Tooth sensitivity - why cold hurts and what actually helps

Cold-triggered pain in five sentences

• Tooth sensitivity is pain that lasts a few seconds and ends together with the stimulus. 
• It arises when the layer beneath the enamel is exposed and the microscopic tubules running through it are opened.
• For cold-triggered pain, a clear advantage over ordinary fluoride toothpaste has been confirmed only for calcium sodium phosphosilicate (CSPS), one type of bioactive glass, and the time needed to achieve an effect depends on the product; improvement has also been observed before four weeks.
• Pain that outlasts the stimulus, or that wakes you at night, points more towards pulpitis, a crack or decay, and calls for an appointment within a few days.

A tooth reacts to cold in two entirely different ways, and each of them is treated differently. The first is tooth sensitivity: a sharp twinge that dies away with the mouthful of cold water; the second is pulpitis, inflammation of the tooth’s living interior, in which the pain stays on long after the stimulus has gone. Patients call both by the same name. They are entitled to, because from the outside the two look identical. Tooth sensitivity, known clinically as dentine hypersensitivity, is short, sharp pain provoked by an external stimulus, which subsides immediately once that stimulus is removed. The difficulty is that no examination confirms tooth sensitivity directly; it is diagnosed by excluding everything else that causes pain from cold. This article is about the symptom: where cold-triggered pain comes from, and how you will recognise that it has crossed the boundary of sensitivity.

Why cold hurts at all

A healthy tooth does not hurt from cold, even though it has a nerve inside, because it is protected by enamel and, near the root, by a thin layer of cementum and by the gum. Beneath that cover lies dentine, the main tissue the tooth is built from, and it is not solid: thousands of microscopic fluid-filled tubules run through it, from the surface towards the pulp, the living interior of the tooth with its vessels and nerves.

Once the cover is gone, the openings of the tubules stand exposed. Cold, a blast of air or the touch of a brush then set the fluid in the tubules moving abruptly, and it is that movement which irritates the nerve endings at the outer edge of the pulp. So the nerve is not measuring temperature. It is responding to the fact that fluid in the tubules has shifted. This account, known as the hydrodynamic theory, explains most observations but not all of them: the cells lining the dentine have cold sensors of their own, and pain can persist even when the tubules have been tightly sealed. The matter is not settled - worth knowing before anyone promises that all it takes is to “plug the holes”.

The practical conclusion is stable: a tooth reacts to cold only in a particular state. Tooth sensitivity requires two conditions at once: exposed dentine and open tubules. Hence two routes of treatment: seal the tubules, or lower the excitability of the nerve. Almost every toothpaste and every procedure described below does one or the other.

Five ways dentine becomes exposed

The scale of tooth sensitivity is greater than what patients report would suggest: a study across seven European countries examined more than 3,500 adults, testing how their teeth responded to a blast of air. Symptoms were found in three out of four participants. The authors point out that this is more than in most earlier work, because the study measured the tooth’s response, not whether the patient considered it a problem.

The cause of tooth sensitivity can usually be identified during the examination. In some patients several causes act at once. Simply switching toothpaste is then only half a solution.

Gum recession

The gum moves towards the root and exposes the neck of the tooth, hence the colloquial name sensitivity at the gumline; and an exposed neck has no enamel, being covered by a thin layer of cementum that wears away within a few years. In the same European study, close to nine adults in ten had a gum that had receded by at least a millimetre, and symptoms occurred more often among them. A high figure does not mean the symptom is trivial. It means that an exposed neck on its own settles nothing. Whether it will hurt is decided by the second condition: whether the tubules are open. A receding gum has causes of its own - from brushing technique to the state of the periodontium - and calls for separate management: gum recession.

Wedge-shaped notches and other cervical lesions

A wedge-shaped notch will not reverse itself, and it deepens for as long as the cause is at work. Shallow lesions are managed conservatively, together with correcting the brushing technique and assessing occlusal overload. Deeper ones, reaching into dentine, are restored with composite, which also seals the exposed surface. Wedge-shaped notches are wedge-like indentations right at the gum, one form of non-carious cervical lesion. Decay does not make them. They are made by a combination of brush pressure, occlusal overload and acids, and the proportions of those three are still under investigation. In a laboratory model on extracted teeth, acid combined with variable occlusal loading produced the greatest tissue loss precisely at the neck, which is consistent with what is seen in practice.

