A new birth cohort study reveals that a mother’s stress-related hormones in late pregnancy, especially cortisol, may quietly influence when her baby’s first teeth appear, uncovering a surprising link between prenatal biology and early childhood development.
Study: Prenatal maternal salivary hormones and timing of tooth eruption in early childhood: a prospective birth cohort study. Image credit: Shevtsova Yuliya/Shutterstock.com
Tooth eruption is a complex process that is not fully understood. The mother’s health, genetics, and environmental exposures, particularly her stress levels, all appear to be important factors shaping when a child’s teeth emerge. A recent study, published in the journal Frontiers in Oral Health, examines the effects of maternal stress and stress-related hormones during pregnancy on tooth eruption.
Stress and dental health
The timing of tooth eruption is crucial because it impacts oral health. Most children have two to eleven erupted teeth by the time they are one year old. Delayed eruption is associated with poor tooth alignment, malocclusion, enamel damage, and an increased risk of tooth decay. It may also signal differences in early development, while early eruption has been proposed as a marker of accelerated biological aging.
The primary teeth begin to develop in prenatal life. A poor diet, smoking, poverty and social deprivation are all factors linked to abnormalities in tooth eruption. Stress may help explain some of these associations, as it has been linked to enamel defects and a higher risk of dental caries.
Stress activates the hypothalamo-pituitary axis, altering several key hormones, including cortisol, the sex steroids, and thyroid hormones. In turn, these factors also affect bone development, as well as the metabolism of vitamin D and calcium. In the current study, the researchers aimed to investigate the relationships between prenatal stress, hormones associated with stress, and the eruption of primary teeth.
Hormones under investigation
The study included 142 pairs of mothers and children drawn from a single birth cohort. Each child was examined up to two years of age for tooth eruption. The mothers’ health records were used to identify the presence of prenatal anxiety and depression. Hormones of interest included cortisol, estradiol, progesterone, testosterone, and the thyroid hormones triiodothyronine (T3) and thyroxine (T4).
Patterns in tooth timing
All mothers in the cohort were from deprived backgrounds, and over half were African Americans. More than half were employed, but only 40 % had a higher education beyond high school. Most stopped breastfeeding within six months of childbirth. All the offspring were full-term babies, with an average birth weight of 3.3 kg.
Of all the children, 17 had between one and six erupted teeth by six months of age, most commonly the lower central incisors. By one year, only three children still had no erupted teeth, while the median tooth count was six. More than 95 % had their lower central incisors, and about 80% had their upper central incisors.
By 18 months, 100% of the children had erupted teeth, with a median number of 14. By the age of two, this number rose to 16, with 25 % of children having all 20 primary teeth. Less than 40 % had erupted upper and lower second molars at this age.
Two types of tooth eruption were identified; the most common was continuous growth, with rapid growth between 12 and 18 months observed in fewer than 3 % of children. Interestingly, tooth eruption was relatively delayed in this cohort compared to earlier studies, followed by more rapid development between 12 and 24 months.
Approximately 37 % of women were diagnosed with anxiety or depression during their pregnancy. The researchers found significant associations between all the hormones and the number of erupted teeth when evaluated on an individual visit basis. There were no associations when all visits and erupted teeth were evaluated together, likely due to the very low stability of tooth counts across visits.
The largest correlation was seen with cortisol levels. Increased cortisol levels were associated with a greater number of erupted teeth at six months. On average, there were four more erupted teeth in the children with the highest cortisol levels compared to those with the lowest cortisol levels.
Conversely, anxiety or depression was not associated with any hormone levels.
Why hormones matter
Weak to modest correlations were identified between the number of erupted teeth and salivary stress-associated hormones at specified time points across the first two years of life. The strongest correlation was observed with cortisol at six months, possibly due to underlying stress. Effect sizes for other hormones, such as sex steroids and T3, were very small and of limited clinical significance.
Maternal salivary hormone levels in late pregnancy may contribute to variations in primary tooth eruption during the first two years of life.
However, future studies, including those with larger and more diverse samples, are needed to validate these observations and better understand the underlying mechanisms.