[Linear correlation between tooth movement and facial profile change in patients with class Ⅱ division 1...

Objective: To investigate the correlation between tooth movement and profile change in patients with class Ⅱ division 1 malocclusion. Methods: Pre- and post-treatment lateral cephalograms of 42 patients [10 males and 32 females, (23.8±6.3) years old, mean treatment time: 1.9 years] with class Ⅱ division 1 malocclusion were collected in Department of Oral & Cranio-Maxillofacial Surgery, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine from June 2012 to November 2017. The patients were treated with extraction of four first premolars or two maxillary first premolars. Cephalometric analysis was carried out before and after treatment. Thirty parameters were measured. The changes of soft and hard tissue after orthodontic treatment and their correlations were analyzed using bivariate linear regression. Related factors affecting the upper and lower lip, nasolabial angle (NLA) and mentolabial angle (MLA) were analyzed according to the standardized regression coefficient (Beta). Results: Among all the 30 parameters, 18 parameters were statistically different before and after treatment. After treatment, upper central incisor sagittal distance [(63.87±7.14) mm] and upper lip sagittal distance [(77.73±7.60) mm] were significantly decreased (P<0.05). The changes in 14 parameters after treatment showed linear relationship including strong positive correlation between upper lip sagittal retraction and upper central incisor sagittal retraction (r=0.649, P<0.01). There were moderate positive correlations between upper lip and upper central incisor vertical movement (r=0.544, P<0.01). While the sagittal change of gnathion and the Y-axis angle showed moderate negative correlations (r=0.537, P<0.01). The stepwise multiple linear regression showed that the retraction of upper lip process was correlated with the retraction of upper central incisor, the increase of occlusal plane angle and the increase of upper central incisor angle, which was most correlated with the retraction of upper central incisor (Beta=0.79). The downward displacement of upper lip process was correlated with the downward displacement of upper incisor, the decrease of upper central incisor angle, the decrease of the distance between maxillary first molar and palatal plane, and the increase of occlusal plane angle, which was more correlated with the downward displacement of upper incisor and the increase of occlusal plane angle (Beta=0.59). The downward displacement of lower lip process was correlated with the downward displacement of upper incisor and lower incisor, which was more correlated with the upper incisor (Beta=0.36). Conclusions: The relationship among nose, lips and chin was more coordinated. Incisor retraction had significant influence on lip prominence, and the lower lip position was highly related to the movement of upper incisor in sagittal and vertical dimension after orthodontic treatment in patients with class Ⅱ division 1 malocclusion. However, tooth movement had limited impact on the chin position.