Polymerization kinetic calculations in dental composites: a method comparison analysis

Abstract

This study aimed to describe the polymerization process and to quantify the parameters of influence in two bulk-fill resin-based composites by comparing two real-time methods: the Fourier transform infrared (FTIR) spectroscopy and the visible light transmission spectrometry. The degree of conversion (DC) was recorded in real time for 5 min using the attenuated total reflectance FTIR spectroscopy (n = 6) on the lower surface of 2, 4, and 6 mm thick samples irradiated for 20 s. The variation in irradiance was recorded during material irradiation at the bottom of the samples (n = 5). Results were statistically analyzed using one-way and multiple-way ANOVAs with Tukey HSD post hoc test (α = 0.05), partial eta-squared statistics, and Pearson correlation. No significant difference was found in DC in any materials as a function of incremental thickness, whereas the irradiance passing the specimens differed consistently within both analyzed increments and materials. These data could be described by the superposition of two exponential functions, the first being attributed to the gel phase and the second to the glass phase, resulting in an exponential sum function. DC data were able to calculate the end of the gel phase and the beginning of the glass phase, whereas irradiance measurements were able to detect only the last phase. The polymerization kinetics in the glass phase was less material-dependent as in the gel phase. The irradiance measurements were more sensitive to variation in thickness, meaning that translucency is continuing to change as a function of thickness at a higher extent than DC. Knowing the impact of the modulation factors describing the calculated sum exponential function allows the manipulation of the polymerization process at different stages to tailor material properties.