Hemanth M, Raghuveer H P, Rani M S, Hegde Chathura, Kabbur Karthik J, Vedavathi B, Chaithra D
Professor and Head, Department of Orthodontics and Dentofacial Orthopedics Dayananda Sagar College of Dental Science, Bengaluru Karnataka, India, Phone: 09845459666, e-mail:
Department of Oral and Maxillofacial Surgery, Dayananda Sagar College of Dental Science, Bengaluru, Karnataka, India.
J Contemp Dent Pract. 2015 Sep 1;16(9):740-3. doi: 10.5005/jp-journals-10024-1750.
Orthodontic tooth movement occurs due to various biomechanical changes in the periodontium. Forces within the optimal range yield maximum tooth movement with minimum deleterious effects. Among various types of tooth movements, extrusion and rotational movements are seen to be associated with the least amount of root resorption and have not been studied in detail. Therefore in this study, the stress patterns in the periodontal ligament (PDL) were evaluated with extrusion and rotational movements using the finite element method FEM.
A three-dimensional (3D) FEM model of the maxillary incisors was generated using SOLIDWORKS modeling software. Stresses in the PDL were evaluated with extrusive and rotational movements by a 3D FEM using ANSYS software with linear material properties.
It was observed that with the application of extrusive load, the tensile stresses were seen at the apex, whereas the compressive stress was distributed at the cervical margin. With the application of rotational movements, maximum compressive stress was distributed at the apex and cervical third, whereas the tensile stress was distributed on cervical third of the PDL on the lingual surface.
For extrusive movements, stress values over the periodontal ligament was within the range of optimal stress value as proposed by Lee, with a given force system by Profitt as optimum forces for orthodontic tooth movement using linear properties. During rotation there are stresses concentrated at the apex, hence due to the concentration of the compressive forces at the apex a clinician must avoid placing heavy stresses during tooth movement.
正畸牙齿移动是由于牙周组织发生各种生物力学变化所致。在最佳范围内的力能产生最大程度的牙齿移动，同时对牙周组织产生最小的有害影响。在各类牙齿移动中，牙齿伸长和旋转移动引起的牙根吸收量最少，且尚未得到详细研究。因此，在本研究中，使用有限元方法（FEM）评估了牙齿伸长和旋转移动时牙周膜（PDL）中的应力模式。
使用SOLIDWORKS建模软件建立了上颌切牙的三维（3D）有限元模型。采用具有线性材料特性的ANSYS软件，通过三维有限元法评估了牙齿伸长和旋转移动时牙周膜中的应力。
观察到，施加伸长载荷时，根尖处出现拉应力，而压应力分布在颈部边缘。施加旋转移动时，最大压应力分布在根尖和颈部三分之一处，而拉应力分布在舌侧牙周膜颈部三分之一处。
对于伸长移动，在使用线性特性的情况下，牙周膜上的应力值在Lee提出的最佳应力值范围内，且在Profitt给出的力系统作用下，是正畸牙齿移动的最佳力。旋转移动时，应力集中在根尖，因此由于根尖处压力集中，临床医生在牙齿移动过程中必须避免施加过大应力。
