engleski

Raman laser heating – the effect in dental composite materials

Raman spectroscopy is commonly used for evaluating the degree of conversion (DC) of C=C bonds in dental composites which generally comprise bifunctional methacrylate resins filled with glass particles1. DC is conveniently calculated from the change in the intensity of the C=C band at 1640 cm-1 during composite polymerization, according to the equation: DC = 1 – Rcured/Runcured, where R = (intensity at 1640 cm-1) / (intensity at 1610 cm- 1). If DC is investigated immediately after light- curing while the post-cure polymerization is still occurring, the laser-induced heating may improve the mobility of reactive species in vitrified polymer, thereby increasing the measured DC. The effect of laser-induced heating in Raman spectroscopy has not been reported for dental composites, although it is recognized in various other compounds2, 3. This study aimed to explore if varying the laser energy between 300 and 1000 mW would measurably affect DC assessed immediately after light-curing two dental composites: an established commercial composite (Tetric EvoCeram) and an experimental composite containing methacrylate resin and silanized barium glass. Raman spectra were collected using a FT-Raman spectrometer with an NdYaG laser excitation (1064 nm) using 40 scans, resolution of 4 cm-1, exposed surface θ = 0.5 mm, and n = 10 per experimental group. Mean DC values were compared among different levels of laser power using Welch ANOVA with Games-Howell post-hoc test. Increasing laser power improved the signal/noise ratio (Figure 1a) which was reflected as a decrease in data variability for Tetric EvoCeram but not for the experimental composite (Figure 1b-c). In both composites, a statistically significant increase in DC was measured with higher excitation power. The effect of laser heating should be taken into account in evaluations of the “immediate” DC in dental composites by Raman spectroscopy, as increasing the laser power in order to improve data quality may have an effect on obtained DC values.

raman laser heating ; dental composites

nije evidentirano