The invention relates to tracking motion of a patient s jaw wherein motion of a tracking item (50) which represents motion of the jaw is followed by at least one camera (22) arranged to a medical x ray imaging apparatus (10) and wherein the motion detected by the at least one camera (22) is applied on a digital model depicting hard tissue of the jaw. The moving digital model of the hard tissue of the jaw thus generated is shown on a display (31 ) to visualize movement of the hard tissue.