Sensitivity or a cavity? The differences that matter, and when to book a dentist.
Teeth feel suddenly sensitive when dentine that used to be covered is newly exposed, by a receding gum, worn enamel or a cavity, and the twinge cannot tell you which of those it is, because the NHS describes sharp pain with hot, cold or sweet things as one of the symptoms of a hole in a tooth1. What to use is a fluoride toothpaste twice a day, with a sensitivity toothpaste if the twinge is spread across several teeth; if it keeps picking out one tooth, or your last dental check was longer ago than the gap your dentist recommended, what to use first is a dentist2. S3 Sensitivity Science™ is a sensitivity toothpaste that keeps fluoride at full adult strength, 1450 ppm in the form of sodium monofluorophosphate.
What was checked25 published studies and reviews, guidance from the NHS, the Oral Health Foundation and NICE, and product information as published by S3
- Decay that is still in the enamel is often not felt at all, and once it reaches the dentine it can bring on the same short twinge with hot, cold or sweet food that an exposed root does, which is how both the NHS and the Oral Health Foundation describe it13.
- Nobody has yet counted how often a newly sensitive tooth turns out to be decayed, so every rule for telling the two apart by feel, including the ones on this page, is clinical teaching rather than a measured test.
- Finding early decay is difficult even from the dentist's chair: two Cochrane systematic reviews rate the evidence on a close visual examination and on X-rays as low certainty, and X-rays on their own picked up fewer than half of the early enamel lesions in the studies they pooled45.
- Unlike the fluoride-free hydroxyapatite pastes, S3 leaves your decay protection in place, but no toothpaste, S3 included, fills a cavity that has reached the dentine; that is a dentist's job.
- NICE asks dentists to set each adult's gap between check-ups somewhere from three months to two years, and the NHS says to see a dentist if you have gone two years without one, so the question to ask about a new twinge is when a dentist last looked61.
Why are my teeth suddenly sensitive: is it sensitivity or a cavity?
It can be either, and in both cases "suddenly" usually describes the day you noticed rather than the day the change began. Tooth decay is a slow process. The Oral Health Foundation describes it as acid made by the bacteria in plaque each time sugar arrives, softening the surface and gradually dissolving it, with each acid attack lasting around an hour and saliva repairing some of the early damage in between3. Trouble builds when sugar comes often, particularly between meals, because the teeth are then left under attack with little time to recover3.
A receding gum or thinning enamel moves at a similar pace. What changes overnight is the moment a lesion, or a patch of root, crosses the point where a cold drink can reach the nerve, and the next glass of water announces it. That cuts both ways. A twinge that feels new does not mean the cause is new, so a tooth that has been quietly decaying for months can present exactly like one that has just lost a sliver of gum. And because decay is a process rather than an event, its early part is the part fluoride can still act on, which comes up further down.
The Journal's article on why teeth can turn sensitive all at once runs through recent dental work, recession, cracks, acid and grinding as causes of an abrupt start. This page stays with the possibility that worries people most, a hole, and with the question underneath it: can you tell from the pain, and if not, who can?
Why does decay feel like sensitivity?
Because decay that hurts has usually reached the same layer that a receded gum or worn enamel lays bare, and that layer is dentine. The Oral Health Foundation's description of a tooth works as a map here: enamel, the hard outer layer, does not feel pain; dentine, underneath it, is softer and contains tiny nerve endings, "which is why decay here can cause sensitivity"; and the pulp at the centre holds the nerves and blood vessels3.
Read the stages of decay against that map and the overlap is plain. While decay is still in the enamel you may not feel anything; as it reaches the dentine, teeth may become sensitive to hot, cold or sweet foods; and if it reaches the pulp, pain can become severe, an abscess may form and the tooth may need more complex treatment or removal3. The NHS puts it in its own words: decay may cause no symptoms at first, and once a hole has formed there may be toothache, sharp pain when eating or drinking hot, cold or sweet things, and white, brown or black spots on the tooth1.
