The short answer
A root canal treatment (Wurzelbehandlung) is needed when the living tissue inside the tooth — the pulp, containing the nerve and its blood supply — is inflamed beyond recovery or has died. The classic sign is pain that lingers: cold or heat that goes on hurting for half a minute or more after the stimulus has gone, pain that starts on its own, pain that wakes you at night, or a tooth that has become sore to bite on. But many teeth needing treatment give no warning at all and are found on an X-ray at a routine check-up, because a nerve that has already died stops sending signals. What decides it is a set of quick tests in the chair, read together with an X-ray — not how much it hurts.
What is actually inside your tooth
Under the hard enamel and dentine, every tooth has a hollow core running from the crown down through each root: a chamber and its canals, filled with soft tissue, blood vessels and nerve fibres. That tissue supplies the tooth and gives it its sensitivity to cold.
The important feature is that it is sealed inside hard walls. Inflamed tissue elsewhere in the body swells; inside a tooth there is nowhere to swell into, so the pressure rises against the walls. That is why toothache from an inflamed nerve throbs, and why it often worsens when you lie down.
That same anatomy explains the harder fact underneath this whole subject. Once bacteria have properly reached the pulp, the tissue cannot clear the infection and cannot regenerate — and once the pulp has died there is no blood supply left inside the tooth, which is why antibiotics cannot reach the bacteria sitting in there. The only routes are to clean and seal the canal system, or to remove the tooth.
How a nerve gets into trouble
Five paths account for nearly everything we see.
Deep decay — the commonest by far. Caries works through enamel and dentine, and once it reaches the pulp, bacteria are inside.
Repeated repairs. Each large filling removes more substance and brings the restoration closer to the nerve; a tooth on its fourth restoration has a thinner buffer than it had at twenty.
A crack, which lets bacteria in without an obvious hole — and is why a tooth can hurt sharply on biting long before anything shows on an X-ray.
Trauma. A knock to a front tooth can kill the nerve without breaking the tooth, and the tell-tale greying appears months or years later.
The gum route. Where advanced gum disease has stripped the support down to the root tip, bacteria can reach the pulp from below.
The symptom map
Read this as patterns rather than as a diagnosis. Several of these overlap, which is exactly why the tests exist.
| What you notice | What it usually suggests | How quickly to act |
|---|---|---|
| Short sharp twinge with cold that stops immediately | Sensitivity or an irritated but recoverable nerve — often not a root canal case | Routine appointment |
| Cold or heat that hurts for 30 seconds or more afterwards | Inflammation that has usually passed the point of recovery | Within days |
| Pain that starts by itself, especially at night | Pressure inside the pulp chamber | Within days |
| Pain that is hard to point to, or seems to move between teeth | Typical of pulp inflammation — the nerve gives poor location information | Within days |
| Severe pain that suddenly stopped | Frequently means the nerve has died, not that it has healed | Book, even though it feels resolved |
| Sore to bite on, tender to tap, tooth feels “high” | Inflammation has reached the tissue at the root tip | Within days |
| Heat makes it worse, cold briefly relieves it | Often a late-stage picture | Promptly |
| A small pimple on the gum that comes and goes, sometimes salty | A drainage channel from an infection at the root tip | Book — it is painless precisely because it is draining |
| Facial swelling, fever, difficulty swallowing or opening the mouth | Spreading infection | Same day, out-of-hours service (Notdienst) if necessary |
The silent cases
This is the part that surprises people, and it is the best argument there is for check-ups you feel you do not need.
A tooth stops complaining once the nerve inside it has died. The infection does not stop: it moves down to the root tip and settles into the bone, where it can sit for years and slowly dissolve a small area around the root. On an X-ray it shows as a dark patch at the tip — and it is very often found at a routine appointment in someone with no symptoms at all.
Three other silent situations come up regularly: a tooth being prepared for a crown, where the X-ray shows the nerve is already dead; a grey front tooth from a childhood accident, still comfortable, with infection quietly developing at the root; and a deep filling placed months ago that gradually stopped responding to cold without ever hurting.
None of these needs emergency treatment. All of them need treating.
early: simple
late: more involved
How the decision is actually made
No single test decides it. The diagnosis is a small set of quick checks read together, and the appointment is far less dramatic than the subject sounds.
The cold test (Sensibilitätstest). No reaction at all suggests the nerve is no longer alive; a reaction that lingers well after the cold is removed suggests inflammation beyond recovery; a brief reaction that stops immediately is a good sign. Neighbouring teeth are tested too, so your own normal reaction is the reference.
Tapping and pressing (Klopf- und Druckprobe). A tooth tender to tapping points to the tissue around the root tip rather than the nerve itself, and tenderness when the gum over the root is pressed points the same way.
The bite test. Biting on a small stick, cusp by cusp, to find the one that produces the pain — the standard way of hunting a crack.
