In vitro mineralization and implant calcium phosphate-hydroxyapatite crystallinity

Biological dissolution of implant calcium phosphate coatings release local concentrations of divalent ions, which may influence mineralization. The objective of this study was to determine the effects of calcium phosphate release from coated commercially pure titanium discs using a bone-like cell culture bioassay. Sandblasted discs were prepared with or without hydroxyapatite crystallinities (50, 75, and 90 percent). Samples of each coating were randomly assigned and either preincubated for 24 hours with media or not before the addition of cells (2200/ mm2). Cultures were grown for 72 hours in culture medium containing 0.5 microCi/mL45 Ca. After rinsing, the remaining calcium phosphate surface was dissolved and counted. Three independent trials were performed. Results indicated proliferation was not altered as a function of crystallinity (P > 0.05) among any of the groups. However, a significant (P < 0.01) inverse relationship was found for biologically mediated mineralization as a function of calcium phosphate crystallinity. Low crystalline surfaces (nominally 50 percent) had the highest level of mineralization, with 75 percent crystalline surfaces being intermediate and 90 percent crystalline samples having the lowest amount of relative mineral formation. Mineralization only occurred on sandblasted commercially pure titanium upon supplementation of the growth medium with an organophosphate (beta-glycerophosphate), although this was less than on culture plastic. The results suggest calcium phosphate dissolution, as a function of implant coating crystallinity, can alter biological mineralization and may be one means in which enhanced mineral formation occurs around calcium phosphate-coated dental implants.