Dentine is dentine, whatever uncovered it. A standard review of the condition describes dentine hypersensitivity as a short, sharp pain that arrives once a lesion has opened the dentine's tubules to the pulp, transient but arresting7. Nothing in that description separates a tubule opened by a shrinking gum from one opened by acid from plaque. Sugar has its own page, on sweet sensitivity and when it points to decay; here it is enough to say that the sweet trigger does not settle the question either.
What can you notice yourself, and what can you not?
You can notice the pattern of the pain, and it is worth noticing, but most of what separates sensitivity from decay is out of sight. Start with where ordinary sensitivity tends to live. In a cross-sectional clinical study of 1,210 dental patients in Turkey, cold was the trigger reported by 97.1% of those diagnosed, incisors were the teeth most often involved, and cheek-facing surfaces were affected far more often than tongue-facing ones, 86.3% against 52.7%8. An industry-funded study across seven European countries, paid for by a toothpaste manufacturer, found the same geography in 3,551 adults: sensitivity most common in the lower front teeth and on the cheek-facing surfaces, where it went with gum recession and acid wear9.
That describes a condition that usually affects several teeth, at the neck, on the side you can see in a mirror. Decay is not bound to that picture, and the surfaces where teeth touch each other, which no mirror shows, are among the hardest places to find it even for a dentist17. The Oral Health Foundation's list of reasons to see a dentist about sensitivity is short for that reason: pain that is severe, sensitivity lasting more than a few weeks, only one tooth affected, or pain that comes on suddenly, any of which "could be signs of tooth decay, a cracked tooth, gum problems or infection"2. If it is one tooth, the pages on one tooth suddenly turning sensitive and on telling a cracked tooth from a sensitive one go through the other causes.
Timing is the next clue. Sensitivity from exposed dentine is brief and tied to its trigger7. Pain that stays after the trigger has gone points past the dentine towards the pulp, and an inflamed pulp blurs the map further, making its healthy neighbours react more to cold as well, according to a clinical study of 64 patients in which that effect faded once the inflamed tooth was treated10. The page on sharp and brief, or dull and lingering pain takes the patterns one by one. Pain when you bite, a high temperature, red gums, a bad taste or a swollen cheek or jaw are on the NHS list of reasons to see a dentist about toothache11.
What nobody can give you is the odds. No study has counted how often a newly sensitive tooth turns out to be decayed. A PubMed search run for this page on the tenth of September 2026, pairing every common name for sensitive teeth with decay and with diagnosis, returned fifty-four records, and a second search looking for predictive values, or for the prevalence of decay among sensitive teeth, returned twenty-five. They are surveys of sensitivity, studies of worn necks and receding gums, and reviews; not one starts from people who feel a new twinge and counts how many have a cavity. The table below is therefore built from guidance and from clinical teaching, and its fifth column says which is which.
The last column says what a sensitivity toothpaste such as S3, which pairs a tubule-blocking mineral with a nerve-calming active, can and cannot do in each case.
| What you notice | Leans towards sensitivity | Leans towards decay | Can you tell at home? | What this rests on | What a sensitivity toothpaste such as S3 does for it |
|---|---|---|---|---|---|
| Several teeth, or one tooth | Several teeth, often the front ones | The same single tooth, every time | Partly: you can count teeth, not see inside them | The Oral Health Foundation lists one affected tooth as a reason to see a dentist2; incisors were the teeth most often involved in a clinical study of 1,210 patients8 | Made for sensitivity across several teeth; for one tooth it is no substitute for a look |
| Near the gum, or between the teeth | The neck of the tooth on the cheek side, where gum has receded | Between the teeth, where it cannot be seen, and on exposed roots in older adults | No: both happen at the gumline, and between the teeth nothing shows | Sensitivity at cheek-facing necks in an industry-funded European study9; a direct look between teeth is mostly impossible17; root decay common with age29 | Works on open dentine at the neck; does nothing to a lesion between the teeth |
| Brief, or lingering | Sharp, and over within moments of the trigger going | Lingers or throbs, as decay nears the pulp | Partly: timing is a clue, not a test | Brief pain in a standard review7; wider cold response from an inflamed pulp in a clinical study of 64 patients10 | May quieten the brief twinge; lingering pain is an appointment |
