When performing root canal retreatment, the dentist is faced with the task of removing the crown or core, which is an artificial object that blocks the above of the root canal. If the dentist fails to remove the crown or metalcore, especially if it is a metal restoration, it will be difficult to perform the re-root canal treatment, and happen the tooth fracture and have to be extracted. For dentists, this is a very stressful job with a lot of responsibility. Few doctors like removal. In other countries, I have heard that root canal retreatment is not favored due to its low clinical success rate, but in Japan, root canal retreatment is not uncommon. I think it is a national trait, but there are a lot of patients who want to preserve their teeth, and dentists also prefer preservative treatment. There is also the economic reason that the cost of root canal treatment is extremely low. In any case, for Japanese dentists, root canal retreatment is not an uncommon task in their daily cli...