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

Introduction: The aim of this study was to evaluate the influenceof different light curing systems and curing times on the micro-hardness of aresin modified glass ionomer. Methods: Forty two samples of ResinModified Glass Ionomer (RMGI) were prepared using stainless steel cylindrical mold(8 × 2 mm) and randomly divided into six groups of seven. Three groups werecured with a Quartz Tungsten Halogen (QTH) light cure unit and the other threegroups were polymerized with LED unit for 20, 30 and 40 seconds. All sampleswere stored in distilled water for 24 hours. The micro-hardness was measured onthe top and bottom surfaces of the samples by Vickers hardness tester. Datawere analyzed by two–way ANOVA and Tukey’s post-hoc tests. Results: Two-wayANOVA showed that QTH light-cure unit had higher percentage in depth of curethan LED light-curing unit in both surfaces; whereas, the application time hasno significant effect on it. There was no interaction between two variables. Inboth light-curing groups, the values of top and bottom surfaces micro-hardnesswere increased as the application time increased, but there was not anystatistically significant difference among these groups except for 40-second groupof LED light-curing unit which was significantly higher than 20-second and30-second groups (P<0.05). The micro-hardness value of QTH light-curing unitwas higher than LED light-curing unit. Conclusion: The application ofQTH light-curing unit for at least 20 seconds produces sufficient micro-hardness and depth of cureof RMGI

Keywords:

Glass Ionomer , light curing unit , micro-hardness