One tooth suddenly sensitive: crack, filling, decay, or recession?

When one tooth, rather than the whole mouth, suddenly turns sensitive, the usual causes are a crack, a recent or failing filling, decay that has reached the dentine, or a patch of gum recession, and each tends to leave a different fingerprint. Three of those four are put right by a dentist, not by a toothpaste, and the Oral Health Foundation's advice is to see a dentist when only one tooth is affected or when the pain comes on suddenly¹. A daily sensitivity paste is the right tool for the fourth alone, and only once a dentist has confirmed it: S3 Sensitivity Science™ keeps full adult-strength fluoride, 1450 ppm as sodium monofluorophosphate, and fluoride acts on early decay, but a hole that has already formed needs a filling².

What was checked16 peer-reviewed studies, the NHS and the Oral Health Foundation

Why would just one tooth turn sensitive?

Because the things that expose or irritate a single tooth are local: a crack in that tooth, a filling in it, decay in it, or gum that has pulled back from it. The Oral Health Foundation puts a single affected tooth, and pain that comes on suddenly, among its reasons to see a dentist, and says either could be a sign of tooth decay, a cracked tooth, gum problems or infection¹. The NHS names the same suspects among the causes of toothache, from decay and a cracked or damaged tooth to a loose or broken filling and gum disease, with sensitive teeth as one more possibility¹¹. Swelling, a bad taste or a temperature belong to a different page, on sensitivity with swelling or a bad taste.

Nobody can sort these reliably from the outside, including the person whose tooth it is. Dentists find it hard too: a 2019 clinical review written for UK primary care sets dentine sensitivity and cracked tooth syndrome side by side, and warns that one complaint can have more than one cause, so the diagnosis rests on a history and an examination⁷.

Is one tooth unusual for ordinary sensitivity? Less than the rule of thumb suggests. In a cross-sectional clinical study of 3,551 adults in seven European countries, funded by a maker of sensitivity toothpastes, sensitivity from exposed dentine was most common on the lower front teeth and on the cheek-facing surfaces, where it went with gum recession and erosive wear⁸. A cross-sectional clinical study of a population sample of 1,023 adults aged 35 and over in Porto Alegre, Brazil, examined at home, found that it typically involved about one tooth per affected person⁹. A single sensitive tooth is therefore not proof of something else, and it is not proof that nothing else is going on, which is why the guidance sends it to be checked. That guidance is a judgement about which teeth deserve a look rather than a measured risk: a PubMed search run for this page in September 2026, pairing dentine hypersensitivity with single tooth, one tooth or localised, returned forty-five records, and none of them tested whether sensitivity in one tooth predicts a crack, a failing filling or decay.

Pain is also poor at giving an address. When one tooth's pulp was inflamed, in a clinical study of 64 patients, its sound neighbour and the corresponding tooth in the other jaw reacted more strongly to cold as well, and calmed down once the culprit had root canal treatment¹⁰. The Journal's short piece on why teeth suddenly become sensitive covers the everyday causes across the mouth, and the guide to the pain pattern that tells sensitivity from something else sorts pains by how long they last.

The table sets the four fingerprints side by side, with a fifth row for that trap. Its rows describe patterns, not diagnoses, and the NHS bands are England's, as printed on nhs.uk on the day this page was written, and may change⁶.

Could it be a crack?

It could, and a crack is harder to recognise than most people expect, because it does not always hurt on biting, or hurt at all. Of 2,858 cracked back teeth enrolled by dentists across the United States in a practice-based observational clinical study, the complaint heard most was pain to cold, in 37% of teeth; biting pain came in at 16%, and pain out of nowhere at 11%⁵. In a smaller practice-based observational clinical study of 147 records from one general practice, 55.1% of the cracked teeth caused no symptoms, and not every one of them reacted to a bite test⁴. Both studies started from teeth already known to be cracked, so neither gives the odds that a cold-sensitive tooth is cracked; what they show is that a crack can pass for sensitivity⁵⁴. The Oral Health Foundation adds that cracks often do not show on standard X-rays, because the crack has to line up with the beam³, and a review of the American registry behind the largest study reports that the crack could be seen on a radiograph for only 2% of the teeth¹².

Pain from a crack comes and goes, too, which is why one good week settles nothing either way. In the one-year follow-up of that practice-based clinical study, which tracked 1,850 cracked teeth nobody treated, 32% of patients had some change in their pain, decreases were more than twice as common as increases, and only 6% of teeth gained a new visible crack¹⁷. Across three years of the same practice-based clinical study, 92% to 99% of the biting and spontaneous pain present at the start had gone at some recall, in treated and untreated teeth alike, and the authors suggest some of the cold pain may have been ordinary dentine sensitivity rather than damage from the crack¹⁸. Pain that settles is not a crack that has mended, though, and the Oral Health Foundation is plain that a cracked tooth cannot heal itself³.

