RADIOGRAPHIC ANALYSIS OF REGENERATED BONE AROUND ENDOSSEOUS IMPLANTS IN THE CANINE USING RECOMBINANT HUMAN BONE MORPHOGENETIC PROTEIN-2

Ideal endosseous implant placement involves a congruent bony housing i n close apposition to the implant surface. Clinical situations are enc ountered, however, in which the entire implant surface cannot be in cl ose apposition to bone. In these instances, bone grafting materials ar e generally used to regenerate bone around the implant. In this study, a biologically active bone differentiation factor, recombinant human bone morphogenetic protein-2 (rhBMP-2), was used with two different ca rriers to regenerate bone around implants in standardized critical-siz ed defects in the canine mandible. Half of the sites had a nonresorbab le membrane placed over the defect. Longitudinal standardized radiogra phs were obtained to assess the amount of bone regeneration on the mes ial 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 bone de nsity were evaluated by computer-assisted densitometric image analysis of discrete areas adjacent to the implant. After 4 weeks of healing, nonmembrane sites had significantly greater bone height than membrane- protected sites. Following 12 weeks of healing, sites treated with rhB MP-2 had significantly greater bone formation than untreated sites. Si tes treated with rhBMP-2 and a membrane had the greatest bone fill, fo llowed by sites treated with rhBMP-2 but no membrane. Sites without rh BMP-2, whether with or without a membrane, had less bone fill than sit es with rhBMP-2. At 12 weeks, sites with a membrane resulted in signif icantly more gain in bone density than sites without a membrane. Furth ermore, sites treated with a collagen carrier resulted in greater gain s in bone density than sites treated with a polylactide/glycolide carr ier. The results from this study demonstrate by radiographic evidence that new bone formation in critical-sized defects around implants is d ependent 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, ca n significantly stimulate bone formation around endosseous dental impl ants.