Experimental study of osteogenic activity of sintered hydroxyapatite--on the relationship of sintering temperature and pore size.

In order to determine the most appropriate properties for hydroxyapatite, four kinds of sintered hydroxyapatite (50-250 microns & 900 degrees C, 50-250 microns & 1,100 degrees C, 300-600 microns & 1,100 degrees C, and dense & 1,100 degrees C, pore size and sintering temperature, respectively) were implanted in the animals and studied histologically. In addition, the responses at different implantation sites were compared. The results are 1) hydroxyapatite sintered at 900 degrees C temperature showed higher osteogenic activity than that sintered at 1,100 degrees C in the early period. However, this difference disappeared with time, and at 26 weeks, there was no significant difference between the two groups. 2) hydroxyapatite with a 300-600 microns pore size demonstrated osteogenic activity superior to that with a 50-250 microns pore size. 3) implantation at the epiphysis produced higher osteogenic activity in the early period, compared to implantations at the metaphysis or diaphysis. This difference in bone ingrowth had disappeared at the 26-week.