Histological and compositional evaluations of three types of calcium phosphate cements when implanted in subcutaneous tissue immediately after mixing.

To evaluate the soft tissue response of calcium phosphate cement (CPC), consisting of an equimolar mixture of tetracalcium phosphate (TTCP) and dicalcium phosphate anhydrous (DCPA) under conditions close to those encountered in actual surgical procedures, we implanted three types of CPC [conventional CPC (c-CPC), fast-setting CPC (FSCPC), and antiwashout type FSCPC (aw-FSCPC; formerly called nondecay type FSCPC or nd-FSCPC)] subcutaneously in the abdomens of rats immediately (1 min) after mixing. At 1 week after surgery, histological examination and compositional analysis were performed using light microscopy and powder X-ray diffraction (XRD), respectively. The implanted c-CPC was crumbled completely, whereas FSCPC and aw-FSCPC retained their shape. Large vesicles containing copious inflammatory effusion were subcutaneously formed around the c-CPC. Histologically, many foreign-body giant cells were collected around the c-CPC, and moderate inflammatory cell infiltration was observed at 1 week after surgery. In contrast, the FSCPC and aw-FSCPC were covered with a thin layer of granulation tissue that included few giant cells and presented slight inflammatory cell infiltration, and no effusion was observed. The XRD analysis of the c-CPC revealed the presence of some unreacted DCPA even 1 week after implantation, whereas almost no DCPA was found in the FSCPC or aw-FSCPC. In conclusion, it was found that CPC does not always show excellent tissue response. When c-CPC is implanted subcutaneously in rats immediately after mixing, it fails to set and causes a severe inflammatory response. Therefore, the type of CPC should be chosen according to the clinical particulars. CPC should be used in a manner that assures its setting reaction. We recommend the use of FSCPC and aw-FSCPC for surgical applications, such as orthopedics, plastic and reconstructive surgery, and oral and maxillofacial surgery, where the cement might otherwise crumble due to the pressure before setting.