The decomposition of HA during plasma-spraying can lead to the appearance of calcium oxide (CaO) in the calcium phosphate coatings and an increase of the Ca/P ratio (> 1.67). Rehydration can cause an increase in the pH of the extracellular fluids in close vicinity to the coating and rapid degradation of its thickness. Metal cylinders coated with HA were implanted in rabbit condyles for two months and analyzed by histology to evaluate the effect of the presence of CaO in the coatings during early implantation. Three groups of coatings containing different amounts of CaO: 0.2, 0.5, and 0.9% were implanted . The mean coating thickness was measured on five different sites randomly chosen on each section. The percentage of the coating perimeter in contact with newly farmed bone tissue was also measured. A very small difference in coating thickness was observed between the 0.5% group and the two others. The percentage of coating perimeter in contact with the bone increased with the CaO content. These results show that CaO contamination of the calcium phosphate coating does not impair integration and does not increase degradation during the early stages of implantation.

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