So what exactly does Fluoride do?

Fluoride can positively affect the teeth- both while they are developing; when they are fully formed and when theyhave erupted into the mouth.

What is the Effect of Fluoride Before Teeth Erupt?

Enamel is made up of many crystals arranged in a regular pattern; fluoride makes these crystals larger, denser, harder and more uniform. Imagine that your enamel is an army… this would be the equivalent of making each of your soldiers 10cm taller, giving them a few extra pounds of muscle, stronger shields and making sure they kept their shape when advancing- it would be so much harder for the enemy to penetrate.

Back in the real world, that means if the enamel layer of your tooth is formed in the presence of fluoride, it becomes more resistant to acid attack and ultimately dental caries.

What is the Effect of Fluoride After Teeth Erupt?

When teeth first erupt into the mouth, the enamel is at its least mature and most vulnerable to problems- the soldiers are younger, weaker and less experienced. The benefit of fluoride at this time is greatest. So what does fluoride actually do? This is a question I often get asked.

To understand this clearly, you need to understand a little about plaque, and how dental caries is formed. . It will also help if you know a bit about the enamel layer of the tooth. We are going to get a bit scientific here so bear with me… all will become clear. The simple points are in bold followed by the explanations in case you are curious.

Fluoride is great for our teeth because it:

  • Reduces the amount of plaque (our enemy)- It slows down the rate at which the bacteria in plaque are able to reproduce and therefore limits their growth.
  • Reduces the amount of acid that plaque produces- It does this by interfering with a key part of their metabolism called glycolysis, so they cannot break down sugars into acid as effectively.
  • Makes plaque less sticky- by interfering with its sticky protective layer (extracellualar polysaccharide matrix), so it is more easily removed by saliva, rinsing and tooth brushing.
  • Stops demineralistation and promotes remineralisation of early enamel caries.
  • Makes enamel harder and less susceptible to acid attack and dental caries.

Fluoride conveys more of these benefits in easy to reach areas, such as the smooth surfaces of your teeth rather than the complex patterns (pits and fissures) on the biting surfaces of your molars.

How Exactly does Fluoride Work?

  • The basics
Enamel, the hardest substance in the body is made up of crystals called hydroxyapetite crystals or HAP for short. Fluoride can get incorporated into the enamel to form a new crystal called FAP or fluoruohydroxiapetite. Enamel made with this is much stronger and more resistant to demineralization and dental caries.

  • The science

Hydroxyapetite crystals are packed tightly together to form a regular solid structure called a lattice. The enamel lattice contains hydroxy ions (OH-). Fluoride (F-) has the same negative charge and can replace the hydroxy ion to form the more acid resistant crystal FAP, by a process known as iso-ionic exchange. It's basically like a substitution on the footy field where you replacing a current player with a better player.

Fluoride reservoir

If the outside layer of enamel has high concentrations of fluoride, calcium fluoride (CaF2) will form on the surface- the calcium comes from saliva. When this is exposed to acid, this calcium fluoride becomes negatively charged, forming an ion CAF2- which diffuses into the enamel to make FAP crystals, thus increasing the strength and resistance of the enamel.


Fluoride in saliva (even at low concentrations) helps encourage remineralisation by forcing calcium and phosphate out of saliva onto the tooth. The higher the pH of saliva, the greater the remineralisation that occurs.