Effect of Aging and Testing Method on Bond Strength of CAD/CAM Fiber-Reinforced Composite to Dentin

Objective. To evaluate and compare the outcomes of shear (S) and microtensile (mu T) bond strength tests of CAD/CAM fiber-reinforced composite (FRC) to dentin. Aging with either fatigue or thermocycling were conducted for comparison with baseline microtensile group. Methods. CAD/CAM FRC (Trinia, Bicon LLC, Boston, USA) blocks were milled to 3-mm diameter cylinders for shear and to blocks (5 x 5 x 5 mm) for mu T. Sixty extracted human molars were flattened to obtain dentin surfaces and randomly divided in four groups (n = 15): (1) SC: samples tested in shear 24 h after bonding; (2) mu TC: samples tested in mu T 24 h after bonding); (3) mu TF: samples submitted to mechanical fatigue prior to mu T test, and; (4) mu TT: thermocycling prior to mu T test. Bonding system was applied onto the FRC material (Cera-Resin Bond, CRB, Shofu Dental, Kyoto, Japan). A conventional three-step adhesive system (All-bond 3, Bisco, Schaumburg, USA) was use with a self-cure resin cement (C&B resin cement, Bisco, Schaumburg, USA). Bond strength tests were conducted at 0.75 mm/min and data analyzed using Weibull distribution (p < 0.05). Results. Weibull contour plots showed a significantly lower characteristic strength (eta) and Weibull modulus (m) for SC (eta = 6.9 MPa and m = 1.4) compared to mu TC (eta = 20.9 MPa and m = 4.5). Fatigued and thermocycled mu T groups presented significantly reduced characteristic strength (eta = 3.1 MPa and eta = 4.1 MPa, respectively) compared to mu TC. Weibull modulus was significantly reduced only for SC and mu TF groups compared mu TC. Failure predominantly occurred at the cement/FRC interface. Significance. FRC bonded to dentin samples presented lower Weibull modulus and characteristic bond strength when immediately tested in shear compared to microtensile. Aging through thermocycling or mechanical fatigue significantly reduced the characteristic strength in microtensile testing, with the majority of failures emerging between restoration material and cement interface. (C) 2018 The Academy of Dental Materials. Published by Elsevier Inc. All rights reserved.