| A spot or a hole | Nothing to see | White, brown or black spots, or a hole | Sometimes, on surfaces you can see; not between the teeth | NHS tooth decay guidance1 | Nothing; a hole needs a filling |
| Pain when you bite | Not the usual pattern | Possible with a deep lesion, and with a crack | No | NHS toothache guidance lists pain when you bite as a reason to see a dentist11 | Nothing |
| Wakes you at night | Not typical of dentine sensitivity | Suggests the pulp is involved | No | Clinical teaching, not measured | Nothing |
| Started after a change in diet or brushing | Hard brushing, a new acidic drink, brushing straight after acid | Sugar more often, especially between meals | No | Oral Health Foundation lists of causes23 | Helps the sensitivity; the habit is yours to change back |
Dentists face a version of the same problem, which is why sensitivity is the diagnosis they reach last. A 2020 evidence-based overview for practitioners states that there is no universally accepted guideline for telling dentine hypersensitivity apart from the conditions that mimic it at different stages12. A 2019 clinical review written for UK primary dental care says the symptoms patients describe have several possible causes, so a firm diagnosis is difficult13. In 2003 a Canadian advisory board of dentists and hygienists built a simple diagnostic algorithm for clinicians, because a survey had shown confusion about how to diagnose the condition14. The gap persists in research: a 2026 scoping review and Delphi consensus of 72 papers found that few studies apply every part of the accepted definition, least of all the step that excludes other causes of tooth pain15.
How does a dentist find decay you cannot see?
By examining the teeth closely and adding X-rays where the eye cannot reach, and the published evidence on how accurate each of those steps is carries low certainty. Five Cochrane diagnostic reviews have looked at the tools, and their findings are more useful for their shape than for any single number. The page on what a dentist checks for sensitive teeth describes the appointment itself; this section is about how well the looking works.
The ordinary tool is a careful look. A 2021 Cochrane systematic review of 67 studies of visual examination with a scoring system, for early decay still confined to the enamel, arrived at summary figures of 0.86 for sensitivity and 0.77 for specificity: across the studies most decayed surfaces were identified, and roughly one healthy surface in four was wrongly flagged4. Its authors are blunt about how far to trust that. Of the 67 studies, 48 were done on extracted teeth, individual results ranged from 0.16 to 1.00, the certainty was low, and the range in which a future study's result should fall was very broad4.
A scoring system is also not what every check-up involves. An analysis that pooled five Cochrane reviews points out that most dentists in primary care do not apply a comprehensive visual scoring system such as ICDAS to every patient, so early lesions risk going unnoticed in routine practice, which is where its authors think extra devices could earn their place16.
X-rays are the second tool, with the opposite profile. The Cochrane systematic review of imaging for early enamel decay, covering 77 studies, reported a summary sensitivity of 0.47 and a specificity of 0.88: images rarely called a healthy surface decayed, and missed more than half of the early lesions that were there5. Only 17 of the 77 studies were carried out in a clinical setting, and the review graded its certainty as low5. When the five Cochrane reviews were compared with each other, radiographic imaging was the least sensitive of the five technologies for early enamel decay, while their specificity was similar16. None of this means X-rays miss cavities: the reviews were about lesions still confined to the enamel, the stage a dentist would manage with fluoride rather than a filling5.
Between the teeth the eye has even less to work with. A 2021 systematic review and meta-analysis of diagnostic studies on the surfaces where teeth touch accepted 129 studies at first, kept 36 after screening for bias and poor reporting, and counted only five of those carried out in patients17. Its authors point out that a direct look at those surfaces is mostly impossible in a mouth, which is why bitewing X-rays are the usual extra step, and they conclude that bitewings and laser fluorescence performed well while warning that the clinical data are too few to lean on17. The patient data show the gap: in the two clinical studies of visual examination alone for decay that had reached the dentine, looking picked up about a third of it, a pooled sensitivity of 0.32, whereas single clinical studies of digital bitewings reported 0.83 and 0.9617.
