Porous hydroxyapatite as a bone graft substitute in alveolar ridge augmentation: a histometric study

Following bilateral alveolectomy, the ridge form was restored in 10 dogs with blocks of porous HA matrix and bicortical iliac autografts. The specimens were retrieved after 11 to 17 months and undecalcified sections were prepared for microscopy and histometry. Within the HA implants, bone ingrowth extended throughout the pores. This bone appeared mature and well vascularized. The autografts united to the mandible. However bone ingrowth into the cancellous spaces of the grafts was minimal or absent. Measurement of implant and graft cross-sectional areas showed the maintenance of alveolar ridge form to be equally permanent for the 2 materials over the 1.5 year duration of the study. The implant specimens were composed of 43.1% HA matrix, 45.2% bone and 11.7% soft tissue. The HA matrix had a surface area averaging 9.3 mm2/mm3 that was 91.1% covered with bone ingrowth. Although this study supported the thesis that a porous HA matrix can function as a bone graft substitute, it is noted that the unyielding nature of the implant blocks, compared to granules, requires a solution to the challenge of long-term denture support without ulceration before it can be used with clinical confidence.