Kinematic analysis of a Duchenne smile H. Jaffer a , E. Ichesco b , G.E. Gerstner c, * a Department of Biomolecular Sciences, College of Literature, Science, and the Arts, University of Michigan, Ann Arbor, MI 48109, USA b Department of Anesthesiology, School of Medicine, University of Michigan, 24 Frank Lloyd Wright Dr. Lobby M, Ann Arbor, MI 48109, USA c Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor, MI 48109-1078, USA A R T I C L E I N F O Article history: Received 5 July 2015 Received in revised form 2 November 2015 Accepted 20 December 2015 Keywords: Smile Kinematics Face Motor behavior Soft tissue movement A B S T R A C T Objective: Facial expressions are communicative motor outputs, whose kinematics likely are due to musculoskeletal anatomy, neuromotor activity and the well-being and internal states of the individual. However, little has been published on the kinematics of facial expression. This study quantified lip, eye and cheek movements during the production of a Duchenne smile involving movement of lips and tissues surrounding the eyes. Design: The three-dimensional positions of 20 markers placed around the eyes, cheeks, lips and chins of 24 young adult female subjects were digitized while they performed smiles after practicing to feedback from an investigator trained in the facial action coding system (FACS). Displacement, velocity and acceleration variables were extracted and analyzed from the markers. Results: Results demonstrated several consistencies across subjects including: (1) relatively high peak velocities, accelerations and displacements for lip and cheek markers in the vertical and anteroposterior dimensions, (2) relatively large movements of the lower lateral eye region compared with other eye regions. Conclusion: The results indicate that there is significant movement in the anteroposterior dimension that is not observable in frontal views of the face alone. ã 2015 Elsevier Ltd. All rights reserved. 1. Introduction Motor behavior is produced by neuromuscular systems acting on hard and soft tissues such as bones and skin. Significant insights into biomechanics (Pileicikiene & Surna, 2004), function (Wain- wright, Mehta, & Higham, 2008; Ross & Iriarte-Diaz, 2014), neuromotor control (Sessle, 2011), development (Barlow, 2009) and evolutionary issues (Sherwood et al., 2005) have resulted from studies of respiration, locomotion, licking, swallowing and chewing (Taylor, Leite, McKenzie, & Wang, 2010; More et al., 2010; Inokuchi et al., 2014; Travers, Dinardo, & Karimnamazi, 1997; Quintero et al., 2013a; Quintero, Ichesco, Myers, Schutt, & Gerstner, 2013b). Also, numerous recent advances in quantitative and descriptive methods promise improved ways of rendering and analyzing human and animal movement (Gerstner, Madhavan, & Crane, 2015; Crane, Childers, Gerstner, & Rothman, 2015; Crane, Cassidy, Rothman, & Gerstner, 2010; Ramsay, Hooker, & Graves, 2009; Brainerd et al., 2010; Gallo, 2005). With respect to chewing, jaw kinematics are relatively easily studied, given that the dentition can be used to represent mandibular movements. Furthermore given its semi-rigid proper- ties, the mandible’s movements can be documented with reference to relatively few markers. By contrast, movements of soft tissues, such as the tongue (Palmer, Hiiemae, & Liu, 1997; Hiiemae, Hayenga, & Reese, 1995; Hiiemae & Palmer, 2003; Hiiemae et al., 2002), lips (Sekita, Minakuchi, Hirano, Kobayashi, & Nagao, 2000) and face (Trotman & Faraway, 2004; Trotman, Faraway, & Phillips, 2005; Trotman, Stohler, & Johnston, 1998; Weeden, Trotman, & Faraway, 2001), are more difficult to document. This is because soft tissues possess unique biomechanical properties including elas- ticity and hysteresis (Bush, Ferguson, Mason, & McGrouther, 2007) and typically have a relatively large number of degrees of freedom. To document variation in soft-tissue movements requires address- ing several challenges. Three initial challenges include determining what behavior to track, what landmarks to track, and how to manage the resultant large data sets. Toward addressing these initial challenges, this study characterizes the kinematics of soft facial tissues during production of the Duchenne smile as defined by Ekman, et al. (Ekman, Davidson, & Friesen, 1990) and by us in previous work on smile esthetics (Lin, Braun, McNamara, & Gerstner, 2013). The * Corresponding author. Fax: +1 734 647 2110. E-mail addresses: hjaffer@umich.edu (H. Jaffer), eichesco@med.umich.edu (E. Ichesco), geger@umich.edu (G.E. Gerstner). http://dx.doi.org/10.1016/j.archoralbio.2015.12.005 0003-9969/ ã 2015 Elsevier Ltd. All rights reserved. Archives of Oral Biology 64 (2016) 11–18 Contents lists available at ScienceDirect Archives of Oral Biology journa l homepage: www.e lsevier.com/locate/aob