Degree of Conversion of Dental Composites Using Modern-day Curing Lights

Objectives: This study measured the degree of conversion (DC) of four composites using three light-curing units (LCUs): Bluephase G4 and Bluephase PowerCure, which reports a 3-second cure of Tetric PowerFill and Tetric PowerFlow, and the Monet Laser Curing Light, which reports a 2.5mm cure in 1-second (see Table 1).
Methods: Each composite (Table 2) was placed in a vinylpolysiloxane mold (4mm depth, 4mm diameter) directly on an attenuated total reflectance (ATR) cell of a Fourier transform infrared (FT-IR) spectrometer. A glass slide was placed on top to ensure uniform thickness of the samples. (n=3/group). FT-IR patterns were collected before and after each light-curing cycle. Curing was completed following manufacturer’s instructions for each LCU. Degree of conversion was calculated using the change in ratio of the aliphatic and aromatic carbon-carbon double bonds. Two-way ANOVA and post-hoc Tukey tests were used to identify significant differences in DC between composite/LCU combinations (alpha=0.05) and repeated measures ANOVA was used to identify differences in DC of each composite following successive curing cycles.
Results: Two-way ANOVA showed DC varied based on the LCU used (p-value<0.0001, F=10.48). Post-hoc Tukey showed significant differences in DC between G-Aenial Bulk Injectable cured with the Monet, which showed a low DC, and all other composite/LCU combinations, which showed a higher DC (see Figure).

Repeated measures ANOVA showed changes in DC over repeated curing cycles varied as a product of composite and LCU. The Monet generally produced lower DC compared to the Bluephase LCUs, which showed similar results.
Conclusions: Degree of conversion of dental composites varies based on the LCU used. In addition, DC may continue to increase following multiple curing cycles, despite manufacturer recommendations of short (1 – 3 second) curing times.