Fluoride’s Vital Role in Caries Prevention and Management

Dental caries, although preventable, remains a challenge for practicing dental professionals. From 2013 to 2016, 13.4% of children and adolescents ages 3 to 19 had active or untreated caries and 22.8% of adults ages 20 to 74 had untreated tooth decay.¹ The caries process involves demineralization of the calcified tooth structures with a breakdown of the organic matrix.² While the process is multifactorial, Streptococcus mutans remains the main culprit. This microorganism populates the tooth surface and penetrates through the tooth-layered structures during favorable conditions, such as in presence of the fermentable carbohydrates.³

Through periods of demineralization and remineralization on the tooth’s exterior, the metabolic processes of acidogenic bacteria begin to penetrate the enamel layer, dissolving the calcium and phosphate minerals from the structure.⁴ For clinicians, managing caries requires collaboration with the patient to support remineralization with adjunctive therapies, such as fluoride, and minimize habits contributing to demineralization.

Properties of Fluoride

Fluoride’s effectiveness is based on its ability to inhibit the acidogenic process of bacteria, preventing demineralization at the tooth’s surface and enhancing remineralization.⁵ Fluoride disrupts biofilm by penetrating it and interfering with acid production. With a decrease in the pH of dental biofilm, fluoride ions join with hydrogen ions creating the compound HF, which then disperse into the bacterial biofilm. HF’s diffusion inside the biofilm leads to the release of additional fluoride ions that inhibit bacterial metabolism.⁶

Once fluoride accumulates in the biofilm, the pH levels within it decrease and the bacteria then require more energy exertion, effectively slowing down the progression of biofilm growth and acidogenic processes.⁵ Fluoride concentration is highest at the enamel’s surface, with 3,000 parts per million (ppm) in fluoridated areas and 1,000 to 2,000 ppm in nonfluoridated areas. The presence of adsorbed fluoride in the fluid surrounding the crystal structure of the tooth surface serves as a protective barrier against cariogenic activity.⁴

After demineralization begins on the enamel surface, the structure is able to absorb more fluoride than on an intact surface, as the fluoride incorporates into the hydroxyapatite crystalline structure.² Remineralization of the tooth involves adding calcium and phosphate back to the affected surface. By bathing the demineralized surfaces with mineral-rich saliva, the pH rises, offsetting cariogenic activity to levels that enable remineralization to occur.⁶ The introduction of fluoride enhances the attraction of calcium and phosphate to the tooth’s surface. Fluoride achieves this by forming a thickened layer on the crystal surface, which draws calcium and phosphate ions.² This process illustrates the dynamic balance between demineralization and remineralization, as phosphate and calcium ions move in and out of the tooth’s outer structure.⁴

Function of Saliva for Remineralization

For remineralization to occur, calcium and phosphate must be reincorporated into the tooth’s structure. Saliva and its components, particularly proline-rich proteins, assist in both creating a protective layer on the tooth’s surface and bringing calcium ions to the tooth to enhance remineralization.⁷ If the pH maintains a neutral level, saturation with the necessary ions occurs more quickly, enabling remineralization to begin.

Saliva plays a critical role in maintaining oral health by buffering pH levels during resting saliva production.⁸ Additionally, its ability to deliver fluoride to the tooth’s outer layer for remineralization highlights saliva’s importance in preventing dental caries.⁹ The buffering capacity of saliva and the immunoglobulin defense factors further highlight saliva’s importance for the health of the oral microbiota.⁸

Various biological components impact not only salivary flow, but also the organic or inorganic makeup of saliva.¹⁰ Thus, clinicians should thoroughly evaluate the presence of saliva when recommending fluoride therapies to maximize the potential for remineralization.

