The history of public health use of fluorides in caries prevention

Caries is a widespread oral disease (1). The prevention of caries with fluoride/s (F) has been proven to be an effective public health measure (PHM), and it is considered to be one of the ten greatest achievements of PH in the 20th century (2).

Fluorides are salts of the chemical element fluorine (3). People can be exposed to F in various ways: through air, soil, water, or beverages (1).

Black and McKay first recognised the preventive effect of F in Colorado Springs at the beginning of the 20th century (4). In 1931, Churchill identified a higher concentration of F in Colorado Spring’s water (5). This discovery encouraged Dean to perform several population interventions with water fluoridation (WF) to prevent caries at the population level (6). His work served as a basis for decades of population caries prevention by using WF. Systemic F had been widely recommended until the 1970s, when the new concept of understanding caries and F anticariogenic action was introduced (7). It was established that F controls caries mainly through its topical effect (3, 8). The topical mechanism is achieved either with systemic F or with topical F. In contrast, WF is a major factor in preventing pit and fissure caries, the most common site of tooth decay (9, 10).

According to the described historical facts, F are still divided into two groups according to their form of action, namely: systemic and topical (local). Systemic F (F water, milk or salt, F supplements as tablets, drops or lozenges) are ingested and incorporated into tooth enamel during tooth development. They also provide some topical protection of already erupted teeth as a reservoir of F in oral mucosa and saliva (12). Topical F (F toothpaste, mouthwashes, varnishes, gels, foams, slow-release F devices) reduce demineralisation of the enamel, promote remineralisation, and disable the metabolism of the bacteria in dental plaque (8, 11).

After nearly 100 years, F remains an important research subject. The availability of many different forms of F in the modern developed world and their cumulative preventive effect are among the most urgent topics in dentistry.

The aim of our study was to chronologically analyse various PH F uses in caries prevention.

The prevention of caries with F has been a significant PH intervention since it started with the implementation of F in drinking water. In our study, we have presented the shift from the traditional to the modern understanding of F use in caries prevention.

Since 1984, when the first review of literature about PH fluoride prevention was conducted, fluorides have remained one of the milestones of caries prevention. Nevertheless, the recommendations and PH programmes have changed, and the number of published reviews about F prevention in the field of PH is constantly increasing.

In the first observed decade (1984-1993), the main points of interest were systemic F. In the second decade (1994-2003), only half of the reviews were about systemic F. In the latest decade, only a minority of the reviews focused on systemic F, with half of the reviews during 2004-2014, describing topical F as a PHM. Most of the research on F prevention was done in groups of children and adolescents. It is thought that F use in caries prevention is also an important measure among adults and especially among the elderly.

In 2004, Fejerskov described the shift from “caries resistance concept” to understanding caries to be a multifactorial disease, following the ecological shift in the tooth-surface biofilm (7).

At first, only WF seemed to be a major PHM, but in recent decades, topical F, especially widespread and very efficient F toothpaste, are considered as possible PHM, especially in populations with low caries increment.

Although all the reviews agree that community WF is safe and effective in caries prevention, its role has been combined with the use of topical F as PHM. WF is cost saving and still recommendedby the US Community Preventive Services Task Force (41) and recent guidelines (52–54). Even in an era with a widespread availability of fluoride from other sources, studies prove that water fluoridation continues to be effective in reducing dental decay (55, 56). WF is believed to be a major factor in preventing pit and fissure caries, the most common site of tooth decay (9, 10). Maximal caries-preventive effects of water fluoridation are achieved by exposure to optimal fluoride levels both pre- and post-eruptively (55). Moreover, the latest Cochrane review on WF from 2015, concluded that there is insufficient information to determine the effect of stopping water fluoridation programmes on caries prevalence (57).

The post-eruptive effect became more important with the decreasing severity of caries attack (58). Efforts of the PH preventive programme for oral health should be directed towards the maintenance of a permanent low concentration of fluoride in the mouth in as many people as possible (3). Even the current guidelines recommend fluoride toothpaste as the basic fluoride regimen for the majority of European communities (52).

In Slovenia, the level of F in the water supply is below 0.2 ppm (59), which is below the level of significance for WF. In addition, artificial fluoridation has never been implemented. In the 1970s, the topical application of a 2% sodium fluoride in school-age children (7–15 years) was introduced, which was changed, in the 1980s, to the application of aminofluoride gel and the widespread use of toothpaste with fluoride (60). Today, preventive dental care in Slovenia follows updated guidelines on the use of F in Europe (52). We wish to (re-)establish a modern, scientific-based collective approach to F use in caries prevention, which is currently, unfortunately, based on the commitment of individuals or smaller professional groups, working in dental (prevention) offices.

Our article presents the F use in caries prevention through the perspective of PH. Independently of the described form of F use, we highlighted the most significantfindings about all forms of F use in order to give the reader the best perspective on the field. A comprehensive knowledge on fluorides is described. At the same time, the comprehensive approach to our topic is also a restriction. We chose to limit our study to review articles; consequently, we could not assess the strength of evidence-based facts for each form of use.

Our review showed that the use of F in caries prevention is very active. It is important to improve the evidence ability for different forms of use, and to research the cumulative effects of using different forms of F. The effect of different F agents should be measured in various ages and social environments. Furthermore, the need for the systematic use of F in societies with low caries prevalence should be scientifically assessed. More research should also be done in the older population groups, not focusing only on children and adolescents.

In contrast to traditional systemic forms of F as PHMs, nowadays, the use of topical F is becoming the primary approach. As the operative treatment of caries is very expensive, and F has proven to be efficient in caries reduction, it remains recommended as the standard for caries prevention. At the same time, it is necessary to promote oral health also at other levels (good oral hygiene, healthy nutrition, regular check-ups, being included in oral preventive programmes).