Influence of low elastic modulus liners on polymerization stress development of restorative composites

Objective: To evaluate the efficacy of low elastic modulus materials used as liners in reducing polymerization stress of two composites(Heliomolar-HM and Herculite-HL). Methods: Flexural modulus (FM) of ten bars of two flowable composites (Revolution flow-RVL and Tetricflow-TTF), one unfilled resin (Scotchbond MP-SBMP), plus HM and HL were assessed by three-point bending test. Polymerization stress (PS)for HM and HL was monitored in three situations: 1) with a 0.5 mm thick layer of either SBMP, TTF or RVL, pre-cured on one of the glasssurfaces; 2) placed directly to the glass substrate and 3) over a layer of HM or HL. Data were analyzed with ANOVA/Tukey’s test (p < 0.05). Results: FM values ranged from 9.4 to 2.8 GPa. All materials presented statistically different modulus, except for HM and TTF. Compliance ranged from 8.2 x 10-6 mm/N (no pre-cured layer) to 17.1 x 10-6 mm/N (SBMP pre-cured layer). HL presented statistically higher PS than HM (7.6 and 5.8 MPa, respectively). All liners were able to reduce contraction stress compared to the no liner group for both composites (p = 0.05), but they were all statistically equivalent (no liner = 8.3; RVL = 6.5; TTF = 6.3; SBMP = 5.8; HL = 7.5; HM = 5.6, all in MPa). Conclusion: In the groups where no liner was applied, the use of a low elastic modulus layer produced stress reduction equivalent to the ones provided by a layer of the higher modulus composites.