Exposed roots are the thinnest part of the evidence. The Cochrane systematic review of tests for root decay could find only four studies, covering 4,997 root surfaces, was unable to pool them, and rated the certainty very low; its conclusion is that a dentist's visual and tactile examination is the mainstay, and that no device has been shown to add to it18.
| How decay is looked for | What it does well | What it misses | Certainty of the evidence | Source |
|---|---|---|---|---|
| A close look, with a scoring system | Identified most early enamel lesions in pooled studies (summary sensitivity 0.86) | About one healthy surface in four wrongly flagged; most studies used extracted teeth; many practices do not score every patient this way | Low | Cochrane review of visual examination4; analysis of five Cochrane reviews16 |
| Bitewing and other X-rays | Rarely calls a healthy surface decayed (specificity 0.88); the usual extra check between the teeth | More than half of early enamel lesions (sensitivity 0.47) | Low | Cochrane review of imaging5; review of between-teeth studies17 |
| Fluorescence, and light shone through the tooth | More sensitive than X-rays for early enamel decay in the pooled comparison | Specificity similar to the other tools; few clinical studies | Low | Analysis of five Cochrane reviews16 |
| A look alone, between the teeth | Little: a direct view is mostly impossible there | About two thirds of decay into dentine in two clinical studies (sensitivity 0.32) | Not graded; very few clinical studies | Review of between-teeth studies17 |
| Any test on an exposed root | A visual and tactile examination is the mainstay | Whether any device adds to it is unknown | Very low | Cochrane review of four studies18 |
What can a toothpaste do about decay, and what can it not?
Fluoride toothpaste works on decay before there is a hole, and nothing in a tube works on the hole. The NHS advice for preventing decay starts with brushing at least twice a day with a fluoride toothpaste, spitting rather than rinsing; for early decay a dentist can prescribe fluoride treatments such as a varnish or a mouthwash to reverse it, a hole will probably need a filling, and decay that has reached the pulp may need root canal treatment1. Saliva does some of the early repair on its own, neutralising acid and hardening the enamel again3. Sodium monofluorophosphate is an established form of fluoride for this: in a double-blind randomised trial over 36 months in 2,222 schoolchildren, whose funding is not stated in the record, a monofluorophosphate paste held back decay as well as a sodium fluoride paste at the same fluoride level19.
Hydroxyapatite has its own caries evidence, and the fair reading of it is "about as good as fluoride", not "better". In a double-blind randomised trial of 189 adults over 18 months, whose authors include scientists employed by the manufacturer of the paste, a fluoride-free hydroxyapatite toothpaste was non-inferior to a fluoride one20. In 150 orthodontic patients at high risk of decay, a six-month randomised trial paid for by a maker of hydroxyapatite toothpaste found no significant difference from a fluoride paste in new enamel lesions around the brackets21. Two systematic reviews that pool this work reach a favourable conclusion for hydroxyapatite used without fluoride, and both have manufacturer-affiliated authors, one of them paid for by a maker of hydroxyapatite toothpaste as well2223. The one randomised trial that kept the fluoride and added hydroxyapatite to it, in 610 children followed for two years, saw more active enamel lesions turn inactive than with a monofluorophosphate paste, and no significant difference for lesions that had reached the dentine24.
So S3's defence against new decay is its fluoride, kept at full adult strength. The hydroxyapatite caries trials above show that ingredient roughly matching fluoride rather than beating it, and most of them come from authors tied to one manufacturer202124. Early decay in the enamel is the stage where minerals can still help a softened surface; the page on nano-hydroxyapatite and remineralisation goes through what happens there. Once the hole reaches the dentine, the NHS answer is a filling1.
Where does S3 sit while you wait for a dental check?
As a daily toothpaste for sensitivity that is spread over several teeth and follows a brief, provoked pattern, and never as a way of finding out whether a tooth is decayed. Its actives are aimed at the two faults behind an exposed-dentine twinge: S3's hydroxyapatite works on the open tubules and its potassium on the nerve's readiness to fire, and neither can do the other's job. Its fluoride is sodium monofluorophosphate at 1450 ppm, chosen because it does not react with the calcium in the hydroxyapatite while both sit in the tube. S3's three actives and its fluoride are there for open dentine, an over-ready nerve and the enamel surface; none of them fills, heals or reverses a cavity that has reached the dentine, and neither does any toothpaste.
