正畸治疗后下前牙拥挤复发的牙性因素

Dental Factors for the Relapse of Lower Anterior Teeth Crowding and Rotation after Orthodontic Treatment

目的评估下前牙形态、接触点及下尖牙间宽度改变对正畸治疗后下前牙拥挤复发的影响。方法选择156例下前牙旋转、拥挤复发患者的矫治前(T1)、矫治后(T2)以及保持3年后(T3)模型;以126例个别正常为对照组并制取模型。测量下前牙不整齐指数(mandibular irregularity index,MD-IRID)、下颌尖牙间宽度(man-dibular intercanine width,MD-ICW),计算下切牙牙冠近远中径(mesiodistal length,MD)与唇舌径(faciolingual width,FL)比例(MD/FL),并观察下前牙间的接触形式,分析以上指标与下前牙拥挤复发的关系。结果试验组T2期的下尖牙间宽度较T1期明显增大,而T3期的下尖牙间宽度较T2期又明显减小;下前牙临床排列整齐且IRID≤1.5 mm者,下切牙MD/FL正常或偏小,MD-ICW偏大;下前牙临床排列不整齐且IRID>1.5 mm者,下切牙MD/FL偏大,MD-ICW偏小;严重复发者(IRID>6.5 mm)下前牙接触点均有异常,邻牙间多为点接触,解剖接触点之间分离度大。结论 MD/FL偏大、下前牙间点接触及过度扩大下尖牙间宽度可能是矫治后下前牙拥挤复发的影响因素。

Objective To evaluate the impact of teeth shape,size and contact points,and mandibular inter-canine width on the post-treatment relapse of lower anterior teeth crowding and rotation.Methods Four hundred and sixty-eight dental models were selected from 156 cases of crowding and rotating lower anterior teeth before therapy（T1）,after therapy（T2） and in retaining therapy for three years（T3） with 126 normal occlusion models there from as the standard control group.Then the irregularity index（IRID） of lower anterior teeth and the mandibular inter-canine width were measured followed by calculation of the mesiodistal length（MD）,faciolingual width（FL）,MD/FL ratio of mandible incisor in the models of the 156 selected cases grouped by above three stages（T1,T2,T3）.Finally,the contact means between lower anterior teeth,the variation of IRID and the interstices between lower canines were observed.The case numbers of relapse in the three stages among the 156 cases were analyzed against the captioned indices.Results Comparing to stage T2 in the experimental group of tooth deformity,inter-canine width was significantly increased in the stage T1,however,obviously decreased in the stage T3 that approach the standard control group basically.In cases where lower anterior teeth in alignment,with IRID≤1.5 mm,the MD/FL ratio of lower incisors was normal or comparatively lower,and mandibular intercanine width was obviously much higher than that of the normal;Where lower anterior teeth in disorder,with IRID3.5 mm,the MD/FL ratio was obviously much higher than that of the normal,and mandibular intercanine width was comparatively lower.where serious relapse occurs（IRID6.5 mm） abnormal position of anterior contact areas and high-degree separation of anatomical contact points of inter-proximal teeth exists,where inter-proximal teeth contact confines to point-contact.Conclusion The mandibular canines of post-treatment relapse of lower anterior teeth crowding and rotation have a tendency of returning to its original position.The decrease of inter-canine width will result in insufficient gap of dental arch.This situation could cause relapse of lower anterior teeth crowding and rotating easily.High MD/FL ratio results in point-contacts of lower anterior teeth,which may construe itself a factor in the post-treatment stability.