This is the most common reason patients eventually come in for a root canal. The pain is often described as a deep, throbbing ache that comes on without a clear trigger. Sometimes it starts as occasional discomfort that you can push through, then becomes something you cannot ignore. Other times it is constant from the beginning.

This kind of pain happens because the soft tissue inside the tooth, which contains nerves and blood vessels, has become infected or severely inflamed. The body is sending pain signals to tell you something is wrong deep inside the tooth.

What distinguishes this from a normal toothache: ordinary sensitivity or mild discomfort can come and go with certain foods or temperatures. But pain that throbs on its own, wakes you at night, radiates toward your jaw or ear, or simply does not clear up after a day or two is pointing to something deeper. Over-the-counter pain relief may reduce it temporarily, but it will not fix the underlying problem.

If biting or chewing on a particular tooth causes a sharp, sudden pain, or a lingering ache that builds under pressure, this is a serious warning sign. It means the tissue around the root of the tooth has become inflamed and is reacting to the force of chewing.

In early stages, the pain might only happen with harder foods or if you press directly on the tooth. As the infection grows, even light biting or the pressure of bringing your teeth together can cause significant discomfort. Some patients start unconsciously chewing only on one side of their mouth to avoid it, which is itself a sign that something is wrong.

This is different from a cracked tooth or a loose filling, though both can feel similar. A dental examination and X-ray are needed to tell the difference, which is exactly why this symptom should be assessed rather than managed around.

Almost everyone has brief sensitivity to cold at some point. That is normal. What is not normal is when the discomfort from a cold drink or hot food continues for 30 seconds, a minute, or longer after you have swallowed. That lingering, slow-fading ache is your tooth telling you the nerve inside is in trouble.

Healthy teeth respond briefly to temperature and recover quickly. An inflamed or infected nerve cannot settle down properly. It stays agitated, which is why the sensation takes far longer to fade than it should. In later stages, heat tends to cause more intense pain than cold, and some patients find that rinsing with cold water is the only thing that provides temporary relief from a hot drink.

That pattern specifically, being set off by heat and temporarily relieved by cold, is a well-known sign that the nerve inside the tooth is severely inflamed and a root canal is almost certainly needed.

When an infection forms inside a tooth, it does not stay contained forever. It spreads down through the tip of the root and begins to affect the bone and gum tissue around it. The result is swelling, tenderness, or a feeling of puffiness in the gum near that particular tooth.

The swelling may be subtle at first, just a feeling that the gum is slightly raised or tender when you touch it. Over time it can become more visible, like a rounded, soft lump in the gum. Sometimes the area aches on its own. Sometimes it is only tender to touch.

If the swelling spreads to your face, jaw, or neck, this is a dental emergency. Facial swelling from a tooth infection can indicate that bacteria are spreading beyond the mouth into deeper tissue spaces. This situation requires same-day care without question.

A small pimple-like bump that appears on the gum near a tooth, then disappears for a while, then comes back, is not a coincidence and is not a normal gum problem. It is called a dental sinus tract, a small channel that forms when the body tries to drain pus from an infected tooth root to the surface of the gum.

The reason it seems to come and go is that when the channel successfully drains some of the built-up infection, the pressure reduces and the bump shrinks. Then infection rebuilds, the bump returns. This cycle of appearing and disappearing can repeat for weeks or months, and many patients mistake it for a minor gum irritation or a mouth ulcer.

It is neither. It is a sign of an active, ongoing infection inside the tooth. The fact that the body is draining it does not mean the infection is clearing. The infection will continue until the tooth is treated. And while this draining process reduces the acute pain for a time, it means the infection has been spreading through the bone for that entire period.

Healthy teeth have a consistent colour. If one tooth has gradually become grey, brown, or significantly darker than its neighbours, this is often a sign that the tissue inside the tooth has died or is in the process of dying.

This happens because when the blood supply to the inner tissue of the tooth is cut off, whether from a deep infection, physical trauma, or a crack, the tissue starts to break down. As it does, it releases compounds that stain the inner walls of the tooth from the inside out, which is why the discolouration appears gradually and cannot be addressed by whitening.

This sign is particularly easy to miss because it develops slowly and there may be little or no pain associated with it, especially if the nerve has already died. Absence of pain does not mean the tooth is fine. An X-ray is the only way to know what is happening at the root level.

Not every cracked tooth needs a root canal. A small surface chip without symptoms often just needs smoothing or a filling. But when a crack runs deep enough to reach the inner part of the tooth, it creates a direct pathway for bacteria to enter. Once bacteria reach the inner tissue, infection follows.

The signs that a crack has gone deep enough to affect the tooth internally are: pain when you release biting pressure rather than when you apply it, sensitivity that lasts after the temperature trigger is removed, intermittent sharp pain with no consistent trigger, or a crack that you can feel with your tongue but that seems to run down into the gum line.

Cracks that extend below the gum line are a particular concern because they can sometimes make the tooth unsaveable even with root canal treatment. This is one reason why a cracked tooth with symptoms should never be left untreated for long. The earlier it is assessed, the more options are available.