Influence of Round-Shaped Block in Flexural Strength of Ce-TZP/Al₂O₃ Nanocomposite with Different Sintering Processes

Zirconia ceramic combined with CAD/CAM fabrication procedures allow the production of large and complex restorations as a superstructure for tooth abutments, bridge frameworks and dental implants. A new generation of zirconia ceramic with better mechanical properties is emerging and is indicated for use in implant abutment. To establish the clinical application of this new zirconia ceramic (C-Pro NANOZR:ceria-stabilized tetragonal zirconia polycrystal alumina nanocomposite), we examined the flexural strength of C-Pro NANOZR for three kinds of round-shaped specimens in different burning methods.<br/> Full-, middle- and pre-sintered C-Pro NANOZR were used in this study. Specimens were assigned to four groups of cross-sectional shape(R=0, R=0.5, R=1.0 and R=1.7). The three-point bending test of specimens was performed according to ISO 6872 in a universal testing machine at the cross head speed of 1 mm/min and with a support span length of 30 mm. After fracture, the obtained values were subjected to statistical analysis (ANOVA and Fisher's PLSD test, p＜0.05). After the three-point bending test, the fractured surface of the specimen was observed by a scanning electron microscope (SEM) at 150× magnification to determine the mode of failure.<br/> The following means in MPa were found for the different groups of full-, middle- and pre-sintered C-Pro NANOZR:R=0(906.0, 740.0, 997.4), R=0.5(918.2, 883.1, 1,101.3), R=1.0 (995.0, 988.5, 1,174.1), R=1.7 (1,212.6, 1,011.4, 1,275.9). The flexural strength was significantly different between the full-, middle- and pre-sintered C-Pro NANOZR in R=0, R=0.5, R=1.0 and R=1.7. Large corner radius exhibited significantly higher flexural strength values than small corner radius in the round-shaped blocks. Pre-sintered blocks showed the highest flexural strength values. From SEM images of the fractured surface of C-Pro NANOZR, the middle- and pre-sintered CPro NANOZR exhibited sharp fracture of the corner, however, the full-sintered C-Pro NANOZR indicated blunt fracture. The full-sintered C-Pro NANOZR showed crack-blunting from the edge of the radius.<br/> Based on the methodology employed, it was concluded that the corner radius of the round-shaped blocks and the difference in burning method had a significant influence on flexural strength values.