This study assessed how the location of the tapping point is affected by changing the head position. An intra-oral tracing device consisted of a metal tracing plate and a central bearing pin was used in five fully dentate subjects. The tracing plate was fixed to the maxillary part of the device parallel to the occlusal plane. The central bearing pin was fixed to the mandibular part of the device and was located at the midpoint of a line connecting the bilateral first molars. The pin was placed perpendicular to the tracing plate. The appliance was inserted in the mouth and the subject was asked to perform tapping movements with the head Camper and Frankfort plane placed horizontally. The tapping movements (n=30) were made at a 30 mm-range of motion, and the incisal and condylar points were tracked with a 6-degree-of-freedom jaw movement tracking system (TRIMET; Tokyo Shizaisha Co., Japan) . The antero-posterior distribution of 30 tapping points and their mean position from intercuspal position were analyzed in incisor and condylar points between two head positions. Result revealed that the condylar points corresponding to the tapping points converged into a small area when the head was positioned with the Camper plane horizontal. However, in both head positions, condylar points were located anteriorly from the intercuspal position. From the results, it can be concluded that head position has it's effects on the distribution and mean position of tapping points. In addition, it can be suggested that from the distribution of scattered tapping points, the head should be positioned with the Camper plane horizontal to record the tapping points at a convergent area.
The present study reports a newly developed laryngeal movement tracking system. The system consists of a metal rod, a displacement sensor, a plastic plate, and two identical magnets. The plastic plate was fixed to the skin over laryngeal prominence. The rod and magnets conduct the movement of the plate in relation to laryngeal movement to the sensor during swallowing. To evaluate the performance of the system, sensor outputs during swallowing were compared with recordings of masseter and digastric muscle EMGs in 6 young and healthy adults. Tests were conducted both in head-fixed (n = 3) and head-free (n = 3) conditions. Each subject was given a test fluid (2.0 ml of tea, at a temperature of 25°C) into the oral cavity and was instructed to swallow it. Actual motion picture of the laryngeal movement during swallowing was also recorded in the sagittal plane using a video tape recorder in one subject. The swallowing event in the laryngeal movement could be recorded as a biphasic curve by the system both in head-fixed and head-free conditions. Temporal analysis of the recorded curve together with the EMGs and the motion picture revealed that; the recorded curve reflects natural movement of the larynx during swallowing; and the inflections on the curve corresponded to laryngeal upward and downward movements respectively. The present results suggest that the developed system may be applicable to obtain temporal aspects of swallowing easily and safely in the clinic and laboratory.