History

Implant Dentistry and the Concept of Osseointegration: A Historical Perspective

Richard M. Sullivan, DDS

Copyright 2001 Journal of the California Dental Association.

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

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.

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).

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).

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.

U.S. Developments After the Toronto Conference

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.).

A Continuing Evolution

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:

* The fully edentulous lower jaw (Figures 9 through 15);

* The fully edentulous upper jaw;

* The short-span edentulous segment; and

* The missing single tooth.

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).

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.

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).

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.

Current and Future Perspectives

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.

Author

Richard M. Sullivan, DDS, is the clinical director of Nobel Biocare USA, Inc.

References

1. Ring ME, A thousand years of dental implants: a definitive history -- Part 1. Compendium 16(10):1060-9, 1995.

2. American Academy of Implant Dentistry (http://www.aaid-implant.org).

3. Ring ME, A thousand years of dental implants: a definitive history -- Part 2. Compendium 16(11):1132-42, 1995.

4. Schnitman PA, Shulman LB, Dental implants: benefits and risks. Proceedings of an NIH-Harvard Consensus Development Conference, U.S. Department of Health and Human Services, December 1980, Publication No. 81-1531.

5. Laney WR, In recognition of an implant pioneer: Professor Dr. André Schroeder. Int J Oral Maxillofac Impl 8(2)135-6, 1993.

6. Schulte W, Heimke G, The Tübingen immediate implant. Quintessence 27(6):17-23, 1976.

7. Williams E, A Matter of Balance. AB Akademiförlaget, Göteborg, Sweden.

Table 1. Implant Systems with ADA Acceptance

Manufacturer Implant System

Astra Tech, Inc. Astra Tech Implants

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

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.