Additive effects of touch-activated polymerization and extended irradiation time on bonding of light-activated adhesives to root canal dentin

Statement of problem. The bonding of light-activated adhesives to root canal dentin with an additional touch-polymerization activator has been insufficiently examined. Purpose. The purpose of this in vitro study was to investigate the effect of touch-polymerization activators and extended light-irradiation time on the microtensile bond strength (mTBS) of light- activated adhesives. Material and methods. Post cavities were prepared in 50 extracted mandibular premolars and bonded using Prime&Bond Universal (PBU); PBU+Self Cure Activator (SCA); Clearfil SE Bond 2 (SEB); SEB+Clearfil DC Activator (DCA); or Clearfil Universal Bond Quick ER (UBQ). After light- irradiation for 10 or 20 seconds, the post cavities were filled with dual-activated resin core materials. Eight beams were prepared per specimen and subjected to the mTBS test. The mTBS data were analyzed by using 3-way ANOVAs with the Bonferroni correction (a=.05). Results. The 3-way ANOVAs indicated that the use of touch-polymerization activators (SCA and DCA) significantly increased the mTBS of PBU and SEB in both the coronal (P=.015) and apical (P=.001) regions. The extension of light-irradiation time to 20 seconds significantly improved their mTBS in the apical region (P<.001), but not in the coronal region (P=.09). Light-irradiation for 20 seconds increased the mTBS of UBQ significantly in the coronal region (P=.014). Conclusions. Touch-polymerization activators improved the bond strength of light-activated adhesives to root canal dentin, especially when combined with an extended light-irradiation time.