Effect of solvent evaporation and photo-irradiation strategy of contact-cure adhesive system on bonding to root canal.

Solvent evaporation in root canal dentin is challenging due to the narrow root canals and increasing the distance might impede effective solvent evaporation hindering the bond strength in the root canal particularly in the apical region. Therefore, this study aims to evaluate the effectiveness of solvent evaporation techniques and photo-irradiation strategies in improving adhesion to root canal dentin. Post cavities were bonded with (a) Clearfil SE Bond 2 + Dual Cure Activator [SEB] and (b) Clearfil Universal Bond Quick ER [UBQ]. Each group was divided based on solvent evaporation (three-way syringe tip [TST], micro-surgical tip [MST], and combination method [TMT]) and photo-irradiation strategy (standard tip and endo tip). A 0.6 mm beams were prepared from apical and coronal root part after 24 h of water storage for a microtensile bond strength test. The data were analyzed using a three-way ANOVA and Tukey's HSD test. Weibull survival analysis was conducted (α = 0.05). A scanning electron microscope was used to analyze the fracture surface and examination of adhesive interface. Higher bond strength resulted for the coronal root region compared to the apical root region. For SEB samples photo-irradiated with ST, solvent evaporation using MST and TMT resulted in significantly higher bond strengths in the apical regions. For UBQ, variations in photo-irradiation and solvent evaporation did not affect bond strength. Air bubbles were observed at the adhesive interface particularly in the apical region. Using a smaller air blowing tip to evaporate the remaining solvent in the contact-cure system improved the bond strength to root canal dentin. However, using a photo-irradiation tip with a smaller diameter is not recommended.