| Objective:By establishing a three-dimensional finite element model of the mandible mandibular dentition,periodontal membrane,clear aligners,the effects of different attachment designs and different angles of anchor resistance on the equivalent stress and tooth displacement trend of the tooth and periodontal tissue were studied when clear aligner moved the first molar mesially at one step after simulating the extraction of the mandibular second premolar.The purpose of this study is to provide valuable references for orthodontists in the rational design of attachments and angles of anchor resistance when using clear aligners to move the mandibular first molar mesially.Method:Select an individual adult female volunteer who is in normal condition,sign an informed consent form with the patient,and then perform CBCT scanning of their maxillofacial region.Save the image data collected after scanning in DICOM format,and import it into Mimics 20.0 software,Geomagic Studio 2015 software,and Unigraphics NX 1911 software to establish a three-dimensional finite element model that simulates the extraction of the mandibular second premolar and mesial movement of the mandibular first molar using clear aligner.The changes in the equivalent stress and tooth displacement trends of the tooth and periodontal tissue under the following 8 working conditions were analyzed using Ansys Workbench 2019 software.Configuration design: Configuration 1: Add rectangular attachments to the clinical crown centers of the mandibular canine,first premolar,and second molar,and do not place any attachments on the mandibular first molar.Simulate the use of clear aligner to move the mandibular first molar mesially,shortening the appliance’s mesial length by 0.25 mm.Configuration 2: Based on configuration 1,a vertical rectangular attachment was placed in the buccal clinical crown of the mandibular first molar.Configuration 3: Based on configuration 1,a double vertical rectangular attachment was placed in the buccal clinical crown of the mandibular first molar.Configuration 4: Based on configuration 1,place a vertical rectangular attachment in the buccal and lingual clinical crowns of the mandibular first molar.Configuration 5: Based on configuration 1,a horizontal rectangular attachment was placed in the buccal clinical crown of the mandibular first molar.Configuration 6: Based on configuration 1,place a horizontal rectangular attachment in the buccal and lingual clinical crowns of the mandibular first molar respectively;Configuration 7: Based on configuration 1,the clear aligner model generated after the mandibular first molar was tilted at a distal angle of1 ° was worn back onto the original dental model.Configuration 8: Based on configuration 1,the clear aligner model generated after the distal inclination of the mandibular first molar by 2 ° was worn back onto the original dental model.Result:1.Successfully established a three-dimensional finite element model of the first molar mesial movement using clear aligners,which has high accuracy and good simulation degree,and can better simulate the characteristics of the physical object.It is conducive to the analysis of experimental results.2.In the process of the molar mesial movement simulated in this experiment,the overall movement of teeth in the sagittal direction cannot be achieved by using different attachment designs or different angles of anchor resistance.The first molar shows a trend of mesial tilt displacement,and the second molar has distal displacement trend.3.Compared with the configurations of different attachments,it is found that the maximum equivalent stress of periodontal membrane is always concentrated in the neck area of the mesial and distal of the first molar,and the maximum equivalent stress of the root is concentrated at the bifurcation of the root of the first molar and the middle area of the root.The addition of attachments reduces the tendency of teeth to move obliquely,but it causes an increase in effect forces such as roots and periodontal membranes of most teeth in the dentition.4.The difference between the groups of designing attachment at both buccal and lingual sides(configuration 4,configuration 6)and the groups of designing attachment at only the buccal side(configuration 2,configuration 3 and configuration 5)is obvious,and there is no obvious difference between the two groups of different accessories designed on buccal and lingual sides and the three groups with different accessories designed only on the buccal side.5.After the first molar is designed to anchor resistance,the tendency of mesial tilt of the teeth decreases,the maximum equivalent stress of the root and periodontal membrane decreases,and the anchor resistance of 2°is better than that of 1°.Conclusion:1.Rectangular attachment can effectively increase the retention,improve the ability of clear aligners to control tooth movement,but can lead to an increase in the maximum equivalent stress of the root and periodontal membrane of most teeth in the dentition.It is suggested that when designing attachments,it is necessary to consider the patient’s periodontal health and the possibility of root resorption in stress concentrated areas.2.During the mesial movement of molars,about the control ability in the sagittal direction,designing attachment on both buccal and lingual sides of the molar is better than designing attachment only on the buccal side,and there is no obvious difference between the horizontal rectangular attachment and the vertical rectangular attachment.3.During the mesial movement of molars,the method of adding the anchor resistance angle to the clear aligners is feasible,through which the tendency of tooth tilt movement can be effectively reduced,and the maximum equivalent stress of the tooth root and periodontal membrane can be reduced,so that the stress distribution is more uniform.4.It is difficult to achieve the ideal overall movement of molars in the sagittal direction only through attachment design or anchor resistance design.If necessary,other auxiliary devices should be used for treatment. |
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