Aim: To analyze the movement of anterior teeth by changing the height of the power-arm and changing the force application points during whole maxillary dentition distalization with the aid of micro-implants in lingual orthodontics to set a biomechanical reference for effective clinical use of lingual orthodontic appliance.
Methods: A three-dimensional finite element model of the maxillary teeth with lingual appliance and the associated support tissue was established. Maxillary dentition with the force of 200g was distalized using implant as anchorage, then the movement of anterior teeth was analyzed by changing the length of power-arm (1mm, 3mm, 6mm, 9mm) and by changing the force location from lingual side to buccal side.
Results: During whole maxillary dentition distalization with aid of the implants in lingual orthodontics: when the height of power arm was 1mm, the anterior teeth rotated clockwise, with the increasing of the height of power-arm, the anterior teeth rotated counterclockwise gradually. When the height of power-arm was 9mm, all anterior teeth rotated counterclockwise. Central incisor and lateral incisor rotated counterclockwise and canine rotated clockwise when the buccal side force was applied.
Conclusion: With the increase of the height of the power-arm, the movement pattern of the upper anterior teeth is different. The canine is more sensitive to the height of the power-arm than the central incisor and the lateral incisor. When the height of the power-arm reaches 9mm, the upper anterior teeth are displayed as crown tipping buccally movement. Compare with lingual side force, the buccal side force do better in preventing the loss of anterior tooth torque. If the upper anterior teeth are up-right or lingually tipped before treatment, it is preferable to use longer power-arm or buccal side traction force. If the anterior teeth are already tipped buccally, then short power-arm or lingual side force is advised.
Keywords: lingual orthodontic, height of power-arm, movement pattern, 3-D finite element analysis, anterior teeth, maxillary dentition