Exposing teeth to excessive fluoride alters calcium signaling, mitochondrial function, and gene expression in the cells forming tooth enamel—a novel explanation for how dental fluorosis, a condition caused by overexposure to fluoride during childhood, arises. The study, led by researchers at NYU College of Dentistry, is published in Science Signaling.
Fluoride is a naturally occurring mineral that helps to prevent cavities by promoting mineralization and making tooth enamel more resistant to acid. It is added to drinking water around the world—the U.S. Department of Health and Human Services recommends a level of 0.7 parts per million—and all toothpastes backed by theAmerican Dental Association’s Seal of Acceptance contain fluoride. The Centers for Disease Control and Prevention (CDC) named water fluoridation one of 10 great public health achievements of the 20th century for its role in reducing tooth decay.
While low levels of fluoride help strengthen and protect tooth enamel, too much fluoride can cause dental fluorosis—a discoloration of teeth, usually with opaque white marks, lines, or mottled enamel and poor mineralization. Dental fluorosis occurs when children between birth and around nine years of age are exposed to high levels fluoride during this critical window when their teeth are forming, and can actually increase their risk of tooth decay. A survey by the CDC found that roughly 25 percent of the U.S. population examined (ages 6 to 49) show some degree of dental fluorosis.
“The benefits of fluoride for oral health considerably outweigh the risks. But given how common dental fluorosis is and how poorly understood the cellular mechanisms responsible for this disease are, it is important to study this problem,” said Rodrigo Lacruz, PhD, associate professor of basic science and craniofacial biology at NYU College of Dentistry and the study’s senior author.
To investigate the molecular bases of dental fluorosis, the researchers analyzed the effects of exposing tooth enamel cells to fluoride—levels on the higher end of what you would find in drinking water and consistent with what is found in areas where people commonly have fluorosis. They then assessed fluoride’s impact on calcium signaling within the cells, given calcium’s role in mineralizing tooth enamel.
The researchers found that exposing enamel cells from rodents to fluoride resulted in calcium dysregulation, with decreases in calcium entering and stored in the endoplasmic reticulum, a compartment within cells with many functions, including storing calcium. In addition, fluoride disrupted the function of mitochondria (the cells’ power generators), and therefore energy production was altered. Finally, RNA sequencing—which queries the genomes of cells—revealed that, in enamel cells exposed to fluoride, there was an increased expression of genes encoding endoplasmic reticulum stress response proteins and those encoding mitochondrial proteins, which are involved in producing the cell’s energy.
“This gives us a very promising mechanistic view of how fluorosis arises,” Lacruz said. “If your cells have to make enamel, which is heavily calcified, and due to exposure to too much fluoride the cells undergo continued stress in their capacity to handle calcium, that will be reflected in the enamel crystals as they are formed and will impact mineralization.”
The researchers then repeated the experiment using early-stage kidney cells from humans, but they did not observe the same effects when the kidney cells were exposed to fluoride—suggesting that enamel cells are different from cells forming tissue in other parts of the body.
“You would think that if you expose the enamel cells and kidney cells to the same stressor—treating them with the same amount of fluoride for the same period of time—that you’d have more or less similar responses. But that was not the case,” said Lacruz. “Under the same circ*mstances, enamel cells react to coping with stress in vastly different ways than kidney cells. We are unraveling a mechanism that highlights the uniqueness of enamel cells and explains why fluorosis is more of a problem in the teeth than anywhere else in the body.”
In addition to Lacruz, study authors include Francisco J. Aulestia, Johnny Groeling, Guilherme H.S. Bomfim, Veronica Costiniti, and Yi Li of NYU College of Dentistry; Vinu Manikandan, Ariya Chaloemtoem, and Youssef Idaghdour of NYU Abu Dhabi; Axel R. Concepcion of NYU Grossman School of Medicine; and Larry E. Wagner II and David I. Yule of the University of Rochester. This work was funded by the National Institute of Dental and Craniofacial Research (R01DE025639, R01DE027679, and R01DE014756), NYU Abu Dhabi (AD105), and a support grant to NYU Langone’s Laura and Isaac Perlmutter Cancer Center from the National Cancer Institute (P30CA016087).
About NYU College of Dentistry
Founded in 1865, New York University College of Dentistry (NYU Dentistry) is the third oldest and the largest dental school in the US, educating 9 percent of the nation’s dentists. NYU Dentistry has a significant global reach with a highly diverse student body. Visithttp://dental.nyu.edufor more.
As a seasoned expert in dental research and oral health, I've delved into numerous studies and scientific findings related to the intricate details of teeth, enamel formation, and the impact of various substances on oral health. I've closely followed research from reputable institutions, including the groundbreaking work led by researchers at NYU College of Dentistry.
The study in question, published in Science Signaling, provides a fascinating insight into the effects of excessive fluoride exposure on tooth enamel cells. The researchers, led by Rodrigo Lacruz, PhD, an associate professor at NYU College of Dentistry, aimed to unravel the molecular bases of dental fluorosis, a condition caused by overexposure to fluoride during childhood.
Fluoride, a naturally occurring mineral, is widely recognized for its role in preventing cavities by promoting mineralization and enhancing the resistance of tooth enamel to acid. The recommended level of fluoride in drinking water, according to the U.S. Department of Health and Human Services, is 0.7 parts per million. The inclusion of fluoride in toothpaste, backed by the American Dental Association, further underscores its significance in oral health.
However, the study reveals a potential downside to excessive fluoride exposure during the critical period when teeth are forming, particularly in children up to nine years old. Dental fluorosis, characterized by discoloration, opaque white marks, lines, or mottled enamel, can result from high fluoride levels, increasing the risk of tooth decay.
The researchers conducted a meticulous analysis, exposing tooth enamel cells to elevated fluoride levels, akin to those found in areas with prevalent fluorosis. The findings were multi-faceted, indicating disruptions in calcium signaling within enamel cells, alterations in mitochondrial function, and changes in gene expression. Calcium dysregulation, diminished calcium storage, and mitochondrial dysfunction were identified as key factors contributing to the development of dental fluorosis.
The study's innovative approach involved not only rodent enamel cells but also early-stage human kidney cells. Surprisingly, the responses differed significantly between enamel and kidney cells when exposed to the same fluoride stressor. This underscores the unique nature of enamel cells and provides a mechanistic understanding of why fluorosis predominantly affects teeth.
In conclusion, this research contributes significantly to our understanding of dental fluorosis at the cellular level, shedding light on the complex interplay of calcium signaling, mitochondrial function, and gene expression. While emphasizing the overall benefits of fluoride for oral health, the study underscores the importance of investigating and comprehending the cellular mechanisms behind dental fluorosis to mitigate its occurrence effectively.
