Influence of Presintering Parameters on the Mechanical Properties of Presintered Dental Zirconia Block

This study aimed to investigate the effects of presintering parameters on the mechanical and microstructural properties of presintered zirconia block. The zirconia block was prepared using colloidal and cold isostatic pressing techniques and subsequently subjected to various presintering procedures at 850 °C, 900 °C, and 950 °C with two different heating rates (3 and 10 °C/min). All samples were evaluated in terms of hardness, density, and morphology. Results showed that the sample porosity decreased with increment in the presintering temperature. On the contrary, the Vickers hardness increased from 1.8 GPa at 850 °C to 2.7 GPa at 950 °C at 10 °C/min heating rate. The sintering temperature of 950 °C with 3 °C/min heating rate was considered the most suitable parameter among presintering procedures, with high theoretical density (96.2%) and appropriate hardness (1.27 GPa) that are within the range of commercial zirconia block hardness values for restoration milling procedure. Furthermore, to sinter the block samples successfully without considerable failure, the heating and cooling rates should be lowered to ≤3 °C/min. Therefore, on the basis of these results, the forming methods and the sintering temperature influence the resultant mechanical and microstructural properties of the final sample

Effect of sintering temperature on the aging resistance and mechanical properties of monolithic zirconia

This study aimed to investigate the effect of final sintering temperature and grain size on the aging resistance and mechanical properties of zirconia fabricated through colloidal and cold isostatic pressing. Zirconia samples appearing as cylindrical discs were prepared and subjected to five different sintering temperatures ranging from 1400 °C to 1600 °C. Grain pullout and rough surfaces were detected on the micrographs of aged samples sintered at more than 1500 °C, indicating surface degradation. The highest flexural strength of non-aged and aged samples was obtained at 1500 °C, whereas excellent fracture toughness was demonstrated by the sample sintered at 1550 °C under non-aged and aged conditions. The hardness properties of all of the samples sintered at various temperatures did not significantly differ. Under the aged conditions, their hardness properties slightly decreased. Overall, the mechanical performance of the aged zirconia slightly deteriorated but remained acceptable for use in an oral environment for 15–20 years. Mechanical performance evaluation after aging revealed that 1500 °C was the appropriate sintering temperature. The mechanical properties and aging resistance of the zirconia samples were greatly dependent on sintering temperature during fabrication. Keywords: Monolithic zirconia, Aging, Biaxial flexural strength, Fracture toughness, Monoclinic transformatio