Three-dimensional Modelling And Finite Element Analysis Of The Human Mandible And The Lower Teeth Under Intermaxillary Elastics

Objective: To construct the 3D finite element model (FEM) including the mandible, the lower teeth, some roots of the teeth and their periodontal ligament, 12 straight-wire brack -ets and the square wire. Then analyze the stress distribution, displacements of the mandible and the lower teeth under intermaxillary elastics.Methods: A series of mandible CT images of the healthy volunteer were collected and reconstructed to establish 3D images using DICOM data and MIMICS software. 3D FEM was constructed using MSC.PATRAN software and calculated using MSC.NASTRAN software.Results and Conclusion:1. The morphology of 3D FEM including the mandible and the lower teeth was as fine as the practicality. The 3D FEM had 16726 nodes and 13343 elements.2. The following conclusions were drawn.(1). Class II elastics: The lower dentition has moved forward in the mandible under class II elastics; To avoid wrong movement of the lower teeth of the patients with asymmetric mandible and dental arch, the force value and direction of class II elastics should be adjusted; To avoid striction of the arch width and inclination of the lower molars and premolars, the lower archwire should be widened; Light force and adjusting archwire can prevent rotation of the first molar; To the patients whose roots of incisor teeth are short, the value of the force should be reduced; To compare short class II elastics with long class II elastics, the former can make the molars extrude less and make the anterior teeth move forward greater. It is benefit for"High-angle"patients. The lower first molar'rotation under short class II elastics is contrary to the rotation under long class II elastics. It should be noticed while the archwire is adjusted.(2). Class III elastics: To avoid striction of the arch width, the lower archwire should be widen ahead of long term Class III elastics. The lower anterior teeth without active torque will move bodily toward lingual direction under light force, but the dental crowns will incline toward lingual direction under great force. This inclination should be counterworked by lingle root torque. The more extrusion of the canine and the lateral incisor under short class III elastics is benefit for"High-angle"patients with open-bite.(3). Up-down elastics: The lower first molar extrude clearly. The long-distance elastics can make the lower first molar incline toward lingual direction which should be pulled both sides. The lower dental arch can be expanded potentially.(4). Anterior box elastics: Anterior box elastics influence the teeth more than the bone.To be brief, the 3D FEM was constructed successfully including brackets and square wire. The mechanism is nailed down through simulating stress distribution and displacement under the six intermaxillary elastics. It will steer the clinic practice.