HISTOLOGICAL-EVALUATION OF PERI-IMPLANT BONE AT IMPLANTS SUBJECTED TOOCCLUSAL OVERLOAD OR PLAQUE ACCUMULATION

Breakdown of bone around oral implants following occlusal overload or plaque accumulation was evaluated in monkeys. 5 screw-type implants of pure titanium (Astra Tech) were inserted in the mandible of 4 monkeys (Macaca Fascicularis). 6 months after insertion of the implants a fix ed partial prosthesis was mounted on the 2 implants in 1 of the latera l segments. The prosthesis was in supra-occlusal contact with an antag onizing splint and caused a lateral directed excessive occlusal load ( overload). Implants retaining the prosthesis were brushed 1 X week and subgingival cleaning was performed 1 X month. The remaining implants were never cleaned and, additionally, a cotton cord was placed around the abutments of these implants to promote plaque accumulation. 6 out of 8 implants with occlusal overload became loose. 2 of these were los t, whereas the remaining 4 were retained in the jaws. After 18 months of occlusal load or plaque accumulation, the monkeys were sacrificed. Tissue blocks with the implants were infiltrated and embedded in acryl ic resin. Approximately 50 mu m thick sections of the implants and sur rounding tissues were made. All implants with plaque accumulation were osseointegrated, but exhibited an average histologic marginal bone lo ss of 2.4 mm (range: 0.8-4.0 mm). Of the 6 implants with occlusal over load available for histologic analysis, 2 implants in 1 monkey had los t osseointegration completely and 2 other implants were osseointegrate d in the apical part only, whereas the remaining 2 were still osseoint egrated but exhibited a bone loss of 1.8-1.9 mm.