Teeth that have been damaged, either in accidents or by decay or gum infections, may run the risk of nerve damage. Many teeth that have old fillings in them, develop cracks through the teeth, which may end up in the nerve of the tooth and cause nerve damage. Although toothache can be a clear sign of tooth and nerve damage, not all nerve damage is made obvious by toothaches. It is very common for the nerves of teeth to "die" or become inflamed, without showing signs of damage except on X ray checks. Nerves (or pulp) of the teeth can also be exposed as a result of excess tooth wear and damage caused by tooth grinding, excessive brushing and cracks in older teeth. Damaged nerves can become infected and cause considerable pain. In the years gone by, when teeth had reached that stage, dentists would remove the tooth. Over the last 30 years or so, people have not been as willing to have teeth removed, and dentists have been able to "save" these damaged teeth by root canal treatment. Root canal treatment involves opening up the inside of the tooth through a small "access" area and removing diseased and damaged tissue that remains where the healthy nerve once lived. This damaged tissue is cleaned away and the inside of the tooth root or "leg" is gently cleaned and disinfected so that no germs can remain in the diseased area. Once all of the germs are killed, the area where the nerve used to be is sealed with a biocompatible plastic material, so that the tooth now can remain in place and its diseased "legs" or roots have been healed. During the healing process of the treatment, there can be some very minor discomfort, but by using local anaesthetics, there is no pain at all during the procedures. The general impression the public has of root canal treatment often is reminiscent of Dustin Hoffman's experiences in "Marathon Man", but in reality, the procedure is very simple. While most teeth can be saved with root canal treatment, in some cases damage to teeth can be so severe that saving them is impossible. In these cases, alternative treatments to replace teeth can be used, such as bridges, partial dentures, or implants.