Fracture Strength of Crowns Made from Current CAD/CAM Materials

Objectives: The aim of this study was to evaluate the fracture strength of crowns made from current CAD/CAM materials. In addition the influence of the occlusal crown thickness and chewing simulation on the fracture strength was evaluated.
Methods: Crowns were fabricated from lithium disilicate (IPS E.max CAD, Ivoclar Vivadent), zirconia reinforced lithium silicate (VITA Suprinity) and a hybrid ceramic (VITA Enamic) with an occlusal of 1.0 mm or 1.5 mm, respectively (n=16). Crowns were cemented with Multilink Automix (Ivoclar Vivadent) on composite dies (Z100 3M ESPE). Subgroups of 8 specimens were loaded with 49N in a chewing-simulator for 1,200,000 cycles with thermocycling. All specimens were loaded till fracture in a universal testing machine. Three-way ANOVA was used to detect statistical interaction. Differences regarding the materials were tested with one-way ANOVA and a Post-Hoc Tukey-Test. Pair-wise comparison of the other parameters was done with T-tests.
Results: All crowns survived the chewing simulation. Fracture strengths are shown in the Table. The material had a significant influence on the fracture resistance (p<0.05), while chewing-simulation had only a significant influence for thick E.max CAD crowns.
Conclusions: All crowns revealed fracture strength above the clinically expected loading forces. Therefore the durability of the tested CAD/CAM materials seems promising.
This study was supported by Ivoclar Vivadent, 3M ESPE and Vita Zahnfabrik.