Endodontics, from the Greek endo (inside) and odons (tooth), is a specialist sub-field of dentistry that deals with the tooth pulp and the tissues surrounding the root of a tooth. The pulp (containing nerves, arterioles and venules as well as lymphatic tissue and fibrous tissue) can become diseased or injured, and is often unable to repair itself; if it dies, endodontic treatment is required.The most common procedure done in endodontics is root-canal therapy. In endodontics, advanced technology, such as operating microscopes, ultrasonics and digital imaging are used to perform these special services. It is important to note that most general dentists are trained to address a variety of patients' endodontic needs, and thus most root canals are performed by general dentists. Other procedures practiced in endodontics include incision for drainage, internal tooth bleaching to fix teeth that have blackened because of infiltration of decayed soft tissue into the dentin in the teeth - most often seen in incisors  that have been injured through a sudden impact, and periradicular surgery (apicoectomy); the more radical treatments generally are needed in cases of abscesses, root fractures, and problematic tooth anatomy, but may be indicated in treating teeth that have persistent root end pathosis following root canal treatment.