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

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.