In the outpatient clinic, we encounter many patients who are referred from outside hospitals, often because of “root canal failure”, and the patients will say “I heard you have advanced machines here, and it will pass as soon as you take a picture!” But is that the truth? The truth is that the advanced machine only helps the doctor to operate more accurately, and only with skillful technique can the maximum effect be achieved. And it depends on the condition of the tooth whether it is “through” or “not through” and whether it should be “through”. There are many reasons for root canal failure, such as severe calcification of the tooth itself, heavy bending of the root, or medical root canal deviation, foreign bodies in the root canal and many other reasons. An inaccessible root canal means that there may be infected material underneath that cannot be removed, and if this is the case, the tooth may still be inflamed and may still have swelling and pain. The choice between access and access, and the prognosis “varies from tooth to tooth”. The situation is complex and variable and requires a doctor’s decision. For example, if the tooth has been “nerve-killed” for many years without a perfect “root canal”, and the tooth is examined and found to be normal, there is no need to forcibly open the root canal or re-treat the tooth if the restorative conditions are met. Sometimes it is even possible to restore the tooth directly, saving time and money. It is also worth pointing out that root canal failure is a difficult endodontic procedure and involves risks.