Similar results were presented in a study of Traini et al. as it was concluded that ZLS was comparable to that of existing zirconia-based ceramics and was suitable for oral function even in the posterior regions. In the literature, there have been few studies on this ceramic and a limited number of them include the failure load of the material. In one of these studies, Preis et al. compared the fracture strength of ZLS molar crowns (adhesive cementation 2612 ± 853 N; conventional cementation 1848 and 1891 N) with LDS crowns (adhesive cementation 2528 ± 668 N) and concluded that they could be compared with LDS ceramics. Although adhesive cementation increased the fracture strength of the material, it was not statistically significant.

The difference from the present study was Celtra Duo (DeguDent) which has lower flexural strength than Vita Suprinity and no need for crystallization. In another study, fracture strength of different monolithic all ceramic implant-supported crowns were compared, and the highest values were observed in ZLS ceramic crowns (3056 ± 642 N; IPS e.max CAD crowns 2377 ± 572 N). It was also concluded that comparison of luting agents showed no significant difference in fracture strength. On the contrary, the failure load of group ZL-M (1750.28 ± 314.96 N) was significantly lower than group L-M (2891.88 ± 410.12 N), and the first hypothesis was rejected. Different results may be associated with cementation type or restoration design (differences in abutment type, porcelain thickness, cusps size, etc.).

Within the limitation of the present study, conventional cementation was used in contrast to cementation of glass ceramic restorations in clinical use. The luting agent fills the voids between the abutment and the inner surface of the crown and eliminates any premature contacts which may cause stress concentrations. Based on this, a conventional cement was used to focus on comparing materials without cement effect. Therefore, the effect of different cements should be evaluated in further studies.