Whether added to tap water or toothpaste, fluoride can protect teeth from acids secreted by bacteria and prevent tooth decay.
In 1945, Grand Rapids, Michigan, became the first city in the world to add fluoride to tap water in an effort to promote oral health. “From epidemiological data, children’s teeth in some areas are less susceptible to decay than others,” said Lucy O’Malley, an applied medical scientist at the University of Manchester in the UK. “Authorities recognize this is because some areas have water supplies with natural fluoride levels of around 1 ppm and that is beneficial for preventing tooth decay.”
For decades afterward, health authorities across the United States, Britain and many other countries introduced similar amounts of fluoride into tap water. But the science behind it involves the structure of teeth, which consists of an extremely special tissue in the body, according to Dr. Alexander Morris, professor of public health dentistry at the University of Birmingham, England.
Teeth have 4 components: enamel (hard and shiny outer coating), dentin (hard tissue inside the tooth), dental pulp (soft tissue on the inside) and bone (thin coating at the base that allows the tooth to attach to the jaw). ). Tooth enamel acts as the first layer of protection against tooth decay.
Composed of a mineral called hydroxyapatite, a hard substance containing calcium, phosphate and hydroxide molecules, tooth enamel is the hardest substance in the human body. The phosphate particles are tightly packed together, with calcium and hydroxide ions in the small spaces in between. The strong attraction between the positively and negatively charged particles holds this structure in place, creating an extremely durable mineral. That shield protects the dentin and underlying pulp from damage and wear.
However, regular consumption of refined sugars such as snacks and soft drinks can damage this protective surface. “When you eat sugar, it’s broken down by bacteria in your mouth,” O’Malley explains. “While bacteria feed on sugar, they secrete acids, which contribute to the loss of minerals from tooth enamel.”
On a chemical level, acids remove negatively charged phosphate and hydroxide ions from tooth enamel, causing the structure to weaken. When holes in the enamel surface reach deep into the dentin, bacteria can penetrate the inner tissue layer and promote decay. If the affected tooth area is large enough, the tooth structure will collapse, creating a large cavity, according to Morris.
Fluoride solves this problem by promoting two key protective mechanisms that help preserve tooth enamel. Integrating fluoride into tooth enamel helps it increase its resistance to acids created by bacteria, helping to prevent tooth decay in the first place. The presence of fluoride can help repair initial tooth decay by creating more acid-resistant enamel.
Called mineral replacement, tiny fluorine ions replace part of the hydroxide in the tooth enamel structure. Fluorine is much smaller than hydroxide, so these particles fit more comfortably into the spaces between the phosphate ions. That creates a compact and stronger crystal structure called fluorapatite. The greater attraction between different ions in fluorinated minerals means that negatively charged particles are less likely to be repelled from tooth enamel. As a result, the process provides better protection against acid damage and corrosion. The benefits of fluoride for oral health prompted manufacturers to add fluoride to toothpaste in the 1970s.