Instruments for widening of canal

Instruments for drilling (reaming) of canal.

Reamers. As the name implies, reamers are used for drilling. They are K-type instruments, so they are usually produced by grinding graduated sizes of round "piano" wire^, into cither a square or triangular configuration. They cut by being tightly inserted into the canal, twisted clockwise one-quarter to one-half turn to engage their blades into the dentin, and then with­drawn—penetration, rotation, and retraction. The cut is made during retraction, fhe process is then re­peated, penetrating deeper and deeper into the canal. When working length is reached, the next size instru­ment is used, and so on. Reaming is the only method that produces a round, tapered preparation, and this only in perfectly straight canals. In such a situation, reamers can be rotated one-half turn before retracting. In a slightly curved canal, a reamer should be rotated only one-quarter turn. More stress may cause breakage, the heavier reamers, size 50 and above, can almost be turned with impunity.

Files as well as reamers can be used for learning, but conversely, reamers do not work well as files - their flutes are too widespread to rasp. The tighter spiral of a file estab­lishes a cutting angle (rake) that achieves its principal cutting action on withedrawal, although it will cut in the push motion as well. The witherawing cutting action of the file can be effected in either a filing (rasping) or reaming (drilling) motion. In a filing motion, the instrument is placed into the canal at the desired length, pressure is exerted against the canal wall, and, while this pressure, is maintained, the instrument is withdrawn without turning. The rake of the flutes ef­fects a cutting action as the instrument is withdrawn. The file need not contact all walls simultaneously. For example, the entire length and circumference of large diameter canals can be filed by inserting the instrument to the desired working distance and filing circumferentially around all the walls. To use a file in a reaming action, the motion is the same as for a reamer - penetration, rotation, and re­traction. The file tends to set in the dentin more read­ily than the reamer and must therefore be treated more gingerly. Withdrawing the file cuts away the engaged dentin.

The cross section of the K-Flex is rhombus- or diamond-shaped. The spirals or flutes are produced by the same twisting procedure used to produce the cut­ting edge of the standard K-type files; however, this new cross section presents significant changes in instru­ment flexibility and cutting characteristics. The cutting edges of the high flutes are formed by the two acute angles of the rhombus and present increased sharpness and cutting efficiency. The alternating low flutes formed by the obtuse angles of the rhombus are meant to act as an auger, providing more area for increased debris removal. The decreased contact by the instru­ment with the canal walls provides a space reservoir which, with proper irrigation, further reduces the dan­ger of compacting dentinal filings in the canal. These files are widely used in North America.

Hedstroem files are made by cutting the spiraling flutes into the shaft of a piece of round, ta­pered, stainless steel wire. It is impossible to ream or drill with this instrument. To do so locks the flutes into the dentin much as a screw is locked in wood. To continue the drilling action would fracture the instrument. Furthermore, the file is impossible to withdraw once it is locked in the dentin and can be withdrawn only by backing off until the flutes are free. This action also "separates" files, Hedstroem files cut in one direction only - retrac­tion. Because of the positive rake of the flute design, they are also more efficient as files per se.

The new nickel titanium instruments are much more flexible and resist breakage even in small sizes.

Дата добавления: 2014-01-05