Degree of conversion and hardness of an orthodontic resin cured with a light-emitting-diode and a quartz-tungsten-halogen light

Abstract

The purpose of this study was to assess the influence of two light units, a quartz-tungsten-halogen (QTH) and a light-emitting-diode (LED) on the hardness and degree of conversion of an orthodontic composite resin.Sixty specimen disk were prepared from Transbond XT composite resin (3M-Unitek) and light-cured for 10, 20 and 30 seconds with a QTH light-curing unit (Curing Light XL 3000, 3M-Unitek) or with a LED light-curing unit (Ortholux, 3M-Unitek) for 5, 10 and 15 seconds. The composite resin polymerization was evaluated by infrared spectrophotometry (FTIR) and Knoop hardness number (KHN). The results were statistically analyzed using analysis of variance and Tukey multiple comparisons test (alpha=0.05). The highest KHN were obtained with the QTH at 30 (25.19 KHN) and 20 (24.01) seconds, which did not differ statistically, and with the LED 15 second (21.86) group. The QTH 10 second group (20.53) did not differ statistically from the QTH 20 second or LED 5, 15 (19.96) or 10 second (18.95) groups. According to FTIR, there was no statistical difference for the degree of conversion among the groups, QTH 10 (43.42%), QTH 20 (46.12%), QTH 30 (45.30%), LED 10 (47.02%) or LED 15 (47.24%) seconds. The lowest degree of conversion was obtained for the LED 5 second group (38.97%), which did not differ statistically from the QTH 10 second group. Light-curing with the LED resulted in a reduction of 50 per cent in the time recommended for use of the QTH light with the composite resin Transbond XT.