The invention relates to a dental treatment instrument for operating a rotational tool. The treatment instrument has a head drive, which is provided for coupling to a shaft of the rotational tool and comprises a sleeve-like guide bushing (1), and a collet (9) for fixing the rotational tool. The guide bushing (1) has surface sections (3) which form parts of a cylindrical shape in at least one first axial region. Recesses (4) are provided which face radially outwards from the surface sections (3) and which impart a shape deviating from a rotationally symmetrical shape to the inner contour of the guide bushing (1). By virtue of the surface sections (3), a circular cylindrical shaft of a rotational tool can be guided or supported in a particularly suitable manner. The recesses (4) are additionally suitable for engaging radial protrusions of a non-circular cylindrical shaft of a rotational tool such that the non-circular cylindrical shaft can be driven in a particularly suitable manner. The treatment instrument according to the invention thus offers the possibility of receiving tool shafts with a correspondingly modified shaft geometry in order to meet particularly high corresponding requirements and counteract the aforementioned disadvantages and weaknesses of a shaft according to DIN EN ISO 1797 and the possibility of additionally using the tools according to DIN EN ISO 1797 for standard applications.