Biomechanical Study Of Different Patterns Of Maxillary Molars Distalization With Clear Aligners

Objectives:By constructing three-dimensional finite element models which included maxilla,maxillary dentition,periodontal ligament(PDL),clear aligner,two different designs of maxillary molars distalization were simulated,to analyze and compare the initial displacement and equivalent stress of PDL of anterior teeth and molars when the first molar started to move distally.In order to provide a theoretical basis and guidance to the clinic in the selection and design of different distal displacement methods for molar distalization.Methods:An adult female volunteer with normal occlusion was selected.The maxillary third molars have been extracted and there is sufficient bone volume in the posterior region of the molar.A CBCT was used to scan the maxillofacial area and obtain data in DICOM format.Mimics21.0,Geomagic Wrap 2021,and Solidworks 2017 were used for establishing 3D models of two sets of bilateral maxillary second molars shifted 3 mm(model 1)and 1.5 mm(model 2)distally respectively,including maxilla,maxillary dentition,PDL,clear aligner.The 3D finite element model was obtained by using Ansys Workbench2021 R1 for material parameter setting,grid segmentation,contact setting,boundary constraints,and other operations.The simulated clear aligner distal displacement of maxillary molars with different distal displacement patterns.The group 1:For models where the maxillary second molar has moved 3 mm distally,the maxillary first molar is pushed 0.25 mm distally using invisible orthodontic appliance.The group 2:For the maxillary second molar that has moved 1.5 mm distally,the maxillary first and second molars were pushed 0.25 mm distally using invisible orthodontic appliance.The initial displacements in the three-dimensional direction and equivalent stress of PDL of anterior teeth and molars were observed and analysed in two distal displacement patterns.Results:Two three-dimensional finite element models including maxilla,maxillary dentition,PDL,clear aligner was successfully constructed to simulate maxillary molar distalization treated with invisible orthodontics combined with different distal displacement methods for molar distalization.To analyse and compare the initial displacement and equivalent stress of PDL of anterior teeth and molars when the maxillary second molars have been moved a certain distance(3 mm,1.5 mm)distally and when the maxillary molars have been moved distally using the single molar distal displacement method and the serial molar distal displacement method,respectively.The results show that both molar distal displacement designs result in varying degrees mesial and labial tipping with intrusion of the maxillary anterior teeth,leading to anchorage loss.When the first molar is designed to move 0.25 mm distally after the second molar has moved 3 mm distally,the maxillary first molar showed distal inclination with a degree of lingual inclination and extrusion,while the maxillary second molar shows a small distal inclination with buccal inclination and intrusion.After the second molar has moved 1.5 mm distally,the first and second molars are designed to move 0.25 mm distally.Both the first and second molars show a distally inclined movement,but the first molar is more distally displaced than the second,and the first molar is accompanied by a small amount of lingual inclination and extrusion of the crown and the second molar by a small amount of buccal inclination and intrusion of the crown.Conclusions:Two three-dimensional finite element models of maxilla,maxillary dentition,PDL,clear aligner was successfully established to simulate the clinical orthodontic process of molars distalization with clear aligners.The following conclusions were reached.1、Two molar distal displacement designs result in varying degrees loss of anterior tooth anchorage,and loss of the serial molar distal displacement pattern more.2、When using the single molar distal displacement design,after the maxillary second molar is distally displaced in place and the first molar is then distally displaced,the second molar is able to maintain its distal displacement effect without proximodistal movement.3、When the maxillary molars are distally displaced using the serial molar distal displacement pattern,the distal displacement efficiency of the second molars decreases when the maxillary first molars begin to be distally displaced.Suggests that a certain amount of overcorrection can be designed in the clinic.