By Susan Volk, RDH — Last updated August 20, 2026
Short answer: That jolt of pain from cold water, ice cream, or even cold air usually means the dentin underneath your enamel is exposed, which lets temperature and pressure reach the nerve inside your tooth more directly. It has a handful of common causes — worn enamel, gum recession, a cracked tooth, or a recent whitening treatment — and most are manageable, but sensitivity that’s new, one-sided, or getting worse is worth a dental visit rather than just switching toothpaste.
Why Exposed Dentin Causes Pain
Enamel — the hard outer layer of your tooth — has no nerve endings and doesn’t feel anything on its own. Underneath it is dentin, a softer layer full of microscopic tubules that lead directly to the nerve at the center of the tooth. When enamel wears away or gums recede and expose the dentin (either on the crown of the tooth or the root surface), hot, cold, sweet, or even a strong stream of air can travel through those tubules and trigger a sharp, short jolt of pain.
The Most Common Causes
Gum recession. As gums recede — from aggressive brushing, gum disease, or just age — the root surface, which was never meant to be exposed, is left uncovered. Root surface doesn’t have enamel at all, so it’s especially sensitive.
Enamel wear. Brushing too hard with a stiff brush, grinding your teeth, or frequent exposure to acidic foods and drinks (soda, wine, citrus, even some sparkling waters) can gradually thin enamel to the point dentin starts to show through.
Whitening treatments. Both professional and over-the-counter whitening can cause temporary sensitivity by allowing peroxide to reach the dentin. This usually fades within a few days of finishing treatment.
A cracked tooth or recent dental work. A crack that isn’t visible to the eye can cause sharp pain specifically when biting down. A new filling or crown can also cause a few weeks of temperature sensitivity as the tooth settles.
A cavity or failing filling. Decay near the nerve, or an old filling with a gap forming at the edge, can present as sensitivity before it becomes an obvious toothache.
What Actually Helps
Toothpaste made for sensitivity (look for potassium nitrate or stannous fluoride on the label) works by either calming the nerve directly or physically blocking the dentin tubules — but it typically needs two to four weeks of consistent use to build up an effect, not one use. Switching to a soft-bristled brush and a lighter hand can prevent further enamel and gum wear. For sensitivity tied to grinding, a night guard addresses the root cause rather than just the symptom. If a specific tooth is sensitive to biting pressure, that’s a sign to get it checked rather than manage it at home — that pattern often points to a crack or a cavity that toothpaste won’t fix.
Frequently Asked Questions
Why did my teeth suddenly become sensitive after years of being fine?
Sudden sensitivity is usually a sign something changed — new gum recession, a new crack, a cavity forming, or a recently started habit like grinding. It’s worth a dental exam to identify the specific cause rather than assuming it’s general wear.
Is sensitivity in one specific tooth different from generalized sensitivity?
Yes, and it’s an important distinction. Sensitivity across many teeth is often related to enamel wear, recession, or a recent whitening treatment. Sharp pain isolated to one tooth — especially with biting — is more often a crack, a cavity, or a problem with an existing filling or crown, and deserves a dental visit.
How long should I try sensitivity toothpaste before it’s considered “not working”?
Give it three to four weeks of consistent twice-daily use. If there’s no improvement by then, or if it’s getting worse, that’s the point to see a dentist rather than switching to a different over-the-counter product.