Rethinking the Future of Caries Prevention

Dental caries, a global public health crisis, necessitates continuous evaluation of preventive measures. For decades, fluoride has been the gold standard of caries prevention, recognized for its ability to strengthen enamel and promote remineralization.¹ However, modern concerns regarding systemic toxicity and dental fluorosis have driven interest in biomimetic alternatives, most notably hydroxyapatite — the fundamental mineral component of teeth and bone.^2,3 This article contrasts the mechanisms, clinical efficacy, and safety profiles of fluoride and hydroxyapatite in the context of professional oral care recommendations.

Any discussion of fluoride should recognize that its well-documented benefits overwhelmingly outweigh concerns, particularly when evaluated alongside its strong safety record despite ongoing public debate. Much of the debate stems from concerns about potential systemic effects, perceived overexposure through multiple fluoride sources, and longstanding skepticism toward community water fluoridation programs. Critics argue that population-wide fluoridation may pose risks, such as dental fluorosis or other health effects, while evidence suggests that these risks are generally minimal at recommended levels and are outweighed by fluoride’s proven protective role against caries.⁴

The controversy persists in part because it lies at the intersection of scientific research, public health policy, and public perception, where differing interpretations of fluoride’s mechanisms, dosage, and safety continue to influence public concern despite extensive research documenting its efficacy and safety when regulated according to established guidelines. These concerns have driven the search for equally effective alternatives such as hydroxyapatite.

Fluoride

Dental caries is the result of oral bacteria, such as Streptococcus mutans and Lactobacillus spp., producing an acid that demineralizes the enamel of teeth. Dental decay often progresses asymptomatically in its early stages, as the demineralization of enamel and dentin can occur without immediate pain or noticeable clinical signs. As a result, individuals may remain unaware of the disease process until lesions advance, potentially leading to cavitation, infection, or more complex oral health complications that require extensive intervention.⁴

Dental decay is a prevalent global health concern, particularly affecting children and adolescents.⁴ Oral health professionals prioritize the reduction of dental caries in their patients through effective prevention strategies, which include the use of fluoride. A naturally occurring element found in various minerals, water supplies, and foods, fluoride is available through a variety of sources, including professional applications in dental settings, as well as in toothpastes, mouthrinses, and dietary sources such as food and drinking water.^4-6

Fluoride Benefits

Fluoride can be obtained systemically, through oral ingestion, or topically, a direct application to an intended surface.^4,5 Systemic delivery refers to the intake of fluoride through ingested sources such as food and beverages. Community water fluoridation is an example of systemic delivery; it provides an effective fluoride source due to the frequency with which individuals consume drinking water. Evidence indicates that systemic fluoride exposure during pre-eruptive enamel development contributes to the incorporation of fluoride into the developing tooth structure, promoting the formation of fluorapatite, which enhances enamel resistance to acid dissolution. In contrast, reductions in dental caries observed after tooth eruption are primarily attributed to fluoride’s post-eruptive effects at the tooth surface. Systemic fluoride also provides a topical effect due to saliva containing some fluoride from ingestion. It is continually available at the tooth surface and becomes concentrated in dental biofilm, where it inhibits acid-producing cariogenic bacteria from demineralizing tooth enamel.⁶

Fluoride provides benefits to both the permanent and deciduous dentition. The enamel surface of a newly erupted tooth is not completely mineralized; therefore, the period when the tooth is most susceptible to a carious attack is the first few months after eruption.^6,8 Furthermore, fluoride remains valuable after tooth development is complete, particularly for individuals at high caries risk.^5,6 Fluoride also impedes bacterial carbohydrate metabolism, thereby reducing acid production and limiting the dissolution of tooth enamel.⁶ Fluoride not only prevents dental caries, but when placed on an area of demineralization, can slow or reverse the process.⁹

Fluoride Disadvantages

Fluoride use is associated with certain risks that must be carefully considered alongside its benefits.⁴ One potential risk is dental fluorosis, a condition characterized by hypomineralization of enamel surfaces, resulting from excessive fluoride ingestion during tooth development. Fluorosis can be identified by white or brown lesions on the enamel and can vary from minimal to severe.⁷ Enamel fluorosis occurs exclusively during tooth development; therefore, children whose permanent teeth have fully erupted and adults are not at risk, regardless of systemic or topical fluoride exposure.⁶ Another potential risk is fluoride toxicity resulting from excessive ingestion; however, this risk is not associated with topical fluoride use.⁵

Hydroxyapatite

Hydroxyapatite (HAp) is an excellent alternative to fluoride due to its unique benefits in both preventive and restorative dentistry.^7,10 HAp is the primary inorganic component of human enamel and dentin, comprising approximately 97% and 70% respectively.² Given its biocompatibility and structural similarity to natural enamel, HAp has been widely studied for its ability to support remineralization, protect against caries, and alleviate dentin hypersensitivity. HAp is gaining popularity in dentistry due to its biomimetic properties and potential to remineralize enamel and reduce sensitivity.¹⁰

Hydroxyapatite Benefits

Nano-HAp (nHAp), a synthetic form of this mineral, specifically produced as nanocrystalline particles, ranges from 20 to 100 nm in diameter. This small size is significant because the natural HAp crystallites that compose enamel are around 50 nm in diameter, meaning nHAp particles possess a rod-shaped morphology that resembles those found in natural enamel. The particle size of 20–50 nm in nHAP matches the nano-sized defects caused by acidic erosion on the enamel surface, potentially leading to improved remineralization.¹¹

