Testing your dentist performs to determine if your tooth needs root canal treatment.

- Percussion testing, electric pulp testing (EPT), thermal (hot/cold) testing, selective anesthesia, cavity test. | How each test is performed. | What you'll feel. | What your test results indicate.

Tests dentists use to evaluate the status of a tooth's nerve.

Once your dentist has formulated suspicions about your possible need for root canal therapy, they'll perform additional testing so they can get a more complete picture about the current status of the teeth they suspect the most.

Why are these additional tests needed?

Your dentist knows that their ability to formulate an accurate diagnosis will rely on collecting as much pertinent information as possible. So beyond only relying on signs & symptoms you have reported, clinical signs they have personally observed and the findings from their x-ray evaluation, they'll probably feel they need to perform several of these additional tests too.


Diagnosing a tooth's need for root canal treatment - Tests your dentist performs.

Here's an overview of the most common tests that dentists/endodontists use to further evaluate teeth suspected of needing root canal treatment. They include: percussion testing, thermal testing, the electric pulp test, selective anesthesia, and the cavity test.

With each, we provide a description of its overall goal, how it's performed, what type of results might be expected under different circumstances and what those results might indicate in regard to the status of your tooth's nerve and its need for root canal treatment.

a) Percussion testing.

Because it's both so simple and informative, one of the first evaluations of a patient's teeth usually performed is a percussion test.

How a percussion test is conducted.

This test simply involves your dentist tapping on selected teeth, both in a vertical direction (straight onto their chewing/biting surface) and possibly horizontally too (from the side).

In most cases, the instrument used is just the butt end of the handle of the dentist's small hand mirror.

The steps.
  • Your dentist will start the process off by applying gentle finger pressure on the teeth that will be tested. Then, if they find you can tolerate that OK, they'll begin the actual process of percussing them.
  • As they test each tooth in turn, they'll just tap lightly at first. Then, as they continue on, they'll gradually use more force.

    But don't worry, their goal is to collect information, not to hurt you. They'll keep your comfort level in mind as they tap.

  • As they test each tooth, they'll evaluate your response. They may need you to clarify things by asking you what you've felt (pain, tenderness, nothing unexpected).
  • They'll test the teeth they suspect the most, their neighbors and even the same teeth on the other side of your mouth, just to see how all of their responses compare.
Test findings.
  • One goal of percussion testing is to identify which tooth (or possibly teeth) seems to have some sort of problem, in the sense that it responds differently, or more so, than all of the others.
  • A tooth that requires root canal therapy frequently (but not always) responds to percussion testing with tenderness or sharp pain. Typically this tooth displays a greater response than all of the others tested.
  • Unfortunately, a positive response (feeling tenderness) doesn't conclusively prove that a tooth needs root canal treatment. Teeth that are healthy but irritated (like those subjected to excessive teeth clenching and grinding) or those that have periodontal (gum) disease may respond in the same way too.
What percussion testing evaluates.

Tapping on a tooth only evaluates the status of its periodontal ligament (the ligament that surrounds the tooth's root and binds it in its socket), as opposed to directly testing the condition of its nerve.

However, since pathology inside the tooth (like the presence of infection) can lead to the inflammation of its ligament (due to infection byproducts leaking out), tenderness or pain to percussion can be an indication that an endodontic problem in fact exists.

b) Thermal testing (hot/cold testing).

Exposing a tooth to hot and cold extremes can give a hint about the status of its nerve tissue and its potential need for root canal treatment.

Possible test findings.
  • Problematic teeth frequently respond painfully to both hot and cold stimuli.

    In some limited cases, application of a hot stimulus will trigger pain whereas a cold one will create pain relief.

    (Related: See our "home remedy" section about root canal pain and how this phenomenon might be used to provide emergency relief in some cases.)

  • A key factor is how long the tooth's reaction to the stimulus lasts. With healthy teeth, the pain usually subsides promptly after it's been removed.

    Pain that lingers (30 seconds or more is usually used as the cut off point) is frequently a sign that a condition exists that will require root canal treatment to resolve.

Ways dentists perform thermal testing.
  • In the case of cold testing, the dentist will hold ice, dry ice, or a cotton swab that's been soaked in a refrigerant, against the tooth.
  • For hot stimulus testing, a heated object (such as a ball of the rubbery compound gutta percha), a metal hand instrument heated in a flame, an electrically-heated instrument/device, or application of hot water (after the tooth has been isolated with a rubber dam) might be used, depending on the dentist's preference.
  • With either type of testing, the dentist will hold the conducting medium against the tooth to see what response is triggered.

    Since it's possible that a temperature extreme placed against the surface of a healthy tooth might create enough of a temperature gradient to damage its nerve, initially the dentist will be cautious in the level of exposure they create (5 to 15 seconds might be used, depending on the actual temperature of the medium).

