Three Dimensional Finite Element Analysis Of Tooth Stress Distribution And Movement Tendency In Maxillary Use Mini-screw Cooperate With Upper Accentuated-curve To Close Tooth Space

In clinical, for patients with maxillary protrusion, we usually extract maxillary first premolars, en mass retraction of upper anterior teeth with mini-implant anchorage to solve the problem. With advantages of small in size, easy to implant and dismantle , small trauma and low cost, reducing the patient's pain and not rely on patient's cooperation,the mini-implant has been accepted by more and more doctors and patients in clinical practice, and become the preferred method of strong anchorages. In order to avoid overbite increase, upper accentuated-curve is usually co-used to close space. However, it often results in distal tipping and intrusion of molar.Objectives: In order to find out the cause of molar intrusion and how to avoid molar intrusion, this experiment analyzed the stress distribution and movement tendency of tooth by changing the angles of upper accentuated-curve and the height of free traction hook.Methods:Spiral CT scanning , Mimics and Ansys software were employed in this study to construct the three-dimensional finite element model of maxillary teeth,periodontal ligaments and alveolar bone as well as the 0.019×0.025 inch stainless steel upper accentuated-curve archwires with different angles(5°,10°,15°,20°,25°) and the free traction hook with different height(2.1mm,4.0mm,5.5mm). By exerting 1.5 N backward force,we analyzed the stress distribution and movement tendency of tooth.Results: We successfully constructed the three-dimensional finite element model of maxillary teeth,periodontal ligaments and alveolar bone as well as the 0.019×0.025 inch stainless steel upper accentuated-curve archwires with different angles. Our results show that teeth stress mainly distributed in braces and around baccal tube, periodontal stress mainly distributed in the neck of tooth. And with the angle of upper accentuated-curve archwires and the height of free traction hook both increased, stress values on each teeth and periodontium increased. Upper accentuated-curve archwires made the incisors labially tip, intruse, distally upright and mesi-labially torsion, Canine labially tip,prolong,mesial- tipped and mesi-labially torsion. The second premolar and the first molar labially tip, intruse, distal upright and mesi-labially torsion. And with the angle of upper accentuated-curve archwires increased, all tooth movement tendency increased. With the height of free traction hook increased, backwards component of force increased, upwards component of force decreased. It is benefit for retracting of upper anterior teeth, and also can reduce the extent of molar intrusion.Conclusion:①Successfully defined the upper accentuated-curve archwires. We simulated the way of placing upper accentuated-curve archwires in clinical. Provided new ideas for researches on the upper accentuated-curve archwires.②Teeth and periodontal stress distribution were similar, stress value of the canine was the largest, second was the lateral incisor, the stress values of premolar and molar were similar, the smallest was central incisor. And with the angle of upper accentuated-curve archwires and the height of free traction hook increased, each teeth and periodontal stress value increased.③Upper accentuated-curve archwires made the incisors labially tip, intruse, distally upright and mesi-labially torsion, Canine labially tip,prolong,mesial- tipped and mesi-labially torsion. The second premolar and the first molar labially tip, intruse, distal upright and mesi-labially torsion. And with the angle of upper accentuated-curve archwires increased, each tooth movement tendency increased.④When the angle of upper accentuated-curve archwires increased, the degree of molar intrusion increased, but when the height of free traction hook increased, the degree of molar intrusion decreased.5°upper accentuated-curve archwires cooperate with 5.5mm free traction hook,the degree of molar intrusion was minimum.⑤In clinical,the angle of upper accentuated-curve archwires should be chose according to the torque of anterior tooth,and cooperated with the high free traction hook,in order to increase favorable tooth movement, and avoid adverse tooth movement。...