Histomorphometric evaluation of the thin hydroxyapatite layer formed through anodization followed by hydrothermal...

By the previously described method of electrochemical and hydrothermal reaction, a thin hydroxyapatite (HA) layer of 1 microm thickness was formed on machined, grit-blasted, and titanium plasma-sprayed implants, the surfaces of which were equipped with a gap zone of 0.15 mm in depth. These implants, together with HA and titanium plasma-sprayed implants as control materials, were placed in dog mandibles for 4 weeks. Histomorphometrical comparison was performed to examine the effects of the thin HA layer and the surface topography on bone formation. The roughened implants, especially the grit-blasted implants, were surrounded with thin bone newly formed along the rough surfaces and showed higher bone apposition than the smooth implants. The gap zone of the HA plasma-sprayed implant was repaired with new bone that had vertically extended from the surrounding bone. The thin HA layer had as much osteoconduction as a plasma-sprayed HA coating but showed significantly different bone response. The results suggest that bone formation on an HA film is affected by degradation in living tissue that is related to the crystallinity and the chemical composition of the HA film itself.