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 @entity601 (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 @entity601 (p = 0.032) and oral commissure asymmetry (p = 0.007). Smoking was associated with canting of the plane of occlusion (p = 0.049) and @entity1736 (p = 0.023). Lastly, @entity10 were also associated with @entity601 (p = 0.024). CONCLUSION: Exogenous factors such as prone sleep position, tooth extractions, dentures, and smoking are significant risk factors for @entity7439 . CLINICAL QUESTION/LEVEL OF EVIDENCE: Risk, II.

Factors contributing to XXXX in identical twins.

@entity7439 :: ('MESH:D005146', 'Disease') :: ['facial asymmetry'] @entity1736 :: ('MESH:D001763', 'Disease') :: ['upper eyelid ptosis'] @entity10 :: ('MESH:D006261', 'Disease') :: ['headaches'] @entity601 :: ('MESH:D009436', 'Disease') :: ['nasal midline deviation']
@entity7439 :: (MESH:D005146,Disease) :: ['facial asymmetry']
