Cracked tooth or deep cavity? How the pain tells you

Decay: chemical, lingering and visible

A deep cavity reacts to sugar and cold, and the giveaway is the tail of the pain: it carries on for ten to thirty seconds after the stimulus has gone. That lingering is inflamed pulp, not sensitive dentine. Decay also shows on a bitewing radiograph as a dark shadow under the enamel, so it can be diagnosed from good images before you ever sit in the chair.

A crack: sharp, on release, invisible on film

A cracked tooth is usually comfortable until you bite on something small and hard, and the pain arrives as you release the pressure rather than as you press. Cracks run vertically, in the same plane as the X-ray beam, so film almost never shows them. We find them with a bite stick tested cusp by cusp, with fibre-optic transillumination and by removing the old filling and looking underneath.

Why the treatment diverges completely

A cavity is a filling, or an onlay if more than half the chewing surface is gone. A crack in dentine needs a restoration that wraps and holds the cusps together, which in practice means a crown. A crack reaching the pulp adds a root canal first. A crack that has split the root vertically has no restorative solution at all.

What we will not do

We will not crown a tooth because it twinged once, and we will not promise that a crown rescues a tooth with a split root, because it does not. A cracked tooth is diagnosed by a bite test in a chair, so a photograph and a message cannot settle it. When a patient sends images we say what is likely, what is possible and what has to wait for the examination.

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