Performance of two blue light-emitting-diode dental light curing units with distance and irradiation-time

To assess the performance of two blue light-emitting-diode (LED) curing units, in terms of their spectral output and irradiance and the depth of cure (dcure) produced in standard hybrid and modified composites, compared with a conventional quartz tungsten halogen (QTH) light curing unit.

The following light curing units (LCUs) were studied: Elipar-Freelight-1 LED (LED-1) 3 M-ESPE, Ultralume-2 LED (LED-2) Optident, and the Optilux-500 QTH (QTH-1) Sybron-Kerr. For each LCU, using a UV-visible spectrophotometer, the output spectrum was measured and the irradiance of emitted light as a function of source-detector distance. Three composites were studied of similar formulation but differing in their initiator concentrations and/or opacity. These were: Tetric Ceram (A3), Tetric Ceram HB containing an additional photoinitiator responding to approximately 435 nm (A3) and Tetric Ceram Bleach (L). dcure was measured using a calibrated digital needle-penetrometer, as a function of source-specimen distance and for irradiance periods of 10, 20 and 40 s.

Each unit delivered a single peak in the blue region of the visible spectrum. The wavelength maxima for LED-1, LED-2 and QTH-1 were 486.4, 458.2 and 495.2 nm, respectively. Cure-depth (dcure) values varied significantly (p<0.001) with irradiance times and source-specimen distance for both LED and QTH sources. The percentage reduction in dcure values resulting from LED versus QTH irradiance increased with source-specimen distance.

The LED-LCUs had an energy-efficient spectral output for conventional composite curing but had a lower irradiance compared with the QTH-LCU, leading to reduced performance in depths of cure. Design improvements to provide greater irradiance from the LED-1 and to a lesser extent LED-2, should result in increased performance.