Although it is known that chlorhexidine application may preserve resin-dentin bonds from degradation, the lowest optimal concentration and application time have yet to be established. This study evaluated the effects of different concentrations of chlorhexidine digluconate and different application times on the preservation of resin-dentin bonds formed using two etch-and-rinse adhesives. In experiment 1, after acid etching, the occlusal demineralized dentin was rewetted either with water or with 0.002, 0.02, 0.2, 2, or 4% chlorhexidine for 60 s. In experiment 2, the surfaces were rewetted with water, or with 0.002% or 2% chlorhexidine for 15 or 60 s. After this, both adhesives and composite resin were applied and light-cured. Bonded sticks (0.8 mm(2)) were tested under tension (0.5 mm min(-1)) immediately or after 6 months of storage in water. Two bonded sticks from each tooth were immersed in silver nitrate and analyzed quantitatively using scanning electron microscopy. Reductions in microtensile bond strengths and higher silver nitrate uptake were observed for both adhesives when the rewetting procedure was performed with water. Stable bonds were maintained for up to 6 months under all chlorhexidine conditions tested, irrespective of the chlorhexidine concentration and application time. The use of 0.002% chlorhexidine for 15 s seems to be sufficient to preserve resin-dentin interfaces over a 6-month period.

This study evaluated the effect of modified tetracycline on the resin-dentin bond strength (µTBS), silver nitrate uptake (SNU) and solution homogeneity (SH) of two adhesives. Dentin surfaces were treated with phosphoric acid, rinsed off and either rewetted with water (control group -CO), 2% minocycline (MI), 2% doxycyline (DO) or 2% chlorhexidine (CH). Adhesive systems (Adper Single Bond 2 and Prime Bond NT) and composite were applied and light-polymerized. Specimens were sectioned to obtain bonded sticks (0.8 mm²) to test under tension at 0.5 mm/min. For SNU, specimens were immersed in silver nitrate and analyzed by EDX-SEM. SH was qualitatively analyzed after mixing the adhesives with different solvent-based solutions containing MI, DO and CH. Lower µTBS values were observed in the DO group compared with MI and CH (p = 0.01). Lower SNU was observed for MI and CH. The lowest µTBS for both adhesives was observed for the DO group (p = 0.01). Signs of phase separation were observed for DO with both adhesives. MI or CH used as rewetting solutions after acid etching did not affect the µTBS and hybrid layer quality.