The International Journal of Oral & Maxillofacial Implants, 03/1995

A review of the literature, provided by a MEDLINE search from 1976 through April 1994 and review of selected journals published from April 1994 to November 1994, relative to reconstructive procedures of the mandible and maxilla in which endosseous implants have been placed in grafted bone was conducted. This review revealed that 591 patients received 733 grafts in which 2,315 implants were placed. The types of grafts reported were block, autogenous bone (nonvascularized or vascularized), and particulate with a variety of materials. Results of these grafts are presented with the different implant systems utilized. Wound dehiscence seems to have the most deleterious effect on implant survival rate. Keywords: bone graft, endosseous implant, reconstruction

Clinical studies indicate that loosening or fracture of dental implant prostheses occurs in 5% to 45% of cases during the first year. The nature of loosening or displacement of prosthetic components is complex, since it involves cycling fatigue, oral fluids, and varied chewing patterns and loads. A finite element contact analysis method was used to study the load-transfer mechanism between prosthetic components caused by torque application to the threaded fasteners used for assembly. Screw elongation is achieved while allowing for elastic recovery of the screw to produce a clamping force on the fastened elements. Clamping forces were additive along the axis of the prosthetic components. When the gold retaining screw is fastened into the abutment screw, clamping force on the implant is increased at the expense of decreasing the clamping force at the abutment screw-abutment interface by 50%. Maximum tensile stresses in the screws after preload were less than 55% of the yield stress. Keywords: biomechanics, contact analysis, finite element analysis, implants, prosthetics

In a retrospective study, 150 patients with edentulous maxillae were selected for treatment with Brånemark implants. The patients were arranged into four different groups, based on jaw shape prior to implant placement. After second-stage surgery, they were provided with either fixed prostheses, removable overdentures followed by fixed prostheses after at least 1 year, or overdentures for the whole period. Patients were followed up for 5 years, with implant and prosthesis survival, annual visits, marginal bone loss, and complications recorded. Results of the study indicated that treatment outcome in edentulous maxillae might be predicted by careful presurgical evaluation of jaw shape. Five-year cumulative implant failure rates varied from 7.9% for patients considered to have enough bone to be provided with fixed prostheses immediately after second-stage surgery to 28.8% for those with severely resorbed jaws receiving an overdenture. The corresponding cumulative prosthesis failure rates were 3.0% and 18.9%, respectively. Patients provided with autogenous bone grafts compared favorably to the group presenting severely resorbed jaws and provided with overdentures, but showed a compromised result compared to the group with the least resorption. Failure of implant treatment correlated significantly with bone quality and ratio of 7-mm implants. All groups, except those treated with bone grafts, showed an average marginal bone level of 1.2 mm after 5 years, irrespective of type of prosthesis. The bone-grafted group showed a corresponding mean level of 2.3 mm after 5 years of function. Regarding clinical complications, a different pattern, mainly related to the type of prosthetic construction used, was observed between the groups. The number of visits clearly indicated that severely resorbed jaws provided with overdentures were the most demanding. Keywords: osseointegration, implants, maxilla, jaw shape, grafting, follow-up, overdenture, maintenance

Four clinical centers, using the Brånemark System and with personnel trained in the use of Gore-Tex Augmentation Material (GTAM), participated in a prospective study of 45 patients 18 to 83 years of age. A total of 55 implants were placed with membranes because of local bony defects (fenestration or dehiscence). Dehiscence and fenestration defects were evaluated as one group. The mean initial defect height was 4.7 mm (SD = 3.0). After healing, the remaining defect height was reduced to 1.1 mm (SD = 2.3). The decrease in surface exposure was significant. Complications were primarily attributed to exposure of six membranes during the early healing period. The cumulative survival rate was 84.7% in maxillae and 95.0% in mandibles after 2 years of follow-up. The surgical application of GTAM to produce bone in localized bony defects around oral implants seems to be a predictable method that may reduce the need for extensive augmentation surgery in patients with insufficient jaw bone volume. Keywords: bone regeneration, ePTFE, implants, membranes

Implant-supported provisional restorations serve several valuable functions. In the anterior region, they are beneficial in determining the best restorative design, ultimately allowing for the most appropriate definitive prosthesis. They also provide a template around which soft tissue contours may be evaluated and manipulated. In areas where bone quality is compromised and implant success is suspect, whether it be anteriorly or more likely posteriorly, implant-supported provisional restorations may be used to "test" the osseointegration prior to fabricating and placing the definitive restorations. Keywords: esthetics, progressive integration, progressive loading, provisional loading, provisional restoration

Thirty-nine patients with implant fractures treated by three of the authors have been analyzed as to probable causes. Thirty-five (90%) of the fractures occurred in the posterior region. Thirty (77%) of the prostheses were supported by one or two implants, which were exposed to a combination of cantilever load magnification and bruxism or heavy occlusal forces. It was concluded that prostheses supported by one or two implants and replacing missing posterior teeth are subjected to an increased risk of bending overload. The literature review indicates that the fracture frequency is low in these situations and this study demonstrates that with appropriate treatment planning, such overload situations can essentially be prevented. Keywords: bending overload, bone resorption, implant fracture, mechanical problems, osseointegrated implant

