorative phase of implantology. These programs also should include expertise in short- and long-term tissue maintenance addressing gingival status as well as radiographic evaluation of tissue support.
Patient selection should be restricted to those patients who show a need and motivation for the implant procedures. The evaluation of the recipient should include a survey of adequate bone structure, medical history, and, where indicated, medical laboratory studies and consultation with the patient's physician. The use of computerized tomography for evaluation of maxillary and mandibular anatomy is suggested when more accurate information regarding implant placement is needed. The patient's dental evaluation also should include a psychosocial appraisal of his or her suitability for implant procedures when psychological symptoms are present.
The panel supports a multidisciplinary approach, and we recommend a preimplant consultation involving the professional participants with the patient. Postimplant procedures should include communication, monitoring, and collection of recorded data by the professional. We recommend that the patient be thoroughly instructed in maintenance therapy with the understanding that the patient serves as a cotherapist.
There is a lack of data detailing the minimum requirements for an adequate maintenance program. The proper recall interval, methods of plaque and calculus removal, and use of antimicrobial agents are critical variables that need further evaluation.
There are at least three areas in which the assessment of patient risk should be considered, including risks associated with the surgery and/or anesthesia, psychological risks, and medical risks. Risks associated with the surgical procedure may include inadvertent perforation of the nasal sinus, local and systemic infection, and nerve injury. Before surgery a medical history should be taken to evaluate the history of the presenting problem and chief complaints. A review of the current status of the patient's organ systems should be made.
Children need special consideration, given long-term morbidity concerns, requirements
of growth, manual dexterity, and coping skills.
Psychological stressors and motivational factors have been shown to influence patient response to surgery and long-term compliance with oral hygiene maintenance. These stressors include both familial and social environmental factors such as job satisfaction, financial status, and health concerns. Specific mental conditions may require psychological intervention to assist with patient cooperation and outcome satisfaction. Individuals with excessive neurotic concerns, depression, anxiety, and specific medical fears or previous negative medical or dental experiences should be appropriately evaluated. Relative contraindications include individuals with psychotic symptomatology, especially requiring psychotropic medication, and somatization disorders or chronic pain complaints where medical symptoms are exhibited in the absence of organic evidence. Tobacco use, alcohol, or drug dependency may interfere with good nutrition or compliance requirements.
Temporary conditions that may result from implant placement may include pain and swelling, speech problems, and gingivitis. Long-term problems may include nerve injury, local bone loss exacerbation, hyperplasias, local or systemic bacterial infection, and infectious endocarditis in susceptible individuals, including those with body part replacement. Existing natural dentition may be compromised.
Factors related to prediction of health risks need to be continuously assessed before the surgical decision, after implantation, during the temporary waiting period, following the loading period, and at 6-month intervals throughout the followup period. Reliable and valid standardized measurements sensitive to both psychological and physical factors should be used in clinical prospective studies to enhance comparison across studies.
v What Are the Future Directions for Research On Materials and Designs of Dental Implants and On Clinical Management?
Materials and Designs
Dental implants have many compositions and surface textures. Manufacturing processing techniques affect these surfaces in subtle ways. To better control clinical protocols, characterization of these surfaces is essential. Ion release from the implant may influence biocompatibility (bioacceptance). To achieve a more complete understanding of tissue response to the implant, basic experiments in host-implant physiology and biology must be continued. Dynamic studies in laboratory animals also should be completed. Other matters that warrant further study are the influence of surface preparation on wettability or bonding of tissues to the implant and the effect of galvanic couples resulting in corrosion. Studies must document the possible release of constituents of
implant materials at the trace and subtrace level into other tissues to determine their significance with respect to toxicity, mutagenicity, or carcinogenicity.
Basic research should be emphasized to develop materials and methodology to allow for predictable bone augmentation. The implant- host interface should be studied to characterize wound repair and tissue adaptation in the peri-implant region.
Among the factors involved in the design of an implant are the force components produced during loading, the dynamic nature of loading, and the mechanical and structural properties of the prosthesis of stress transfer to tissues. Unfortunately, accurate data on such parameters are incomplete. Such information is essential for efficient design of implants.
