Evaluation of fracture strength for single crowns made of the different types of lithium disilicate glass-ceramics.

Lithium disilicate glass-ceramics with high mechanical strength are being widely used as ingots for heat-pressing technique and blocks for CAD/CAM processing in clinical dentistry as aesthetic prosthetic materials. The purpose of this study was to evaluate the fracture strength of single crowns made of the different types of lithium disilicate glass-ceramics. Single crowns for mandibular second premolar with thickness of 1.5 mm were manufactured. IPS e.max Press and Amber Press crowns were produced by heat-pressing, and IPS e.max CAD and Rosetta SM crowns was produced by milling. Amber Lisi-POZ crown was produced by heat-pressing on the zirconia frame. Fracture strength test was performed at 10 degrees of inclination toward the load after bonding crown on metal abutment using dual-curing resin cement. Statistical analysis of fracture strength was conducted through Weibull statistics (n = 15 per group). The mean fracture strength (2087.4 N) of Amber Lisi-POZ group produced by heat-pressing on the zirconia frame was significantly higher than that (1479.8 N) of Rosetta SM group produced by milling. Weibull coefficients for IPS e.max CAD and Rosetta SM groups were, respectively, 14.44 and 9.39, and those for IPS e.max Press, Amber Press, and Amber Lisi-POZ groups produced by heat-pressing were in the range between 4.72 and 5.16. In conclusion, the fracture strength of Amber Lisi-POZ crown with zirconia framework was the highest, and the buccal cusps fractured from the central groove of the all crowns. Weibull modulus of crowns produced by milling was higher than those of crowns produced by heat-pressing.