Silicon nitride laser cladding: A feasible technique to improve the biological response of zirconia

Zirconia is the most common ceramic used in dental implants. Even if it possesses both mechanical strength and esthetics, its intrinsic bio-inertness often results in a lack of biological integration. On the other hand, Si3N4 has been proved to be bio-active and to be able to easily osteointegrate. In this work, a Si3N4 powder-based laser-cladding process has been developed in order to improve the biological response to biomedical zirconia. The process resulted in the formation of a composite coating with Si3N4 particles dispersed in nano-crystalline/amorphous silicon. Microscopic observation showed that the layer is adherent to the substrate. The application of the laser cladding treatment resulted in an increase of the roughness, further enhancing the probability of interaction with biological tissues and consequently the bioactivity. Testing with human osteosarcoma cell lines resulted in the formation of bone tissue with high collagen maturity, high carbonate to phosphate ratios and good tissue mineralization, but lower cell proliferation when compared to stoichiometric Si3N4. The bone tissue quality parameters, as measured by Raman spectroscopy, resulted to be comparable to healthy human bone tissue and suggest that laser-cladded Si3N4 treatments might be able to improve the stability of zirconia implants.