title: Influence of light source and extended time of curing on microhardness and degree of conversion of different regions of a nanofilled composite resin.
abstract: OBJECTIVE
  The aim of this study was to evaluate the effects of different light sources and curing time on the degree of conversion and microhardness of two surfaces within a nanofilled composite resin.
  
  
  METHODS
  Four experimental groups (n=10) were formed in accordance with the light source (quartz-tungsten halogen (QTH - 600mW/cm(2)), or light-emitting-diode (LED - 800mW/cm(2))) and the time of curing (20 s or 40 s). The specimens were prepared with a circular mould (5 mm ∅ and 2 mm thick), according to the respective protocol, and the Knoop microhardness and degree of conversion was measured at the top and the base of the specimens. The degree of conversion was evaluated by the Fourier transform infrared spectrometer (FTIR). The results were analyzed by ANOVA two-way repeated measures and Tukey's test (α=,05).
  
  
  RESULTS
  Both the degree of conversion and microhardness were higher at the top than at the bottom of the specimens. The QTH light source presented better values on the degree of conversion evaluation, but this result was not observed in the microhardness evaluation. Although forty seconds of curing promotes an increased level of microhardness, it did not influence the degree of conversion.
  
  
  CONCLUSIONS
  It could be concluded that increasing the time of curing to 40 s promotes an increase in microhardness, but it does not influence the degree of conversion of a nanofilled composite resin. QTH promote better monomeric conversion; however, the microhardness values are similar to LED curing. For all situations tested, the bottom of the specimens presented lower results than the top.
authors.affiliation: Department of Restorative Dentistry, Piracicaba School of Dentistry, State University of Campinas, BRAZIL.
authors.forename: Adriano Fonseca
authors.initials: AF
authors.lastname: Lima
authors.forename: Kamila Menezes Guedes
authors.initials: KM
authors.lastname: de Andrade
authors.forename: Louise Esther
authors.initials: LE
authors.lastname: da Cruz Alves
authors.forename: Giulliana Panfiglio
authors.initials: GP
authors.lastname: Soares
authors.forename: Giselle Maria
authors.initials: GM
authors.lastname: Marchi
authors.forename: Flávio Henrique Baggio
authors.initials: FH
authors.lastname: Aguiar
authors.forename: Alessandra Rezende
authors.initials: AR
authors.lastname: Peris
authors.forename: Fábio Hiroyuki Ogata
authors.initials: FH
authors.lastname: Mitsui