The effects of alloplastic implant onlays on bone in the rabbit mandible.

The relative importance of the factors that contribute to the bone erosion seen underlying alloplastic implants remains unknown. This study was designed to examine the effects of different alloplastic onlays on the mandible in a rabbit animal model. Three alloplastic materials (soft solid silicone, methyl methacrylate, and porous polyethylene) were examined to determine the importance of implant composition in bone resorption. Thin (1.5-mm) and thick (6-mm) onlays were used to determine the relative importance of implant thickness. Fluorescent markers were administered at different time intervals to evaluate the patterns of new bone formation. A total of 96 implants placed on the mandibles of 16 animals were examined grossly, histologically, and under fluorescent microscopy after 12 and 24 weeks. The frequency and degree of bone erosion were related both to the type of alloplast and to the thickness of the implant. Silicone implants were associated with the greatest amount of bone resorption (p < 0.01). Thicker silicone implants were associated with a greater degree of thinning (p < 0.05). Bone resorption beneath the implants was documented by the presence of osteoclasts actively eroding bone and by changes in the normal patterns of the fluorescent markers. Both the thin methyl methacrylate and the thin porous polyethylene implants had a low incidence of bone thinning. The thick methyl methacrylate implants caused more erosion than the thin implants of the same material, although this was less than the silicone groups. Increasing the thickness of porous polyethylene implants did not adversely affect the underlying bone.(ABSTRACT TRUNCATED AT 250 WORDS)