Effect of Heat on Epoxy-Resin and Calcium-Silicate Based Endodontic Sealers.

Objectives: To evaluate the effect of heat application on the chemical structure of epoxy resin- and calcium silicate-based endodontic sealers.
Methods: Freshly mixed samples (n=5/group) of epoxy resin-based sealer AHPlus®(DENTSPLY, Konstanz,Germany) and calcium silicate-based sealer BioRoot^TM(Septodont,Saint Maur Des Fosses,France) were exposed to heat at 200°C or 250°C for 30 or 60 seconds. Additional two sets of samples were examined without exposure to heat directly after mixing or after setting. Averaged Raman spectra representing each experimental group of each sealer were compared, and measurable peaks that exhibited changes were quantified and analysed using Two-way analysis of variance. Additionally, Thermogravimetric analysis (TGA) was performed to compare changes on the mass of sealers upon heating ; mixed sealers were heated to a temperature of 250°C at a rate of 20°C/min (11 min duration) or were maintained at fixed temperature of 37°C for 8 hours.
Results: No detectable differences were found in Raman spectra of calcium silicate samples among the different groups, while TGA revealed weight loss of around 15% and 18% upon heating at 250°C and 37°C respectively. Differences were detectable in the spectra of epoxy resin-based sealer, mainly in samples heated for 60s. Changes involved peaks representing bonds of benzene rings and aromatic amines in the uncured resin, which were statistically significant. The TGA, however, revealed minimal changes in sealer mass (1.2% and 1.8%) upon heating to 250°C and 37°C respectively.
Conclusions: Heating caused no detectable changes in the chemical structure of calcium silicate-based sealer, unlike epoxy resin-based sealer where changes were time and temperature dependant. Heat application on the resinous sealer within the recommended temperature range for 30s induced very minimal changes. However heating at higher temperatures and/or longer duration was associated with changes in the chemical structure of epoxy monomers, amine hardeners, and calcium tungstate filler.