Clinical Management
Randomized, controlled, prospective multicenter clinical studies should be initiated. These studies should investigate the role of several factors on the long-term effectiveness of dental implants. These factors include, in addition to implant characteristics, the operator's skills in implant placement, tissue management, various patient characteristics, including the intraoral location of the implant, and occlusal and prosthetic considerations.
The panel feels that one important method of accumulating accurate data on implant performance is to establish a National Dental Implant Registry, which will standardize reporting forms to collect information on this activity in the United States. A rating scale based upon function and discomfort should be developed for evaluation of all implant procedures. In this way, the causative factors involved in success and failure of implants can be more accurately identified. Consideration also should be given to the establishment of centers for training, treatment, and research in dental implantology.
To ensure continued safety evaluation of dental implants, long-term prospective studies should specifically address failures due to medical or psychological complications that led to premature removal of the implant. When failures occur in either implants or an existing dentition, a failure analysis should be performed and reported.
All patient data should be recorded, including age, education, socioeconomic level, number of previous implants, nutritional status, periodontal status, acute or chronic coexisting diseases, and pharmacologic use.
Patient Considerations
Considering that edentulousness is frequently the result of the patient's high susceptibil
ity to destructive forms of periodontal disease, the relationship of implant success rates to the patient's relative susceptibility to periodontitis should be studied. Also, data are needed on both the acute and chronic or long-term morbidity that may result from various types of implants.
The public is entitled to educational materials that enable informed participation in implant treatment decisions, and the panel recommends that these materials be developed.
Conclusion
During the 10 years since the first Consensus Development Conference on Dental Implants, a great deal of activity in the field has occurred with the development of better materials and newer techniques that have resulted in improved implant-bone interface. This conference examined case series studies, and the panel concluded that a large proportion of endosseous, subperiosteal, and transosteal implants have remained in place for more than 10 years. The indications and contraindications of various types of dental implants have been described. The complexity of the surgical, restorative, and periodontal procedures used to successfully insert and maintain dental implants demonstrates the need for a multidisciplinary approach in this field.
Long-term studies that concurrently compare various types of implants are needed to provide information beyond mere survival rates. Functional success of various implants should include such criteria as the ability to support fixed or removable prostheses in the absence of discomfort, the presence of satisfactory esthetics, and clinical and radiographic evidence of tissue health. A suggestion for the establishment of a National Dental Implant Registry was proposed with the objective of collecting data and documentation on various procedures being conducted in the United States. Future studies in materials and techniques were proposed.
Consensus Development Panel
D. Walter Cohen, D.D.S.
Conference and Panel Chairperson
President
The Medical College of Pennsylvania
Philadelphia, Pennsylvania
James D. Beck, Ph.D.
Professor and Chairman
Department of Dental Ecology
University of North Carolina at Chapel Hill
School of Dentistry
Chapel Hill, North Carolina
Chester W. Douglass, D.M.D., Ph.D.
Associate Professor and Chairman
Department of Dental Care Administration
Harvard School of Dental Medicine
Boston, Massachusetts
Manville G. Duncanson, Jr., D.D.S., Ph.D.
Professor and Chairman
Department of Dental Materials
University of Oklahoma College of Dentistry
Oklahoma City, Oklahoma
Lawrence J. Emrich, Ph.D.
Cancer Research Scientist
Department of Biomathematics
Roswell Park Memorial Institute
Buffalo, New York
Max A. Listgarten, D.D.S.
Professor and Chairman
Department of Periodontics
University of Pennsylvania School of
Dental Medicine
Philadelphia, Pennsylvania
Barbara G. Melamed, Ph.D.
Professor of Psychology
Departments of Clinical and Health
Psychology and Community Dentistry and
Psychiatry University of Florida College of Health
Related Professions Health Sciences Center
Gainesville, Florida
Carl E. Misch, D.D.S.
Codirector
Oral Implantology Center
University of Pittsburgh School of Dental Medicine
Director Misch Implant Institute
Dearborn, Michigan
Ralph W. Phillips, D.Sc., M.S.
Research Professor of Dental Materials
Indiana University School of Dentistry
Indianapolis, Indiana
Mary Kaye Richter
Executive Director
National Foundation for Ectodermal Dysplasias
Mascoutah, Illinois
Elaine A. Stuebner, D.D.S., F.A.C.D.
