What Causes a Toothache? Common Reasons a Tooth Hurts

The one thing every toothache has in common

Different causes, same pain. Inside every tooth is the pulp, a small core of nerve and blood vessels sealed inside hard walls. Almost anything that reaches it, decay, a crack, a leaking filling, an infection, makes it inflame, and because it is trapped inside walls that will not move, that inflammation has nowhere to go but into pain. That is why the causes below feel so alike from the outside even though the trigger is different, and why you usually cannot name your own from the chair at home.

It is also why a toothache rarely settles for good on its own. The pain can fade, but the trigger, the cavity or the crack or the dying nerve, is still there. Our main guide to toothaches covers relief and timing; this one is about what is actually behind the pain.

The common causes of a toothache

Most toothaches trace back to one of a handful of problems. Roughly in order of how often we see them:

• Tooth decay that has reached the nerve. A cavity that started small keeps working inward through the enamel until it reaches the pulp. This is the single most common cause of a toothache, and once decay is that deep the tooth aches rather than just twinges.
• An infection or abscess at the root. When the nerve dies, a pocket of pus builds at the tip of the root. A tooth abscess brings a deep, constant throb, often with swelling, a bad taste, or a gum boil on the gum.
• A cracked or broken tooth. A crack lets bacteria and hot and cold reach the nerve, and it often hurts most when you bite down and then let go. A visibly broken tooth can expose the sensitive layers directly.
• A lost or failing filling or crown. When a filling fails or a crown comes off, the soft part of the tooth underneath is suddenly open to everything, and the nerve reacts. A temporary filling that falls out does the same.
• A receding gum and an exposed root. Roots have no enamel to shield them, so a bare root can be sharply sensitive to cold and sweet.
• Gum disease. Inflamed, infected gums can ache around a tooth rather than inside it, and left alone they loosen the tooth's support. Our guide to painful, inflamed gums covers the signs.
• A wisdom tooth pushing in. A wisdom tooth coming in at an angle aches at the back of the jaw and can inflame the gum flap over it.

You often cannot tell these apart from the outside, and the fix is different for each. That is what an examination, and usually an X-ray, sorts out.

Causes that are not the tooth at all

Not every toothache starts in a tooth. Pain can be referred from nearby structures, which is why a tooth can ache while the tooth itself is perfectly sound.

• A sinus infection. The roots of the upper back teeth sit right against the sinuses, so a sinus infection can feel like a toothache, usually across several upper teeth at once and worse when you bend forward or have a cold.
• Grinding or clenching. Night-time grinding puts teeth under pressure they were not built for, leaving them aching and tender in the morning.
• The jaw joint. A strained jaw joint or its muscles can send a dull ache into the back teeth, so jaw pain and tooth pain get mistaken for each other.
• The ear, or the tooth via the ear. Because they share nerves, a back-tooth problem can be felt as ear pain, and an ear problem can be felt as toothache.

A dentist can usually tell a referred ache from a true toothache, which saves you treating the wrong thing.

Matching the pain to the likely cause

The pattern of the pain is a rough clue to what is behind it. It is never a diagnosis on its own, but it points in a direction.

• Sharp pain only when you bite down, easing when you let go. Often a crack or a filling sitting too high.
• A quick zing to cold or sweet that fades in a second or two. Usually sensitivity or early decay, and a milder problem. Pain to heat that lingers, though, points to a nerve in real trouble.
• An ache that comes and goes over days or weeks. A nerve that is inflamed but not yet dead. It tends to get worse, not better, if it is left.
• Constant, deep throbbing that keeps you awake. More like a dying nerve or an abscess, and the kind worth being seen for quickly. A tooth that has died can also go grey.

None of this beats an actual look, but it explains why two people with a toothache can need two completely different treatments. For taking the edge off while you wait, our guides to which painkillers help and dental pain relief cover what is safe.

Why the cause decides the fix, and why it is worth catching early

Because each cause is different, so is each repair. Early decay is a filling. A nerve that has become infected is cleaned out with a root canal, which keeps your own tooth. An abscess is drained and the tooth treated. Only a tooth too broken down or too far gone to rebuild has to come out with an extraction.

The catch is that the same problem gets more expensive the longer it waits. Waiting to see whether it settles is usually the more expensive choice, because a cavity caught early is a filling, and the same tooth left until the nerve dies is a root canal or, later still, an extraction and the gap that follows. What happens if you skip the root canal spells out where that road ends.

When the cause needs a dentist the same day

Most toothaches are a same-day or next-few-days visit, not a crisis. A brief zing to cold, a small chip with no swelling, or a mild ache that a painkiller settles can usually wait a day or two for an ordinary appointment. You do not need to rush in for those.

Be seen the same day if you have swelling in the face or gum, a fever alongside the pain, a gum boil that keeps coming back with a bad taste, or pain that no painkiller touches. Those point to an infection that has taken hold. Go straight to a hospital emergency room, not a dental clinic, if swelling is spreading toward your eye or down your neck, you have trouble breathing or swallowing, you cannot open your mouth more than a finger's width, or you have a high fever with chills and feel genuinely unwell. Facial swelling from a tooth that is moving fast is beyond what a dental chair is built for, and we set out exactly where that line sits in when a toothache is a dental emergency.

The short version: what causes a toothache is almost always the nerve inside the tooth reacting to decay, a crack, a lost filling, an infection, or an exposed root, and now and then it is a sinus, the jaw, or grinding rather than the tooth at all. The cause decides the fix, so the useful step is having it looked at rather than guessing. Mild, brief sensitivity can wait; swelling, fever, or pain nothing touches should be seen the same day.

We treat tooth pain, infections, and abscesses at our emergency dental clinic in Beit Shemesh, at Harav Kook 28/1. Call or WhatsApp 055-985-8845, Sunday to Thursday 8:00 AM to 8:00 PM and Friday 8:00 AM to 2:00 PM, with after-hours emergency treatment outside those hours. You can send a photo or a recent X-ray before you come in. If any of the emergency signs above apply, though, do not message first: go straight to a hospital emergency room.

For guidance from sources with nothing to sell, the ADA's MouthHealthy runs through the most common dental symptoms and what they mean and which ones count as an emergency, and the American Association of Endodontists explains what different kinds of tooth pain point to.