Self-setting Apatite Cement : II. Hydroxyapatite as Setting Accelerator

Abstract

Self-setting apatite cement consisting of an equimolar mixture of tetracalcium phosphate and dicalcium phosphate dihydrate was found to set to a phase of hydroxyapatite when mixed with diluted phosphoric acid. The addition of hydroxyapatite to the cement greatly reduced the setting time to one acceptible for clinical application. Physicochemical properties such as crystallinity and wet compressive strength of set cement strongly depended upon nature of hydroxyapatite added as a setting accelerator. As crystallinity of added hydroxyapatite increased, the crystallinity of the set apatite cement increased. This finding makes it possible to prepare the most desiable self-setting apatite cement for different portion of hard tissues such as enamel, dentine and bone. The wet compressive strength measured when the set cement was stored in synthetic saliva decreased as the crystallinity of added hydroxyyapatite increased. Setting time and pH of the paste after spatulation, however, were negligibly affected by the added hydroxyapatite. In great contrast to the currently available cements, the self-setting apatite cement with components of particle size less than 37μm expands slightly, but notably during the setting reaction.