The International Journal of Oral & Maxillofacial Implants, 06/1997

Ideal endosseous implant placement involves a congruent bony housing in close apposition to the implant surface. Clinical situations are encountered, however, in which the entire implant surface cannot be in close apposition to bone. In these instances, bone grafting materials are generally used to regenerate bone around the implant. In this study, a biologically active bone differentiation factor, recombinant human bone morphogenetic protein-2 (rhRMP-2), was used with two different carriers to regenerate bone around implants in standardized critical-sized defects in the canine mandible. Half of the sites had a nonresorbable membrane placed over the defect. Longitudinal standardized radiographs were obtained to assess the amount of bone regeneration on the mesial and distal of the implants after 4 and 12 weeks of healing. Ninety-six implants were placed in 12 foxhounds. Bone fill was determined by linear measurement of bone on the radiographs, and changes in bond density were evaluated by com puter-assisted densitometric image analysis of discrete areas adjacent to the implant. After 4 weeks of healing, nonmembrane sites had significantly greater bone height that membrane-protected sites. Following 12 weeks of healing, sites treated with rhBMP-2 had significantly greater bone formation than untreated sites. Sites treated with rhBMP-2, whetehr with or without a membrane, had less bone fill than sites with rhBMP-2. At 12 weeks, sites with a m embrane resulted in significantly mroe gain in bone density than sites without a membrane. Furthermore, sites treated with a collagen carrier resulted in greater gains in bone density than sites treated with a polylactide/glycolide carrier. The results from this study demonstrate by radiographic evidence that new bone formation in cirtical-sized defects around implants is dependent on time after defect treatment, the type of carrier used, the use of a barrier membrane, and the presence of rhBMP-2. In addition, these findings suggest that rhBMP-2, a bone differentiation factor, can significantly stimulate bone formation around endosseous dental implants.

Between November 1988 and July 1992, a total of 320 ITI screw implants were consecutively placed in 109 patients. The patients were observed in a prospective longitudinal study focusing on implant success and clinical proof. Radiologic and clinical parameters were established at specific time intervals to examine hard and soft tissue reactions. Clinical parameters and the measured bone resorption were analyzed for possible correlation. Seventy-five percent (n = 82) of patients were edentulous, and 16% (n = 17) had distal extensions or extended edentulous spaces. Nine percent (n = 10) of the implants were for single-tooth replacement. During the follow-up period, a total of 10 patients with 29 implants dropped out, and 6 implants were lost as a result of failed osseointegration. The cumulative implant survival rate was 98.1%, and the cumulative implant success rate, using strict criteria for success, was 97.1% after 3 years. The mean bone loss between implant placement and prosthetic restoration was 0.8 mm. For the period between prosthetic treatment and the 3-year examination, a mean annual bone resorption of approximately 0.1 mm was observed. The periodontal parameters indicated a healthy soft tissue response during the time of observation. The statistical correlation analysis showed a definite relationship between th e crevicular fluid volume and bone resorption. The results of this 3-year study indicate that ITI screw implants, with their nonsubmerged healing characteristic, can serve as a reliable foundation for implant-supported restorations.

In this study of six greyhound mandibles, 24 implants were placed into extraction sockets. Eighteen of the implants were connected with abutments and immediately placed into normal function, and the remaining six submerged implants serv ed as controls. At placement, dehiscence areas were created adjacent to 12 of the implants to study bone regeneration in extended membrane-portected defects. Six of the defects were covered with expanded polytetrafluooethylene membranes, and six of the defects were augmented with autologous bone grafts and covered with expanded polytetrafluoroethylene material. The clinical and radiographic evaluation demonstrated that all implants achieved functional osseointegration and no implants were lost. Implant sites where membranes were used to regenerate bone over dehiscence defects demonstrated a high rate of membrane exposure and variable response to treatment. On completion of the study at 16 weeks, histomorphometric analysis demonstrated osseointegration with direct bone-to-implant contact for all implants, although the percentage of contact varied considerably. Histomorphometry indicates that the quality of osseointegration may be less favorable than the clinical and radiographic result would suggest.

Fifty patients with inadequate bone volume for implant placement were treated with mandibular bone grafts from the symphysis or ramus. The choice of donor site was determined by defect morphology and recipient site location. Although the harvest of bone was associated with low morbidity, the ramus donor site resulted in fewer complications. Implants were placed secondarily following a 4- to 6-month healing period. The onlay grafts exhibited minimal resorption and maintained their dense quality. The symphysis grafts were larger in overall volume, with a corticocancellous morphology. The ramus area provided essentially a cortical graft that was well suited for veneering ridge deficiencies; however, the surgical access in some cases was more difficult than in the anterior mandible.

