Skeletal and dental features of extraction cases in the second phase of two-phase treated Class II malocclusion

Abstract

Objective To investigate the skeletal and dental features of extraction cases in the second phase of two-phase treated Class Ⅱ malocclusion. Methods Twenty-one two-phase treated Class Ⅱ cases with satisfied treatment results were chosen (11 extraction cases and 10 non-extraction cases). The sagittal skeletal pattern, vertical skeletal pattern, incisors' position and overjet were examined from cephalograms before treatment (T0), at the end of phase Ⅰ treatment (T1) and at the end of phase 2 treatment (T2). Results (1) There was no difference in skeletal and dental factors between extraction and non-extraction groups before treatment (T0) (P ＞ 0. 05). (2) In nonextraction group, improvement of Wits in the first phase was significant than that in extraction group (P＜0. 05). SNB increased and wits decreased significantly in the second phase of treatment in nonextraction group (P＜0. 05), which indicated favorable growth pattern. (3) MP-SN was reduced approaching statistical significance (P=0. 052) in extraction group in the second phase of treatment.(4) In the first-phase treatment, reduction of U1-NA was significant in non-extraction group (P＜0. 05). (5) In the first-phase treatment, LI-NB was significantly increased (P＜0. 001) in extraction group. (6) The overjet at the end of treatment (T2) was less in extraction group than that in non-extraction group, which indicated over-correction. Conclusions (1) Decision can not be made only according to the skeletal and dental factors before treatment. (2) Extraction and over-correction in the second phase may be considered for those cases which show limited improvement of sagittal skeletal pattern after the first phase of treatment. (3) Extraction may be considered if upper incisors are not much retracted while lower incisors are much proclined during the first-phase treatment. (4)Extraction in the second phase may be considered for cases with vertical growth pattern, which could benefit vertical control and achievement of balanced Tweed triangle by lower incisors' retraction.

目的 分析比較雙期矯治Ⅱ類錯(牙合)畸形患者第二期減數與非減數病例的骨性及牙性特征.方法 選擇21例雙期矯治以下頜后縮為主的Ⅱ類錯(牙合)臨床療效滿意病例,頭影測量比較拔牙組和不拔牙組各冶療階段骨性及牙性因素的差異,從而分析第二期減數病例的特征.結果 1.治療前拔牙組與不拔牙組矢狀向、垂直向骨型、上、下切牙位置及覆蓋均無差異(P＞0.05).2.矢狀向骨型:不拔牙組第一期治療Wits埴改善較拔牙組顯著(P＜0.05).第二期治療中不拔牙組SNB增大(P＜0.05),Wits值減小(P＜0.05),表現利于矢狀向骨型改善的生長型.垂直向骨型:拔牙組第二期治療中MP-SN減小.3.下切牙:經第一期治療后兩組下切牙均唇傾(P＜0.05),拔牙組LI-NB增大顯著(P＜0.001).第二期治療不拔牙組LI-NB進一步增大(P＜0.01),而拔牙組有效回收下切牙(P＜0.05).結論 1.通過治療前的骨性、牙性特征不能判斷第二期治療是否需要減數.2.經第一期治療矢狀向骨型改善有限、下切牙唇傾過多的病例第二期拔牙可能性大.3.對于表現為不利于矢狀向Ⅱ類骨型改善的垂直生長型病例,第二期減數利于垂直向控制.