Movement Of Maxillary Canine And The Effect On Torque Expression In Tip-Edge Plus Appliance

Differential straight wire technique is an efficient orthodontic technique by usingdifferential forces and mechanics to move tooth and finish orthodontic treatment.Compare to the Tip-Edge brackets, there is a deep tunnel on the lingual of Tip-EdgePlus brackets and there is a mainly change on the third phase when treatment. Indifferential straight wire technique, the phases of treatment and the objective of eachphase is relatively definite. The active orthodontic forces are different among phasesand the relationship between forces and tooth movement are more apparent. Tomake clear the characteristic of tooth movement on each phase will be better for thetreatment. The correction of canine are pointed out in many orthodontic techiniquesand they also take more attention on canine movement. It is because that canine ison the corner of arch, have the longest root among dention and paly an importantrole on orthodontic treatment. In differential straight wire technique, not only thedesign of canine brackets but also the flexible usage of the characteristics of caninemovement, make canine paly an important on the technique. Especially on the thirdphase of treatment, the changes of canine angulation is a mainly factor to effect theactivation of nickel-titanium, which is the only active force during uprighting andtorque on this period and the relationship between tooth movement and orthodonticforce are better reflected during treatment.Based on the specific characteristics and importance of canine in Tip-Edge Plusappliance, we use the method of finite element analysis to analyze the caninemovement on each phase of treatment and the relationship between toothmovement and active orthodontic force with Tip-Edge Plus appliance. On the otherhand, we conduct material experiments and combine the results with torqueexpression characteristics to analyze the characteristics of canine movement ontorque expression. There are five parts on this research.Experiment1: Finite element analysis of canine movement when bite opening inTip-Edge Plus appliance.Objective: Research the distribution of stress and tendency of canine movementwith different tip back bend and class II elastic on the phase of bite opening by themethod of finite element analysis. Methods: Set up the finite elemnt models ofmaxilla, maxillary dentition and Tip-Edge Plus brackets and archwires in ANSYS by CT scanning and measurements in vitro. To simulate the bite opening treatment inTip-Edge Plus orthodontics with tip back bend and class II elastic. Changed thedegree of tip back bend,30°,35°,40°,45°relatively, to observe the changes ofstress and movment of canine. Results: Under the combined effect of tip back bendand class II elastic, the stress were concentrated on the apical of root in canine.Canine had the tendency of distal and palatally tipping movement and the tendencyof instrusion. Accompany with the increase of the degree of tip back bend, the stressand concentration and the tendency of movement were increased too. Conclusion:During the bite opening of differential straight wire technique, in addition to thetendency of distal tipping movement and instrusion, canine are inclined to tilt topalatal in the meantime. The more degrees of the tip back bend the more tendencyof the canine movement.Experiment2: Finite element analysis of canine movement when space closurein Tip-Edge Plus appliance.Objective: Research the distribution of stress and tendency of canine movementwith the use of different degrees of reverse-curve archwire and different closing forceon the second phase of treatment by the method of finite element analysis. Methods:Used the models in the first experiment, set up models of reverse-curve archwire oftwo degrees (5°and10°),50g and100g retraction force were applied to close theextraction space, observed the changes of stress and movment of canine. Results:The stress was concentrated on the apical of root in canine. Canine had thetendency of distal and palatally tipping movement. Accompany with the increase ofthe degree of reverse-curve, the stress and concentration and the tendency ofmovement were increased too. There were differences on the tendency of verticalmovement under various degree of reverse-curve archwire. The tendency of verticalmovement of canine was from instusion to extrusion along with the increase of thedegree of reverse-curve. In the reverse-curve archwire of5°, the palatal parts ofcrown and root of canine had the tendency of instrusion, but had the tendency ofextrusion both the crown and root in the reverse-curve archwire of10°. Conclusion:During the space closure of differential straight wire technique, canine has thetendency of distal and palatal tipping movement, the more degrees of thereverse-curve and the retraction force the more tendency of the canine movement.With the changes of the degrees of the reverse-curve archwire, the tendency of vertical movement of canine is from instusion to extrusion along with the increase ofthe degree of reverse-curve.Experiment3: Finite element analysis of canine movement on torque expressionin Tip-Edge Plus appliance.Objective: Research the distribution of stress and tendency of movement of theanterior tooth on the third phase of treatment when uprighing and torque by themethod of finite element analysis, then observed the effect on the active force andthe anterior tooth movement with the changes of angulation of canine. Method:Adjusted the models in the prior experiments to simulate the third phase of thedifferential straight wire orthodontic, where the extraction space had been closed.Each anterior tooth had their own angulation, which were-2°in incisor,-15°in lateralincisor and-25°,-19°,-13°in canine. Simulated the use of nickel-titanium archwire onthe third phase to calculate forces applied on the each tooth. Fixed the center ofcrown of each tooth and applied10N mm couples on them in lingual root direction.Results: The stress was concentrated on the cervix of root in incisor and lateralincisor, and was concentrated on the mesial parts of root in canine. With the increaseof the canine angulation, the degree of the stress on antertior tooth increased tooand the lateral incisor took the largest stress all the time. The tendency of rootmovement was larger than the movement of crown in anterior tooth. They had thetendency of uprighting movement