Erosion and wear

Citrus juices, wine, fizzy drinks, effervescent tablets and reflux dissolve enamel chemically, and mechanical wear adds to this, for instance in bruxism; in the European study, symptoms were reported more often by participants who complained of heartburn. What counts for enamel is how often it meets acid - not the size of any single serving: diet and dental health. Enamel erosion, the chemical dissolution of the tooth by acids, is a structural cause and will have an article of its own.

After dental procedures

The reaction after whitening is predictable and in most patients temporary. It can also be temporary after scaling and after a deep filling. A review comparing in-office with tray-based at-home whitening found that the home method hurts less, while the chance of any pain at all is similar for both; the certainty of that finding is low, meaning further studies may change it: teeth whitening at the dentist and at home.

Cracks that reach the dentine

Superficial craze lines within the enamel itself usually do not hurt, and it is cracks reaching the dentine that matter, because they open a route into the tubules at a single point. The signal here differs from classic sensitivity: one tooth hurts, and it hurts characteristically at the moment the pressure is released after biting down. Not on every contact with cold.

What desensitising toothpaste does, and after how long

In trials, the timing of effectiveness assessments varied by product; improvement was also reported before four weeks. For some people that is enough. For cold-triggered pain, a clear advantage has been confirmed only for calcium sodium phosphosilicate (CSPS), one type of bioactive glass. For stannous fluoride, potassium and arginine the data are strong with other stimuli.

How this is known. A meta-analysis of 125 trials involving more than 12,000 people compared active ingredients, and several performed clearly better than ordinary fluoride toothpaste, among them:

• calcium sodium phosphosilicate (CSPS), one type of bioactive glass (a material that deposits in the openings of the tubules),
• stannous fluoride,
• potassium,
• arginine (an amino acid also present in saliva).

The result depended, however, on the type of stimulus. On the ingredient list on the pack, calcium sodium phosphosilicate appears as Calcium Sodium Phosphosilicate (CSPS; sometimes with the note NovaMin), and if that name is not there, the toothpaste may work on other stimuli - but for cold specifically the evidence is weaker. A more recent review of 32 trials involving more than 4,600 people upheld the recommendation for formulations with stannous fluoride, potassium and arginine used twice daily.

The reviews compare ingredients against one another and give no single figure for the amount of relief, so there is no answer to the question “by how much better”. Your own result may also be weaker than in a trial: participants are selected, they brush under supervision and usually have a single cause of exposed dentine, whereas in the surgery two or three are visible at once.

In our everyday clinical practice at Modern Dental & Orthodontics (Klinika MDO) we encounter patients who have changed three toothpastes before anyone looked at the way they brush.

None of those toothpastes could remove the cause, because nobody had checked what had exposed the dentine.

Twice daily is a condition, not a suggestion: these preparations seal the tubules gradually, or quieten the nerve, and they need time. In the European study, people using an electric toothbrush had symptoms less often. This was an observational study: it shows co-occurrence, it does not prove cause.

What you can do today

• After brushing, rub a little toothpaste into the painful spot with a finger and do not rinse the mouth vigorously afterwards.
• Change to a soft brush and brush without pressure, because hard bristles speed up wear at the necks of the teeth.
• After an acidic meal, wait before brushing.

This does not treat the cause. In some people it does, however, reduce the complaint before the treatment takes effect.

The limit of home measures is clear. Eight weeks without improvement, with two applications a day, means the cause requires a dental practice, not another toothpaste.

What the dental practice adds

In the surgery, tooth sensitivity is above all a diagnostic problem. The exclusion has a definite sequence. The clinician directs a stream of air and cold onto tooth after tooth, checking which one responds and how long the pain lasts after the stimulus. Then biting is tested, because pain on release of pressure argues for a crack, while a radiograph can help assess the presence and extent of caries; pulp status is assessed from the history and clinical tests. Finally the clinician assesses brushing, the occlusion and the extent of recession. Tooth sensitivity is what is left at the end of that path, though sometimes nothing tangible is left at all - no recession, no lesion, no crack - and yet there is pain. The symptom itself is then treated.

