The Evidence Supporting Fluoride Varnish

Oral health professionals are charged with preventing dental disease, and some of the most common are, in fact, preventable. Dental caries — a microbiological disease involving the bacterial metabolism of fermentable dietary carbohydrates that leads to mineral dissolution of tooth structure — ranks among these preventable conditions. Because dietary sources of carbohydrates are key etiological components of the caries process, patients’ diet and self-care patterns are integral to successful caries management. Therapeutics can also play a significant role in prevention.¹ For example, fluoride is one of the most clearly supported therapeutics for caries prevention in the scientific literature. Along with pit and fissure sealants, fluoride use remains paramount to reducing the risk of caries.

Fluoride counteracts caries in at least three ways: it enhances the uptake of minerals — such as calcium and phosphate — during remineralization; its incorporation into the crystal structure of enamel increases resistance to acid attack; and fluoride ions can disrupt cariogenic bacterial activity.² Fluoride derived from low-concentration sources, such as fluoridated drinking water (0.7 ppm), for example, tends to exist in ionic form in oral reservoirs, such as saliva and plaque. High-concentration delivery methods, such as fluoride varnish, result in the formation of a calcium fluoride layer near the enamel surface. This layer stands ready to provide an anticariogenic effect when oral pH levels drop.²

Clinicians and patients can choose between a wide range of fluoride delivery modes. Toothpastes and rinses are available in over the counter and prescription forms. The highest concentration fluoride products in dentistry are designated for professional application, typically in-office. These modalities historically have contained at least 9000-ppm fluoride and include gels, foams, varnishes and, most recently, silver diamine fluoride. The focus of this article is fluoride varnish.

RECOMMENDED THERAPIES

Although fluoride varnish has received U.S. Food and Drug Administration clearance for treating dentinal hypersensitivity, it has been used off-label for years in managing caries. In its most common form, fluoride varnish is 5% sodium fluoride (NaF) suspended in a colophonium resin. A 5% NaF formulation consists of about 22,600-ppm fluoride, and the sticky resin allows the varnish to cling tenaciously to tooth surfaces. This potent combination contributes to its effectiveness in preventing caries.

Numerous health care associations have issued evidence-based recommendations for its use. The American Dental Association (ADA) first published evidence-based guidelines for in-office fluoride treatment in 2006, with an update in 2013 to include prescription take-home products. The process that resulted in these recommendations began with the formation of a panel of content and methodology experts, as well as other stakeholders. The panel developed two primary clinical questions for the recommendations to address. Does topical fluoride reduce the incidence of new caries? And does prophylaxis prior to topical fluoride application add to the preventive effect? A systematic review of the literature was conducted with these questions in mind, and the recommendations reflect the results.³

Regarding the efficacy of topical fluoride in reducing the incidence of caries, the scientific evidence suggests that in-office treatments, such as fluoride varnish or gel, prevent caries. The level of evidence that in-office fluoride prevents caries was rated as moderate, which was the highest designation received by any modality. For patients at risk for caries, the ADA recommendation is for in-office application of fluoride varnish or gel every three to six months.³

Because its stickiness allows varnish to adhere to tooth surfaces — thus minimizing swallowing risk — the application of varnish is recommended for all age groups. Contrast this with in-office fluoride gel, which is not recommended for children younger than 6 due to risk of swallowing. The guidelines for varnish use are based on research conducted on patients age 18 and younger, and the results are extrapolated to apply to older age groups³ (Figure 1).

There are limited studies regarding the added caries-prevention benefit of prophylaxis prior to in-office fluoride treatment. Three studies examining prophylaxis before fluoride gel therapy suggest there is no apparent caries-reducing benefit to performing a prophylaxis in children prior to fluoride gel use. No studies of this nature have been conducted with adult subjects or fluoride varnish, and, at this time, the panel does not recommend mandatory prophylaxis prior to in-office fluoride application for caries prevention.³

The knowledge of fluoride varnish’s anticaries efficacy extends beyond oral health professionals. In 2014, the U.S. Preventive Services Task Force (USPSTF) published its recommendations regarding the prevention of caries in children up to age 5. These recommendations support primary care clinicians (such as pediatricians) applying fluoride varnish to the primary teeth of infants and young children, starting with the eruption of the first deciduous tooth.⁴ This is a slight expansion of the recommendation found in the ADA guidelines, which bases fluoride application on caries risk level.³

