It is mainly used to expand the root canal from the 8th to the 120th. The length is divided into 21MM, 25MM, 29MM, and other lengths. It is also divided into hand and machine files. It is the most commonly used file in root canal therapy. The most commonly used models are 21MM, 25MM, 8, 10, 15, 20, and 25.

The root canal expansion needle rotary drill has strong cutting ability, deep penetration and smooth root canal wall, which is suitable for penetrating the root canal and cutting the lateral wall, but it is easy to form steps or lateral penetration in the curved root canal.

The root canal file has strong lifting and cutting force and is not easy to break. It is used to bend the root canal and is not easy to penetrate laterally. It is suitable for elliptical or uneven root canals with irregular shape. Generally speaking, the two should be used alternately. For straight and thick root canals, first use an expanding needle, and for curved root canals, first use a file, and then use alternately.