It Has a Name, and It Is Telling You Something

Somewhere over the Atlantic a molar starts to throb, and by landing it has stopped. Most people put it down to the cabin air.

It isn’t the air. It has a name — barodontalgia — and it is worth paying attention to, because a healthy tooth does not do this.

The physics

Cabin altitude on a commercial flight is typically pressurized to the equivalent of about 1,800 to 2,400 meters. That is not sea level, and the difference is enough to matter.

Boyle’s law: at constant temperature, the volume of a gas rises as the pressure around it falls.

So any pocket of gas trapped in a sealed space in your body expands during climb. Ears and sinuses handle this by equalizing through passages built for the purpose — which is why swallowing works.

A tooth has no passage. If gas is trapped inside one, it expands with nowhere to go and presses on the nerve.

Which is why it means something

Here is the diagnostically useful part.

A healthy tooth contains no gas. Enamel and dentin are solid mineral, and the pulp chamber is full of living tissue, blood vessels and fluid. There is nothing compressible in there.

For pressure change to produce pain, there has to be a void — and a void means something has already gone wrong.

The usual candidates:

A microscopic gap under a filling. Composite shrinks slightly as it sets, and an imperfect seal leaves a space that fills with air or gas.

Decay under a restoration, producing a pocket.

A pulp that is inflamed or dying. Necrotic tissue produces gas, and an inflamed pulp is already under pressure inside a rigid chamber — so a small extra expansion is enough to tip it into pain.

A recent root canal that has not fully settled, or a filled canal with a void in it.

Or a sinus sitting directly above the roots of the upper back teeth, which is the commonest confusion of all — the sinus is the pressurized space, and the pain is referred to the teeth beneath it.

So the pain is doing something genuinely useful. It names the tooth.

Diving is the same problem, larger

Aviation medicine takes this seriously and diving medicine takes it much more seriously, because the pressure changes are far bigger.

Descending ten meters underwater doubles the ambient pressure — a change no flight comes close to. Divers experience it in both directions, and there are documented cases of restorations being displaced and teeth fracturing from trapped gas expanding on ascent.

That is why military aircrew and professional divers get screened for it. Pain in an aircraft seat is unpleasant. Pain at depth, in a mask, holding a regulator, is a safety problem.

There is a specific piece of advice from that world worth borrowing: don’t fly or dive immediately after dental work. Give a new filling or an extraction time to settle before subjecting it to a pressure cycle.

What to do about it

Note which tooth. Which side, upper or lower, how far back. This is the entire value of the episode, and by the following week most people have forgotten.

Notice when it happened. Pain on climb points at expanding gas in a tooth. Pain on descent points more often at the sinuses.

Get it examined. The pain resolves when pressure equalizes and the cause does not. A tooth that hurts at altitude has told you something a routine check-up might not find for another year.

And if it happens repeatedly on every flight, that is a tooth with a persistent void in it. It is not going to stop on its own.

The thing it illustrates

There is something quietly good about this.

A tooth is a sealed mineral box with a nerve inside it, and that arrangement means it has almost no way to report on its own condition. Decay travels through enamel in complete silence, because there are no nerves there to report with. Pain arrives late, when the pulp is already involved.

Then an aircraft climbs to eleven kilometers, the pressure drops, and a fault that was producing no symptoms at sea level becomes audible for two hours.

It is an accidental diagnostic test, run for free, on everybody on the plane.

The short version

Barodontalgia. Trapped gas expanding as cabin pressure falls, pressing on a nerve inside a rigid tooth.

A healthy tooth has no gas in it, so the pain means something is already there — a leaking filling, decay underneath, or a pulp in trouble.

Write down which tooth, and get it looked at. The aeroplane found it for you.