The nerve inside your tooth hurts because something has irritated or inflamed the soft tissue at the tooth’s core, called the pulp. This pulp contains nerve fibers that detect changes in temperature and pressure, and when they’re aggravated by decay, a crack, or infection, they fire pain signals as a warning that something is wrong. The type of pain you’re feeling, how long it lasts, and what triggers it all point to different causes and different levels of urgency.
How the Nerve Inside Your Tooth Works
Each tooth has a hollow center filled with living tissue: blood vessels, connective tissue, and nerve endings. This is the pulp. It sits beneath two hard layers, enamel on the outside and dentin underneath, which normally shield it from the outside world.
Dentin isn’t solid, though. It’s laced with thousands of microscopic tubes called dentinal tubules, and each one contains a tiny column of fluid. When something hot, cold, sweet, or acidic reaches these tubes, the fluid inside expands or contracts. That movement triggers pressure-sensitive nerve endings at the inner edge of the dentin, producing a sharp jolt of pain. The fluid in those tubes expands roughly ten times more than the tube walls themselves in response to temperature changes, which is why a sip of ice water can feel so intense on an exposed tooth.
This system is remarkably sensitive to small changes. If the radius of a dentinal tube is reduced by even half, fluid movement drops to one-sixteenth of its original rate. That’s why treatments that seal or shrink those tubes (like desensitizing toothpaste) can reduce sensitivity so effectively.
Tooth Decay: The Most Common Cause
A cavity is the most frequent reason for tooth nerve pain. When bacteria eat through enamel and penetrate into the dentin, their byproducts seep through the dentinal tubules toward the pulp long before the decay physically reaches it. In a shallow cavity, bacterial toxins diffuse through those tubes but haven’t contacted the pulp directly, so the irritation is mild and often reversible.
In a deep cavity, where the decay extends into the inner quarter of the dentin or deeper, bacteria can invade the pulp itself. This triggers a more intense inflammatory response. Blood flow to the pulp increases, pressure builds inside the rigid walls of the tooth, and the nerve fibers become hypersensitive or start firing on their own. Because the pulp chamber can’t expand to accommodate the swelling, the pressure alone can cause severe, throbbing pain.
Reversible vs. Irreversible Inflammation
Dentists classify pulp inflammation into two categories, and the distinction matters because it determines whether your tooth can heal on its own or needs more significant treatment.
Reversible pulpitis means the pulp is irritated but not permanently damaged. You’ll feel a sharp sting when something cold or sweet touches the tooth, but the pain disappears within a couple of seconds once the trigger is removed. The pain is never spontaneous. It only shows up when something provokes it. At this stage, removing the source of irritation (filling a cavity, for example) typically lets the pulp recover.
Irreversible pulpitis is a different situation. The inflammation has progressed to the point where the pulp can’t repair itself. Pain from a hot or cold stimulus lingers for 30 seconds or longer after the trigger is gone. You may also experience spontaneous pain that hits without any obvious cause, sometimes waking you at night. The pain can radiate to your jaw, ear, or temple, making it hard to pinpoint which tooth is the problem. At this stage, the pulp needs to be treated directly, usually with a root canal or, in some cases, a partial removal of the damaged pulp tissue.
Cracks and Fractures
A cracked tooth can produce nerve pain that’s tricky to identify because the crack may be invisible to the eye and even hard to spot on an X-ray. The hallmark of a cracked tooth is a sharp, sudden pain when you bite down, particularly when you release the bite. Chewing forces flex the crack open and closed, pulling on the pulp tissue underneath and stimulating the nerve. You may also notice sensitivity to temperature changes or sweet foods, similar to a cavity, but concentrated in a tooth that looks perfectly intact.
Cracks can result from grinding your teeth, chewing ice or hard objects, biting down on something unexpected, or simply from years of wear. A large filling can also weaken the remaining tooth structure enough to allow a fracture. If the crack extends into the pulp, the nerve becomes directly exposed to bacteria and oral fluids, and irreversible inflammation often follows.
Infection and Abscess
When pulp inflammation goes untreated, bacteria can kill the nerve tissue entirely. The infection then spreads through the root tip and into the surrounding bone, forming a pocket of pus called a periapical abscess. The pain at this point changes character: it becomes a severe, constant, throbbing ache that can radiate into your jawbone, neck, or ear.
Other signs of an abscess include fever, swelling in your face or cheek, tender lymph nodes under your jaw, and a foul taste in your mouth. If the abscess ruptures on its own, you may notice a sudden rush of salty, bad-tasting fluid followed by temporary pain relief. Facial swelling that makes it hard to breathe or swallow is a medical emergency. An abscess won’t resolve on its own, and allowing bacteria to spread deeper can lead to bone loss or systemic infection.
Sinus Pressure Mimicking Tooth Pain
Not all upper tooth pain comes from the teeth themselves. Your maxillary sinuses sit directly above the roots of your upper back teeth, and when those sinuses become inflamed from a cold or sinus infection, the pressure can push down on the nerve endings of several teeth at once.
There are a few ways to tell the difference. A true toothache is usually isolated to one tooth, responds to temperature changes, and may involve swollen gums. Sinus-related tooth pain tends to affect multiple upper teeth at the same time and gets worse when you change head position, like bending over or lying down. If your “toothache” came on alongside nasal congestion and facial pressure, your sinuses are the more likely culprit.
Managing the Pain Before Your Appointment
Over-the-counter anti-inflammatory medications are the most effective option for tooth nerve pain, outperforming even prescription opioids in clinical studies. The American Dental Association recommends NSAIDs like ibuprofen as the first choice for acute dental pain.
For mild pain, 200 to 400 mg of ibuprofen every four to six hours as needed is a reasonable starting point. For moderate to severe pain, combining ibuprofen with acetaminophen is significantly more effective than either one alone, because they block pain through different pathways. A large review covering data from over 58,000 patients found that 400 mg of ibuprofen combined with 1,000 mg of acetaminophen outperformed every opioid-containing regimen tested, with fewer side effects. There’s also an FDA-approved over-the-counter combination product containing both, if you’d prefer a single pill.
These medications manage symptoms, but they don’t treat the underlying cause. If your pain is spontaneous, lingers after hot or cold exposure, throbs constantly, or interferes with eating and sleeping, you need professional treatment. Delaying care gives bacteria more time to spread deeper into the tooth and surrounding bone, turning a fixable problem into a more complex one.