Effects of TiO2 on microstructural,mechanical properties and in-vitro bioactivity of plasma sprayed yttria stabilised zirconia coatings for dental application

One of the most compatible coatings, known as yttria-stabilised zirconia polycrystal (YZP) is deposited on metallic Ti alloys due to its excellent hardness and aesthetic value as well as its low affinity for plaques. However, poor bioactivities of YZP and the existence of micro crack propagations due to the aging of YZP may result in spontaneous implant failure thus limiting its clinical use. In this work, YZP coating reinforced titania (TiO₂), which is formed via a plasma spray technique was investigated in order to enhance the bioactivity and the mechanical properties of YZP coatings for dental implants. Based on microstructural studies performed on the deposited coating, a distinguished lamellar structure comprising YZP and TiO₂ was observed. It was found that the reinforcement of TiO₂ in YZP coating significantly reduced the crack due to the improved densities and the lamellar structure. The mechanical properties were also found to improve with 90% of hardness, 45% of adhesion strength and 54% of Young's Modulus with TiO₂ addition, which is desirable for dental implants. An in-vitro bioactivity test was then conducted by immersing the coatings in a simulated body fluid (SBF). As a result, an apatite formation was found on the YZP/TiO₂ coating surface after 3 days of immersion. Besides, it was verified in an XRD analysis that the crystalline TiO₂ was found in a rutile phase which was highly effective in generating apatite (natural mineral in human bones) on YZP coatings, proving that the bioactivities of the coating were significantly improved. Further studies were also performed on the SBF treatment, which took up to 14 days also demonstrated that only a small decrease in hardness was noted, indicating that YZP/TiO₂ coatings had reached an excellent mechanical stability.