Why Does the Dentist Tap Your Teeth?

By Lovik Mirzaeian, DDS. Updated November 2026.

Your dentist taps your teeth to check whether the tissue around the root is inflamed. The tap is called a percussion test, and a tooth that is sore when tapped usually has trouble at the root end, such as an infected nerve, a crack, or a bite that is hitting too hard. A healthy tooth does not mind being tapped at all. It is one of the oldest tests in dentistry, and still one of the most useful because it takes five seconds and costs nothing.

This post explains what the tap is measuring, what a sore response means, and the other quick tests we run alongside it to find the tooth causing your pain.

What the Tap Is Measuring

Each tooth sits in its socket held by a thin ligament, the periodontal ligament, which acts like a shock absorber. That ligament is full of nerve endings that sense pressure. When everything is healthy, a light tap with the handle of a mirror is felt as a dull thud and nothing more.

When the ligament is inflamed, the same tap produces a sharp jolt. The inflammation almost always comes from something at the tip of the root. Infection leaking out of a dying nerve, pressure from a crack, or a tooth overloaded by a high filling or grinding will all irritate that ligament. The ligament cannot tell us which of those it is, but it tells us clearly that this tooth, not its neighbor, is the one in trouble.

Why We Tap More Than One Tooth

Tooth pain is famously hard to pin down. The nerves from your upper and lower back teeth travel along shared pathways, so an infected lower molar can feel like an upper toothache. Patients often point confidently at a tooth that turns out to be fine.

So we tap several teeth, starting away from the sore area and working toward it, and we watch your face as much as we listen to your answer. If none of them react, that itself is useful, because it moves our attention toward the gum, the sinus, or the jaw joint.

What a Sore Response Usually Means

The most common reason a tooth hurts when tapped is that the nerve inside has died or is dying, and infection has started to collect at the root tip. This is the early stage of a dental abscess, and it can happen before there is any swelling you can see. Our post on dental abscess signs covers what happens if that goes untreated.

The second common reason is a crack. The third is a simple bite problem: a new filling or crown that sits slightly high gets hammered every time you close, and the ligament under it becomes bruised. That one is fixed in a minute by adjusting the bite.

When a Sore Tap Is Not the Tooth

Sinus infections make the upper back teeth tender to tapping because the roots sit just under the sinus floor. If several upper teeth on one side all tap sore and you have a stuffy head, the sinus is the likely culprit, and we will usually send you to your doctor rather than drilling anything.

The Cold Test

After tapping, we usually check the nerve directly by touching the tooth with something very cold, most often a cotton pellet sprayed with a refrigerant. A healthy nerve feels the cold sharply and the feeling fades within a few seconds. A nerve that is inflamed but still alive gives a pain that lingers for thirty seconds or more. A dead nerve feels nothing.

Combining the two tests tells a story. A tooth that taps sore and feels nothing to cold almost certainly has a dead nerve and needs a root canal or an extraction. A tooth that taps sore but responds normally to cold is more likely to be cracked or overloaded. If you have been wondering about your own cold sensitivity, our post on why teeth hurt when you drink something cold goes into the everyday causes.

The Bite Test

For suspected cracks, we ask you to bite down on a small plastic wedge, one cusp at a time, and let go. A crack typically produces a sharp pain as you release rather than as you bite. Cracks are often invisible on x-rays, so this simple test is sometimes the only thing that finds one.

Probing the Gums

A thin probe slid gently between the gum and the tooth measures how deep the gum pocket is. A single very deep pocket on one side of an otherwise healthy tooth can mean a root fracture, or a gum abscess rather than a tooth abscess. Those look similar from the outside but are treated very differently.

Where X-Rays Fit In

The tests above tell us which tooth and roughly what kind of problem. An x-ray then confirms it. A dark shadow at the root tip shows a longstanding infection, and bone loss around a root supports a gum diagnosis. X-rays on their own can miss early infections and almost always miss cracks, which is why we do the hands-on tests first. Our post on why you need dental x-rays if nothing hurts explains what films show that an exam cannot. The American Dental Association has a plain summary of the different types.

When to See a Dentist

If a tooth feels sore when you tap it yourself, or when you bite on it, that is worth a visit within a few days rather than a few months. A tender ligament rarely settles on its own, and the problems behind it get more expensive to fix the longer they go. If there is swelling, a bad taste, or pain that keeps you awake, call our emergency dentist line for a same-day appointment. For a tooth that is only slightly tender, book a routine exam and mention it when you arrive so we can run these tests on the spot.

Frequently Asked Questions

Why does my tooth hurt when I tap on it?

A tooth that hurts when tapped usually has inflammation in the ligament around its root. The most common causes are an infected or dying nerve, a crack in the tooth, or a filling or crown that is sitting too high in the bite. It is worth having a dentist check it within a few days.

What is a percussion test at the dentist?

A percussion test is when the dentist taps gently on a tooth, usually with the handle of a mirror, to see whether it is tender. A healthy tooth feels a dull thud. A tooth with an inflamed root ligament gives a sharp jolt, which helps identify which tooth is causing pain.

Can a sinus infection make my teeth hurt when tapped?

Yes. The roots of the upper back teeth sit just under the floor of the sinus, so a sinus infection can make several upper teeth on one side feel tender when tapped or when you bend forward. If the teeth themselves test normally, your dentist may refer you to your doctor to treat the sinus.

Does a tooth that hurts when tapped always need a root canal?

No. A sore tap tells the dentist the ligament is irritated, but not why. If the nerve is dead, a root canal or extraction is usually needed. If the cause is a high filling or a small crack, adjusting the bite or placing a crown may be all that is required.

Have a Tooth That Hurts When You Tap It? Dr. Mirzaeian Can Help

Finding the right tooth is half the job, and a few simple tests usually do it in the first ten minutes. Lovik Mirzaeian, DDS will find the cause and lay out your options plainly. contact us to set up a consultation.

Lovik Mirzaeian, DDS has achieved extensive training in multidisciplinary dental treatments. His credentials include Dental Implants, Cosmetic Dentistry, Full Mouth Reconstruction, Endodontics, Oral Surgery, Orthodontics, and Sleep Sedation. Our office puts your comfort and smile first, and we are dedicated to giving you top-notch dental care. Get ready to show off your perfect smile!

Looking for a trusted family dentist in Clovis? Dr. Mirzaeian welcomes new patients of all ages.