Effect of preparation depth on the fracture resistance of two monolithic ceramic laminate veneers

Abstract

Aim: This study aims to measure and compare the fracture resistance of two CAD/CAM monolithic ceramic veneers with and without dental preparation.Materials and methods: Twenty-eight extracted mandibular premolars were selected and randomly assigned into four groups (n = 7): Group NP/ED = No preparation with 0.3 mm thick ceramic veneer (IPS e.max CAD); Group P3/ED = Tooth preparation with 0.3 mm depth and 0.3 mm ceramic veneer (IPS e.max CAD); Group NP/TT = No preparation with 0.3 mm thick ceramic veneer (Top translucent zirconia, Upcera); and Group P3/TT= Tooth preparation of 0.3 mm and 0.3 mm ceramic veneer (Top translucent zirconia, Upcera). In all groups, the veneers extended 1 mm to the occlusal surface of the buccal cusp. All the preparations were digitally scanned, and the veneers were milled using CAD/CAM milling machine. After surface treatment and cementation of veneers, all groups were thermocycled (2000 cycles, 5°C-55°C) and subjected to fracture resistance test under the occlusal compressive load at cross-head speed 0.5 mm/min. The failure mode analysis was inspected at X 25 maginifications. Data were statistically analyzed with one-way analysis of variance (ANOVA), followed by post-hoc test for pairwise comparison of the groups, Differences were considered significant at P<0.05. Results:The mean fracture resistance (M±SD) was 436.71± 63.68 in NP/ED, 561.43±88.21 in P3/ED, 458.57±46.70 in NP/TT, 582.86±66.51 in P3/TT. There were significant differences in the mean values of fracture resistance between the groups (P ≤ 0.001). NP (no preparation) showed mean fracture resistance values significantly lower than P3 (0.3 dental preparation depth) groups irrespective to the ceramic veneering material type. However, ED veneers showed non-significant differences mean fracture resistance values lower than TT veneers irrespective to the preparation depth. Cohesive failure mode (laminate fracture) was predominant in P3/ED group. While mixed failure was common in NP/ED group. On the other hand, in both NP/TT and P3/TT (translucent zirconia veneer groups), showed more adhesive failure. Root fracture is uncommon in all groups.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.