| Introduction. This study examined the differences in physical properties of Y-TZP sintered in conventional and microwave furnaces.Material and methods. (I) Flexural strength: Twenty bars of Y-TZP were prepared from Zircad blocks (Ivoclar Vivadent, Buffalo, NY) to the dimension of 25mm x 4.5mm x 2.5mm. Ten samples were utilized for sintering in a conventional zirconia furnace (Sintramat, Ivoclar Vivadent). The remaining ten samples were sintered in a microwave furnace (ThermWave, TW 1.3, EPL Ceramic Materials LLC, Youngstown, NY). The sintering temperature used for both techniques was 1500°C. Microwave sintering of the samples was completed within an hour while conventional sintering was completed within eight hours. All specimens were tested to measure the flexural strength with the three point bending test using an Instron Universal testing machine (Instron series 4204 loading frame, Norwood, MA) with a cross head speed of 0.5 mm/min. (II) Bulk density measurements: Density was measured by applying the Archimedes method according to the American Society for Testing and Materials standards (ASTM). (III) Pre and Post-sintering measurements: The sintered samples were measured by digital micrometer with respect to their length, width, and thickness. The differences between the pre-sintered and the post sintered samples were recorded and firing shrinkage was calculated. (IV) Microstructure characteristics: the phase composition and average grain size of these ceramics were examined using X-ray diffraction. Microstructure characteristics were studied by scanning electron microscopy (SEM).Results. Results indicated no statistically significant difference between conventional and microwave sintering furnace for either flexural strength, t18=0.49, p=0.63, or density, t 18=0.07, p=0.95. Samples in both groups exhibited a uniform firing shrinkage of &ap 24.6% in all dimensions, which is similar to the manufacturer's specifications. The surface of selected samples examined under a scanning electron microscope showed no visible difference in grain shape or porosity size between the two sintering methods. The surface elemental analysis revealed presence of Zr and O2 on the surface of all samples.Conclusion. Under conditions of this study, it appears that either microwave or conventional zirconia furnace satisfies ordinary processing requirements related to processing zirconia for dental use. Microwave energy provides uniformity of heating, allowing the use of higher heating rates to increase productivity and provide energy savings. |
