Comparison of Three Biphasic Calcium Phosphate Block Substitutes: A Histologic and Histomorphometric Analysis in the Dog Mandible.

The purpose of this animal study was to determine which ratio of hydroxyapatite (HA) and tricalcium phosphate (TCP) is the most appropriate in the composition of alloplastic biphasic block grafts, in terms of bone density and bone formation, for the regeneration of alveolar defects. Different concentrations of HA/TCP were used for the alloplastic block grafts: 100/0 (HA100 group), 79/21 (HA75 group), and 57/43 (HA50 group); the control treatment filled the defect with a collagen plug. All control and test sites were covered with a resorbable collagen membrane. Sacrifices were performed at 4, 12, and 24 weeks after grafting. Microcomputed tomography and histologic and histomorphometric analyses were performed to determine bone density and the characteristics of the regenerated bone as well as the percentages of newly formed bone (NB), residual material (RM), and connective tissue (CT). Bone density increased significantly over time (P < .001), with stabilization between 12 and 24 weeks (P = 1.000). No differences in density were observed between the different test blocks (P = .813). The percentage of NB increases over time, independent of the concentration (P < .001). At 12 weeks, the control group exhibited more NB than the HA100 group (P < .001). At 24 weeks, the HA50 group exhibited more NB than the HA100 (P < .001) and control (P = .066) groups. At 24 weeks, the HA100 and HA75 groups showed high RM percentages. The HA50 group exhibited an increased tendency of less RM percentage compared with the HA100 and HA75 groups. Although slight differences were found, the HA50 group's HA/TCP ratio seems the appropriate concentration when taking into account the bone density and percentage of NB and RM at 12 and 24 weeks of healing.