title: Analysis of gap formation at tooth-composite resin interface: effect of C-factor and light-curing protocol.
abstract: OBJECTIVE
  The aim of this study was to evaluate the effect of C-factor and light-curing protocol on gap formation in composite resin restorations.
  
  
  METHODS
  Cylindrical cavities with 5.0 mm diameter and three different depths (A=1.0, B=2.0 and C=3.0 mm) were prepared on the occlusal surface of 30 human molars and restored in a single increment with P 60. The composite resin was light-cured according to two protocols: standard - 850 mW/cm(2) / 20 s and gradual - 100 up to 1000 mW/cm(2) / 10 s + 1000 mW/cm(2) / 10 s. After storage in distilled water (37 degrees C/7 days), the restorations were cut into three slices in a buccolingual direction and the gap widths were analyzed using a 3D-scanning system. The data were submitted to ANOVA and Student-Newman-Keuls test (alpha=0.05).
  
  
  RESULTS
  ANOVA detected a significant influence for the C-factor and light-curing protocol as independent factors, and for the double interaction C-factor vs. light-curing protocol. Cavities with higher C-factor presented the highest gap formation. The gradual light-curing protocol led to smaller gap formation at cavity interfaces.
  
  
  CONCLUSIONS
  The findings of this study suggest that the C-factor played an essential role in gap formation. The gradual light-curing protocol may allow relaxation of composite resin restoration during polymerization reaction.
authors.affiliation: Department of Restorative Dentistry, School of Dentistry, Federal Fluminense University, Ingá, Niterói, RJ, Brazil.
authors.forename: Gustavo Oliveira
authors.initials: GO
authors.lastname: dos Santos
authors.forename: Antônio Henrique Monteiro da Fonseca Thomé
authors.initials: AH
authors.lastname: da Silva
authors.forename: José Guilherme Antunes
authors.initials: JG
authors.lastname: Guimarães
authors.forename: Alexandre de Araújo Lima
authors.initials: Ade A
authors.lastname: Barcellos
authors.forename: Eduardo Martins
authors.initials: EM
authors.lastname: Sampaio
authors.forename: Eduardo Moreira
authors.initials: EM
authors.lastname: da Silva