Polymerization Shrinkage Stress in Composite-resin Restorations Associated Liner/base

Objectives: The aim of this study was to evaluate the efficiency of liner or base materials under composite-resin restoration to reduce the stress resulting from polymerization shrinkage and loading. Methods: Four groups were assigned: G1) Control - composite-resin restoration (Z250-3M ESPE); G2) 0.5mm flowable-composite liner (Filtek Flow-FF, 3M ESPE) + composite-resin restoration (Z250); G3) 0.5mm resin-modified-glass-ionomer liner (Vitrebond-VT, 3M ESPE) + composite-resin restoration (Z250), and G4) Base with resin-modified-glass-ionomer (VT) + composite-resin restoration (Z250). The study was divided in three phases: Photoelasticity (P1), Tensilometry (P2) and Finite Element-FE (P3). P1 - Photoelastic models (n=7) for all groups were used to determine polymerization shrinkage stress. The Maximal Shear Stress (t_max) was calculated along adhesive interface and statistically analyzed (ANOVA, Tukey's, p<0.05). P2 – The polymerization shrinkage stress was determined using a tensilometer. The materials (M1-Z250, M2-FF e M3-VT) were inserted into 2mm space, between two dentin bovine cylindrical bases, which one was connected to a load cell (n=7). Results were statistically analyzed (ANOVA, Tukey's, p<0.05). P3 - The polymerization shrinkage stress resulting from phases P1 and P2 were used to create a 2D FE model in combination with occlusal loading. Loading conditions: I - vertical (occlusal surface/60N); II - lateral (buccal cusp/30N); III - lateral (lingual cusp/30N). Von Mises-s_e, Tangencial-s_t and Normal-s_n stresses in bonded interface were calculated. 

Results: t_max in Phase P1 were G1<G2<G3<G4 (p<0,001). Polymerization shrinkage stress in Phase P2 were M1<M2<M3 (p<0,001). FE analysis (s_e, s_t and s_n) in Phase 3 showed higher stress in adhesive interface after loading. The maximum stress value found for adhesive interface were G1<G2<G3<G4.

Conclusions: Using a liner or base material under composite-resin restoration is not likely to reduce the effects of stresses produced by polymerization shrinkage or loading.