This study aims to measure and compare the fracture resistance of two CAD/CAM ceramic veneers with and without dental preparation.Twenty-eight mandibular premolars were randomly assigned into four groups (n = 7): NP/ED = No preparation with 0.3 mm veneer (e.max CAD); P3/ED = Tooth preparation with 0.3 mm depth and 0.3 mm veneer (IPS e.max CAD); NP/TT = No preparation with 0.3 mm veneer ( translucent zirconia); and P3/TT= Tooth preparation of 0.3 mm and 0.3 mm veneer ( translucent zirconia). All the preparations were digitally scanned, and the veneers were milled. After cementation of veneers, all groups were thermocycled and subjected to a fracture resistance test. The failure mode analysis was inspected. Data were statistically analyzed with one-way ANOVA, followed by post-hoc test (P<0.05). There were significant differences in the mean fracture resistance between the groups. NP showed mean fracture resistance significantly lower than P3 groups irrespective of the ceramic material type. ED showed non-significant differences in fracture resistance lower than TT veneers irrespective of the preparation depth. Cohesive failure mode was predominant in P3/ED. While mixed failure was common in NP/ED. On the other hand, both NP/TT and P3/TT showed more adhesive failure. A root fracture is uncommon.
Conclusions: Preparation within the enamel is necessary to increase the fracture resistance of the veneered premolars. The type of ceramic material had an impact on the failure mode of laminate veneers.