EVALUATION OF FILLING MATERIALS IN MEMBRANE-PROTECTED BONE DEFECTS - A COMPARATIVE HISTOMORPHOMETRIC STUDY IN THE MANDIBLE OF MINIATURE PIGS

In recent years, bone grafts and bone substitutes have been increasing ly utilized underneath barrier membranes to optimize the treatment out come of bone reconstructive therapy for defects in the alveolar proces s. In the present study, 4 different filling materials were evaluated in bone defects of similar dimensions in the mandible of miniature pig s. Blood clots and autografts were used as controls. The defects were covered with barrier membranes and allowed to heal for 4, 12 or 24 wee ks. Histologic examination demonstrated that bone repair progressed th rough a programmed sequence of maturation steps closely resembling the pattern of bone development and growth regardless of whether bone gra fts or substitutes were present or not. Histomorphometric analysis sho wed that autologous bone grafts (autografts) had the best osteoconduct ive properties during the initial healing period, with 39% of newly fo rmed bone inside the membrane-covered defects at 4 weeks of healing. I n addition, 87% of the graft surfaces were already covered by bone at this time. Both values were significantly higher for autografts than f or the 4 alternative bone fillers (P less than or equal to 0.05). At 1 2 weeks, these differences were no longer apparent, with all 5 filling materials showing similar values. Among the tested bone substitutes, tricalcium phosphate (TCP) showed a significantly higher percentage of bone fill at 24 weeks of healing. It can be concluded that sites fill ed with autografts clearly demonstrated the best results underneath ba rrier membranes in the early phase of healing. As far as degradation a nd substitution are concerned, TCP showed the most promising results. This filler, however, needs to be tested further in a more demanding a nimal model. Less favorable results were obtained for coral-derived hy droxyapatite granules and for demineralized freeze-dried bone allograf ts.