Abstract:

Objective To establish a three-dimensional finite element model of mandibular teeth during retraction in sliding mechanics， by simulating the application of different torque controls of anterior teeth， and to clarify the impact of different torque controls on the movement of mandibular teeth during the retraction process. Methods Using cone beam computed tomography （CBCT） data from a permanent dentition patient scheduled for mandibular first premolar extraction in orthodontic treatment， a three-dimensional finite element model of straight-wire sliding retraction of mandibular teeth was constructed via Mimics， Geomagic Wrap， and Solidworks software. In Ansys Workbench software， six conditions with different torques of -11°， -6°， -3°， +3°， +6° and+11° were applied to the mandibular anterior teeth， with a 1.5 N retraction force loaded. The initial displacement trends of each mandibular teeth in the labiolingual， mesiodistal， and vertical directions were analyzed under these conditions. Results In the buccolingual directions， different anterior torques exerted a tendency to procline and intrude the central and lateral incisors， with this tendency becoming increasingly evident as the torque increased. For other teeth in the lower arch， it induced a lingual tip and extrusion trend， with the canines and second premolars being the most affected by torque changes， followed by the first molars. The second molars were primarily influenced by the retraction force， exhibiting a displacement trend of mesiallingual rotation and were less affected by torque changes. In the mesialdistal direction， the changes in anterior torques had no significant impact on the posterior teeth. Conclusion Different anterior torques lead to extrusion and lingual tipping movements of other teeth in the mandibular arch， with this influence also depending on the position of the teeth within the arch. Teeth located more posteriorly are less affected by torque changes but are more influenced by the retraction force. When applying different torques to control anterior teeth clinically， the clinicans should pay more attention to the movements of other teeth.

Key words: Torque, Three-dimersional finite element analysis, Sliding straight wire, Tooth movement, Extraction treatment