Thermal analysis of dental resins cured with blue light-emitting diodes (LEDs)

Thermal analysis was used to measure the characteristics of dental resins cured with the use of a new light-activation unit equipped with high illuminant blue light-emitting diodes (LEDs). The characteristics were compared with those of resins cured with the use of two conventional halogen lamp units. The prepared base monomer consisted of a mixture of Bis-GMA and TEGDMA (60:40 by weight), with 0.5 wt% CQ/DMPT or CQ/DMAEMA. The two experimental visible-light-cured resins were polymerized for 40 s. Differential scanning calorimetry (DSC) was used to examine the thermal characteristics of the cured resins. The activation energy for the decomposition of the dental resin was calculated from the peaks of the endothermic curves obtained when the specimens were heated at three different rates (5, 10, and 15 C/min) during DSC. The activation energies calculated for the LED-cured specimens were more than 220 kJ/mol; specimens cured with the use of the halogen units had activation energies of less than 192 kJ/mol. The Knoop hardness number (KHN) of the same specimens was measured, and was higher with the blue LED units than with halogen lamp units. Therefore, dental resins cured using blue LEDs have a higher degree of polymerization and more stable three-dimensional structures than those cured with halogen lamps.