Cracked teeth are a major cause of tooth ache and discomfort, but not all teeth crack in the same way. You can have a crack running through the tooth from the biting surface towards the root sometimes involving the nerve. The tooth may not necessarily appear split but the softer tissue inside is usually damaged and can cause severe sensitivity particularly with cold and/or on biting.
Craze lines are tiny cracks that only involve the outer enamel. They are common and need no treatment but can appear unsightly.
A cracked cusp occurs when the pointed part of the biting surface breaks off. This can be very sensitive to temperature but also often leave a very sharp edge that irritates the adjoining cheek or tongue.
A split tooth occurs when the tooth splits in two starting at the root and heading up to the biting surface. Often the smaller part is mobile but still attached to the gum causing pain on biting.
Teeth can crack due to extreme grinding or biting forces; an unexpected hard piece of food (such as a stone in fruit) or even a sudden change in temperature or pressure. A tooth already weakened with a large restoration or decay is far more likely to crack.
It is usually possible to repair a cracked tooth with resorting to extraction. Treatment may involve a large filling or (more commonly) a crown and possibly root canal treatment. Even if a broken tooth is causing no immediate discomfort it is important to consult your dentist as soon as possible to prevent further damage.