HISTOMORPHOMETRIC EVALUATION OF THE THIN HYDROXYAPATITE LAYER FORMED THROUGH ANODIZATION FOLLOWED BY HYDROTHERMAL TREATMENT

By the previously described method of electrochemical and hydrothermal reaction, a thin hydroxyapatite (HA) layer of 1 mu m thickness was fo rmed on machined, grit-blasted, and titanium plasma-sprayed implants, the surfaces of which were equipped with a gap zone of 0.15 mm in dept h. These implants, together with HA and titanium plasma-sprayed ed imp lants 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 r oughened implants, especially the grit-blasted implants, were surround ed with thin bone newly formed along the rough surfaces and showed hig her bone apposition than the smooth implants. The gay zone of the HA p lasma-sprayed implant was repaired with new bone that had vertically e xtended from the surrounding bone. The thin HA layer had as much osteo conduction as a plasma-sprayed HA coating but showed significantly dif ferent bone response. The results suggest that bone formation on an HA film is affected by degradation in living tissue that is related to t he crystallinity and the chemical composition of the HA film itself. ( C) 1997 John Wiley & Sons, Inc.