The device for infiltration of approximal tooth surfaces, with a flexible planar element and with a holder into which the planar element is clamped, is characterized in that the planar element is a liquid-impermeable plastic film which has a surface area for taking up a liquid to be used for treatment, and in that the holder is a bow-shaped element with a web and two lateral arms which extend from the latter and are arranged in an arc-shape or U-shape, to which the plastic film is connected in a liquid-impermeable manner.