The aim of this in vitro study was to evaluate the marginal adaptation before and after cyclic thermo-mechanical fatigue of class II restorations with cervical margins in dentin realized with an experimental bulk fill dual cured composite resin with and without occlusal coverage with a light cured composite resin (Synergy D6, Coltène-Whaledent), in combination with a non-rinse conditioner/adhesive system (ParaBond, Coltène-Whaledent) with and without H 3 PO4 etching of enamel