Professor, Oral and Maxillo Facial Surgery
Department of Pediatric Dentistry
College of Dentistry
University of Illinois
Chicago, Illinois
Allan M. Weinstein, Ph.D.
President and Chief Executive Officer IatroMed, Inc.
Phoenix, Arizona
Speakers
Robert E. Baier, Ph.D., P.E.
Director Health-care Instruments and Devices Institute
State University of New York at Buffalo
Buffalo, New York
Burton E. Balkin, D.M.D.
Director Implant Dentistry
University of Pennsylvania
School of Dental Medicine
Narberth, Pennsylvania
Charles L. Bolender, D.D.S., M.S.
Professor and Chairman
Department of Prosthodontics, SM-52
University of Washington
School of Dentistry
Seattle, Washington
Per I. Branemark, M.D.
Professor
Institute for Applied Biotechnology
SWEDEN
John B. Brunski, Ph.D.
Associate Professor
Department of Biomedical Engineering
Rensselaer Polytechnic Institute
Jonsson Engineering Center
Troy, New York
Ulrich M. Gross, M.D.
Professor
Institute of Pathology,
Steglitz Clinic
Free University of Berlin
FEDERAL REPUBLIC OF GERMANY
Jack E. Lemons, Ph.D.
Professor and Chairman
Department of Biomaterials
University of Alabama at Birmingham
School of Dentistry
Birmingham, Alabama
Krishan K. Kapur, D.M.D., M.S.
Professor-in-Residence Removable Prosthodontics
University of California at Los Angeles
Chief Dental Services
Veterans Administration Medical Center
Sepulveda, California
Victor J. Matukas, D.D.S., Ph.D., M.D.
McCallum Professor and Chairman
Department of Oral and Maxillofacial Surgery
University of Alabama at Birmingham
Birmingham, Alabama
Ralph V. McKinney, Jr., D.D.S., Ph.D.
Professor and Chairman
Department of Oral Pathology
Medical College of Georgia
School of Dentistry
Augusta, Georgia
Roland M. Meffert, D.D.S., F.A.C.D., F.I.C.D.
Professor and Chairman
Department of Periodontics
Louisiana State University
School of Dentistry
New Orleans, Louisiana
Anthony H. Melcher, M.D.S., H.D.D., Ph.D., D.Sc.
Professor of Dentistry
Faculty of Dentistry
Associate Dean of Life Sciences
School of Graduate Studies
University of Toronto
Toronto, Ontario CANADA
Lawrence H. Meskin, D.D.S., Ph.D.
Dean of Graduate School
University of Colorado
Health Sciences Center
Denver, Colorado
Joseph R. Natiella, D.D.S.
Professor and Chairman
Department of Stomatology and
Interdisciplinary Sciences
State University of New York at Buffalo
School of Dental Medicine
Buffalo, New York
Michael G. Newman, D.D.S.
Adjunct Professor
University of California at Los Angeles
School of Dentistry
Section of Periodontics
Center for Health Sciences
Los Angeles, California
W. Eugene Roberts, D.D.S., Ph.D.
Professor of Orthodontics
Director
Bone Research Laboratory
University of the Pacific
School of Dentistry
San Francisco, California
Paul A. Schnitman, D.D.S., M.S.
Associate Professor and Head
Department of Implant Dentistry
Harvard School of Dental Medicine
Boston, Massachusetts
Leonard B. Shulman, D.M.D., M.S.
Associate Clinical Professor and Head
Department of Implant Research
Forsyth Dental Center
Boston, Massachusetts
Dennis C. Smith, D.Sc., Ph.D., M.Sc., F.R.S.C.
Professor and Head
Department of Biomaterials
Faculty of Dentistry
University of Toronto
Toronto, Ontario CANADA
Charles M. Weiss, D.D.S., F.I.C.D.
President
Director of Research and Development
Oratronics, Inc.
The Chrysler Building
New York, New York
Philip Worthington, M.D., F.D.S.R.C.S.
Professor of Oral and Maxillofacial Surgery
Department of Oral and Maxillofacial Surgery
University of Washington
Seattle, Washington
Franklin A. Young, Jr., D.Sc., M.S.E.
