The Optimization Scheme For Maxillary Molar Distalization Based On Finite Element Analysis And Five Cases Of Clinical Pulp Diseases

Background:From prevention,occlusion to timely treatment,children’s bite induction can largely avoid or reduce the occurrence and development of malocclusion,induce children to establish a normal occlusal relationship,and promote the development of children’s physical and mental health.Molar distancing technique is a common clinical treatment method for Angle Class II malocclusion.It can effectively transform the class II Relationship of children’s molars into class I relationship,and solve the problems of crowded arrangement and deep coverage of children’s teeth.Objective:In this study,a three-dimensional finite element model of distal displacement of maxillary first molars with different force values and different force application methods was constructed to analyze the initial displacement and periodontal membrane stress distribution and characteristics of maxillary first molars,so as to provide the biomechanical basis and theoretical guidance for the scheme design of clinical distal maxillary molars.Methods:The three-dimensional finite element model including maxillary alveolar bone,dentition,periodontal ligament,the buccal canal of the extraoral arch,and pendulum appliance was established by taking CBCT data and combining Mimics,Geomagic Wrap,Solidworks,and ANSYS Workbench software.Loads of extraoral arch were0.0 N,2.0 N,3.0 N,4.0 N,and 5.0 N,and loads of pendulum appliance were 0.0 N,2.0N,2.5 N,and 3.0 N.the two appliances were used alone or in combination,a total of 19 groups of experiments.Three groups of working conditions with different loading modes are compared and analyzed: working condition 1 is the buccal side of the extraoral arch plus 4.0 N displacement force;The second condition is the palatal side of the pendulum appliance with a distancing force of 2.5 N;The third condition is the buccal side of the extraoral arch plus 4.0 N and the palatal side of the pendulum appliance plus 2.5 N.The initial displacement and displacement trend of seven displacement markers on maxillary first molar and central incisor in buccal palatal direction(X-axis),mesial-distal direction(Y-axis),and coronal root direction(Z-axis)were detected,and the stress distribution of periodontal ligament of the maxillary first molar was analyzed.Results:1.The three-dimensional finite element model of maxillary alveolar bone dentition periodontal ligament extraoral arch buccal tube pendulum appliance was successfully established.The model has 1131109 elements and 654412 nodes.2.In the 19 groups of experiments designed,when the extraoral arch or pendulum appliance was used alone,the equivalent effect load of the periodontal ligament of the maxillary first molar and the three-dimensional displacement of the maxillary first molar increased with the increase of the appliance load.When the two appliances are used together,the extraoral arch is loaded with 3.0 N and the pendulum appliance is loaded with 2.0 N,or the extraoral arch is loaded with 4.0 N and the pendulum appliance is loaded with 2.5 N,the adverse displacement of the maxillary first molar in the buccal palatal and vertical directions is small,and the molar displacement is greater when the extraoral arch is loaded with 4.0 N and the pendulum appliance is loaded with2.5 N.3.Working condition 1: when the buccal side of the extraoral arch is loaded with 4.0 N,the peak value of equivalent stress of periodontal ligament is 0.0307 MPa;Working condition 2: when the palatal side of the pendulum appliance is loaded with 2.5 N,the peak value of equivalent stress of periodontal ligament is 0.0397 MPa;When the buccal side is 4.0 N and the palatal side is 2.5 N in condition 3,the peak value of equivalent stress of periodontal ligament is 0.0148 MPa,which is 52% lower than condition 1 and62% lower than condition 2.Under the action of the extraoral arch,the maxillary first molar tilted and moved away,accompanied by lateral palatal rotation and slight depression of tongue tip;Under the action of pendulum appliance,the maxillary first molar is accompanied by buccal lateral rotation and slight elongation of tongue tip;Under the joint action of the two appliances,the maxillary first molar showed a trend of overall distal movement,and the buccal palatal rotation and vertical elongation and depression decreased significantly.Conclusion:1.The combination of CBCT data and a variety of software can effectively establish a high-precision three-dimensional finite element model of the distal maxillary molar,which provides a reliable model basis for the in-depth study of distal molar movement.2.The combination of extraoral arch and pendulum appliance can effectively realize the overall distal movement of maxillary molars and control the rotation of molars.Its distal movement effect is significantly better than that of the extraoral arch or pendulum appliance alone.