Introduction

Tooth coloured resin based composites have the benefit of better aesthetic properties and are widely used aesthetic restorative materials in modern dentistry (Rajkumar et al.,Influence of Curing Light Type on the Discoloring Stability of Dental Restorative Composite Articles 2011). Initially, resin composites were manufactured as chemically activated materials; two pastes system based on initiator (benzoyl peroxide) and activator (a tertiary amine such as N,N-dimethyl p toluidine) system. The key drawbacks of chemically activation are the limited working time, difficulty in finishing and colour stability (Anusavice, 2003). These drawbacks led to the development of light cured resin composites, which could provide a better control over working and finishing times while improving colour stability. In addition, light cured Best Phillips Sonicare Toothbrush Black Friday Deals resin materials are activated by visible blue light (wavelength = 400-470 nm) hence avoiding from the hazardous effects of radiation. Light cured composites contain canphorquinone as photo-initiator which facilitates better control over working time and enhances colour stability (Rajkumar et al., 2011; Anusavice, 2003), but discolouration still remains the main concern.

In order to cure light activated resin composites, various types of light sources have been used including Quartz Tungsten Halogen (QTH) and Light Emitting Diode (LED).

The QTH system is comprised of a quartz bulb and tungsten filament that works in the halogen environment. In order to activate the canphorquinone initiator, the emitted light is filtered to dissipate heat and to transmit only the violet-blue part of the visible light spectrum. These systems produce a spectrum of 400-500 nm with an output range of 400-800 mW/cm² (Filipov and Vladimirov, 2006). There are several disadvantages of using QTH system, among these there are the prolonged curing time, the source larger size and the need of filters and fans to dissipate the generated heat (Yazici et al., 2007; Aversa et al., 2016 a-o).

The LED systems include Gallium nitride blue diodes and silicon carbide diodes with a power output of 7 µW (Park et al., 2005). The LEDs sources are generally cordless, lightweight, of compact size and powered by batteries. The wavelength is usually in the range of 400-500 nm. All the emitted condensed light is fully utilized and no additional filters or cooling fan are required. Finally, due to the electronic natue of the emitted light, there is no drop in intensity and diodes do not need replacement (Christensen, 2002). The main disadvantages are the relatively high cost of the equipment and that the batteries require recharging (Mirsayar et al., 2017; Aversa et al., 2016 a-o, 2017 a-e).