[Three dimensional changes of lower teeth with NiTi round or square rocking chair archwire]

To observe the three-dimensional change of lower arch when NiTi round and square rocking chair archwire was used to open overbite in patients of Angle Class I or Class II with deep overbite,in order to providing experimental basis for clinicians.

Forty patients were chosen according to the inclusion standard. The patients were divided into four groups according to different archwire and with or without use of lace back and cinch back. The patients were taken plaster model before and after the overbite opened by using typical swinging chair labial arch, Laser scan and imageware software were used to make digital model and measure the three dimensional changes of the lower teeth,All data were analyzed with SPSS 12.0 software package.

When Rocking chair archwire was used to open overbite, it made the teeth changed in three dimensions, but the arch shape changed unconspicuously. The width between molars increased while the width between the canines and premolars had little change. The arch length had a tendency to increase and the incisors were intruded and had the tendency of labioclination, the incisor labioclination was more significant with lace back and cinch back. The canines showed the tendency of apical clination and there were obvious changes with the lace back and cinch back,the intruding-extruding change was not obvious. The second premolars were elevated, and the mesio-buccal cusp of the first molar did not move while the apo-buccal cusp was intruded.The first molars have the tendency of distal movement and lingual movement when using NiTi square wire.

In the process of opening overbite using rocking chair labial arch, there are different three-dimensional changes of the mandibular arch with NiTi round or square archwire, with or without lace back and cinch back.