KHN and DC of composites using 3rdgen LED LCU covered with a glass plate. The sample was polym- for Knoop hardness testing and the top and bot- erized according to the six experimental groups tom surfaces were analyzed by FT-Raman spec- (n=10). Polymerization was performed with the troscopy. The spectra of uncured and cured resins light tip positioned 3mm above the top surface of were obtained by a FT-Raman spectrometer (RFS the sample. For Radii Cal, a 25 seconds exposure 100/S, Bruker Inc, Karlsruhe, Germany) using 100 time was used since it was not possible exclude scans. The spectrum resolution was set to 4cm-¹. the 5 initial seconds in the exponential mode. Ul- The samples were excited by the defocused line of tralume 5 required 20 seconds in the continuous an Nd:YAG laser source at λ=1064nm with a maxi- mode. Immediately after, the hardness on the bot- mum laser power of approximately 100 mW at the tom and top of the specimen was tested using a sample. Knoop hardness test (FM - Future Tech Corp., Ja- The uncured composite (n=3) was positioned on pan) under a 10g load for 10s. Ten measurements an aluminum rod in a sample holder mounted on were taken for each surface, at the approximate an optical rail for spectrum collection. Three spec- center of the specimen.10 The values obtained were tra were collected. converted to Knoop Hardness Numbers (KHNs). The average FT-Raman spectra were analyzed The hardness ratio was calculated according to by selecting a range between 1590 and 1660 cm-¹. the formula: A comparison of the height ratio of the aliphatic Hardness Ratio= Hardness of bottom surface/ carbon-carbon double bond (C=C) at 1640 cm-¹ with hardness of top surface that of the aromatic component at 1610 cm-¹ for the The data obtained from microhardness testing cured and uncured conditions was performed in were submitted to an ANOVA with three factors order to estimate the DC using equation (1). The (composite, LCU and surface - as repeated mea- aromatic C=C peak at 1610 cm-¹ originated from sures), and a Tukey test at the α=.05 signiﬁcance the aromatic bonds of the benzene rings in the level. monomer molecules, and its intensity remained unchanged during the polymerization reaction. FT-Raman Spectroscopy The percentage of DC was then calculated by: Each specimen (n=10) was prepared with DC (%) = 100*[1 – Rcured/Runcured] (1) 160mg of uncured composite placed in a circular where R = band height at 1640cm-¹/band height cavity (7mm in diameter X 2mm thick) centered at 1610cm-¹ . The DC ratio was calculated using the in a stainless steel mold in the same manner as formula: Table 3. Mean of Knoop Hardness Number for composites and surfaces, compared by Tukey tests and Hardness Ratio (P>.05). Composite Resin Supreme XT Z350 Esthet X Light-Curing Unit Radii Cal Ultralume 5 Radii Cal Ultralume 5 Radii Cal Ultralume 5 Top 41.41Bb 40.2Aa 34.9Bb 35.49Aa 23.78Bb 21.18Aa Bottom 44.98Aa 39.01Aa 39.29Aa 35.15Aa 26.22Aa 22.16Aa Ratio 1.08 0.97 1.12 0.99 1.1 1.04 Means followed by different letters and signs (upper case letters: row; lower case letters: column; signs: column) are signiﬁcantly different. Table 4. Mean and standard deviation (SD) of the DC (%) and DC ratios (P>.05). COMPOSITE LCU SURFACE ESTHET X SUPREME XT Z350 TOP 63.87(2.08)Aa 58.98(3.76)Ab* 65.93(4.29)Aa RADII CAL BOTTOM 63.97(1.57)Aa 56.52(2.77)Bb 62.02(3.65) Ba ratio 1.00 0.95 0.94 TOP 64.12(3.36)Aa 63.49(4.94)Aa 62.59(2.78)Aa* ULTRALUME 5 BOTTOM 61.83(3.20)Ba 59.29(4.45)Ba 62.02(2.33)Aa ratio 0.96 0.93 0.99 Means followed by different letters (upper case letters: column; lower case letters: row) are signiﬁcantly different. (*) indicate statistically least DC when LCUs were compare. 398 European Journal of Dentistry