Fluoride Susceptibility Changes Between Adolescent and Mature Mice

Objectives: The optimal fluoride level is beneficial for tooth and bone health, however excessive fluoride can lead to dental and skeletal fluorosis. Fluoride metabolism and absorption in mineralized tissues (teeth and bones) change with age. In young children, fluoride is taken up by mineralized tissues more than in adults. However, studies on age-related fluoride health effects on mineralized tissues are limited. Here, we demonstrate different fluoride susceptibility in teeth and bones between adolescent and mature mice.
Methods: C57BL/6 mice (Male: Adolescent 5-9 weeks, and Mature 10-23 weeks) were given water containing fluoride (0, 50, 100, or 125 ppm) for six weeks. Thereafter, maxillary and mandibular incisors and femurs were analyzed for microhardness, Quantitative light-induced fluorescence (QLF), IHC, micro-CT, and three-point bending testing.
Results: Enamel: In adolescent groups, fluoride (all doses) significantly decreased microhardness compared to control (0 ppm). Whereas in mature groups, microhardness was reduced only by 125 ppm fluoride. In adolescent groups, fluoride (all doses), significantly increased QLF, while no significant differences were observed by fluoride in mature groups. These results suggest that fluoride-induced enamel malformation was more severe in adolescents compared to mature mice.
Femur: Micro-CT results showed fluoride (all doses) significantly increased bone mineral density (BMD) in adolescent groups. While, intriguingly, BMD significantly decreased in mature groups at fluoride concentrations of 100 and 150 ppm. Three-point bending test showed that in adolescent groups, fluoride at 125 ppm significantly decreased the maximum load (N) and stiffness (N/mm), whereas no changes were observed in mature groups (all doses). These results suggest that fluoride could reduce bone strength more in adolescent mice.
Conclusions: Our results suggest that fluoride biological effects can change over the lifespan. This study warrants further investigation for optimal age-related fluoride levels to keep benefits and prevent fluoride adverse health effects, especially for young children.