What you notice first

It is rarely pain. It is the edge of a front tooth that looks a little more see-through than it used to. A smile that reads warmer in photos than it did. Cold water that suddenly registers. Or nothing at all, until a dentist points at something on the screen and says it has been there a while.

People reach for whitening at this point, and it disappoints them. The colour is not a stain. Enamel is translucent, and the layer underneath it is naturally yellow. When enamel gets thinner, more of that layer shows through. You are not looking at dirty teeth. You are looking at thinner ones.

Where the mineral goes

Enamel is almost entirely mineral, and it has no living cells to repair itself. What it has instead is a daily exchange. Every coffee, meal, snack or acidic drink drops the pH at the tooth surface and pulls a little mineral out. Saliva then spends the better part of an hour buffering the acid and carrying calcium and phosphate back in.

One exposure a day and the surface keeps up. Coffee at the desk, lunch, a sparkling water, a snack at four and a glass of wine at nine, and the repair phase keeps getting interrupted before it finishes. The balance tips by a fraction, and it tips in the same direction every day.

What that looks like, in order

1. The surface roughens. Stains catch faster, a film settles along the lower teeth by evening, and breath goes off earlier in the day.
2. Cold starts to register. The colour shifts, because the enamel is thinner, not dirtier.
3. Chalky white patches appear near the gum line. This is the last point at which mineral can still move back in.
4. The surface gives way. A filling follows, and the tooth is never original again. Fillings get replaced, each one takes a little more, until there is not enough left to hold one.

Brushing morning and night is the right thing to do. It is also two moments in a day that has fourteen hours of exposures in between, and none of those exposures happens next to a sink.

The mineral with the unfamiliar name

Hydroxyapatite is what enamel is made of. It sounds like a laboratory word; it is the same crystal that has been in your teeth since they came through. Oral-care formulas use it for a simple reason: offering the surface the mineral it is built from, at the moment it has lost some, is the most direct way to support that daily exchange.

The catch has always been delivery. Toothpaste needs a sink. Mouthwash needs a sink. The hours that do the damage are spent in cars, offices, meetings and restaurants.

A spray for the hours between

CariSpray Adult is a hydroxyapatite oral spray for exactly those hours. Two or three sprays across the teeth after a meal or a coffee, held for a few seconds, and you carry on. No water, no sink, no spitting. It also carries xylitol, a substance the main cavity-causing bacteria cannot use. It works alongside whatever toothpaste you already use.

The tooth in Specimen 01 was brushed for decades. What it never had was anything for the hours in between.