Mechanical stability of dental CAD-CAM restoration materials made of monolithic zirconia, lithium disilicate, and lithium disilicateestrengthened aluminosilicate glass-ceramic with and without fatigue conditions

Statement of problem. Studies investigating the mechanical stability of lithium disilicateestrengthened aluminosilicate glass-ceramic that do not require sintering after milling compared with other computer-aided design and computer-aided manufacturing (CAD-CAM) materials are lacking. Purpose. The purpose of this in vitro study was to investigate the flexural strength of CAD-CAM zirconia, lithium disilicate, and lithium disilicateestrengthened aluminosilicate glass-ceramics with and without fatigue conditions. Material and methods. Specimens (N=90, n=15) (12x4x3 mm) from the following CAD-CAM materials were prepared and polished: lithium disilicate glass-ceramic (IPS e.max CAD); lithium disilicateestrengthened aluminosilicate glass-ceramic (N!ce); and zirconium dioxide ceramic (IPS e.max ZirCAD). All specimens were divided into 2 subgroups: immediate testing without aging and simulation of aging by using a mastication simulator for 1 200 000 cycles (5 degrees C-55 degrees C). Thereafter, flexural strength testing was performed by using a universal testing machine (1 mm/min) on nonaged and aged specimens. The data were evaluated by using nonparametric 2-way ANOVA and Wilcoxon rank post hoc tests (alpha=.05). Results. Both the material type and aging significantly affected the results (P<.001). The interaction was not significant (P>.05). Under nonaged conditions, zirconium dioxide ceramic (1136 +/- 162 MPa) showed significantly higher mean +/- standard deviation flexural strength (P<.001) than lithium disilicate (304 +/- 34 MPa) and lithium disilicateestrengthened aluminosilicate glass-ceramic (202 +/- 17 MPa). The glass-ceramic groups were also significantly different from each other (P<.001). After aging, zirconium dioxide (1087.9 +/- 185.3 MPa) also presented significantly higher mean +/- standard deviation flexural strength (P<.001) than lithium disilicate (259 +/- 62 MPa) and lithium disilicateestrengthened aluminosilicate glass-ceramic (172 +/- 11 MPa) (P<.001). Aging significantly decreased the flexural strength of lithium disilicate (14.6%) (P=.03) and lithium disilicateestrengthened aluminosilicate glass-ceramic (14.5%) (P=.01) but had minimal effect on the zirconium dioxide ceramic (4.3%) (P=.29). Conclusions. Among the tested CAD-CAM materials, the mechanical performance of lithium disilicateestrengthened aluminosilicate glass-ceramic was comparable with that of lithium disilicate and considerably lower than that of zirconia. Aging decreased the flexural strength of both lithium disilicate and lithium disilicateestrengthened aluminosilicate glass-ceramic.

Automated summary

This in vitro study compared the flexural strength and aging conditions of CAD-CAM zirconia, lithium disilicate, and lithium disilicate-strengthened aluminosilicate glass-ceramics. The results showed that zirconia had the highest mechanical performance, while lithium disilicate-strengthened aluminosilicate glass-ceramic had the lowest. Aging significantly decreased the strength of lithium disilicate and lithium disilicate-strengthened aluminosilicate glass-ceramic.