The file broken inside the root of tooth has to be removed. If you dentist is not able to remove it then he can refer you to endodontist who has special instruments to remove the broken needles inside the root canal. If it cannot be retrived then your root canal will be a failure as it is difficult to remove the infection from root of the tooth in which the file is broken and lateron this infection can cause pain in the tooth and in that case you have to get the tooth pulled out . So go ahead and talk to your dentist and get yourself referred to an Endodontist. For more info on root canal treatment you can read this article... www.identalhub.com/articlecategory-root-canal-therapy-17.aspx