That design has a consequence this page has to spell out. A sensitivity toothpaste works on the twinge from open dentine whatever opened it, which means that if decay is the cause, the paste can make its only warning quieter. Whether that delays anyone's diagnosis has never been measured: a PubMed search on desensitising products and masked or delayed diagnosis returned twenty-one records, a second pairing sensitivity pastes and hypersensitivity with decay and missed or delayed diagnosis returned seven, and none of them examines whether a sensitivity product holds back a diagnosis of decay. It is an inference, and this page would rather state it as one than wave it away.
There is a second limit, about the actives themselves. The most recent network meta-analysis of desensitising toothpastes, covering 93 randomised trials, names stannous fluoride and arginine as the first-line options for self-care25, and S3 contains neither of them. Potassium nitrate, S3's nerve active, has a more divided record: the Cochrane systematic review of potassium toothpastes measured less sensitivity to an air blast and a probe at six to eight weeks, saw no significant change in how patients themselves rated it, and concluded that there is no clear evidence to support the pastes26.
Put together, the sensible use of a paste like this while you wait is narrow. If several teeth give a brief twinge, none of the warning signs in the next section applies, and your last check falls within the interval your dentist gave you, a sensitivity toothpaste used morning and night is a reasonable thing to try, judged over a few weeks and not on the first evening. If one tooth keeps doing it, or the pain lingers, or you cannot remember your last check, book first; the paste can wait until someone has looked. The page on how long to try a sensitivity toothpaste before seeing a dentist covers the timing in detail.
When should you book, and how soon?
Book promptly if the pain has lasted more than two days or any of the NHS warning signs is present, book soon if a single tooth keeps reacting or you can see a spot or a hole, and otherwise make sure you are seen within the interval your dentist set, which for an adult is somewhere between three months and two years116.
The NHS threshold for toothache is two days. It advises a dental appointment when the pain has gone on longer than that, when painkillers are not touching it, or when it comes with a high temperature, pain on biting, red gums, a bad taste or a swollen cheek or jaw, and it is clear that a GP cannot provide dental treatment11. Swelling around the eye or in the neck, or swelling that makes it hard to breathe, swallow or speak, is a matter for A&E rather than a dental list11. Without a dentist, or without an urgent appointment, the NHS route is to call 111 or use 111 online, or to ask practices near you for an emergency slot11; the page on free and low-cost NHS dental options goes through the rest.
For a twinge that has not become toothache, the Oral Health Foundation's markers are the ones to check against yourself: severe pain, sensitivity lasting more than a few weeks, a single tooth, or a sudden start2. The last two describe the reader this page was written for, and both point to a dentist before a tube.
If none of that applies, the question becomes how long it has been. NICE's guideline on dental recall asks the dental team to choose each patient's interval from an assessment of their disease and their risk, with three months as the shortest and 24 months as the longest for anyone aged 18 or over, and it tells patients that new disease can still develop between visits, which is why they are asked to seek advice before the next review if their risk changes6. The NHS check-up page gives the same span in months and years, and expects someone whose mouth is healthy to be seen every one to two years, with shorter gaps for people who have more problems27.
The UK evidence behind letting the gap vary comes from the INTERVAL randomised trial, which followed 2,372 adults in 51 UK dental practices for four years and found no difference in gum bleeding or in oral health-related quality of life between six-monthly and risk-based check-ups, or, among the 648 people their dentists judged suitable, between those and two-yearly ones28. Two limits keep that result from reaching this page's reader: it measured gum bleeding rather than decay, and everyone taking part had seen a dentist within the two years before they joined28.
