Breakage of a file in the root canal can happen due to multiple factors and is an acceptable error while doing root canal treatment. The wrong act would be not informing the patient as he has done. And also further treatment should not have been continued without passing on the appropriate information to the patient. All cases of broken files do not lead to root canal treatment failure and in some cases, the file can be retrieved back and in other cases, it can be bypassed to complete the root canal treatment. I can understand your agony and frustration, but my job is to provide an honest opinion which is the fact that you can sue him for wrongful treatment if you have all the details of the treatment done, but unfortunately getting the licence cancelled or putting him behind the bars would be impossible for this mistake. Please understand that doctors are also humans and humans make mistakes and more importantly in this case, when we are dealing with such small metallic files, the physical and chemical properties of the metal also define such instances, which are not rare worldwide. As I mentioned previously, not passing the information to you at the right time was the main mistake he will be held guilty for. Regards.