The extensive studies on the replacement of osseous tissue recommended the use of bone substitutes { for filling defects caused by various reasons, and many investigators had experienced with variety of materials such as calcium salts and calcium phosphate ceramics.
F
Until now dense hydroxyapatite.. a form of calcium phosphate ceramic, is neglected for a bone j substitute because this material is very hard and very low bioresorption rate and does not present some of concern about bone ingrowth.
E
The granules of dense hydroxyapatite were implanted in the posterior portion of the right iliac crest of fourteen dogs. Two dogs were sacrificed at each time at 2, 4, 6, 8, 12, 16, and 20 weeks after implantation.
The results were evaluated by scanning electron microscopy for all fourteen specimens,´ and by light microscopy for the specimens of 2, 4, 8, and 12 weeks.
The scanning electron microscopy showed that a granule of dense hydroxyapatite was loosely attached to the surrounding tissue until 6 weeks and the implant was progressively adhered to the adjacent bony structure without intervening fibrous tissue form 8 weeks. The light microscopy showed scanty osteoid tissue formation and mild inflammatory response with some lymphocytes and small amount of fibrous connectiv, tissue at 2 weeks: From 4 weeks, there was proliferation of osteoblast that lined newly formed osteoid tissue without inflammatory and foreign body response. At 8 weeks, maturation of osteoid tissue was noted without abnormal tissue response.
These results suggested that a granular form of dense hydroxyapatite like as a porous hydrox- . yapatite provides pores and interconnecting macropores for the space of bony ingrowth; and that this material is suitable for filling osseous defect.
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