1. Introduction

Dental decay is considered a very important oral health problem because it is a multifactorial oral disease that affects hundreds of millions of people throughout the world ^[1]. 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). Under favorable conditions, a reversal phenomenon with a mineral gain is possible (remineralization). 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 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 ^[3].

Fluoride can be delivered topically and systemically. Topically applied modalities can be divided into self-applied and professionally applied topical fluorides. Professionally applied topical fluorides are used by a dental professional in the dental office, and they could be in the form of a gel, varnish, foam, or mouthrinse ^[4]. These products have a much higher fluoride concentration than self-applied fluorides.

This paper aimed to examine and summarize the results of controlled clinical trials, systematic reviews, and meta-analyses to evaluate the effectiveness of professionally applied fluoride for the prevention of dental caries in primary and permanent dentition.

2. The effectiveness of professionally applied fluorides

2.1. Fluoride Gels
The most widely used fluoride gels are: acidulated phosphate fluoride (APF) with 1.23% (12,300 ppm) fluoride ion and 2% sodium fluoride (NaF) with 0.90% (9050 ppm) fluoride ion. Studies conducted on professionally applied fluoride gel showed that caries-preventive fractions ranged between 23% and 60% ^[5][6][7].

The European Academy of Paediatric Dentistry (EAPD) does not recommend the use of fluoride gels under the age of 6 years due to the danger of swallowing. In permanent dentition, EAPD moderately recommends 2 to 4 applications per year in appropriately sized trays, in an upright position, associated with suction devices during and after application to reduce swallowing, and interdiction to eat or drink 20–30 min after fluoride gel application ^[8].
The Australian Research Center for Population Oral Health (ARCPOH) recommended the use of high concentration fluoride gels (more than 1.5 mg/g fluoride ion) to be used for people aged 10 years or more who are at an elevated risk of developing caries ^[9].

Recently, atmospheric plasma activation of a hydroxyapatite enamel-like model proved to be almost twice as effective regarding fluoride incorporation from a 1450 ppm fluoride gel (Fluor Protector, Ivoclar Vivadent, Schaan, Liechtenstein) than usual gel application. Furthermore, a certain antimicrobial and biofilm modulation was observed ^[10].

2.2. Fluoride Varnishes

There are three principal fluoride varnishes most commonly used: Duraphat (Colgate Oral Pharmaceuticals, Cologne, Germany) containing sodium fluoride with 2.26% F (22,600 ppm), Fluor Protector (Ivoclar Vivadent, Schaan, Liechtenstein) containing 0.9% difluorsilane with 0.1% [1000 ppm] F, and Bifluoride (Voco, Cuxhaven, Germany) containing sodium fluoride with 5.6% F.

Varnishes must be reapplied at regular intervals, effective caries protection requiring two applications per year ^[4]. Studies and meta-analyses concluded that fluoride varnishes exhibited an important caries-inhibiting effect in both permanent and primary dentitions, with reductions in caries ranging from 28 to 70% ^[11][12][13]. Several studies have reported that fluoride varnish and fluoride gel have a similar effect regarding caries prevention ^[2][4].

In their network meta-analysis, Urquhart et al. (2019) concluded that a combination of sealants and 5% NaF varnish was the most effective in arresting or reversing lesions on occlusal surfaces versus non-treatment. For non-cavitated carious lesions on smooth surfaces, this network meta-analysis demonstrated that 5% NaF varnish application had a twice greater possibility of arresting or reversing enamel lesions vs. no treatment, while the association of the same fluoride varnish with resin infiltration increased this possibility to five times ^[2].

There is no evidence in the specialty literature to point at professionally applied fluoride varnish as a risk factor for dental fluorosis, even among children younger than 6 years of age ^[4].

The EAPD moderately recommends 2–4 applications of fluoride varnishes for the prevention of caries in both dentitions, especially in children of increased risk of caries development, as well as in children with special oral health care needs, orthodontic patients, or during sensible periods such as tooth eruption ^[8]. According to the EAPD and ADA, fluoride varnish is the only topical agent to be used in preschool ^[8][14]. Australia’s ARCPOH recommends the application of fluoride varnish in patients with an elevated risk of developing caries, including children under the age of 10 years ^[9].

2.3. Fluoride Foams

Data showed that fluoride foams are more effective in permanent dentition (PF = 76%) ^[15] than in primary dentition (PF= 24.2%) ^[16](62). Australian ARCPOH finds no evidence to support the use of foam ^[9].

2.4. Fluoride Mouthrinse

The fluoride mouthrinses may contain two fluorides: APF and stannous fluoride. Compared to other professionally applied fluorides, the mouthrinses can be more easily swallowed, and, consequently, there is a greater risk for ingestion. The use of fluoride mouthrinses is contraindicated in young children because acute fluoride toxicity could result if they were swallowed. Furthermore, these rinses have a sharp, metallic taste and are not well tolerated by patients. For all these reasons, professional fluoride rinses are not recommended for the prevention of dental caries because other effective in-office fluoride products are readily available ^[17].

Future research regarding the prevention of dental caries is oriented towards the improvement of antimicrobial properties of restorative materials, combining this well-known inorganic, monoatomic anion with other antimicrobial substances (e.g., chlorhexidine, quaternary ammonium compounds), development of chemical modifications enhancing drug release, and surface modification for an antimicrobial and biofilm modulation effect.

Conclusions
Professionally applied fluorides are useful and recommended for caries prevention in patients with an elevated risk of dental decay, especially in patients with active caries on smooth tooth surfaces, in children with special oral health needs, or orthodontic patients.
Prevention of dental caries in temporary and permanent dentition can be done effectively using APF gel or fluorinated varnishes. For children under the age of 6, only 2.26% fluoride varnish is recommended.
The European Academy of Pediatric Dentistry and the American Dental Association have similar recommendations regarding topical fluoride applications based on caries-risk assessment. Community water fluoridation is seen by both organizations as an important element in a complex approach of caries prevention, to which is added the use of topical fluoride in relation to caries-risk assessment. Australian authorities recommend the use of local fluoridation for patients at high risk of caries development, using gels for children aged 10 years and older, while fluorinated varnishes are recommended for children under 10.