[A study of three dimensional changes in superior teeth with rocking chair archwire]

To observe the three dimensional changes of upper arch using laser scan.

40 patients aged from 15 to 21 suffering from Angle's Class II subdivision I malocclusion combined with deep overbite were selected from the Department of Orthodontics, School of Stomatology, Shandong University. The patients were divided into two groups randomly, after the overbites of the two groups were opened using different methods, plaster models were made for each patient. Then, digital research models were available through laser san and three dimensional imaging technique. Finally, the changes in three dimensions of the maxillary teeth were measured. Student's t test was performed using SPSS 13.0 software package.

In the sagittal dimension, the incisors had a tendency of labial inclination. Canines and the first permanent molars were likely to move distally. No distinct changes were found in the second premolars. According to whether or not there were tip back of the archwires and "8" shaped ligation there was significant difference in the change of both incisors and the first molars (P<0.05), while there was no significant difference in the change of canines and the second molars. In the vertical dimension, incisors and the distal-buccal cuspids of the first molars had a tendency of intrusion while the second premolars were likely to extrude; there was no significant change in canines and the mesio-buccal cuspids of the first molars and there was no significant difference between the two groups(P>0.05). In the transverse dimension, the widths of arches in the molar zone had a tendency to increase, while there was no significant change in canine and premolar zones between the two groups(P>0.05).

Standard Ni-Ti rocking chair arch wire can bring about many changes to the teeth and dental arch in three dimensions and its effect on deep overbite is remarkable.