Bone augmentation with hydroxyapatite: histological findings in 55 cases

Bone augmentation was performed for 55 implant patients (21 male, 34 female) with hydroxyapatite granules. In 38 patients the hydroxyapatite was covered with lyophilized dura mater to avoid its loss during the healing phase. Sixty-seven punch biopsies were obtained between 14 days and 7 years. The undecalcified specimens were embedded in poly(methyl methacrylate), sectioned and stained to demonstrate bone formation. Increasing metaplastic formation of woven bone trabeculae was observed beginning with the earliest specimens. The hydroxyapatite was in intimate contact with the bone and later was partially included within its matrix. In some areas, the woven bone was resorbed by osteoclasts together with the hydroxyapatite, and mature lamellar bone was deposited by dense layers of osteoblasts. After 20 months, sufficient new bone formation occurred to permit implant insertion. In a whole mandible specimen obtained 5.6 years after implant placement, there was almost complete ossification of the hydroxyapatite. The inclusion of the titanium implants within the newly formed bone was evident, and the hydroxyapatite granules applied during second-stage surgery were firmly embedded within the newly formed trabecular bone. The bone augmentation technique described has been used successfully in over 600 cases and can be considered as safe. Bone formation in contact with hydroxyapatite was demonstrated histologically in a large number of human biopsies.