A hybrid ultra-violet light emitting diode (UV LED) comprising short and long wavelength UV LEDs (310, 340, and 365 nm) was developed and compared with the high-pressure mercury lamp for UV curing of a mixture of diurethane dimethacrylate, 1-hydroxycyclohexyl phenyl ketone, and diphenyl (2,4,6-trimethylbezoyl) phosphine oxide. The curing ability of the hybrid UV LED combinations was evaluated by comparing the thickness of the un-polymerized layer, calculated from the mass before and after rinsing the UV-cured film under air. The results indicated that among the combinations of UV LEDs, the combination of 365 nm and 310 nm UV LEDs provided the thinnest un-polymerized layer. This result was comparable to that obtained with the high-pressure mercury lamp. Nevertheless, the thickness of the un-polymerized layer achieved with the high-pressure mercury lamp was less than that with any of the UV LED combinations. The data show that the 405 nm line of the highpressure mercury lamp functions to photopolymerize the monomer and is indispensable for the UV curing process.

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