Short answer: tooth sensitivity happens when the dentine underneath your enamel becomes exposed, either because enamel has worn away or because the gum has receded and left the root surface uncovered. Dentine contains microscopic tubules that run towards the nerve, so cold, heat, sweetness or pressure at the surface registers as a sharp sensation. A brief zing that stops as soon as the stimulus is removed is usually surface sensitivity. Pain that lingers, throbs, wakes you at night, or is confined to one specific tooth is a different problem and should be looked at rather than managed with a toothpaste.
That distinction between a short sharp response and a lingering ache is the most useful thing in this article, and it is what the rest of it builds on.
What is actually happening when a tooth is sensitive?
A tooth has three relevant layers. Enamel is the hard outer shell on the crown of the tooth, and it contains no nerves. Underneath it is dentine, which is softer, and which is threaded with thousands of microscopic channels running inwards. At the centre is the pulp, which contains the nerve and blood supply.
When enamel is intact and the gum covers the root, dentine is sealed off and you feel nothing. When dentine becomes exposed, those channels are open at the surface. Cold, heat, sweet or acidic food, or even air, causes fluid movement inside the tubules, and the nerve interprets that movement as a sharp, short lived pain.
The key point is that sensitivity is a symptom rather than a diagnosis. It tells you that dentine is exposed somewhere. It does not tell you why, and the why is what determines whether anything needs to be done.
Cause 1: gum recession and exposed root surface
This is the most common cause in adults. When gum tissue recedes, it exposes the root of the tooth. Root surface is covered by a thin layer called cementum rather than enamel, and that layer wears away readily, leaving dentine open.
Recession itself has several drivers, including gum disease, brushing too hard or with a firm brush over many years, grinding and clenching, tooth position, and simply having thin gum tissue.
Exposed root is worth taking seriously beyond the discomfort, because root surface has no enamel and decays more readily than the crown of the tooth. Sensitivity at the gum line is often the first thing that draws attention to recession that has been developing quietly for years.
Cause 2: acid erosion thinning the enamel
Erosion is chemical rather than bacterial. Dietary acid, reflux or repeated vomiting dissolves enamel across broad surfaces rather than in the sheltered spots where decay starts.
Eroded teeth often look thinner and more translucent at the biting edges, appear more yellow as the underlying dentine shows through, and can look cupped or dished on the biting surfaces. Sensitivity tends to develop gradually and affect several teeth at once rather than one.
Common contributors are citrus and citrus drinks, soft drinks including sugar free versions, sports and energy drinks, wine, vinegar based foods, and reflux. As with decay, frequency of exposure matters more than volume. A drink sipped over an hour does more than the same drink finished in five minutes.
One habit worth correcting: enamel is temporarily softened straight after acid exposure, so brushing immediately afterwards removes surface material that would otherwise have re-hardened. Rinse with plain water and wait before brushing.
Cause 3: abrasion from brushing technique
Firm bristles, heavy pressure and a horizontal scrubbing motion produce a characteristic notch at the gum line over years. The tooth is being worn mechanically, the gum is being pushed back, and the two combine to expose dentine in exactly the spot that is most sensitive.
This is a frustrating cause because it happens to people who are conscientious about their teeth. Force does not improve plaque removal. A soft brush angled towards the gum line at roughly 45 degrees does the job, and switching the technique stops further damage even though the existing wear does not grow back.
Cause 4: grinding and clenching
Grinding, whether during sleep or as daytime clenching, wears the biting surfaces flat and thins the enamel until dentine is exposed. It also flexes the tooth at the gum line, which contributes to the same notching described above.
Signs worth noticing include waking with jaw or temple soreness, teeth that look shorter or flatter than they used to, edges that chip repeatedly, and a partner mentioning the noise. Grinding is worth raising because the wear accumulates slowly and is much easier to manage while it is still early.
Cause 5: a cracked tooth
This one behaves differently from the causes above and it is the reason the pattern of your sensitivity matters.
A cracked tooth typically produces a sharp pain on biting or, distinctively, on releasing the bite, and it is usually confined to one tooth. It may come and go, and it may not be visible on an x-ray. Sensitivity that is limited to a single tooth, especially with a biting element, warrants examination rather than desensitising toothpaste.
Cracks are more common in teeth with large existing restorations, in people who grind, and in teeth that have been heavily filled over many years.
