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This study evaluated the effect on microtensile bond strength (microTBS) of chlorhexidine application to dentin at different times during an indirect restoration luting procedure. Sixty bovine incisors had their superficial dentin subjected to 0.12% and 2% chlorhexidine solutions for 15 seconds before, during and after 37% phosphoric acid etching, resulting in six groups (n=10): 1) 0.12% chlorhexidine + etching; 2) 2% chlorhexidine + etching; 3) etching + 0.12% chlorhexidine; 4) etching + 2% chlorhexidine; 5) etching with 2% chlorhexidine; 6) etching without chlorhexidine (control). An adhesive system (Adper Single Bond 2) was applied and an indirect resin composite restoration (Filtek Z250) was luted using dual cured resin cement (Rely X ARC). After 24 hours of water storage, the specimens were tested by microtensile bond test (microTBS) at 0.5 mm/minute in a universal testing machine. The data were analyzed by one-way ANOVA (alpha=0.05), demonstrating no significant differences among the groups. The microTBS values in MPa were: 6: 22.83+/-3.53; 5: 22.4+/-3.52; 2: 21.62+/-2.5; 1: 21.28+/-3.17; 3: 19.62+/-2.05; 4: 19.55+/-2.34. The use of chlorhexidine at concentrations of 0.12% and 2% before, after or associated with acid etching did not significantly affect the microTBS values to dentin.

The insertion of bonded resin composites into cavity preparations leads to a competition between polymerization contraction forces and the strength of bonds to tooth structure. The degree of stress development can be controlled, to some extent, by the cavity design (C-factor), the use of bases, the size, shape, and position of increments of composite resins placed in the cavity, and whether the resin is light- or chemically cured. Stress relief can be accomplished by maintaining the C-factor as low as possible, using chemical-curing resins, low modulus liners, and, over time, by water sorption. A thorough understanding of these principles permits clinicians to exercise more control over these variables, thereby improving the quality of their bonded restorations.