Characterization of Wet Powder-Sprayed Zirconia/Calcium Phosphate Coating for Dental Implants

Purpose: Yttria-stabilized zirconia (TZ) is used for dental applications because of its low toxicity and beneficial mechanicalproperties, but it does not stimulate bone regeneration around the implant due to its bioinertness. Therefore, hydroxyapatite(HA) coatings are often utilized to increase the surface bioactivity and to achieve a better osseointegration. Thesecoatings, however, are chemically nonstable and provide a weak bonding to the substrate surface.Materials and Methods: In this study, zirconia substrates were coated with a calcium phosphate/zirconia mixture to achieveceramic coatingswith a high bioactivity potential and a good mechanical stability.The coatingswere obtained bywet powderspraying (WPS).PureHAandTZcoatingswere employed as reference materials.The coatingswere characterizedwith regardto microstructure, surface roughness, and phase composition. Scratch tests were carried out to investigate the coatingadhesion. The influence of the coating on the mechanical strength was evaluated with the ball on three balls test (B3B). Inaddition, zirconia dental implant screws were also coated and inserted in a biomechanical test block and bovine rip bone.Results: After sintering, the mixed coating exhibited a porous morphology with a surface roughness of about 4 mm and atotal porosity of 17%. Phase analysis showed a transformation from TZ and HA to calcium zirconium oxide and tricalciumphosphate. Investigations of the bond strength confirmed a strong adhesion of the mixed coating to the substrate, while thebiaxial fracture strength was only slightly affected. Insertion experiments confirmed the scratch test results and evidencedan intact mixed coating on the zirconia screw.Conclusions: The present study revealed a higher stability and firm adhesion of the mixed coating compared with a purecalcium phosphate coating. We also successfully demonstrate the particular versatility of the WPS technique for dentalimplants by coating a complex curved surface.