Effect of Evaporation of Solvents from One-step, Self-etching Adhesives

Purpose: To investigate whether and to what extent the bonding capacity of one-step, self-etching adhesives is influenced by the degree to which solvent is evaporated. Materials and Methods: Seven one-step, self-etching adhesives were tested (Adper Prompt L-Pop, Clearfil S3 Bond, Futurabond NR, G-Bond, Hybrid Bond, iBond, Xeno III). The variation in degree of evaporation was obtained by varying the duration of the air-blowing step. The duration required to immobilize the adhesive layer, as established in a pilot study, was used as control. Two experimental air-blowing durations, shorter (half the control duration) and longer (double the control duration) than the control duration, were chosen. The resin composite Herculite XRV was bonded to flat human dentin surfaces treated with one of the adhesives following manufacturer's instructions, except for the air-blowing duration after application. After being stored in water at 37°C for 1 week, the bonded specimens were broken in shear. Failure modes were evaluated under stereomicroscope. Results: Air-blowing duration and brand of adhesive both had an effect on shear bond strength. An interaction was found between adhesive and air-blowing duration. Some adhesives were insensitive to variations in air-drying duration, but in general, air-blowing durations shorter than the control duration produced lower shear bond strengths. Significant effects of adhesive and air-blowing duration were also detected in relation to failure mode. More adhesive failures were observed with shorter air-blowing durations. A significant negative correlation between number of adhesive failures and bond strength was found. Conclusion: On the basis of this in vitro study, it may be concluded that the one-step, self-etching adhesives evaluated were sensitive to degree of evaporation of the solvents. Keywords: bond strength, composite resins, dental bonding, dentin-bonding agents, volatilization