The Truth About Whitening Sensitivity

A large number of people have tried whitening once, found it painful, and concluded that their teeth are simply sensitive. In most cases what actually happened is that three separate things went wrong at once.

Where the pain comes from

Peroxide gel reaches the pulp of a tooth through the dentinal tubules. In a healthy tooth with intact enamel, that transit is slow and the pulp handles it comfortably. Where the enamel is thin, worn, or absent — at the gum line, on an exposed root surface, over a crack — the gel arrives quickly and in concentration. That is what produces the sharp, short, unmistakable twinge.

So the question is not whether your teeth are sensitive. It is whether anyone checked where your gel was going.

Three things an unsupervised kit gets wrong

• The tray does not fit. A stock tray leaks gel onto the gums and over exposed root surfaces. A custom tray made from a scan of your teeth has a reservoir that keeps gel on enamel.
• Nothing was examined first. Untreated decay, a leaking filling or an exposed root is a direct channel to the pulp. Fifteen minutes of examination finds all three.
• No desensitising was done. This is the largest factor and the most commonly skipped.

What desensitising actually does

Two weeks of potassium nitrate and high-fluoride application before whitening does two things: the fluoride partially occludes the dentinal tubules, slowing gel transit, and the potassium nitrate reduces the excitability of the nerve endings inside the pulp.

It is boring, it takes two weeks, and it is very close to the entire difference between a comfortable course of whitening and a miserable one.

We do it as standard before every case, and we continue it afterwards. In our own records, the proportion of patients reporting any sensitivity at all is in the low single digits.

The other thing nobody mentions

Composite fillings and ceramic crowns do not whiten. They stay exactly the shade they were made in.

If you have visible restorations on your front teeth — and a great many people do without thinking about it — whitening the natural teeth around them makes those restorations obvious. The sequence matters: whiten first, wait two weeks for the shade to stabilise, then replace the restorations to match.

Done in the other order, you end up with a brighter smile containing two teeth that are suddenly the wrong colour, and the only fix is to do it again.