Production of ZrO2-Si3N4 composite for dental applications

Demand for hygienic and non-allergic materials with the developing technology has significantly increased in dental applications. Therefore, zirconia ceramics are considered as an important dental material. Yttria stabilized tetragonal zirconia polycrystal (Y-TZP) has been used in dental applications since 1989 because of its superior mechanical properties, aesthetically pleasing appearance, low tendency to plaque accumulation and excellent biocompatibility. However, there are some drawbacks of zirconia which are related to low temperature degradation and its radiopaque property. In this project, to overcome these drawbacks by combining of beneficial properties of silicon nitride that is its antibacterial behavior, partial radiolucency, stability in aqueous environment and those of zirconia which are superior mechanical properties and translucency in visible region were studied. For this purpose, zirconia and silicon nitride composites (silicon nitride content varies between 0-20 wt. %) with necessary additives were formed as a bulk sample by uniaxial dry pressing. Sintering processes at 1500°C under air and nitrogen atmosphere furnace were done. After sintering processes, characterization tests were done to obtain phase development, physical, microstructural and optical properties. High X-ray absorption property of zirconia both caused the suppression of the silicon nitride peaks in the XRD pattern and prevention of the partial radiolucent property of silicon nitride for zirconia and silicon nitride composites. As the amount of silicon nitride in zirconia was increased, the bulk density decreased and hardness of the composite declined from 11.7 to 2.6 GPa. Zirconia and silicon nitride composites did not show the expected antibacterial activity. The possibility of oxide layer formation was evaluated by FTIR analyses and other causes were discussed.