The effects of Exposure Times and Light Curing Sources on Surface Micro-Hardness of a Resin Modified Glass Ionomer

The aim of this study was to evaluate the influence of different light curing systems and curing times on the micro-hardness of a resin modified glass ionomer. Forty two samples of Resin Modified Glass Ionomer (RMGI) were prepared using stainless steel cylindrical mold (8 × 2 mm) and randomly divided into six groups of seven. Three groups were cured with a Quartz Tungsten Halogen (QTH) light cure unit and the other three groups were polymerized with LED unit for 20, 30 and 40 seconds. All samples were stored in distilled water for 24 hours. The micro-hardness was measured on the top and bottom surfaces of the samples by Vickers hardness tester. Data were analyzed by two–way ANOVA and Tukey’s post-hoc tests. Two-way ANOVA showed that QTH light-cure unit had higher percentage in depth of cure than LED light-curing unit in both surfaces; whereas, the application time has no significant effect on it. There was no interaction between two variables. In both light-curing groups, the values of top and bottom surfaces micro-hardness were increased as the application time increased, but there was not any statistically significant difference among these groups except for 40-second group of LED light-curing unit which was significantly higher than 20-second and 30-second groups (P<0.05). The micro-hardness value of QTH light-curing unit was higher than LED light-curing unit. The application of QTH light-curing unit for at least 20 seconds produces sufficient micro-hardness and depth of cure of RMGI