Tooth pain happens when something irritates the nerve inside or around a tooth. That nerve sits in a soft core called the pulp, protected by layers of hard enamel and a porous layer called dentin. When decay, damage, or infection breaches those layers, or when gums recede and expose the sensitive root surface, pain signals fire. But teeth can also hurt for reasons that have nothing to do with the teeth themselves.
How Decay Triggers Pain
Cavities are the most common reason teeth hurt. Bacteria in the mouth, particularly streptococci and lactobacilli, feed on sugars and release acid. That acid dissolves the minerals in enamel and dentin, slowly eating through the tooth’s protective shell. As the damage deepens, it reaches a layer of specialized cells that line the inner surface of dentin. These cells are the first to detect trouble, and they respond by releasing inflammatory signals: proteins that dilate blood vessels, increase blood flow, and recruit immune cells to the area.
The problem is that all of this inflammation happens inside a rigid, enclosed space. Unlike a swollen ankle that can expand freely, swollen pulp tissue has nowhere to go. Pressure builds against the nerve fibers packed inside the tooth, and those fibers become increasingly sensitized. Inflammatory chemicals like prostaglandins and bradykinin lower the threshold for pain, meaning stimuli that wouldn’t normally bother you (a sip of cold water, a bite of candy) suddenly register as sharp discomfort. This is why a cavity that caused no pain for months can seemingly become agonizing overnight. The decay itself progresses slowly, but the inflammatory tipping point can feel sudden.
Why Temperature Makes It Worse
That jolt you feel when ice cream hits a sensitive tooth comes down to fluid movement. Dentin is riddled with microscopic tubes that run from the outer surface toward the nerve. These tubes contain fluid, and that fluid expands or contracts with temperature changes roughly ten times faster than the tube walls themselves. Cold causes the fluid to contract and pull away from the nerve; heat causes it to expand toward it. Either way, the rapid movement triggers pressure-sensitive nerve endings at the base of the tubes.
This is why exposed dentin, whether from a cavity, a crack, or receding gums, creates temperature sensitivity. Healthy enamel seals those tubes shut. Once that seal is broken, every hot coffee or cold drink creates a tiny hydraulic pulse aimed directly at the nerve.
Reversible vs. Irreversible Nerve Inflammation
Not all tooth pain means the tooth is doomed. Dentists distinguish between two stages of pulp inflammation, and the difference matters for what happens next.
In the early, reversible stage, a stimulus like cold or sweetness causes a brief sting that disappears within a couple of seconds after the stimulus is removed. There’s no spontaneous pain (pain that shows up on its own without any trigger), and X-rays look normal around the root tip. At this point, treating the cause, usually placing a filling or sealing exposed dentin, allows the nerve to calm down and recover.
Irreversible inflammation is a different situation. The hallmarks are pain that lingers 30 seconds or longer after a cold or hot stimulus, pain that strikes without any trigger at all, and discomfort that gets worse when you lie down or bend over. Over-the-counter painkillers often barely take the edge off. At this stage, the nerve tissue can no longer heal itself, and a root canal or extraction becomes necessary. One tricky detail: sometimes irreversible inflammation produces no symptoms at all, discovered only when a dentist spots deep decay on an X-ray. Pain level doesn’t always match severity.
Cracked and Fractured Teeth
A cracked tooth produces a distinctive pattern: sharp pain when you bite down, sometimes only when you bite on a specific spot, and sometimes only when you release the bite rather than when you apply pressure. Temperature sensitivity and sensitivity to sweet foods are also common. Cracks can be maddeningly hard to find because they don’t always show up on X-rays, and the pain can come and go unpredictably depending on how the crack shifts under chewing forces.
Cracks range from superficial craze lines in the enamel (harmless and extremely common) to deep fractures that split the root. The deeper the crack extends toward the pulp, the more likely it is to cause persistent pain and eventually require a crown, root canal, or extraction.
Gum Disease and Root Exposure
Gum disease is sneaky because it’s usually painless in its early stages. The process starts with bacterial buildup beneath the gum line, which gradually destroys the ligaments and bone that anchor teeth in place. As the disease progresses, gums pull away from teeth and recede, exposing root surfaces that were never designed to face the outside world. Unlike the crown of a tooth, roots have no enamel covering. Their dentin tubules are essentially open to the environment, which is why gum recession often brings sudden sensitivity to cold, heat, and touch.
In moderate to advanced stages, the bone loss becomes significant enough that teeth loosen, pus may appear along the gum line, and chewing becomes painful. By that point, the infection has been quietly progressing for months or years. Treatment can include deep cleaning beneath the gums, gum grafting to cover exposed roots, and in severe cases, extraction of teeth that have lost too much supporting bone.
Tooth Abscess
When bacteria reach the pulp and the nerve tissue dies, infection can spread beyond the tooth itself, forming a pocket of pus at the root tip. This is a dental abscess, and it produces a different kind of pain: deep, throbbing, constant, and often accompanied by visible signs. Your face, cheek, or neck may swell. Lymph nodes under the jaw can become tender and enlarged. Chewing or even lightly tapping the tooth sends a shock of pain through the area.
An abscess won’t resolve on its own. Antibiotics can slow the infection but can’t eliminate it without draining the pus and addressing the source, typically through a root canal or extraction. Facial swelling that spreads toward the eye or throat, a fever above 102°F, or difficulty breathing or swallowing are signs the infection is becoming dangerous and needs immediate emergency care. Untreated dental infections can, in rare cases, spread to the brain or bloodstream.
Sinus Pressure and Referred Pain
Sometimes your teeth hurt and the teeth are perfectly healthy. The roots of your upper back teeth sit very close to the maxillary sinuses, the large air-filled cavities behind your cheekbones. In some people, the roots actually extend into the sinus floor. When those sinuses become inflamed from a cold, allergies, or a sinus infection, the swelling presses directly against nearby tooth roots, producing an ache that feels exactly like a toothache.
A few clues can help you tell the difference. Sinus-related tooth pain usually affects multiple upper back teeth at once rather than a single tooth, gets worse when you bend forward, and comes with other sinus symptoms like congestion, facial pressure, or a runny nose. If only one tooth hurts and you can pinpoint it precisely, the problem is more likely dental.
Other Common Causes
Teeth grinding (bruxism) puts enormous repetitive force on teeth, especially during sleep when you can’t consciously stop. Over time, this wears down enamel, cracks fillings, and strains the ligaments around each tooth root, producing a dull ache that often feels worst in the morning. Many people grind without knowing it until a dentist spots the wear patterns.
Recent dental work can also cause temporary pain. Fillings, crowns, and whitening treatments can irritate the pulp, leaving the tooth sensitive for days to weeks. This type of sensitivity usually resolves on its own as the nerve calms down, but sensitivity that persists beyond a few weeks or gets progressively worse rather than better deserves a follow-up visit.
Heart attacks occasionally produce pain that radiates to the jaw and mimics a toothache, particularly on the left side. This is rare, but worth knowing: jaw pain combined with chest tightness, shortness of breath, or pain radiating down the arm is a medical emergency, not a dental one.