Effect of porous and dense hydroxyapatite implantation on periodontal tissue regeneration in monkeys.

Two different kinds of hydroxyapatite (HA) granules (size: 400-630 microns), 1) porous HA fabricated by the H2O2 bubbling method and 2) dense HA, were placed into the experimentally created, 3-wall, wide periodontal defects in two monkeys to evaluate whether the different structures of hydroxyapatite influence the periodontal response after implantation. Defects without HA implantation served as controls. The HA implant groups showed excellent biocompatibility. Both the porous HA and the dense HA showed a greater amount of "connective tissue attachment or adhesion" than the control group. The amount of the increase by the porous HA group was statistically significant when compared with the control group. However, the three groups showed a similar amount of new cementum formation. These results indicate that the improvement of tissue regeneration by hydroxyapatite implantation was probably due to the prevention of the epithelial downgrowth rather than to the acceleration of the coronal proliferation of the periodontal ligament cells. In the porous HA group, ingrowth of fibrous and osseous tissue in the HA and indefinite tissue-apatite interface were observed. These findings suggest that the porous HA granules formed a firmer attachment to the surrounding periodontal tissue.