Despite your dentist's best efforts to clean and seal a tooth, new infections might emerge. Among the likely reasons for this include:
1. More than the normally anticipated number of root canals in a tooth (leaving one of them uncleaned)
2. An undetected crack in the root of a tooth
3. A defective or inadequate dental restoration that has allowed bacteria to get past the restoration into the inner aspects of the tooth and recontaminate the area
4. A breakdown of the inner sealing material over time, allowing bacteria to recontaminate the inner aspects of the tooth