One result is worth knowing before the appointment. In a six-month randomised trial, in a group of 51 patients, toothpastes with stannous fluoride or with bioactive glass performed better at three months than fluoride varnish applied in the practice. Immediately after application the varnish came out ahead only of the bioactive glass paste, and only for the tactile stimulus. The group was small, so the advantage needs confirming in a larger one. On some measures no difference is visible, which does not mean there is none.

Fluoride varnishes and desensitising agents are applied to the necks of the teeth, and over six months and longer the best-lasting were glutaraldehyde-based agents, which coagulate proteins within the tubules, and low-level laser, which instead of blocking the tubules lowers the excitability of the nerve. After a week almost everything looks effective. What a procedure is worth is told only by the review a few months later.

A separate option is silver diamine fluoride (SDF): in a review of four studies it reduced reported pain intensity by 23 to 56 per cent, but there are few studies, and the agent darkens dentine, which rules it out for teeth that show in the smile.

Where the cause is a distinct lesion, more sense than further varnishes may lie in restoring the lesion with a composite filling, which seals the exposed surface mechanically; with extensive recession, surgical treatment is considered - in a meta-analysis of thirteen studies involving 701 patients, sensitivity after root coverage resolved in roughly seven cases out of ten. The technique is decided by the type of recession: connective tissue graft.

Cause	What the practice does	What you do at home
Gum recession	Desensitising agent on the neck of the tooth; with extensive recession, assessment for root coverage	Toothpaste with bioactive glass, stannous fluoride, potassium or arginine; soft brush
Wedge-shaped notch and other cervical lesions	Composite restoration, assessment of the occlusion	Desensitising toothpaste; brushing without pressure
Erosion and wear	Assessment of the extent of the lesions, varnishing, referral to a gastroenterologist if needed	Fewer acidic drinks; a pause after them before brushing
After procedures: whitening, scaling, deep filling	Change of concentration or protocol, desensitising agent before the next stage	Desensitising toothpaste before the procedure and during treatment
Crack reaching the dentine	Diagnosis under magnification, assessment of the tooth’s prognosis	No home treatment

When it is no longer tooth sensitivity

Tooth sensitivity has a constant pattern: stimulus, a few seconds of pain, end. How long the pain persists is an important clue, but does not by itself determine the diagnosis:

• A few seconds: tooth sensitivity.
• More than ten seconds: more likely reversible pulpitis.
• Longer, spontaneous, at night: irreversible inflammation, a crack, or decay reaching deep.

A departure from the typical pattern requires differential diagnosis by a clinician.

Green flag, meaning observation and toothpaste. The pain is short, subsides immediately once the stimulus is removed, is provoked by cold or a blast of air, and affects several teeth at once, most often on the same side, near the gum. If sweet things hurt, or if one particular tooth hurts, the flag stops being green: that is usually how a cavity announces itself. What to do: desensitising toothpaste for two months and a review at the next appointment.

Amber flag, meaning an appointment within a few days. The pain persists for more than ten seconds after the stimulus is removed, wakes you at night, appears spontaneously, affects a single tooth, hurts on biting or responds to heat. Such a picture argues more for pulpitis, a crack, or decay that has gone deeper than a lesion confined to the enamel. The longer the pain lasts after the stimulus, the stronger the suspicion of advanced pulp inflammation; the extent of treatment depends on the clinical examination and pulp status. Lack of improvement after eight weeks belongs here too. Until the appointment: avoid extremes of temperature and biting on that tooth, and do not warm the cheek. Painkillers may be used, but the fact that the pain went after a tablet excludes nothing.

Red flag, meaning a dentist the same day. Swelling of the cheek or gum, fever, difficulty opening the mouth, enlarged and tender lymph nodes. These are signs of infection, not of exposed dentine. Until the appointment, do not warm the swelling, do not incise it yourself and do not start an antibiotic from the medicine cabinet at home.

