Why Are My Teeth Sensitive?

Tooth sensitivity that fades within seconds of the trigger comes from exposed dentin, while pain lingering past 30 seconds signals an inflamed tooth nerve. The gap between those two matters more than how much it hurts. At Mary Qian Dental Group in Palo Alto, we check duration first, because both problems feel almost identical in the moment.

Highlights:

• Sensitivity that fades within a couple of seconds of the trigger points to exposed dentin and is manageable
• Pain that lingers 30 seconds or longer, or starts with no trigger at all, needs a dentist within days
• Dentin hypersensitivity affects an estimated 11.5% of patients, based on a 2019 review of 77 studies
• Desensitizing toothpaste blocks the pain signal and does nothing for a cavity, a crack, or an infection underneath
• Gum recession, enamel erosion, grinding, and recent dental work all expose dentin

How Do You Tell Normal Sensitivity From a Real Problem?

Duration is the test, not intensity. A tooth with healthy nerve tissue reacts to cold for one to two seconds after the cold is gone, according to the American Association of Endodontists. Exposed dentin behaves the same way. A tooth whose nerve is inflamed keeps hurting for 30 seconds or longer, and sometimes hurts with nothing touching it at all.

Patients almost always describe the wrong variable. They tell us how bad it hurts. We need to know how long it lasts after they swallow the cold water.

Does tooth sensitivity always mean a cavity?

Not usually. Decay tends to hit one tooth, so pain spread across several teeth on the same side points away from a cavity and toward worn enamel or receded gums. The trap runs the other direction. A cavity can produce short, sharp cold pain that feels exactly like ordinary sensitivity, which is why one stubborn tooth deserves an X-ray.

Why is my tooth sensitive to hot but not cold?

Cold pain is common and often harmless. Heat pain is the one that concerns us. When a tooth reacts more to hot coffee than to ice water, the nerve tissue inside is usually inflamed rather than just exposed at the surface. Heat sensitivity that has appeared in the last few weeks should be looked at, not managed with toothpaste.

One patient came in having used desensitizing toothpaste for three months on a single upper molar. The toothpaste had been working, in the sense that it was doing precisely what it is built to do: quieting the nerve signal. Underneath, decay had reached the pulp. She needed a root canal that a visit in month one would likely have prevented.

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What Causes Tooth Sensitivity?

Anything that strips enamel above the gumline or cementum below it exposes the dentin underneath, and exposed dentin is what hurts.

Dentin is not solid. Thousands of microscopic tubes run through it, from the tooth’s surface down toward the nerve, packed side by side like straws in a box. Enamel keeps the tops of those straws sealed. Wear the enamel away, or let the gum slide back off the root, and cold, heat, sugar, and even a puff of air travel straight down to the nerve.

Gum recession

Gums that pull back expose root surfaces that never had enamel on them in the first place. Root dentin sits closer to the nerve and reacts faster than the crown of the tooth does. Aggressive brushing, grinding, and gum disease all drive gums pulling back from the tooth root, and recession does not reverse on its own.

Enamel erosion from acid

Citrus, soda, sports drinks, wine, and vinegar dressings soften enamel a little at a time. Stomach acid does more damage than anything you eat, because it is stronger and because repeated acid reflux wears enamel away while you sleep, when saliva production drops. Enamel does not grow back once lost, so catching the pattern early changes the outcome.

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Grinding and clenching

Grinding flattens the biting surfaces and flexes the tooth near the gumline, which wears enamel in both places at once. Most people who grind do it in their sleep and have no idea. Morning jaw tightness, headaches on waking, and flat, shiny wear facets on the back teeth are the signs we look for during an exam.

Brushing too hard

Plaque is soft and comes off with very little pressure. Scrubbing hard with a firm brush wears enamel at the gumline and pushes the gum tissue back, which produces sensitivity in the exact spot where the two problems overlap. A soft brush held loosely does the same cleaning job without the damage.

A cavity, a crack, or a failing filling

Decay, fractures, and old restorations that have started to leak all open a path to the nerve. Each of these affects one tooth rather than a whole quadrant, and each tends to add pain on biting to the temperature pain. Depending on what we find, the fix is a filling or, for a cracked or heavily restored tooth, a crown.

