Very bad toothache is often caused by a tooth abscess. When a cavity in a tooth gets large enough, the living part of the tooth (or pulp) becomes damaged. The pulp can then die and start to decompose. Bacteria from the mouth can get inside the tooth and cause an abscess at the very tip of the root. The pain you feel with an abscess is actually the nerves in the jawbone that are registering the pain, not the nerve inside the tooth although the decomposing remnants of the nerve and its blood supply are the source of the infection.
A typical dental abscess symptom is greatly increased pain when biting on the tooth. From the above it is clear why: you are pushing the tooth into its own abscess therefore increasing the pressure on the abscess even further. With the nerve having died, you tooth will not be sensitive to temperature changes. If that is the case it is unlikely to be an abscess.
Your body will try and find a way out for the pus that is building up inside the abscess and it does so by eventually creating fistula into your mouth. The exit point of the fistula you will see in your mouth as a gum boil. Out of the gum boil you will intermittently get a discharge of pus, straight into your mouth. This is obviously not the healthiest thing so treatment is essential. The pain is likely to reduce the moment a fistula has formed as the pressure that was building up inside the jaw bone can escape.
With a dental abscess we have two treatment options to eradicate the infection:
Either a root filling is done with the aim to remove all the infectious debris inside the tooth which is the cause of the infection. If this is done successfully, the abscess will disappear. The success rate of root treatments is approximately 85% if no root treatment has been done before on the tooth. If a root treatment has already been done in the past and has been unsuccessful, then the chance of success with a re-root treatment is considerably lower at approximately 50%.
The second method of eradication the abscess is by extracting the complete tooth. This removes the source of the infection within it and is certain to cure the abscess.
What is really important to understand is that a course of antibiotics will only alleviate the symptoms briefly but it does not remove the source of the infection. The abscess will still be there, be it slightly reduced in size but it will flare up as soon as the antibiotics have stopped working.