The ability to access and remove a broken instrument will be influenced by the cross-sectional diameter, length and curvature of the canal, and further guided by the depth of external concavities. As a rule of thumb, if one-third of the overall length of an obstruction can be exposed, it can usually be removed. Clinicians need to radiographically visualize if the broken instrument is in the coronal, middle or apical one-thirds of the root. Instruments that lie in the straightaway portions of the canal can usually be removed. If a separated instrument lies partially around the curvature and if safe access can be established to its most coronal extent, then removal is oftentimes still possible. If the entire segment of the broken instrument is apical to the curvature of the canal and safe access cannot be accomplished, then removal is usually not possible.
The techniques required to remove a broken instrument first begin with establishing complete coronal access. Before establishing radicular access, attention is directed towards pre-operative radiographs and working films to better appreciate the root bulk, thickness of the dentinal walls, and if present, the depth of an external concavity. If radicular access is limited, then hand files are used serially small to large, coronal to the obstruction, to create sufficient space to safely introduce gates glidden (GG) drills. GG’s are used like "brushes" and each larger GG is stepped out of the canal to create a smooth flowing funnel which is largest coronally and tapers down to the head of the broken file.
The microscope, in conjunction with ultrasonic techniques, has led to precise microsonic techniques. Once the head of the broken instrument is readily visible then specially designed contra-angled, parallel-walled and abrasively-coated ultrasonic instruments (ProUltra ENDO Tips #3, 4, 5, Dentsply Tulsa Dental) are selected to sand away dentin and trephine circumferentially around the obstruction. The idea is to transfer ultrasonic energy to the broken instrument so that it will loosen, unwind and then spin. Oftentimes, the broken instrument will "jump out" of the canal.
When ultrasonic techniques fail, the fall-back option is to use the File Removal System (Dentsply Tulsa Dental) which provides a breakthrough in the retrieval of broken instruments lodged within the root canal space. The File Removal System is composed of variously sized microtubes and screw wedges. The microtube has a small handle to enhance vision and its distal end is constructed with a 45° beveled end and side window. The microtube is inserted into the canal and, in the instances of canal curvature, the long part of its beveled end is oriented to the outer wall of the canal to "scoop-up" the head of the broken instrument and guide it into its lumen. The screw wedge is then placed through the open end of the microtube and passed down its internal lumen until it contacts the broken instrument. Rotating the screw wedge handle counterclockwise (CCW) tightens, wedges, and oftentimes, displaces the head of the file through the microtube’s side window. With the broken instrument strongly engaged, it can generally be readily removed. More information on the File Removal System is posted to the Inventions page of this site. In addition, I also refer you to my Ruddle on Retreatment DVD "Removal of Posts and Broken Instruments" to exactly explain this precise clinical technique.
It’s true that sometimes it becomes a fine line between the good of removing the fragment versus the negative of thinning or perforating the root. My approach is to remove as little tooth structure as possible while still doing everything I can to get slightly past the broken instrument. Importantly, the canal is enlarged and ideally shaped no bigger than it would have otherwise been prepared if there was no broken instrument obstructing the canal.
Just to clarify - the ultrasonic instruments I designed and have extensively lectured and written about or shown in my videos were CPR. However, the high quality source who manufactured my ultrasonic instruments elected to have Dentsply Tulsa Dental manufacture/distribute the instruments and they are now being sold under the "ProUltra" name. CPR stood for Cliff & Phyllis Ruddle, but Spartan trademarked my CPR name under their company name and not mine. Currently, Spartan continues to sell "CPR" ultrasonic instruments; however, I cannot confirm the quality, performance or durability of their instruments. The ultrasonic instruments I recommend for broken instrument removal are the ProUltra ENDO Tips #3, 4 or 5. More information on these tips is posted to the Inventions page of this site. In addition, I also refer you to my Ruddle on Retreatment DVD "Removal of Posts and Broken Instruments".