Abstract: In order to optimize the handling of a rotating surgical tool for producing a depression in bone material, provision is made for an ultrasonic transducer which is capable of emitting and receiving ultrasonic waves to be arranged in the tool, and for the ultrasonic transducer to be connectable to an ultrasonic generator and to a receiver which generates signals in dependence upon the strength of the ultrasonic radiation received by the ultrasonic transducer and upon the length of time between the emission of ultrasonic radiation and the reception of reflected ultrasonic radiation, which are a measure of the condition of the bone material in the direction of emission.