Histological observations of coated and prestressed dental implants under flexible or rigid loading conditions

Hydroxyapatite-coated and hydroxyapatite-prestressed titanium implants were implanted under load-free, flexible-loaded and rigid-loaded conditions in dog mandibula in vivo. The bone response, bone contact and the quality of the coating were evaluated histologically and histometrically. Hydroxyapatite coating on titanium implants enhanced the bone apposition. The bone contact can still be present while the coating is resorbed. Gingiva contact with the coating led to a faster degradation of the coating. There was no significant difference in bone contact between hydroxyapatite-coated and -prestressed implants with regard to the loading systems: rigid, flexible and load-free. All three implants showed the highest amount of bone contact apically. Only at the mesial side of the implant did the flexible element show rather high amounts of bone contact compared to the rigid and load-free implants. The hydroxyapatite coating more or less degraded during the implantation period. The degree of degradation varied in the implant itself, between the implants and between the animals.