Influence of the photoinitiator system and light photoactivation units on the degree of conversion of dental composites

The aim of this study was to observe the influence of two light polymerization units (LED or halogen light) on the degree of conversion (DC) of three dental composites with lighter shades and a different pho-toinitiator system. The top (T) and bottom (B) surfaces of 60 discs of composite resin (Filtek  Supreme, Filtek Z250, Tetric Ceram Bleach) cured either by LED or by halogen lamp (HL) were studied using an FT-Raman spectrometer. The degree of conversion (DC) was evaluated by following the changes in the intensity of the methacrylate C=C stretching mode at 1640 cm -1 . The calculated DC ranged from 54.2% (B) to 73.4% (T) and from 60.2% (B) to 76.6% (T) for the LED and HL, respectively. LED and halogen devices were able to produce an adequate DC for all the resins tested. Descriptors: Composite Resins; Dental Equipment; Curing Lights, Dental. Introduction The crucial point to contemplate during restorative dentistry proce-dures with composite resins is to obtain satisfactory restorations with an adequate photopolymerization technique. This procedure requires sufficient light energy intensity and an adequate wavelength in order to activate the photoinitiator within these materials, which will react with the reducer agent to form free radicals and initiate the polymerization process.Camphorquinone (CQ) is the most common photoinitiator used in composites, and it presents maximum energy absorption at 468 nm with-in the electromagnetic spectrum close to the emission spectrum of the light-emitting diode (LED - λ: 450-490 nm) light-curing unit (LCU).