Aesthetic and mechanical properties of oxide coated Ti-Nb-Ta-Zr alloys as a dental material

Metallic materials have been used as load-bearing materials in dental and biomedical field since they have good mechanical properties such as good ductility and strength, however, aesthetic property is inferior to ceramic or resin. Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) is a β-type Ti alloy with excellent mechanical properties, low Young's modulus and controllable yield strength. Furthermore, oxide layer coating will improve its aesthetic property, as a dental material since it's oxide layer is firm and white. Therefore, effect of color tone change of oxide layer on Ti and TNTZ on oxidation condition was studied. The oxide formation behavior investigation was also carried out with focusing on peeling behavior. From the results of our color tone evaluation, L* and b* were increased with increasing heating time. From cross sectional observation, a firm white oxide layer formed on top which is consisted of TiO2 and Ti(Nb, Ta)₂O₇, whereas stratified TiO ₂ was formed on CP Ti. Thickness increased with increasing oxidation time. Peel test results indicated that peel stress of oxide layer on TNTZ was much higher than that on CP Ti, indicating microstructure of oxide affected on peel strength. Our obtained results suggests that oxide layer coating on Ti alloys will be a promising candidate for a "white metal" having merits of metal in terms of mechanical properties besides improving excellent aesthetic property.