What is pulpitis: reversible or irreversible?

The outer shell of the tooth is enamel, and beneath it is a softer layer full of microscopic channels called dentine. In the centre is the pulp: the blood vessels that nourish the tooth and the nerves that give it feeling. MSD Manuals writes that pulpitis starts in three ways: decay advancing deep into the dentine, a tooth having procedures done more than once, and a knock disrupting the blood and lymph circulation of the pulp. The pulp has a particular weakness: inflamed tissue elsewhere in the body can swell, but the pulp sits squeezed between hard walls that do not give. MSD explains that in irreversible pulpitis, the swelling within this enclosed space disrupts the circulation and leads the pulp to die, followed by infection.

The yardstick that most clearly describes the distinction between reversible and irreversible is how long the pain lasts. According to MSD, in reversible pulpitis the pain usually starts when a cold or sweet stimulus touches the tooth and goes within 1–2 seconds of the stimulus being removed. In irreversible pulpitis, the pain either comes on its own or lasts for minutes after the stimulus is removed; in this picture the trigger is mostly heat, and less often cold. The position statement of the American Association of Endodontists (AAE) also defines the key sign of more severe inflammation as an exaggerated, lingering, prolonged response to cold.

You can roughly try this distinction at home: count how many seconds the ache lasts after a sip of something cold, and note whether a hot drink starts the pain and whether the pain comes when nothing is touching the tooth. This test does not make a diagnosis, but it gives you a ready answer to the first question the dentist will ask at the examination. The rest of the page explains what happens after that answer: the dentist's tests, how much of the nerve can be preserved, and the evidence for each treatment.

Pulpitis pain has two misleading features. The first is location: MSD writes that the patient may find it hard to identify the painful tooth, and may even confuse the upper and lower jaws, but does not confuse the right and left sides. That is why the dentist's tests are not limited to the tooth where you feel the pain. The second is its course: according to MSD, the pain can stop for a few days because the nerve has died. This is not healing; once the nerve has died completely, the tooth does not respond to heat and cold but hurts when tapped. When the infection spreads out of the root tip, the tooth becomes very sensitive to pressure and tapping, an abscess forming at the root tip lifts the tooth in its socket, and the tooth feels high when you bite.

How reliable is the clinical diagnosis? In one practice, the nerve tissue of 95 teeth extracted for other reasons over five years was examined under the microscope and compared with the clinical diagnosis made before extraction. Of the teeth diagnosed with a normal pulp or reversible pulpitis, the tissue examination gave the same result in 57 of 59 (96.6%); for a diagnosis of irreversible pulpitis, this agreement was reached in 27 of 32 teeth (84.4%). The authors state that the classification guides the right treatment in the great majority of cases, but that more reliable diagnostic methods are still needed. The practical meaning is this: if your dentist says reversible, the diagnosis is very likely to be correct; with a diagnosis of irreversible, roughly one tooth in six may be in better shape than expected.

This uncertainty has changed the approach to treatment in recent years. The AAE's 2021 position statement writes that tissue examinations do not show a clear boundary at which the pulp becomes beyond repair, that pulpitis can be seen as a disease that progresses by degrees in time and place, and it draws attention to the grading of initial, mild, moderate and severe pulpitis proposed by some researchers. The statement's conclusion is clear: a diagnosis of irreversible pulpitis made before treatment does not always call for complete removal of the nerve, and a more conservative treatment can be considered. The European Society of Endodontology (ESE) position statement on deep caries and the exposed pulp also lists keeping the pulp alive, and minimally invasive, biologically based treatments, among the main aims of modern endodontics.

There are also early data on how the new grading works in practice. In a study of 92 patients in Sudan, run jointly by the universities of Khartoum and Belfast, agreement between clinicians on this four-grade classification was, in the authors' words, only 'fair'; agreement was higher with the classic AAE classification. The researchers reported that a three-grade model of mild, moderate and severe discriminated better, and that with treatments based on this classification, 87% of pulps could be preserved. So the picture has not yet settled: the classic two categories are more consistent between clinicians, while the new grading aims to preserve more of the nerve. It is a fair question to ask your dentist which approach they use and why they have made that decision for your tooth.

