Effect of Delayed Photo-polymerization on the Bond Strength of Dual-polymerizing Resin Cements

Objectives: To examine the effect of delaying the photo-polymerization process on dentin shear bond strength (SBS) of different dual-polymerizing resin cements.
Methods: Shear bond strength of two dual-polymerizing adhesive (RelyX Ultimate, 3M) and self-adhesive (RelyX Unicem 2, 3M) resin cements were evaluated. Dentin specimens (n=80) were prepared for SBS test according to ISO standard 29022:2013. Teeth were randomly allocated into 8 groups based on the type of dual-polymerizing resin cement, and the photo-polymerization delay times (0-2-5-10 minutes), (Figure 1). Irradiance measurement and calibration of the photo-polymerizing unit was done prior to each polymerization cycle. The statistical analysis was performed using linear regression to fit a model with explanatory variables for resin cement (categorical), polymerization time (continuous), and their interactions.
Results: Mean and standard deviation (SD) of dentin shear bond strength for each group are provided (Table 1). The interaction between resin cement and polymerization time was highly significant (p < 0.0001).
The variable for resin cement type was also statistically significant (p<0.0001). When RelyX-Ultimate was used, the dentin SBS values were higher than RelyX-Unicem2 groups.
Conclusions: Photo-polymerization time had an effect on dentin SBS, with higher bond strengths when photo-polymerization time was performed between 2 and 5 minutes.