Three Dimensional Finite Element Analysis Of Upper Incisors Stress Distribution And Movement Tendency Using Class â…¡ Elastic Cooperated With J Hook And Rocking Chair Archwire

Class II division1malocclusion is one of the most commonproblems in orthodontic clinical practice. In clinical, forpatients with maxillary protrusion and crowded dentition, weusually extract the first premolars in maxillary, en mass retractionof upper incisors with strong anchorage to solve the problem. Inorder to avoid the the crown lingual inclination and overbitedeepening, J hook cooperated with rocking chair archwire were usedto close the extraction spaces.Objectives: This experiment, by simulating clinical upperincisors retraction,was aimed to analyze the stress distributionand movement tendency of upper incisors by changing the angles ofrocking chair archwire and the location of J hook, so as to providetheoretical basis for clinical application. Methods：Second-generation Brilliance64CT scanning, theMimics modeling software and Ansys analysis software were employedin this experiment to construct the three-dimensional finiteelement model of maxillary teeth(which maxillary first premolarsare extracted, pull canine to far reaches the second premolar teethmesial distal),its support organizations and different curvatureof rocking chair archwire (0°,5°,10°and15°), simultaneouslyto establish J hook in distal and mesial lateral incisor, engagingclass II elastic model(100g). The angle of J hook model is37°.Thetraction force is200g on both sides.Results： We have constructed the three-dimensional finiteelement model of maxillary teeth, its support organizations anddifferent curvature of rocking chair archwire successfully. Theresults show that upper incisors stress mainly distributed nearbraces area and periodontal ligament (PDL) stress mainlydistributed around alveolar crest. The stress value on PDL has thesame variation tendency as upper incisors,but it is further smallerthan the stress on upper incisors. J hook lowered upper incisorsduring space closing. Additionally,J hook situated distally tolateral incisor tended to retract upper incisors. When J hook situated mesially to lateral incisor, upper incisors were apt tobe intruded. With increasing of rocking chair curvature, theintrusion effect of upper incisors are becoming more obvious.Conclusion：①Constructing J hook and rocking chair archwiremodels, we obtain the stress distribution and movement tendency ofupper incisorsand provide a new idea for furtner research on theJ hook and rocking chair archwire.②The upper incisors and its PDLhave the different stress concentration area. The upper incisorsstress mainly distributed near braces area and PDL stress mainlydistributed around alveolar crest. The stress value on PDL has thesame variation trend as upper incisors, but it is further smallerthan the stress on upper incisors.③There is a little differencein the stress between central incisor and lateral incisor when Jhook situated distally to lateral incisor. But there is muchdifference in the stress between central incisor and lateral incisorwhen J hook situated mesially to lateral incisor.④The rockingchair archwire made upper incisors tip labially, intrude, uprightdistally and rotate mesio-labially. With increasing of rockingchair curvature, the intrusion effect of upper incisors is moreobvious.⑤With J hook upper incisors were intruded during space closing. While J hook, situated mesially to lateral incisor, upperincisors were easier to be intruded. As far as class II Division1malocclusion be concerned, deep overjet and deep overbite, labialtipping of upper incisors should be corrected. In order to attaintreatment objective, we’d better use J hook situated mesially tolateral incisor coordinated with the appropriate rocking chairarchwire curvature to close extraction space and effectivelyretrude upper incisors.