Test-retest reliability of smile tasks using three-dimensional facial topography

Objectives: To evaluate the test-retest reliability of three types of facial expression tasks using three-dimensional (3D) facial topography. Materials and Methods: Twelve adult volunteers were enrolled in this study. They were instructed to perform three different facial expression tasks: rest posture, posed smile, and maximum effort smile. Each task was recorded using a 3D image-capturing device on two separate occasions with an interval of 1 week between sessions. The images of two sessions were superimposed based on the forehead. For each participant and for each facial expression, a wire mesh fitting was conducted. This method generated 6,017 points on the wire mesh. Intraindividual reliability between sessions for each task was statistically tested by intraclass correlation coefficients (ICCs) and the 95% confidence interval minimal detectable change (MDC95). Results: The MDC95 for the repeated measures of the rest posture, posed smile, and maximum effort smile exhibited means of 0.8, 1.5, and 1.3 mm, respectively, on the z-axis. The ICCs ranged from substantial to almost perfect agreement for repeated measures for the rest posture and maximum effort smile (0.60 < ICC <= 1.00). The right corner of the mouth in the posed smile showed moderate agreement (0.40 < ICC <= 0.60). Conclusions: The overall test-retest reliability of the maximum effort smile and rest posture showed substantial to almost perfect agreement, and this was clinically acceptable.