Histological and histomorphometrical comparative study of the degradation and osteoconductive characteristics of α- and β-tricalcium phosphate in block grafts

The purpose of the present study was to compare α- and β-tricalcium phosphate (TCP) as bone graft material for augmenting highly resorbed alveolar ridges. The cranial bones of 15 rabbits were used. Three titanium chambers filled with porous blocks of α-TCP, β-TCP, or blood clots were placed in each slit. The two TCP blocks had similar inner/outer structures and purities. Animals were sacrificed after 2, 4, and 8 weeks. Specimens were embedded in polyester resin as nondecalcified specimens, and evaluated both histologically and histomorphometrically. In both TCP groups, blocks had hardly degraded at 2 weeks while in the α-TCP group, the block had notably started degrading after 4 weeks. In the β-TCP group, degradation began at 4 weeks and this degradation had increased just slightly after 8 weeks. The α-TCP block degraded significantly more than the β-TCP block. Residual α-TCP particles surrounded by newly formed bone decreased over time, and both particles and newly formed bone were simultaneously absorbed by osteoclast-like cells. These observations suggest that residual α-TCP particles surrounded by newly formed bone may disappear progressively from bone and could be incorporated into the bone remodeling cycle in combination with newly formed bone.