effect of thermomechanical loading on fracture resistance and failure mode of new pressable zirconia-reinforced lithium disilicate onlay restoration

Background. insufficient information exists regarding the fracture resistance and failure pattern of newly developed zirconia-reinforced lithium disilicate (zl, vita ambria) onlays. this in vitro study compared the fracture resistance of two types of onlays: monolithic lithium disilicate (ld) and monolithic zl. methods. forty-eight ceramic onlay restorations were fabricated on epoxy dies using a maxillary first premolar model. the samples were divided into two main groups: ld and zl. half of each group was subjected to thermomechanical fatigue loading (tml) using a chewing simulator. all the samples were cemented with self-adhesive resin cement. subsequently, they were loaded until failure in a universal testing machine, and the fracture patterns and resistance were recorded. results. before tml, zl demonstrated the highest statistically significant mean fracture resistance (499.76±34.14n) compared to ld (470.40±27.38n). after tml, zl showed the highest non-statistically significant mean fracture resistance (429.27±131.42n), while ld’s mean fracture resistance decreased (377.31±62.18n). conclusion. monolithic zirconia-reinforced onlays demonstrated higher fracture resistance and a more favorable failure mode compared to ld. however, the impact of thermomechanical aging resulted in reduced fracture resistance for both materials, with a notable preference observed for zl.