What's the underlying basis of thermal testing?

In regard to healthy nerve tissue:

  • With cold testing, the stimulus causes fluid inside the tooth (in its dentin tubules) to contract. This fluid movement triggers pain receptors in the the tooth's nerve.
  • With heat testing, the thermal gradient that's created directly stimulates pain receptors within the tooth's nerve tissue.
  • With both types of testing, it's expected that the sensation will be felt, and then immediately diminish once the stimulus has been removed. When variant symptoms are observed, nerve tissue pathology is suspected.

It must be stated that even healthy teeth may not give a diagnostic response to thermal testing. And related to issues with the dentist's technique, false positives are possible. Also, a seemingly normal response isn't necessarily an indication that the nerve's status is fully normal.

 Reference: 

Hargreaves KM, et al. Cohen's Pathway of the pulp. Chapter: Pathology of the periapex.

Torabinejad M, et al. - linked above.

c) Electric pulp testing (EPT).

As its name implies, with this type of testing the tooth's nerve is exposed to electrical stimulation and the results observed.

How a dentist performs electric pulp testing.

For this test, the dentist uses a battery operated device whose tip can pass a variable low voltage current. The dentist controls the level of the devices output.

  • The dentist will first isolate, and then clean and dry off, the surface of the tooth being tested. (Maintaining moisture control is imperative in performing an accurate test.)
  • They'll then dip the tip of the tester in a conducting medium. (Toothpaste is often used.)
  • With the electric tester set to its zero current position, the dentist will place its conductive tip on the tooth's surface.
  • They'll then gradually increase the level of current that's passed to the tooth until a point is reached where the patient indicates that they feel (usually a warm or tingling) sensation in their tooth.
  • Once a sensation has been felt, the tip of the pulp tester is removed from the surface of the tooth. The device's current level setting is recorded.
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As horrible as all of this sounds, in practice it isn't. Your dentist will start off with a very low tester setting and then gradually increase its level. At the first sign of a response from you, they'll immediately remove the tester from your tooth.

Test findings.

The general idea is that healthy nerve tissue will respond to electrical stimulation, as compared to deteriorating or necrotic (dead) tissue that will display a reduced or negative (no sensation) response.

There are a number of tooth-related issues (such as the presence of a metal dental restoration or the tooth having comparatively small root canals) that can affect the reliability of electric testing.

So even a negative response doesn't necessarily indicate that the tooth requires endodontic treatment. False positive or negative responses occur in roughly 10 to 20% of cases (Torabinejad).

What's the underlying basis of electric pulp testing?

Somewhat similar in nature to cold testing, exposure of a tooth to electrical current creates fluid movements within its dentinal tubules (due to the ionic properties of this fluid). It's the resulting fluid movement that then triggers receptors associated with the tooth's nerve. (Hargreaves)

 Reference: 

Hargreaves KM, et al., Torabinejad M, et al. - both linked above.

d) Selective anesthesia.

There can be times when a patient's endodontic pain is:

  • Vague and diffuse - The situation where it's difficult to tell exactly which tooth the pain is coming from, either because it's nondescript or else several teeth seem to hurt.
  • Referred - The case where the pain the patient feels is sensed in a healthy tooth that just happens to be serviced by the same nerve as the culprit one, possibly even one that's some distance away. (Such as a problematic lower tooth refers pain to an upper one.)

As a test, the dentist may selectively numb up suspected teeth as a way of identifying which one lies at fault. The idea is that when the culprit tooth is numbed up, the patient's pain will disappear.

How an anesthesia test is performed.

This type of testing will involve your dentist giving you a series of dental "shots" as they serially numb up each tooth they feel might be a suspect.

In regard to injection technique, infiltration or intraligamentary injections are often used.

 Reference: 

Tronstad L. - linked above.

e) The Cavity test.

  • If a dentist has been unable to conclusively prove that a suspected tooth is in fact the culprit one ...
  • And they have a high level of suspicion that the pulp tissue inside the tooth in question is necrotic (meaning the tooth's nerve is dead) ...
  • ... a Cavity test may be performed.

This test simply involves the dentist drilling a divot into the suspected tooth, without numbing it first.

The idea is that if the nerve tissue inside the tooth is healthy, at some point during the process sensations will start to be felt. But if the nerve is necrotic as anticipated, no pain will be felt at all, even when the drilling finally penetrates into the tooth's interior nerve space.

A test of last resort.

Historically the cavity test has been considered to be one only used when no other means of evaluating the tooth's condition is available. However, the decision to use it at all is debatable.

While making a repair is possible, performing this test is invasive and irreversible. The patient's apprehension about the procedure can easily confound their response. And in most cases, it seems what is learned could have been revealed by other testing methods.

 

Last revision/review: 11/16/2018 - Page created.

 
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