Photoelastic Analysis Of Open Bite Treatment Using Multiloop Edgewise Arch Wire (MEAW) And Reverse-curve Arch Wire With Vertical Elastics In Anterior Teeth Area And Their Applications

Openbite is not a minority in malocclusion, and it has serious influence on mastication, deglutation, cutting, pronunciation and many other functions. Furthermore, it has great influence on patients's beautiful outlook and mental health. The complicated etiology and mechanism, difficult diagnosis and therapy,high relapse rate of openbite make it as multiple point and hard point in orthodontic. In clinical, you must first grasp the mechanism of openbite treatment: the anterior teeth were moved lingually and extruded, the posterior teeth were moved mesially and rotated to distal and intrused.Kim applied first Multiloop edgewise archwire (MEAW) for openbite treatment and make favourate effect. Then several scholars investigate the mechanism of MEAW by finite element and photoelastic method, and certificated its efficiency. However, it's not often used in clinic, because you need longer running time to bend MEAW, the oral hygiene is unpleasant. In 1996, Enacar first reported that used reverse-curve arch wire with vertical elastics in anterior teeth area for open-bite treatment and could get similar effect as MEAW. Then Miyajima, Nazan and HuMin used this technique in clinic and treated open bite successfully. Meantime, HuMin etal investigated the stress distribution of left infradentale, the first and second molar using reverse-curve arch wire with vertical elastics in anterior teeth area, and proved that these teeth moved as mechanism of openbite treatment. But this research has not investigated other teeth's movement trendency. Three-dimensional photoelastic method is direct-viewing,and experimental model is similar as human body on physical parameter and dimension, and is loaded by practical arch wires. So the finding is true and reliable.My advisor discovered that the posterior teeth were moved mesially and the anterior teeth were moved lingually is more profit for the treatment result through many years clinical practice. You must extract teeth to move other teeth as above. And you can choose different extraction method for different open-bite.Objective①To investigate the mechanism of open bite treatment using MEAW and reverse-curve arch wire with vertical elastics in anterior teeth area by three-dimensional photoelastic analysis. And estimate the curative effect of MEAW and reverse-curve arch wire with vertical elastics in anterior teeth area and establish the rationale for clinical application.②By clinical controlled experiment to investigate the different mechanism of open bite treatment using different extraction methods, and to find out a better method for open bite treatment.Methods①Photoelastic experiment: Using photoelastical material to make teeth, alveolar bone and periodontal membrane, combine to full teeth and periodontium photoelastical model as solidify temperature curve. The photoelastical model of full teeth is similar as human body on physical parameter and dimension. The first stress of model's alveolar bone is small, and the modulus of elasticity of every part is similar with human body's. Loading by practical arch wires. Condition 1: 0.016×0.022 inch MEAW, with 25°reverse-curve ,and vertical elastics on"L"between lateral incisor and canine. Condition 2: 0.016 inch stainless arch wire of 15°reverse-curve with vertical elastics on collar between lateral incisor and canine. Blade every freezing model-tooth by anteroposterior axes and vertical axes, examine the stress of every point of alveolar bone by three-dimensional shear-equation method, investigate the stress distribution regularity of per-tooth to describe their move tendency.②Clinical experiment: Collect twenty successfully treated anterior openbite cases,include 8 cases by extracting the third molars and 12 cases by extracting the bicuspid teeth. Measure the cephalometrics on the superimposition of the lateral head films, and choose 11 skeletal measurements and 21 dentoalveolar measurements. Input the measured dates to computer and analysised by matched-pairs t test using SPSS 13.0. Compare the change of measurements by different extracting methods.Result①Photoelastic experiment: Condition 1: The second molar was intruded and rotated to distal and inclined as negative torque, the first molar was distal moved and rotated to distal ,the mesial side was rotated buccally and the distal side was rotated lingually, the second pre-molar was extruded and inclined as crown to mesial and root to distal, inclined as negative torque, the canine was intruded slightly and inclined as positive torque, lateral incisor was extruded and labial moved and inclined as positive torque. Condition 2: The second molar was intruded and moved to distal on bodily and the crown was rotated to distal, the first molar was intruded and moved to distal on bodily and the crown was inclined to distal, the second pre-molar was extruded and moved to distal on bodily and the crown was rotated to distal, the canine was extruded slightly and inclined as positive torque, the lateral incisor was extruded and labial moved on bodily and inclined as positive torque.②Clinical experiment: By extracting the third molars , the upper and lower molars were uprighted to distal, the upper and lower incisors were extruded ,the occlusal plane was leveled, and meet three of mechanism of openbite treatment; by extracting the bicuspid teeth ,the upper and lower molars were mesial moved and uprighted to distal, intruded relate to occlusal plane, the upper and lower incisors were retracted and extruded, the occlusal plane was leveled,and meet all of mechanism of open bite treatment. Conclusion①Using MEAW with several"L"loop can control every tooth in three dimensions, and the molars can be rotated to distal and the front teeth can be extruded. so it can be used for open bite and difficult case treatment.②Using reverse-curve arch wire with vertical elastics in anterior teeth area is accordance with the mechanism of open bite treatment,and is easy for orthodontists and suite for patients with mesial inclined molars who are not serious on skeleton deformity.③By extracting the third molars can meet three of mechanism of openbite treatment,so it is valid for suitable cases. By extracting the bicuspid teeth meet all of mechanism of open bite treatment, so it is more profit for openbite treatment. In clinical, we command extracting the bicuspid teeth for unsure open bite cases.