No abstract

©Operative Dentistry, 2008, 33-2, 183-188 SUMMARYThis study evaluated the effect on microtensile bond strength (µTBS) 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 (µTBS) at 0.5 mm/minute in a universal testing machine. The data were analyzed by one-way ANOVA (α=0.05), demonstrating no significant differences among the groups.

This study evaluated the influence of the method and period of storage on the adhesive bond strength of indirect composite resin to bovine dentin. Ninety bovine incisors were stored in three different solutions: 0.2% thymol, 10% formalin, and 0.2% sodium azide, during 3 periods of storage: 7 days, 30 days and 6 months, resulting in 9 groups (n = 10). The roots were cut off and the buccal surface was ground with #600-grit silicon carbide paper. The surface was conditioned with 37% phosphoric acid for 15 s and a composite resin restoration (TPH Spectrum) was fixed using a one-bottle adhesive system (Adper Single Bond) and a dual-cured resinous cement (Rely X ARC) under a load of 500 g for 5 minutes. The samples were serially cut perpendicular to the bonded interface to obtain slices of 1.2 mm in thickness. Each slab was trimmed with a cylindrical diamond bur resulting in an hourglass shape with a cross-sectional area of approximately 1 mm(2). The microtensile bond strength (microTBS) testing was performed in a testing machine (EMIC 2000 DL) at a 0.5 mm/minute crosshead-speed until failure. After fracture, the specimens were examined under SEM to analyze the mode of fracture. muTBS Means were expressed in MPa and the data were analyzed by two-way ANOVA (3X3) and the Tukey test (alpha = 0.05). The storage times of 7 and 30 days produced no significant difference irrespective of the solution type. The formalin and thymol solutions, however, did have a negative influence on bond strength when the teeth were stored for 6 months.

The storage time did not affect the results, but differences were found among the adhesives and methods. For comparisons of bond strength from tests with different bonding areas, the normalization for area seemed essential. The microshear bond test should not be used for bond strength evaluation, and the microtensile test needs improvement to enable reliable results regarding stress concentration and failure mode. The micropush-out test may be considered more reliable than the microtensile in the bond strength investigation, as demonstrated by the uniform stress concentration and adhesive failure pattern.