| Objective: To use the six-axis force sensor test platform of the appliance to study the overall adduction of the mandibular anterior teeth in the case of invisible orthodontic cases of bilateral mandibular first premolars,and to measure and record the instantaneous stress of all other teeth in the buccal tongue,near and far,middle and vertical directions when the inclination angle of the axis of the back mandibular teeth changes.Methods: In the Zheng Ya invisible orthodontic design system,the correction scheme for the extraction of bilateral mandibular first premolars was designed,and the process of clinical adduction of the mandibular anterior teeth by 0.25 mm,that is,moving the mandibular canine teeth and incisors at the same time.According to the different inclination angles of the posterior teeth,four groups of mandibular dentition were designed with equal differences: the axial inclination of the posterior teeth of the F1 group was set as the upright group,the posterior teeth of the F2 group were tilted 5° backward on the basis of the F1 group,the posterior teeth of the F3 group were tilted forward by 5° on the basis of the F1 group,and the posterior teeth of the F4 group were tilted forward 10° on the basis of the F1 group,in order to strengthen the retention force of the invisible appliance,the horizontal rectangular attachment was bonded to the buccal side of the first molars and the second molar,and the vertical rectangular attachment was bonded to the buccal surface of the second premolars and the canine buccal side,and the size of the attachment was 3mm×2mm×1mm,both located in the clinical crown center of the corresponding tooth.The designed and printed four sets of dentitions were connected to the six-axis force test platform of the appliance,and the corresponding invisible appliances were respectively worn to measure and record the instantaneous force of each tooth in the buccal tongue,near and far,middle and vertical directions.Each group printed 12 pairs of invisible appliances,i.e.measured 12 times in each group,and the collected data was analyzed using SPSS 26.0 software.Results: Compared with the F1 group,the elongation force of incisors decreased,the distal and middle force of the canine teeth increased,the proximal middle force of the posterior teeth decreased,and the buccal force and elongation force of the molars increased,and the difference between the above results was statistically significant(P<0.05).In addition,compared with the F1 group,the tongue force and elongation force of incisors in F3 and F4 groups increased,the distal and middle force of the canine teeth increased,and the proximal middle force,buccal force and elongation force of the posterior teeth were increased,and the differences were statistically significant(P<0.05).Conclusion: When the front teeth are adducted as a whole after the extraction of bilateral first premolars of the lower jaw by using invisible correction technology,the change of inclination angle of the posterior teeth has different effects on the threedimensional force of all teeth in the lower jaw.When the posterior teeth are tilted forward,the torque loss will be lost when the anterior teeth of the lower jaw are adducted,but when the forward tilt angle is increased to 10°,the phenomenon of " derailment " will occur,and the posterior teeth should be upright first in the clinic to help control the torque,and the retention of the appliance should be enhanced by bonding accessories.When the posterior teeth are tilted backwards,it is conducive to the maintenance of the posterior teeth branch,but it increases the buccal elongation of the posterior teeth.Therefore,before adduction of the anterior teeth,support preparation should be carried out,and the negative torque and low overcorrection of the posterior teeth should be designed according to the target position of treatment. |
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