Journal of Peking University (Health Sciences) ›› 2020, Vol. 52 ›› Issue (6): 1107-1111. doi: 10.19723/j.issn.1671-167X.2020.06.020

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Evaluation of the reproducibility of non-verbal facial expressions in normal persons using dynamic stereophotogrammetric system

Tian-cheng QIU,Xiao-jing LIU,Zhu-lin XUE,Zi-li LI()   

  1. Department of Oral and Maxillofacial Surgery, Peking University School and Hospital of Stomatology & National Clinical Research Center for Oral Diseases & National Engineering Laboratory for Digital and Material Technology of Stomatology & Beijing Key Laboratory of Digital Stomatology, Beijing 100081, China
  • Received:2018-10-10 Online:2020-12-18 Published:2020-12-13
  • Contact: Zi-li LI E-mail:kqlzl@sina.com

Abstract:

Objective: To assess the reproducibility of non-verbal facial expressions (smile lips closed, smile lips open, lip purse, cheek puff) in normal persons using dynamic three-dimensional (3D) imaging and provide reference data for future research. Methods: In this study, 15 adults (7 males and 8 females) without facial asymmetry and facial nerve dysfunction were recruited. Each participant was seated upright in front of the 3D imaging system in natural head position. The whole face could be captured in all six cameras. The dynamic 3D system captured 60 3D images per second. Four facial expressions were included: smile lips closed, smile lips open, lip purse, and cheek puff. Before starting, we instructed the subjects to make facial expressions to develop muscle memory. During recording, each facial expression took about 3 to 4 seconds. At least 1 week later, the procedure was repeated. The rest position (T0) was considered as the base frame. The first quartile of expressions (T1), just after reaching the maximum state of expressions (T2), just before the end of maximum state of expressions (T3), the third quartile of expressions (T4), and the end of motion (T5) were selected as key frames. Using the stable part of face such as forehead, each key frame (T1-T5) of the different expressions was aligned on the corresponding frame at rest (T0). The root mean square (RMS) between each key frame and its corresponding frame at rest were calculated. The Wilcoxon signed ranks test was applied to assess statistical differences between the corresponding frames of the different facial expressions. Results: Facial expressions like smile lips closed, smile lips open, and cheek puff were reproducible. Lip purse was not reproducible. The statistically significant differences were found on the T2 frame of the repeated lip purse movement. Conclusion: The dynamic 3D imaging can be used to evaluate the reproducibility of facial expressions. Compared with the qualitative analysis and two-dimensions analysis, dynamic 3D images can be able to more truly represent the facial expressions which make the research more reliable.

Key words: Three-dimensional images, Facial expression, Reproducibility of results

CLC Number: 

  • R782.2

Figure 1

Four facial expressions recorded by dynamic 3D imaging A, smile lips closed; B, smile lips open; C, lip purse; D, cheek puff."

Figure 2

Six important 3D facial frames of facial expressions A, the start of motion (T0); B, the first quartile of expressions (T1); C, just after reaching the maximum state of expressions (T2); D, just before the end of maximum state of expressions (T3); E, the third quartile of expressions (T4); F, the end of motion (T5)."

Figure 3

Key frame (T2) of smile lips closed expression was aligned on the corresponding frame at rest (T0), and the root mean square values of all corresponding collection points were calculated"

Table 1

Corresponding RMS values of all subjects at the T3 frame of smile lip closed motion"

No. of subject RMS/mm
First time Second time
Participant 1 1.80 1.13
Participant 2 1.04 1.29
Participant 3 1.11 1.10
Participant 4 1.71 1.23
Participant 5 1.13 2.06
Participant 6 1.09 1.48
Participant 7 1.17 1.18
Participant 8 0.88 0.82
Participant 9 1.55 1.80
Participant 10 3.14 2.68
Participant 11 2.69 1.34
Participant 12 0.79 1.03
Participant 13 1.18 0.80
Participant 14 2.33 1.93
Participant 15 1.43 1.82

Table 2

Reproducibility of facial expressions"

Items P values
T1 T2 T3 T4 T5
Standard smile 0.173 0.256 0.477 0.394 0.140
Maximum smile 0.132 0.069 0.124 0.460 0.776
Lip purse 0.079 0.027 0.932 0.513 0.093
Cheek puff 0.570 0.691 0.118 0.691 0.233
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