The recommendation to apply fluoride varnish to all children may reflect the target audience of the USPSTF recommendations: primary care clinicians, in general — especially those outside of dentistry.⁴ Because caries risk is determined, at least in part, by detection and diagnosis of existing disease, practitioners outside of dentistry are not trained to comprehensively assess caries risk (and thus cannot base fluoride varnish therapy on caries risk level). While fluoride varnish may not necessarily benefit patients in a low-risk category, it is not known to be detrimental. Thus, from a community-based caries-prevention standpoint, it seems reasonable that dentists utilize their expertise to assess caries risk and apply fluoride varnish accordingly,³ while those outside of dentistry who have been granted the clinical privilege of providing fluoride varnish do so more broadly.⁴ One trend in support of this position is that, in the United States, nondentist primary care providers, such as pediatricians, are more likely to encounter children age 5 and younger than dentists.⁴ In regard to caries prevention in young populations, the USPSTF recommendations are therefore collaborative in nature.

CONSIDER THE EVIDENCE

When considering any clinical question, it is prudent to seek the highest level of scientific evidence relating to the topic of investigation. This is because high-level evidence is less prone to many, if not most, types of unintentional bias. In researching a clinical question, it is important to discern the level of scientific rigor that an article or report represents, as answers to clinical questions supported by high-quality evidence are preferred.

When ranking the strength of scientific articles, the weakest evidence is expert opinion. As the name suggests, this type of paper or communication represents the thoughts of a respected individual in the profession. Ranking higher on the scale of scientific strength are the various types of study designs, with randomized controlled trials (RCTs) ranking as the most rigorous. Systematic reviews, especially those that include meta-analyses, are at the top of the evidence-base pyramid. A systematic review employs a series of predetermined filters to sift through all existing studies regarding a specific clinical question, only retaining the most rigorous of scientific studies (e.g., RCTs) for inclusion in the review. The remaining high-level studies are then statistically analyzed in an attempt to coalesce the data, with the intention of drawing broad and valid conclusions that may be used to make clinical recommendations.⁵

The effectiveness of fluoride varnish in preventing caries has been evaluated at the highest level of evidence — the systematic review. The Cochrane Collaboration has published several systematic reviews on fluoride varnish. One review examined the effectiveness of fluoride varnish (versus placebo treatment) in preventing caries in children and adolescents. The review included 22 clinical trials, accounting for 12,455 subjects in randomized scenarios.⁶ The metric used to assess efficacy of fluoride varnish in preventing caries in this population (age 16 and younger) was prevented fraction. This was defined as the difference in average caries increments between treatment and nontreatment groups, divided by the average for the nontreatment group (expressed as a percentage). The key finding included an average 43% reduction in decayed, missing and filled tooth surfaces (DMFT) in permanent teeth, and a 37% reduction in DMFT in primary teeth.6 Efficacy of fluoride varnish in achieving these prevented fractions did not seem significantly associated with patient characteristics, such as baseline caries severity, background exposure to fluoride, or frequency of application.⁶

Regarding the prevention of early childhood caries specifically, limited, moderate-quality evidence exists for the use of fluoride varnish, according to a non-Cochrane systematic review that examined a diversity of modalities for reducing early childhood caries. Out of 33 included studies, six involved fluoride varnish.⁷

The quality of evidence for preventing early childhood caries (which primarily affects deciduous teeth) is not as strong as evidence supporting fluoride varnish to prevent caries in young permanent teeth. It does seem to suggest, however, that fluoride varnish has the greatest benefit for teeth that were sound at baseline — with maxillary incisors experiencing the greatest caries-prevention benefit. The implication is that fluoride varnish treatments may be most effective if started early in high-caries populations.⁷

Another Cochrane review examined the use of fluoride to prevent white spot lesions during traditional orthodontic treatment. A number of fluoride modalities, ranging from toothpaste to varnish, were compared with placebo or no treatment. Although the three studies included in the systematic review represents a small number, the key finding related to a study in which fluoride varnish was applied at every orthodontic adjustment visit. It found a nearly 70% reduction in white spot lesion development in the groups that received fluoride varnish⁸ (Figure 2).

