Theory 06/Dentistry & Oral Biology /Preventive dentistry/3 min
Fluoride Shifts a Threshold
Fluoride is described as antibacterial and as a mineral. Its effect may be a shift in a chemical threshold.
Fluoride protects teeth by shifting the critical pH and the remineralisation kinetics rather than by killing bacteria, so its benefit should be independent of the oral flora and should appear at concentrations too low to inhibit bacterial growth.
01The evidence
- The caries process and the role of fluoride in maintaining enamel integrity have been described together, with fluoride acting on the demineralisation-remineralisation balance rather than only on the biofilm.JADA
02The tension
Fluoride is described as both an antibacterial agent and a mineral agent, and the two mechanisms are mixed in public messaging. The antibacterial story predicts that benefit should scale with flora suppression, which it does not, and it invites the objection that fluoride is a drug rather than a nutrient.
03The theory
Fluoride substitutes into the mineral lattice and adsorbs to crystal surfaces, which lowers the solubility of enamel and shifts the pH at which dissolution begins. It also speeds remineralisation when the pH recovers.
On this account the effect is chemical and threshold-based. It does not require the bacteria to die, which is why low concentrations work and why the benefit is seen in populations with very different flora.
The prediction is that benefit should be independent of bacterial load, that it should scale with the shift in critical pH rather than with dose above a saturation point, and that it should persist where the flora is resistant to the antibacterial effect.
The communication consequence is that the antibacterial framing should be dropped, which would also remove a line of criticism that is based on the wrong mechanism.
04What this is not
Dual accounts mix two mechanisms and cannot say which produces the benefit. This makes the effect chemical and threshold-based, which predicts benefit at sub-inhibitory concentrations and independence from flora.
05Predictions
- P1Benefit should appear at concentrations below bacterial inhibition.
- P2Benefit should be independent of bacterial load.
- P3Benefit should scale with the shift in critical pH, saturating at low dose.
06What would refute it
Benefit scaling with flora suppression at constant chemistry would restore the antibacterial mechanism.
07What it would change
It would simplify the mechanism story and change how fluoride is communicated.
08Evidence base
- Maintaining the integrity of the enamel surface — fluoride mechanism — JADAhttps://jada.ada.org/article/S0002-8177%2814%2963879-4/fulltext