The accessory canals are more problematic. They often occur near the third of the root nearest the tip. If they are detected, it is impossible to clean them and difficult to fill. These accessory canals contain dead nerve tissue that keeps the foreign body reaction going. The only possible way to try and remedy the situation is a surgical procedure that removes part of the root tip and hopefully allows the surrounding area to heal.
Fractures are a real problem and at times difficult to detect.
Very seldom are they detected visually. The fracture can be held tightly together by the encasement in bone. Only upon applying biting pressure does the tooth hurt. Special disclosing solutions may be helpful in identifying a fracture line, but it is not predictable. If the fracture splits the root or extends to far underneath the bone, the tooth is usually not salvageable.