thermal stability and monomer elution of bulk fill composite resins cured from different irradiation distances

objectives: this study aimed to evaluate the thermal stability and monomer elution of bulk fill composite resins cured at different irradiation distances. materials and methods: forty cylindrical-shaped (3×4mm) specimens were fabricated from two composite resins (x-tra fil, x-tra base) and cured from 0 and 7mm distances. in 9 specimens, the degree of conversion was determined by the release of monomers. for this purpose, after curing of composites, they were immersed in 5 ml of 99.9% methanol and stored at 37°c for 24h. the eluted monomer was then analyzed by gas chromatography (gc). also, thermal stability of one sample from each group was assessed by thermogravimetric analysis (tga) at a rate of 10°c/min. data were analyzed using two-way anova and tukey’s post-hoc test (p 0.05). results: x-tra fil had significantly higher degree of conversion than x-tra base (p=0.001). specimens cured at 7mm distance had significantly lower degree of conversion compared with those cured at 0 mm distance (p=0.001). the interaction effect of composite type and distance of light curing unit from the surface of samples was statistically significant (p=0.001). regarding the tga results, the lowest and the highest percentages of weight loss were detected in x-tra fil cured at 0 mm distance and x-tra base cured at 7mm distance, respectively. conclusion: x-tra fil composite cured at 0mm distance had the highest degree of conversion and thermal stability, and x-tra base composite cured at 7mm distance had the lowest values.