Objective: The aim of the present study was to evaluate the marginal adaptation of class II restorations after using two different dentine bonding agents in vitro. Methods: Sixty freshly extracted human molars, free from any cracks, caries or restorations were used. To simulate the clinical situation as closely as possible, during restorations placement, teeth were imbedded in a model of plaster and put in a phantome head. In the mesial and distal part of each tooth a standardized class II cavity was prepared. The cervical margin was located 0.5mm below the cemento-enamel-junction. After having completed all preparations, the teeth were randomly assigned into four groups with fifteen teeth each. Group 1: Excite/ Tetric; group 2: Excite/ Tetric/ Tetric Flow; group 3: Xeno/ Spectrum; group 4: Xeno/ Spectrum/ X-Flow. Metall matrix bands and cervically wedges were placed. All materials were applied according to the instructions of the manufacturer and light cured. All teeth were then subjected to 1150 thermal cycles (5°C-55°C). All specimens were stored for 24h in methylen blue and penetration depths were measured under a light microscope. Results: For the four experimental groups following penetration depths were evaluated (mean values and stadard deviations in microns): Group 1: 4145 (± 604); group 2: 3492 (± 593); group 3: 4161 (± 782); group 4: 2872 (± 1748). Statistical analysis showed a significant influence of the different material combinations (ANOVA, pConclusions: Within the limitations of an in vitro investigation it can be concluded that the use of flowable composites might improve marginal adaption in class-II-restorations. Keywords: flowable composites, class-II-restorations, marginal adaptation, dentin bonding agent