Important to the understanding of the dynamics associated with dental implant anchorage over time is a knowledge of the supporting anatomy for common endosseous implants prior to being placed into function. This study followed 20 screw-shaped dental implants placed in edentulated (2 months' healing time) posterior jaws of five adult female baboons. Implants made of three biomaterials were placed and allowed to heal for 3 months prior to processing for evaluation. Percentage integration and bone area data from six horizontal sections along the entire length of each implant were collected and analyzed for differences between jaws, implant biomaterials, jaw/biomaterial, and sections of the implants (ANOVA, pairwise comparison using LSM with Bonferroni adjustment). The results indciated that overall mean percentage integration was 46.5 and mean percentage bone area was 39.9. Maxillary and mandibular differences for both parameters were statistically different (integration: maxillary = 38.1%, mandibular = 56.7%, bone area: maxillary = 35.8%, mandibular 44.9%; both were significant at the P .05 level). The biomaterial analyses revealed significant differences for percentage integration between the metal implants and the hydroxyapatite-coated implant (commercially pure titanium = 39.1%, titanium-aluminum-vanadium = 40.0%, hydroxyapatite-coated = 61.5%), but no such difference was noted for percentage bone area (commerically pure titanium = 38.8%, titanium-aluminum-vanadium = 38.9%, hydroxyapatite-coated = 42.3%). Discussion of the relative importanceof the two parameters highlights the fact that resi stance to functional loads requires establishing and then maintaining an adequate volume of bone, which may have a functionally specific structure based on the mechanical properties of the local jaw environment.

The purpose of this study was to evaluate bone formation and osseointegration using titanium dental implants in the subantral space following surgical implantation of recombinant human bone morphogenetic protein-2 (rhBMP-2). In each of four cynomolgus monkeys, one subantral site was treated with rhBMP-2 (0.19 mg per implant) in an absorbable collagen sponge (ACS). The contralateral site was treated with vehicle in ACS (control). Three months later, two screw-type titanium dental implants were placed into each augmented sinus, and one additional implant was placed immediately anterior to the sinus. Thus, each animal had three experimental sites: rhBMP-2, control, and non sinus. Animals were sacrificed after an additional 3 months, and block sections were harvested and prepared for histometric analysis. Analysis of variance and t tests were used to evaluate differences between experimental conditions. Mean (± SD) vertical bone gain was significantly greater in rhBMP-2 than in control sites (6.0 ± 0.3 versus 2.6 ± 0.3 mm; P .002). Bone density in rhBMP-2 sites averaged 14.4 ± 2.9% versus 13.9 ± 4.6% and 14.1 ± 3.6% for control and nonsinus sites, respectively, without significant differences between experimental conditions. Bone-implant contact in rhBMP-2 sites (41.4 ± 7.7%) was not significantly different from that in control (38.9 ± 12.4%) and nonsinus sites (46.8 ± 10.6%). The present study provides evidence for considerable vertical bone gain in the subantral space following surgical implantation of rhBMP-2, thus allowing placement of dental implants. The newly formed bone appears to be of similar quality and to be as suitable for osseointegration as the residual bone in this nonhuman primate model. Thus, sugrical implantation of rhBMP-2 appears to have clinical utility and may provide a realistic alternative to autogenous bone grafts for subantral augmentation procedures.

Complete-arch implant prostheses continue to exhibit horizontal and vertical misfit between frameworks and abutments. It has been suggested that these gaps may be eliminated and that restoration-induced stresses may be reduced by luting frameworks to screw-retained abutments intraorally. This study measured and compared the strains generated by clinically acceptable, conventional frameworks and abutment-luted frameworks to a bone simulant model. Three conventional and three resin-luted frameworks were made from a single master cast representing a bone simulant model of an edentulous mandible with five Nobel Biocare implants and 4-mm abutments. Two strain gauges were also embedded in the bone si mulant model to measure strains at two locations. Resin-luted frameworks were made by securing abutments to the clinical model with five gold slot screws tightened to 10 Ncm. Frameworks were then luted to these abutments with TwinLook cement following manufacturer's specifications. Both groups of frameworks were sequentially secured to the cli nical model with screws tightened to 10 Ncm. Strain-indicator readings were recorded at a standardized time following the initial fastening of each prosthesis (n = 3). Mean principal strains were determined and compared using a one-way repeated measures analysis of variance. A statistically significant difference was found in the principal strains between the conventional cast and the resin-luted frameworks. Overall, there was a decrease in the magnitude of strain for the resin-luted frameworks. Intraoral luting of frameworks may decrease the strains produced in the bone around implants.

Nineteen patients received tumoricidal doses of radiation and subsequently underwent mandibular endosseous implant reconstruction, followed by dental rehabilitation with complete arch fixed osseoprostheses. Eight of the 19 patients also underwent autogenous bone graft reconstruction for mandibular discontinuity. A surgical and prosthetic protcol for irradiated head and neck oncology patients is presented. The 10-year retrospective study of 19 consecutively treated patients revealed an endosseous implant survival of 99%, dental osseoprosthesis continuous service of 100%, and successful bone graft reconstruction of 89%.

