Temperature rise and degree of photopolymerization conversion of nanocomposites and conventional dental composites

The aim of the study was to investigate the temperature rise of a nanocomposite and a conventional hybrid dental composite during photopolymerization when cured with halogen curing lamp (QHT) and light-emitting diode (LED). Temperature rise during photopolymerization of two commercially available composites (Filtek Supreme (R) and TetricCeram (R)) were measured using a K-type thermocouple and a digital thermometer. Different curing modes were utilized to cure the composites: a high-intensity QHT unit (Optilux 501) in two different modes (standard and ramp), a low-intensity QHT unit (Coltolux 50), and an LED unit (Ultralume-2). Total temperature rise, polymerization reaction exotherm, and irradiation-induced temperature rise of the composites were determined. Degree of conversion of the specimens was measured using FTIR spectroscopy. The results revealed that the Filtek Supreme (R) nanocomposite showed lower temperature rise and degree of conversion in comparison with the hybrid composite (p< 0.05). It was also found that the LED curing unit induced considerable total and irradiation temperature rise without any improvement in the degree of conversion. Ramp curing mode showed lower temperature rise and delayed gel point and was found to be more effective than QHT standard mode and LED units. Although it is claimed that the LED curing units exhibit lower temperature rise during the photopolymerization, the present study showed that the curing units have no advantage over the conventional QHT units regarding the temperature rise and degree of polymerization conversion.