The study of soft tissue profile ehanges and the relationship with the hard tissue in the adult patients with bimaxillary prtrusion treated with premolar extraction and Nance arch

Abstract

Objective To investigate the changes of soft tissue profile and the relationship with hard tissue.Methods Twenty-nine adult female patients with bimaxillary protrusion who met the including criteria were included into this retrospective study.Nance arch was used in anchorage control and four first premolars were extracted for each patient.Lateral cephalographs of pre and post treatment were traced by hands,thirtyfive linear and angular measurements were analyzed by SPSS version 15.0.paired t test and Pearson correlation were used.Results The prominence of upper and lower lips,soft tissue A and B point was decreased significantly after orthodontic treatment.The thickness of upper lip increased and lower lip decreased after orthodontic treatment.The retraction of upper incisor was the only measurement positively correlated with upper lip retraction.( r=0.469,P＜0.01) ;ΔSNA(r=0.436,P＜0.05) 、ΔU1-SL(r=0.374,P＜0.05)、ΔL1-SL(r=0.478,P＜0.01)was correlated with the lower lip retraction; the upper lip retractiom was positively correlated with lower lip retraction.The nasio-labial angle was negatively correlated with ΔU1-SL(r=-0.534,P＜0.01)、ΔUL-E(r=- 0.394,P＜0.05),and positively correlated with ΔA'-SL(r=0.478,P＜0.05)、ΔULL(r=0.474,P＜0.05) and ΔA'-A(r=0.423,P＜0.05).the depth of soft tissue B(B'-E)was correlated with(ΔL1-SL)and (LL-SL).The retraction of the upper lip to the retraction of upper incisor was 1 ∶ 0.6(to E line)or 1∶ 0.62(to S line).The retraction of the lower lip to the retraction of lower incisor was 1 ∶1.13;The retraction of the lower lip to the retraction of upper incisor was 1 ∶ (0.83±0.21) (LL-SL/U1-SL).Conclusions Soft tissue profile improved significantly after four first premolars extraction and the use of Nance arch.The changes of soft tissue profile was moderate correlated with hard tissue. Key words: Bimaxillary protrusion; Extraction; Anchorage; Soft tissue profile