Preliminary Analysis Of The Degree Of Alveolar Bone Resorption Of The Maxillary Incisor Periodontal Tissue Biomechanics - Dimensional Finite Element Analysis

Objective: This' study was designed to investigate the stress distribution in periodontal tissues of maxillary incisors with various alveolar bone heights , under various orthodontic forces simulating clinically used rectangular archwire with T loop by the 3-D finite element method, and to define the location of the center of resistance of maxillary incisors with various alveolar bone heights in order to clarify the biomechanism of orthodontic tooth movement and component of optimal orthodontic force system for adult orthodontics.Methods: Through embedding, section, node selection and discretization, five three-dimensional finite models were constructed on the basis of general anatomic morphology of Chinese maxillary incisors, which including anchwire , brackets, incisors, periodontal ligaments, and alveolar bone with various heights. In order to analyse the stress distribution induced in periodontal tissues, these models were subject to various loadings simulating force system of clinically used rectangular archwire with T loop. Then on the basis of these 3-D models the center of resistance of the central incisor the lateral incisor and the maxillary incisors with various alveolar bone heights were determined with differential and integral calculus.Results:l.Five 3-D finite element models of maxillary incisors including orthodontic appliances and pulp cavity were successfully constructed. vv ith various alveolar bone heights.2.Under horizontal loading the stress distribution induced in periodontal ligament were similar with concentration of stress in cervical margin and apex and a zero stress level zone at the middle part stresses on one side of root surface mainly were compression and on the other side were tension, which represent bending. The characteristics of stressdistribution on the surface of alveolar bone were very complex and the value of three principle stresses varied widely . With increasing resorption of alveolar bone, the three stresses at cervical margin and apex induced in periodontal ligament were rising.3.Under vertical loading, the stress distribution induced in periodontal ligament were similar too with concentration of stresses in cervical margin and apex . With increasing resorption of alveolar bone, the three stresses at cervical margin and apex induced in periodontal ligament were rising.4.Under torque loading, the stress distribution induced in periodontal ligament were similar too,with concentration of stresses in cervical margin of mesia and distal side.5. With increasing resorption of alveolar bone, the centers of resistance of the maxillary central incisor and the maxillary lateral incisor shifted apicaly, including and not including pulp cavity.6. With increasing resorption of alveolar bone, the center of resistance of the maxillary incisors including pulp cavity, were located within the mid-sagittal plane,6.1mm lingual to archwire's labial side, respectively at 38.5 %, 47.3%, 55.2%, 64.1%, 75.2%length of the central incisor measured from the alveolar crest.Conclusion:1. With various alveolar bone heights, the stress distribution of the central incisor and the lateral incisor subjected to various loadings were similar: the highest stress observed firstly on the root,secondly in the alveolar bone,and thirdly in the periodontal ligament. Three principal stresses of the same location in periodontal ligament were very similar, namely definite compression or tension, and in coincidence with tendency of tooth movement. On the surface of roots, the Differences of three principle stresses are obvious and represent typical bending deformation. Stress distribution on the surface of alveolar bone is very complex , notsimple compression or tension. Three principal stresses of the same location have significant difference and mostly opposite sign.2.When intrusion, retraction and torque, stress distribution induced in the periodontal ligament of the central incisor and the lateral incisor was charictarized with tipp...