A conceptual framework implant therapy
Albert D. Guckes, DDS, MSD,” Mark S. Scurria, DDS,b and Daniel A. Shugars, DDS, PhD, MPHC School of Dentistry, University of North Carolina, Chapel Hill, N. C. The use of implants has expanded so rapidly that its effectiveness for many clinical situations has not been firmly established. Dentists are responsible for making appropriate therapeutic recommendations for the management of partial and complete edentulism. These decisions require an understanding of the consequences or outcomes of treatment approaches. Outcome measures to evaluate the benefits of alternative therapies include longevity as well as physiologic, psychologic, and economic impacts. Future research should include outcome measures beyond implant prosthesis survival to more fully assess the practical impact of dental implants on the patient’s oral health and to determine the most cost-effective approaches for managing completely and partially edentulous patients. (J PROSTHET DENT 1996;75:633-9.)
reatment with titanium endosseous root form implants has moved to the forefront ofprosthetic dentistry. The seminal work of Branemark et al.le4 demonstrated that when surgical and prosthetic protocols are carefully followed, titanium endosseous root form implants will predictably integrate with the hard and soft tissues of the anterior mandible and support a fixed retrievable dental prosthesis for many years. Subsequently, implants have been used in a wide array of conditions, including restoring partially edentulous arches, single missing teeth, and intraoral and extraoral maxillofacial prosthetic applications.5-7 Implant design modifications and innovative diagnostic and surgical techniques have been developed to address challenges presented by minimal bone volume and the esthetic demands of implants placed in anterior regions of the maxillary arch. 8-1o Clinical reports describe the use of implants in preadolescent and adolescent children.11,r2 These innovations and the commercial promotion of various implant materials and designs have resulted in the clinical use of oral implants far beyond Branemark’s originally reported protocols regarding implant design, materials, and surgical technique. Dentists are responsible for helping patients make appropriate therapeutic decisions for the management of partial and complete edentulism. Implant use has increased so quickly that questions concerning the efficacy and especially the effectiveness of oral endosseous implants for many clinical applications lack scientific trials. Appropriate decisions require sound understanding of the consequences of outcomes of treatment. Dentists and patients need to know whether a treatment is safe and how well it “works,” both in the ideal and real world situations.
Presented at the Annual meeting of the Academy of Prosthodontics, Tucson, Ariz., 1995. aAssociate Professor and Director of Graduate Prosthodontics. bAssistant Professor, Department of Prosthodontics. cProfessor, Department of Operative Dentistry.
The purpose of this article is to provide a framework to examine the issues central to making determinations about the appropriate use of oral implants. To accomplish this, a discussion of four major concepts is required: safety, efficacy, effectiveness, and outcomes. Figure 1 is a concept map used to graphically demonstrate the interrelationships between each of these.i3 This article focuses on how each of these concepts may be considered to make appropriate therapeutic choices for the rehabilitation of the partially and completely edentulous patient. Examples to illustrate the concepts, explain the framework, and highlight areas needing further work are provided.
SAFETY Before the efficacy and effectiveness of a medical treatment can be determined, the treatment must be demonstrated to be safe. For example, the safety and biocompatibility of titanium and surgical alloy endosseous cylinders and transosteal dental implants have been demonstrated in laboratory studies and controlled prospective clinical trials.ls r4-16 One significant finding that led to the relatively rapid acceptance of the endosseous titanium cylinders was that failure of a titanium cylinder to osseointegrate was usually a biologically benign event that caused little irreversible damage to a patient’s hard and soft tissues. Currently, the United States Federal Food and Drug Administration (FDA) considers many endosseous implants as preamendment class III medical devices. Consequently only a 5 10(K) Premarket Notification submission to the FDA is necessary. This requires a new device to be “substantially equivalent to one or more predicate devices legally marketed in the United States.“17 However, this may change as the FDA soon may call for Premarket Approval applications for endosseous implants, which will require well-designed clinical trials that demonstrate safety and efficacy.
Partial or Complete
and Should have demonstrated4 The Ilkely benefit of a treatment
The probablllty d benellt to individuals il a defined population from a medical technology applied for a given medical problem under Ideal conClltlorIS of use .
Should provide e 1 Outcomes Assessment for Each Strategy
map for management
The term efficacy as applied to medical care was defined originally as the net of benefits and risks of a medical intervention.ls Currently, efficacy is more precisely defined as the probability of benefit to individuals in a defined population from a medical technology applied for a given medical problem under ideal conditions of use.lg In contrast, effectiveness is the likely benefit of treatment when provided under ordinary conditions by the average clinician for the typical patient.20 For oral endosseous implants, the efficacy and effectiveness of implants should measure the extent to which implants help to achieve the goals of prosthetic dentistry: preservation of the remaining oral tissues and the restoration and maintenance of a functional and esthetic occlusion consistent with the patient’s needs and expectations.
