Setting Behavior and in Vitro Bioactivity of Hydroxyapatite/Calcium Sulfate Cements

The transformation of calcium sulfate hemihydrate into gypsum via reaction with water has been used for many years to produce materials for bone augmentation. In this work, a mixture of CaSO 4 · 1 / 2 H 2 O and hydroxyapatite was prepared, and its behavior as cement was studied and compared with that of pure calcium sulfate hemihydrate. The setting process was monitored with Gillmore needles, X-ray diffraction, and differential scanning calorimetry. The utilization of the mixture allows one to prepare homogeneous pastes with better manipulation characteristics than pure calcium sulfate hemihydrate. The workability and setting time of the hydroxyapatite-containing cements are higher than those of pure CaSO 4 · 1 / 2 H 2 O. The different techniques employed allow us to relate the initial setting time with the chemical transformation of the calcium sulfate hemihydrate into calcium sulfate dihydrate. The biphasic specimens show an improved bioactivity response compared to pure hydroxyapatite or gypsum when soaked in a simulated body fluid.