Probing the gum, to check whether the problem comes from the gum rather than the nerve, and whether the tooth still has enough support to be worth treating.
The X-ray, which shows how deep the decay runs, whether there is a change at the root tip, and what any previous treatment left behind. In selected cases a 3D X-ray (DVT) adds a dimension a flat image cannot.
Where the tests can mislead. Worth knowing, because it explains why a dentist sometimes says “let us watch this for a few weeks”. Teeth under crowns and large metal restorations respond unreliably to cold. Canals narrow with age, so an older tooth may react weakly while being perfectly healthy. After an injury a tooth may not respond for weeks and then recover completely. And pain from an upper back tooth can be indistinguishable from sinus pain. A responsible answer sometimes takes two appointments, and that is not indecision.
When it is not a root canal
Plenty of teeth that feel alarming do not need the nerve treating. These are the common ones.
- A new filling that is sensitive to cold for days to a few weeks — irritation from the work itself, usually settling on its own.
- Exposed tooth necks from receding gums: sharp, brief, triggered by cold air and drinks, and typically across several teeth at once.
- Grinding and clenching (Bruxismus) — soreness, tenderness on biting and morning jaw ache. The treatment is a night guard, not endodontics.
- A cracked cusp that has not yet involved the nerve, where the answer is often a crown to hold the tooth together.
- Sinus problems, which can make several upper back teeth ache at once, worse when you bend forward.
The pattern that separates most of these from a pulp problem: they are triggered and they stop. Pulp pain lingers, arrives unprovoked, and does not respect the clock.
What is normal — and when to contact us
Book a normal appointment for sensitivity in one tooth that has been worsening over weeks, a front tooth that has changed colour, a tooth that once hurt badly and then stopped, or a tooth that simply feels different when you bite. Add to that list: no X-ray in several years — silent findings are caught this way and no other.
Book within a few days for pain that lingers half a minute or more after hot or cold, pain that starts unprovoked or wakes you at night, a tooth that is sore to bite on or feels raised, or a recurring pimple on the gum near a root.
Special situations
Pregnancy. Treatment can be carried out during pregnancy, and an untreated infection is the greater risk to mother and baby. Local anaesthetic is used routinely; X-rays only where necessary and with protection. Tell us before anything is planned.
Children and teenagers. A permanent tooth whose root is still developing is treated differently, with methods aimed at keeping the pulp alive so the root can finish forming — never assume the adult answer applies.
If you are anxious. Endodontics has an outdated reputation that keeps people away for years, and the delay costs teeth. The appointment is done under local anaesthetic and is generally experienced as long rather than painful; sedation or laughing gas (Lachgas) is available. Say so when you book.
If you have just moved to Germany. A check-up is covered by your statutory fund once per calendar year and takes minutes — and it is the appointment at which silent findings are caught. Whether treatment is covered depends on rules that differ from most other countries: Does German health insurance pay for a root canal? (EN). If describing a pain in German feels risky, choose a practice where you can describe it precisely: English-Speaking Dentist in NRW.
Mainly by the cold test and the X-ray, compared against your other teeth. A tooth that gives no response to cold while its neighbours do is likely to have lost its nerve supply, and darkening at the root tip supports that. Neither finding alone is conclusive, which is why they are read together and sometimes rechecked after a few weeks.
No. Antibiotics travel in the bloodstream, and a tooth with a dead pulp no longer has one inside — so the bacteria in the canals are effectively out of reach. They have a genuine role in controlling a spreading infection, swelling or fever, which is a different job. The source itself is dealt with only by cleaning the canals or removing the tooth.
No, and this is why early treatment is worth the appointment. Where decay has not yet reached the pulp, the tooth is cleaned and filled and the nerve stays alive. Where it is very close, careful techniques can sometimes protect the pulp and let it settle. Only when bacteria are already inside the pulp chamber does the choice narrow to treatment or removal.
Yes. Discoloration of that kind usually means the nerve died at some point, often after an old knock. If the diagnosis is confirmed the tooth is treated internally, and it can then usually be lightened again from the inside or restored to match its neighbours. Nobody can promise an exact shade — but a grey tooth is not something you simply have to live with.
The decision is not made by how much a tooth hurts. It is made by whether the pulp inside it is inflamed beyond recovery or already dead — established with a cold test, a tap, a bite test and an X-ray, in a few minutes. Lingering pain after hot or cold, pain that arrives unprovoked and soreness on biting are the signals worth acting on within days. Silence is not proof of health: some of the teeth most in need of treatment are the ones that stopped complaining. If in doubt, have it looked at while your tooth still has every option open to it.
Zahnarztpraxis Tsypin · Wuppertal. This article was medically reviewed and is provided for information; it does not replace an examination. Updated August 2026.