Outcome measures used to assess the benefit of alternative therapies include factors related to longevity or survival and physiologic, psychologic, and economic impacts.21 Table I highlights outcome measures specific to
implant therapy. Current research has focused on longevity and survival issues with wide variation reported between efficacy and effectiveness. Some attention has been paid to the physiologic, psychologic, and economic impacts for completely edentulous therapies, yet little research has documented these impacts for partially edentulous implant therapies and, most unsettling, for longused nonimplant therapies.
Efficacy may be assessed by randomized controlled clinical trials and nonexperimental prospective clinical trials. Prospective studies by experienced clinicians on groups of patients with strict inclusion or exclusion criteria usually evaluate implants and prostheses in terms of longevity. Numerous reports established that endosseous titanium cylindrical implants or transosteal implants can be successfully placed in a stable functional relationship with investing bone and soft tissue to provide support for a fixed mandibular prosthesis for several years. l-32 15, 6 22, 23 Later efficacy trials have reported similar implant and prosthesis survival rates for partially edentulous patients. These
reports document a survival rate greater than 90% for implants placed throughout the oral cavity, although for shorter follow-up periods. 24-27 Some efficacy trials reported lower survival rates associated with maxillary implant placement and overdenture prostheses.1-3> 25, 28 Effectiveness is assessed most often with retrospective studies and community-based trials. More often, patient selection criteria are less stringent and the clinician’s level of experience is more variable. Retrospective studies may be conducted by experienced clinicians from academic health centers or by less experienced clinicians in various clinical settings. The greater variability of patient selection criteria and practitioner experience may represent more “real world” results for various therapies. For example, such studies have reported lower implant and prostheses longevity for partially edentulous arches and overdentures, especially when associated with the maxillary arch.2g-34 These studies point out that failures must be anticipated, especially when implant therapy is used beyond the original protocol.
Longevity/survival Implant fixture and prosthesis survival Treatment related morbidity/mortality Physiologic impact Masticatory efficiency Bite force Maintenance of bone Effect of treatment on dietinutrition Psychologic impact Orofacial body image Perceived quality of life Perceived satisfaction with prosthesis Self-esteem and interpersonal relations Economic impact Direct costs of treatment Maintenance costs Indirect costs *Adapted from Bader JD, Shugars DA. Variation, treatment outcomes, practice guidelines in dental practice. J Dent Educ 1995;59:61-95.
The physiologic impact of treatment of the edentulous mandible with implant-assisted oral prostheses has been studied primarily with nonexperimental prospective longitudinal clinical trials. Most studies did not control variables such as length of time edentulous, patient age, patient sex, quality of the bone, bone volume, systemic hormonal factors, and occlusal factors. These factors may not be as critical for the anterior mandible, given the high longevity rates that were reported.
Bone loss Lundquist et a1.35 followed up bone resorption around implants in the anterior mandible for 3 to 6 years in 46 edentulous patients; they found 0.40 to 0.45 mm resorption during the first year and only 0.06 to 0.08 mm per year from years 3 to 6. The findings of similar values25a 26, 31 suggest that bone resorption in the anterior mandible of patients with implant assisted complete dentures can be expected to be significantly less than in a comparable population of edentulous patients with nonimplant assisted complete dentures.36 However, factors that may affect bone resorption such as length of time of edentulousness, quality of supporting bone, occlusal habits, and age were not well controlled. Ahlqvist et. al. 28 found that marginal bone loss around implants in both jaws was greater in individuals who had less bone resorption at the time ofimplant placement. They also found that men had more marginal bone loss in the maxillae than women. A study conducted by Jacobs et al.37 found that wearing implant assisted mandibular fured complete dentures or an implant assisted overdentures resulted in less bone resorption in the opposing maxillary ridge than wearing a
nonimplant assisted mandibular complete denture.37 The authors attribute the greater resorption to the instability of the mandibular denture and cautioned that proper maintenance of the occlusion is important.
Mastication The ability of completely or partially edentulous patients to masticate food has been reported to be related to biting force, mandibular bone resorption, and prostheses quality; it may also affect systemic health.38-41 Therefore it is important to ascertain whether management of complete or partially edentulous conditions with implant assisted prostheses affects masticatory efficiency. Efficacy studies have consistently demonstrated a positive effect of implant assisted complete denture prostheses on objective measures of masticatory function.42-44 However, the desirability of a control group to determine the extent of that effect compared with treatment with new complete dentures is emphasized by the finding od Gunne and Wa1145 that 28 of 43 patients felt they chewed better simply after receiving new complete dentures. Objective measures of mastication also increased in these patients. However, Lundquist et al. 46 did not find a significant improvement in bite force and chewing efficiency after providing new dentures or optimizing the existing dentures of patients awaiting treatment with implant assisted complete dentures. Conflicting results might be reconciled if satisfaction with existing dentures and volume of remaining bone available for denture support and other variables were controlled. Despite the improvements in biting force and masticatory efficiency provided by implant assisted complete dentures, a significant impact on diet has not been demonstrated.47, 48
An analysis of the research results related to the physiologic impact of implant assisted mandib~ar complex dentures does not lead to a conclusion that all partially or completely edentulous patients demonstrate or perceive an improvement in oral function after treatment with implant assisted mandibular partial or complete dentures. However, the physiologic impact of decreased residual alveolar ridge resorption must be considered a substantial benefit.
