Effect of aging and testing method on bond strength of CAD/CAM fiber-reinforced composite to dentin.

ABSTRACT

OBJECTIVES: To evaluate and compare the outcomes of shear (S) and microtensile (µT) 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 (5×5×5mm) for µT. Sixty extracted human molars were flattened to obtain dentin surfaces and randomly divided in four groups (n=15) (1) SC samples tested in shear 24h after bonding; (2) µTC samples tested in µT 24h after bonding); (3) µTF samples submitted to mechanical fatigue prior to µT test, and; (4) µTT thermocycling prior to µT 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 0.75mm/min and data analyzed using Weibull distribution (p<0.05). RESULTS: Weibull contour plots showed a significantly lower characteristic strength (η) and Weibull modulus (m) for SC (η=6.9MPa and m=1.4) compared to µTC (η=20.9MPa and m=4.5). Fatigued and thermocycled µT groups presented significantly reduced characteristic strength (η=3.1MPa and η=4.1MPa, respectively) compared to µTC. Weibull modulus was significantly reduced only for SC and µTF groups compared µTC. 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.