Influence of Different Preparation Designs on Fracture Resistance of Full-Coverage Occlusal Veneers After Thermo-Mechanical Aging Simulation

Abstract

Aim: To evaluate the fracture resistance maxillary molars restored with lithium disilicate glass-ceramic (LDG) occlusal veneers with two preparation designs. Subjects and methods: Twenty extracted maxillary molars were assigned to two groups (n = 10). In group 1 (GROUP S ), the teeth received a preparation for a conservative full-coverage occlusal veneer restoration with a 90 rounded shoulder margin. In group 2 (GROUP c), were prepared with a minimally invasive chamfer. LDG restorations (IPS e.max CAD) were obtained with the Cerec 3 CAD/CAM system and luted with Variolink II cement. After thermo-mechanical aging (120,000 cycle with vertical movement 1mm, horizontal movement 3mm and frequency 1.6Hz), All the samples were individually mounted on the Instron testing machine with a load cell of 5 KN and fracture test was done by compressive mode of load applied occlusally using a metallic rod with spherical tip (5.6 mm diameter) at cross-head speed of 1mm/min. The load required to fracture was recorded in Newton and tabulated to be statistically analyzed. The fractured specimens were examined to detect the mode of failure. Results: The fracture resistance of samples with chamfer finish line (2453.2 N ± 104.83) was higher than the values of samples with shoulder finish line (2440.6 N ± 119.36) but with no statistical significant difference (p value > 0.05). Most of the observed specimens exhibited restorable fractures. Conclusion: This study demonstrated similar satisfactory performance of the two considered preparations designs for occlusal veneer with lithium disilicate glass-ceramic. Conclusion: A new minimally invasive occlusal veneer preparation with marginal chamfer exhibited encouraging fracture resistance that were comparable to those of a standard conservative preparation for the restoration of molars with CAD/CAM lithium disilicate occlusal veneers.