Influence of adhesive application method and thermocycling on the bonding performance of different adhesive systems to dentin

Aim: To assess the effect of multiple layers application of different adhesive systems on the microshear bond strength (μSBS) of dentin with and without thermocycling. Materials and Methods: Two hundred forty sound human premolars had their enamel surfaces removed to expose even surfaces of dentin. The teeth were mounted in acrylic resin blocks and then assigned arbitrarily into four main groups (n = 60) representing the investigated adhesives (a self-etch [SE] adhesive, a total-etch [TE] adhesive, and a multimode [MM] adhesive used in TE and SE modes). Individually, the main groups were equally alienated into three subgroups (n = 20), each representing the number of the applied adhesive layers (one layer [1L], two layers [2L], and three layers [3L]). Then, each respective subgroup was divided subsequently into two equal divisions with n = 10 each according to thermocycling (with and without thermocycling). Each occlusal surface received three composite microrods. Prepared specimens were reserved in distilled water at temperature of 37°C until the μSBS test was performed after 24 h or after thermocycling for 3000 cycles at 5°C–55°C water bath. Results: A three-way analysis of variance (ANOVA) disclosed that multilayer application, adhesive type, and thermocycling showed a significant statistical impact on μSBS. The 1L, 2L, and 3L groups showed a statistically significant difference between the groups. The 3L groups showed the highest μSBS, whereas 1L groups recorded the least μSBS. Within the adhesive groups, a statistically significant difference was evident. The highest μSBS was recorded for TE, whereas SE recorded the least μSBS. Thermocycling (TC) has a statistically significant effect on μSBS and “no-thermocycling” (T0) groups recorded higher μSBS than thermocycled groups. Conclusion: Multilayer application of the tested adhesives had the potential to increase dentin μSBS.