The effect of polymerization procedure on Vickers hardness of dual-curing resin cements.

To investigate the surface hardness (Vickers hardness, HVN) of one light-curing flowable resin composite and five dual-curing resin cements after different polymerization procedures. The HVN was measured with a hardness-indentation device on one light-curing flowable resin composite (Tetric EvoFlow) and five dual-curing resin cements (Panavia F2.0, SpeedCEM, RelyX Unicem Clicker, SmartCem2 and iCEM) after the resin material had been cured at constant 30 degrees C according to one of five polymerization procedures (n = 30/procedure and material): (1) 5-minute light-curing (positive control; prolonged light-curing), (2) 40-second light-curing (immediate light-curing), (3) 6-minute auto-curing (negative control; dual-curing resin cements only), (4) 6-minute auto-curing followed by 40-second light-curing (delayed light-curing), and (5) 5-second light-curing, 1-minute auto-curing and 40-second light-curing (instructions for removal of excess cement). A Kruskal Wallis test followed by pairwise Wilcoxon ranksum tests with Bonferroni-Holm adjustment was applied for each material and procedure (level of significance: alpha = 0.05). For each material, Procedure 1 showed the significantly highest HVN and Procedure 3 the significantly lowest HVN. Procedure 4 showed significantly increased HVN for each material compared to Procedure 3. With Procedure 1, Panavia F2.0 and RelyX Unicem yielded significantly higher HVN than the other resin materials. With Procedure 3, no significant differences in HVN were found between Panavia F2.0, SpeedCEM and SmartCem2 which all showed significantly higher HVN than RelyX Unicem and iCEM.