The biocompatibility of hydroxyapatite implanted in the human periodontium

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Abstract
A TEM study was made of the response to synthetic hydroxyapatite prepared in powder form and implanted for 6 and 12 months respectively in infrabony lesions in 2 adult patients with chronic periodontitis and tooth mobility. Round or oval‐shaped crystal aggregates, ranging in diameter from 1 to 20 μm, were surrounded by connective tissue free of inflammatory cells. The aggregates were made up of loosely‐packed individual synthetic hydroxyapatite crystals, with a mean diameter of 128.12±14.57 nm, separated by an amorphous matrix containing few collagen fibrils. In the 6‐month implants small apatite crystals, of a size similar to those found in adjacent alveolar bone and giving similar diffraction patterns, appeared in the center of the aggregates between the relatively large crystals of synthetic hydroxyapatite. These new apatite crystals filled the amorphous matrix progressively from the center to the periphery of the aggregate. The latter was surrounded either by fibroblasts or by osteoblasts and osteoid tissue. In the 12‐month samples a calcified collagenous bone matrix enveloped the crystal aggregates. Typical osteoclasts, lacking a brush border, were evident around certain aggregates. Some osteoclasts contained large vacuoles filled with synthetic hydroxyapatite crystals.