title: Evaluation of degree of conversion and hardness of dental composites photo-activated with different light guide tips.
abstract: OBJECTIVE
  The aim of this study was to evaluate the degree of conversion and hardness of different composite resins, photo-activated for 40 s with two different light guide tips, fiber optic and polymer.
  
  
  METHODS
  Five specimens were made for each group evaluated. The percentage of unreacted 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)). The Vickers hardness measurements were performed in a universal testing machine. A 50 gf load was used and the indenter with a dwell time of 30 seconds. The degree of conversion and hardness mean values were analyzed separately by ANOVA and Tukey's test, with a significance level set at 5%.
  
  
  RESULTS
  The mean values of degree of conversion for the polymer and fiber optic light guide tip were statistically different (P<.001). The hardness mean values were statistically different among the light guide tips (P<.001), but also there was difference between top and bottom surfaces (P<.001).
  
  
  CONCLUSIONS
  The results showed that the resins photo-activated with the fiber optic light guide tip promoted higher values for degree of conversion and hardness.
authors: Department of Restorative Dentistry, Araraquara School of Dentistry, Univ. Estadual Paulista-UNESP, Araraquara, SP, BRAZIL ; Department of Dentistry, Rio Grande do Norte Federal University-UFRN, Natal, RN, BRAZIL.
authors: Marília Regalado
authors: MR
authors: Galvão
authors: Sergei Godeiro Fernandes Rabelo
authors: SG
authors: Caldas
authors: Vanderlei Salvador
authors: VS
authors: Bagnato
authors: Alessandra Nara
authors: AN
authors: de Souza Rastelli
authors: Marcelo Ferrarezi
authors: MF
authors: de Andrade
keywords: Composite resins; hardness; polymerization