Age shifts the odds on an exposed root. A review of the epidemiology of root decay reports its prevalence anywhere between 25% and 100% across published studies and concludes that most find the burden high in older people, while warning that the studies are too different to yield a single figure29. In a longitudinal study of 358 South Australians aged 60 or over, examined four times across 11 years, untreated decay on root surfaces kept accumulating, by about 0.07 surfaces a year, and more so among people who brushed irregularly, smoked, or went to a dentist only when something was wrong30. A root that starts to twinge in your sixties is therefore a weaker bet for "just sensitivity" than the same twinge in your twenties29, and the page on sensitivity and age takes that further. For decay already on a root, a dentist can prescribe a stronger fluoride toothpaste: in a six-month randomised trial of 130 adults with root caries, whose pastes and per-patient payments came from the maker of the stronger paste and two of whose authors were its employees, root lesions hardened more with 5,000 ppm fluoride than with 1,350 ppm31.
So work out your own interval. If your dentist gave you one and you are inside it, a brief twinge on several teeth can wait for that visit, unless it lasts more than a few weeks or changes. If you have no idea when you were last seen, or it was more than two years ago, treat that as your answer and book.
Frequently asked questions
Will S3 hide a cavity?
It could make a cavity's twinge quieter, and it would do nothing to the cavity. S3's potassium works on the nerve and its two hydroxyapatites on the tubule and the surface, and a tooth whose dentine was opened by decay gives those actives the same target as one opened by a receding gum. If that twinge is the only sign of decay, a quieter twinge is a quieter warning; nobody has measured whether that delays a diagnosis, so treat it as a reason to book a check rather than as an established risk. The fluoride in S3, 1450 ppm as sodium monofluorophosphate, helps protect the rest of your teeth against new decay, and the hole itself still needs a dentist.
Can a cavity be there without any pain?
Yes, and early on that is often how it is. The NHS says decay may not cause any symptoms at first, and the Oral Health Foundation says that while decay is still in the enamel you may not feel anything at all13. How often decay in adults is painless is not something this page can put a number on: a PubMed search for it, run on the tenth of September 2026, returned thirty-eight records, mostly population surveys of toothache, and none gives the share of decayed teeth that do not hurt. That silence is the case for being seen at the interval your dentist sets.
Can toothpaste reverse early decay?
Fluoride can help early decay that is still confined to the enamel, and no toothpaste reverses a cavity. The NHS describes dentist-prescribed fluoride varnish or mouthwash as a way to reverse early decay and a filling as the usual answer to a hole, and it recommends a fluoride toothpaste at least twice a day, spat out rather than rinsed away1. Hydroxyapatite pastes have randomised trials showing them roughly equal to fluoride against new decay, run by authors employed by, or paid for by, a maker of those pastes2021.
How often should I have a dental check-up?
As often as your dentist decides from the state of your teeth and gums, which for an adult is somewhere between every three months and every two years6. In the INTERVAL trial, adults who were already attending showed no difference in gum bleeding over four years whether they were seen every six months, at a risk-based interval or, if judged suitable, every two years28. If you do not know your interval, ask the practice; if you have not been seen for two years, the NHS says to see a dentist1.
What if I cannot get an NHS dental appointment?
Call NHS 111 or use 111 online for advice, and ask dental practices near you for an emergency appointment, which is the NHS's own route for people without a dentist11. The page on free and low-cost NHS dental options sets out the rest.
Where S3 sits
The twinge of sensitivity and the twinge of early decay can be the same twinge, so the useful answer to "which is it?" is a dental check within your interval, and a cavity is never a toothpaste's job. For brief sensitivity across several teeth in the meantime, a paste needs one ingredient for the open tubule and one for the nerve, because hydroxyapatite occludes, potassium desensitises and neither does the other's job. S3 carries both with full-strength fluoride kept in, so it does not trade decay protection for sensitivity actives, and it is owned by more than 20 UK dentists.
S3 Sensitivity Science™ pairs potassium nitrate with two hydroxyapatites and adult-strength fluoride in one daily paste.
See the toothpasteS3 Sensitivity Science™ is a daily toothpaste built around 5% potassium nitrate, with nano-hydroxyapatite at 10% and biomimetic hydroxyapatite at 5%, both measured as solution, and fluoride held at full adult strength. It sets out to calm the nerve, strengthen the enamel surface and protect against further wear, all from the one tube. Its formula, S3 Repair Technology™, is patent-pending under UK application GB2604755.5. Read more about S3.