# Review of Professionally Applied Fluorides for Preventing Dental Caries in Children and Adolescents
## 1 Introduction  
Dental decay is considered a very important oral health problem because it is a multi-factorial oral disease that affects hundreds of millions of people throughout the world [1]. A decline in caries prevalence has occurred in most advanced countries since 1970; however, dental caries is the most common chronic disease in the world, affecting between 60% and 90% of school children and the majority of adults [2]. Factors involved in caries etiology are cariogenic bacteria, fermentable dietary sugars, and susceptible tooth surfaces. The activity of cariogenic bacteria involves the formation of organic acid that can contribute to the solubilization of minerals (e.g., calcium, phosphate) from the tooth surface (demineralization) [2, 3]. Under favorable conditions, a reversal phenomenon with a mineral gain is possible (remineralization). If the demineralization process prevails, visually detectable caries lesions occur. The caries disease process is dynamic; it may progress, stop, or even reverse. The proper assessment of the grade and activity of the caries lesion is challenging [3]. Early signs of caries consist of non-cavitated carious lesions (i.e., initial or white spot lesions). If the carious lesion is not controlled, further loss of teeth minerals occursand leads to a cavitated lesion [2]. Early detection, proper diagnosis, and the use of effective remineralization therapies (e.g., fluorides) are essential for the management of non-cavitated carious lesions [2]. Fluoride has been considered a very important factor in the decrease in the prevalence and severity of dental caries in developed countries [4]. Fluoride has a long-term relationship with dental practice and preventive dentistry; documents older than 200 years refer to the probable link between fluoride and carious activity [5]. Future research seems to aim for improving the antimicrobial and anti-degradative properties of current restoration materials [6], associated with the modification of their composition in order to reduce microbial attachment and biofilm formation [7]. Fluoride can be delivered topically and systemically. Topically applied modalities can be divided into self-applied and professionally applied topical fluorides. Self-applied fluorides are typically for home use: toothpastes, mouth rinses, and gels. Home-use dental products in the European Union have a maximum concentration of 1500 ppm (1500 mg/kg) for adults and children older than 6 years, while for younger children, the upper limit is 1000 ppm [8]. The quantity of systematically available fluoride depends on the percentage of toothpaste swallowed per application [9]. Immediate intoxication is very rare as the toxic dose is 5 mg/kg [10]. Children younger than 6 do not have a well-controlled swallowing reflex; fluoride being ingested in age-dependent proportions (65% in 2-year-olds, 50% in 4-year-olds, and 34% in 5-year-olds) [10] requires more parental control on ingested fluoride in order to reduce the development of fluoride lesions in the upper incisors [11]. Adults swallow around 10% of the quantity used for tooth-brushing [9]. Serious systemic toxicity and fatalities following acute exposure to fluoride are rare, but toxic signs of overexposure are not so rare with gastric signs and symptoms prevailing [12]. The overdose in adults is more likely to happen in regions with high levels of fluoride in tap water rather than in regions with artificially fluoridated water, while for children the risk increases for younger ages due to swallowed toothpaste [9]. The occurrence and severity of dental fluorosis depend on the parameters of fluoride exposure (dose, duration, timing) during the period of enamel formation [13]. Some studies showed that there is a higher risk for dental fluorosis if an excessive quantity of fluoride is environmentally present during the first two years of life, regarded as a critical period of greater susceptibility [14]. Therefore, the risk of dental fluorosis following professionally topical applied fluoride is low.