Effect of low-elastic modulus liner and base as stress-absorbing layer in composite resin restorations

ObjectivesThe 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.MethodsA 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 (τmax) 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).ResultsA significant difference was found among the experimental groups (p = 0.001); therefore, the null hypothesis was rejected. The mean maximum shear stress was: 38.0 kPa for RC, 52.1 kPa for FLRC, 72.8 kPa for VLRC, and 90.2 kPa 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.SignificanceUsing 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.