Abstract
To evaluate one aspect of osteoclastic resorbabilities of calcium phosphate bone substitutes, their dissolution behaviors were compared in a weak acid solution without strong agitation to mimic the subosteoclastic zone. Of calcium phosphate bone substitutes, β-tricalcium phosphate (β-TCP)-associated material of CERASORB (CS) , ArrowBone-β-Dental (AB) , SynthoGraft (SG) and OSferion (OS) , apatite-associated material of Geistlich Bio-Oss (BO) and sintered carbonate apatite (CA) were used as particulates. Particle sizes of OS and CA were adjusted to those of CS, AB and SG; the latter three materials had essentially the same particle size ranging from 300 μm to 500 μm. Reaction kinetics were followed by measuring proton activity and by analyzing solution calcium and inorganic phosphate, and further analyzed by chemical potential plots obtained based on the solution composition. At one week of dissolution, CS, AB, SG, OS and CA reached quasi equilibrium with thermodynamic solubility of β-TCP, and BO reached quasi equilibrium with thermodynamic solubility of hydroxyapatite (HA). Estimation of Gibbs free energy of the degree of supersaturation or undersaturation with respect to HA at 1 h dissolution, which could be used to estimate dissolution rate, clearly showed that CA was much more soluble than β-TCP-associated materials of CS, AB, SG and OS, which were more soluble than BO, indicating that CA was easily dissolved by hydrogen ions secreted by osteoclasts. This finding strongly suggests that CA would be superior as an osteoclast-mediated bioresorbable bone substitute to any other calcium phosphate bone substitutes commercially in use today.
