Three-dimensional intra-rater and inter-rater reliability during a posed smile using a video-based motion analyzing system

ObjectivesThe purpose of this study was to determine the three-dimensional reproducibility of lip movement during a posed smile using a video-based motion analyzing system.Materials and methodsIn six adult volunteers (4 males and 2 females), the lip motions during a posed smile were recorded six times. Using our recently-developed motion analyzing system, range images were produced across the whole sequence during the posed smile. Virtual grids of 5 × 5 were fitted onto the surfaces, and the three-dimensional coordinates of the intersections of these grids were then computed. The magnitude of the shift of the intersections during smiling was calculated and summed in each area. Intraclass correlation coefficients (ICC), ICC (1,1) for intra-rater reliability and ICC (2,1) for inter-rater reliability were calculated. The number of repeated measurements necessary for an ICC level beyond 0.8 was determined using the formula of Spearman–Brown.ResultsThe ICC (1,1) and ICC (2,1) ranged from 0.71 to 0.83 and from 0.77 to 0.99, respectively. The number of repeated measurements necessary for an ICC beyond 0.8 was 2.ConclusionsFrom the present study, both the three-dimensional intra-rater and inter-rater reliabilities during a posed smile were considered to be relatively high, and enough reliability could be expected by calculating the average of the values measured two times. However, the sample size was very small, this could not be generalized simplistically.