According to new research, identical twins may be more likely to develop dental fluorosis (DF) in their primary teeth compared to fraternal ones.  

The Journal of the American Dental Association (JADA) recently examined DF development in both identical and fraternal twins to determine if genetics played a role. Researchers found a “moderate heritability and higher diagnostic coincidence” in identical twins, which means they may have a unique genetic preponderance. 

Why this study was conducted 

Fluorosis typically develops due to environmental factors, most commonly by ingesting too much fluoride when teeth are in their critical stage of development. Swallowing fluoridated toothpaste or consuming fluoride supplements may also cause this condition. It is characterized by “increased enamel opacity, presence of diffuse white spots on the crown, structural loss in the most severe cases, and symmetry between hemiarches.”¹ Since DF is influenced by the duration and amount of fluoride ingested, those regularly drinking from fluoridated water supplies are more likely to develop mild forms. 

However, any genetic influence on the likelihood of DF development remains murky—which is why researchers wanted to investigate this topic. By understanding potential genetic factors behind DF, clinicians can help identify at-risk children early. They can also develop targeted preventive strategies, help parents manage fluoride exposure in their children, and use evidence-based interventions to minimize DF risk. 

Results and methodology 

JADA researchers studied DF in preschool-aged twins (3-5 years) with predominantly high community water fluoridation levels in Brazil. Researchers noted that: “Considering that monozygotic (MZ) twins share identical genetic material and dizygotic (DZ) twins share, on average, 50% of their genes, 15 comparative studies between these groups have become relevant for estimating the relative contributions of genetic and environmental factors to dental conditions in the population.” 

For the study, 438 children (219 pairs) participated with parental consent in 2024, with trials spanning from January to August. The children’s socioeconomic, health, and heritability-related aspects were also taken into account when determining DF likelihood. 

DF levels were then assessed using the Thylstrup-Fejerskov Index, which is a 10-point scoring system measuring the severity of DF development. A score of 0 indicates normal, translucent enamel, 1–4 indicate mild changes (such as narrow/pronounced lines of opacity but showing no major structural loss), and anything above a 5 indicates moderate to severe changes (marked opacity, distinct pitting, outer enamel loss, and anatomical changes in the tooth).² 

Researchers concluded that “our results showed an association between the use of fluoridated toothpaste during the first years of life and DF. This may be related to the mineralization of the second primary molar, which occurs during the child’s first year.” They also observed a higher diagnostic coincidence among identical twins, which suggests a genetic influence on the development of DF. 

Other factors at play

However, genetics are not the only factors that increase the chance of DF development. As previously mentioned, external environmental factors play a significant role. JADA researchers took this into account during data collection, reporting that “attending a private school, shorter duration of exclusive breastfeeding, and early-life use of fluoridated toothpaste were associated with DF.”¹ 

Here’s how elements outside of genetics impacted DF development: 

Schooling: Attending a private school may have increased DF risk because it exposed kids to fluoride at a younger age. 

Parental education: Mothers lacking higher education may not be aware of the appropriate amount of toothpaste to give their children, leading to a higher DF occurrence. As the study pointed out: “Children whose mothers had less than 6 years of schooling exhibited a higher prevalence of DF than their peers.” 

Breastfeeding: Children who are weaned off breastmilk early consume infant formula sooner. This may increase their fluoride intake if the formula is prepared with fluoridated water. 

Ultimately, DF isn’t predominantly caused by one specific factor. While this study emphasizes the impact of pre-established influences (like early exposure to fluoride toothpaste and fluoridated water), it also highlights genetics as another important variable. Understanding all possible causes of DF in young children can help clinicians better treat and protect young children from developing this condition. 

References 

1. 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. doi:10.1016/j.adaj.2026.02.012

2. Adelário AK, Vilas-Novas LF, Castilho LS, Vargas AM, Ferreira EF, Abreu MH. Accuracy of the simplified Thylstrup & Fejerskov index in rural communities with endemic fluorosis. Int J Environ Res Public Health. 2010;7(3):927-37. doi:10.3390/ijerph7030927