the absorption of camphorquinone (CQ), the most common photoinitiator used in dental composites. Thus, no ﬁlters are required in LED LCUs. Fur- ther, LED LCUs are less energy-consuming than QTH LCUs and have a lifetime of several thousand hours4 without a signiﬁcant intensity loss.5,6 The introduction of LEDs LCUs occurred in 2000 and these have been subjected to three main changes in technology over the years.7 The ﬁrst generation of LED LCUs usually contained mul- tiple low power LEDs, however these lights pre- sented low irradiance and were unable to cure resin composites as well as QTH LCUs.8,9 Second- generation LED LCUs used one high power LED to provide greater light output, but the spectral bandwidth remained narrower than that of QTH LCUs.9 This narrow spectrum is a problem for lighter composites that uses photoinitiators other than CQ, (e.g, 1-phenyl-1,2-propanodione (PPD), bisacylphsphine oxide (BAPO), triacylphosphine oxides (TAPO)). For these composites, the absorp- tion proﬁle is shifted to the shorter wavelengths with maximum absorption centered at roughly 400nm,10 320nm,10 and 390nm11 respectively. Third- generation LED LCUs use a combination of blue Table 1. Technical proﬁle of composite resins evaluated in this study. Composite (manufacturer) Color Lot Organic Matrix* and ultraviolet LEDs to produce a broader spectral output, and these lights may polymerize a broader range of resins than the second-generation curing lights.9 The aim of this study was to directly and indi- rectly evaluate the degree of conversion by means of FT-Raman Spectroscopy and Knoop Hardness testing of composites light-cured with 2nd and 3rd generation LED LCUs. The hypotheses were: (1) use of 2nd and 3rd-generation LED LCU does not affect the microhardness of composites; (2) use of 2nd and 3rd-generation LED LCUs does not affect the degree of conversion of composites. MATERIAL AND METHODS Three commercial composites (Table 1) and two LED LCUs (Table 2) were selected for this study. Knoop Hardness Test Sixty cylindrical specimens were prepared in stainless steel molds (5mm in diameter and 2 mm thick). A mylar strip was positioned on the bottom of the mold. The cavity was randomly ﬁlled in one increment and covered with another Mylar strip in order to provide a ﬂat surface and the strip was Description Irradiance (mW/cm²) Density Total <440nm 450-490nm Second-generation LED curing using one high power LED, cordless, lithium battery operated Third-generation LED curing using a combination of ﬁve LEDs, hand-held wand, not battery operated 1250 780 40 89 964 520 397 European Journal of Dentistry Giorgi, Aguiar, Soares, Martin, Liporoni, Paulillo Photoinitiator Unknown(§) Unknown(§) Camphorquinone Exposure duration 25s 20s Energy Density (J/cm²) ≈25 15,6 Filtek Supreme XT (3M ESPE Dental Products, St Paul, MN, USA) Filtek Z350 Esthet X (3M ESPE Dental Products, St Paul, MN, USA) LCU (manufacturer) Radii Cal (SDI Limited, Bayswater, Australia) UltraLume 5 (Ultradent, South Jordan, USA) October 2012 - Vol.6 (Dentsply/Caulk Milford, DE) TEGDMA (§) Manufacturer information – available in 3M ESPE Technical Speciﬁcations Table 2. Technical details of Light-Curing Units used in this study. WE Lot 8BY A1 Lot 7CA WE Lot 0707000200 Bis-GMA Bis-EMA6 UDMA TEGDMA Bis-GMA Bis-EMA6 UDMA TEGDMA Bis-GMA Bis-EMA Filler non-agglomerated/non-aggre- gated, 20 nm silica nanoﬁller and 0.6–1.4 nm agglomerated silica nanocluster. 78.5 wt.% 58-60% by volume(§) non-agglomerated/non-aggre- gated, 20 nm silica nanoﬁller and 0.6–1.4 nm agglomerated silica nanocluster. 78.5 wt.% 58-60% by volume(§) barium ﬂuoro alumino boro silicate glass, with mean particle size be- low 1µm and nanoﬁller silica par- ticle size 0.04 µm 60% by volume