The development of modern implant dentistry has been extremely rapid.The admirable clinical achievements based on osseointegrated implants have occurred within slightly more than 30 years. It was only 20 years ago that the osseointegration concept was first introduced in North America. The rapid changes of implant dentistry make it difficult to speculate on future directions of implant dentistry.
At a conference in Toronto in 1982, Dr Per-Ingvar Brånemark presented osseointegration and its experimental and clinical background based on more than 2 decades of research and clinical experience.1 (He placed the first osseointegrated implants in a human patient in 1965!) This started a remarkable worldwide evolution of treatments with osseointegrated implants that has dramatically changed many areas of clinical dentistry and revolutionized prosthodontic therapy for completely and partially edentulous patients. The enormous growth of interest in dental implants is evident in numerous books and journal articles, as well as in a variety of conferences, courses, and symposia. A search in Medline/PubMed in May 2002 listed approximately 6,000 references for “dental implants” and slightly fewer when “prostheses” was added.
During the early period, the Brånemark group considered prosthodontic treatment associated with implants synonymous with fixed implant-supported prostheses. It is well established that this system provides great benefits of oral function and quality of life for edentulous patients with denture problems. However, such treatment is expensive and available only to a small portion of edentulous patients. Less costly alternatives were needed. Therefore, when osseointegrated implants entered the international arena, other prosthodontic alternatives were introduced and tested. Implant-supported or -retained overdentures were described in 1985 in the first textbook on “tissue-integrated implants.”2 In the broadened arsenal of implant-related prosthodontic solutions, implant overdentures have become an important and increasingly common altern a-tive. This treatment modality has been investigated widely during the past few years, and reviews of the growing literature confirm that implant overdentures are a successful prosthetic treatment.3-5 In May 2002, PubMed revealed 660 references for implant overdentures, demonstrating the rapid growth of this section of implant literature.
The relevant literature has been well reviewed in this book, with a focus on mandibular implant overdentures.The main findings can be summarized as follows:
- Treatment with mandibular implant overdentures, in general, is very successful. However, routine maintenance is required to ensure long-term success.
- Implant survival is high and comparable to that for fixed prostheses.
- Patient satisfaction levels are high.
- The treatment procedure is relatively simple, and the prosthodontic treatment time is similar to that for conventional complete dentures.
- The initial treatment costs are low compared to fixed prostheses.
- Various attachment systems can be used with similar success.
Even if there is near consensus regarding most of the above statements according to the literature reviews, controversy persists concerning treatment concepts and indications for mandibular implant overdentures. Some issues are still debated among clinicians, eg, number of implants, anchorage design, immediate loading, maintenance aspects, patient satisfaction, long-term costs of different retention systems, and removable versus fixed prostheses. Efforts at finding evidenced-based answers to these concerns will be important in the future of implant dentistry. Furthermore, new problems certainly will appear. The solutions will be found in continuing research in close collaboration with clinical activity and development.
Trends and Possible Goals for Mandibular Implant Overdentures
Patient Satisfaction and Masticatory Function
At a conference in Toronto in 1998, a critical review of literature on the patient-based outcomes of implant therapy surprised the audience. What every prosthodontist considered evident—the great benefits of implant-supported prostheses—was questioned because most studies had design flaws that threatened their internal validity.6 The reviewer noted that, from a strictly scientific point of view, the studies conducted up to 1998 provided relatively little scientific evidence that implant therapy is of substantially more benefit to edentulous patients than alternative forms of treatment. It was concluded that further research was needed using randomized controlled trial (RCT) designs. Outcome measures need to be more carefully selected so as to reflect patients’ concerns. More recent studies have addressed patient satisfaction and verified that patients with implant overdentures had higher satisfaction scores than complete denture wearers, even in comparison with those who had preprosthetic surgery to enlarge the denture-bearing area.7 In one of the recent studies using patient-based assessments (eg, O ral Health Impact Profile, or OHIP), it was found that patients who chose complete dentures when implant overdentures also were available reported significant improvement after treatment, as did those who received implant treatment. Both groups reported much greater improvement compared to the patients who requested implants but received complete dentures. 8 During the past few years, a series of RCTs have shown higher satisfaction and oral health-related quality of life among patients with implant overdentures than among those with conventional dentures (see chapter 5).
Cross-over studies have been conducted for comparison of fixed ve rsus removable implant-supported prostheses. The removable design was selected (by half of the patients) for ease of cleaning, among other reasons, whereas the fixed prosthesis was chosen because it provided better stability and ability to chew.9 There was no difference in general satisfaction between the fixed and removable treatments, but patients found the fixed prosthesis to be better for chewing harder foods.10 Improvements in bite force and chewing efficiency following implant treatment in edentulous patients has been demonstrated for many years,11 and similar results for mandibular implant overdentures have been presented.12
Number of Implants
The theory that more implants will better support a heavy functional load may be true from a theoretical biomechanical point of view, and it explains the early uncertainty about how many implants to use for supporting or retaining an overdenture. However, numerous clinical prospective studies up to 12 years have proven that two mandibular intraforaminal implants, splinted or unsplinted, retaining an overdenture provide successful treatment for edentulous mandibles.5,13,14
A few studies have compared mandibular overdentures supported by two, three, or four implants. Results indicate that two implants are sufficient, in general, and this seems to be the most common choice today. The recommendations to use more than two implants in special situations5 appear to be based on speculation rather than on results of controlled clinical studies. Such studies would be desirable to provide a better basis for decision making. However, there is consensus that, for the great majority of edentulous patients, two intraforaminal implants are sufficient for a successful mandibular implant overdenture.
The possibility of reducing the number of implants to one has been tested in a 5-year prospective study of 21 elderly patients.15 None of the implants was lost during the follow-up period and “remarkable improvement of oral comfort and function was evidenced with the overdenture treatment.” Similar success was reported in a more recent investigation with fewer patients and a shorter observation period (Figs 14-1a and 14-1b).16 The authors of both studies emphasized the benefit of their method, especially for geriatric patients with severe denture problems, because it is relatively inexpensive and is a surgically and prosthodontically simple way of retaining a complete denture. In spite of these successful results, the method with only one implant does not seem to have become more widely accepted. However, this alternative deserves to be investigated using an RCT that compares the outcome of complete dentures to mandibular overdentures anchored to one implant.