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Research on automatic facial expression recognition has benefited from work in psychology, specifically the Facial Action Coding System (FACS). To date, most existing approaches are primarily based on 2D images or videos. With the emergence of real-time 3D dynamic imaging technologies, however, 3D dynamic facial data is now available, thus opening up an alternative to detect facial action units in dynamic 3D space. In this paper, we investigate how to use this new modality to improve action unit (AU) detection. We select a subset of AUs from both the upper and lower parts of a facial area, apply the active appearance model (AAM) method and take the correspondence between textures and range models to track the pre-defined facial features across the 3D model sequences. A Hidden Markov Model (HMM) based classifier is employed to recognize the partial AUs. The experiments show that our 3D dynamic tracking based approach outperforms the compared 2D feature tracking based approach. The results are also comparable with the manually-picked 3D facial features based method. Finally, we extend our approach to validate the experiment for recognizing six prototypic facial expressions.