Caries Risk and Fluoride Therapies

The adoption of minimally invasive dentistry has shifted caries management away from surgical interventions to relatively low-cost, less-invasive interventions such as fluoride application.¹¹ Fluoride recommendations are based on individual caries risk assessments, in which specific concentrations are recommended for patients at low, medium, and high risk.² A personalized assessment must include the presence of any active carious lesions; modifiable risk factors, such as diet; and protective factors related to daily biofilm control.¹²

Low Caries Risk

Patients at low caries risk have adequate health literacy; acceptable oral hygiene habits, including the daily use of an over-the-counter (OTC) fluoride toothpaste; a healthy diet low in fermentable carbohydrates; and effective biofilm removal regimen.² Patient education should encourage and reinforce these behaviors. Patients should consume optimally fluoridated water of 0.7 ppm and use OTC fluoride toothpastes with lower ppm concentrations.²

Many patients drink only bottled water, thus eliminating the potential benefits of community water fluoridation. The benefits vs risks of consuming fluoridated water should be part of patient education. Brushing with toothpastes containing 1,000-1,100 ppm of fluoride decreases the number of decayed, missing and filled surfaces (DMFS) when compared to brushing with nonfluoride toothpastes.¹³ For patients at low caries risk, supplemental fluoride therapies at higher concentrations are not necessary. Studies reveal limited evidence on the benefits of prescription or professionally applied fluoride therapies in a low caries risk individual.¹⁴

Moderate Caries Risk

Moderate caries risk indicates an increase in risk factors, tipping the balance away from protective factors and creating an environment more conducive to caries development. Patient education should focus on meticulous biofilm removal and increasing protective factors. Individuals with moderate caries risk benefit from oral hygiene instructions and nutritional counseling.² These methods in conjunction with fluoride therapies have the potential to maximize remineralization and prevent caries development.

Research suggests that higher concentrations of fluoride may have a greater impact on remineralization of tooth surfaces.¹⁵ Self-applied fluoride mouthrinses in concentrations ranging from 230 ppm to 900 ppm are effective when used regularly in combination with effective biofilm removal.¹⁶ Mouthrinses with 0.05% sodium fluoride inhibit caries by disrupting the cariogenic processes on the tooth’s surface.¹⁷ Research shows the use of fluoride mouthrinse decreases DMFS by 27% in permanent teeth.¹⁶

The use of mouthrinses requires active patient compliance for optimal remineralization and caries prevention.¹⁷ Patients at moderate caries risk unable to comply may benefit from more frequent maintenance appointments and professionally applied fluoride therapies at higher concentrations.¹⁵

High/Severe Caries Risk

Patients at high or severe risk for caries require proactive approaches and collaboration between the dental team and the patient. The effectiveness of fluoride for high caries risk depends on merging antibacterial and fluoride therapies to offset the bacterial processes and maximize opportunities for remineralization.¹⁸ Evidence indicates the use of OTC fluoride products in lower concentrations (1,000-1,100 ppm) is inadequate for caries prevention in high-risk patents.² Thus the clinician must implement evidence-based treatments according to the severity of disease and risk level to promote remineralization.

Those at high caries risk individual should have 5% NaF varnish professionally applied, brush with 5,000 ppm fluoride toothpaste twice daily, use chlorhexidine gluconate 0.12% mouthrinse once daily each month for 1 week, and consume xylitol products daily.¹⁸ The 5% NaF varnish contains 22,600 ppm of concentrated fluoride, with biannual application reducing incidence of caries by up to 43% in the permanent dentition.^2,12 Patients at high risk should receive varnish applications three to four times per year.² Some research shows that more frequent intervals for varnish application are more effective in both the primary and permanent dentition.¹⁹ Future studies should focus on establishing a more standardized protocol.

Prescription toothpastes with 5,000 ppm of fluoride show significantly greater surface remineralization and inhibition of demineralization when compared to toothpastes with 1,500 ppm or less.¹⁵ Toothpastes with 5,000 ppm of fluoride remain in saliva for longer periods of time. A study evaluating salivary fluoride with different toothpaste concentrations identified higher levels of available salivary fluoride after just 3 weeks of use with the 5,000 ppm formulations.²⁰ The available salivary fluoride dropped within days upon switching to lower concentration toothpastes within the same study. Patient compliance and consistency of use are necessary for effectiveness.