The reason to book is what a dentist finds and what treatment achieves. When dentists in the network opened 435 cracked teeth for treatment, in a practice-based clinical study, 89% had cracks running inside the tooth, and a tooth that hurt on biting had about 2.6 times the odds of one¹⁹. In a retrospective clinical study of 199 cracked teeth whose pulp was judged able to recover, 29.1% went on to an irreversibly inflamed or dead pulp, and teeth that never received a crown were far more likely to²⁰. Caught and treated, a cracked tooth is usually kept: a 2024 systematic review and meta-analysis of 27 studies found that cracked teeth still holding a living pulp were kept in 92.8% to 97.8% of cases over one to six years²¹. A 2017 review for dentists in the British Dental Journal treats a cracked tooth as a problem practices meet often and find hard to diagnose and manage²², and a 2021 practice paper for UK primary care says that spotting a possible fracture on examination is essential to the diagnosis and that the outlook depends largely on how far the fracture runs²³. The page on teeth sensitive to hot and cold at the same time covers what the timing of a pain can and cannot tell you.

Could it be the filling?

If the tooth was filled in the last few weeks, quite possibly, and some sensitivity after a filling is common enough that trials of filling materials measure it as an outcome in its own right¹⁵. A 2015 systematic review and meta-analysis of randomised trials on composite fillings in back teeth did exactly that, and found that the type of bonding agent used made no measurable difference to how often the sensitivity happened or how strong it was¹⁵. What did matter, in a clinical study of 600 composite fillings placed by supervised students in 231 patients at a German dental school, was depth: at a check about two weeks later that counted reported sensitivity, pain on chewing or a failed vitality test, 6% of fillings had failed, fillings in deep decay carried about four times the risk, and those where the pulp had been exposed about 14 times the risk¹⁴. The Journal's page on tooth sensitivity after a filling covers what usually settles and how to stay comfortable in the meantime.

Two signs outrank any reassurance, whether the filling is new or old. The first is pain when you bite down, which the Oral Health Foundation lists as a sign of a loose filling, a crack or decay, and says should always be checked¹³. The second is pain that lingers or grows: an ache that comes and goes and needs painkillers may mean the nerve inside the tooth is irritated or damaged, in the Foundation's words, and the NHS sends people to a dentist for toothache that lasts more than two days¹³¹¹. An older filling can fail as well; a loose or broken filling is on the NHS list of causes of toothache, and a lost or worn filling is on the Oral Health Foundation's list for sharp pain to cold¹¹¹³. How long normal sensitivity lasts has no clock you can rely on. A PubMed search for this page, pairing post-operative sensitivity with duration, weeks, resolution or follow-up, returned a hundred and fifty-seven records; most measure the sensitivity at one or two fixed visits in order to compare materials, and the few that follow it day by day are too small to set a timetable for anyone else's tooth. The dentist who placed the filling is the one to set the expectation, and on the NHS in England, further treatment in the same band within two months costs nothing extra⁶. The page on sensitivity that lingers after the trigger has gone goes further into the second sign.

Could it be decay?

Yes, and the word sudden needs care here, because decay itself is slow. The NHS says tooth decay may cause no symptoms at first; if it gets worse it can form a hole, and a tooth with a hole may bring toothache, a sharp pain with hot, cold or sweet food and drink, or white, brown or black spots². What feels sudden is the moment the decay reaches the dentine, the layer under the enamel, and the tooth starts to answer back. A twinge on sweet things in one particular tooth is the familiar version, and the page on sweet sensitivity and decay goes through it.

Whether a toothpaste can help depends on the stage, and the answer has two halves. Before a hole forms, fluoride works: the NHS says a dentist can prescribe fluoride treatments such as a mouthwash or varnish to reverse early tooth decay, and advises brushing at least twice a day with fluoride toothpaste, spitting rather than rinsing². The fluoride in any full-strength paste, S3's included at 1450 ppm, belongs on that early side of the line; a cavity that has formed needs a filling, and decay that has reached the pulp may need root canal treatment². That part is not a toothpaste's job, and no paste should be used to wait one out.

If it turns out to be recession, where does a paste like S3 fit?

Recession is the one candidate where a daily paste is the main tool, and even there a dentist should confirm it first. When gum pulls back from a tooth, dentine is left exposed, and the Oral Health Foundation explains that exposed dentine makes it easier for heat, cold and sweetness to reach the nerve; it lists brushing too hard, gum recession and gum disease among the causes of sensitive teeth¹. The NHS lists shrinking gums among the things gum disease can lead to, which is one reason a receded gum on one tooth deserves an examination rather than a guess¹⁶. The spot itself is another: a worn notch or early decay can sit at the same gum line, and telling them apart is a dentist's work, not something to settle in a mirror.

