First, when a twinge isn’t just a twinge
Pain that lingers for a long time after the cold has gone, pain that wakes you at night, pain that arises without a trigger, or pain accompanied by swelling, is different from ordinary sensitivity and should be assessed promptly. So should sensitivity confined to a single tooth that has appeared recently, particularly after a knock or after dental work.
The rest of this piece is about the common, generalized version — the sharp, brief, unpleasant response to cold air, cold water or ice cream that stops almost as soon as the stimulus does.
The layer underneath, and why it feels anything
Enamel has no nerve supply. Underneath it lies dentin, which does, in an indirect way that is genuinely interesting. Dentin is not solid: it is threaded with microscopic tubules running from the outer surface toward the pulp at the center of the tooth, and those tubules contain fluid.
The leading explanation for sensitivity is that a stimulus at the exposed surface — cold, evaporation from a draft of air, a sugary or acidic solution — causes rapid movement of fluid within the tubules, and that movement is registered by nerve endings at the inner end. The nerve doesn’t detect cold directly, it detects the disturbance, which is why the sensation is a sharp brief jolt rather than a temperature reading.
This is called the hydrodynamic theory and it is the accepted working model, though it does not account for every observation. That caveat is worth including, because dentistry contains a number of well-supported explanations that are not quite complete, and pretending otherwise does nobody any favors.
How dentin ends up exposed
For dentin to respond, the tubules must be open to the mouth at one end. Gum recession exposes root surface, which has no enamel over it and is more permeable. Erosion thins enamel until dentin shows through, particularly at the biting edges and the necks of teeth. Abrasion from heavy brushing wears a notch at the gum line. Grinding and clenching wear the biting surfaces.
Cracked or chipped teeth, decay, a filling with a defective margin, and recently placed restorations can all cause sensitivity too, and those are the causes that need identifying rather than managing. Sensitivity after professional cleaning or after whitening treatment is common and generally temporary, though it should settle rather than persist.
In many people more than one of these is present at once, which is a further reason why a description over a phone or an article can’t sort it out.
Why it varies so much from person to person
Not everyone with exposed dentin is sensitive, and this puzzles patients who compare notes. Tubules can become blocked over time by mineral deposition from saliva, by a layer of debris on the surface, or by reactive dentin the tooth lays down internally. A surface exposed slowly over years may be entirely comfortable, while the same exposure occurring quickly is not.
Sensitivity also fluctuates with the season, with acid exposure, with stress-related grinding, and with cleaning habits. A tooth that was fine in summer and unbearable in December is usually reacting to cold air rather than to any change in the tooth.
This variability is why symptoms alone are a poor guide to severity. A very sensitive tooth may have a minor and stable cause; a comfortable one may have decay progressing quietly.
What is reasonable to do, and where the line is
In general terms, the sensible measures are the ones that stop further exposure: light brushing with soft bristles, attention to how often acidic food and drink reach the teeth, and not brushing immediately after acid. Toothpastes formulated for sensitivity are widely available and can genuinely help, typically after a few weeks of consistent use rather than immediately.
What I wouldn’t do is treat persistent sensitivity as a purchasing decision indefinitely. It is a symptom with a cause, and the causes range from a receded gum that needs no treatment at all to decay that does. A dentist can test the tooth, look at what is exposed, check how your teeth meet and decide whether anything is required.
There are also treatments applied in the chair for stubborn sensitivity, and which of them is appropriate depends entirely on the cause. That is precisely the sort of decision that cannot be made from a description, and it is the reason a persistent twinge deserves an appointment rather than another tube.
Common questions
Why does sweet food make a tooth hurt as well as cold?
A concentrated sugar solution at an exposed dentin surface can draw fluid outward through the tubules, producing the same fluid movement that cold does. Sweet sensitivity in a single tooth is worth reporting, since it is also associated with decay.
Do sensitivity toothpastes work?
They help a substantial proportion of people, working either by blocking the tubules or by reducing nerve excitability, and they generally need a few weeks of consistent use. They manage the symptom rather than the cause, so ongoing reliance without an examination is not wise.
My tooth hurts only when I bite on it. Is that the same thing?
No, and it is worth taking seriously. Pain specifically on biting or on release can point to a crack, a high spot on a filling, or a problem at the root, and none of those is addressed by a sensitivity toothpaste. Have it examined.
Dental Surgeon, Dr. Shruti Goel
Dr. Shruti Goel is a dental surgeon in practice since 2006 — around 20 years of clinical work — at Advanced Dental Clinic in Faridabad. She writes here about hygiene and prevention: the part of dentistry that happens at home, between appointments, and that decides how much of the rest is ever needed.