Fracture toughness of chairside CAD/CAM materials Alternative loading approach for compact tension test.
OBJECTIVE This in vitro study determined plane strain fracture toughness (KIC) of five different chairside CAD/CAM materials used for crown fabrication, following alternative innovative loading approach of compact tension test specimens. METHODS Rectangular shaped specimens were cut from CAD/CAM blocks (n=10) Vita Mark II (Vident) (VMII) Lava Ultimate (3M/ESPE) (LU) Vita Enamic (Vident) (VE) IPS e.max CAD (Ivoclar Vivadent) crystallized and un crystallized (E max and E max U, respectively) and Celtra Duo (Dentsply) fired and unfired (CD and CD U, respectively) Specimens were notched with thin diamond disk prior to testing. Instead of applying tensile loading through drilled holes, a specially made wedge shaped steel loading bar was used to apply compressive load at the notch area in Instron universal testing machine. The bar engaged the top 1/4 of the notch before compressive load was applied at a cross head speed of 0.5mm/min. Fracture load was recorded and KIC calculated. Data was statistically analyzed with one way ANOVA at 95% confidence level and Tukey's tests. RESULTS Means and SDs of KIC in MPam(1/2) for VMII, LU, VE, E max, E max U, CD and CD U were: 0.73 (0.13) 0.85 (0.21) 1.02 (0.19) 1.88 (0.62) 0.81 (0.25) 2.65 (0.32) and 1.01 (0.15) respectively. ANOVA revealed significant difference among the groups (p<0.001) CD and E max had significantly highest mean KIC values. SIGNIFICANCE Mean KIC values of the tested materials varied considerably, however, none of them reached mean KIC of dentin (3.08MPam(1/2) previously reported. For E max and CD, specimens firing significantly increased mean KIC. The modified test arrangement was found to be easy to follow and simplified specimen preparation process.
Dental materials official publication of the Academy of Dental Materials