Influence of thickness and restorative system on the mechanical behavior of CAD/CAM minimally invasive occlusal veneers - in vitro study

Aim: The aim of this study was to evaluate the physical-mechanical behavior of the occlusal veneers when subjected to thermomechanical cycling.
Materials and Methods: Sixty specimens were divided into 04 groups (n=15 per group), according with the different restorative materials and thicknesses: material – lithium dissilicate LD (IPS e.max CAD, Ivoclar Vivadent) and nano- ceramic-resins NCR (ESPE Lava Ultimate, 3M); thickness - 0.6 and 1.2mm. The occlusal veneers were bonded over human flattened fresh extracted molars with dual-polymerizing luting agent (Variolink N, Ivoclar Vivadent and RelyX Ultimate 3M) using the respective adhesive system following the selective-etch technique (self-etch in dentin and total etch in enamel). The resin cement was light cured for 40 seconds each face, using a LED light cure equipment (BlueStar II, Microdont, 1100 mW/cm2). The response variables consisted of veneer survival rates (crack formation, catastrophic cracks and debonding) when subjected to thermal cycling from 5° to 55° C and simultaneous mechanical cycling performed at load intensities of 100, 200, 300, 400 and 450N for 20,000 cycles each.
Result: Data were submitted to the Kruskall Wallis test and Pairwise Comparison, adopting a significance level of 5%. NCRs presented a lower incidence of failures (p<0.05) when compared to LD. According to thickness factor, 1.2mm thick occlusal veneers withstand higher cycling loads.
Conclusion: NCR occlusal veneers with 1.2mm thickness presented superior physical-mechanical behavior than lithium disilicate and 0.6mm restorations.