Effect on in vitro fracture resistance of the technique used to attach lithium disilicate ceramic veneer to zirconia frameworks

ObjectivesThis in vitro study should assess the fracture resistance of veneered zirconia-based crowns with either luted or fused veneer.MethodsThirty-two identical zirconia frameworks (IPS e.max ZirCAD; Ivoclar/Vivadent), were constructed (inLab 3.80; Sirona Dental Systems). All frameworks were veneered with CAD/CAM-fabricated lithium disilicate ceramic (IPS e.max CAD; Ivoclar/Vivadent). For half the crowns (n = 16) the veneer was luted to the framework (Multilink Implant; Ivoclar/Vivadent); for the other it was fused (IPS e.max Crystall./Connect; Ivoclar/Vivadent). Half of the specimens were then loaded until failure without artificial aging; the other half underwent artificial aging before assessment of the ultimate load. To compare the two techniques further, finite element analysis (FEA) and fractographic assessment using SEM and EDX analysis were conducted. Statistical assessment was performed by use of non-parametric tests.ResultsInitial fracture forces were higher in the fusion group (mean: 1388 ± 190 N versus 1211 ± 158 N). All specimens were insensitive to artificial aging. FEA showed that tensile stresses in the veneer at the frame–veneer interface were much higher for crowns with luted veneer; this may be the reason for their lower fracture resistance. Fractographic analysis revealed that both fused and luted specimens had cohesive and adhesive fracture patterns which resulted in partial delamination of the veneer.SignificanceFused crowns are superior to luted crowns. Comparison of fracture resistance with the maximum loads which may occur clinically (Fmax = 600 N on one tooth) suggests both techniques might be used clinically, however.