A surgical technique for the placement of titanium screw-type implants (Branemark system) in the pterygomaxillary-pyramidal region is presented. The correct direction, location, and length of the implant is decided during surgery. Cylindric osteotomes are used as bone-site formers, thus minimizing the use of drills in bone preparation. This not only conserves bone, but greatly reduces the potential surgical risks, especially of hemorrhage.

Ablative surgery of the oral tissues may result in significant facial deformity, poor oral function, and psychologic detriment. Immediate surgical reconstruction with vascularized free flaps has become increasingly popular, but the oral rehabilitation of these patients with conventional dental prostheses is usually unsuccessful. The results and clinical experiences of treating a group of 17 patients with ablative surgery, immediate reconstruction with free flaps, and restoration with mandibular implant-retained prostheses are presented after follow-up periods of 6 months to 7 years. Most patients expressed a high degree of satisfaction with their prostheses. General principles and guidelines for the provision of this effective treatment modality are discussed.

Metal ion release from metallic implants is known to occur, but its extent and implications are controversial. In spite of the rapidly growing use of such implants, little is known about metal ion release. Blood levels of titanium, aluminum, and vanadium were measured using an atomic absorption spectrophotometric technique preoperatively and at intervals over a 3-year period for 52 patients (17 men, 35 women), each of whom had three mandibu lar porous-surface endosseous dental implants. The results showed that there was no evidence of change from preoperative to long-term values for the three metals measured in the study. These findings are reassuring, but do n ot rule out local or remote accumulation of released ions, which was not measured in this study.

PerioGlas is a silicate-based synthetic bone augmentation material that has been used to fill periodontal defects with bonding and integration to both soft tissue and bone. The purpose of this research was to determine the PerioGlas interface with titanium dental implants and bone. Seven live rabbits were used; however, one rabbit was euthanized at 3 days as a result of a tibial fracture through the implant placement site. Each rabbit received four 3.3 x 8 mm Imtec titanium plasma-sprayed dental implants, two in each proximal tibia. One implant in each rabbit was placed in the standard fashion. Two implants in each rabbit had a surgically created defect adjacent to one side of the coronal aspect of the implant. The defect was subsequently filled with PerioGlas. One implant in each rabbit had a surgically created defect that was not filled with PerioGlas. The rabbits were sacrificed at 1, 2, 3, 6, 12, and 24 weeks. Each specimen was prepared for histologic viewing, yielding a nondecalcified specimen demonstrating the interface of bone, implant, and PerioGlas. The results demonstrate peripheral formation of osteoid, followed by bone deposition within the defect from host (surgical margin) bone, toward the implant. The new osteoid and bone form around the PerioGlas particles. Newly formed trabeculae connect these areas of osteoid and new bone around the PerioGlas, interconnecting the PerioGlas particles. The new bone eventually reaches the implant, and osseointegration occurs with incorporation of the PerioGlas particles.

The combined use of bone grafts and osseointegrated implants a ppears to improve the long-term prognosis of transplanted bone. One question pertaining to the use of grafted bone is whether the biologic reaction to implants placed in grafted bone is the same as that seen under nongrafted conditions. A mandibular discontinuity defect in a 63-year-old female patient was repaired with a nonvascularized block graft into which 3 titanium implants were placed. After a 10-month loading period, one of the implants was retrieved and treated to obtain thin ground sections. The histologic examination showed mature bone in close contact with the implant surface; no gaps, fibrous tissue, or inflammatory cells were seen at the interface. No resorption phenomena were present. The bone at the interface was highly mineralized. The features of the regenerated bone and the bone-implant interface in grafted bone were similar to those seen in nongrafted situations; no differences were found with results presented in the literature concerned with retrieved implants placed into vascularized grafts.

The purpose of this clinical investigation was to compare the new resorbable collagen membrane, Bio-Gide, to the conventional expanded polytetrafluoroethylene material (Gore-Tex) for guided bone regeneration in situations involving exposed implant surfaces. Over a 2-year period, 25 split-mouth patients were treated randomly: one defect site was treated with Bio-Gide and the other defect site with Gore-Tex; all 84 defects were filled with Bio-Oss and covered with the respective membrane. The defect types, their dimensions, and their morphology were measured in detail initially and at re-entry to allow for calculation of the exposed implant surface. Changes in defect surface for both types of membranes were statistically significant (P .0001); however, no statistical significance (P > .94) could be detected between the two membranes. The mean average percentage of bone fill was 92% for Bio-Gide and 78% for Gore-Tex sites. In the latter group, 44% wound dehiscences and/or premature membrane removal occurred. The resorbable membrane, Bio-Gide, in combination with a bone graft, can be a useful alternative to the well-established expanded polytetrafluoroethylene membranes. Schlagwörter: biodegradable membranes, Bio-Oss, defect morphology, guided bone regeneration, implants, membrane exposures, nonresorbable membranes, timing of implant placement