Professor and Chairman
Department of Materials Science
Medical University of South Carolina
Charleston, South Carolina
George A. Zarb, B.Ch.D., D.D.S., M.S., M.S., F.R.C.D.(c)
Professor and Chairman
Department of Prosthodontics
University of Toronto
Toronto, Ontario CANADA
Planning Committee
D. Walter Cohen, D.D.S.
Conference and Panel Chairperson President
The Medical College of Pennsylvania
Philadelphia, Pennsylvania
Michael J. Bernstein
Director of Communications
Office of Medical Applications of Research
National Institutes of Health
Bethesda, Maryland
Jerry M. Elliott
Program Analyst
Office of Medical Applications of Research
National Institutes of Health
Bethesda, Maryland
Albert D. Guckes, D.D.S., M.S.D.
Chief Commissioned Officer's Dental Clinic
Warren Grant Magnuson Clinical Center
National Institutes of Health
Bethesda, Maryland
H. David Hall, D.M.D., M.D.
Professor and Chairman
Department of Oral Surgery
Vanderbilt University School of Medicine
The Vanderbilt Clinic
Nashville, Tennessee
Jack E. Lemons, Ph.D.
Professor and Chairman
Department of Biomaterials
University of Alabama at Birmingham School of Dentistry
Birmingham, Alabama
Jack L. Lewis, Ph.D.
Professor of Orthopaedic Surgery and Mechanical Engineering
University of Minnesota Medical School
Minneapolis, Minnesota
Marie U. Nylen, D.D.S., Dr. Odont. h.c.
Director Extramural Program
National Institute of Dental Research
National Institutes of Health
Bethesda, Maryland
Anthony Rizzo, D.M.D.
Planning Committee Chairperson
Chief Periodontal and Soft Tissue Diseases Branch
National Institute of Dental Research
National Institutes of Health
Bethesda, Maryland
Patricia Sheridan
Technical Writer/Editor
Office of Planning, Evaluation, and Communication
National Institute of Dental Research
National Institutes of Health
Bethesda, Maryland
D. Gregory Singleton, D.D.S.
Dental Officer Center for Devices and
Radiological Health
Food and Drug Administration
Silver Spring, Maryland
Thomas M. Valega, Ph.D.
Special Assistant for Manpower Development and Training
Extramural Program
National Institute of Dental Research
National Institutes of Health
Bethesda, Maryland
Philip A. Watson, D.D.S., M.S.D.
Professor
Department of Biomaterials
Faculty of Dentistry
University of Toronto
Toronto, Ontario CANADA
Wayne T. Wozniak, Ph.D.
Assistant Secretary
Council on Dental Materials, Instruments, and Equipment
American Dental Association
Chicago, Illinois
Conference Sponsors
National Institute of Dental Research
Harald Loë Director
The Office of Medical Applications of Research
John H. Ferguson Director
The Food and Drug Administration
Frank Young Commissioner
Wise Choices for Maxillary
Single-Tooth Implants
By Belinda L. Gregory-Head, BDS, MS; Alex McDonald PhD, DDS; and Eugene LaBarre DMD, MS
Abstract: The purpose of this article is to demonstrate to general practitioners who have no experience with dental implant treatment the esthetic limitations of such treatment. The criteria for wise case selection will be described so that esthetic excellence can be predictably achieved in general practice. A checklist of criteria will be provided as a treatment-planning tool to determine if a patient is likely to have an esthetically successful outcome.
While the anterior implant patient may come into the office fixed on the notion of having an implant, further questioning often reveals that his or her chief concern is to have a missing tooth replaced with something that looks good, feels good, and works like a real tooth. The challenge of treatment planning is to fulfill these goals. If any of these criteria cannot be satisfied, then the treatment may be considered a failure.1-3
California dentists may very well face a greater challenge than most in satisfying the esthetic demands of their patients. Practitioners here must satisfy an extremely esthetically aware population. Unreasonable demands from patients and unrealistic promises by practitioners can led to unsatisfactory experiences for all parties. A clear understanding of the esthetic limitations of dental implants and the practitioner's own expertise in this area will reduce the risk of unforeseen problems.
