STABILITY ASSESSMENTS AND HISTOLOGY OF TITANIUM IMPLANTS PLACED SIMULTANEOUSLY WITH AUTOGENOUS ONLAY BONE IN THE RABBIT TIBIA

A disc-shaped bone graft was harvested from the calvarium in ten rabbi ts and anchored as an onlay bone graft, using a titanium implant, at t he proximal tibial metaphysis. The contralateral tibia served as the c ontrol, where an implant was placed without a graft with the implant h ead at a height corresponding to the thickness of the graft on the tes t side. Resonance frequency measurements were performed 4, 8, 16 and 2 4 weeks postoperatively and removal torque measurements were performed at 24 weeks. A statistically significant higher implant stability, as assessed by resonance frequency measurements (RFM), was measured from 4 weeks throughout the 24-week period. The mean peak removal torque f or the test implants was 50.4+/-10.0 Ncm and 30.0+/-6.9 Ncm for the co ntrol implants, which was a statistically significant difference. Hist ologically, the grafted bone was well incorporated and morphometry rev ealed more bone around the test implants. Calculations of shear stress es indicated that the grafted bone had similar biomechanical propertie s to the cortical bone of the recipient site. It is concluded that the integration of titanium implants in autogenous onlay bone grafts resu lts in an increased biomechanical support of the implant. The use of R FM may also serve as a useful instrument for noninvasive monitoring of implant stability in vivo.