Three-dimensional Finite Element Analysis Of The Influence Of The Position Of The Traction Hook On The Upper Anterior Teeth Depression And Adduction Under The Complex Force System

Objective:Maxillary protrusion is one of the most common malocclusion deformities in the clinic.For the maxillary protrusion patients,the incidence of gingival smile is close to 20.Gingival smile is when the maxillary anterior teeth are exposed to more than4 mm of the gums when they smile.The investigation shows that gingival exposure above 2mm will affect the beauty of the face.The maxillary anterior protrusion is sagittal and affects the beauty of the side,while the gingival smile is perpendicular,and the abnormal relationship exists between lips and teeth.Microimplant Anchorage is often used to resist adduction and depression of anterior teeth and to improve sagittal and vertical unregulation.At present,there are more researches on simple anterior tooth adduction or simple anterior tooth depression.Scholars such as Sung E Hhave only implanted posterior dental implants,and anterior teeth torque is slightly out of control during adduction.Cho S M and other scholars have only implanted anterior dental implants.The anterior teeth with depression were accompanied by oblique movement rather than simple depression.It can be seen that simple adduction and low pressure effect are not good.The Namburi study shows that the combination of indentation and adduction has more advantages than that of simple adduction or simple indentation.In the study of depressed anterior teeth,there were many studies on the position of implant and the displacement trend of anterior teeth,but the influence of different traction hook positions on anterior teeth biomechanical effects under complex force system was not found.In this study,using three-dimensional finite element analysis,a finite element model of maxillary-periodontal ligament-teeth was finished.The implant was implanted into the anterior and posterior teeth to establish the complex force system to explore the effect of traction hook position on the biomechanical effect of maxillary anterior and posterior teeth,and to provide theoretical direction for the treatment of maxillary protrusion and gingival laughter.This study divided two parts:The first part: Constructing a finite element model of maxillary-periodontal ligament-teethMethod: In accordance with the inclusion criteria,a case of adultpatients with maxillary protrusion with gingival smile was selected.The maxilla and dentition were scanned by conical beam CT.The images were induced by Mimics17.0 ? Geomagic 12.0 and created three-dimensional entity.The attachment of bracket,arch wire and implant were generated by Solidworks software.The three-dimensional finite element model of maxillary-periodontal ligament-tooth group was established by introducing Abaqus6.14 software.Result: A three-dimensional finite element model of maxillary-periodontal ligament-teeth was established.Conclusion: By using reverse engineering software,3D finite element model with high geometric similarity and good mechanical similarity can be established.The second part: Three-Dimensional finite element Analysis of the influence of the position of the traction Hook on the Upper anterior teeth depression and adduction under the complex Force systemMethod: On the basis of the finite element model established in the first part,three implants were implanted between the root of the central incisor and the root of the first molar,and the three groups of models were established in accordance with the different positions of the traction hook.On the basis of the finite element model established in the first part,4implants were implanted in the anterior incisor region: between themaxillary bilateral central incisor and the lateral incisor,between the lateral incisor and the canine root.Posterior region: five groups of models were established according to the different positions of the traction hook between the maxillary bilateral second premolars and the first molars.The initial displacement and periodontal ligament stress of the anterior teeth and maxillary first molars were calculated.The biomechanical effects of implant depression and adductive anterior teeth in 8 groups were compared and analyzed.Result: 1 ? In sagittal direction,the anterior teeth showed a tongue moving trend when implanted with 3 implants.When the traction hook moves distantly,the central incisors changed from labial movement to global tongue movement,and lateral incisor moved from lingual side to lingual side with tilting movement,and the lateral incisor moved from the lingual side to the lingual side with oblique movement.The canine does lateral movement of the tongue with the tendency of proximal rotation.When 3 implants were implanted,the anterior teeth showed a downward movement trend in the vertical direction,and the central incisor moved along with the far position of the traction hook.The depression of lateral incisor decreased.The traction hook was seated between the central incisor and the lateral incisor,and the incisor showed a tendency of elongation,the traction hook was located between the lateral incisor and the canine,the canine was inclined to the palatal side,and the traction hook was betweenthe canine and the second premolar.The fangs tend to hold down.2 ? In the sagittal direction,when wedged 4 implants,the anterior teeth are apt to move in the tongue direction.The central incisors,lateral incisors and incisors tend to lean toward the tongue,and the canine teeth is apt to lean in the vertical direction,and the anterior teeth tend to decrease in the vertical direction.As the traction hook moved far away,the anterior tooth depression decreased.3?The difference of sagittal root displacement can reflect the degree of lip and tongue tilt,lateral incisor is the largest,the canine is the smallest,and the inclination of the central incisor under the four implant nails is smaller than that of the three implants,the torque control is better,and the lateral incisor is better.Canine is on the contrary.Model 5 anterior teeth were least inclined.In all models,the anterior teeth of Model 5 were more evenly depressed than those of three implants,and were closer to the overall depression.4?When 3 or 4 implants were implanted,the maxillary first molars tended to tilt distal to the buccal side.5 ? Periodontal ligament stress: the maximum stress of periodontal ligament is concentrated on the lateral incisor,and the maximum stress is distributed generally at the cervical margin,which indicates that the tooth is inclined to move.The stress distribution of periodontal ligament is consistent with the trend of tooth displacement.Conclusion: According to the three-dimensional finite element model established in this text and the analysis of relevant data,the following conclusions can be drawn: 1?During the adduction process of anterior teeth,with the posterior traction hook moving backward,the anterior teeth showed a tendency from labial inclination to tongue inclination,which may be related to the increase of the angle between the force and the arch wire and the increase of sagittal force,and the increase of sagittal force in the process of anterior tooth depression.With the position of the posterior traction hook moving backward,the effect of anterior tooth depression was gradually reduced.2 ? The angle of incisor in the four implants is smaller than that in the three implants,and the torque control of the anterior teeth is better.The four implant nails hold down the force more evenly and are closer to the whole.3?In all models,the torque control of Model 5 is better and closer to the integral indentation.It is recommended that Model5 should be used clinically.4?The stress distribution of periodontal ligament near the traction hook is almost the same as the tooth displacement,and the tooth is inclined to move.