Solubility and tissue reaction of α-tricalcium phosphate (α-TCP) plasma-coated layers on titanium were examined by subcutaneous implantation tests. The α-TCP plasma-coated layers were prepared by plasma spraying of β-TCP powder on titanium. Hydroxyapatite (HAp) plasma-coated layers on titanium were used as control samples. An in vivo solubility test was carried out, as follows: Thirty-six samples, 10×10×1 mm, were implanted in subcutaneous tissue of a mongrel dog's back. At 1, 2, and 3 months after implantation, the coated layers were investigated by X-ray diffractometry (XRD) and SEM observation, weight-loss measurement, and histological estimation.
The transformation of the surface of the α-TCP coated layers into HAp was detected by the XRD more than 1 month after implantation. Weight loss of the α-TCP coated layers 2 months after implantation was 1.5 times greater than that of the HAp coated layers, and at 3 months, 1.6 times greater than previously. Histological examinations showed that connective tissues surrounded the α-TCP and HAp coated samples. Slight inflammatory reaction was observed in the connective tissue on the α-TCP coated layers as well as on the HAp coated layers.