A recent twin study published in the Journal of the American Dental Association evaluated the relative contributions of genetic and environmental factors to dental fluorosis (DF) in the primary dentition. The investigation compared monozygotic (MZ, identical) and dizygotic (DZ, fraternal) twins to assess whether concordance rates differed by zygosity, which can indicate heritability.
The authors report a “moderate heritability and higher diagnostic coincidence” for DF among identical twins, suggesting a measurable genetic component alongside known environmental drivers of fluorosis.
DF is classically associated with excess fluoride exposure during enamel formation, producing increased enamel opacity, diffuse white spots, and in severe cases structural loss and pitting. Because fluoride exposure is largely environmental — for example, ingestion of fluoridated water, fluoride supplements, or swallowing fluoridated toothpaste — the role of genetic predisposition has been less clear.
Researchers designed the twin study to clarify the relative importance of heredity versus environmental exposures. Understanding genetic susceptibility could help clinicians identify children at higher risk and refine counseling on fluoride exposure during critical tooth mineralization periods.
The study enrolled 438 children (219 twin pairs) aged 3–5 years, with parental consent, in a Brazilian setting characterized by predominantly high community water fluoridation. Data collection occurred from January through August 2024. The study collected information on socioeconomic, health, and heritability-related variables to analyze DF likelihood in relation to both genetic and environmental factors.
Researchers framed the comparison on the established principle that MZ twins share identical genetic material while DZ twins share, on average, 50% of segregating genes. This structure allows estimation of the relative contributions of genetics and environment to dental conditions.
DF severity in the sample was assessed using the Thylstrup-Fejerskov Index, a 10-point scale commonly used in epidemiologic studies of fluorosis. On this scale: 0 indicates normal translucent enamel; scores 1–4 indicate mild changes such as narrow or pronounced lines of opacity without major structural loss; and scores greater than 5 indicate moderate to severe alterations including marked opacity, pitting, outer enamel loss, and anatomical deformation.
The JADA report states that DF was evaluated in the preschool-aged children using this index, allowing standardized classification of mild through severe presentations.
The investigators found a higher diagnostic coincidence of DF among identical (MZ) twins compared with fraternal (DZ) twins. The report characterizes this as evidence of moderate heritability, meaning genetic factors appear to contribute to the risk of developing DF in primary teeth in this cohort.
The article does not provide specific heritability coefficients or detailed statistical values in the summary; those figures are reported in the primary JADA publication (Leitão de Souza et al., 2026), which the summary cites.
Although the study highlights a genetic signal, researchers also identified multiple environmental and sociodemographic variables associated with DF prevalence in the cohort:
Early-life use of fluoridated toothpaste: The study found an association between using fluoridated toothpaste during the first years of life and DF. The authors suggest this may be relevant to mineralization timing for the second primary molar, which mineralizes during the child’s first year.
Community water fluoridation: Given the study population’s predominantly high fluoridation levels, duration and amount of fluoride exposure via drinking water remain important contributors to DF risk, especially for mild forms.
Breastfeeding duration: Shorter duration of exclusive breastfeeding was associated with higher DF. Investigators note that earlier transition to infant formula prepared with fluoridated water could increase fluoride intake.
Schooling and maternal education: Attending private school was associated with higher DF in this sample, potentially reflecting earlier exposure to fluoride in those environments. Lower maternal schooling (less than six years) was also associated with greater DF prevalence, which the authors suggest may reflect gaps in caregiver knowledge about appropriate amounts of toothpaste for young children.
These findings underscore that DF arises from multiple interacting factors rather than a single cause.
The study’s combined genetic and environmental findings have practical implications for clinicians:
Screening and risk assessment: Awareness of potential genetic predisposition may prompt clinicians to consider family history or twin status when assessing DF risk in young patients.
Preventive counseling: Reinforcing caregiver guidance on appropriate toothpaste amounts for infants and toddlers, supervised brushing to minimize swallowing, and cautious use of fluoride supplements in high-fluoridation areas remain important.
Timing of exposure: Clinicians should be mindful of critical mineralization windows (for example, the first year for the second primary molar) when advising on fluoride exposure and oral hygiene practices.
The authors suggest that identifying children at higher risk could enable earlier, targeted preventive strategies to reduce DF incidence while still preserving the caries-preventive benefits of fluoride.
The summary cites the primary twin study: Leitão de Souza RR, Lopes LCA, Matias-Santos FADS, et al. "Genetic and environmental contributions to dental fluorosis in the primary dentition: A census-based twin study." J Am Dent Assoc. 2026;157(9):1005–1017. The article also references literature on the Thylstrup & Fejerskov index accuracy.
Details such as exact numerical heritability estimates and statistical test values were not provided in the summary and are reported in the full JADA publication.
Clinicians should consult the primary JADA article for comprehensive statistical results and methodology if those details are needed for research or guideline development.