Fracture Toughness and Dynamic Elastic Moduli of Commercial Core Materials

The main deficiency of dental cores is the inability to withstand the functional stress imposed, which limits their use under high stress conditions.

Objective: To evaluate the fracture toughness and dynamic elastic moduli for five commercial cores materials.

Methods: Five commercial cores, RockCore (Danville Materials), CosmeCore (Cosmedent Inc), ParaCore (Coltene/Whaledent), MultiCore Flow (Ivoclar/Vivadent) and Filtek Supreme (3M/ESPE) were used. Notchless triangular prism (NTP) specimens (6mm X 6mm x 12mm) were made and soaked in deionised water at 37ºC for seven days prior to testing. NTP fracture toughness (n=15) was evaluated using an Instron Universal testing machine (model # 3345) at a crosshead speed of 0.1mm/min. The density of the specimens (n=3) was determined by water displacement method. The dynamic Young's, shear moduli and Poisson's ratio (n=3) were determined by an ultrasonic method using lithium niobate piezoelectric crystals at 10MHz resonant frequency. Statistical analysis of the data was conducted using one way analysis of variance (ANOVA) and a Tukey B rank order test at p=0.05.

Results: The fracture toughness of the core materials ranged from 0.89 to 1.69MPa.m^0.5. The dynamic Young's, shear moduli and Poisson's ratio ranged from 14.44 to 22.64GPa, 5.59 to 9.38GPa and 0.204 to 0.309 respectively.

Conclusions: The NTP fracture toughness of RockCore was significantly lower among the five core materials, P<0.05. Filtek Supreme exhibited significantly higher dynamic Youngs's and shear moduli than the rest of the core materials, p<0.05. Values of Poisson's ratio of the five core materials were not significantly different at p>0.05.