Effect of thermo-mechanical cycling and chlorhexidine on the bond strength of universal adhesive system to dentin

Objectives: This study evaluated the influence of thermo-mechanical cycling (TMC) on the bond strength (BS) of a universal adhesive system (UAS - Adper Single Bond Universal, 3M ESPE) to dentin treated or not with 0.2% chlorhexidine (CHX). Methods: Eighty human molars were flattened until reach the dentin and separated into 4 groups according to the bonding protocol: ENR Group: 37% phosphoric acid thorn 3-step etch-and-rinse adhesive system (ENR); UAS Group: UAS in self-etch mode; ENR thorn CHX Group: 37% phosphoric acid thorn CHX thorn ENR; UAS thorn CHX Group: CHX thorn UAS in self-etch mode. After treatments, teeth were restored (Filtek Z350, 3M ESPE). Samples (n = 10) were submitted to aging process: stored in distilled water at 37 degrees C/30 days or TMC (ERIOS - 98N/1.6Hz thorn thermal cycling 5/37/55 degrees C - 1,200,000 cycles). Specimens were sectioned into sticks (1.0 mm(2)) and submitted to the microtensile test (Mechanical Test Machine - 0.5 mm/min). Fracture patterns and hybrid layer integrity were analyzed under Stereomicroscope and Scanning Electron Microscopy (SEM). Results: The BS results (3-way ANOVA, Bonferroni's test, alpha = 5%) showed that groups treated with CHX presented higher BS values than control groups; significant in all cases (p<.05), except for ENR submitted to TMC (p>.05). When CHX was applied and samples were cycled, UAS revealed higher BS (p<.05) than ENR. After TMC, cohesive fractures increased for UAS, regardless of CHX application. SEM analysis demonstrated different hybridization patterns for the adhesive systems tested. Conclusion: The performance of the universal adhesive system used in self-etch mode was better than that of the 3-step etch-and-rinse adhesive system. Clinical significance: Universal adhesive systems have been developed in order to simplify the dentin hybridization protocol. It is important to determine the longevity of the adhesive interface using these bonding materials after chewing.