The psychologic impact of treatment with implant assisted prostheses has been evaluated both in nonexperimental prospective longitudinal trials, retrospective longitudinal studies, and case reports.4gu54 The importance of psychological factors was demonstrated in a study by Carlson and Lindquist,55 who found that patients who already had an implant assisted mandibular denture perceived an improvement in masticatory function when provided with an implant assisted maxillary complete denture, even though functional tests did not demonstrate an improvement. An almost universally reported finding is that completely edentulous persons treated with implant assisted dentures express satisfaction with treatment results.53-58 However, studies often include only persons who are evaluated or referred for treatment with dental implants. Patients seeking dental implants may differ with respect to satisfaction with conven~on~ removable prostheses from those who do not seek treatment.53, 57,58 Therefore the psychologic impact of treatment with implant assisted dentures may differ among patients, depending on their adaptation to conventional dentures. Implant dentures may not be perceived as highly beneficial or worth the trouble and financial expense to all patients.2* Too few randomized clinical trials have assessed satisfaction between alternate therapies. In a comparative trial of patients with Kennedy class I and class II partially edentulous mandibular arches, Kapur et a1.58randomized and treated patients with either blade implant-suppo~d fixed partial dentures or nonimplant removable partial dentures. They reported that improvements in mastication as measured by standardized tests were essentially the same for both groups of patients after 60 months.“” Some differences in patient satisfaction regarding quality of life issues such as improvement in social life, eating enjoyment, and food particles were in favor of the implant treatment.5g The authors did not feel the differences were large enough to generally favor treatment with implant assisted removable partial dentures over treatment with nonimplant assisted removable partial dentures. In a study of 52 completely edentulous patients randomized to receive either new conventional dentures or a new maxillary denture and an implant assisted fixed mandibular prostheses, Guckes et al. 6ofound significant increases
in satisfaction with the mandibular prostheses and increased orofacial body image scores in both groups. The increase in satisfaction with the mandibular prostheses was statistically significantly greater for patients receiving an implant denture. However the differences may not be clinically significant. Increases in orofacial body image were similar for both group~.~*
The goal of an economic analysis of a medical treatment is to answer the question “Is the treatment a better use of financial resources than alternative [email protected]
A useful analysis must be based on “real world” effectiveness data. Analysis of the economic aspects of various dental treatments can be complex and reach different conclusions depending on the purpose of the analysis. A third party payer may solely be interested in the cost of alternative treatments over a patient’s lifetime and place little value on quality of life factors. In contrast, some patients may only be interested in quality of life regardless of financial costs. Often critical data necessary for an economic analysis is not available. For example, an analysis comparing the cost of three alte~ative treatments for a single missing tooththe single tooth implant, the resin retained fixed partial denture, and the porcelain-fused-to metal f?ed partial denture-requires valid survival data for the alternative treatments in all locations in the oral cavity.62 This information is not available. Because effectiveness data is presently scarce for the three alternative treatment, an economic analysis would be speculative. Little information has been presented regarding the cost/utility ratio of treatment with dental implantsels 62 For whom is the increase in quality of life associated with easier masti~tion of some foods, increased sense of security in social situations, increased comfort, and the biologic benefit of maintenance of alveolar bone, worth the increased cost of initial treatment, the increased time reqnired for oral hygiene, and perhaps an increased cost of maintenance over the lifetime of the prostheses? Comp~cations with implant assisted prostheses occur, even with experienced treatment teams.32, 63-65Implants may be placed in positions that require expending extra resources to provide fixed restorations. Implants may be placed in such a way to threaten the health of adjacent teeth. Implants, screws, and frameworks fracture and implants can fail after the prostheses has been in function for months or even years. Significant postsurgical complications can occur.66 There are currently no readily available data from the practice community at large about the costs of failure or complications.
