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The European Journal of Orthodontics Advance Access published online on September 2, 2009
The European Journal of Orthodontics, doi:10.1093/ejo/cjp048
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© The Author 2009. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org.

Degree of conversion and hardness of an orthodontic resin cured with a light-emitting diode and a quartz–tungsten–halogen light

Guilherme Pessôa Cerveira*, Telmo Bandeira Berthold*, André A. Souto**, Ana Maria Spohr* and Ernani Menezes Marchioro*

* Preventative Department, School of Dentistry
** School of Chemistry, Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Brazil

Address for correspondence Ana Maria Spohr, Laboratory of Dental Materials, School of Dentistry (Block 6)Pontifical Catholic University of Rio Grande do Sul (PUCRS)Avenue Ipiranga 6681, CEP: 90616-900 Porto Alegre—RSBrazilE-mail: anaspohr{at}terra.com.br


  Abstract

The purpose of this study was to assess the influence of two light units, a quartz–tungsten–halogen (QTH) and a light-emitting diode (LED), on the hardness and degree of conversion of an orthodontic composite resin. Sixty specimen disks were prepared from Transbond XT composite resin (3M Unitek) and light cured for 10, 20, and 30 seconds with a QTH (Curing Light XL 3000, 3M Unitek) or a LED (Ortholux, 3M Unitek) light-curing unit for 5, 10, and 15 seconds. Composite resin polymerization was evaluated by Fourier-transform infrared (FTIR) spectrophotometry and Knoop hardness number (KHN). The results were statistically analysed using analysis of variance and Tukey's multiple comparisons test ({alpha} = 0.05).

The highest KHN was obtained with the QTH at 30 (25.19 KHN) and 20 (24.01) seconds, which did not differ statistically, and in the LED 15 second (21.86) group. The QTH 10 second group (20.53) did not differ statistically from the QTH 20 second or the LED 5 (19.96) and 15, or 10 second (18.95) groups. According to FTIR, there was no statistical difference for the degree of conversion among the groups, QTH 10 (43.42 per cent), QTH 20 (46.12 per cent), QTH 30 (45.30 per cent), LED 10 (47.02 per cent), or LED 15 (47.24 per cent) seconds. The lowest degree of conversion was obtained for the LED 5 second group (38.97 per cent), which did not differ statistically from the QTH 10 second group.

Light curing with the LED resulted in a reduction of 50 per cent in the time recommended for use of the QTH light with the composite resin, Transbond XT.


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