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Objective: The objective of this study was to investigate the effect of light-curing protocols on degree of conversion (DC) and glass transition temperature (Tg) of a dual-cured resin cement (Variolink N). The correlation between DC and Tg was further investigated.
Materials and methods: Different light-curing protocols (no irradiation, irradiation with light tip directly contact to specimen, and irradiation with light tip positioned at 10 mm from specimen) were used in-order to investigate the influence of energy density (ED) on DC and Tg of the resin cement. 15 and 45 specimens of mixed cement were prepared for DC and Tg observation respectively, then subjected to irradiating protocols underneath a ceramic block (10 mm length x 10 mm width x 0.95 mm thickness) and light cure for 40 sec in light curing groups. DC was measured by Raman microspectroscopy and Tg was measured by differential scanning calorimetry at 5 min, 15 min and 24 hrs after post-polymerization. Data were submitted to two-way ANOVA. The DC and Tg data were subjected to linear regression analysis.
Results: Increasing of distance between light tip and specimens decreased ED. Curing protocols with different ED influenced DC (p<0.01) and Tg (p<0.01) of the cement. The increasing of ED significantly increased DC and Tg. The DC and Tg improved significantly with the extension of post-polymerization times up to 24 hrs. A significantly positive correlation was found between DC and Tg.
Conclusion: ED of curing light and post-polymerization times influenced DC and Tg of the dual-cured resin cement.
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