Initial histological evaluation of anti-washout type fast-setting calcium phosphate cement following subcutaneous implantation.

Anti-washout-type fast-setting calcium phosphate cement using chitosan (aw-FSCPC(chi)), conventional CPC (c-CPC), CPC mixed with citric acid (CPC(citric)) and CPC mixed with polyacrylic acid (CPC(acrylic)) were implanted subcutaneously in rats immediately after mixing to shed some light on the understanding of the appearance of excellent tissue response to CPC. CPC(citric) and CPC(acrylic) set quickly, similar to aw-FSCPC(chi), but the former two stopped their transformation to apatitic minerals. The c-CPC, which required a long setting time, was found to be crumbled, but the other CPCs maintained the shape at implantation. The aw-FSCPC(chi) and CPC(citric) showed no inflammatory response whereas c-CPC and CPC(acrylic) showed an inflammatory response one week after implantation. A component of the aw-FSCPC(chi) and c-CPC was an apatitic mineral whereas CPC(citric) and CPC(acrylic) showed no transformation to apatite. We concluded that the non-crumbling property plays a more dominant role in the appearance of excellent tissue response to CPC than the transformation to apatite. Also, a non-crumbling property is not a sufficient condition, but a necessary condition for the appearance of the excellent tissue response to CPC.