title: Effect of low-elastic modulus liner and base as stress-absorbing layer in composite resin restorations.
abstract: OBJECTIVE
  The aim of this study was to evaluate the effectiveness of liner and base materials to reduce the stress resulting from polymerization shrinkage. The null hypothesis tested was that the presence of low-viscosity liner and base materials under the composite resin restoration reduces the polymerization shrinkage stress.
  
  
  METHODS
  A quasi-three-dimensional photoelastic model of a second premolar with a class I preparation was restored using four experimental groups (n=7): RC, resin composite (Filtek Z250); FLRC, flowable liner (Filtek Flow)+resin composite restoration; VLRC, resin-modified glass-ionomer liner+resin composite restoration; and VBRC, resin-modified glass-ionomer base+resin composite restoration. The maximum shear stresses (tau(max)) were calculated along the adhesive interface in 13 predefined and standardized point locations. Data were submitted to one-way ANOVA, followed by a Tukey's post hoc test (p<0.05).
  
  
  RESULTS
  A significant difference was found among the experimental groups (p=0.001); therefore, the null hypothesis was rejected. The mean maximum shear stress was: 38.0kPa for RC, 52.1kPa for FLRC, 72.8kPa for VLRC, and 90.2kPa for VBRC. The polymerization shrinkage stress level from least to greatest was: RC<FLRC<VLRC<VBRC. The overall stress distribution in class I restoration indicated that stresses were primarily accumulated at the cavosurface and internal line angles.
  
  
  CONCLUSIONS
  Using a flowable composite or resin-modified glass-ionomer as liner or base material under composite resin restoration increases the polymerization shrinkage stresses at the adhesive interface leading to a possible adhesive failure.
authors.affiliation: Department of Cariology and Restorative Dentistry, Nova Southeastern University, College of Dental Medicine, 3200 South University Drive, 3rd Floor, Fort Lauderdale, FL, USA. wluana@nova.edu
authors.forename: Luana C A
authors.initials: LC
authors.lastname: Oliveira
authors.forename: Sillas
authors.initials: S
authors.lastname: Duarte
authors.forename: Cleudmar A
authors.initials: CA
authors.lastname: Araujo
authors.forename: Anthony
authors.initials: A
authors.lastname: Abrahão
mesh_terms: D000704:Analysis of Variance; D001718:Birefringence; D003188:Composite Resins / Q000737:chemistry* / Q000528:radiation effects; D003198:Computer Simulation; D003736:Dental Cavity Lining; D018772:Dental Marginal Adaptation; D019232:Dental Restoration Failure; D003793:Dental Restoration, Permanent / Q000379:methods*; D003799:Dental Stress Analysis; D055119:Elastic Modulus; D005899:Glass Ionomer Cements / Q000737:chemistry; D006801:Humans; D055115:Light-Curing of Dental Adhesives; D008422:Materials Testing; D008954:Models, Biological; D019279:Resin Cements / Q000737:chemistry; D033081:Shear Strength; D018709:Statistics, Nonparametric
chemical_list: D003188:Composite Resins; D005899:Glass Ionomer Cements; D019279:Resin Cements