Volumetric analysis of osteoclastic bioresorption of calcium phosphate ceramics with different solubilities

Commonly, to determine osteoclastic resorption of biomaterials only the resorbed area is measured. The depth of the resorption pit, however, may also be important for the performance of a material. To generate such data we used two calcium phosphate ceramics (Ca(10) and Ca(2)). The solubility of the materials was determined according to DIN EN ISO 10993-14. They were scanned three-dimensionally using infinite focus microscopy and subsequently cultivated for 4 weeks in simulated body fluid without (control) or with human osteoclasts. After this cultivation period osteoclasts number was determined and surface changes were evaluated two- and three-dimensionally. Ca(10) and Ca(2) showed solubilities of 11.0+/-0.5 and 23.0+/-2.2 mgg(-1), respectively. Both materials induced a significant increase in osteoclast number. While Ca(10) did not show osteoclastic resorption, Ca(2) showed an increased pit area and pit volume due to osteoclastic action. This was caused by an increased average pit depth and an increased number of pits, while the average area of single pits did not change significantly. The deduced volumetric osteoclastic resorption rate (vORR) of Ca(2) (0.01-0.02 microm(3)microm(-2)day(-1)) was lower than the remodelling speed observed in vivo (0.08 microm(3)microm(-2)day(-1)), which is in line with the observation that implanted resorbable materials remain in the body longer than originally expected. Determination of volumetric indices of osteoclastic resorption might be valuable in obtaining additional information about cellular resorption of bone substitute materials. This may help facilitate the development of novel materials for bone substitution.