A root end surgery, also known as apicoectomy (L. apex, apicis: a summit or a tip), retrograde root canal treatment (c.f. orthograde root canal treatment) or root-end filling, is an endodontic surgical procedure whereby a tooth's root tip is removed and a root end cavity is prepared and filled with a biocompatible material. Microsurgical endodontics - dental surgery using a microscope - may be performed. This is usually necessitated when a conventional root canal therapy had failed and a re-treatment was already unsuccessful or is not advised. State-of-the-art procedures make use of microsurgical techniques, such as a dental operating microscope, micro instruments, ultrasonic preparation tips and calcium-silicate based filling materials. Removal of the root tip is indicated to remove the entire apical delta ensuring no uncleaned missed anatomy.