Cause 6: decay, or a problem with existing dental work
Decay can cause sensitivity, though often not until it has progressed into dentine. A leaking or failing filling, a lost filling, or decay at the margin of an older crown can all produce the same symptom.
The distinguishing feature here is that it is usually localised, it usually gets worse rather than staying stable, and it may be accompanied by food packing into a space that did not used to trap food, or by a rough edge you can feel with your tongue.
Cause 7: sensitivity after dental treatment
Some sensitivity after treatment is expected and settles.
- After a scale and clean, particularly where calculus has been removed from around the gum line and root surface that was previously covered is now exposed.
- After a new filling, while the tooth settles.
- After teeth whitening. Whitening related sensitivity is common, generally short lived, and covered in more detail in our article on whether teeth whitening is safe.
- After crown or veneer preparation, during the temporary phase.
The reasonable expectation is that treatment related sensitivity improves over days to a couple of weeks. Sensitivity after treatment that is getting worse rather than better, or that has not settled within a few weeks, is worth reporting to the practice rather than waiting for the next appointment.
How do I tell ordinary sensitivity from something that needs attention?
Use the pattern rather than the intensity. Sharp does not mean serious, and dull does not mean harmless.
Usually surface sensitivity
- Short and sharp, stopping as soon as the cold or sweet stimulus is removed
- Affects several teeth, often on the same side or along the gum line
- Triggered by cold air, cold drinks, sweet foods or brushing
- Stable over time rather than steadily worsening
Worth having examined
- Pain that lingers for more than a few seconds after the stimulus is removed
- Pain that wakes you at night, or that is spontaneous rather than triggered
- Sensitivity to heat specifically, which behaves differently from cold sensitivity
- Confined to one tooth, particularly with pain on biting or on release
- Accompanied by swelling of the face or gum, which should be treated as urgent
- Getting steadily worse over weeks
- A tooth that has discoloured relative to its neighbours
- Any sensitivity accompanied by a bad taste, a persistent odour, or a lump on the gum
Swelling is the one item on that list that should not wait. Everything else warrants an appointment rather than an emergency.
What can you do at home?
- Switch to a soft bristled brush and reduce pressure. Let the bristles do the work rather than your arm.
- Use a desensitising toothpaste consistently. These generally work by blocking the tubules or calming the nerve response, and they need several weeks of continuous use to take effect, so a few days is not a fair trial.
- Try smearing a small amount of desensitising toothpaste onto the sensitive area with a fingertip after brushing at night and not rinsing it off.
- Spit rather than rinse after brushing, so the fluoride and the active ingredient stay on the tooth.
- Reduce the frequency of acidic food and drink, and use plain water between meals.
- Wait after acidic food or drink before brushing.
- Do not use whitening or abrasive toothpastes on already sensitive areas without discussing it first.
If several weeks of consistent home management has not improved things, that is useful diagnostic information rather than a failure, and it is a reasonable point to have it looked at.
What can a dentist do about it?
The first step is working out which of the causes above is responsible, because the management differs substantially. An examination looks at the pattern of wear, the gum levels, existing restorations, the bite, and whether there is decay or a crack involved, with radiographs where indicated.
Depending on what is found, options discussed may include professional fluoride application or desensitising agents applied in the studio, addressing the cause where it is behavioural, such as brushing technique or acid frequency, managing grinding, restoring worn or notched areas, treating decay or replacing failing restorations, or periodontal treatment where gum disease is driving recession. Where a crack or pulp involvement is suspected, the assessment and the options are different again.
What is appropriate depends entirely on the individual mouth, which is why this article stops at describing the categories rather than recommending a treatment.
Does sensitivity rule out cosmetic treatment?
Not on its own, but it is relevant to sequencing. Sensitivity indicates exposed dentine, and the reason for that exposure, whether recession, erosion, wear or a failing restoration, is usually something to understand before elective cosmetic work is planned. Underlying oral health is addressed before cosmetic treatment, which is covered in more detail in our article on the difference between general and cosmetic dentistry.
If you are considering whitening in particular, existing sensitivity is worth raising at the consultation stage rather than discovering it partway through.
Talking it through in Ballarat
If sensitivity has been bothering you, or you are not sure which category yours falls into, you can book an appointment online at Smile Creative or call the studio on 03 4320 0777. Dr Karishma Wijeyesinghe personally treats all patients at the Ballarat Central studio, and general and preventative treatments are outlined on the general dental treatments page.