Dissolution and mineralization of sintered and thermally sprayed hydroxy-fluoroapatites

Hydroxyapatites are commonly used as bone cement, coatings on implants for dental and orthopaedic applications, but also as middle ear implants. These applications all require a different tissue healing response that can be attained by different manufacturing processes or by chemically modifying the composition. During implantation apatites undergo a process of dissolution and mineralization. The degree of dissolution is dependent upon the manufacturing process & is higher for thermally sprayed implant materials. This allows them to integrate to the natural bone. This study tests the dissolution and mineralization of fluoride containing hydroxyapatites through immersion in simulated body fluid. It shows that mineralization occurs more readily in hydroxyapatites than fluorapatites because of their higher dissolution rate. Mineralization was detected most readily by image analysis using scanning electron microscopy than by weight changes using a microbalance. Microscopy allowed small heterogeneous precipitates to be observed during the initial stages of mineralization.