title: Experimental and FE displacement and polymerization stress of bonded restorations as a function of the C-Factor, volume and substrate stiffness.
abstract: OBJECTIVE
  To determine the free surface displacement of resin-composite restorations as a function of the C-Factor, volume and substrate stiffness, and to compare the results with interfacial stress values evaluated by finite element analysis (FEA).
  
  
  METHODS
  Surface displacement was determined by an extensometer using restorations with 4 or 6mm diameter and 1 or 2mm depth, prepared in either bovine teeth or glass. The maximum displacement of the free surface was monitored for 5 min from the start of photoactivation, at an acquisition rate of 1s(-1). Axisymmetric cavity models were performed by FEA. Structural stiffness and maximum stresses were investigated.
  
  
  RESULTS
  For glass, displacement showed a stronger correlation with volume (r=0.771) than with C-Factor (r=0.395, p<0.001 for both). For teeth, a stronger correlation was found with C-Factor (r=0.709; p<0.001) than with volume (r=0.546, p<0.001). For similar dimensions, stress and displacement were defined by stiffness. Simultaneous increases in volume and C-Factor led to increases in stress and surface displacement. Maximum stresses were located at the cavosurface angle, internal angle (glass) and at the dentine-enamel junction (teeth). The displacement of the restoration's free surface was related to interfacial stress development.
  
  
  CONCLUSIONS
  Structural stiffness seems to affect the shrinkage stress at the tooth/resin-composite interface in bonded restorations. Deep restorations are always problematic because they showed high shear stress, regardless of their width. FEA is the only tool capable of detecting shear stress due to polymerization as there is still no reliable experimental alternative.
authors.affiliation: University of Santo Amaro, Department of Dentistry, Implantology Unit, São Paulo, SP, Brazil. Electronic address: leticiacidreiraboaro@gmail.com.
authors.forename: Letícia Cristina Cidreira
authors.initials: LC
authors.lastname: Boaro
authors.affiliation: University of Santo Amaro, Department of Dentistry, Implantology Unit, São Paulo, SP, Brazil.
authors.forename: William Cunha
authors.initials: WC
authors.lastname: Brandt
authors.affiliation: University of São Paulo, School of Dentistry, Department of Dental Materials, São Paulo, SP, Brazil.
authors.forename: Josete Barbosa Cruz
authors.initials: JB
authors.lastname: Meira
authors.affiliation: University of Birmingham, School of Dentistry, Biomaterials Unit, Birmingham, UK.
authors.forename: Flávia Pires
authors.initials: FP
authors.lastname: Rodrigues
authors.affiliation: University of Birmingham, School of Dentistry, Biomaterials Unit, Birmingham, UK.
authors.forename: William M
authors.initials: WM
authors.lastname: Palin
authors.affiliation: University of São Paulo, School of Dentistry, Department of Dental Materials, São Paulo, SP, Brazil.
authors.forename: Roberto Ruggiero
authors.initials: RR
authors.lastname: Braga
mesh_terms: D000134:Acid Etching, Dental / Q000379:methods; D000818:Animals; D017438:Bisphenol A-Glycidyl Methacrylate / Q000737:chemistry; D002417:Cattle; D003188:Composite Resins / Q000737:chemistry*; D003737:Dental Cavity Preparation / Q000145:classification; D003743:Dental Enamel / Q000648:ultrastructure; D045662:Dental Etching / Q000379:methods; D003764:Dental Materials / Q000737:chemistry*; D003793:Dental Restoration, Permanent / Q000145:classification; D003804:Dentin / Q000648:ultrastructure; D004548:Elasticity; D020342:Finite Element Analysis; D005898:Glass / Q000737:chemistry; D006244:Hardness; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D058105:Polymerization; D012821:Silanes / Q000737:chemistry; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors
chemical_list: D003188:Composite Resins; D003764:Dental Materials; C444701:Filtek Z250; D012821:Silanes; C115612:single bond; D017438:Bisphenol A-Glycidyl Methacrylate
keywords: Bonded restorations; C-Factor; Displacement; Finite element analysis; Interface; Polymerization shrinkage; Stiffness; Volume