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

Abstract

<span style="font-family: 'Times New Roman','serif'; font-size: 10pt; mso-ascii-theme-font: major-bidi; mso-hansi-theme-font: major-bidi; mso-bidi-theme-font: major-bidi; mso-fareast-font-family: 'Times New Roman'; mso-bidi-language: FA; mso-ansi-language: EN-US; mso-fareast-language: EN-US;">Introduction: </span><span style="font-family: 'Times New Roman','serif'; font-size: 10pt; mso-ascii-theme-font: major-bidi; mso-hansi-theme-font: major-bidi; mso-bidi-theme-font: major-bidi; mso-fareast-font-family: 'Times New Roman'; mso-bidi-language: FA; mso-ansi-language: EN-US; mso-fareast-language: EN-US;">The aim of this study was to evaluate the influence<br/>of different light curing systems and curing times on the micro-hardness of a<br/>resin modified glass ionomer. Methods: Forty two samples of Resin<br/>Modified Glass Ionomer (RMGI) were prepared using stainless steel cylindrical mold<br/>(8 × 2 mm) and randomly divided into six groups of seven. Three groups were<br/>cured with a Quartz Tungsten Halogen (QTH) light cure unit and the other three<br/>groups were polymerized with LED unit for 20, 30 and 40 seconds. All samples<br/>were stored in distilled water for 24 hours. The micro-hardness was measured on<br/>the top and bottom surfaces of the samples by Vickers hardness tester. Data<br/>were analyzed by two–way ANOVA and Tukey's post-hoc tests. Results: Two-way<br/>ANOVA showed that QTH light-cure unit had higher percentage in depth of cure<br/>than LED light-curing unit in both surfaces; whereas, the application time has<br/>no significant effect on it. There was no interaction between two variables. In<br/>both light-curing groups, the values of top and bottom surfaces micro-hardness<br/>were increased as the application time increased, but there was not any<br/>statistically significant difference among these groups except for 40-second group<br/>of LED light-curing unit which was significantly higher than 20-second and<br/>30-second groups (P<0.05). The micro-hardness value of QTH light-curing unit<br/>was higher than LED light-curing unit. Conclusion: The application of<br/>QTH light-curing unit for at least 20 seconds produces <span class="hps"><span style="color: #222222;">sufficient</span></span> micro-hardness and depth of cure<br/>of RMGI</span>