Transformation of biphasic calcium phosphate ceramicsin vivo: Ultrastructural and physicochemical characterization

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Abstract
Specially prepared biphasic calcium phosphate (BCP) macroporous ceramics consisting of an intimate association of beta tricalcium phosphate (b̃‐TCP) and hydroxyapatite (HA) with b̃‐TCP/HA weight ratios of 15/85, 35/65, and 85/15 were implanted in surgically created periodontal osseous defects in dogs and recovered after 6 months. A decrease in average size of crystals in BCP ceramics and an increase in the size of microporosities in the surface and at the core of the ceramic after implantation were observed, indicating thatin vivodissolution has taken place. The resorbability (reflectingin vivodissolution) of BCP ceramics depended on their b̃‐TCP/HA ratios, the higher the ratio, the greater the resorbability. The formation of microcrystals with crystallographic properties and Ca/P ratio similar to those of bone apatite crystals were also observed. The abundance of these crystals were directly related to the b̃‐TCP/HA ratio of the BCP ceramic before implantation. The formation of the bone apatite‐like crystals may be due to the precipitation of calcium and phosphate ions released from the dissolving ceramic crystals (the b̃‐TCP component dissolving preferentially to the HA component). Results from this study suggested that one of the means of controlling resorbability (in vivodissolution) of BCP ceramic is by varying its b̃‐TCP/HA ratio.