Effect of High-Irradiance Light-Curing on Micromechanical Properties of Resin Cements

This study investigated the influence of light-curing at high irradiances on micromechanical properties of resin cements. Three dual-curing resin cements and a light-curing flowable resin composite were light-cured with an LED curing unit in Standard mode (SM), High Power mode (HPM), or Xtra Power mode (XPM). Maximum irradiances were determined using a MARC PS radiometer, and exposure duration was varied to obtain two or three levels of radiant exposure (SM: 13.2 and 27.2 J/cm²; HPM: 15.0 and 30.4 J/cm²; XPM: 9.5, 19.3, and 29.7 J/cm²) (n = 17). Vickers hardness (H ) and indentation modulus (E_IT) were measured at 15 min and 1 week. Data were analyzed with nonparametric ANOVA, Wilcoxon-Mann-Whitney tests, and Spearman correlation analyses (α = 0.05). Irradiation protocol, resin-based material, and storage time and all interactions influenced H and E_IT significantly (p ≤ 0.0001). Statistically significant correlations between radiant exposure and H or E_IT were found, indicating that high-irradiance light-curing has no detrimental effect on the polymerization of resin-based materials (p ≤ 0.0021). However, one resin cement was sensitive to the combination of irradiance and exposure duration, with high-irradiance light-curing resulting in a 20% drop in micromechanical properties. The results highlight the importance of manufacturers issuing specific recommendations for the light-curing procedure of each resin cement.