title: The spontaneous smile in dynamic motion.
abstract: BACKGROUND
  The purpose of this study was to record and analyze the dynamic nature of spontaneous smiles.
  
  
  METHODS
  Fifteen children (9 girls and 6 boys; average age, 10.5 years) were filmed with a hidden camera while they watched a funny cartoon video. Spontaneous smiles were recorded, and the video frames were digitized. Time-graphs of the measurements were constructed, and plots of the movement of the mouth points were drawn.
  
  
  RESULTS
  Facial measurements showed that the upper lip elevated by 28%, relative to the rest position, and the mouth increased in width by 27%. The corners of the mouth moved laterally and superiorly at an angle of approximately 47 degrees . Time analysis showed that the smiles developed in a staged fashion. The first stage (attack phase) was the shortest, lasting an average 500 ms. It was followed by a sustaining phase that included waxing and waning. The smile ended with a fade-out stage. The second and third stages were of variable duration and could be interrupted by the attack phase of a subsequent smile.
  
  
  CONCLUSIONS
  The dynamics of the spontaneous smile and the findings of this study raise concerns about the validity of a single photographic capture for esthetic assessment and treatment planning.
authors: Orthodontic Department, Dental School, University of Athens, Greece.
authors: Vicky V
authors: VV
authors: Tarantili
authors: Demetrios J
authors: DJ
authors: Halazonetis
authors: Meropi N
authors: MN
authors: Spyropoulos
mesh_terms: D000293:Adolescent; D002648:Child; D005152:Facial Muscles / Q000502:physiology; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008046:Lip / Q000502:physiology; D008297:Male; D009055:Mouth / Q000502:physiology*; D009799:Ocular Physiological Phenomena; D010781:Photography; D012904:Smiling / Q000502:physiology*; D013997:Time Factors; D014743:Videotape Recording