Does fluoride work by being ingested or by physically touching the teeth?

From the Guidelines

Fluoride primarily works by physically touching the teeth, though it can provide some benefits when ingested during tooth development. When fluoride comes in direct contact with tooth enamel, it helps prevent tooth decay by remineralizing weakened enamel, inhibiting bacterial acid production, and making teeth more resistant to acid attacks. This is why topical fluoride applications like toothpaste, mouthwash, and professional dental treatments are so effective, as supported by the Centers for Disease Control and Prevention's recommendations for using fluoride to prevent and control dental caries in the United States 1.

While ingested fluoride (from water, supplements, or foods) can provide some systemic benefits during tooth formation in children, particularly before teeth erupt, the primary cavity-fighting mechanism occurs through direct contact with tooth surfaces. This is why dentists recommend brushing with fluoride toothpaste twice daily and why fluoride treatments are applied directly to the teeth in dental offices, as emphasized in the guidelines for using fluoride to prevent and control dental caries 1.

The concentration of fluoride in saliva after ingestion is much lower than what's achieved through direct topical application, making the contact method more effective for cavity prevention in existing teeth. Furthermore, the use of fluoride toothpaste is a cost-effective way to reduce the prevalence of dental caries, but it's essential to follow guidelines for its use, especially in children aged <6 years, to minimize the risk of enamel fluorosis 1.

In terms of the effectiveness of different fluoride concentrations, toothpaste containing 1,500 ppm fluoride has been reported to be slightly more efficacious in reducing dental caries, but it's not available in all areas and might be more beneficial for persons aged >6 years at high risk for dental caries 1. Ultimately, the regular use of fluoride, whether through topical applications or community water fluoridation, is crucial for maintaining good oral health and preventing dental caries throughout life, as highlighted in the recommendations for using fluoride to prevent and control dental caries in the United States 1.

Key points to consider:

• Fluoride's primary mechanism is through direct contact with tooth surfaces
• Topical fluoride applications are more effective than ingested fluoride for cavity prevention in existing teeth
• Fluoride toothpaste is a cost-effective way to reduce dental caries, but its use should be guided by recommendations to minimize enamel fluorosis risk
• Regular fluoride use is essential for maintaining good oral health and preventing dental caries throughout life.

From the Research

Fluoride Mechanism

• Fluoride works by physically touching the teeth, as evidenced by the effectiveness of topical fluoride applications such as toothpastes, mouthrinses, gels, and varnishes in preventing dental caries 2, 3.
• The use of fluoride toothpaste has been shown to reduce caries increment when compared to non-fluoride toothpaste, with higher concentrations of fluoride associated with increased caries control 2.
• Topical fluoride therapy has been found to be effective in preventing dental caries in children and adolescents, with a prevented fraction of 26% (95% CI, 24% to 29%; p < 0.0001) 3.

Ingested Fluoride

• Ingested fluoride, such as through fluoridated drinking water, has also been shown to have a caries-preventive effect, although the evidence is less clear-cut 4, 5.
• High concentrations of ingested fluoride can lead to adverse effects such as dental fluorosis, skeletal fluorosis, and other health problems 4, 5.
• The optimal level of ingested fluoride for caries prevention is still a topic of debate, with some studies suggesting that low levels of fluoride (around 0.7-1.5 ppm) are sufficient for caries prevention 5.

Comparison of Topical and Ingested Fluoride

• Topical fluoride applications have been found to be more effective than ingested fluoride in preventing dental caries, particularly in children and adolescents 2, 3.
• The combination of topical and ingested fluoride may provide additional caries prevention benefits, although the evidence is limited 6.
• The use of topical fluoride in addition to ingested fluoride has been found to achieve a modest reduction in caries compared to ingested fluoride alone 6.