Objective: To investigate the changes and symmetry of facial soft tissue during posed smile, to analyze the feature of posed smile in different gender, and verify the reproducibility of posed smile.
Methods: Three-dimensional (3D) facial images of 41 adults (16 males and 25 females with an average age of 26.76±2.70 years) which were taken by FaceScan three-dimensional sensor, including one rest position and two posed smile images. Then these images were imported into 3D soft tissue analysis software for model repositioning. 3D morphable model method (3DMM) was carried out to automatic landmarks setting. After that, the measurement of the eyes, cheeks, nose and perioral area were carried out for 3D soft tissue analysis. Finally, the changes and symmetry of the soft tissues between the two expression states and the gender differences during the posed smiles were compared. Meanwhile, the reproducibility of posed smile was statistically tested.
Results: Compared with the rest position, except for nasolabial angle (1.45°±7.65°), the measurements of 3D soft tissue in other region were changed in posed smile (P < 0.001). It should be noted that the eye region was also significantly changed (P < 0.001). Furthermore, the prominent feature of posed smile was that the alar base length became longer, the upper and lower vermilions were narrow and thin, and the mentolabial furrows became shallow. Meanwhile the chin extended anteriorly while the mouth retracted; During posed smile, the labial fissure asymmetry [2.78 (1.73, 3.49) mm], mid-infraorbital asymmetry [2.36 (1.22, 3.27) mm] and outercanthal asymmetry [2.31(1.29, 2.80) mm] were most apparent. Compared with the rest position, the asymmetry was not significantly increased except for cheilion and alar curvature points during the posed smile (P>0.05). In the posed smile, the changes of the right palpebral fissure height and the thickness of lower vermilion (|Li-Stoi| z) of males were greater than those of females (P < 0.05), and asymmetry of exocanthion and cheekbone increased more than that of females (P < 0.05). There was no obvious difference between the two posed smiles.
Conclusion: In this study, during the posed smile the soft tissues of the eyes, cheeks, nose, lips and chin changed in different degrees, and the asymmetry of cheilion and alar curvature point was greater than that of the rest position; In addition, the reproducibility of posed smile was excellent, which can be a reference for clinical aesthetics and functional research of smile.
目的: 研究姿势性微笑时三维面部软组织变化和对称性，并分析姿势性微笑的性别差异，同时验证姿势性微笑的一致性。
方法: 应用光学面部三维扫描设备获取41名成年志愿者每一张休息位和两张姿势位的面部软组织图像，其中男性16人，女性25人，年龄(26.76±2.70)岁。将面部图像数据导入三维分析软件进行模型定位后应用三维可变模型(3-dimensional morphable face model method, 3DMM)标定软组织特征点，选取眼部、面颊部、鼻部及口周测量指标进行软组织分析，比较两种表情状态下的面中下部软组织变化情况和对称性，并分析男女差异，同时对两次姿势性微笑的测量结果进行统计学检验。
结果: 与休息位相比，除鼻唇角变化量(1.45°±7.65°)差异无统计学意义外，姿势性微笑时其余软组织测量值均有改变，且眼部区域也有显著变化(P < 0.001)。面下部软组织主要表现为鼻基底变宽，上下唇区域后向运动，颏部前移，唇红变窄变薄，颏唇沟变浅；姿势性微笑时不对称性以口角点[2.78 (1.73，3.49) mm]、眶下中点[2.36 (1.22, 3.27) mm]和外眼角点[2.31(1.29，2.80) mm]最为显著，另外与休息位相比，除口角点和鼻翼基部外不对称性变化差异无统计学意义(P>0.05)；姿势性微笑时，男性右眼高和下唇红深度变化量大于女性(P < 0.05)，外眼角点和脸颊点的不对称性增加程度较女性大(P < 0.05)；两次姿势性微笑的一致性较好。
结论: 姿势性微笑时眼部、面颊部、鼻部及口周软组织存在不同程度的变化，且口角和鼻翼基部不对称性较休息位增加；另外，姿势性微笑时面部软组织的一致性较好，可为临床面部微笑美学研究提供参考。
Keywords: 3D morphable model; Posed smile; Reproducibility; Symmetry; Three-dimensional(3D)facial analysis.