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目的 探讨应用上颌牙弓反复快速扩缩配合较轻前方牵引力矫治安氏Ⅲ类错(牙合)的效果.方法 选取替牙晚期或恒牙早期安氏Ⅲ类反(牙合)患者20例,随机分为两组.实验组患者戴用扩弓器后每天早晚各加力一次,每次转1/4圈(0.25 mm),反复扩缩至第9周扩大后停止加力,开始戴用面具式前方牵引器,每侧牵引力约300 g;对照组患者戴用扩弓器后每天早晚各加力一次,每次转1/4圈(0.25m m),连续扩大一周后停止加力,开始戴用面具式前方牵引器,每侧牵引力约500 g.所有患者治疗前后均拍摄头颅侧位定位片进行测量分析.结果 所有患者前牙反(牙合)均解除,X线头影测量分析显示:实验组患者矫治前后SNA平均增加2.62°,ANB平均增加2.97°,WITS值平均增加2.48mm,A点平均前移2.47 mm,且差异有显著性(P＜0.05);对照组患者矫治前后,SNA平均增加1.80°,ANB平均增加2.06°,WITS值平均增加2.39mm,A点平均前移2.44 mm,且差异有显著性(P＜0.05);实验组与对照组矫治前后相比上颌都发生前移,但两组差异无统计学意义(P＞0.05).结论 上颌牙弓反复快速扩缩配合较轻前方牵引力可以有效地前移上颌骨.“,”Objective The purpose of this study was to evaluate the effect of alternate maxillary expansions and constrictions (Alt-MEC) with lighter maxillary protractionforce in treatment of Class Ⅲ malocclusions.Methods Twenty children with Class Ⅲ malocclusion were selected and randomly divided into two groups.In experimented group (n =10),an alternate rapid maxillary expansion and constriction protocol (Alt-MEC) and then maxillary protraction (MP)commenced with 300g force each side.In control group (n=10),rapid maxillary expansion was conducted for 1 week,and then maxillary protraction (MP) is started with about 500 g at each side.Pretreatment (T1) and posttreatment (T2) cephalometric radiographs were taken and then analyzed.Results The sagittal skeletal variables all showed significant improvements (P＜0.05) in the experimental group (SNA,2.62°;ANB,2.97°;WITS appraisal,2.48mm;point A protracted 2.47mm) and the control group (SNA,1.80°;ANB,2.06°;WITS appraisal,2.39mm,point A protracted 2.44mm),but the changes between two groups showed insignificant differences (P＞0.05).Conclusions Alternate rapid maxillary expansions and constrictions (Alt-MEC) with lighter force of maxillary protraction is effective in maxilla advancement in the treatment of the children with Class Ⅲ malocclusions.