In-Vitro investigation of the degree of conversion and discoloration of flowable composites polymerized by different polymerization methods

Aim: The aim of this study is to evaluate the effect of different curing modes on the degree of conversion and color stability of different flowable composites. Material and method: In this study, four different flowable composites [Estelite Bulk Fill Flow (EBF), G-aenial Universal Injectable (GUI), Tetric N-Flow Bulk Fill (TNF), Filtek Bulk Fill Flowable (FBF)] were used. The composite materials were polymerized using three different curing modes (standard mode: 1000 mW/cm², 1*20 s; high power mode: 1400 mW/cm², 3*4 s; extra power mode: 3200 mW/cm², 2*3 s) of an LED light device (VALO Cordless, Ultradent, USA). A total of 120 cylindrical samples with a 5 mm diameter and 4 mm height were prepared, with 10 samples per group (n=10). The degree of conversion of the samples was recorded using FTIR spectroscopy. The color values of the samples were recorded initially and on the 7th and 14th days after being immersed in a coffee solution, using a spectrophotometer. Color change values were calculated according to the CIEDE2000 formula. The data were statistically analyzed using SPSS, with two-way ANOVA, one-way ANOVA, post hoc Tukey, and Tamhane's T2 tests (α=0.05). Results: The effect of composite material type, polymerization mode, and the interaction between material and polymerization mode on the degree of conversion and color change was found to be statistically significant (p<0.001). The highest degree of conversion was observed in all composites when cured using the high power mode. The degree of conversion in the extra power mode was lower compared to the high power mode, and this decrease was statistically significant for FBF and GUI (p<0.05). The least color change was observed when curing with the high power mode. Color change in the extra power mode on day 7 was significantly higher in EBF and FBF compared to the high power mode, while on day 14, it was significantly higher in TNF, FBF, and EBF compared to the high power mode. (p<0.05). Conclusions: With the development of LED light devices, the time-saving extra power curing mode may lead to a decrease in the degree of conversion and an increase in discoloration in flowable composites. Keywords: Flowable composite, bulk-fill composite, degree of conversion, curing mode, color stability