from to distal to mesial and the tendency of torquemovement in lingual root direction. On the other hand, there were tendency ofrotation from the view of occlusion and canine and the largest tendency of movementamong tooth. Accompany with the changes of the angulation of canine, the tendencyof movement were increased too in all tooth. Conclusion: During the third phase ofdifferential straight wire technique, the course of uprighting and torque in anteriortooth are interacted among each other. The changes of canine angulations have theeffect on the changes of active force by changing the deflection of nickel-titaniumarchwire and affect the movement of anterior tooth finally. Lateral incisor takes thelargest stress and has the largest changes along with the increase of canineangulations. Besideds that, space in dentition is another factor that affect theuprighting and torque.Experiment4: Mechanical properties of nickel-titanium archwire used in the finaltreatment phase of Tip-Edge Plus technique: An in-vitro study Objective: To evaluate the mechanical properties of the nickel-titanium wire in thefinal treatment phase of Tip-Edge Plus technique in simulated oral environments.Research the effects of corrosion and deflections on the changes of mechanicalproperties of nickel-titanium archwire in simulated enviorment. Methods: Simulatedorthodontic treatment with Tip-Edge Plus brackets on typodont model. Inserted0.014-in thermal nickel-titanium wires into the deep tunnel of Tip-Edge Plus bracketson the final phase of treatment. Changed the canine crown angulations oncasts(-25°,-19°,-13°,-7°,-1°,+5°) to mimic different amounts of deflection of wires anddivided all the samples into8groups: as-received (1group), straight (1group) andbended (6groups). Immersed the straight and bended groups in artificial saliva (PH6.8) and preserved at37.0℃. Eight durations of incubation were tested:1to8weeks.Scanning electron microscope was used to observe the surface of the archwires.Three-point bending test was performed on all samples at a constant temperature(37.0℃). Stiffness (YS: E) and the load-deflection characteristic of unloading plateausection were obtained. Micro-X diffraction technique was used to research themechanism of the changes of mechnical properties. Results: The corrosion of thewire became obvious along with the use of the archwire. Significant changes inspecific mechanical properties were observed in long-term immersed and largedeflected wires compared with as-received groups. Stiffness (YS: E) increased andaverage plateau force and ratio of variance each decreased correspondingly. Notonly immersion time affected the wire, but the changes of canine angulation affectedthe amounts of deflection of wires and affected the mechanical propertiesconsequently in the simulated oral environment. In the meantime, the two factors hadsynergistic effect on wires. Properties in group-25°had the earliest and the mostobvious changes among groups. The micro-X diffraction study shown that thechanges of the ratio of martensite(M111) to austenite(A110) was increasing alongwith the length of corrosion time and the increased of deflection caused by canineangulation.Conclusion: In the final treatment phase of Tip-Edge Plus technique,long-time use of nickel-titanium archwire in large deflection may be associated withdegradation in performance of wires. The corrison on the surface of the archwirebecomes serious along with time. The deflection of the archwire is increased by thecanine angulation and it will have earlier and obvious degradation of wires. Themechanism of the changes of mechanical prperies is the changes of the ratio of martensite to austenite.Experiment5: Finite element analysis of the combined effects of canineangultion on the movement of anterior tooth on the third phase of Tip-Egde Plusorthodontcs.Objective: Research the distribution of stress and tendency of movement of theanterior tooth on the third phase of treatment when uprighing and torque by themethod of finite element analysis when changing the modulus of elasticity of thenickel-titanium archwire and the canine angulation.To analyze the combined effectsof canine angultion on the movement of anterior tooth.Methods: Used the models inthe third experiment, changed the modulus of elasticity of the nickel-titaniumarchwire only and the force application were same as the third experiment. So it wasthe numerical simulation but not the clinical simulation in finite element analysis.Then observed the stress and movement of anterior tooth when different canineangulation. Compared the results with the third experiment and calculated the ratio ofchange on stress and movement on tooth. Rseults: The distribution of stress andtendency of movement were same as the third experiment. The stress andmovement were increased with the decrease of modulus of elasticity. Comperaed theresults with the third experiment, the ratio of changes on movement were differdentamong tooth, lateral incisor had the largest changes, followed by canine andincisor.Conclusion: Not only use the function of clinical simulation of finite elementanalysis, but also take the adventages of use of numerical simulation could be a newthought of use of finite element analysis on orthodontic field, and maybe a newmeans to analysis the combined effects on tooth movement. During the third phaseof differential straight wire technique, under the combined effects of canineangulation, lateral incisor is the most sensitive tooth to the changed of active forceand canine is the most special tooth when the active force changes. Along with theincrease of canine angulation, the orthodontic force is proned to enter bad circulationand it is adverse to the uprighting and torque expersion of anterior tooth.The innovation of this research is research the movement of tooth in Tip-EdgePlus appliance systematically, especially on the characteristics of canine movementand the effect on torque expression. Combine the material experiments and resultswith the finite element analysis to take adventage of the use of numerical simulation,which bring in a new thought of the use of finite element analysis on orthodontic field, and maybe a new means to analysis the combined effects on tooth movement.The results of this research make the theoretical basis for the use of Tip-EdgePlus appliance in clinical and the adjustment of canine movement during treatment,has theoretical and clinical meanings.