Abstract
Objective This study aimed at evaluating the degree of conversion (DC) of four composite resins, being one nanofilled and 3 microhybrid resins, photo-activated with second- and third-generation light-emitting diodes (LEDs). Material and methods FiltekTM Z350 nanofilled composite resins and Amelogen® Plus, Vit-l-escenceTM and Opallis microhybrid resins were photo-activated with two second-generation LEDs (Radii-cal and Elipar Free LightTM 2) and one third-generation LED (Ultra-Lume LED 5) by continuous light mode, and a quartz halogen-tungsten bulb (QHT, control). After 24 h of storage, the samples were pulverized into fine powder and 5 mg of each material were mixed with 100 mg of potassium bromide (KBr). After homogenization, they were pressed, which resulted in a pellet that was evaluated using an infrared spectromer (Nexus 470, Thermo Nicolet) equipped with TGS detector using diffuse reflectance (32 scans, resolution of 4 cm-1) coupled to a computer. The percentage of unreacted carbon-carbon double bonds (% C=C) was determined from the ratio of absorbance intensities of aliphatic C=C (peak at 1637 cm-1) against internal standard before and after curing of the specimen: aromatic C-C (peak at 1610 cm-1). Results The ANOVA showed a significant effect on the interaction between the light-curing units (LCUs) and the composite resins (p<0.001). The Tukey's test showed that the nanofilled resin (FiltekTM Z350) and Opallis when photo-activated by the halogen lamp (QTH) had the lowest DC compared with the other microhybrid composite resins. The DC of the nanofilled resin (FiltekTM Z350) was also lower using LEDs. The highest degrees of conversion were obtained using the third-generation LED and one of second-generation LEDs (Elipar Free LightTM 2). Conclusions The nanofilled resin showed the lowest DC, and the Vit-l-escenceTM microhybrid composite resin showed the highest DC. Among the LCUs, it was not possible to establish an order, even though the second-generation LED Radii-cal provided the lowest DC.
Highlights
Widely used in diverse industries such as biomedicine, electronics, aerospace, and means of transportation, it is only recently that nanotechnology has begun to be applied to Dentistry[8]
Composite resins $ QDQR¿OOHG FRPSRVLWH UHVLQ )LOWHNTM Z350) and three microhybrid composite resins (Amelogen® Plus, Vit-l-escenceTM and Opallis), all indicated for dentin at shade A2, were used
It is possible to state that, independent of the light-curing units (LCUs), the composite resins can be arranged in a crescent order according to their degree of conversion (DC) mean values: FiltekTM =2SDOOLV$PHORJHQ® Plus
Summary
Widely used in diverse industries such as biomedicine, electronics, aerospace, and means of transportation, it is only recently that nanotechnology has begun to be applied to Dentistry[8] Due to their small size, it is possible to LQFRUSRUDWH PRUH ¿OOHU FRQWHQW RQ FRPSRVLWH UHVLQV based on this technology[10], which results in better mechanical properties[8]. Composites should have most of their monomers converted into polymers during polymerization. Resin-based material polymerization involves free radical reaction in which the material is transformed from a viscous to a rigid state. During this process, the terminal aliphatic C=C bonds are broken and converted to primary C-C covalent bonds between methacrylate monomers. Authors like Conti, et al.[2] (2005) consider that the emission spectra of LCUs and absorption photoinitiators are essential for adequate polymerization
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