Silver Diamine Fluoride

Since receiving approval from the United States Food and Drug Administration in 2014 for dentinal hypersensitivity, silver diamine fluoride (SDF) has demonstrated efficacy in preventing and treating caries. The most common formulation contains 255,000 ppm of silver ions for their antibacterial properties and 44,800 ppm of fluoride ions to enhance remineralization and decrease demineralization.²¹

When in contact with the hydroxyapatite crystals on the tooth’s surface, the free calcium and fluoride react to create calcium fluoride (CaF2) and silver phosphate.²² SDF provides effective antimicrobial properties capable of disrupting the acidogenic processes of S. mutans, Actinomyces naeslundii, and Lactobacillus acidophilus.

SDF provides clinicians with an effective option for addressing patient anxiety and discomfort while also arresting active lesions in a simple application. The straightforward, noninvasive application of SDF requires minimal training and only basic supplies, and produces no aerosols during application.²¹

Jabin et al²² found that individuals who received SDF had higher levels of fluoride concentration when compared to those who received fluoride varnish. The well-defined benefits of SDF come with minor side effects, such as staining. Once placed on any demineralized lesion of dentin or enamel, the treated surface turns dark in color, indicating the success of the treatment.²² This requires thorough patient education on the benefits of the procedure prior to placement.

Research shows the application of SDF arrested active lesions in children at high caries risk and older adults with root caries.²³ In a 30-month study on the effectiveness of varying concentrations of SDF on active caries in the primary dentition found that the application of 38% SDF had was the most successful at arresting lesions.²⁴ Additionally, researchers found a relationship between biofilm reduction and SDF effectiveness. Children with higher scores on the Visible Plaque Index were less likely to have lesions arrested after SDF application.²⁴ This finding confirms the importance of daily, mechanical biofilm removal in managing dental caries and the role of the dental hygienist in preventive patient education. For children, this requires collaboration between caregivers and the dental team. Current evidence identifies the use SDF as a preventive agent alone or in conjunction with other therapies for older adults at risk for root caries.²³ Further studies on the clinical application of SDF should examine its use in prevention and treatment of root caries in addition to studying different types of adult populations.

Conclusion

The ability of fluoride to remineralize surfaces, inhibit demineralization, and disrupt bacterial processes related to caries development cement its importance in dentistry. The various modalities for application and delivery of fluoride provide the clinician with numerous options for individualized patient recommendations. The effectiveness of fluoride products must coincide with the patient’s caries risk level.

Patient assessment should also evaluate individuals’ readiness to assist in their own fluoride delivery. Patients with special needs or those who are medically complex may need additional support. Those with limited dexterity, mobility concerns, or swallowing abilities may need more potent professionally applied concentrations.¹⁵ Regardless of the type of fluoride chosen for prevention, any dental caries management plan should include patient education on the need for daily, frequent mechanical biofilm removal to maximize caries prevention.

