Light emitting diode lighting units (LED LCUs) have become more popular in routine dental restorative treatment than halogen LCUs. The aim of this study was to compare the effects of two conventional halogen (Hilux Plus and VIP) and two LED (Elipar FreeLight 2 and Smart Lite) light curing units on the curing depth and microhardness of various aesthetic restorative materials.
Materials and methods: One compomer (Dyract Extra), one resin-modified glass ionomer (Vitremer), one packable composite (Sculpt It), one ormocer (Admira), one hybrid composite (Tetric Ceram), two micro-hybrid composites micro hardness (Dyract Extra) Miris and Clearfil Photo Posterior) and a nanofil composite (Filtek Supreme) were determined using an engraving method and a hardness tester. A total of 320 samples were prepared using eight different materials (n = 10 samples for each subgroup). The scraping test is based on ISO 4049: 2000. Vicker's microhardness test was performed using a hardness tester (Zwick 3212). Data were analyzed using one-way analysis of variance (ANOVA), Bonferroni and Kolmogorov-Smirnov tests.
Results: The best micro hardness values were obtained with LED light drying units and Tetric EvoCeram and Filtek Supreme reached the highest hardness values. Nanofil composite, Filtek Supreme, showed the best curing depth results in all tested lighting systems. LEDs were found to be more successful than halogen units in terms of both depth and micro hardness.
The use of light-activated resin composites in restorative dentistry has increased considerably in recent years. There are a number of photopolymerization techniques that have advantages and disadvantages with respect to the properties of the last restoration and the long-term status of the restored teeth. Inadequate polymerization has been associated with loss of biocompatibility, discoloration, loss of retention, fracture, excessive wear and restoration softness. Many visible light-activated composite resins employ diketon photoinitiators such as camphorquinone. The relationship between the spectral distribution of the outputs from the light-curing sources and the maximum absorption of the photoinitiator is expected to have an effect on the physical properties of the cured composite.
In addition, some dental composites are not suitable for light emitting diode (LED) curing technology. The spectra of LED light drying units (LCUs) are different from those of halogen units. The photoinitiator systems of some composites need to be adjusted according to the spectra of these new light sources.
Halogen LCUs are currently the most widely used for curing dental composites, but this technology has some drawbacks. Halogen bulbs have a limited life and as time passes, the bulbs, reflectors and filters deteriorate due to high operating temperatures, which reduces their curing efficiency. To overcome these shortcomings, LED technology has been proposed for the use of light-curing dental materials. [5], [6], [7] The spectral output of the blue LEDs is suitably reduced in the absorption spectrum of the camporinone photoinitiator (400-500 nm) and therefore no filter is required when using LED LCUs. In addition, the LED LCUs have an expected life of several thousand hours without significant deterioration of the luminous flux. The efficiency of converting electrical energy to usable curing energy is higher than for conventional halogen lamps for blue LEDs (percent 8 and percent 14, respectively). In halogen lamps, the percent 1 of the input power is converted to heat, only the percent 70 results in visible light. There is more loss of this visible light due to the use of cut filters. As a result, the blue light output represents only 10 percent of the total energy input.
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