What is dental caries - and why we need fluoride

Dental caries is a widespread disease; it can be assumed that everyone, at some point in their lives, will experience caries.At the same time, it is a preventable disease -it is possible to maintain caries under control throughout the life course, with resources we have available.This apparent contradiction may be based on how we define this disease.This editorial would like to present a conceptual framework to answer the question: Can we define caries in a simple way, from an actionable point of view?Different visual diagrams defining the caries process have been developed over the decades of studying this disease and its causes (1-3).The pioneer diagram of Paul Keyes, with the three interconnecting circles representing the host, the microbiota, and the diet (1), is the most wellknown and widely used until today.Although it is easily understandable, the Keyes diagram leaves behind one important actor in the caries control saga: fluoride.When we use this diagram to explain caries until today, we miss the opportunity to put fluoride into the important context it deserves: caries epidemiology, all around the world, would be much worse nowadays in the absence of fluoride.Although we know that in the absence of a dental biofilm (the microbiota) and its exposure to sugar (the diet) caries lesions would not develop (i.e. if individuals maintain a strict control of their oral hygiene and sugar consumption they can maintain caries under control), most therapies and approaches to control this disease throughout the life course rely on fluoride (4).Fluoride's effect on caries was identified more than a century ago, through observations of individuals with fluorotic teeth (known as "mottled enamel" at that time) who had much reduced caries experience (5).Thirty years passed before the confirmation that the effect on both caries and fluorosis was due to higher levels of naturally present fluoride in the water (6).Decades of research followed to understand the process through which fluoride reduces caries, and although there is still a reminiscence of the original theory that fluoride would "strengthen teeth" if incorporated into the tooth mineral while teeth are forming, currently it is well recognized that the effect of fluoride is mainly local: it happens anytime fluoride is available in the oral fluids (saliva, dental biofilm fluid), and for everyone with teeth (irrespective of age, or if teeth were formed in the presence of fluoride or not) (7-10).Systematic reviews of the literature have provided extensive evidence for the anticaries effect of fluoride, used through any delivery system -from community approaches like water fluoridation, to individual use approaches, like toothpastes and rinses, to professional application products such as gels and varnishes (11)(12)(13)(14)(15)(16).Beyond controlled studies, observing epidemiological data of the significant decline in caries since fluoride was introduced in different forms in different populations provides indisputable evidence of its central role in caries control (17)(18)(19).Therefore, it would be extremely helpful if all visual diagrams explaining caries included fluoride.Dental caries is observable through its signs, the caries lesions; understanding the process of caries lesions formation is very important, because, at any point in time, this process can be modulated into "caries progression" or "caries reversal".This dynamics is critical to understand the disease; it is the basis behind caries activity/risk assessments (7,20); it is the basis behind minimum intervention oral care (21), giving support to all the non-operative treatments for caries management (22,23), which are considered the best, most conservative approaches for caries control over the life course (4).In this reversible process involved in a caries lesion development/progression vs. arrest, two antagonistic forces can be described (Fig. 1): 1. Biofilm + sugar leading to acid production and mineral loss: Dental caries can be defined as a biofilm and sugar-dependent disease, meaning that in the absence of a biofilm, no lesions are formed; if a biofilm is present but there is no dietary sugar to be fermented leading to acid production, no lesions are formed.This represents a "summary" of the diagram designed by Keyes (1), whose studies early on demonstrated the necessity of having both a microbial component and a cariogenic diet for the disease to occur.