Grain size, crystalline phase and fracture toughness of the monolithic zirconia

PURPOSE: This study evaluated the relationship among translucency, crystalline phase, grain size, and fracture toughness of zirconia. MATERIALS AND METHODS: Four commercial zirconia - Prettau(®)Anterior(®) (PA), Prettau(®) (P), InCorisZI (ZI), and InCorisTZI (TZI)- were selected for this study. The bar specimens were prepared to determine fracture toughness by using chevron notched beam method with four-point bending test. The grain size was evaluated by a mean linear intercept method using a scanning electron microscope. X-ray diffraction and Rietveld refinement were performed to evaluate the amount of tetragonal and cubic phases of zirconia. Contrast ratio (CR) was measured to investigate the level of translucency. RESULTS: PA had the lowest fracture toughness among other groups (P < .05). In addition, the mean fracture toughness of P was significantly less than that of ZI, but there was no difference compared with TZI. Regarding grain size measurement, PA had the largest average grain size among the groups. P obtained larger grain size than ZI and TZI (P < .05). However, there was no significant difference between ZI and TZI. Moreover, PA had the lowest CR value compared with the other groups (P < .05). This means PA was the most translucent material in this study. Rietveld refinement found that PA presented the greatest percentage of cubic phase, followed by TZI, ZI, and P, respectively. CONCLUSION: The different approaches are used by manufacturers to fabricate various types of translucent zirconia with different levels of translucency and mechanical properties, which should be concerned for material selection for successful clinical outcome.