A novel gradated zirconia implant material embedding bioactive ceramics: Osteoblast behavior and physicochemical assessment

Bioactive ceramic coatings have been proposed to improve the bioactivity of zirconia although the coating detachment can occur during implant placement. The main aim of this study was to enhance bioactivity and strength of the implant surface by using a gradated bioactive zirconia structure. Zirconia discs (8 × 3 mm) embedding gradual content of hydroxyapatite (YTZP-HA) or beta-tricalcium phosphate (YTZP-βTCP) were produced by hot-pressing technique. Specimens were initially studied regarding hardness, roughness, wettability, and shear bond strength of the gradated zone. Functionally gradated ceramic discs and zirconia (control group) were placed in contact with human osteoblast culture for 1, 3, 7, and 14 days. Field emission guns scanning electron microscopy (FEGSEM) was used to assess the morphology and adhesion of osteoblasts while cell viability was assessed by fluorometric method. The mineralization on the test and control discs was evaluated by Alkaline phosphatase (ALP) activity and fluorescent microscopy. Shear strength mean values of the outer layer bioactive ceramic and zirconia bulk were recorded at 150 MPa. Mechanical assays demonstrated that the novel design and manufacturing approach proposed for producing gradated zirconia embedding bioactive ceramics resulted in significantly higher mechanical strength as compared to monolithic zirconia. Also, cell viability and ALP levels increased on gradated zirconia containing HA or βTCP over time. Gradated zirconia containing hydroxyapatite revealed an increased viability, bioactivity, and mineralization of human osteoblasts when compared to conventional zirconia surface, without substantial loss of strength.