PURPOSE: To investigate the influence of composite resin consistency and placement technique on proximal contact tightness of Class II composite resin restorations. MATERIALS AND METHODS: A manikin model (KaVo Dental) was used with an artificial first molar in which a standardized MO preparation was ground. This preparation was duplicated 360 times. Cavities were restored using Clearfil Photo Bond (Kuraray) combined with one of three composite resins of different consistencies: a low-viscosity (X-Flow, Dentsply), a medium-viscosity (Clearfil AP-X, Kuraray) and a high-viscosity composite (Tetric Ceram HB, Ivoclar Vivadent). Each composite was combined with 6 different matrix systems and separation techniques (n = 20). Groups 1 and 2: precontoured metal circumferential matrix (KerrHawe 1101-c) in a Tofflemire retainer combined either with hand instrument (OptraContact, Ivoclar Vivadent) or separation ring (Composi-Tight Gold, Garrison Dental Solutions). Group 3: pre-contoured metal sectional matrix (Lite-Flex, Danville Materials) with separation ring. Groups 4 and 5: pre-contoured metal circumferential dead-soft matrix (Adapt SuperCap, KerrHawe) with or without separation ring. Group 6: flat metal circumferential matrix (OptraMatrix, Ivoclar Vivadent) in a Tofflemire-retainer with hand instrument (OptraContact). Proximal contact tightness was measured using the Tooth Pressure Meter (University of Technology, Delft). To determine the effect of experimental variables on the proximal contact tightness, a multiple linear regression model was constructed. RESULTS: Measurements in group 6 were not possible; therefore, this group was excluded. The use of medium- or high-viscosity instead of a low-viscosity composite resin resulted in statistically significantly tighter proximal contacts (p