Recent dental work

Fillings, deep cleanings, and crown preparations all irritate the nerve temporarily. Post-treatment sensitivity should trend downward week over week. Sensitivity that holds steady or worsens after a procedure is information your dentist wants, so call rather than wait it out.

Why Are My Teeth Sensitive to Cold, Hot, or Sweet Things?

Each trigger reaches the nerve by a different route, which is why what sets the pain off narrows down the cause.

Sensitivity to sweets

Sugar draws fluid through the dentin tubules by osmosis, so sweet foods can hurt even when nothing hot or cold is involved. Sugar sensitivity on one specific tooth is the pattern most often linked to decay in our experience, and it deserves an X-ray rather than a change of toothpaste.

Sensitivity to cold air and cold drinks

Cold makes the fluid inside the tubules contract and pull, which fires the nerve. Cold is the most common trigger and the least alarming one, as long as the pain stops when the cold does. Cold air catching the front teeth on a walk usually points to recession or thin enamel at the gumline.

Sensitivity after whitening

Whitening gels open the dentin tubules temporarily, and short-term sensitivity is a normal, well-documented response to the treatment rather than a sign something went wrong. The effect is tied to gel concentration and how long the gel stays on, which is part of why supervised treatment is easier to adjust than a strip bought off a shelf. Our teeth whitening patients who report sensitivity are usually managed by shortening wear time or spacing sessions further apart.

Why Are My Teeth Sensitive All of a Sudden?

Sudden sensitivity is usually slow wear that finally crossed a threshold, with three genuine exceptions.

Enamel thins and gums recede over years. You feel nothing at all until the dentin is exposed enough to register, and then it seems to arrive overnight. The wear had been building the whole time.

Three things genuinely do appear quickly: a cracked tooth from biting something hard, a filling or crown that came loose, and a sinus infection pressing on the roots of the upper back teeth. Sinus-related tooth pain hits several upper teeth at once and gets worse when you bend forward.

How long does tooth sensitivity last?

Sensitivity after a routine cleaning settles within a few days. Sensitivity after a filling or a crown eases over several weeks and should improve steadily in that window. Whitening sensitivity fades once treatment stops. Sensitivity from recession or enamel wear does not resolve on its own, because the exposed surface stays exposed until someone covers or seals it.

What Can You Do About Sensitive Teeth at Home?

Home care works well on exposed dentin and does nothing for the other five rows of the table above.

Desensitizing toothpastes work in one of two ways. Some calm the nerve directly. Others plug the open tubules so the trigger cannot reach it. The American Dental Association points to stannous fluoride, potassium, or arginine as the ingredients supported for reducing dentin hypersensitivity pain, based on a 2023 network meta-analysis. Relief builds with repeated use rather than arriving after one brushing, so give any product a fair run of daily use.

Recommended:

• A toothpaste containing stannous fluoride, potassium nitrate, or arginine, carrying the ADA Seal of Acceptance
• A soft-bristled brush, held lightly, in short circles rather than long side-to-side strokes
• Water after acidic food or drink, with brushing delayed about an hour so softened enamel is not scrubbed
• A straw for anything acidic

Every toothpaste carrying the ADA Seal has to score 250 or lower on the Relative Dentin Abrasivity scale, so the Seal handles the abrasiveness question without you having to research individual products.

Red flags: stop managing this yourself and call a dentist if any of these apply.

• Pain that lingers 30 seconds or longer after the trigger is gone
• Pain that starts on its own, with no trigger
• Pain that wakes you up or gets worse when you lie down
• One specific tooth rather than a general area
• Swelling, a bad taste, or pain on biting
• Over-the-counter painkillers that are not touching it

How Does a Dentist Treat Sensitive Teeth?

Treatment follows the cause, so the visit starts with working out which cause you have.

Dr. Mary Qian tests the suspect tooth against its neighbors and against the matching tooth on the other side, because a response only means something in comparison. The test is a cold stimulus and a stopwatch, roughly speaking. She times how long the sensation lasts once the cold comes away. She checks for pain on biting, examines the gumline for recession and wear, and takes X-rays to rule out decay and cracks.

