The pulp is where the blood vessels and nerves of the tooth are located and extends from the crown part of the tooth to the tip of the roots. The root of the tooth is located in the jaw underneath the gum. When there is a disbalance to the outer tooth structure due to trauma or caries the nerve can become infected/ inflamed and can become non-vital (die off).
Root canal treatment is an option to save and keep the tooth, rather than to have it removed. The procedure is carried out under local anaesthesia, so that the patient is relatively comfortable and pain free. The root canal system of the tooth is cleaned, shaped and filled in order to kill the bacteria, that has affected the pulp of the tooth.
In most cases RCT is not painful as your dentist will numb the tooth with local anaesthetic and would make sure you are comfortable before proceeding. In some cases some fibres of the pulp may still be alive and very inflamed and the anaesthetic may not be as effective. In these cases the dentist will place medicine inside the tooth and dress it for a few days to let it settle before they continue with your treatment.