Abstract
This study characterized the light emitted by a quartz-tungsten-halogen (QTH) and three light-emitting diode (LED) light curing units (LCUs) and investigated the temperature rise and composite hardness promoted by these sources. XL2500 QTH (3M ESPE), Freelight LED (3M ESPE), Ultrablue Is LED (DMC) and Cool Blue Wand LED (Milestone Scientific) were investigated. The irradiance was measured with a power meter, and the light spectral distribution obtained with a spectrometer. Temperature rise was recorded using a thermocouple connected to a digital thermometer during light-activation of Filtek Z250 (3M ESPE) resin composite. Data were submitted to ANOVA and Tukey’s test (α=0.05). Knoop hardness was assessed at different composite depths (20, 1000 and 1980μm), and data submitted to split-plot design two-way ANOVA and Tukey’s test (α=0.05). Correlation between irradiance and temperature rise was investigated by Pearson’s test. All units presented 95% of irradiance between 400-515nm. Temperature rise means (ºC) varied between 1.05}0.16 and 2.74}0.27. The Cool Blue LED presented significantly higher temperature increase than the other LCUs, and the QTH promoted significantly higher temperature rise than Ultrablue Is and Freelight LEDs. Significant relationship between irradiance and temperature increase was detected (r=0.867; p<0.001). Hardness means (kg/mm2) varied between 40.1}3.6 and 92.7}6.6. Samples activated by the Freelight LED presented significantly lower hardness than samples activated by the others units.
Highlights
It has been advocated that light-emitting diode (LED) can prevent overheating as compared to QTH units,[21,24,25] which produce a broader band of wavelengths and require filters to remove those that are not useful.[15]
Narrower wavelength spectra were observed for LED units as compared to the QTH one
The Cool Blue LED presented significantly higher temperature rise than all other units (p
Summary
Photo-activation of resin composites has been an issue of major interest in dental research during the last years. Although quartz-tungsten-halogen (QTH) light-curing units (LCUs) are the most traditional ones, blue light-emitting diodes (LEDs) are increasingly popular among clinicians. These LCUs emit a narrow spectrum that is better correlated with the spectral absorbance peak of camphorquinone (CQ), the most commonly used photo-initiator in dental composites.[15]Therefore, it has been advocated that LED can prevent overheating as compared to QTH units,[21,24,25] which produce a broader band of wavelengths and require filters to remove those that are not useful.[15]The first-generation of LED sources, however, presented lower power outputs compared to QTH units.[5] In order to increase the emitted irradiance and thus enhance the polymerization potential of LED lights, manufacturers are currently using large surface-emitting chips.
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