Three-dimensional Finite Element Analysis Of Mandibular Expansion With Modified Screw Expander

Objective:To establish a high precise and efficient three dimensional finite element model, including mandibular dentition, periodontal ligament, mandible, mucosa and modified screw expander. Mandibular expansion with screw expander in different firmed way or arm shape is simulated, which is aimed at modified characteristics of the expander, in order to discuss biomechanical mechanism of modified expander, provide clinical evidence for the application of modified screw expander, and conduct orthodontists to design expander for satisfying expansion effect.Methods:1.A healthy adolescent female volunteer with complete dentition and individual normal occlusion was selected as experimental material and scanned by head CBCT to acquire DICOM data and construct three dimensional finite element model with finite element modeling software, which contains dentition, periodontal ligament, mandible, mucosa, band and modified Hyrax expander.2. Two models were built on the finite element model. Model two and three were added first premolar band and second premolar band on the modified expander respectively. The property of modified expander was set to be the rigidity. Three models were loaded 0.2mm expansion quantity. To observe the initial placement and the stress distribution of teeth, the stress distribution of the periodontal ligament and jaw bone.3. The modified expanders of model four and five were set to be the variant. The net trestle of modified expander was wiped out in model five. Two models were also loaded 0.2mm expansion quantity to observe the initial placement and the stress distribution of teeth and the stress distribution of the periodontal ligament and jaw bone.Result:1.The high precise and efficient three dimensional finite element model was established including dentition, periodontal ligament, mandible, mucosa and modified Hyrax expander, which contains 201080 nodes and 154318 elements. The finite element model of modified Hyrax expander contains 17188 nodes and 5359 elements. 2. The initial placement of posterior teeth, the tooth and the periodontal ligament maximum Von-mises stress of three models were nearly equaL The initial placement of molars was more than premolars, and moved to buccal side in inclination. The tooth and the periodontal ligament maximum Von-mises stress of the first molar were larger than other teeth. The stress distribution of the jaw bone in three models was also similar, which distributed widely on alveolar bone and basal bone.3. The initial placement of posterior teeth, the tooth and the periodontal ligament maximum Von-mises stress, the stress distribution area of the jaw bone in model five were less than model four. The initial placement of premolars was more than molars in two models. The tooth and the periodontal ligament maximum Von-mises stress of the first molar were larger than other teeth in two models. The expander arm in model four produced nearly the whole deformation. The maximum deformation of expander arm in model five approached to the spiral spring.4. The initial placement of posterior teeth, the tooth and the periodontal ligament maximum Von-mises stress, the stress distribution area of the jaw bone in model four were less than model one.Conclusion:1.The finite element model is high precise and can simulate clinical practice well, which made basement for researching biomechanics mechanism of modified Hyrax expander to expand mandible.2. The modified Hyrax expander added premolar band increases rather retention force than expansion effect. However, the expander with two molar bands is capable for providing enough retention force and can be placed easily in clinic.3. The torque force that produced by the expander deformation has more influence on the initial placement of posterior teeth and the tress distribution of the jaw bone. The expander arm can enhance the rigidity and decrease the deformation by adding net trestle structure, which can acquire high expansion effect. 4. More stable increase in dental arch width can be acquired by means of improving the rigidity of the expander, which is helpful for transmitting expansion force effectively and rebuilding alveolar bone to acquire more stable expansion effect. The results of the experiment provides biomechanics basis for orthodontists to modify mandibular expander.