| Objective:There are some patients in orthodontic patients with periodontitis,and periodontitis results in the absorption of alveolar bone,the decrease of bone height of the alveolar bone and the crown root ratio imbalance.Maxillary anterior teeth retraction at this moment,due to the change in alveolar bone quantity and quality,make the periodontal tissue reaction to orthodontic force is different from the normal orthodontic patients with periodontal support.For these patients,imposed by the size and composition of orthodontic force is very different from normal patients’ periodontal tissue.In this study,the method of three-dimensional finite element method was used to simulate the bone absorption of the alveolar bone,and analyze the distribution of the periodontal stress,and direct the appropriate orthodontic force system.Methods:This study by tapered beam of CBCT scanning for CT images of upper jaw and maxillary teeth,imported into the 3-d finite element calculation software Mimics,using Geomagic software for processing,the model fitting,merger,united in UG raphe processing surface,make the model be materialization,outward of periodontal membrane pump shell,generated contains upper jaw,maxillary teeth,straight wire bow and correcting device,3 d finite element model of periodontal membrane,and simulating stress distribution of patients with alveolar bone resorption.On the basis of the established height of the normal alveolar bone model 1,the model of 2,3and 4 was respectively reduced 2mm,4mm and 6mm horizontal balanced alveolar bone by deleting the elements.Then simulated load on the model,analysis in 60 g,80 g,100 g,150 g orthodontic force,removing the first premolar adduction front teeth teeth in each model group,to study the posterior set of tooth distribution of stress and the tooth initial displacement.Results:1.Same orthodontic force system,the same orthodontic force,with the loss of the alveolar bone height,posterior teeth total displacement increases,the parodontium stress increases gradually;the same alveolar bone height,with the increase oforthodontic force,the total displacement of the posterior teeth increased,and the paradontium stress gradually increased.when alveolar bone absorption of more than 4mm,the total displacement trend,parodontium stress significantly increases.2.With 150 g of adduction,normal alveolar bone height compared biggest parodontium Von Mises stress: when 2 posterior teeth(second premolar.first molar)adduction,reduce 2 mm of the alveolar height,the adduction force reduce to about 100 g,or increased to 3 posterior teeth(second premolar.first molar.second molar)adduction,force can achieve 150g;When the bone height of the alveolar bone is reduced by 4mm,the force will decrease to about 80 g,or increase to 3 posterior teeth,and the force can reach 150 g.When the bone height of the alveolar bone is reduced by 6mm,the force should be reduced to below 60 g,or increase to 3 posterior teeth,and the adduction force can be between 60 g and 80 g.3.With 150 g of adduction force,normal alveolar bone height compared to the maximum total displacement value: when 2 posterior teeth adduction,reduce 2 mm of the alveolar height,the adduction force to reduce to about 100 g,or increased to 3posterior teeth,adduction force can achieve 150 g;When the height of the alveolar bone is reduced by 4mm,the force should be reduced to about 60 g,or increase to 3 posterior teeth,and the force can reach nearly 150 g.When the bone height of the alveolar bone is reduced by 6mm,it will be increased to 3 posterior teeth,and the force can reach about80 g.Conclusions:1.In this study,the stress distribution of the parodontium and the distribution of tooth displacement were calculated by applying different size force to the posterior teeth of different bone height.2.In the same alveolar bone height,the anterior teeth in the posterior teeth of the three abutment teeth were lower than two teeth in initial displacement,and get more adduction force;In the same adduction force,the absorption of alveolar bone increases gradually,all the initial displacement also is increasing,three abutment teeth get significantly smaller than that of two abutment teeth teeth.3.Same size force on different alveolar bone height of stress and displacement distribution is different,the same exerting strength to produce different size of the alveolar height of displacement,stress distribution is also different,for patients withalveolar bone loss,according to the degree of loss should determine the size of the force value,in patients with severe loss more than molar root bifurcate should avoid stress or significantly reduce stress,must increase the plant resistance to auxiliary adduction,in order to avoid the stress caused by periodontal tissue irreversible damage and persistent root,alveolar bone absorption,in order to better improve the quality of medical treatment. |
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