References

1. United States Department of Health and Human Services. Reduce the proportion of adults with active or untreated tooth decay Available at health.gov/healthypeople/objectives-and-data/browse-objectives/oral-conditions/reduce-proportion-adults-active-or-untreated-tooth-decay-oh-03. Accessed November 20, 2024.
2. Boyd LD, Mallonee LF. Wilkins’ Clinical Practice of the Dental Hygienist. 14th ed. Burlington, Massachusetts: Jones and Bartlett Learning; 2023.
3. Forssten SD, Björklund M, Ouwehand AC. Streptococcus mutans, caries and simulation models. Nutrients. 2010;2:290-298.
4. Rošin-Grget K, Peroš K, Sutej I, Bašić K. The cariostatic mechanisms of fluoride. Acta Med Acad. 2013;42:179-188.
5. Aoun A, Darwiche F, Al Hayek S, Doumit J. The fluoride debate: the pros and cons of fluoridation. Prev Nutr Food Sci. 2018;23:171-180.
6. Featherstone JD. The science and practice of caries prevention. J Am Dent Assoc. 2000;131:887-899.
7. Hegde MN, Attavar SH, Shetty N, Hegde ND, Hegde NN. Saliva as a biomarker for dental caries: a systematic review. J Conserv Dent. 2019;22:2-6.
8. Kubala E, Strzelecka P, Grzegocka M, et al. A review of selected studies that determine the physical and chemical properties of saliva in the field of dental treatment. Biomed Res Int. 2018;2018:6572381.
9. Dowd FJ. Saliva and dental caries. Dent Clin North Am. 1999;43:579-597.
10. Pedersen AML, Sørensen CE, Proctor GB, Carpenter GH, Ekström J. Salivary secretion in health and disease. J Oral Rehabil. 2018;45:730-746.
11. Gao SS, Zhang S, Mei ML, Lo EC, Chu CH. Caries remineralisation and arresting effect in children by professionally applied fluoride treatment — a systematic review. BMC Oral Health. 2016;16:12.
12. Nassar Y, Brizuela M. The role of fluoride on caries prevention. StatPearls. Available at ncbi.nlm.nih.gov/books/NBK587342. Accessed November 20, 2024.
13. Walsh T, Worthington HV, Glenny AM, Marinho VC, Jeroncic A. Fluoride toothpastes of different concentrations for preventing dental caries. Cochrane Database Syst Rev. 2019;3:CD007868.
14. Truin GJ, van’t Hof MA. Professionally applied fluoride gel in low-caries 10.5-year-olds. J Dent Res. 2005;84:418-421.
15. Gibson G, Jurasic MM, Wehler CJ, Jones JA. Supplemental fluoride use for moderate and high caries risk adults: a systematic review. J Public Health Dent. 2011;71:171-184.
16. Marinho VC, Chong LY, Worthington HV, Walsh T. Fluoride mouthrinses for preventing dental caries in children and adolescents. Cochrane Database Syst Rev. 2016;7:CD002284.
17. Marsh, L, Cahoon, M. Improve oral health through mouthrinse use. Dimensions of Dental Hygiene. 2018;16(11):14-18.
18. Featherstone JDB, Chaffee BW. The evidence for caries management by risk assessment (CAMBRA^®). Adv Dent Res. 2018;29:9-14.
19. Lenzi TL, Montagner AF, Soares FZ, de Oliveira Rocha R. Are topical fluorides effective for treating incipient carious lesions? A systematic review and meta-analysis. J Am Dent Assoc. 2016;147:84-91.
20. Staun Larsen L, Nyvad B, Baelum V. Salivary fluoride levels after daily brushing with 5000 ppm fluoride toothpaste: a randomised, controlled clinical trial. Eur J Oral Sci. 2023;131:e12934.
21. Zheng FM, Yan IG, Duangthip D, Gao SS, Lo ECM, Chu CH. Silver diamine fluoride therapy for dental care. Jpn Dent Sci Rev. 2022;58:249-257.
22. Jabin Z, Nasim I, Priya VV, Agarwal N. Comparative evaluation of salivary fluoride concentration after topical application of silver diamine fluoride and sodium fluoride: a randomized controlled trial. Int J Clin Pediatr Dent. 2022;15:371-375.
23. Crystal YO, Niederman R. Evidence-based dentistry update on silver diamine fluoride. Dent Clin North Am. 2019;63:45-68.
24. Fung MHT, Duangthip D, Wong MCM, Lo ECM, Chu CH. Randomized clinical trial of 12% and 38% silver diamine fluoride treatment. J Dent Res. 2018;97:171-178.ˇ

From Dimensions of Dental Hygiene. January/February 2025; 23(1):14-17.