You should also know where untreated pulpitis leads. The consequences MSD lists are inflammation and abscess at the root tip, infection spreading into the tissues of the face (cellulitis) and, rarely, infection of the jawbone. Infection spreading from the upper teeth can reach the sinus and the area around the eye; infection from the lower teeth can spread to the floor of the mouth and the neck. These pictures are rare, but they all come from the same start: pulp inflammation quietly advancing inside. That is also why the pain stopping is not reassuring in itself.

The first list is the typical behaviour of pictures in which the nerve can be preserved, or has a good chance of it. If an item from the second list applies to you, see a clinician the same day or at the first opportunity.

The diagnosis of pulpitis does not rest on a single test but on reading the history, the tests and the X-ray together. The order is usually as follows.

1. 1

   The history of the pain

   You are asked what starts the pain, how many seconds it lasts after the trigger is removed, whether it comes on its own, whether it wakes you at night, and whether it gets worse with heat or cold. Describe the result of the cold water test you did at home here.

2. 2

   Sensitivity tests

   The cold test and the electric pulp test show whether the nerve responds. The AAE points out that these tests actually measure the sensitivity of the nerve, not its vitality; MSD also writes that the electric test shows whether the pulp is alive but not whether it is healthy. For comparison, healthy teeth next to it and on the opposite side are also tested.

3. 3

   Tapping and biting tests

   Pain when the tooth is gently tapped or bitten on shows that the inflammation has reached the root tip. The AAE writes that if there is pain on tapping, the pulp is regarded as irreversibly inflamed.

4. 4

   X-ray

   How close the decay has come to the pulp, whether there is any sign of inflammation at the root tip and, in young patients, whether root development is complete are assessed. The AAE recommends intraoral X-rays of diagnostic quality.

5. 5

   Seeing the pulp directly if needed

   If a treatment that preserves part of the nerve is being considered, the decay is cleaned out completely and the exposed pulp is examined, preferably under magnification as the AAE recommends. Whether the bleeding can be controlled, and how the tissue looks, decide how much pulp can be left.

6. 6

   The treatment decision and your questions

   At the point of decision, ask: is the diagnosis reversible or irreversible, is pulpotomy suitable for this tooth and if not why not, will the tooth get a permanent filling at the same visit at the end of the procedure, and will the tooth need a crown later. The AAE regards placing a permanent filling straight away after nerve-preserving treatment as a strong predictor of success.

The treatment of pulpitis is stepped according to how much of the nerve is still healthy. All of these are single-tooth treatments and fall to your own dentist or an endodontist (a root canal specialist).

The following are wrong decisions often seen with this condition. We set them out so that, whichever clinician you see, you can ask the right questions.

The timescales depend on the treatment done. The sequence below is a general framework; what the clinician treating you says takes priority.

1. The day of the procedure

   The NHS writes that numbness can last a few hours after root canal treatment. Put off eating until the numbness has gone so that you do not bite your cheek or tongue.

2. The first days

   There may be swelling and a feeling of tenderness around the tooth; the NHS states that this should settle within a week or two. Paracetamol or ibuprofen can be used for pain.

3. Permanent filling or crown

   Do not wait long with a temporary filling. The AAE states that placing a permanent filling straight away after nerve-preserving treatments strongly determines success, and recommends waiting a suitable time before the tooth is prepared again for a crown.

4. Check-ups over the months

   After root canal treatment, healing at the root tip is seen on X-rays over months; after pulpotomy, whether the nerve has stayed alive is tested at check-up appointments. Do not skip your check-ups.

We do not give a single figure here, because the treatment of pulpitis ranges from a filling in a single visit to root canal treatment over several appointments and a crown. These are the items that determine the scope:

The state of the nerve

In the reversible picture a filling is enough; in the irreversible picture, pulpotomy, root canal treatment or extraction comes into consideration.

The type of tooth and number of roots

Root canal treatment of a single-rooted front tooth and of a molar with three or four canals differ greatly in time and difficulty.

How the tooth is restored

Whether the tooth is finished with a filling or a crown after treatment depends on how much sound tissue is left.

Who does the treatment

Curved canals or repeat root canal treatments may call for referral to an endodontist.