Using the mandibular inferior border of four fox hounds from an extraoral approach, six high-profile Brånemark implants were placed in each animal and bone grafted. Graft materials studied included demineralized freeze-dried allograft with and without irradiation sterilization (3.8 × 104 Gy), corticocancellous iliac autograft, blood clot, and a control. Corticocancellous grafts were studied with and without expanded polytetrafluoroethylene (ePTFE) barriers. The barrier function improved both graft volume incorporated and bone-implant interface contact. The autograft performed better than the allograft. Irradiation of the allograft did not appear to affect graft performance. The barrier functioned to improve graft incorporation for augmentation and interface contact and gives credence to the use of barriers in conjunction with vertical augmentation grafting of jawbone. Keywords: bone-volume preservation, corticocancellous iliac bone autograft, demineralized freeze-dried bone allograft, guided bone graft augmentation, inferior mandible, irradiated allograft, membrane, orthopedic graft fixation, osseointegration content

Maximal occlusal force and oral tactile sensibility were recorded in (1) a group of partially edentulous patients restored with ITI implants supporting fixed prostheses or single crowns and (2) a control group consisting of fully dentate subjects with healthy natural teeth. Maximal occlusal force was measured with a miniature force transducer placed between antagonistic implant/tooth pairs in the test group and antagonistic teeth in the control group. The detection threshold of minimal pressure (ie, passive tactile sensibility) was recorded with dynamometers, and minimal perceived thickness (active tactile sensibility) was assessed using steel foils with a thickness from 100 to 10 µm. Highest maximal occlusal force was measured in fully dentate subjects on second premolars (average 450 N). A significant reduction on the first premolars (300 N) was observed. With fixed prostheses supported by implants, the average value of maximal occlusal force was distinctly lower, about 200 N for first premolars and for molars, and 300 N for second molars. The maximum force was again found on second premolars. The detection threshold of minimal pressure was significantly higher on implants than on natural teeth. The average number of wrong assessments when testing steel foils was 3.2 for antagonistic implant/tooth pairs and 2.6 for natural teeth. The comparison of test sides (with implants) and control sides (without implants) in patients of the test group did not reveal significant differences of measurements. It seems that patterns of oral function depend primarily on the state of dentition, type of prosthodontic restorations, and on psychological aspects, and secondarily on the presence of implants. Keywords: fixed prostheses, implants, occlusal force, oral tactile sensibility, partial edentulousness

A new system (the IL system) for supporting the distal extension of a cantilevered prosthesis is designed from a short implant and a special ball-type attachment. The finite element method was employed to analyze this system and the surrounding bone, as well as a conventional prosthesis, in two dimensions. Effective and maximum stresses in tension and compression were determined. A comparison of these quantities between the IL-supported prosthesis and a conventional prosthesis was carried out. It was observed that use of this system to support the distal extension of a cantilevered prosthesis dramatically lowers the stresses in the bone, cantilever, and implants. Therefore, this system may reduce failures within the implants, prostheses, and surrounding bone. Moreover, employment of a relatively long-span prosthetic extension in the posterior region of the jaw should be possible. This new system is recommended for completely and partially edentulous patients. Keywords: bone, cantilever, dental prosthesis, endosseous implant, finite element analysis, stresses

Seven failed endosseous dental implants that were removed from humans were examined histologically. Results suggest that the hollow-basket portion or the vent should be located as far from the gingiva as possible, and that an adequate healing period is needed for implant placement following tooth extraction. In addition, findings also suggest that the hollow-basket implant is not suitable for a healing socket, that periodic inspection is necessary for two-stage implants to evaluate adaptation of the embedded junction between the abutment and implant in the gingiva, and that there is risk of coating separation from hydroxyapatite-coated implants and possibilities of coating resorption. Keywords: endosseous implant, failed implant, hollow-basket, hydroxyapatite coating, two-stage implant

The outcomes of 153 ITI titanium plasma-sprayed screw implants were studied in 39 patients. Four implants were placed in the edentulous mandible between the mental foramina and used as support for a denture prosthesis. Thirteen implants in six patients had been lost during the follow-up time of 3 to 10 years (mean 5.6 years). The mean annual bone resorption was 0.25 mm (SD 0.29 mm; range 0 to 1.37 mm). Bone loss was smaller in patients with prosthetic loading applied within 7 postoperative days than in those with delayed prosthetic treatment. No evidence of bone loss was seen around 37 (26.4%) implants. The cumulative and overall success rates for titanium plasma-sprayed implants were 80.8% and 91.5%, respectively. The corresponding figures for the patients were 86.8% and 94.9%. Keywords: bone resorption, edentulous mandible, oral implantology