Remineralization and Fluoride

When the pH of dental plaque rises above the critical threshold, typically around 5.5, the oral environment shifts from favoring demineralization to enabling remineralization. At this point, the interbacterial plaque fluid and saliva become saturated, and eventually supersaturated, with calcium, phosphate, and hydroxyl ions. This supersaturation is essential for the deposition of minerals back into demineralized enamel and dentin.

Remineralization of early carious lesions depends on the presence of partially demineralized enamel crystals that that serve as scaffolds for mineral redeposition. These residual crystals can grow back toward their original size when exposed to fluids supersaturated with respect to hydroxyapatite or fluorapatite. Because incipient carious lesions (such as white spot lesions) retain a crystalline framework, remineralization is not only possible, it can be substantial, particularly at the lesion surface. Studies have shown that considerable remineralization can occur in the outer layer of carious lesions. However, due to limited permeability and slower diffusion, the lesion body (subsurface zone) remineralizes at a much slower rate - if it occurs at all. This creates a paradox: while the remineralized surface layer helps protect the lesion from further acid attack, it also forms a diffusion barrier, limiting further ion penetration and thus inhibiting full remineralization of the deeper lesion body.

The Role of Fluoride in Remineralization Fluoride plays a central role in enhancing the remineralization process. It promotes the formation of fluorapatite, a more acid-resistant and stable mineral phase, by incorporating fluoride ions into the enamel crystal lattice during the remineralization process. Fluoride also facilitates the precipitation of calcium and phosphate by lowering the solubility of enamel and shifting the demineralization–remineralization equilibrium in favor of mineral gain.

Additionally, fluoride enhances remineralization even at low concentrations by:

• Attracting calcium ions to the enamel surface

• Inhibiting bacterial metabolism and acid production

• Forming a calcium fluoride-like reservoir on the tooth surface, which can release fluoride in response to future acid challenges

Topical fluoride sources such as toothpaste, gels, varnishes, and fluoridated water are critical in providing a continual supply of fluoride ions that help drive the remineralization process.

In conclusion, remineralization is a naturally occurring process that depends on pH, ion availability, and lesion accessibility. Fluoride is an essential adjunct that enhances this process, especially in early caries lesions. However, the structural barrier posed by the outer remineralized layer means that complete restoration of deeper enamel may be limited, underscoring the importance of early intervention and prevention.

Figure 8. Caries Lesion Initiation and Progression - Remineralization

Figure 8. Caries Lesion Initiation and Progression - Remineralization