[The establishment of three dimensional finite element model of a maxillary impacted canine and its support tissues].

PURPOSE: To establish a three dimensional finite element model of a maxillary impacted canine and its support tissues by means of finite element method (FEM) and spiral CT which can offer digital model for orthodontic traction. METHODS: A patient with a completely bony impacted maxillary canine was chosen. The CAD model of the canine and its surrounding tissues was established using spiral CT equipment, Mimics and Unigraphic. The CAD model was changed to FEM models by MSC. Mentat which could cut nets in CAD models. RESULTS: With the use of spiral CT,Mimics,UG and MSC, FEM model of the maxillary impacted canine and its support tissues and the whole maxilla was constructed and the model was of high geometrical similarity. CONCLUSION: The FEM model of maxillary impacted canine established by spiral CT,Mimics,UG and MSC has high accuracy, integrated constitution and optimized mesh which can be taken into account in the course of the treatment planning prior to starting therapy.

[Myoelectricity study on wearing flat bite plate under different raised distances in deep overbite therapy].

OBJECTIVE: To analyze changes of myoelectrical activity of anterior funicle of temporal muscle (TA) and masseter muscle (MM) after raising vertical distance of occlusion by flat bite plate during treatment of deep overbite in order to approach an optimal raised vertical distance. METHODS: A total of 70 persons were selected and divided into two groups: Experiment group (36 patients) with deep overbite and control group (34 persons) with individual normal occlusion. The experiment group was subdivided into three groups that were respectively raised D, D+2 mm and D+4 mm (D means free way space, mm). Electromyologram (EMG) was utilized to measure the average peak potential of TA and MM on quiescent condition before treatment and two weeks after wearing flat bite plate. RESULTS: 1) Before treatment, the average peak potential of experiment group was obviously higher than that of the control group (P<0.05). 2) After two weeks the potential of TA and MM of all persons in experiment group was obviously lower than before (P<0.05), the degree between the group D+2 mm and the group D+4 mm was not manifestly different, but both of the two groups were more obvious than the group D. CONCLUSION: The raised vertical distance of occlusion by flat bite plate, which exceeded free way space, was favourable to the functional recovery of masticatory muscles.

[3-dimensional finite element analysis of periodontal stress distribution when impacted teeth are tracted].

OBJECTIVE: To analyze stress around the impacted tooth by constituting a 3-dimensional finite element model of impacted tooth, consequently offer reference basis for clinic traction treatment. METHODS: The 3-dimensional finite element model of the impacted tooth was constituted by CT scan, append pericementum and alveolar bone model was used to constitute impacted model. 3 forces were loaded to 3-dimensional finite element model and the periodontal stress of impacted tooth was calculated. RESULTS: When force 1 was loaded to the model, the maximum stress was smaller, but the stress distribution was more average. When force 3 was loaded to the model, the maximum stress was larger, but the stress concentrated at the side of the force. When force 2 was loaded to the model, the stress distribution was medium. CONCLUSION: When the direction of the force is in line with the central axis, the maximum stress is smaller, and the stress distribution is more average, while this has advantage to the eruption of the impacted tooth. When the direction of the force has angle with the central axis of the impacted tooth, the angle is larger, the maximum stress is larger and the stress distribution is more concentrate, and this goes against the eruption of the impacted tooth. The angle between the orientation of the traction and central axis of the impacted tooth is smaller, there are more advantages to the eruption of the impacted tooth. So the angle should be properly selected in order to make sure of the eruption of the impacted tooth. When the angle is quite large, more anchorage is needed to resist to the large force.