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

Objective. This in-vitro study determined plane-strain fracture toughness (K-IC) 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 0.5 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. Results. Means and SDs of K-IC in MPa m(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 K-IC values. Significance. Mean K-IC values of the tested materials varied considerably, however, none of them reached mean K-IC of dentin (3.08 MPa m(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. (C) 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.