Effect of setting atmosphere on apatite cement resorption: An in vitro and in vivo study

Objectives: The aim of this present study was to investigate the effect of setting atmosphere on replacement of apatite cement with new bone both in vitro and in vivo. Material and methods: Apatite cement consisting of an equimolar mixture of tetracalcium phosphate and anhydrous dicalcium phosphate was mixed with distilled water and allowed to set at 37 °C and 100% relative humidity under 0%_, 5%, and 100% CO₂ atmospheres. X-Ray diffraction and Fourier Transform Infrared Spectroscopy were employed to confirm the carbonate apatite formation. Micro-CT and histological evaluation was made at 1 and 6 month(s) using twelve 10-week-old specific-pathogen-free male Wistar rats. Results: B-type carbonate apatite was found when the apatite cement was set under 100% CO₂ and 5% CO₂. More carbonate apatite was formed in the case of 100% CO₂ when compared with 5% CO₂, and none was formed under 0% CO₂. Interestingly, unreacted tetracalcium phosphate was significant when apatite cement was set under 0% CO₂, indicating the formation of Ca-deficient hydroxyapatite. When a bone defect of rat tibia was reconstructed in these conditions of apatite cement and sintered hydroxyapatite, replacement of the apatite cement was confirmed 6 months after implantation, whereas no replacement was observed in the case of sintered hydroxyapatite. The amount of replacement of apatite cement with bone was greater, on the order of 100% CO₂ and 5% CO₂, followed by 0% CO₂. Conclusion: The results obtained in the present study demonstrated that setting atmosphere clearly plays an important role in the replacement of set apatite cement with bone.