Cracked Tooth Syndrome:

Cracked tooth syndrome is a very common problem, usually affecting teeth that are heavily filled.  The decay and subsequent filling causes a weakening of the remaining tooth structure.   Like all materials, teeth are subject to stress fatigue.   After many bites on the tooth, a hairline fracture can develop, usually at the bottom corner of the cavity.   If you grind or clench your teeth, the stress on the teeth is increased dramatically, often by up to 300%.   Even unfilled teeth can get cracks.

A cracked tooth may present with pain on biting, and sensitivity to hot and cold.   As the tooth flexes microscopically on biting, the nerve is stimulated via tiny tubes (tubules) which are situated in the dentine).  The tubules run down to the nerve and there is a movement of fluid in them, which you feel as a sharp pain.   The nerve becomes aggregated and inflamed due to an inflow of bacteria down the tubules, which release toxins into the nerve tissue.  This inflammation causes an increase in hot and cold sensitivity.

Left untreated, the crack continues to slowly propagate.   Sometimes the crack goes off to the side and the fragment of tooth breaks off.    The crack can also go deep into the root and at times right into the nerve.   It is hard to predict the course of the untreated tooth, but usually it is a slow downhill slide as the crack deepens.   The nerve can become attacked by the bacteria, leading to extreme pain as the nerve dies.  The infection in the nerve can then spread into the bone underneath, causing an abscess.   This pain is usually severe, not effectively controlled by pain killers.  

Treatment of a cracked tooth involves removal of the cracked section of tooth, if possible, and restoration of the tooth, or immobilisation and splinting of the cracked tooth section.   The ideal method of splinting the cracked sections is to bind the whole tooth together with a crown, so that any chewing forces move the tooth as a whole, rather than splitting it apart.

Despite the best possible treatment, 10% of cracked teeth have nerves that go on to die.  

Propagating

Crack

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Inflamed

Nerve

This is usually due to existing bacterial damage to the nerve of the tooth, from which the nerve does not recover.   In these situations, the tooth requires Root Canal Treatment to clean out the infected nerve tissue in the tooth.

If a crack propagates down into the root structure of a tooth, often the only treatment is extraction of the tooth.   If you end up losing a tooth, there are several options for replacement.   Please discuss these with your dentist.

In many instances, prevention is better than cure.   If you are aware of grinding or clenching your teeth, an occlusal splint or night-guard - a plate worn to protect the teeth - may be indicated.   Again, please discuss this with your dentist.