Dense hydroxyapatite inserted into post-extraction sockets. A histologic and histomorphometric 20-year case report.

Background: The biologic behavior, i.e., the degradation of hydroxyapatite (HA) in the human body, is of relevance for clinicians. The present investigation is a long-term (20-year) histologic and histomorphometric evaluation of dense HA used in postextraction sockets. Methods: Dense HA particles were used in a patient in postextraction alveolar sockets to maintain the alveolar ridge height. The patient returned after 20 years for implant treatment. A ridge remodeling was necessary during implant insertion surgery, and the HA/bone tissue was harvested with bone-cutting forceps from the canine and premolar area. The specimen was processed for histology and histomorphometry at the Implant Retrieval Centre, Dental School, University of Chieti-Pescara. Results: Most of the particles (56%) were surrounded partially by bone, whereas some particles (39%) were surrounded completely. At higher magnification, bone was in close contact with the particles, and neither gaps nor flbrous tissues were present at the bone-biomaterial interface. Microscopically, the particles had a dense appearance. In only a few fields, it was possible to observe that the outer part of some particles had detached from the original particles' surface. Histomorphometry showed that bone represented 25.4% +/- 3.2%, marrow spaces represented 41.3% +/- 5.2%, and residual HA particles represented 38.1% +/- 4.1%. Conclusions: Intimate binding between bone and HA particles was present after a long-term implantation period (20 years). The fact that HA particles were surrounded closely by bone is very promising for the long-term stability of the augmentation.