Efficacy of new LED light-curing units in hardening of Class II composite restorations.

PURPOSE The aim of this study was to determine the efficacy of new light-emitting diode (LED) curing units in the hardening of Class II composite restorations. METHODS AND MATERIALS Disk specimens 2 mm in diameter and 2.5 mm thick were prepared from 2 composites (Vit-l-escence, shade A3, Ultradent; Herculite XRV, shade A2, Kerr) in the following manner. An extracted permanent molar tooth was prepared to receive a Class II restoration with proximal slot only. The tooth was sectioned horizontally on a plane above the gingival floor level such that the remaining depth of the proximal box was 4 mm. A Tofflemire matrix band and retainer were secured around the tooth. Composite specimens were placed below the tooth to coincide with the location of the slot opening at the bottom of the gingival floor. The specimens were subjected to light polymerization with various combinations of curing cycle and light unit: 1 of 3 continuous curing cycles (20 seconds, 40 seconds or 60 seconds) and 1 of 2 LED units (Utralume-5, Ultradent; IQ Smartlite, Dentsply) or a control quartz-tungsten-halogen (QTH) unit (Optilux 501, Kerr). Specimens were stored at 37 degrees C for 24 hours. A hardness tester was used to obtain 4 measurements of Knoop hardness number (KHN) for each surface (upper and lower) of each specimen. Relative hardness (RH) was calculated as the KHN of the lower surface divided by the KHN of the upper surface. Data were analyzed with analysis of variance (ANOVA) and Tukey"s test. RESULTS ANOVA indicated significant differences in mean RH among the groups (p < 0.001). RH increased with increasing curing time. For the 60-second cycle with Vit-l-escence composite, mean RH was 0.47, 0.25 and 0.39 for the Ultralume-5, IQ Smartlite and Optilux 501 curing units, respectively. For the 60-second cycle with Herculite XRV composite, mean RH was 0.71, 0.81 and 0.56 for the Ultralume-5, IQ Smartlite and Optilux 501 curing units, respectively. CONCLUSIONS In general, the 2 LED units performed as well as the QTH unit; however, brand of composite and curing cycle had significant effects on RH values.