Introductory Chapter: Fluoride and Dental Health – From Water Fluoridation to Essential Medicine

1. Introduction

To understand the role of fluoride in the twenty-first century, it is important to revisit some historical milestones and scientific advances related to the topic.

When was the connection between fluoride and teeth first made? When was fluoride first associated with oral health? Both questions are difficult to answer because interest in fluoride has changed over the years since its discovery.

Primarily, fluoride raised interest due to its presence in bones [1]. In 1805, Domenico Morichini, an Italian chemist-physician, identified fluoride in human dental enamel shortly after the discovery of the fluorine element by Scheele in 1771. Interestingly, fluorine isolation was only achieved by Henri Moissan in 1886 [2].

It is of utmost importance to differentiate FLUORINE from FLUORIDE. The first is the chemical element (atomic number 9) with the symbol F. It is a highly reactive, toxic, pale yellow gas at room temperature. Fluorine is rarely found isolated in nature because it can form compounds with nearly all other elements, sometimes explosively. On the contrary, fluoride is much safer than fluorine gas and is used for dental health. It is rather stable and much less reactive than elemental fluorine. Therefore, fluoride, whose symbol is F⁻, is the negatively charged ion of fluorine, and it is commonly found in dental products, such as sodium fluoride (NaF), calcium fluoride (CaF₂) and monofluorphosphate (PO3F2−).

It is well documented that interest in fluoride (F-) in dental health began before scientific evidence of its positive anticavity effects when added to drinking water. For example, there are reports of the use of calcium fluoride powder in Germany in 1896 and the use of calcium fluoride tablets (“Fluoridens”) in Denmark and other parts of Europe. In England, Fluoridens was mixed with table salt 60 years before the Swiss canton of Zurich began selling fluoridated salt [3, 4, 5].

Fluoride was introduced to dentistry only 40 years later when Dr. Frederic McKay moved to Colorado Springs (the Mountain West part of the United States), an area with naturally occurring fluoride in the water and a high prevalence of “mottled enamel” (dental fluorosis). First, McKay discovered that the “Colorado Stains,” as referred to by the local inhabitants, were very similar to the spots called the “denti di Chiaie,” a condition observed in Italian immigrants. A second notable discovery was the fact that these tooth stains were related to high levels of fluoride in drinking water [3, 4].

It is important to remember that for many years (1916–1944), fluoride was basically a compound that could cause tooth stains, ugly unmistakably dental defects. As a result, this first historical link of fluoride in dentistry significantly impacted the conception of fluoride as a serious harmful compound to human health. Emphasizing or focusing on the harmful effects of fluorides still has repercussions today! Fortunately, the benefits of regular fluoride use have become clear. Dr. H. Trendley Dean was the researcher who pursued evidence that fluoride levels should not exceed 1 ppm in drinking water, which could result in less dental caries. Dean’s efforts, studies and publications led to the first experiment in artificial water fluoridation in the United States and the acceptance of fluoride as an anti-caries agent. In 1958, the World Health Organization concluded that fluoride in drinking water was an indisputable caries-preventive strategy and an effective public health measure [3].

Fluoride is a ubiquitous natural compound found in soil, water and sometimes air. Since it is an odorless, tasteless and transparent compound, a physical-chemical technique is needed for its detection [6]. Hence, when a water fluoridation system is implemented in a city, no “new” or “strange” substances are added to the drinking water. Artificial fluoridation of the water is an adjustment for adequate fluoride exposure to reduce the prevalence of dental caries. Furthermore, a “fluoride-free world,” as envisioned by some anti-fluoride groups, is a utopia due to the abundance of fluoride in nature.

A curiosity in the history of fluoride is the fact that the first studies on community water fluoridation were based on the hypothesis that it was necessary to drink fluoridated water to achieve its full preventive effect. The conceptual idea was simple: if high intakes of fluoride can lead to defective tooth enamel formation (dental fluorosis), moderate intakes can lead to more resilient dental tissue. However, a Dutch longitudinal study (Tiel-Culemborg) carried out from 1952 to 1959 proved that caries reduction was mainly observed in smooth surfaces and less in pits and fissures. This was clear evidence that some local intra-oral preventive effects were effective [7]. Eventually, a report from the same fluoridated city (Tiel) showed clinical remineralization of initial carious lesions, proving that fluoride has a positive post-eruptive effect on tooth enamel [8]. Additionally, Russel observed an increase in dental caries in children who moved out of fluoridated areas, suggesting that resistant enamel does not have a lasting effect. In other words, the preventive effect of fluoride only occurs if the person has been constantly exposed to fluoride [9].

Finally, in the 1980s and after several laboratory experiments, it was established that fluoride controls caries mainly through its topical effect. Fluoride inhibits demineralization of hard dental tissue when present in the oral fluid. In fact, fluoride can be absorbed into the surface of apatite crystals during acidic stress, and when the pH is restored, traces of fluoride in the solution result in strong supersaturation with respect to fluorohydroxyapatite, accelerating the process of remineralization [10, 11]. So, its effect is essentially topical while it is still in the oral cavity and when fluoride returns to the oral cavity after absorption via saliva [11].

