The Impact of Core/Veneer Thickness Ratio and Cyclic Loading on Fracture Resistance of Lithium Disilicate Crown

Abstract

Purpose: To investigate the effect of core/veneer thickness ratio on the fracture strength of lithium disilicate crowns subjected to cyclic loading in a simulated oral environment. Materials and Methods: A typodont molar tooth received a standard complete crown preparation according to the manufacturer's instructions. Sixty lithium disilicate crowns were prepared and assigned to three groups with the following core/veneer thickness ratios A: 0.7 (0.6/0.9), B: 1.1 (0.8/0.7), and C: 2 (1.0/0.5). The cores were milled from lithium disilicate e.max CAD blocks and hand-layered using e.max Ceram. Ten specimens from each group acted as control, while the remaining ten specimens were subjected to thermal mechanical loading in a chewing simulator. All specimens were then subjected to the single load to fracture test at 1 mm/min crosshead speed. Data were analyzed using two-way ANOVA, Tukey multiple comparison test, Pearson correlation test, and quadratic regression (p < 0.05).

Influence of Antagonist Material on Fatigue and Fracture Resistance of Zirconia Crowns

“…Also, in a finite element study, Yucel et al 27 demonstrated different stress distributions on the restoration, depending on the abutment materials; when a restoration was attached to dentin and epoxy resin die, the distribution of stresses was similar, but that was different when the restoration was bonded to a metal die. 27 Therefore, epoxy resin material has been used in several previous studies [28][29][30][31][32][33] as a simulation of the natural teeth.…”

Influence of Core‐Veneer Thickness Ratio on the Fracture Load and Failure Mode of Zirconia Crowns

“…However, it appears that the thermomechanical cycling test in water did not significantly affect restoration strength, insofar as the mean fracture load values between the same CVT ratios were not significantly different. Previous studies on bilayered systems have reported similar results . One explanation for these results lies in the possibility that the zirconia core was veneered, and, hence, did not come into direct contact with the chewing forces; therefore, the veneering ceramic may have acted as a protective layer .…”

“…Previous studies on bilayered systems have reported similar results. 36,39 One explanation for these results lies in the possibility that the zirconia core was veneered, and, hence, did not come into direct contact with the chewing forces; therefore, the veneering ceramic may have acted as a protective layer. 31 Furthermore, the degradation mechanism is usually very slow in oral temperatures, and this may lead to a significant decrease in the strength of dental restorations over periods of several decades of wear.…”

“…Moreover, the core‐veneer thickness ratio and the properties of the veneering material affect the strength of bilayered restorations, as well as the ideal core proportion for sufficient support of the veneering material is difficult to determine . Several studies addresses an increase in the strength of bilayered systems as core‐veneer thickness increases, although others have found that strength has not being dependent on relative layer thicknesses . These contradictory findings suggests the need for more investigation to optimize the core‐veneer thickness ratio required for different all‐ceramic restorations.…”

“…4,36 Several studies addresses an increase in the strength of bilayered systems as core-veneer thickness increases, 12,15,16,19,[21][22][23][24] although others have found that strength has not being dependent on relative layer thicknesses. 25,[39][40][41] These contradictory findings suggests the need for more investigation to optimize the core-veneer thickness ratio required for different all-ceramic restorations.…”