Osteoclastic responses to various calcium phosphates in cell cultures

Disks made of hydroxyapatite, p-tricalcium phosphate, carbonate apatite, te tracalcium phosphate, a-tricalcium phosphate, dicalcium phosphate dihydrate , and octacalcium phosphate were incubated in osteoclastic cell cultures fo r 2 days. The first five salts were sintered and the last two were compress ed before incubation. Osteoclasts resorbed only the sintered carbonate apat ite disks. However, osteoclasts were able to resorb octacalcium phosphate d isks that were preincubated for 1 day in medium without cells, indicating t hat surface conditioning was important for osteoclastic resorption of this calcium phosphate. Although resorption did not occur, medium calcium and ph osphorus changed to an appreciable extent after a 2-day incubation of p-tri calcium phosphate, tetracalcium phosphate, ol-tricalcium phosphate, and dic alcium phosphate dihydrate. These changes in the medium calcium and phospha te concentrations could explain why osteoclasts appeared to have lost their activity on these calcium phosphate disks and were not capable of resorbin g them. With hydroxyapatite disks no changes were observed in the medium ca lcium and phosphorus before and after incubation. Moreover, the osteoclasts appeared to be essentially the same as with the sintered carbonate apatite disks and with bone slices used as a control. Nevertheless, no pits or lac unae were observed on the hydroxyapatite disks, indicating that sintered ca rbonate apatite should be superior to sintered hydroxyapatite as a bioresor bable bone substitute. (C) 1999 John Wiley & Sons, Inc.