Does reducing the acid-etching time increase the micro-tensile bond strength of a bulk fill composite to dentin using different universal adhesives?

Abstract

The objective of this in vitro study was to evaluate whether a reduced phosphoric acid etching time would have an impact on the microtensile bond strength (µTBS) of different universal adhesives to dentin using a bulk-fill composite. Forty-eight freshly extracted non-carious human molars were immersed in acrylic resin and cut to a height of 4 mm from the highest tubercle crest towards the cervical region. Dentin surfaces were subjected to 37% phosphoric acid pretreatment for 0, 3, or 15 s (s), rinsed with water for 20 s and gently dried, and wet-bonded. Two universal adhesives (Single Bond Universal, 3 M-ESPE; Adhese Universal, Ivoclar Vivadent) were used in this study. The Tofflemire matrix was added to each tooth, and a bulk-fill resin composite (Tetric EvoCeram Bulk-Fill, Ivoclar Vivadent) with a thickness of 5 mm was applied. The tooth composite blocks were cured using a light-emitting diode unit for either 20-40 s. Twelve groups were included (four teeth per group). All samples were immersed in distilled water for 24 h at 37°C. The samples were sectioned under water cooling to obtain multiple sticks approximately 1.0 × 1.0 × 8 mm in size using a non-trimming technique with water cooling. The µTBS test was performed (n = 20 sticks for each group). The data were analysed via a Welch analysis of variance (ANOVA) and the Games-Howell post hoc test (SPSS 23.0). The interactions between the three factors were analysed with a three-way ANOVA. Significant differences were observed among the experimental groups (p < 0.05). Both adhesives exhibited the highest bond-strength values in the groups for which acid was applied to the dentin for 3 s and the composite resin was light-cured for 40 s, resulting in statistically significantly higher values for these two groups compared with the other groups (p < 0.05). Reducing the etching time to 3 s compared to the traditional etching time of 15 s increased the micro-tensile bond strength of the bulk-fill composite to dentin using universal adhesives.