One day cold water tastes normal. The next morning you take a sip and a sharp jolt shoots through your jaw. Sudden tooth sensitivity feels like it came out of nowhere — but it almost never does.
There is always a cause. Sometimes it is something small, like a hairline crack from biting on a bone or a piece of hard candy. Sometimes it is something you can spot at home with a mirror. Sometimes it needs us. Here is how to figure out which it is, and what to do right now while you wait for an appointment.
A hairline crack you cannot see
A small crack in a tooth can be invisible to the eye but very real to the nerve. It often happens after biting something hard — a bone in chicken, a kernel of popcorn, ice, hard candy. The crack widens just enough to let cold liquid touch the inner layer of the tooth.
How to spot it: the sensitivity is usually limited to one tooth, sharp, and only happens with cold or when you bite down. If it hurts when chewing on that tooth, suspect a crack.
Worn enamel from grinding or brushing too hard
If you grind your teeth at night (and many people start during stressful weeks without realising it), or if you have been brushing too hard for years, the outer enamel slowly wears down. Eventually it gets thin enough that everyday food and drink set off the nerve.
How to spot it: sensitivity is spread across multiple teeth, you wake up with sore jaw muscles, or your partner has mentioned grinding sounds at night.
Gum recession — the gum line has moved
The gums protect the lower part of the tooth (the root). If the gum line has receded — from gum disease, hard brushing, or just age — the exposed root is much more sensitive than the rest of the tooth. Cold air or water sets it off instantly.
How to spot it: your teeth look slightly longer than they used to. The sensitivity is at the gum line, not the biting surface. Sometimes you can feel a small step where the gum used to be.
A loose or old filling
Fillings do not last forever. If an old filling has loosened or developed a tiny gap underneath, cold liquid can seep in and reach the nerve. The tooth feels suddenly sensitive without any obvious damage.
How to spot it: the sensitive tooth has a filling, and the sensitivity is new (not chronic). You might also notice a slightly off taste near that tooth after meals.
A cavity reaching the inner layer
Small cavities do not hurt. But once a cavity passes through enamel and reaches the dentine layer underneath, sensitivity starts. The tooth reacts to cold, then to sweet, then later to hot. Sometimes you can see a small dark spot, but often the cavity is between teeth and invisible.
How to spot it: sensitivity is in one tooth, it has gotten worse over weeks, and sweet foods now trigger it too. This needs treatment soon — not next month.
“Sudden sensitivity is the tooth's early warning. Address it now and you may avoid a root canal in six months. Wait it out and the tooth often gets there anyway.”
Recent dental work
Sensitivity is normal for a few days to two weeks after a deep filling, a crown placement, professional whitening, or a thorough cleaning. It is the tooth settling down. If it gets worse instead of better, or lasts more than two weeks, it needs a check.
How to spot it: easy — the sensitivity started right after a dental visit. Usually settles on its own. If not, come back.
What to do right now
Until you can see a dentist, here is what helps:
- Use a desensitising toothpaste — ones with potassium nitrate or stannous fluoride. Smear a thin layer on the sensitive tooth at night with a finger, do not rinse, let it sit overnight.
- Switch to a soft-bristled toothbrush — today, not next week. Use gentle circular motions, no sawing.
- Chew on the other side — give the sensitive tooth a break from pressure.
- Lukewarm water for brushing — cold water on an already-sensitive tooth makes brushing worse.
DIY whitening kits, charcoal toothpaste, very hot or icy drinks, hard foods on the sensitive side, and that “just one more” ice cube to chew. Anything that puts thermal shock or pressure on the tooth can turn mild sensitivity into a major problem fast.
When to come in — soon
If the sensitivity is in one tooth and has lasted more than a week, or if it now reacts to hot drinks (not just cold), come in this week. Cracks, leaking fillings, and growing cavities only get bigger with time — and the difference between a small filling and a root canal is often just a few weeks of waiting.
Sudden sensitivity that won't go?
One short visit usually finds the cause — a small crack, a worn filling, a cavity catching up. The earlier we look, the smaller the fix. Book a quiet consultation before mild becomes major.
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