Qualitative and quantitative expression of bovine bone mineral in experimental bone defects. Part 2: Morphometric analysis

Background: The purpose of this study was to evaluate morphometrically the rate of resorbability of an inorganic bovine bone material in a standardized intrabony defect in dogs whether protected or unprotected by a bioabsorbable membrane at different healing periods, and to assess histomorphometrically the amount of osteoconductivity of this material and final healing site configuration. Methods: In eight mongrel dogs, four round intrabony defects (5 x 4 mm) were made on the lateral mandibular angle, bilaterally at a different given time. Bovine bone mineral randomly filled two sites, while the other two were left with blood clot. A bioabsorbable collagen membrane covered each type of defect. The blood clotted uncovered sites served as controls. Section blocks for histology were made at 3, 6, 12, and 24 months. Following the non-decalcification method and staining with Stevenel's blue and van Gieson's picro fuchsin, morphometric analysis was performed on each specimen lesion type. Results: Average bone area fraction at the bovine bone mineral uncovered sites (BBM) was 23.1%, 44%, 63.4%, and 58.8% at 3, 6, 12, and 24 months, respectively. Differences were statistically significant between 3 to 6 and 6 to 12 months (P<0.001). Average particle area fraction was 35.6%, 29%, 27.6%, and 26.8% at the respective periods. Differences were statistically significant between 3 to 6 months (P<0.05). In the bovine bone mineral membrane-protected (BBMM) sites, average bone area fraction was 26.4%, 51.7%, 61.2%, and 52.4% at 3, 6, 12, and 24 months, respectively. Differences were statistically significant between 3 to 6 months (P<0.05). Average particle area fraction was 37.9%, 29.8%, 26.8%, and 33.7%, respectively. Differences between the two sites with regard to the newly formed bone and particle presence were insignificant. In both, the increasing pattern of osteoconduction as expressed by the osteoconductivity test along the different healing periods was similar, as well as the decreasing pattern of the remaining concavity of the healing site configuration. Multiple comparison analysis of bone area fraction disclosed statistically significant superiority (P<0.05) of the membrane-ungrafted sites over BBM sites at 3 and 6 months and over BBMM sites at 6 months. Bone area fraction of the BBMM sites (51.7%) was statistically higher than the control sites (37.5%) (P<0.05). At 12 months, all test sites were statistically superior over the controls with regard to the regenerated bone and its healing configuration; i.e., remaining concavity of the defect. The healing site configuration of the test sites was persistently different from the control sites at 24 months. Conclusions: Newly formed bone and complete healing were evident in the BBM and BBMM sites. The membrane contributed no substantial benefits. Bovine bone particle resorptive phase was observed up to 6 months. Thereafter, there was no continued resorption up to 24 months observation.