Degree of conversion of nanofilled and microhybrid composite resins photo-activated by different generations of LEDs.
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).


METHODS
Filtek™ Z350 nanofilled composite resins and Amelogen® Plus, Vit-l-escence™ and Opallis microhybrid resins were photo-activated with two second-generation LEDs (Radii-cal and Elipar Free Light™ 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 Tukeys test showed that the nanofilled resin (Filtek™ 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 (Filtek™ 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 Light™ 2).


CONCLUSIONS
The nanofilled resin showed the lowest DC, and the Vit-l-escence™ 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.
Dental School Prof. Albino Coimbra Filho, Federal University of Mato Grosso do Sul, Campo Grande, MS, Brazil. becarol.odonto@uol.com.br
Benicia Carolina Iaskieviscz
BC
Ribeiro
Juliana Maria Capelozza
JM
Boaventura
Joel de
Jd
Brito-Gonçalves
Alessandra Nara de Souza
AN
Rastelli
Vanderlei Salvador
VS
Bagnato
José Roberto Cury
JR
Saad
D000704:Analysis of Variance; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D055117:Curing Lights, Dental; D008027:Light; D008422:Materials Testing; D053761:Nanocomposites / Q000737:chemistry* / Q000528:radiation effects; D044367:Phase Transition; D058105:Polymerization; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013997:Time Factors
D003188:Composite Resins; C452440:Vitalescence composite resin; C106662:amelogen; C533204:filtek Z350