CERASMART Composite Crowns and IPS Empress Ceramic Crowns: Fracture Strength

Objectives: To compare the fracture strength of ceramic crowns (IPS Empress^® CAD (IPS), Ivoclar Vivadent) with that of composite crowns (CERASMART™ (CE), GC America) milled with CEREC III (Sirona Dental).
Methods: Forty molars of similar shape and size were prepared. Twenty ceramic crowns and twenty composite crowns were cemented utilizing Rely-X™ Ultimate resin cement (3M). Both groups were subjected to 5000 cycles of thermocycling (5°-55°) followed by compressive loading to catastrophic fracture. A non-parametric significance testing (Mann-Whitney U test) was conducted to assess the difference in fracture strength between the two materials. The difference in mode of fracture between the two materials was assessed via the chi-square test. The association between fracture strength and cement space was evaluated via the Spearman correlation, with a separate analysis conducted for each material.
Results: IPS had a median (IQR) fracture strength of 5.96 (2.73) MPa. CE had a median (IQR) fracture strength of 12.64 (3.32) MPa. A statistically significant difference was found between the two groups (P< 0.001). No significant correlation was found between cement space and fracture strength except for the mesial cervical line for IPS and the distal marginal ridge for CE. The study showed a 55% adhesive fracture rate for CE, a 45% adhesive fracture rate for IPS, a 45% mixed fracture rate for CE and a 55% mixed fracture rate for IPS. The difference was not significant (P= 0.527). No cohesive fractures were reported.
Conclusions: Within the limits of the present study, the performance of CE relative to that of IPS was higher as the CE demonstrated higher fracture strength than IPS.