Analyze Force System Of Utility Arch And Rocking-chair Arch In Deep Overbite Orthodontic Treatment Adopting Finite Element Method

Objective: To study the force system of teeth when using different arch wires,and provide a theoretical basis for the clinical use of the utility arch and rocking-chairarch in the treatment of deep overbite.Methods: Set up finite element model of mandible, mandible teeth, edgewisebrackets, utility arch and rocking-chair arch adopting the finite element method, designmethods of fitting arch wires into slots in accordance with the clinical and relevantliterature, and calculate and analyze the force direction and magnitude of molars andincisors by ANSYS.Results: When using the utility arch, incisors bear intrusive force and molars bearextrusive force. With the utility arch wire giving intrusive force to canine, the intrusiveforce to incisors reduces, but the extrusive force to the first molars increases. Whenapplying rocking-chair arch only to the central incisors, lateral incisors and the firstmolars, the incisors bear intrusive force and the first molars bear extrusive force. Whenadding application to canines on the original basis, the intrusive force to incisorsincreases, but the extrusive force to the canines and the molars reduces. With applyingto the second premolars, the intrusive force to the incisors continues to increase, theextrusive force of canines increases, the second premolars bear the extrusive force, andthe force direction of the first molars changes from the extrusive direction to theintrusive direction. In this point, we delete the canine bracket, then the intrusive force tothe incisors decrease, the extrusive force to the second premolars and the intrusive forceto the first molars increase.Conclusions:1. While the utility arch exerts intrusive pressing force to the canines,the canines will produce large reacting force to the arch wire, which has obvious impactto the intrusive force value of the incisors, especially of the lateral incisors, therefore, pressing of canines shall be independently completed by adding elastic connectionsbetween the canines and the arch wire after completing pressing of incisors.2. Differentapplication methods of rocking-chair arches will produce different force magnitude anddirections to teeth. With addition of teeth applied with rocking-chair arch, the force tolateral incisors and molars changes the most. The force of the rocking-chair arch to thelower canines always is extrusive force, so it shall be avoided in the cases which need toextrude the canines.3. When applying rocking-chair arch only to the lower incisors andthe first molars, the intrusive force to the molars is almost the same with using theutility arch. On the premise of adding anchorage to the molars, it also can be used forthe treatment of curve of spee for the high-angle cases. To the deep overbite patientswith lowest point of curve of spee curve close to the incisors, it will obtain rather idealtreatment results by choosing the rocking-chair arch and putting it into the brackets atthe incisors, canines, premolars and molars.