Long-term data on the success of implant-supported single-tooth restorations in the anterior maxilla have been available since 19964 and have been corroborated in many more recent studies.5-7 Success rates of between 90 percent and 98 percent have been consistently reported. Early papers documented complications as being mainly mechanical in nature, including screw loosening, component fracture, and loss of integration. Studies seeking to define success in the anterior region have, until recently, focused on retention and not on esthetic success.
The push for better function and esthetics has led to a growing appreciation of the biomechanical limitations of implants. Wider-diameter implants have been introduced.8,9 This addition to the armamentarium along with better engineering of the components and screw-tightening systems10,11 have brought us to a time when a dental implant can be a predictable and functional success. Advances in determining the ideal position of the implant and more accurate surgical techniques have greatly enhanced esthetic outcomes.12 These have been significant improvements, but they may never be enough to allow a dental implant to be the treatment of choice for all edentulous spaces in the anterior region.
The purpose of this article is to demonstrate that there are some esthetic limitations to dental implant treatment. It is aimed at practitioners with no experience with implant treatment. The criteria for wise case selection will be described so that esthetic excellence can be predictably achieved in general practice.
The following checklist of nine issues will be discussed. The checklist provides a treatment-planning tool to determine if a patient is likely to have an esthetically successful outcome:
Patients' desires are often overlooked in guides to treatment planning, yet they may be the most important criterion assessed by the dentist. An experienced practitioner will be better able to judge a patient's esthetic demands, but in any case a clear understanding of the patient's wishes must be established before any treatment recommendations are made. It is possible to satisfy some demanding patients, but significant cooperation is required of them. It is critical that the patient be involved and educated as to the risks, esthetic or otherwise, that may be inherent in the treatment. The patient will be expected to maintain rigorous dental hygiene and deal with various provisional restorations as treatment progresses. For this reason, an emphasis on the team approach is recommended. The patient should become an integral member of the treatment team along with the laboratory technician, hygienist, and dentists.13,14 Pretreatment intraoral photographs and carefully selected patient-education videos can help bring the patient's level of understanding up to that required for an esthetic case.15 For a practitioner's first anterior implant case, it is recommended that he or she choose a cooperative patient with realistic expectations.
After initial assessment of patient expectations, the evaluation of the smile line or gingival display will provide the best indicator as to the esthetic risk of the case. Excessive gingival display may be due to a number of factors, including vertical maxillary excess, short clinical crowns, and hypermobility of the upper lip.16 Whatever the underlying etiology, it is important to evaluate the patient's ability to display gingiva.17,18 Being asked to smile can result in a forced or half smile and may be misleading. It is recommended that the patient be asked to sneer or lift his or her upper lip as high as possible so the dentist can assess the situation. If a "gummy" smile is presented, the patient should be fully informed of the difficulties ahead. Additional periodontal procedures such as crown lengthening of remaining maxillary dentition may be considered.19 If the patient is unable to display gingival tissue, it is still important to discuss the risks, but it is also possible to reassure the patient that any gingival esthetic compromise will be hidden from view. The single most important factor for esthetic success in anterior implants is the smile line. It is highly recommended that the first few patients treated in a practice have a low lip line.
The morphology of gingival tissue has been discussed extensively in the periodontal literature. It is relevant to esthetic success with anterior implants since gingival recession has been identified as a significant complication in these cases.20 The forms of
periodontium can be broadly divided into two distinct "biotypes," which have been correlated to specific tooth forms.21 Thin, highly scalloped gingival tissues are associated with long, narrow, and tapered tooth forms. The second important biotype is the thick, flat, more fibrous form associated with a shorter, wider, and squarer tooth shape. The two tissue types are associated with different responses to inflammatory stimuli. The thin, highly scalloped type tends to respond with marginal recession and loss of papillary height, while the thick, fibrous type tends to develop a chronic inflammatory response that may result in periodontal pocketing.22 An ideal first implant patient would have an abundance of thick, flat, fibrous gingival tissue and therefore be more resistant to gingival recession around the restoration. This biotype also allows for the use of metal abutments with less chance of show-through at the gingival margin. This gingival form is also associated with a favorable square tooth form.
