A plug connection for jaw stump models for the releasable connection of tooth crown segments or jaw segments to a model base, which includes a plug pin which can be connected in snap-lock fashion with a sleeve. When a change for the starting gear position is instructed from the starting gear change instruction device, the controller controls the gear change actuator so as to shift the transmission to the instructed gear position only when the operation of the brake has been detected. Each instrument tray includes at least one RFID transponder tag storing identification information about that tray.