Finite Element Study Of Physiological Anchorage Control Concept On Anchorage Molars In Lingual Orthodontics

Objective: To study the effect of the physiological anchorage control concept in lingual and buccal orthodontic techniques to anchorage molars during the sliding method extraction space closure stage.Methods: The three-dimensional finite element model of the right maxillary first molar、periodontal ligament and alveolar bone of the right maxillary was established according to CBCT.The three-dimensional finite element model of XBT buccal tube and MBT buccal tube was established according to the data of PASS appliance and MBT appliance.The finite element model was divided into the MBT group with the axial inclination of 0° and the PASS group with the axial inclination of-7°.The simulated 100 g,150g,and 200 g sliding retraction force was loaded on the buccal and lingual sides respectively.At the same time,50 g,75g,100 g sliding retraction force was loaded on the buccal and lingual sides simultaneously.The displacement and periodontal ligament stress of the anchorage molar under different conditions were derived.Results: In different conditions,the anchorage molars showed different degrees of rotation,tipping,intrusion,and extrusion.As the force increases,these displacement trends also increase.The mesial displacement of buccal and lingual sides respectively load force group is less than the other two groups.Under the same force load,the mesial displacement of the PASS group is less than the MBT group,the maximum stress of the periodontal ligament is smaller than the other two groups when the lingual force is loaded only.Compared to the MBT group,the maximum stress of the periodontal ligament of PASS group is higher when the force is loaded buccal side,but less when the force is loaded to the lingual and buccal-lingual sides.Conclusions: The concept of physiological anchorage control applied to lingual orthodontics has better sagittal anchorage control and vertical control.The maximum stress of the periodontal ligament on the anchored molars is also lower,but attention needs to be paid to torque and rotate.