Fracture toughness of chairside CAD/CAM materials – Alternative loading approach for compact tension test

•Fracture toughness (KIC) of a group of CAD/CAM nonmetallic blocks was measured.•Two were glass-ceramic-based, 2 were resin-composite-based, and one feldspathic porcelain, testing both glass-ceramic materials before and after firing.•An alternative loading approach was followed, using a modified test arrangement that was quite easy to follow, with a simplified specimen preparation.•ANOVA revealed significantly different mean KIC among materials, with the fired specimens revealing significantly highest values.

ObjectiveThis 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.MethodsRectangular-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 ¼ of the notch before compressive load was applied at a cross-head speed of 0.5 mm/min. Fracture load was recorded and KIC calculated. Data was statistically-analyzed with one-way ANOVA at 95% confidence level and Tukey's tests.ResultsMeans and SDs of KIC in MPa m1/2 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.SignificanceMean KIC values of the tested materials varied considerably, however, none of them reached mean KIC of dentin (3.08 MPa m1/2) 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.