Effect of Photo-polymerization Delay on the Bond Strength and Microhardness of Dual-polymerizing Resin Cements

Statement of Problem: To fully maximize the potential of dual-polymerizing resin cements, a thorough understanding of how the light- and chemical-polymerizing components interact in a resin system is required. Disorder in the polymerization process between the two components may hurt one of the components versus the other, affecting the overall properties and performance of the resin cements. Purpose: Evaluate photo-polymerization delay time on dentin shear-bond strength and Vickers microhardness of dual-polymerizing resin cements. Methods and Materials: Shear bond strength (SBS) of self-adhesive (RelyX Unicem 2, 3M ESPE) and adhesive (RelyX Ultimate, 3M ESPE) dual-polymerizing resin cements were evaluated. Dentin specimens (n=80) were prepared for the SBS test according to ISO standard 29022:2013. Teeth were randomly allocated into eight groups based on the type of cement, and photo-polymerization delay times (0, 2, 5, and 10 minutes). Vickers microhardness test (HV) was performed following ASTM E384-17 (n=32) prepared based on cement type and photo-polymerization delay times; specimens were tested after 24 hours of storage. Statistical analysis was performed using twoway ANOVA to determine the individual and combined effects of resin cement type and photopolymerization delay time on SBS and HV. Results: Resin cement and photo-polymerization delay times for the adhesive cement at 0- and 2-minute pairings had significantly higher SBS means than all other combinations (p<0.0001). Resin cement type was also statistically significant (p<0.0001). Resin cement type and photopolymerization delay times were not significant (p=0.3550) for HV. Conclusions: Photo-polymerization delay time affected dentin SBS with higher bond strength when photo-polymerization delay time was performed between 2 and 5 minutes with a selfadhesive resin cement, and between 0 and 2 minutes with an adhesive resin cement. Delaying photo-polymerization time to 10 minutes led to inferior dentin SBS and HV for both self-adhesive and adhesive dual-polymerizing resin cements.