All current rotary files cut the root canal into a form that has a round cross section. Substantial untouched areas may be left on the buccal and lingual sides of a flat root canal or on the side facing the isthmus in tear-shaped root canals. However, the self-adjusting file(SAF) can address these problems. SAF is a hollow file designed as a compressible, thin-walled, pointed cylinder composed of a nickel-titanium lattice. When inserted into a root canal, SAF adapts itself to the canal’s shape both longitudinally and along the cross section and removes a relatively uniform dentin layer with a reciprocating movement. A special irrigation device, VATEA, is connected to SAF to provide a continuous flow of irrigation into the recess of the canal at low pressure. Debris and the smear layer can be removed efficiently during the simultaneously mechanical and chemical preparations. Compared with popular rotary instruments, SAF can cut more of the root canal area. However, its efficiency in eliminating viable bacteria is debatable. SAF can easily remove bacteria in oval root canals. However, insufficient apical preparation and inadequate apical irrigation has also been reported. Hence, the removal of debris, smear layer, and bacteria in the apical region of the root canal is difficult for SAF. Furthermore, SAF plays only an additional flushing role in root canal retreatment because of its poor negotiation ability. The use of SAF with rotary instruments results in a significant reduction in the amount of filling residual. SAF cannot be totally separated, and the detachment of one of the arches at either of its ends is a common mechanical failure. Furthermore, the damaged file can easily be retrieved from the canal. The combination of SAF and hand instruments rarely results in dentinal microcracks. In conclusion, the emergence of SAF is important for the further improvement of the instruments that enhance the efficiency of root canal preparation as well as for reducing complications.
