Effect of smear layer thickness and acidity of self-etching solutions on early and long-term bond strength to dentin

Objectives To evaluate the effect of smear layer thickness (SL) on early and 6-month bond strength (BS) of self-etching adhesives to dentin and to measure the ultimate microtensile strength (UTS) of the adhesives. Methods Clearfil SE Bond; Optibond Solo Plus Self-Etch Primer; Tyrian Self Priming Etchant (TY) and as controls, Single Bond (SB) and Scotchbond Multi-Purpose Plus (SBMP) were applied on flat superficial dentin surface with thick and thin SL thicknesses. After adhesiveʹs application (n=6) a resin build-up was made. After 24 h, resin–dentin beams (0.8 mm2) were prepared to be tested immediately and after 6-month (6M) at 0.5 mm/min. For the UTS measurement, hour-glass specimens were prepared with the bonding resin alone or after mixing (1:1). BS values were analyzed by three-way repeated measures ANOVA and Tukeyʹs multiple comparison tests. Two-way ANOVA (bonding resin and bonding resin+self-etching primer) and Tukeyʹs test were used for the UTS values. The bonding resins were re-evaluated separately by a one-way ANOVA and Tukeyʹs test, since Single Bond is a one-bottle adhesive (α=0.05). Results The SL thickness was not significant (p=0.64). BS values were reduced after 6M, except for the SBMP. TY provided the lowest BS mean while SB and SBMP the highest BS. The UTS of the SBMP was the highest. TY yielded the lowest UTS. Regression analysis revealed a linear and significant relationship between the UTS of self-etch systems and the mean BS (R=0.95, p=0.02). Conclusions The performance of a self-etching system does not seem to be dependent on the SL thickness. The total-etch, three-step system provided the highest BS to dentin and maintained the BS stable over 6 months. The performance of the self-etching systems can be envisaged by their UTS.