Sometimes, a tooth that has had a previous root canal may need to be retreated. There are several reasons for a retreatment including: an untreated canal, contamination, new decay, as well as many other reasons.
In a retreatment, a small access hole is created in the crown of the tooth. Small instruments and disinfectants are used to carefully remove the previous root canal filling material. After all the material is removed, the canals are cleaned and prepped for a new filling material.
The filling is a rubber-like substance called gutta-percha. The gutta-percha placed with sealer and is heated up and packed into the canal space. In most cases, the tooth is temporally sealed with cotton and a temporary filling. This filling will last up to 4 to 6 weeks, until you can get back into your general dentist for your final restoration.