Testing your dentist performs to determine if your tooth needs root canal treatment.
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 of 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 just relying on signs & symptoms you have reported What to look for., indications they have personally observed Clinical signs. and the findings from their x-ray evaluation What do x-rays show?, 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.
- 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.
- 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.
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, the application of a hot stimulus will trigger pain whereas a cold one will create pain relief.
(Related: See our “home remedy” First aid. 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 cutoff 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 What’s this?), 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 What’s this?) 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?
- With cold testing, the stimulus causes fluid in the tooth’s dentin tubules to contract. This fluid movement triggers pain receptors in 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.
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 device’s 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.
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.
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?
▲ Section references – Hargreaves, Torabinejad
d) Selective anesthesia.
- 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.
▲ Section references – Tronstad
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.
Page references sources:
Hargreaves KM, et al. Cohen’s Pathway of the pulp. Chapter: Pathology of the periapex.
Torabinejad M, et al. Endodontics. Principles and Practice. Chapter: Diagnosis, treatment planning, and systemic considerations.
Tronstad L. Clinical Endodontics. Chapter: Clinical examination.
All reference sources for topic Root Canals.
This section contains comments submitted in previous years. Many have been edited so to limit their scope to subjects discussed on this page.
Thermal testing for root canal
If thermal testing of a tooth, hot and cold, show no reaction at all (where surrounding teeth show reaction but it subsides quickly when stimuli is removed), does that suggest #3 nerves are dead. Tooth (#3) under a bridge completed 3 years ago experienced intense pain for several days duration on 2 occasions about a year apart, 2 years after bridge completed. Xrays show no indications suggestive of need for root canal. Is thermal reactions enough to diagnose need for root canal?
Yes, no response to hot or cold could mean that the tooth is necrotic (has no live nerve tissue). But there are possible complicating issues too.
The tooth’s nerve could be fine but the tooth doesn’t respond because the crown (bridge abutment) that covers over it insulates the tooth, thus inhibiting the transmission of hot or cold stimuli.
With age or after experiencing extensive work (like being trimmed for bridge placement), it’s common for some of the nerve space inside a tooth to calcify in (the nerve remains healthy). As a result the nerve inside the tooth is smaller, thus further away from the tooth’s surface from which the thermal stimuli would come. Hence, no response.
So, if a dentist was just randomly testing teeth and discovered one that didn’t respond to thermal testing, and the tooth has no other indication that it has an endodontic problem, a dentist would not initiate root canal therapy based on that evidence alone.
In your case, only your dentist can decide if that test, combined with your description of the tooth’s symptoms historically, justifies initiating treatment. No doubt they would much prefer to have supporting evidence from other types of testing too.