Endodontic files and reamers are surgical instruments used by dentists when performing root canal treatment. These tools are made of NiTi alloys, which contain approximately 56% nickel and 44% titanium. They are used to clean and shape the root canal, with the objective of performing a complete chemimechanical debridement of the root canal along the apical hole. This preparation facilitates chemical disinfection to a satisfactory length, as well as providing a shape conducive to sealing.
When it comes to endodontic files, there are several types available for use. K files are the most common and practical, while machined files are more expensive and fragile in the distal segments. K files are made of rectangular blanks that are turned so that the functional end of the instrument rotates in a spiral. The cross section of the K file is square, and its angle between the cutting groove and the long axis is generally in the range of 25 to 40 degrees.
Stainless steel endodontic files and other instruments can be sterilized by dry heating immersion in a “bath” of molten metal, salt, glass beads or steel balls. Hand files according to the ISO standard have a standardized cone of 2%, which is equivalent to an increase of 0.02 mm in diameter per mm of file. The introduction of single-use files has reduced the risk of damage, but it is still important to inspect them periodically when removing them from channels. A file can apically join the root canal wall due to its larger diameter compared to the canal, which causes friction. The file is then rotated 360 degrees counterclockwise to collect dentin from the flutes that was formed during the first rotation.
H-files are designed for a vertical movement instead of a rotating movement, as it is easier to damage the root canal wall. Among ISO stainless steel files currently on the market are K-Flex, K-Flexofile and Hedström, with standardized tips and cones. Nickel-titanium is a superelastic alloy that allows it to withstand greater tensions compared to stainless steel, so files have a reduced risk of fracture. They are usually torsion-loaded during use, but they also tend to bend. The angle between the cutting groove and the long axis of an H file is generally in the range of 60 to 65 degrees.
D files are custom-made rotating files that are commonly used in cases of retreatment to effectively eliminate guttapercha, although their cutting force is weaker than that of stainless steel files. The slight vibrations produced by an ultrasound or by a rotation of light with a Masserann extractor usually “explode” a NiTi file. It is vital for astute professionals to have deep knowledge of options, skill in recommended techniques for revision, appreciation for support provided by complementary technologies, and understanding of potential hazards presented in order to enjoy success in preventing, identifying and managing endodontic challenges.