[Study on two-dimensional tooth mobility]

Tooth mobility was measured with the use of a two-dimensional displacement measuring system. This small-sized system can measure the displacement both in the direction of the tooth axis and the buccolingual direction simultaneously with no contact. As test teeth, lower right first premolars with no clinical mobility were examined. The load was applied from the lingual to the buccal direction, to the vertical direction as well as from the buccal to the lingual direction. The results obtained were as follows: 1. This system possesses sufficient accuracy and reproducibility for tooth mobility measurement (measurement range 500 microns, resolving power 1 microns). 2. Most of the load-displacement curves showed diphasic displacement. 3. As to the amount of displacement in the buccolingual direction, 3 of 8 cases showed greater values by the load in the buccal direction and the remaining 5 by the load in the lingual direction. 4. As to the displacement direction of loaded teeth, the lingual and buccal load displaced teeth to the lingual-coronal and buccal-radicular directions respectively. Teeth under the vertical load were displaced almost to the radicular and slightly to the buccal direction. 5. As to the direction of tooth displacement in relation to load directions, it appeared that the teeth not only rotated within the dental sockets but also indented or extruded into the dental sockets.