title: Factors contributing to facial asymmetry in identical twins.
abstract: BACKGROUND
  This study examines the potential contributions of environmental factors to variations in facial symmetry between identical twins.
  
  
  METHODS
  Identical male and female twins were recruited from the Twins Days Festival in 2009 and 2010. Subjects independently completed a comprehensive questionnaire on their medical and personal history, and then posed for digital facial photography from several different angles. Eight facial features from these photographs were measured using Adobe Photoshop, and these facial features were then analyzed against survey responses between twins through multivariate regressions.
  
  
  RESULTS
  A total of 147 pairs of identical twins were included. Twins who slept primarily prone had greater nasal midline deviation (p = 0.047) and oral commissure asymmetry (p = 0.027). Tooth extractions were significantly associated with canting of the plane of occlusion (p = 0.043), and use of dentures was associated with nasal midline deviation (p = 0.032) and oral commissure asymmetry (p = 0.007). Smoking was associated with canting of the plane of occlusion (p = 0.049) and upper eyelid ptosis (p = 0.023). Lastly, headaches were also associated with nasal midline deviation (p = 0.024).
  
  
  CONCLUSIONS
  Exogenous factors such as prone sleep position, tooth extractions, dentures, and smoking are significant risk factors for facial asymmetry.
  
  
  METHODS
  Risk, II.
authors.affiliation: Cleveland, Ohio From the Department of Plastic Surgery, University Hospitals Case Medical Center and Case Western Reserve University School of Medicine; the Department of Surgery, Cleveland Clinic; and the Department of Surgery, MetroHealth Medical Center.
authors.forename: Mengyuan T
authors.initials: MT
authors.lastname: Liu
authors.forename: Rodrigo A
authors.initials: RA
authors.lastname: Iglesias
authors.forename: Sahil S
authors.initials: SS
authors.lastname: Sekhon
authors.forename: Yumeng
authors.initials: Y
authors.lastname: Li
authors.forename: Kelsey
authors.initials: K
authors.lastname: Larson
authors.forename: Ali
authors.initials: A
authors.lastname: Totonchi
authors.forename: Bahman
authors.initials: B
authors.lastname: Guyuron
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D004200:Diseases in Twins / Q000151:congenital / Q000209:etiology*; D004777:Environment; D005146:Facial Asymmetry / Q000151:congenital / Q000209:etiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D014430:Twins, Monozygotic; D055815:Young Adult