Fractured Tooth Letting Bacteria In: The Hidden Cause of Persistent Pain

Some dental pain announces itself clearly. A deep cavity, an abscess, a tooth that responds unmistakably to cold — these are relatively straightforward to locate and explain.

Cracked teeth are not like that. Patients often describe a pain that comes and goes, that they cannot reliably point to, that seems to move between teeth, and that has been investigated more than once without a cause being found. It is one of the more frustrating diagnostic problems in dentistry, both for the patient and for the clinician.

The underlying mechanism, once understood, explains most of the confusion.

Enamel is hard but brittle. Dentine beneath it is more resilient. Under repeated loading — years of chewing, a heavy bite, grinding, or a single unlucky bite on something hard — microscopic cracks can initiate and gradually propagate.

Two things then happen.

Mechanically, the crack allows the segments of the tooth either side of it to move independently when you bite. That flexure stimulates the nerve inside the tooth. It also means the pain is provoked by biting and, characteristically, by releasing the bite — the segments springing back together produce a sharp jolt. Pain on release rather than on pressure is one of the more distinctive features.

Biologically, the crack is a pathway. Dentine is not solid — it contains millions of microscopic tubules running from the outer surface towards the pulp. A crack that reaches dentine opens these tubules to the oral environment. Bacteria, their toxins and their metabolic products travel along that route towards the pulp.

This is why a crack that is far too fine to be seen on a radiograph, and that has caused no visible cavity, can nevertheless produce inflammation and eventually infection of the nerve.

Several factors combine to make cracked teeth difficult to diagnose.

The pain is intermittent. It occurs only when the tooth is loaded in a particular direction, on a particular cusp, with a particular consistency of food. Between those moments the tooth may feel entirely normal.

It is poorly localised. Pulpal pain is transmitted by nerve fibres that do not carry precise positional information. Patients frequently cannot say which tooth is involved, and pain from an upper tooth is often felt in the lower jaw or vice versa, because the nerves converge centrally.

Radiographs often show nothing. A crack running vertically through a tooth is usually parallel to the X-ray beam and simply does not appear. Radiographs are excellent for detecting decay and bone loss around roots, but they are unreliable for cracks.

The tooth may look intact. Many cracked teeth have no visible fracture line at all until they are examined under magnification with special lighting, or until an existing filling is removed.

Symptoms evolve. In the early stage there may be nothing but occasional sharpness on biting. Later, cold sensitivity develops. Later still, the pain becomes spontaneous and throbbing, indicating irreversible pulp inflammation. Eventually the pulp dies and the pain may stop entirely — before returning as an infection around the root tip.

That last point deserves emphasis: pain stopping does not mean the problem has resolved.

• Sharp pain on biting, particularly on releasing the bite

• Pain that occurs only with certain foods or in one specific spot

• Sensitivity to cold that is sharper or lasts longer in one tooth than others

• Discomfort that has been present intermittently for weeks or months without a clear cause

• A tooth that feels different when you tap it with a fingernail

• Recurrent tenderness in a tooth that has a large old filling

• A dull ache that is difficult to localise

Our articles on cold water sensitivity in broken teeth and whether a crown can stop a tooth cracking cover related aspects.

Large existing restorations. This is the most common factor. A tooth that has lost a substantial amount of internal structure to decay and filling material has thinner, less supported walls. Every bite flexes those walls slightly. Our article on whether a large filling can break your tooth explains the mechanics.

Grinding and clenching. Sustained heavy loading, often at night and often without the patient's awareness, is a major contributor. A night guard distributes and reduces those forces.

Root canal treated teeth. These have lost internal structure and, being no longer vital, do not benefit from the small ongoing repair processes of a living tooth. They are generally recommended for crown protection for this reason.

Biting something unexpectedly hard. An olive stone, a fragment of bone, an unpopped popcorn kernel. Sometimes the crack initiates at that moment and propagates over months or years.

Temperature extremes. Very hot food followed immediately by very cold drink causes expansion and contraction. It is a minor contributor but a real one.

Steep cusps and a heavy bite. Some people simply generate more force and have tooth anatomy that concentrates it.

Because radiographs are unreliable, diagnosis depends largely on clinical detective work.

History. The pattern of pain — what provokes it, how long it lasts, whether it occurs on release — is frequently the most informative part of the assessment.

Bite testing. A small device is used to load individual cusps one at a time. Reproducing the patient's pain on a specific cusp localises the crack.

Transillumination. A bright light held against the tooth passes through intact tooth structure but stops at a crack, revealing it as a dark line.

Magnification. Loupes or a microscope, sometimes with dye staining, can reveal cracks invisible to the naked eye.

Removing existing restorations. Sometimes the only way to see a crack is to remove the filling covering it.

Vitality testing. Establishes whether the pulp is still alive and healthy, which determines whether root canal treatment is required.

Radiographs. Still taken, not usually to see the crack itself but to assess bone around the root, check for decay, and look for signs of infection at the root tip.