The existence of papillae filling the interdental spaces is a key indicator for future success. If the remaining dentition exhibits "black triangles" due to lack of complete fill of the spaces, then the risk of similar incomplete fill around the implant restoration is high. "Black triangles" may be pre-existing for a number of reasons, including gingival recession, highly tapered triangular tooth form, and previous periodontal surgery. The problem is difficult to resolve, and the patient should be educated as to the esthetic risks involved. Attempts have been made to classify loss of papillae and provide prognostic indicators.23 Surgical techniques aimed at regenerating lost papillae have been developed.24,25 Such regeneration remains challenging, and it may be unwise for a general dentist who is new to implants to treatment plan a first case anticipating the need for additional periodontal plastic procedures.
The position of the osseous crest is a critical indicator for potential loss of papillae after a surgical intervention such as extraction or implant placement.26 The greater the distance from the free gingival margin to the osseous crest, the greater the esthetic risk. A sounding depth of greater than 3 mm at the midfacial aspect or 4 mm at the interproximal position would indicate an esthetic risk.27 An ideal patient would therefore have excellent periodontal health and a high, flat bone profile.
Complete papillary fill of the interdental space after implant restoration is also closely related to tooth form, particularly the position and shape of the contact areas.
It has been determined that if the apical limit of the contact area is 5 mm or less from the osseous crest, then a papilla will be present almost 100 percent of the time in the
Figure 2. The triangular crown form is associated with thin, highly scalloped gingival tissues.
Figure 4. The broader, squarer tooth form is associated with thicker, flatter gingival
tissue.
Figure 1. The tapered crown form results in a short, incisally positioned contact area. A
small interdental space is visible in this natural dentition.
Figure 3. Shorter, broader tooth forms have longer contact areas and better prognosis
for fill of the interdental space.
Figure 6. Example of a patient with excellent bone height and favorable tooth form, note
long contact areas.
Figure 5. Ideal vertical placement of implant 3 mm apical to the cement oenamel junction of adjacent teeth allows for appropriate emergence of crown form (Nobel Biocare implant with a custom abutment).
natural dentition. An additional 1 mm distance drops the likelihood of a papilla being present to only 56 percent.28 While the position of the osseous crest may be difficult to adjust, the position of the contact areas may be changed by the restorative dentist. A careful evaluation of the patient's natural tooth morphology should be made. Long, narrow tapered teeth tend to have short incisally positioned contact areas (Figure 1) likely to be further from the osseous crest and therefore likely to have incomplete fill of the interdental space. The triangular shape (Figure 2) is also associated with thinner highly scalloped gingival tissue that tends to recede. More predictable anterior esthetics will be gained with patients who have broader tooth forms and longer, more cervically positioned contact areas (Figures 3 and 4). Pretreatment photographs are an essential tool for evaluation of tooth shape and educating the patient as to potential risks.
Crown shape is related to root form. Ironically, unfavorable clinical crowns with a triangular morphology taper into a narrow neck and narrow, tapered root form with more interdental bone. This would be a favorable variable providing for more bone between the titanium implant and the adjacent natural roots. This makes placement easier and reduces the risk of root proximity issues. It is generally believed that at least 1.5 mm of healthy bone should exist between the dental implant and the adjacent root surface. Recent work on treatment-planning criteria for multiple implant restorations has suggested that at least 3 mm should separate neighboring implants to reduce interimplant crestal bone loss and hence preserve vital osseous support for the interimplant papillae.29
Adjacent tooth morphology has an additional effect on treatment planning a single dental implant. The length of the adjacent clinical crowns will have biomechanical consequences for the implant restoration regardless of tooth shape. Neighboring long clinical crowns must be replicated in the final restoration and may result in a long lever arm acting on the dental implant itself. Unless excellent bone height is available to facilitate the placement of a long implant, an unfavorable crown-to-implant ratio will result for most implant systems available.
In relation to adjacent tooth morphology, the ideal implant patient would have short, wide clinical crowns with long contact areas and existing papillae.
Occlusal forces act obliquely on anterior teeth. Likewise, an anterior implant restoration will be loaded nonaxially. Longer implants resist nonaxial loading better and have been associated with higher success rates. Implants of 11 mm or longer have proven to be successful in the anterior maxilla.30 If the replacement being proposed is for a single tooth only, there is often adequate remaining bone height to facilitate fixture placement.
