Lower face asymmetry as a marker for developmental instability.

OBJECTIVES: Fluctuating asymmetries in the craniofacial skeleton have been shown to be predictive for mortality from degenerative diseases. We investigate whether lower face asymmetries are a potential marker for the developmental origins of health and disease.

METHODS: The lower face of a representative sample of 6654 12- to 17-year old United States (US) adolescents (1966-1970, National Health Examination Survey III) was classified as asymmetric when the mandibular teeth occluded prognathically (forward) or retrognathically (backward) on one side of the face only. It was investigated whether these lower face asymmetries were directional (preferentially to the left or the right) or fluctuating (random left-right distribution) in the US population.

RESULTS: Lower face asymmetries affected 1 in 4 of the US adolescents. Unilateral retrognathic dental occlusions were fluctuating asymmetries, had a US prevalence of 17.0% (95% confidence interval: 15.5-18.4) and were associated with race/ethnicity (P < .0001), not with handedness (P < .7607). Unilateral prognathic dental occlusions were directional asymmetries (P < .0001), had a US prevalence of 7.6% (95% confidence interval: 6.4-8.7) and were associated with large household size (P < .001) and handedness (P < .0223). Lower face asymmetries were not associated with distinct heritable traits such as color blindness.

CONCLUSIONS: The findings suggest that lower face asymmetries are a marker for environmental stress and cerebral lateralization during early development.