The influence of involuntary facial movements on craniofacial anthropometry: a survey using a three-dimensional photographic system

In the modern anthropometry of complex structures, such as the face, different technical approaches for acquisition of three-dimensional data have become increasingly more common. Results of meticulous evaluations have shown high degrees of precision and accuracy under both ideal and clinical circumstances. However, the question remains as to which level of accuracy is adequate to meet clinical needs. Apart from the measuring technique itself, potential sources of error must be identified and dealt with. Subjects' involuntary facial movements can potentially influence clinical reliability. The 3dMDface™ system was used clinically to investigate the influence of involuntary facial movements. Other factors of influence were systematically excluded. The mean technical error of the system (0.09 mm) was investigated in a previous study and taken into account for interpretation of the data. The handling of the system was straightforward for both acquisition and analysis of data. Including technical error and the influence of involuntary facial movements, the mean global error was 0.41 mm (range 0-3.3). Taking into account the technical error of the system known from the previous study, involuntary facial movements account for a mean error of 0.32 mm. This range of involuntary facial movements clearly exceeds the known technical error of the three-dimensional photographic system used. Given this finding, future research should shift its focus from the analysis of the technical aspects of such systems to other influential factors.