Recession and pain do not always travel together. Of the teeth with receded gums in that Brazilian population study, roughly one in ten was sensitive⁹. When sensitivity does come from a receded root, that is the case S3 was built for: sensitivity from gum recession, where exposed tubules and a reactive nerve are both in play. The reasoning is that two things are going on at an exposed root, and hydroxyapatite works on the open tubules while potassium calms the nerve, with neither able to do the other's job. The Oral Health Foundation names potassium nitrate among the toothpaste ingredients that help with sensitivity, alongside potassium citrate and stannous fluoride, and advises a soft toothbrush and gentle brushing in small circular movements¹. Relief from this kind of paste builds over weeks, and S3 is judged at two to four weeks, which is exactly why it is the wrong thing to wait on for a crack, a filling or decay.

What the paste cannot do matters as much. None of its ingredients closes a crack, refits a filling or fills a cavity, and a gum that has receded does not grow back because of a toothpaste. The dentist's own options for sensitivity at the gum line, from applying a desensitising treatment or recommending a high-fluoride toothpaste to placing a filling over a worn area near the gum or treating gum disease, are on the Oral Health Foundation's list¹. If the sensitivity at the gum line turns out to be on several teeth rather than one, acid wear may be part of it, and the Journal's page on tooth enamel erosion explains that route; the guide to gum recession and sensitivity covers why exposed roots hurt and what daily care can change.

What will a dentist do, and what will it cost?

A dentist will ask when it hurts and what sets it off, look at the tooth and its neighbours, and may test the bite, try cold on each tooth and take X-rays; what you pay depends on what they find. In England, as shown on nhs.uk on the tenth of September 2026, an examination, with X-rays if clinically needed, falls in Band 1, at £27.90; a filling or root canal treatment in Band 2, at £76.60; and a crown in Band 3, at £332.10⁶. The same page's paragraph on scaling prints £27.40 and £75.30 for the first two bands, so check the figures on the day you book⁶. You pay once for the highest band in a course of treatment, some people pay nothing, including under-18s and anyone pregnant or with a baby under a year old, and charges are set separately in Scotland, Wales and Northern Ireland⁶².

What happens next follows the fingerprint. For a crack, the dentist may use a bright light, a dye or a 3D scan because an ordinary X-ray often misses it, and a larger crack usually needs a crown, with root canal treatment first if the nerve is affected³. For a filling that sits high or has worn, loosened or broken, the fix is usually an adjustment or a new filling, and one urgent filling is included in the urgent treatment charge of £27.90⁶. For decay, putting fluoride on the teeth is part of the first band, while a hole means a filling⁶². For recession, the examination looks at the gums as well as the root; scaling, if clinically needed, is usually in the first band, and the urgent charge list includes treatment of sensitive dentine or cementum⁶.

Book a routine appointment for a single tooth that has turned sensitive; do not wait on a paste first. The NHS says to see a dentist, not your GP, for toothache that lasts more than two days, does not go away with painkillers, or comes with a high temperature, pain when you bite, red gums, a bad taste or a swollen cheek or jaw¹¹. The page on free and low-cost NHS dental options explains who pays what, and the page on what a dentist checks for sensitive teeth walks through the examination.

Frequently asked questions

Can S3 help a tooth that went sensitive after a filling?

Start with the two signs that send it back to the dentist: pain when you bite on it, and pain that lingers or keeps growing¹³. Either one needs the filling checked, and a toothpaste should not be used to wait it out. For a twinge to cold that is clearly easing, nobody appears to have tested a home sensitivity toothpaste, ours included, on a newly filled tooth. A PubMed search for this page, pairing post-operative sensitivity with toothpaste, dentifrice or desensitising agents and fillings, returned nineteen records, and those that looked at a treatment looked at agents a dentist applies in the chair before or under the filling. So this page makes no claim for our paste on a new filling, and the Journal's page on sensitivity after a filling covers what usually settles.

Do cracked teeth show up on X-rays?

Often not. The Oral Health Foundation explains that a crack has to line up with the X-ray beam to be seen, so a dentist may use a bright light, a dye or a 3D scan instead³. In the American Cracked Tooth Registry, which followed 2,858 patients with a visibly cracked back tooth, the crack could be seen on a radiograph for 2% of the teeth, according to the investigators' review of their own study¹².

Can a cracked tooth heal by itself?

No. The Oral Health Foundation says that, unlike a broken bone, a cracked tooth cannot heal itself³. The pain can fade, which is easy to mistake for healing: in the three-year follow-up of the registry, most biting pain went away even in cracked teeth that were never treated¹⁸. The crack does not leave with it, and a week or two of comfort tells you little about what is happening inside the tooth, so it still needs to be looked at.

Is one sensitive tooth an emergency?

Usually not, but it is a reason to book rather than to wait. The Oral Health Foundation lists a single affected tooth among its reasons to see a dentist¹, and facial swelling, swelling that is getting bigger or significant pain are its reasons to contact a dentist urgently for same-day care¹³. The NHS sends people to A&E when toothache comes with swelling around the eye or in the neck, or swelling in the mouth or neck that makes breathing, swallowing or speaking difficult¹¹.