Influence Of Elastic Layer On The Composite Resins Shrinkage Stress L. Graiff*, M. Calabrese, M. Maranto, P.N. Mason (Dept. Of Restorative Dentistry, Dental School, University Of Padova Italy) Objectives The aim of this study was to evaluate the effect of some lining materials (flowable compomers, resin modified glass Ionomer, flowable composites) as elastic layer, under composite resins to reduce shrinkage stress. Besides, we achieved photoelastic resin samples to determine the distribution and the magnitude of internal stress in resin composite restorations.   Methods It was recorded the contraction strength of a micro-hybrid composite (Tetric Ceram, TC, Vivadent) alone and with lining materials. Four flowable composites (Tetric Flow - Vivadent; Revolution - Kerr; Flow Line - Kulzer; ÆliteFlo - Bisco); two flowable compomers (Compoglass Flow - Vivadent; Prima Flow - DMG); one resin modified glass-ionomer cement (Vitrebond - 3M) were used. The measurements were maked by using 64 titanium cilinders(5mm Ø X 12 mm h) connected to a Universal Testing Machine (Erichsen 476). The circular surfaces of cilinders were sandblasted with 95-micron alpha alumina particles coated with a bonding agent (Scotchbond one – 3M). The resin samples was inserted between two titanium cilinders and photocured, than the contraction strength was recorded for 30 minutes. Photoelastic analysis was achieved by bidimensional premolar photoelastic resin samples with MOD cavities. The photoelastic resin was PL-1 (Measurements Group Inc. Photolastic Division, Raleigh, NC, USA).These samples, were sandblasted with 95-micron alpha alumina particles before the restoration for increase the adhesion. Photoelastic anlysis showed the isocromatics produced by the composite shrinkage.   Results The contraction strength recorded at 30 minutes was: TC (3.48 MPa); TC + Tetric Flow (3.20 MPa); TC + Revolution (2..90 MPa); TC + Flow Line (3.10 MPa); TC + ÆliteFlo (3.04 MPa); TC + Compoglass Flow (2.70 MPa); TC + Prima Flow (2.94 MPa); TC + Vitrebond (2.29 MPa).   Conclusion In our study, the use of flowable composites under resin composite restorations (Tetic Ceram), reduce the contraction strength of micro hybrid composite from Vivadent. The use of Vitrebond and Compoglass Flow under Tetric Ceram restoration reduced the contraction strength of 34% and 22.3% respectively versus Tetric Ceram alone.