Micro-shear Bond Strength of Self-Adhesive Versus Conventional Low-viscosity Composite Resins: In vitro Study

Aims: This study aimed to evaluate the micro-shear bond strength of a self-adhesive versus conventional low-viscosity composite resins adhered to enamel.

Study Design: In vitro study.

Place and Duration of Study: Dental Clinic of the Western State University of Paraná, between October 2022 and September 2023.

Methodology: In this in vitro study, the crowns of ten bovine incisor teeth were separated from the roots and embedded in polyvinyl chloride cylinders with acrylic resin. The teeth were divided into two groups (n=5) according to the type of low-viscosity composite resin used on the enamel, resulting in a total of fifteen specimens: one group with self-adhesive composite resin and another with conventional composite resin. Specimens measuring 3 × 2 mm were prepared with low-viscosity composite resin and applied to the adhesive areas according to their respective groups. The micro-shear test was carried out after 7 days of immersion in distilled water in a universal mechanical testing machine with a 50 kg load cell. The statistical analysis in this study employed the Shapiro-Wilk test to assess data normality. Due to non-normal distribution, the non-parametric Mann-Whitney U test was utilized for group comparisons (p < 0.001). Supplementary analyses were performed using the Dwass-Steel-Critchlow-Fligner (DSCF) test for multiple comparisons (p < 0.001) to detect intergroup differences. Fractures were analyzed using a stereoscopic magnifying glass at 40x magnification.

Results: The lowest micro-shear bond strength was observed in the self-adhesive composite resin group, while the highest was observed in the conventional composite resin group. On average, the micro-shear bond strength was higher for the conventional composite resin group compared to the self-adhesive composite resin group (p < 0.001). Most fractures in the conventional composite resin group were mixed, whereas in the Self-Adhesive composite resin group they were predominantly adhesive.

Conclusion: Based on this study, it can be concluded that self-adhesive flowable composite resin exhibited lower enamel bond strength values compared to conventional flowable composite resin.