CALCIUM-PHOSPHATE COATINGS FOR MEDICAL AND DENTAL IMPLANTS

Long-term fixation of metallic dental and medical implants in bony tissues continues to be a problem. One possible solution involves the application of calcium phosphate (Ca-P) ceramic coatings such as hydroxyapatite (HA) onto the metallic devices. Two methods being investigated for producing the coatings include plasma spraying, a commercially available process, and ion-beam sputter deposition, a technique being experimentally investigated. The plasma spraying process produces coatings on the order of 40-60 mum thick. The chemistry and structure of the coatings are similar to those of HA; however, the plasma spraying process will result in the formation of amorphous and other Ca-P phases in the resulting coatings. One concern with respect to these coatings is their relatively low bond strength. The ion-beam sputtering process produces thin (0.6-1 mum) Ca-P coatings that have a significantly higher bond strength than the plasma-sprayed coatings. One concern with the sputtered coatings relates to the amorphous structure obtained after sputtering. These amorphous coatings have high dissolution,rates, and a post-deposition heat treatment is required to form more stable crystalline phases in the coatings. The chemistry and structure of the heat-treated coatings are again similar to those of HA; however, other phases can result from this process as well. Both deposition processes result in the formation of HA-type coatings; however, optimization of various coating properties such as stability and bond strength remain a challenge which must be addressed before an optimal tissue response can be attained.