However, the osseous crest may be positioned apical to ideal. Ideal placement of a dental implant will result in the top of the fixture being placed 2-4 mm apical to the cemento-enamel junction of the adjacent teeth (Figure 5). The exact ideal distance will be modified by the diameter of the chosen implant, the desired emergence profile of the final crown, and the tissue biotype. If the top of the implant closely replicates the diameter of the missing tooth, the placement will be more coronal. If the top of the implant is narrower, then placement will be deeper to facilitate harmonious broadening of the crown form as it emerges from the tissue. Implant placement in a patient with thin, highly scalloped tissue would also be deeper to accommodate the tendency to recede and to reduce the risk of metal show-through.
Available bone height can be evaluated with periapical radiographs and clinical examination. The ideal patient would have adequate height to house a long implant (13 mm or more) with the crest of the residual ridge 2 mm below the cementoenamel junction of the adjacent teeth (Figure 6).
Successful placement of dental implants depends on adequate osseous housing in all dimensions. At least 1.5 mm of healthy bone is required between the implant and neighboring root surfaces and the "standard" implant from most manufacturers approximates 4 mm in diameter. Therefore the minimum mesiodistal space that can accommodate an implant between two teeth is 7 mm. Replacement of a central incisor or cuspid would not usually present a problem in this dimension, but loss of a small lateral incisor could present risk. In such a case, a narrower implant may be considered or orthodontic correction carried out.
The implant must also be fully encased in bone in the labiolingual dimension. Again, a minimum of 7 mm is required for a standard diameter implant. It is this requirement that presents the most common complication of treatment planning for the anterior maxilla. The labial plate of cortical bone is often missing and remodeled before implant treatment planning begins. This may be due to previous periodontal or periapical infection, traumatic loss, or loss during extraction. Even if an atraumatic extraction technique is employed, the labial plate will inevitably remodel and become positioned lingually within three to six months. A distinct labial concavity will be evident when the site is viewed from the occlusal aspect (Figures 7 and 8).
A significant labial defect that would result in the facial aspect of the implant being located entirely outside the osseous structures should be considered for hard tissue augmentation prior to implant placement. A less-significant defect may be accommodated by slightly deeper and more lingual placement of the fixture to allow for good osseous contact while maintaining the proper emergence profile (Figure 9).
Figure 7. Occlusal view of poten-tial implant site showing significant labial concavity. Hard tissue onlay grafting will idealize the site prior to implant placement.
Figure 8. The same patient as Figure 6. Excellent ridge width in both edentulous
lateral incisor sites.
Figure 9. Graphic illustration of placement lingually and apically from ideal due to loss
of labial cortex. This technique can be used to avoid grafting but should be employed
with caution since significant deviation from ideal position can result in unfavorable
cantilevers and maintenance problems (Illustration by Annette Kramer).
Figure 10. CT scans can significantly increase accuracy in determining available bone for
fixture placement (Image made with GE Lightspeed Plus, Advanced Imaging Center,
Sacramento, Calif.).
Figure 12. Morphology of provisional is accurately duplicated in final restoration.
Figure 11. Ideal placement and provisionalization of implant #5 site results in excellent
emergence profile.
Figure 13. Final restoration in place.
Figure 14. Key anatomic features of an ideal anterior implant patient: low smile line; abundance of attached keratinized tissue (thick, flat biotype); papillae preserved after extraction; wide, square-shaped teeth with long contact areas; and excellent bone height and width (Illustration by Annette Kramer).
Assessment of available bone in the mesiodistal and buccolingual dimensions can be achieved with a thorough clinical examination, or measuring directly from study casts. Anesthesia and "sounding" of the osseous structures is also a useful technique. The most accurate diagnostic aid is the CT scan (Figure 10). Unlike Panorex films, where measurements have to be corrected for varying magnification, the CT film can be measured directly and is accurate to within 0.1 mm. Dental CT scans have become economic (as low as $275 to $350 per arch). They should be considered if there is a question as to whether bone augmentation will be required.
After thorough treatment planning and ideal fixture placement, there is still opportunity for esthetic excellence or mediocrity in the restoration phase. Several months of provisionalization allows for maturation of the gingival tissues to an appropriate (noncylindrical) emergence profile. The tooth form generated through excellent provisionalization must be carried through to the final restoration so that crown and papilla form is maintained (Figures 11 through 13).
