2022: Dental Fluorosis and Thyroid Hormones

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Wang C, Li D, Liu L, Zhao Q, Xie L, Tian Z, Tang H, Liu W, Hou H, Chen G, Wang A - "Effects of low-to-moderate fluoride exposure on Chinese school-age children's health: a potential role of thyroid hormones in dental fluorosis" SSRN Electronic Journal (2022)
https://doi.org/10.2139/ssrn.4268991

Background
Tooth and thyroid development occur around the same period in childhood. Thyroid hormone (TH) deficiency in children can lead to delayed tooth eruption, suggesting that THs may play a critical role in dental development. However, the specific role of THs in the development of dental fluorosis (DF) remains unclear.

Objectives
This study aimed to investigate the relationship between thyroid hormones and low-to-moderate fluoride exposure in relation to the development of dental fluorosis in children using a cross-sectional approach.

Methods
A total of 595 children aged 7 to 13 years were recruited from Tianjin, China. Water and urinary fluoride levels were measured using a fluoride ion-selective electrode. Thyroid hormone levels, including total triiodothyronine (TT3), free triiodothyronine (FT3), total thyroxine (TT4), free thyroxine (FT4), and thyroid-stimulating hormone (TSH), were assessed using a chemiluminescent microparticle immunoassay. Multivariable linear, logistic, and ordinal regression models were applied to evaluate the relationships between water fluoride, urinary fluoride, TH levels, and the prevalence of DF.

Results
A significant difference was observed between children with DF and those without DF in terms of TT4 levels (6.76 ± 1.10 vs. 6.98 ± 1.20, respectively). After adjusting for potential confounding factors, it was found that for every 1.0 mg/L increase in water fluoride, TT4 levels decreased by 0.105 pg. Similarly, each 1.0 mg/L increase in urinary fluoride was associated with a 0.107 pg reduction in TT4 levels. TT4 levels were found to modify the effect of urinary fluoride on the occurrence of moderate DF. The prevalence of moderate DF was influenced by an interaction between fluoride exposure and gender.

Conclusions
Changes in TT4 levels may be associated with low-to-moderate fluoride exposure, potentially affecting the development of dental fluorosis (DF) in children. Higher serum TT4 levels may serve as a protective factor against fluoride-induced dental fluorosis.