Three-dimensional motion analysis - an exploratory study. Part 1: assessment of facial movement

To objectively quantify facial movement in response to facial expression and spoken word.

Experimental study. Setting - Department of Dental Health and Biological Sciences, University Dental Hospital, Cardiff, UK.

Facial movement was assessed in response to a standardized smile expression and the utterance 'puppy'. The sequences were recorded using a non-invasive, three-dimensional motion analysis image capture system (3dMDface Dynamic System) at 48 frames per second.

To quantify the facial movement, sequential frames of a sequence were aligned to the baseline/reference frame three-dimensionally using best fit on non-moveable points in the upper half of the face. Accuracy of the alignment process for each sequence was tested using the percentage of stable points (i.e. within +/-0.5 mm) within the upper half of the face.

Quantifiable changes in facial topology were seen during both the standardized smile expression and the utterance 'puppy'. The mean percentage of points (SD) that remained stable within the upper half of the face during the utterance 'puppy' was 88.8% (4.7). During the standardized smile expression, there were a much lower percentage of stable points in the upper half of the face with a mean (SD) of 60.9% (3.2).

The 3dMDface Dynamic System allows objective, three-dimensional, non-invasive assessment of facial movement. The utterance 'puppy' is a more appropriate measure of facial movement when compared with the standardized smile expression.