Sex-specific effects of environmental temperature during gestation on fluctuating asymmetry in deciduous teeth.

ABSTRACT

OBJECTIVES: External environmental heat exposure during gestation impacts the physiology of human development in utero, but evidence for these impacts has not yet been explored in dentition. We examined deciduous teeth for fluctuating asymmetry (FA), a measure of developmental instability, together with gestational environmental temperature data drawn from historical weather statistics. MATERIALS AND METHODS: We measured dental casts from the longitudinal Burlington Growth Study, representing 172 participants (ages 3-6 years) with health records. FA was calculated from crown dimensions and intercuspal distances that develop during gestation. Multiple regression separated by sex (nfemale = 81) examined the effects of mean temperatures in each trimester, controlling for birth year. RESULTS: In females, increased temperatures during the first trimester are significantly associated with an increase in FA (p = 0.03), specifically during the second and third prenatal months (p = 0.03). There is no relationship between temperature and FA for either sex in the second or third trimesters, when enamel is formed. DISCUSSION: Dental instability may be sensitive to temperature in the first trimester in females during the scaffolding of crown shape and size in the earliest stages of tooth formation. Sexual dimorphism in growth investment strategies may explain the differences in results between males and females. Using enduring dental characteristics, these results advance our understanding of the effects of temperature on fetal physiology within a discrete period.