Histologic and histomorphometric evaluation of the bone response around a hydroxyapatite-coated implant retrieved after 15 years.

Concerns have been raised about the degradation of hydroxyapatite (HA) coatings on dental implants over time. It has been speculated that the resorption of HA could produce a space between implant and bone, resulting in mechanical instability and implant failure. A screw-shaped HA-coated implant was retrieved after the abutment had fractured after a loading period of 15 years, and was evaluated histologically. At the interface with the implant, compact mature bone, with small marrow spaces, was present. Higher magnification showed that only a few osteoblasts were present. No multinucleated giant cells were present. Bone remodeling was evidenced by the presence of many secondary osteons close to the implant surface and many reversal lines. No fibrous or granulation tissues were present at the interface. The HA coating had been completely resorbed, and just 5.1% +/- 2.3% of the implant surface was covered by the HA coating. The bone-implant contact percentage was 77.6% +/- 5.1%. The almost complete resorption of the HA coating did not appear to have interfered with osseointegration. The implant was osseointegrated and was still providing adequate function; thus the HA coating resorption probably had little clinical significance.