In this presentation, the density and porosity of commercially available hydroxylapatite (HA) bone grafting materials analyzed by scanning electron microscopy (SEM). The calcium phosphate phases and molecular constituents responsible for dissolution/ resorption of hydroxylapatite (HA) were analyzed by x-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. The lack of microporosity explains the nonresorptive nature of truly dense HA while the presence of microporosity leads to cell-mediated resorption. The latter was evaluated using the in vitro cell culture model with human fibroblasts. Scanning electron and light microscopy confirmed the endocytosis mechanism for porous HA and illustrated the inhibition of cellular invasion/resorption by dense HA. A multi-analytical /spectroscopic approach coupled to in vitro cell culture studies provides insight into the dissolution/resorption of HA grafting materials and HA coating on implants.