Fracture toughness evaluation at the interface of universal adhesives and tooth dentine using mini-interfacial fracture toughness test

Abstract

Using a modified mini-interfacial fracture toughness test (mini-IFT) and a designed mould for notch preparation, this study assessed the bonding effectiveness of self-etch universal adhesive systems. A total of 20 selected non-carious third molars were divided into four groups; G1: Clearfil SE Bond, G2: Clearfil S3 Bond Plus, G3: 3 M-Single bond Universal, G4: Ivoclar Tetric N-Bond Universal. The teeth were sectioned to obtain 1.5 × 2 mm wide longitudinal rectangular sections. A single notch then was prepared at the adhesive/dentine interface using a designed mould. The mini-iFT test was done via a 4-point bend testing until failure and the K IC was calculated. All specimens were observed using SEM. The data of each experimental group were analysed using one-way analysis of variance (ANOVA) and Weibull analysis. The results of one-way ANOVA did not indicate a significant difference between the four study groups (p > 0.05). The Weibull analysis showed that the characteristic strength of the groups ranges from 1.20 MPa to 1.39 MPa. The Weibull modulus m showed almost a similar plot in all study groups. According to SEM observations, the mode of failure for all samples was considered adhesive. Based on the results, the differences in mean mini-iFT values between the UAs and conventional self-etch adhesive group were not statistically significant. However, based on the left-censored data and the sample loss before and during the aging process, SE-bond showed better bonding quality than UAs. The low Weibull modulus in this study indicates nonuniform notches. More studies are needed to develop a repeatable and feasible method for preparing equal notches in mini-IFT test.