Evaluation of moldable, in situ hardening calcium phosphate bone graft substitutes

Abstract

Moldable in situ self-stabilizing and hardening bone graft materials facilitate handling and may be suitable for membrane-free bone regeneration methods. This study aimed to compare two moldable synthetic calcium phosphate materials in a rabbit calvarial defect model. In 12 New Zealand white rabbits, four evenly distributed 6mm diameter defects were drilled in the calvarial bone. Three filler materials were randomly applied to 48 defects: an in situ hardening polylactide-coated ß-tricalcium phosphate (TCP), an in situ hardening polylactide-coated biphasic calcium phosphate (BCP), and a granular deproteinized bovine bone matrix (DBBM, positive control). One defect remained untreated and served as a negative control. Six animals were sacrificed after 4weeks, and the remaining animals were sacrificed after 16weeks. Biocompatibility, bone graft substitute integration and resorption, bone formation, defect bridging, and height of reconstructed hard tissue were assessed histologically and histomorphometrically. All tested materials showed good biocompatibility. Semi-quantitative analysis and pair-wise comparison suggested that BCP was more efficient in centripetal bone formation when compared with TCP. After 4weeks, significantly more bone had formed in the defects treated with either TCP or BCP materials compared with the untreated sites. BCP and DBBM did not show macroscopic signs of degradation, whereas the TCP material was partially resorbed after 16weeks. Otherwise, no major differences were detected between the three materials. The moldable, synthetic calcium phosphates are safe and suitable bone graft substitutes with outcomes that are comparable to the control material.