Today, water fluoridation is used to combat caries in many countries, but it is now recognized that the mechanism of action of fluoride is primarily topical. Fluoride is now available in toothpaste, mouthwashes, gels, varnishes and many other products. Undoubtedly, fluoride is a cornerstone in preventive dentistry.

Despite the robust scientific evidence of its positive effect on dental caries, there is always this “smell a rat” feeling for many consumers and, surprisingly, for some dentists as well. In addition to the historical facts mentioned previously, today, the “fake news” phenomenon is also operating and supporting misinformation.

Fortunately, there is growing evidence of the therapeutic benefits of regular fluoride use. With the keyword “fluoride” 23,526 publications can be accessed in the PubMed® database between 2015 and 2025. Since this topic can be related to other areas of science, a more targeted search is worthwhile. Using the following MeSH terms for TITLE-ABSTRACT-KEYWORDS (fluoride AND dentistry), a bibliometric study for the period 1945–2019 showed that interest in fluoride has increased since 1965. The main areas of published material were pediatric dentistry, dental hygiene, dental materials, restorative dentistry, periodontology, orthodontics, endodontics and prosthodontics [12].

A recent breakthrough in dentistry is the WHO (World Health Organization) list of essential medicines in 2021. The new category contains fluoride (paste, cream or gel with 1000 or 1500 ppm) and fluoride-releasing products (38% silver diamine fluoride and glass ionomer cement). This list will increase the availability and accessibility of fluoride products in many countries. Furthermore, this document provides strong support for the rational and regular use of fluoride to combat dental caries in different scenarios at an individual or community level [13].

A review of the history of fluoride, from discovery to essential medicine status, helps us understand the achievements and challenging problems on the horizon.

2. Fluoride and challenges for the 21st century

It is necessary to have an unbiased view of fluoride and how events in the past created the environment we face today. It is also important in dentistry to be prepared for new technologies. Here are some issues that still challenging the use of fluoride in the twenty-first century.

The first issue is the misinformation about the benefits and toxicity of fluoride. This was a difficult issue, and it is still a problem. Information about the safety of fluoride can be challenging for public health professionals to communicate the benefits of fluoride. It can be particularly challenging for pediatric dentists because many parents are unwilling to use fluoride in children. A recent study examined the false or misleading online oral health content spread on social media to deceive people about the economic and health benefits of fluoride to prevent dental caries. The authors concluded that most contributions were related to the toxicity of fluoridated water and F⁻ products. Social media posts were often motivated by social, psychological and/or financial interests [14].

A second problem is the excessive fluoride intake. There are difficult situations where there are high levels of fluoride from natural sources (groundwater) and/or multiple sources of fluoride, as these situations can lead to dental fluorosis. However, there are strategies to control or minimize the risk of dental fluorosis. The World Health Organization maintains a maximum guideline level of 1.5 mg/L in drinking water. However, many people from Asia and Africa live in areas where the fluoride content in drinking water is above this limit [3, 6]. The point is that water with high levels of fluoride (>1.5 ppm) is not potable water. High levels of fluoride from natural sources can lead to dental fluorosis and this situation cannot be compared to artificial controlled fluoridation of water. In addition, it must be emphasized that so far there is no evidence that artificial water fluoridation can reduce the intelligence coefficient of children. In addition, current evidence does not support a connection between fluoride and neurological damage due to the high heterogeneity of studies [15].

A third point is the variability of effectiveness. Dental caries is not only a lack of fluoride exposure. Dental caries is a complex chronic non-communicable disease modulated by individual factors such as diet, oral hygiene habits, and socioeconomic determinants. As a result, some populations may not benefit as much from fluoride, which could lead to disparities in oral health outcomes.

Despite the challenges, there are clear opportunities for new strategies for fluoride in dentistry. New compounds and associations of fluoride and F-boosters are already on the market, and many dentists are unaware of these improvements [16, 17]. The idea is to increase the remineralizing effectiveness of fluoride, and several strategies are proposed. For instance, there is the observation that 2% arginine in combination with sodium fluoride in toothpaste can have a synergistic effect [18]. There are promising results for bioactive silicon-silica-toothpaste for remineralization and enamel repair. These bioactive Si-toothpastes with fluoride can form a mineral layer under various conditions and promote deep remineralization of the tooth enamel surface [19].

Finally, there is no doubt that adequate fluoride intake reduces the risk of early-stage dental caries. Fluoride can significantly inhibit demineralization and promote remineralization of teeth. To date, there is no chemical element or chemical compound that has such an effect. In appropriate doses, fluoride can be viewed as an “anti-caries vaccine”. At moderate levels of exposure, side effects can be minimal and controlled. Fluoride is a cost-effective strategy to promote oral health. It can reduce dental treatment costs and improve health outcomes in children and adults [20].

Over time, access to fluoridated water or dental products can contribute to long-term improvements in public health and reduce the oral health gap between wealthy and disadvantaged groups. This is consistent with broader efforts to promote health equity. While fluoride alone cannot eliminate health disparities, it plays a significant role in reducing inequalities in dental health, especially when combined with other preventive health measures.