Formation of carbonate-apatite crystals after implantation of calcium phosphate ceramics

SummaryThe aims of this study were (1) to determine at the crystal level, the nonspecific biological fate of different types of calcium phosphate (Ca−P) ceramics after implantation in various sites (osseous and nonosseous) in animals and (2) to investigate the crystallographic association of newly formed apatitic crystals with the Ca−P ceramics.Noncommercial Ca−P ceramics identified by X-ray diffraction as calcium hydroxylapatite (HA), beta-tricalcium phosphate (β-TCP), and biphasic calcium phosphates (BCP) (consisting of β-TCP/HA=40/60) were implanted under the skin in connective tissue, in femoral lamellar cortical bone, articular spine bone, and cortical mandibular and mastoidal bones of animals (mice, rabbits, beagle dogs) for 3 weeks to 11 months. In humans, HA or β-TCP granules were used to fill periodontal pockets, and biposies of the implanted materials were recovered after 2 and 12 months.Results of this study demonstrated the following: (1) the presence of needle-like microcrystals (new crystals) associated with the Ca−P ceraiic macrocrystals in the microporous regions of the implants regardless of the sites of implantation (osseous or nonosseous), type of Ca−P ceramics (HA, β-TCP, BCP), type of species used (mice, rabbits, dogs, humans), or duration of implantation; (2) decrease in the area occupied by the ceramic crystals and the subsequent filling of the spaces between the ceramic crystals by the new crystals; (3) these new crystals were identified as apatite by electron diffraction and as carbonate-apatite by infrared absorption spectroscopy; (4) high resolution transmission electron microscopy (Hr TEM) revealed one family of apatite lattice fringes in the new crystals in continuity with the lattice planes of the HA of β-TCP ceramic crystals; (5) Hr TEM also demonstrated the presence of linear dislocations at the junction of the new apatite crystals and ceramic crystals.It is suggested that the formation of the CO3 apatite crystals associated with the implanted Ca−P ceramic is due to dissolution/precipitation and secondary nucleation involving an epitatic growing process and not to an osteogenic property of the ceramic.