The relative value an individual places on oral health, function, and esthetics varies greatly. Ultimately, a cost/
utility analysis must be considered for a specific patient and his or her motivations, needs, and financial resources. Significant factors to be considered include age, satisfaction with conventions removable prostheses, bone volume available for prosthesis support, prognosis concerning alveolar hone resorption, condition of remaining teeth, oral habits, diet, and occupation. In the final analysis, the appropriate therapeutic choice for a given patient requires a determination of the likelihood of a desirable set of outcomes, given the patient’s condition and risk factors. Despite the many unknowns concerning the effectiveness of dental implants, if one subscribes to Devan’s philosophy, 67 “Our objective should be the perpetual preservation of what remains rather than the meticulous restoration of what is missing,” then the appropriate use of implants becomes clearer, at least in the situations of the partially and completely edentulous patient. The only predictable and scientifically supportable management strategy in prosthodontics to preserve bone may be through treatment with implant-supported prostheses. ~though the extent or the mechanism of the prese~ation is not completely clear, it is indisputable that bone is preserved in the edentulous anterior mandi.ble. Some reports have even suggested that some implant supported prostheses may stimulate an increase in mandibular bone volume.68afiYThese reports suggest that the ability of an implant to partially restore the complexity of the tooth-bone interface and thereby transfer the stresses associated with oral function directly to the bone may allow an adaptive response by the bone. However, more research is required to provide insight to this phenomenon.70-72Therefore, implants may offer the best presently available biologic solution to replacing the missing dentition in the completely edentulous and perhaps the partially edentulous mandible.
In 1992, Zarb and Lewis 73cautioned against assuming that implant success data in the anterior mandible can be extrapolated to other locations in the oral cavity. Perhaps caution should also be exercised against the assumption that success data achieved in academic and institutions settings can be applied to the co~u~ty practice or vice versa, or that outcome data concerning psychologic and physiologic impacts of using implant assisted prostheses for treating the completely edentulous mandible will be similar for other locations and edentulous situations found in the oral cavity. A problem with most of the implant studies reporting physiologic and psychologic outcomes of treatment with implant assisted prostheses is a lack of randomization to either a group managed with implant assisted prostheses or a control group managed with nonimplant assisted prostheses. ~onexpe~ment~ prospe~ive lon~tud~a~ clinical trials can provide valid information regarding the
safety and physiologic effects of treatment, but usually do not control for patient expectations or other psychologic factors. Consequently results often do not allow a valid comparison to the efficacy of other treatment modalities. A significant need exists for implant assisted complete and partial denture outcome data from community-based dental practices. Keller74 wrote “. . . efficacy research is best carried out in large academic settings where the laboratory and technical skills exist. Effectiveness and appropriateness are best studied where most of the medicine is practiced: in the community.” The comments are equally valid if applied to dentistry. The effectiveness and appropriateness of the use of dental implants in the dental practice community outside of academic and gove~ment settings has not been addressed. The extent and type of training necessary to make the necessary treatment decisions and to carry out the necessary procedures to manage the completely and partially edentulous patient with implant assisted restorations have not been determined. The recently released Institute of medicine (IOliQ report on the future of dental education, “Dental Education at the Crossroads,” makes numerous recommendations in support of collaborative outcomes research between dental educators and public and private organizations.75 Specifically, more research is required to define patient factors that influence the appropriateness of implant use for the management of the partially or totally edentulous patient. Information is particularly essential concerning the costeffectiveness of treatment that uses dental implants in all areas ofthe mouth. In addition, the long-term effectiveness of different implant materials and designs, the maintenance costs of implant supported restorations, the appropriateness of the use of implants in preadolescents and adolescents, and the long-term psychologic and biologic benefits of implant assisted restorations need to be determined. Recommendation 6 from the IO&l study specifically calls for individual academic clinics and faculty practices to evaluate practice patterns and the outcomes of care. Reports from these centers combined with reports from larger data sets such as the Veterans AfYairs Dental Implant Registry could provide a wealth of effectiveness data. Finally, community-based studies are essential to evaluate the practical impact of dental implants on the patient’s oral health and to determine the cost-effectiveness of various treatment strategies for the partially or completely edentulous patient. These data are crucial to the long-overdue work ofthe profession and specifically the prosthodontic specialty for the development of dental implant practice guidelinesT6
CONCLUSIONS Of the prostl~odontic treatment technologies now available for the management of the completely or partially
edentulous arch, a prosthesis supported and/or retained by endosseous dental implants is most likely to be physiologically and psychologically incorporated into the ora cavity. However, despite the many advances and published studies concerning dental implants since the introduction of osseointegration to North America in 1982, most of the information available is limited to the efficacy of dental implants. Rigorous and long-term follow-up of implants placed as part of academic and government studies and co~unity-based clinical studies are necessary to obtain implant prostheses effectiveness data. The effectiveness data can then serve to focus questions to be studied in more expansive randomized controlled trials. The framework outlined should guide future research toward study designs with broader outcome measures that will markedly enhance the profession’s ability to make appropriate therapeutic decisions for individual patients.
7. 8. 9. 10. 11.
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