Restoring dental implants in the esthetic zone can be fun if wise choices are made. If the factors discussed above are carefully considered, patients who present significant esthetic risks will be screened out and patients with predictably good prognoses will be taken on. While much emphasis has been placed on the anatomic features of the ideal first patient (Figure 14) possibly more important is the patient's desire to cooperate with the team and have realistic expectations. A thorough understanding of the esthetic limitations of dental implants by all members of the team will result in a rewarding and satisfying experience.
Authors
Belinda L. Gregory-Head, BDS, MS, is an associate professor and director of dental implants at the University of the Pacific School of Dentistry.
Alex McDonald, PhD, DDS, is an associate professor and surgical coordinator at the Implant Clinic at UOP School of Dentistry.
Eugene LaBarre, DMD, MS, is an associate professor and chair of removable prosthodontics at UOP.
Legends
Figure 1. The tapered crown form results in a short, incisally positioned contact area. A small interdental space is visible in this natural dentition.
Figure 2. The triangular crown form is associated with thin, highly scalloped gingival tissues.
Figure 3. Shorter, broader tooth forms have longer contact areas and better prognosis for fill of the interdental space
Figure 4. The broader, squarer tooth form is associated with thicker, flatter gingival tissue.
Figure 5. Ideal vertical placement of implant 3 mm apical to the cementoenamel junction of adjacent teeth allows for appropriate emergence of crown form (Nobel Biocare implant with a custom abutment).
Figure 6. Example of a patient with excellent bone height and favorable tooth form, note long contact areas.
Figure 7. Occlusal view of potential implant site showing significant labial concavity. Hard tissue onlay grafting will idealize the site prior to implant placement.
Figure 8. The same patient as Figure 6. Excellent ridge width in both edentulous lateral incisor sites.
Figure 9. Graphic illustration of placement lingually and apically from ideal due to loss of labial cortex. This technique can be used to avoid grafting but should be employed with caution since significant deviation from ideal position can result in unfavorable cantilevers and maintenance problems (Illustration by Annette Kramer).
Figure 10. CT scans can significantly increase accuracy in determining available bone for fixture placement (Image made with GE Lightspeed Plus, Advanced Imaging Center, Sacramento, Calif.).
Figure 11. Ideal placement and provisionalization of implant #5 site results in excellent emergence profile.
Figure 12. Morphology of provisional is accurately duplicated in final restoration.
Figure 13. Final restoration in place.
Figure 14. Key anatomic features of an ideal anterior implant patient: low smile line; abundance of attached keratinized tissue (thick, flat biotype); papillae preserved after extraction; wide, square-shaped teeth with long contact areas; and excellent bone height and width (Illustration by Annette Kramer).
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Copyright 2001 Journal of the California Dental Association. Vol. 29, No. 11, Nov. 2001
Reprinted with permission.
Dental Implant
By Gordon L. Douglass, DDS, and Robert L. Merin, DDS, MS
Abstract: Numerous clinical studies have shown that dental implants can be placed immediately in extraction sockets with success when sites are carefully selected. Dental implants have been placed at the time of extraction with a variety of techniques. All the techniques report survival rates of 94 percent to 100 percent over a varied healing period of three months to approximately seven years. This article will review clinical criteria for determining patient selection for immediate implants and the advantages and disadvantages of immediate implant placement.
During the past 10 years, numerous clinical studies have shown that dental implants can be placed immediately in extraction sockets with success when sites are carefully selected. Dental implants have been placed at the time of extraction with a variety of techniques including without augmentation, with bone grafting, with bone grafting and a barrier membrane, and with and without primary closure. The techniques report survival rates of 94 percent to 100 percent over a varied healing period of three months to approximately seven years.1-7 Investigators have reported high success rates with all type of implants, including screw, cylinder, Hydroxylapatite-coated, tapered, and single-stage.
This article will review the important clinical criteria for determining patient selection for immediate implants and the advantages and disadvantages of immediate implant placement. It will also discuss the clinical steps for the placement of dental implants in extraction sockets. The single-tooth implant restoration has been the most common immediate implant application, but immediate implants have also been successfully utilized in full-arch restorations.8 Single-rooted teeth, predominately incisors and premolars, have been the most frequent sites for
