Why do some root canals fail?

Root canal failure: Root canals fail for many reasons. For example the tooth may fracture or split. Sometimes infection at the end of the tooth is very resistant to antibiotic and cause failure. Occasionally, the seal in the root canal may fail and allow bacteria to invade the canal. Although there are other reasons, these are the most common.

Science & Art: Becasue dentistry is a healing art and science does not have answers to everything. There are patient factors beyond your dentists control that can lead to failure and then there are some that are realted to technique and etiology of the issue that led to root canal.

Root canal failure: There are many reasons for root canal failures but only one culprit, bacteria. Filling and crowns can leak. Roots can develop fractures. Root surfaces and crown surfaces can allow moisture within. Biofilms can develop around root surfaces. All these scenarios will allow bacteria to thrive in and around teeth. Don't worry as over 20 million root canals are done annually and 95% arsuccessfull.