Evaluation of the thermal stability and monomer elusion of bulk fill composites cured in different irradiation distances one day after light curing

Abstract

Objectives : Increasing the depth of curing and allowing them to be used in higher thickness are of advantages of bulk fill composites. One of the main concerns about these materials is their polymerization rate. The aim of this study was to evaluate the thermal stability and monomer elusion of bulk fill composites cured in different irradiation distances one day after light curing. Methods & Materials : In this experimental study, 40 composite samples were made of two composite resin materials (X-tra fil, X-tra base: voco, Germany) in a cylindrical form with a diameter of 3 mm and a height of 4 mm, using a Teflon mold. For this purpose, the mold was placed on a glass slab and filled with composite resin in Bulk form. After placing a thin celluloid matrix , they were cured at two distance of 0 and 7 mm. After preparation of composite specimens in 9 samples, the degree of conversion was measured by the release of monomers. To do this, after composites had been cured,we inserted them into brown glass containing 5 ml of 99.9% methanol, kept at 37 ° C for 24 hours. The monomer was then eluted and analyzed by gas chromatography. Also, to determine the thermal stability, a sample of each group was placed in a thermogravimetric machine at a rate of 10 ° C / min, and its weight loss curve was plotted in terms of temperature. Data were analyzed using descriptive statistics . To evaluate the variables, analysis was performed by Two Way Anova and SPSS17 software. Significance level was considered at P-value <0.05. Results: The X-tra fil composite, independent of considering the light cure tip distance from samples surface, had significantly higher degree of conversion than X-tra base composite (P= 0.001) . Specimens with 7 mm distance of the tip of light curing device from the samples surface had statistically significant decreased degree of conversion compared with the 0mm distance (P= 0.001) . The interaction effect of two factors of composite type and distance of light cure device from the surface of samples was statistically significant (P= 0.001). Conclusion: X-tra fil composite at 0 mm distance had the highest degree of conversion and thermal stability and X-tra base composite at 7 mm distance had the lowest amounts.