BACKGROUND: The movement of a rigid body through space may be comprehensively described by constructing a "finite helical axis" (FHA). The rigid body carries out a rotation around this axis for discrete periods of time while at the same time moving along this axis. MATERIAL AND METHODS: The free opening and closing movement of the mouth was registered in eight asymptomatic test persons, using the CADIAX electronic axiography system (GAMMA-DENTAL, Klosterneuburg, Austria). Subsequently, the position of the FHA in space, the angle of rotation around this axis, and the amount of translation along the FHA were determined for each subject, using the coordinates of the measuring styluses. RESULTS: During the initial phase of the mouth-opening movement, the FHAs were near the condyle. Over the course of the opening movement, they moved toward downward backward, downward and downward forward, and finally to forward upward toward the condyle upon reaching maximum mouth opening. During the closing movement, the FHAs shifted back in the reverse direction. During both the opening and the closing movement, there was a slight translational movement along the FHAs, which provided an indication of mandibular deviation.
BACKGROUND: The movement of a rigid body through space may be comprehensively described by constructing a "finite helical axis" (FHA). The rigid body carries out a rotation around this axis for discrete periods of time while at the same time moving along this axis. MATERIAL AND METHODS: The free opening and closing movement of the mouth was registered in eight asymptomatic test persons, using the CADIAX electronic axiography system (GAMMA-DENTAL, Klosterneuburg, Austria). Subsequently, the position of the FHA in space, the angle of rotation around this axis, and the amount of translation along the FHA were determined for each subject, using the coordinates of the measuring styluses. RESULTS: During the initial phase of the mouth-opening movement, the FHAs were near the condyle. Over the course of the opening movement, they moved toward downward backward, downward and downward forward, and finally to forward upward toward the condyle upon reaching maximum mouth opening. During the closing movement, the FHAs shifted back in the reverse direction. During both the opening and the closing movement, there was a slight translational movement along the FHAs, which provided an indication of mandibular deviation.