The Design And Biomechanical Analysis Of A Simple Device For Anterior Tooth Root Control

Anterior tooth torque is the angle between the tangent line at the most protruding part of the crown lip surface and the perpendicular line of the occlusal plane.It plays an important role and is the difficulty as well as the hotspot in clinic orthodontic treatment.The anterior tooth torque can be controlled by several methods who follow different theories and principles,such as controlling the relationship between force lines and the center of resistance,controlling root movement with curved edgewise,and using force and torque simultaneously.However,those methods all have different limitations on clinic work.In this paper,elastic rubber bands are used to control torque.The gap between the bracket groove and the edgewise arch is the basis of the method.Tooth move around the wire under the action of force and torque while the edgewise arch is an inanimate body,and so,tooth can only be rotated in a fixed axis.In other words,edgewise arch becomes the fixed axis of the tooth.As the center of rotation is located near the incisal edge of the anterior tooth but far from the root apex,the distance of root moves is greater than the incisal edge does.And as a result,we adjusted the root position and achieved torque adjustment.Unlike previous methods for controlling anterior tooth torque,this method utilizes materials commonly used in orthodontics,such as elastic rubber bands,free traction hooks,and resin attachments.During clinical work,the method has some merits:easy gain,simple structure,low irritation to adjacent tissues,relatively simple mechanical mechanism.We find the root position can be effectively adjusted by our method.With three-dimensional finite element analysis,this study investigates the stress-strain distribution effect,tooth movement trend,when using elastic rubber bands to control the torque of anterior tooth.The results showed that the highest stress strain area on the central incisor was located in the palatine side neck,occupying a small area,and the moderate stress strain area occupied a large area.When two central incisors was adjusted at the same time,on the canine teeth and the first premolar the area occupied by the moderate stress strain area was significantly larger than that of the adjustment of one central incisors.In terms of instantaneous movement,the central incisor moves in the directionof palatine,the maximum movement is at the biting edge,towards the root of the tooth,the movement trend gradually decreases.the canine elongated,mesial inclinated,the first premolar depressed,mesiolingual torsioned.It is concluded that this device can effectively control the torque of the upper centrol incisor;The adjacent teeth of the traction hook have stress concentration,and the canine teeth and the first premolar are at risk of moving when controlling two central incisors at the same time.In summary,we innovatively use elastic rubber bands to control anterior tooth torque,which provides an effective method for anterior tooth torque adjustment.The low technical sensitivity and the relatively stable mechanical system of this method are conducive to clinical promotion.