Laboratory Evaluation of LED Lights

LED (light-emitting diode)-based activation units are gaining in popularity and becoming more numerous. Questions persist as their ability and the time required to adequately polymerize resin composite materials. Objectives: To examine the ratio of the top and bottom surface hardness of three resin composites in 2 mm thick specimens activated with three LED units and a QTH control. Methods: The resins included were Vit-l-escence(Ultradent) {VL}, Z250(3M){Z} , and Matrixx(Discus){MX}, all A3 shade. The lights used were the VIP {VIP}(Bisco), the Ultralume 2 {UL2} (Ultradent), the Freelight {FR}(3M)/Espe) and the Flashlite{FL}(Discus)The resins were inserted into stainless steel molds and activated for 10,20,30 and 40 seconds with the unit tip 5 mm from the top surface. 5 specimens were made for each variable. Barcol hardness readings (3 per sample) were taken one hour after activation, averaged and the bottom to top ratio recorded. Results:

	10sec	20sec	30sec	40sec
VL/VIP	0.91	0.93	0.95	0.96
VL/UL2	0.78	0.90	0.93	0.96
VL/FR	0.73	0.79	0.86	0.92
VL/FL	0.58	0.84	0.87	0.93
Z/VIP	0.95	0.96	0.98	0.98
Z/UL2	0.92	0.98	0.98	0.98
Z/FR	0.92	0.95	0.98	0.98
Z/FL	0.92	0.98	0.98	0.99
MX/VIP	0.81	0.94	0.97	0.97
MX/UL2	0.71	0.91	0.95	0.96
MX/FR	0.69	0.85	0.91	0.96
MX/FL	0.67	0.81	0.92	0.97

Previous literature has suggested that when the bottom hardness of a resin sample 2 mm in thickness reaches 80% of the top hardness the resin is adequately polymerized.(Watts et al, 1984, Breeding et al, 1991, Manga et al, 1995) Conclusions: Under that assumption, most materials are adequately polymerized by the LED lights under the simulated clinical conditions of this study in 20 seconds or less of exposure. The halogen light achieved adequate polymerization in 10 seconds with all three materials.