The indication of non- or minimally invasive desensitizing therapies as a former treatment option, and the subsequent persistence of the etiological factor of dentin exposure, may possibly exert a significant influence on bond strength (BS) to hypersensitive dentin, when it is to be restored. The role of the persistence of the etiological factor (acid challenge) on BS of a self-etching adhesive system plus a resin composite to simulated hypersensitive dentin irradiated with Nd: YAG laser will be, thus, evaluated over time. Superficial occlusal dentin of third molars (n=28) will be submitted to a 600-grit SiC paper (1 min) and to an acidic challenge with citric acid (6%; 1 min; simulated hypersensitive dentin: open tubules). Next, it will be, or not (C: control, n=14), irradiated with Nd: YAG laser (L: Laser, 1.5 W, 10 Hz, 100 mJ, 4 irradiations of 15 sec each; n=14) and resubmitted, or not (L-, n=7; C-, n=7), to the acidic challenge with citric acid (6%; 1 min; A: citric acid; LA, n=7; AC, n=7). Clearfil SE Bond adhesive system will be applied and composite buildups will be constructed with Filtek Z350. After 24 h (deionized water/37ÚC), specimens will be sectioned in beams, which will be tested (µTBS; 0.5 mm/min) immediately or after 6 months aging. An extra tooth for each group will be treated just like the others, but the fluorescent dye rhodamine B will be previously added (0.02 mg/mL) to the bond constituent of the adhesive system to allow a qualitative evaluation of the adhesive interface by means of Laser Scanning Confocal Microscopy. If obtained BS data are considered normal and homogeneous, a three-way ANOVA and a subsequent analysis of multiple comparisons, if necessary, will be applied, with a significance level of 5%.
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