Fluoride is the most studied subject in dentistry and the most argued-about subject in parent groups. Both of those things can be true at once. Here’s the version I give in the clinic.

What it actually does

Three things, in order of importance:

  • It puts minerals back. When acid pulls calcium and phosphate out of enamel, fluoride helps drive them back in — and it does this while the damage is still a soft white patch, before there is any hole.
  • It builds harder enamel. The rebuilt surface contains fluorapatite, which dissolves at a lower pH than the original enamel. Plain English: it takes more acid, for longer, to hurt it.
  • It slows the bacteria down. At the concentrations found in toothpaste, fluoride interferes with how plaque bacteria produce acid in the first place.

Fluoride is the only tool we have that can turn an early cavity back into a tooth. A filling repairs damage; fluoride can undo it.

How much, by age

The amounts that matter
  • First tooth to 3 years: a smear the size of a grain of rice — toothpaste with at least 1000 ppm fluoride.
  • 3 to 6 years: a pea-sized amount, 1000–1450 ppm.
  • 6 years and older: a full brush head, 1450 ppm.
  • Always: twice a day, last thing before bed, spit out and don’t rinse, and supervise the amount until around seven.

That last instruction is the one almost every family gets wrong, and it’s free to fix. Rinsing with water — or with mouthwash — immediately after brushing washes away the thin layer of fluoride that would otherwise keep working on the enamel for the next half hour. Spit, and stop there.

Why this matters more in Lebanon

In countries with fluoridated water, children get a small, constant background dose all day from the tap. Lebanon does not fluoridate its water supply, and most families here drink bottled water, which typically contains very little fluoride. Some brands publish the figure on the label; most are well under half a milligram per litre.

The practical consequence: in Beirut, the toothpaste on the brush and the varnish applied at the clinic are doing essentially all of the work. That’s why I ask more carefully than dentists elsewhere might when a family tells me they’ve switched to a fluoride-free toothpaste — not to argue, but because something else then has to cover that gap.

Fluoride varnish at the clinic

Varnish is a highly concentrated fluoride in a sticky resin base. I paint it on with a tiny brush; it sets the moment it touches saliva. No drill, no needle, no suction, about two minutes, and most children think the flavour is the best part of the appointment.

Applied two to four times a year depending on your child’s risk, varnish reduces decay by roughly a third — one of the strongest, most consistent findings in paediatric dentistry. Afterwards: soft, non-crunchy food for a few hours, and skip the brushing until that evening so it can stay on.

So what about fluorosis?

Dental fluorosis is the real risk, and it deserves a straight answer. It appears as faint white flecks or lines on the permanent teeth, and in almost all cases in a country like Lebanon it is so mild that only a dentist notices it. It is cosmetic, not a disease, and the teeth are not weaker.

It’s caused by regularly swallowing too much fluoride while the permanent teeth are forming under the gum — so, roughly, before the age of six. In practice that means eating toothpaste from the tube, using an adult-sized blob on a child’s brush, or unsupervised brushing with a flavour your child likes a bit too much.

Which is why the amount is the whole conversation. A rice grain twice a day, spat out, with an adult watching, is not a fluorosis risk. Keep the tube out of reach, and choose a mild flavour if your child is a swallower.

Drops, tablets and supplements

Please don’t buy these over the counter. Fluoride supplements are only appropriate after someone has added up what your child is already getting — water, toothpaste, food, any varnish — and found a genuine gap, and the dose depends on both age and risk. This is the one part of the subject where more is clearly not better.

If you’d still rather avoid it

I’d rather work with a family’s actual decisions than lose them to a forum, so if you’ve decided against fluoride, tell me and we’ll build the strongest plan we can without it: hydroxyapatite toothpaste, xylitol after meals, fissure sealants on the molars as soon as they erupt, a stricter approach to snack frequency, and three-monthly check-ups instead of six-monthly so that anything starting gets caught while it’s still reversible.

It’s a harder road, and I’ll say so honestly. But it’s a real plan, and it’s a great deal better than a silent disagreement.

This article is general information for parents, not a diagnosis. Every child is different — if something about your child’s teeth worries you, message the clinic and we’ll take a look.