title: Influence of cavity dimensions and their derivatives (volume and 'C' factor) on shrinkage stress development and microleakage of composite restorations.
abstract: OBJECTIVE
  To determine, in vitro, the influence of cavity dimensions on shrinkage stress development and microleakage of composite restorations.
  
  
  METHODS
  Cylindrical cavities with 2, 3, 4 or 6 mm diameter and 1 or 2 mm depth were prepared in bovine incisors (with enamel margins) and reproduced in photoelastic resin. Cavities were restored in bulk (Single Bond+Filtek Z250). Stress fringes were analyzed 10 min after photoactivation. Restored teeth were stored for 24 h, coated with nail polish and immersed in 50% AgNO3 for 2 h, followed by 6 h in developing solution. Specimens were sectioned twice and microleakage was measured under 20x magnification. Photoelastic data were analyzed descriptively only, due to lack of variability in some groups. Microleakage was analyzed through (generalized linear) regression models. Pearson correlation coefficients were computed to evaluate the relationship between microleakage and 'C' factor or volume.
  
  
  RESULTS
  Fringe order was higher at the internal angles than at the margins of the restorations. There was a trend for higher fringe orders with increasing diameter and depths. Regression analysis revealed a significant influence of restoration depth for diameters above 2mm. The effect of diameter on microleakage is significantly higher (p < 0.0001) for 2-mm deep restorations, compared to those 1-mm deep. Pearson correlation coefficients suggest some relationship between microleakage and volume (r = 0.724, p < 0.0001), but not between microleakage and 'C' factor (r = 0.048, p = 0.6120).
  
  
  CONCLUSIONS
  Shrinkage stress and microleakage were higher in restorations with larger diameters and depths. Microleakage seemed to be related to a restoration's volume, but not to its 'C' factor.
authors.affiliation: Department of Dental Materials, FOUSP, Av. Prof. Lineu Prestes, 2227, University of São Paulo, School of Dentistry, São Paulo, SP 05508-900, Brazil. rrbraga@usp.br
authors.forename: Roberto R
authors.initials: RR
authors.lastname: Braga
authors.forename: Leticia C C
authors.initials: LC
authors.lastname: Boaro
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Kuroe
authors.forename: Caio L N
authors.initials: CL
authors.lastname: Azevedo
authors.forename: Julio M
authors.initials: JM
authors.lastname: Singer
mesh_terms: D000818:Animals; D001718:Birefringence; D017438:Bisphenol A-Glycidyl Methacrylate; D002417:Cattle; D003188:Composite Resins / Q000528:radiation effects*; D003737:Dental Cavity Preparation / Q000009:adverse effects*; D003763:Dental Leakage / Q000209:etiology*; D018772:Dental Marginal Adaptation; D003799:Dental Stress Analysis; D016014:Linear Models; D044367:Phase Transition; D019279:Resin Cements; D018709:Statistics, Nonparametric
chemical_list: D003188:Composite Resins; C444701:Filtek Z250; D019279:Resin Cements; C115612:single bond; D017438:Bisphenol A-Glycidyl Methacrylate