极坐标测量方法在Twin-Block矫治下颌后缩疗效分析中的应用

Applications of Polar Coordinate Method in Analyzing the Treatment Effect of Mandibular Retrusion Using Twin-Block Appliance

目的探讨极坐标测量分析方法用于Twin-Block矫治器矫治骨性Ⅱ类错疗效评价测量分析的临床应用价值。方法随机选取处于发育高峰期的骨性下颌后缩患者20例,男女各10例,采用Twin-Block矫治器矫治。对患者治疗前后的头颅侧位片采用极坐标测量分析方法,以S点为极坐标原点,前颅底平面(S-N)作极轴,建立极坐标测量体系,选取7个颌骨标志点A、Ptm、B、Po、Gn、Go、Ar,分别测量各标志点治疗前后极径和极角的大小,并作相应统计分析。结果 Ptm的极角和极径无明显改变,A点的极角和极径则均明显增大,说明Twin-Block矫治器对上颌骨生长无明显抑制作用;下颌标志点B、Po、Gn、Go点的极径在治疗后明显增大,但反映下颌骨改建方向的极角在治疗后则均无明显改变,说明Twin-Block矫治器对下颌骨的生长起到明显的促进作用,而对下颌骨生长方向没有明显影响。结论极坐标测量分析方法可以对颌骨标记点的生长量和生长方向作出准确的定量测量和定性分析,可弥补传统测量方法的不足;极坐标测量分析也表明,Twin-Block矫治器主要通过促进下颌骨的生长,而非通过抑制上颌骨的生长来调整上下颌骨矢状不调的位置关系,改善下颌后缩患者的侧貌美观。

Objective To investigate the clinical value of polar coordinate measuring method through analyzing effect of class Ⅱ malocclusion treated by Twin-Block appliance.Methods Case selection： twenty adolescent patients（10 girls and 10 boys） were randomly selected at the peak of development with mandibular retrusion.All were treated by Twin-Block appliance.The cephalometric was carried with polar coordinate method.S point was selected as the polar origin,coordinates polar axis is anterior cranial base plane（SN）.Seven bony landmarks A,Ptm,B,Po,Gn,Go,Ar were selected and measured before and after treatment,including polar angle and polar radius size.Results Polar angle and radius size of Ptm point had no significant change,while the result of A has increased significantly.Maxillary development was not restrained by Twin-Block.These polar radius sizes of points B,Po,Gn and Go increased significantly,but their polar angle had no changes.It showed that mandibular changed significantly but remained its original directions.Conclusion The polar coordinate measuring method could show the accurate direction and size of skeletal growth and development.The method can compensate for the deficiencies of traditional methods,and give an effective assessment.The result also showed that Twin-Block improved the jaw relationships and mandibular retrusion mainly by promoting the mandibular growth（not by inhibiting the growth of the maxilla）,so that the patients＇ profile get better.