Aggressiveness of the recurrent acidic challenge on bond strength to simulated hypersensitive dentin irradiated with Nd:YAG laser

Abstract

Favorable effects of the irradiation of hypersensitive dentin (HD) with Nd:YAG laser may not be kept in light of admittedly erosive challenges, which promote tooth wear, repeatedly reported as determinants of the first condition. Thus, present study intends to evaluate bond strength (BS) of a self-etching adhesive system plus a resin composite to simulated hypersensitive dentin in function of previous Nd:YAG laser irradiation and of aggressiveness of the recurrent acidic challenge after referred minimally invasive treatment of HD. Superficial occlusal dentin of third molars (n=56) 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). Then, it will be, or not (C: control, n=28), irradiated with Nd:YAG laser (L: Laser, 1.0 W, 10 Hz, 100 mJ, 4 irradiations of 50-60 s each; n=28) and submitted to a mild recurrent acid challenge (S: 6% citric acid, 1 min, LS group [n=7]); or to an aggressive one (A: 1% citric acid, 10 min, LA group [n=7]); or to a pH cycling (CpH: 1% citric acid/ artificial saliva, 6x/day, 3 min/60 min each, 5 days, LCpH group [n=7]); or directly led to the next stage of the experiment (no challenge/-: control, L- group [n = 7]). Non-irradiated specimens will be treated exactly in the same way (C- [n=7], CS [n=7], CA [n=7] and CCpH [n=7]). Clearfil SE Bond adhesive system will be applied and composite buildups will be constructed with Filtek Z350. After 24 h (distilled water/37ÚC), specimens will be sectioned in beams, which will be immediately and individually tested (µTBS; 0.5 mm/min). An extra tooth for each group will be treated exactly 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. After conducting tests to verify the normality and homogeneity of the sample distribution, a two-way Analysis of Variance and a subsequent analysis of multiple comparisons, if necessary, will be applied, with a significance level of 5%. (AU)