Besides preventing caries, fluoride varnish also appears to be effective in arresting caries. A systematic review by Lenzi et al⁹ explored this use of varnish and gel by analyzing 21 studies from a pool of 754, with five studies ultimately included in the review. Three of the five examined using fluoride varnish for caries arrest, while the remaining two examined fluoride gel. The varnish studies reported the effect of fluoride varnish on caries lesions in enamel in primary and permanent teeth. The mean age of study subjects ranged from 3.4 to 11.7 years, and participants received multiple applications of varnish. Fluoride varnish was found to be effective in reversing incipient enamel caries lesions (p <0.05), and baseline caries level did not seem to affect results. The small number of available studies, and variation in study design, led to a recommendation for further evaluation.⁹

Indeed, arresting lesions and preventing the progression of caries continue to be the subject of investigation. While limited studies have demonstrated fluoride varnish’s efficacy in reversing incipient lesions,9 other pathways are being explored to achieve this end. In recent years, for example, microinvasive therapies have garnered attention. Resin sealants or resin infiltration over an active lesion, proceeded by an acid etch (hence, “microinvasive”) fall under the category of microinvasive therapies.¹⁰

Examining the evidence supporting microinvasive therapies for arresting interproximal caries lesions, a recent Cochrane review included eight trials encompassing 365 randomized patients. Some of the studies compared the efficacy of microinvasive therapies to fluoride varnish; the limited data suggest that microinvasive therapies significantly reduce the odds of lesion progression when compared to noninvasive therapies, such as varnish.¹⁰ This should be interpreted carefully, as there was a high risk of bias in seven of the studies (a lack of blinding of participants and personnel, for example).¹⁰

Overall, however, the systematic reviews indicate fluoride varnish is effective in preventing, and perhaps arresting, caries. A recent conference paper that assessed 39 of the available systematic reviews regarding various caries-prevention strategies affirmed fluoride varnish’s efficacy, determining that moderate-quality evidence supports the use of fluoride varnish to prevent caries — contrasted with lowlevel evidence supporting modalities such as fluoride gel or mouthrinse.¹¹ Thus, the use of fluoride varnish to prevent caries is both reasonable and evidence-based.

BOTTOM LINE

Although dentistry has been characterized as both an art and science, the management of primary diseases should always involve a scientific approach in which best practices stem from sound evidence. Fluoride stands out among various modalities as being efficacious in preventing, and possibly arresting, caries lesions. Based on the evidence, fluoride varnish is one of the most potent tools for managing caries.

In fact, the literature supporting the use of fluoride varnish for caries prevention has led to its endorsement by leading professional organizations. A number of systematic reviews — which represent the highest quality of scientific evidence — affirm its effectiveness. With the goal of preventing and successfully managing disease, oral health professionals can look to the scientific record to support the regular use of fluoride varnish in dental practice.

REFERENCES

1. Fontana M, Young DA, Wolff MS. Evidence-based caries, risk assessment, and treatment. Dent Clin N Am. 2009:53:149–161.
2. Recommendations for using fluoride to prevent and control dental caries in the United States. Centers for Disease Control and Prevention. MMWR Recomm Rep. 2001;50:1–42.
3. Weyant RJ, Tracy SL, Anselmo T, et al. Topical fluoride for caries prevention: Executive summary of the updated clinical recommendations and supporting systematic review. J Am Dent Assoc. 2013;144:1279–1291.
4. Moyer VA. Prevention of dental caries in children from birth through age 5 years: U.S. Preventive Services Task Force Recommendation Statement. Pediatrics. 2014;133:1102–1111.
5. Straus SE, Richardson WS, Glasziou P, Haynes RB. Evidence-Based Medicine: How to Practice and Teach It. 4th ed. Edinburgh: Churchill Livingstone; 2010.
6. Marinho VCC, Worthington HW, Walsh T, Clarkson JE. Fluoride varnishes for preventing dental caries in children and adolescents. Cochrane Database Syst Rev. 2013;7:CD002279.
7. Twetman S, Dhar V. Evidence of effectiveness of current therapies to prevent and treat early childhood caries. Pediatr Dent. 2015;37:246–253.
8. Benson PE, Parkin N, Dyer F, Millett DT, Furness S, Germain P. Fluorides for the prevention of early tooth decay (demineralized white lesions) during fixed brace treatment. Cochrane Database Syst Rev. 2013;12:CD003809.
9. Lenzi TL, Montaner AF, Soares FZM, Rocha RO. Are topical fluorides effective for treating incipient carious lesions? A systematic review and meta-analysis. J Am Dent Assoc. November 5, 2015. Epub ahead of print.
10. Dorri M, Dunne SM, Walsh T, Schwendicke F. Micro-invasive interventions for managing proximal dental decay in primary and permanent teeth. Cochrane Database Syst Rev. 2015;11:CD010431.
11. Twetman S. The evidence base for professional and self-care prevention— caries, erosion and sensitivity. BMC Oral Health. 2015;15(Suppl 1):S4.

Featured image courtesy of NATIONAL INSTITUTES OF HEALTH/SCIENCE SOURCE

From Decisions in Dentistry. January 2017;3(1):50-53.