Effect of Immersion in Warm Water on Bonding Strength between Autopolymerizing Resin and Denture Base Resin

Purpose: The purpose of this study was to investigate the influence of immersion in warm water and the timing of the immersion on bonding strength between a built-up self-curing resin and a heat-cured denture base resin.Methods: In this study, self-curing resins (Unifast II or Unifast Trad) were built up on denture base resins after surface treatment of the latter with or without primer. The specimens were cured under three conditions (immersion in warm water for 10 s after build-up (E), immersion in warm water for 210 s after build-up (L), and without immersion in warm water (N)), and shear bond strength and failure patterns were measured.Results: For Unifast II without primer, there were significant differences in shear bonding strength between conditions E and L, or conditions E and N. A cohesion failure rate of 70% was noted under condition E. Bonding strength of Unifast II with primer also differed significantly between conditions E and L. There were no correlations between the failure patterns and the curing conditions. For the case of Unifast Trad without primer, no significant difference was in the bonding strength were observed under the different conditions, whereas for that with primer, significant differences in bonding strength were observed between conditions L and N. Since the failure pattern in all cases was represented by cohesion failure, there was no statistically significant relationship between the curing conditions and the failure pattern.Conclusion: Immersion in warm water at the beginning of the polymerization response enhances the bonding strength of Unifast II to denture base resin without primer. On the other hand, for the cases of both Unifast II with primer and that of Unifast Trad with and without primer, there was no correlation between immersion in warm water during polymerization of the resin and bonding strength.