[Experimental study of the trajectories of the upper first molar with extraoral force. Practical measurement of the movements in the three planes by a magnet-magnetic sensing system].

The upper first molar trajectory under the loading of extraoral force was studied in human subjects. The five loading directions, that is horizontal, upper, lower, high-pull and cervical were tested. Using a magnet-magnetic sensing system, the rectilinear and rotational movements were traced in the three planes, i.e. sagittal, frontal, and horizontal planes. It was concluded; 1. The molar inclined buccally with the loading in all the applied directions. 2. New evidence was found in the horizontal plane, i.e. the molar rotated mesially with the loading in the lower direction. The rotation may depend on the direction of the loop at the terminal of the inner-bow. Therefore it was suggested that the form of the loop affected the molar movements. 3. With the loading in the horizontal direction, the distal movement of the molar was evident and small displacement was observed in the extruded direction. 4. Loading both in upper and lower directions, the rotation of the molar was more evident than the rectilinear displacement. It was suggested that these loading would not be applicable to control the tooth in the rectilinear movements. 5. With the high-pull loading, the molar inclined mesially and shifted distally a little. On the other hand, it was greatly intruded. The results suggested that effective distal and intrusive movements would be expected by bending the outer-bow downward, since this procedure would prevent the tooth from tipping mesially. 6. The loading in the cervical direction caused large distal movement of the molar. Extrusion was also evident as it was expected from the loading direction.