From there the paths separate:

• Exposed dentin at the gumline. In-office fluoride varnish or a desensitizing agent, applied directly to the sensitive spot. Fluoride treatment is quick and often repeated across a few visits.
• Worn or notched root surfaces. Dental bonding covers the exposed area with tooth-colored resin, usually in one appointment.
• Gum disease or deep recession. Periodontal care, including scaling and root planing, treats the bacteria driving the recession.
• Grinding. A custom guard worn at night protects the surfaces from further wear while the sensitivity settles.
• Decay, a crack, or a failing restoration. Restorative treatment, which fixes the sensitivity as a side effect of fixing the tooth.
• An inflamed nerve. Root canal treatment, which is the outcome we are trying to help you avoid by catching the lingering-pain pattern early.

Sensitivity you have been managing on your own for weeks has a cause, and an exam tells you which of the six rows above you are actually in.

Find out what’s causing it

Consultations are free, and you leave with an explanation rather than a quote.

When Should You Call a Dentist About Sensitive Teeth?

Three signs turn this from a next-visit conversation into a phone call this week.

Pain that lingers past 30 seconds is the first. Pain with no trigger at all is the second, and it is the most urgent of the three. Pain isolated to one tooth, especially with discomfort on biting, is the third.

Swelling, fever, a foul taste, or pain that spreads across your jaw needs same-day emergency care rather than an appointment next week. Our Palo Alto office keeps time open each day for patients in pain.

Frequently Asked Questions About Sensitive Teeth

Can tooth sensitivity go away on its own?

Sometimes. Sensitivity after a cleaning, a filling, or whitening usually fades on its own within days to a few weeks. Sensitivity caused by gum recession or enamel wear will not resolve by itself, because the exposed surface stays exposed. If it has lasted longer than a month, have it examined.

Why is only one of my teeth sensitive?

One sensitive tooth is a different situation from a sensitive area. General sensitivity across several teeth suggests worn enamel or receded gums. A single tooth points toward decay, a crack, a failing filling, or an inflamed nerve. Single-tooth sensitivity should be examined and X-rayed rather than treated with toothpaste.

How long does tooth sensitivity last after a filling?

Sensitivity after a filling is common and should improve week by week. What matters is the direction of travel rather than the exact number of days. Sensitivity that holds steady, worsens, or starts lingering after the cold is gone means the filling needs checking, so call your dentist rather than waiting it out.

Does sensitivity toothpaste work, and how long does it take?

Desensitizing toothpaste does work for sensitivity caused by exposed dentin. Relief builds with twice-daily use over time rather than after a single brushing, so give it a consistent run. It has no effect on decay, cracks, or nerve inflammation, and using it on those problems delays treatment while they progress.

Can teeth whitening cause lasting sensitivity?

Whitening commonly causes temporary sensitivity that fades once treatment stops. Gel strength and wear time both affect how much you feel, which is one advantage of supervised whitening over strips bought off a shelf. Sensitivity that persists for weeks after whitening ends is unusual and should be checked.

Why do my teeth hurt when I brush them?

Pain during brushing usually means exposed root surfaces at the gumline, most often from recession or from brushing too hard. Switch to a soft brush and lighter pressure, then watch for a few weeks. Bleeding gums alongside the pain suggest gum disease, which needs treatment rather than a technique change.

What To Remember About Sensitive Teeth

• Sensitivity lasting 1 to 2 seconds after the trigger points to exposed dentin; 30 seconds or longer points to an inflamed nerve
• Desensitizing toothpaste quiets the signal and treats none of the underlying causes
• Gum recession, acid erosion, grinding, and hard brushing are the four most common sources of exposed dentin
• One sensitive tooth means something different from a sensitive area, and needs an X-ray
• Sensitivity after a filling or cleaning should improve each week; sensitivity from wear will not improve on its own

Sensitive teeth that have bothered you for weeks have a cause, and the cause has a fix.

Book a sensitivity exam with Dr. Mary Qian in Palo Alto.

Serving Palo Alto, Menlo Park, Redwood City, and Los Altos.

Reviewed by Mary Qian, DMD, Mary Qian Dental Group, Palo Alto, CA.