Two human hydroxyapatite-coated dental implants retrieved after a 14-year loading period: A histologic and histomorphometric case report

Background: Controversy over the long-term clinical effectiveness of hydroxyapatite (HA)-coated dental implants still persists, despite numerous clinical studies documenting high survival rates. Concerns about the degradation of the coating over the years have been raised; it has been speculated that resorption of the HA could produce a space between the implant and the bone with a resultant mechanical instability. Methods: Two HA-coated implants were retrieved due to a fracture of the abutment screws after a loading period of 14 years and were treated to obtain thin ground sections for histologic evaluation. Results: At low-power magnification, it was possible to observe that the HA coating was in contact with mature bone. No gaps or connective fibrous tissue was found at the implant-bone interface. No epithelial downgrowth was present. No acute or chronic inflammatory cell infiltrate was present at the implant-bone interface. No foreign body reaction was present in the peri-implant tissues. Some osteocytes were in direct contact with the coating. For implant 1, the percentage of bone-titanium contact was 25% +/- 2.1 %, and the percentage of bone-HA contact was 35% +/- 1.4%. The total bone-implant contact was similar to 60%. The HA coating appeared to be resorbed in 46% +/- 3.2% of the implant perimeter, especially in the coronal portions of the implant. For implant 2, the mean percentage of bone-HA contact was 13% +/- 1.8%, and the mean percentage of bonetitanium contact was 15% +/- 2.3%. The total bone-implant contact was similar to 28%. The HA coating appeared to be resorbed for a mean of 68% +/- 4. 1 % of the implant perimeter, especially in the coronal portion of the implant. Conclusions: No acute or chronic inflammatory cell inflitrate was present in the peri-implant tissues. No signs of coating infection, fatigue, or failure were observed in two specimens. The HA coating may not be susceptible to degradation or dissolution under longterm function.