Hospital emergency department rather than a dental practice. Difficulty swallowing or breathing, a change of voice, swelling that closes the eye or spreads to the neck.

Frequently asked questions

How long does it take before toothpaste for sensitive teeth works? In clinical trials, the timing of effectiveness assessment varied by product; improvement was also reported before four weeks. Some patients feel the first relief earlier, but a lasting effect requires consistency: the preparation seals the tubules or quietens the nerve gradually, and an interrupted course starts, in practice, from the beginning.

How am I to know whether it is tooth sensitivity or decay? Guesswork gives no certainty; a dental examination does, and the clinician decides whether a radiograph is needed. Decay is suggested, however, by pain from sweet things, by pain that can be assigned to one particular tooth, and by a cavity visible in the mirror or detectable with the tongue. Sensitivity usually affects several teeth at once and announces itself with cold.

Does tooth sensitivity go away on its own? Tooth sensitivity sometimes resolves on its own, because dentine seals its own tubules over time and the symptom can fade without treatment; in the European study the frequency rose in young adults and began to fall roughly between the ages of 38 and 47. It is not worth counting on that, though, if the cause - recession, erosion or a cavity - is still at work.

Does whitening always cause sensitivity? Not always, but often, and it is a predictable reaction. A review of the evidence found that desensitising toothpastes reduced complaints after tray-based whitening with a high concentration of carbamide peroxide (a compound that releases hydrogen peroxide) and after a single in-office procedure, whereas with some protocols there was no difference. The complaints are temporary, and how long they take to settle is individual.

How does tooth sensitivity differ from the pain of pulpitis? By the behaviour of the pain once the stimulus has gone, and the time thresholds are set out in the section on flags. The practical difference is that sensitivity usually involves several teeth and does not wake you at night, whereas pulpitis more often sits in a single tooth, announces itself unprompted and responds to heat as well.

Does hard brushing make things worse? Yes, hard brushing makes sensitivity worse: heavy pressure and hard bristles speed up wear of exposed necks and encourage the gum to recede, and safer are soft bristles and a technique without pressure, with a sweeping movement from the gum towards the edge of the tooth. After an acidic meal it is worth waiting before you reach for the brush.

Do mouthwashes help with sensitivity? A mouthwash will not replace a desensitising toothpaste and will not remove the cause of the symptom, though it can be an adjunct; the strongest data concern toothpastes used twice daily, and the reviews cited here did not assess mouthwashes separately. An exposed neck or a deepening lesion requires assessment in the practice, not a change of preparation.

What toothpaste will not do in the dentist’s place

Toothpaste acts on the symptom and on the symptom only. It will not restore a lesion, will not reverse recession, will not change an acidic diet or an occlusal overload. Once it is stopped, the complaints return in some people. That is not an argument against toothpastes, but a marker of their limit. Eight weeks is time to check whether the symptom can be quietened, not time to postpone diagnosis. Tooth sensitivity is diagnosed by exclusion, so pain that has stopped disappearing along with the stimulus has stopped being a matter to settle in the bathroom.

Read more:

• Aesthetic and Restorative Dentistry
• Gum recession — why the gum recedes and when surgical treatment is needed
• Connective tissue graft (CTG) — how to cover exposed root surfaces
• Teeth whitening at the dentist and at home. Which methods are safe for your teeth?
• Tooth decay stages: when can it be stopped without drilling

Content and liability disclaimer

This article is informational and educational in nature and does not constitute medical advice, a diagnosis or a therapeutic recommendation — it does not replace a consultation with a specialist. If you are experiencing symptoms, have doubts or are facing a decision about treatment, consult a dentist. The methods described and the data cited are general in nature. The results of scientific studies relate to populations, not to an individual patient. The course and outcome of therapy depend on the individual clinical situation and may vary between patients. No information contained in this article constitutes a guarantee of result. The content has been prepared with due care, based on publicly available medical knowledge and the scientific publications indicated in the Sources section. We do not advise taking or refraining from any health-related action solely on the basis of the content of this article, without prior consultation with a doctor.

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