Evaluation of the conversion degree of bulk fill short fiber reinforced composite resin with different photoactivation modes

Abstract

Background and objectives. This in vitro study aimed to evaluate the degree of conversion of a bulk-fill short fiber-reinforced composite resin (EverX Posterior, GC, Japan) polymerized using different photoactivation modes. Material and methods. Thirty-two specimens of bulk-fill short fiber-reinforced composite resin were prepared in cubic silicone molds measuring 4 mm × 4 mm × 4 mm and randomly allocated to four groups (n = 8 per group). Each group was polymerized using a different photoactivation mode with the same LED curing unit: continuous cure (NR), pulse-delay (PD), soft-start (SS), and turbo/high-intensity (TR). The degree of conversion, defined as the primary outcome, was determined before and after curing using Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR). Data were analyzed using one-way ANOVA followed by the least significant difference (LSD) post hoc test after confirmation of normality with the Shapiro–Wilk test and homogeneity of variance with Levene’s test. The significance level was set at p < 0.05. Results. Photoactivation mode had a statistically significant effect on the degree of conversion (one-way ANOVA, p = 0.001). The highest mean degree of conversion was recorded in the PD group (33.47 ± 7.14%), while the lowest value was observed in the NR group (16.56 ± 4.73%). Intermediate values were recorded for the TR group (27.76 ± 11.03%) and the SS group (20.65 ± 5.07%). Post hoc LSD analysis identified significant differences between NR and PD (p = 0.001), NR and TR (p = 0.005), and PD and SS (p = 0.002). Conclusion. Within the limitations of this in vitro study, pulse-delay photoactivation produced the highest degree of conversion for the tested bulk-fill short fiber-reinforced composite resin. Photoactivation mode appears to influence the polymerization efficiency of this material. However, further studies evaluating mechanical, thermal, biological, and clinical outcomes are needed before clinical recommendations can be made.

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