Giorgi, Aguiar, Soares, Martin, Liporoni, Paulillo DC Ratio= DC of bottom surface/DC of top sur- and indirect methods by means of FT-Raman face Spectroscopy and Knoop Hardness respectively. The data obtained in FT-Raman test were sub- The hardness of composite resin is inﬂuenced mitted to an ANOVA (factors: composite, LCU and by the composition of the resin matrix, ﬁller type surface), and Tukey test at the α=.05 signiﬁcance and ﬁller load.4 According to material’s proﬁle, level. Filtek Supreme XT and Filtek Z350 have the same composition (although the percentage of mono- RESULTS meric components was not mentioned). For this Knoop Hardness test study, these composites were selected in differ- The ANOVA showed a signiﬁcant difference for ent shades since Z350 is not available in the WE each factor, as well as an interaction among the shade. Different shades probably produce differ- “LCU” and “surface” factors (Table 3). Composites ences in translucency, opacity, and the type and resins were all signiﬁcantly different from each content of pigment. These can control the trans- other. For the LCU versus surface interaction, the mittance spectrum of each shade of each mate- highest hardness was obtained in the bottom for rial15 and may explain the higher KHNs obtained by light curing with Radii Cal. This condition was sig- the Filtek Supreme XT samples. niﬁcantly different from the others and no other The microhybrid composite Esthet X had the differences were noted. The hardness ratio was > lowest hardness value (Table 3). This ﬁnding can 0.9 in all groups. be explained by composite composition, especially by the ﬁller load and content. Esthet X presented FT-Raman test an irregular ﬁller made of barium ﬂuoro alumino There were signiﬁcant differences between boro silicate glass with a mean particle size below the factors “composite” and “surface” as well as 1µm and nanoﬁller silica size of 0.04 µm. Filtek a “composite versus surface versus LCU” interac- Supreme XT and Filtek Z350 presented 0.02µm tion (Table 4). For the “composite” factor there was nanosilica ﬁller and loosely bound agglomerated no signiﬁcant difference between the groups, with zirconia/silica ﬁller particles with a size of 5-20nm. the exception of Filtek Supreme XT lightcured by The cluster particle size ranged from 0.6 to 1.4 µm Radii Cal on either the top or bottom surfaces. For (Table 1). These are classiﬁed as nanocomposites; the “LCU” factor, there was a signiﬁcant difference due the reduced dimensions of the particles and for the Supreme XT top surface, for which the 3rd- the presence of a wide size distribution, these generation LED LCU obtained a higher DC. For the composites showed increased ﬁller load, reduced Z350 top surface, a signiﬁcant difference in the DC polymerization shrinkage and improved mechani- was also noticed; Radii Cal obtained better results cal properties (e.g., increased microhardness16). than Ultralume 5. For the “surface” factor, most Higher KHNs were obtained using Radii Cal on groups presented top surfaces with higher de- the bottom surface, this difference was signiﬁcant grees of conversion than the bottom surfaces; the compared to the others conditions, and no further only exceptions to this rule were for Esthet X light- differences were noted (Table 3). Two possibilities cured by Radii Cal and Filtek Z350 light-cured by may explain these results. First, the samples were Ultralume 5. The degree of conversion ratio was prepared in one increment and were compressed >0.9 for all experimental conditions. so as to extrude excess material and obtain a ﬂat surface. This could allow the resin matrix to accu- DISCUSSION mulate at the top and condensate the ﬁller at the The degree of conversion is related to the bottom, thereby decreasing the hardness value performance of resin-based dental materi- of the top surface. Second, due to the difference als. When higher degrees of conversion are ob- in irradiance, light may have reached the bottom tained, improved mechanical properties are also surface differently.9,17 Radii Cal delivered radiant achieved.12,13 Hardness is a parameter that has exposure above 25 J/cm² whereas Ultralume 5 de- relevance for the behavior of composite resin res- livered 15.6 J/cm². torations in the oral environment.14 In this study, For the Ultralume 5, no difference was ob- curing effectiveness was measured using direct served. We thus conclude that the lowest radiant October 2012 - Vol.6 399 European Journal of Dentistry