HAp acts as a source of calcium and phosphate ions, essential for enamel repair.¹¹ Studies indicate that nano hydroxyapatite particles integrate into the enamel matrix, filling microdefects and restoring lost mineral content.⁷ HAp directly supplements the natural enamel composition, leading to enhanced structural integrity.¹²

Similar to fluoride, HAp is effective in occluding dentinal tubules, thereby redirecting fluid movement within the tubules that contribute to hypersensitivity. Clinical trials have shown significant reductions in dentin hypersensitivity with patients using HAp-based toothpaste and mouthrinses.¹²

HAp particles can deposit onto and penetrate into demineralized enamel and dentin, providing a direct source of calcium and phosphate ions to facilitate remineralization.^3,10,11 Some studies suggest that HAp can reach deeper layers of the lesion compared to fluoride, which primarily acts on the surface.^3,10 Clinical trials have shown that HAp-containing oral care products can effectively reduce the risk of dental caries.^{3, 13}

HAp is considered safe if swallowed, making it an ideal substitute for fluoride in oral care products tailored for young children who are more prone to ingesting toothpaste.^{2,3, 11} HAp has also demonstrated anti-adherent and antibacterial effects, contributing to the management of oral biofilms, and nHAp can adhere to both enamel and artificial dental surfaces, potentially disrupting bacterial colonization.^3,7,14

Hydroxyapatite Disadvantages

While promising, HAp-based oral care products also present certain limitations. Although research on HAp is growing, more extensive long-term clinical trials are needed to fully establish its effectiveness compared to fluoride under various conditions.^8,11 Another limiting factor associated with HAp is availability and cost. HAp-based products may not be as readily available or as cost-effective as traditional fluoride-containing products.¹¹

Furthermore, the remineralization potential of nHAp may be concentration-dependent, with studies suggesting an optimal concentration of 10% for efficacy.^{11, 12} Aggregation of HAp particles at higher concentrations could potentially hinder its penetration into carious lesions. This is due to the unavoidable aggregation of particles at higher concentrations, which causes them to clump together and physically block surface pores, which restricts the further penetration of HAp into the deeper regions of the lesion and results in a self-limiting plateau of the remineralization effect.^11,12

HAp’s mechanism of action in caries prevention is primarily based on biomimicry.^11,12 HAp particles dissolve slightly in the oral environment, releasing calcium and phosphate ions that can precipitate onto demineralized enamel and dentin, rebuilding the lost mineral.^2,12 Nano-HAp particles can directly bind to the damaged enamel surface and fill in porous irregularities, restoring surface integrity. HAp can interact with bacterial biofilms, inhibiting their adhesion and growth.^10,11

Better Together

Combining HAp with fluoride enhances enamel microhardness and provides a stronger remineralization effect. Novel research has increasingly focused on investigating the benefits of combining hydroxyapatite and fluoride in oral care products, often exploring synergistic effects.^11,15

Studies have demonstrated a synergistic effect between sodium fluoride and HAp for remineralization.¹¹ Studies have demonstrated that HAp can be purposefully combined with fluoride, among other active agents, depending on the desired product outcome. A harmonious effect between sodium fluoride and HAp for remineralization has been documented.² This combined approach resulted in significantly less demineralization depth when used to prevent enamel demineralization adjacent to orthodontic brackets. Furthermore, the combination of nHAp with fluoride has been shown to provide better enamel resistance to erosion in bovine teeth.¹¹

The inclusion of HAp nanoparticles alongside a high fluoride concentration has also been utilized in experimental dentifrices aimed at managing root demineralization.¹⁵ Moreover, some in vitro results suggest that HAp’s remineralization capabilities may be improved by substituting ions like zinc or fluoride into the HAp lattice, which aids in improving the stability, solubility, and strength of the HAp.¹¹ Additionally, an in vitro study found that a toothpaste containing nHAp along with fluoride exhibited a higher remineralizing effect and greater increase in microhardness on initial dentin carious lesions compared to the fluoride-only control group.¹⁵

Conclusion

Based on an expanding body of clinical and in situ evidence, fluoride-free oral care products containing hydroxyapatite have been shown to be effective and consistently demonstrate noninferiority to conventional fluoride toothpastes in reducing the risk of dental caries across all age groups.^2,3,12 While fluoride remains a powerful anticaries agent whose topical effects are crucial for oral health maintenance, its associated risks of dental fluorosis and potential systemic toxicity, particularly in infants and pregnant women, are unavoidable consequences of systemic ingestion.

Hydroxyapatite offers a clear advantage in safety and biocompatibility, as it is nontoxic if swallowed and carries no risk of fluorosis. Given the growing demand for safe, biomimetic, and multifunctional preventive agents, hydroxyapatite stands as a highly viable and scientifically supported alternative for comprehensive preventive oral healthcare.

References

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12. Anil A, Ibraheem WI, Meshni AA, Preethanath RS, Anil S. Nano-hydroxyapatite (nHAp) in the remineralization of early dental caries: A scoping review. Int J Environ Res Public Health. 2022;19: 5629.
13. Campus G, Cocco F, Wierichs RJ, et al. Effects of hydroxyapatite-containing toothpastes on some caries-related variables: A randomised clinical trial. Int Dent J. 2024;74:754–761.
14. Meyer F, Amaechi B, Fabritius H, Enax J. Overview of calcium phosphates used in biomimetic oral care. Open Dent J. 2018;12,406-423.
15. Ebadifar A, Nomani M, Fatemi SA. Effect of nano-hydroxyapatite toothpaste on microhardness of artificial carious lesions created on extracted teeth. J Dent Res Dent Clin Dent Prospect. 2017;11:14–17.

From Dimensions of Dental Hygiene. March/April 2026;24(2):9-13