Summary: Toothache may present in several ways, none of which is pleasant. The type and nature of the pain experienced is usually an indicator of the level of decay of the offending tooth.
When you attend the dentist with toothache, they will ask you a series of questions relating to when the pain occurs, where it hurts and what sets it off. Generally your responses will fit into one of the types below.
Sharp Pain which is set off by hot or cold drinks is usually due to a hole in the tooth or filling. The hot/cold food enters the tooth and sends a heat stimulus to the nerve. In the early stages of decay the pain will usually stop within a few seconds to one minute.

The usual solution is for the dentist is to drill and fill the tooth. A temporary filling can help if a patient attends at short notice as this should prevent further stimulation of the nerve.

Dull Pain , this pain may start without stimulus such as a hot drink. The pain is dull as bacteria have invaded the nerve space and caused damage to the living cells of the nerve. Cells of the immune system break open in response to the bacteria and release chemicals which stimulate the nerves. Further symptoms of pulpal death are pain when lying in bed at night. This is because the blood pressure increases inside the tooth when the patient lies down.

The usual treatment is to root fill the tooth, which cleans away the dead pulp tissue and bacteria. The other option is to have the tooth extracted especially if it is very badly decayed.

Sharp pain only when biting:

Pain may only occur when the patient bites together, usually involving the molar teeth. This finding is usually isolated to one cusp and is caused by a minute fracture in the enamel which allows the tooth to flex during biting. As the tooth flexs it stimulates the nerve which produces the pain.

Sharp pain when toothbrushing near the gums:

With age and wear our gums recede back from the teeth exposing the root surface. The root surface is protected by a thin and weak layer of cementum. This is lost quickly which exposes the dentinal tubules resulting in pain when brushing. Using Sensodyne toothpaste may solve the problem, otherwise your dentist can apply a special fluoride varnish which protects the root surface.

Many methods have been tried in order to stop dental pain.

Painkillers (analgesics) : the best off the shelf drug for dental painn is ibuprofen which is available marketed under the Nurofen label. If the pain is persistant then you should seek a dentist rather than chronically taking painkillers.

Placing aspirin on the gum next to the offending tooth is not recommended as it won't give any pain relief as the drug cannot enter the tooth via the gum, secondly aspirin may cause a chemical burn on the gum if left in contact for a long period of time. Aspirin should also be avoided in children, especially in those under the age of 12 years due to the possible cross reaction in those who may suffer from Reyes syndrome.