For many years the standard cutting instruments have been the reamer, K-type file and Hedstroem file. These root canal preparation instruments have been manufactured to a size and type advised by the International Standards Organisation (ISO). The specifications recommended are complex and differ according to the type of instrument. For most standardized instruments the number refers to its diameter at the tip in one-hundredths of a millimetre; a number 10, for example, means that it has a tip diameter of 0.10 mm. Colour coding originally denoted the size, but now represents a sequence of sizes. All these instruments have a standard 2% taper over their working length.
Recent changes in both metallurgy and endodontic concepts have led to the introduction of a range of new instruments which do not conform to these specifications. These are described individually later and in Part 7. These instruments have been widely adopted, and appear to give consistently better results in root canal treatment. However, the conventional 2% taper instruments are essential for the initial exploration of most root canals, for difficult procedures such as bypassing separated instruments, and for the apical preparation of some difficult canals.
Conventional standardized instruments are made of steel, which may wear quickly in dentine, and small size files may be regarded as disposable. Although some hand files are now available in a nickel titanium alloy, which is more resistant to wear than ordinary steel, the increased cost and inability to pre-curve has not led to their widespread use. The majority of these modern files are manufactured with a modified non-aggressive tip to prevent iatrogenic damage to the canal system, and improve performance of the instrument. Figure 10 shows the different appearance of the principal types of these instruments.
Recent changes in both metallurgy and endodontic concepts have led to the introduction of a range of new instruments which do not conform to these specifications. These are described individually later and in Part 7. These instruments have been widely adopted, and appear to give consistently better results in root canal treatment. However, the conventional 2% taper instruments are essential for the initial exploration of most root canals, for difficult procedures such as bypassing separated instruments, and for the apical preparation of some difficult canals.
Conventional standardized instruments are made of steel, which may wear quickly in dentine, and small size files may be regarded as disposable. Although some hand files are now available in a nickel titanium alloy, which is more resistant to wear than ordinary steel, the increased cost and inability to pre-curve has not led to their widespread use. The majority of these modern files are manufactured with a modified non-aggressive tip to prevent iatrogenic damage to the canal system, and improve performance of the instrument. Figure 10 shows the different appearance of the principal types of these instruments.