Your Enamel Is 97% One Mineral. You Can Buy It.

There’s a mineral called hydroxyapatite. It makes up about 97% of your tooth enamel and roughly 70% of your bones.

You can buy it in a tube. That’s the entire premise, and it’s a good one — but the labels have become a mess of percentages that almost nobody explains, so here’s what the numbers are actually arguing about.

The idea is not new and not fringe

It came out of NASA research in the 1970s, on how to rebuild bone in astronauts losing density in zero gravity. A Japanese company took the material and put it in toothpaste. Apagard has been on shelves since the 1980s, which means this has had four decades of consumer use in a country that pays close attention to teeth.

It reached Europe and the US properly only in the last few years. That’s why it feels like a trend. It isn’t one — it’s an import.

What it’s doing, mechanically

Enamel is not inert. It runs a constant exchange.

Eat something, mouth turns acidic, enamel gives up a little calcium and phosphate. Saliva recovers, pH climbs back, minerals go back in. Demineralisation and $1ization, all day, every day. A cavity is what happens when the first side of that ledger wins for long enough.

Fluoride helps by swapping into the crystal and making a version that dissolves at a lower pH — harder to attack.

Hydroxyapatite helps differently: it supplies the missing material directly. Same mineral your enamel is made of, delivered to the surface rather than waiting for saliva to bring it. Under an electron microscope you can see particles sitting into the surface, filling the microscopic pits where mineral was lost.

That’s also why people report sensitivity dropping. Sensitivity is largely open dentinal tubules — microscopic tunnels — and small particles plug them:

I had one really sensitive tooth a few months ago, either hot or cold caused me pain. Now it’s completely back to normal. And my teeth look whiter too. r/Biohackers

I really can’t say enough good things about nanohydroxyapatite; my teeth were never this happy before. r/Biohackers

Now the argument

Go into any thread about this and someone will tell you the percentage on your box is too low. The claim usually runs: it has to be around 10%, the particles have to be nano-sized, and anything that just says “hydroxyapatite” is marketing.

The particle-size half of that is fair. “Nano” means below 100 nanometres, close to the size of the crystals in real enamel. Bigger particles sit on the surface; smaller ones integrate into it. A label saying only hydroxyapatite is genuinely telling you less than one saying nano-hydroxyapatite.

The percentage half is where it gets sloppy, because a percentage means nothing without knowing how long the product stays on the tooth.

Toothpaste is a rinse-off product. It’s in contact for two minutes and then most of it is spat out. To move any mineral in that window, you need a high concentration — hence the 10% figure people quote.

A leave-on product is a different equation entirely. Something that stays on the enamel and isn’t rinsed has vastly more contact time, and needs proportionally less material to deliver the same daily amount. Sprays and gels are formulated around replacing what enamel loses in a day, not around winning a two-minute race.

Comparing those two numbers as if they measure the same thing is like comparing a sprinter’s top speed to a marathon runner’s, and concluding the marathon runner is slow.

What to actually read on a label:

• Does it say nano-hydroxyapatite, or just hydroxyapatite?
• Is it rinse-off or leave-on? That reframes the percentage completely.
• Is anything else doing work — xylitol starves cavity bacteria, buffers push pH back up?
• Is it replacing your fluoride, or sitting alongside it?

Is it instead of fluoride?

This is where the topic gets tribal, and it doesn’t need to be.

Fluoride has the deepest evidence base of anything in oral care, by a wide margin. Hydroxyapatite has a smaller but real and growing one, and the EU’s own consumer safety committee has assessed the nano form as safe.

They do different jobs and can be used at different times. Plenty of people run fluoride toothpaste at night and something hydroxyapatite-based during the day. The person who mattered most in these threads wasn’t picking a side:

a lot of people don’t realise this. I was born with mild enamel hypoplasia… the fancy toothpastes don’t change much if you can brush consistently, but if you can’t, then try to get the long-lasting enamel protection kind r/ADHD

Which is the sanest framing anyone offered. If you brush well, twice a day, every day, this is a marginal upgrade. If you don’t — if you’re inconsistent, if your mouth is dry, if you’re prone to cavities anyway — the margins are where you live, and they’re worth buying.

The reasonable expectation

It is not a cure and it does not regrow a cavity. Once enamel is gone past a certain point, that hole is permanent and needs a dentist.

What it does is shift the daily balance slightly toward repair. Over years, slightly is the whole game — because that’s the timescale teeth work on anyway.