A dental apparatus that includes a turbine, a rotor, and a disruptive contour. The turbine drives a tool by compressed air. The rotor is arranged in a turbine compartment and rotates about its longitudinal axis. The rotor includes a plurality of blades that extend up to a front side of the rotor. The disruptive contour is at least one protrusion on a wall opposite the front side of the rotor which extends over a height in a direction of the longitudinal axis of the rotor.