RESORPTION OF HYDROXYAPATITE AND FLUORAPATITE CERAMIC COATINGS ON WEIGHT-BEARING IMPLANTS - A QUANTITATIVE AND MORPHOLOGICAL-STUDY IN DOGS

Resorption (defined as loss of ceramic coating because of cellular act ivity or dissolution) of ceramic coatings is a matter of concern for t he long-term performance of ceramic-coated implants. A new fluorine-co ntaining coating, fluorapatite (FA), has been shown to be more stable than hydroxyapatite (HA) in unloaded models. Ln a weight bearing model in trabecular bone, we evaluated loss (defined as reduction of coatin g irrespective of type of mechanism) of KA and FA coatings during 25 w eeks of implantation. Eight mature dogs had HA-or FA-coated implants i nserted bilaterally into the weight-bearing region of the medial femor al condyle. Quantified loss of ceramic coating was estimated at the li ght microscopic level using stereological methods. The experiment show ed significant loss of both types of coatings. However, no statistical difference in loss of ceramic coating was found regarding surface are a, implant coverage, volume, and thickness (p = 0.77, p = 0.13, p = 0. 56, p = 0.23, respectively). Completely resorbed HA coating was replac ed by 36 +/- 6.0% (range: 26-42) bone in direct contact with the impla nt surface compared with 29 +/- 16.0% (range: 12-59) for FA (p = 0.40) , suggesting that the implant was firmly fixed despite loss of the cer amic coating. Transmission electron microscopy in combination with ele ctron energy spectroscopy and electron spectroscopic imaging showed th at osteclast-like cells, osteocytes, macrophage-like cells, and fibrob lasts had phagocytosed calcium-containing fragments, indicating cell-m ediated resorption of the ceramic coating. (C) 1998 John Wiley & Sons, Inc.