A medical, in particular dental, device for determining the quality of a bone by cutting a thread into the bone by a rotating threaded element having at least one cutting edge, wherein the medical, in particular dental, device comprises a control unit which comprises a first electrical contact device for connection to a motor drive, a second contact device for connection to a display unit and a measurement circuit, which is operatively connected to the first electrical contact device and to the second contact device, wherein the measurement circuit is configured: (i) to determine values of the motor current via the first electrical contact device, the motor current being supplied to the motor drive to rotatably drive the threaded element that can be connected to the motor drive, wherein the motor current values correlate with or are substantially proportional to transmitted torque values of the motor drive, and wherein the motor current values or torque values are a measure of the quality of a bone, (ii) to monitor and/or determine the depth of penetration of the threaded element into the bone, and (iii) to generate measurement signals which show the relationship between the determined motor current values, the torque values which correlate with or are substantially proportional to the motor current values or the quality of a bone derived from the determined motor current values or the torque values and the depth of penetration, and to transmit these measurement signals via the second contact device to the display unit, so that the display unit displays on the basis of the transmitted measurement signals the relationship between the depth of penetration and at least one of the following parameters, namely the determined motor current values, the torque values which correlate with or are substantially proportional to the motor current values or the quality of a bone, characterized in that the control unit comprises an evaluation circuit which is configured to combine into bone quality classes or assign to bone quality classes the motor current values determined by the measurement circuit or the torque values which correlate with the motor current values or are substantially proportional thereto. (i) to determine values of the motor current via the first electrical contact device, the motor current being supplied to the motor drive to rotatably drive the threaded element that can be connected to the motor drive, wherein the motor current values correlate with or are substantially proportional to transmitted torque values of the motor drive, and wherein the motor current values or torque values are a measure of the quality of a bone, (ii) to monitor and/or determine the depth of penetration of the threaded element into the bone, and (iii) to generate measurement signals which show the relationship between the determined motor current values, the torque values which correlate with or are substantially proportional to the motor current values or the quality of a bone derived from the determined motor current values or the torque values and the depth of penetration, and to transmit these measurement signals via the second contact device to the display unit, so that the display unit displays on the basis of the transmitted measurement signals the relationship between the depth of penetration and at least one of the following parameters, namely the determined motor current values, the torque values which correlate with or are substantially proportional to the motor current values or the quality of a bone,