Cracked teeth are not a single condition, and treatment varies enormously.

A crack confined to enamel (a craze line) usually requires no treatment. These are extremely common, particularly in older teeth, and are generally harmless. Our article on micro-fractures and enamel crazing covers cosmetic management where appearance is a concern.

A crack extending into dentine with a healthy pulp is typically managed by covering the tooth to hold the segments together and prevent flexure. A crown or onlay is the usual approach. Our dental crowns page explains what this involves. Sometimes a temporary band is placed first to confirm that stabilising the tooth resolves the symptoms before committing to a crown.

A crack that has caused irreversible pulp inflammation or infection requires root canal treatment followed by a crown.

A fractured cusp that has separated can often be removed and the tooth restored, provided enough structure remains.

A crack extending vertically into the root — a vertical root fracture — has a poor outlook. Bacteria colonise the fracture line, which cannot be cleaned or sealed, and progressive bone loss follows. Extraction is usually the only realistic option, and replacement with a dental implant or bridge is then considered.

A split tooth, where the crack has separated the tooth into segments, cannot be saved in most cases.

The critical point is that this is a progression. A crack treated early may need only a crown. The same crack left for two years may need root canal treatment as well, and left longer may not be treatable at all. Early assessment materially changes the outcome.

Seek urgent care if you develop:

• Severe or throbbing pain, particularly at night

• Swelling of the gum, face or jaw

• Fever alongside dental pain

• A bad taste or discharge near the tooth

• A tooth that has become mobile

• Pain that no longer settles between episodes

Facial swelling with fever indicates infection that is spreading and requires same-day attention. Our articles on fever with facial swelling and fever with toothache explain the warning signs, and our emergency dentist page sets out how urgent appointments work.

Can a cracked tooth heal by itself?

No. Unlike bone, tooth structure has no capacity to repair a fracture. The crack will not close, and it will not seal itself against bacteria. What can happen is that the pulp lays down a layer of reparative dentine in response to the irritation, which sometimes reduces symptoms temporarily. That is a defensive response, not healing, and it does not stop the crack propagating.

Why can my dentist not see the crack on the X-ray?

Radiographs produce a two-dimensional image, and a crack running vertically through a tooth is usually oriented parallel to the beam, so it does not create a shadow. Cracks are also extremely thin. Radiographs remain valuable for assessing decay, the extent of existing fillings and bone around the roots, but a normal radiograph does not exclude a crack.

How long can a cracked tooth be left?

There is no safe interval, because propagation is unpredictable. Some cracks remain stable for years; others extend rapidly. What is predictable is the direction of travel — cracks do not improve. Given that treatment options narrow considerably as a crack extends towards and into the root, early assessment is worthwhile even when symptoms are mild.

Will a crown definitely fix the pain?

Not definitely. A crown works by binding the tooth so the segments cannot flex independently, which resolves symptoms in many cases. But if the pulp has already been irreversibly damaged by bacterial ingress, symptoms will persist and root canal treatment will be needed. If the crack extends into the root, a crown will not help at all. This is why the extent of the crack is assessed before treatment is chosen, and why some clinicians place a temporary band first to test the response.

Can bacteria really get through a crack I cannot even see?

Yes. Bacteria are measured in micrometres, and the tubules within dentine are wide enough to permit their passage. A crack does not need to be visible to the naked eye to function as a route into the tooth. It is also not only whole bacteria that matter — bacterial toxins and breakdown products diffuse readily and can provoke pulpal inflammation on their own.

Does grinding my teeth cause cracks?

It is a significant contributing factor. Grinding applies sustained, heavy, often lateral forces that teeth are not well designed to withstand, and it happens for prolonged periods during sleep when there is no protective reflex to stop it. If grinding is identified, managing it is an important part of preventing further cracks, particularly if you already have heavily restored teeth. Our TMJ treatment page covers assessment of jaw function.

If you have had intermittent, hard-to-locate pain on biting that has not been explained, a cracked tooth is worth specifically investigating. It requires a targeted examination rather than a routine one — bite testing, transillumination and magnification are not part of a standard check-up.

Bring as much detail as you can: which foods provoke it, whether the pain occurs when you bite down or when you let go, how long it lasts, and roughly when it started. That history is often the most useful diagnostic information available.

You can contact our team to arrange an appointment at our Wimpole Street practice. Our general dentistry and restorative dentistry pages set out the treatments available.

This article provides general information and does not constitute individual dental advice. The presence, extent and prognosis of a cracked tooth can only be determined following clinical examination and appropriate investigations. Outcomes vary between individuals, and not all cracked teeth can be saved. If you have severe pain, facial swelling, fever or difficulty swallowing or breathing, seek urgent care immediately; in an emergency call 999 or attend an emergency department. Wimpole Dental is regulated by the Care Quality Commission, and our clinicians are registered with the General Dental Council.

Next review due: 6 September 2027