OBJECTIVE: To establish the Chinese Han national criteria for the thickness of upper lip in Chongqing and to investigate the effect of lip thickness on lip retraction in orthodontic treatment.
 METHODS: A total of 240 adult patients (male=120, female=120) of Chinese Han nationality aged 18-35 years in Chongqing were treated with cephalograms and measured the thickness of upper lip. We established the Chinese Han national criteria for the thickness of upper lip in Chongqing according to the results. Sixty-eight female patients with Angle II 1 from Department of Orthodontics Stomatological Hospital of Chongqing Medical University were treated with maxillary premolars extraction, and pre- and post-treated with lateral cephalograms, then divided into 3 groups according to our criteria: a thin lips group, a normal lips group and a thick lips group. The ratio of the incisors retraction and the upper lip retraction were measured and calculated. The correlation between incisors retraction and the upper lip retraction was analyzed by the Pearson correlation method.
 RESULTS: There was statistical significance in the thickness of upper lip between males and females (P<0.01). The ratio of maxillary inscior retraction to the upper lip soft tissue retraction was 1.6:1, 2.2:1 and 2.9:1 in the thin lips group, the normal lips group and the thick lips group, respectively.
 CONCLUSION Gender differences exist in the thickness of upper lip. Upper lip retraction with the incisors was negatively correlated with the soft tissue thickness of the upper lip in females with Angle II 1.
Adolescent ; Adult ; Bicuspid ; Cephalometry ; Female ; Humans ; Incisor ; Lip ; anatomy & histology ; Male ; Tooth Extraction ; Young Adult