Instruments used for endodontic treatment A. Instruments used for coronal and \or access opening



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LECTURE II

PRECLINICAL ENDODONTIC



Instruments used for endodontic treatment

A. Instruments used for coronal and \or access opening:

It includes some instruments familiar in restorative dentistry and others which have been specially adapted for endodontics.

The endodontic explorer is a double-ended, extra-long, sharp designed to help in the location of canal orifices and probing for fractures on the pulp chamber floor. A long spoon excavator is required to scoop out pulp chamber contents and flick away pulp stones during access cavity preparation. Mirrors and locking tweezers are ideally suited to the handling of paper points, gutta-percha and root canal instruments. Plastic instruments and amalgam pluggers are needed to place interappointments restorations. An endodontic millimeter ruler should be available to assess root canal length. Irrigating syringe is important to deposit endodontic irrigant in the pulp spaces.

Burs both friction grip are used in the initial stages of access preparation to established correct outline form and round burs for low speed handpiece (normal and extra-long length), are used to lift the roof of the pulp chamber and eliminate overhanging dentine. Safe-ended diamond or tungsten-carbide bur, both with a non-cutting tip, is used to taper and smooth the access opening. The non-cutting tip is used to prevent gouging on the floor of the pulp chamber, where important landmarks could be lost in pinpoint the location of root canals. Pulp chamber act as a map road for you toward the canals



Rubber dam

B. Instruments used for radicular portion of root canals:

1. Barbed broaches: they are made from soft steel wire. The barbs are formed by cutting into the metal and forcing the cut portion away from the shaft, so that the tip of the barb points towards the handle. They are mainly used for the removal of the pulp tissues from the root canals and removal of cotton- wool dressings.

2. Reamers: reamers were the original intracanal instruments, used for removal of the pulp contents and for widening and smoothing the canal walls. They are usually made by twisting a tapered three-sided triangular blank of stainless steel, with cross-sectional less than k-file, which makes reamers more flexible than K-files. Because each angle of the blank is approximately 60 degrees, a sharp knifelike edge is available. These instruments have between half to one flute per millimeters of length. The basic action of reamers is reaming, which involves placement of the instrument toward the apex until some binding is felt and then turning the handle more than a full revolution. Clockwise turning will remove materials from the canal by way of the flutes’ revolution, whereas counterclockwise turning will force materials apically. The major effectiveness of hard tissue removal by reaming is the insertion of the instrument by shaving the dentin walls.


3. K-files: There are various types of root canal file; the followings are the main types: K-file, Kflex, Flexofile, Flex-R, Hedström and Safety Hedström, and S-file. The following is a brief description for each:

K-file: This instrument is manufactured from stainless steel, by twisting four-sided square blank. The instruments have one and a half to tow and a half flutes per millimeter length. The square blank had angles of 90 degrees, which did not cut as well as the 60 degrees angle of the reamer. However, reamers a half to one flute per millimeters of length and thus files had many more cutting edges. The Files less flexible and less prone to fracture than reamers.

Files are predominantly used with a filing or rasping action, in which little or no rotation of the instrument in the root canal. Filing involves placement of the instrument toward the apex until some binding is felt and then removing the instrument by scraping against a side of the dentin wall with little or no revolution of the handle. This dragging against the side of the wall is also referred to as rasping action. The major effectiveness of hard tissue removal by filing is in the outstroke or withdrawal of the instrument by dragging the flutes on the dentin walls.



K-flex file: The K-flex file has a tapered diamond shaped cross-section. This instrument has a series of cutting flutes with alternate sharp less than 60° cutting edges and obtuse non-cutting edges. The cutting efficiency of the K-flex file is greater than many brands of K-file, due to increased flexibility and ability to remove debris as its alternating blades provide a reservoir for debris

Flexofile: This type manufactured in the same manner as the K-file but it has a triangular cross-section and non-cutting tip that gives sharper cutting blades and more room for debris than the conventional K-file.

Flex-R file: This type of files has a non-cutting tip, although most root canal instruments have a sharp tip. Removal of the sharp cutting edges from the tip of instruments helps to prevent undesirable ledge formation. The notion that the tip of the instrument demonstrates potentially active cutting surfaces led to the theory of balanced force and the eventual design of the Flex-R file.


Hedström and safety Hedström files: Hedström (H-type) files are made by cutting the spiraling flutes into the shaft of a piece of round, tapered stainless steel wire. Hedström files cut only in one direction, which is retraction. The efficiency of various endodontic instruments has been tested and, they found the Hedström instruments significantly more effective than other files types. The safety Hedström file feature which is the non-cutting safety side along the length of the blade reduces the potential for strip perforations. Hedström files, has two serious drawbacks. It is weakened at each position of gouging during manufacturer, resulting in a place for fracture if the flutes bind in dentin and the handle rotated. Also, if it is handled incorrectly and rotated clockwise after binding in dentin, its screw like configuration may further drive the instrument apically and crack the weakened and stressed root. They are especially indicated in the instrumentation of immature teeth, where the walls are irregular and may harbor considerable debris, also useful in removing silver points or loose broken instruments from canals.

Both K-style of reamers and files are available in three shaft lengths 21, 25 and 31 mm for anterior and posterior teeth. The sizes of both K-styles are designated according to the diameters of the instrument at specified positions along its length. The tips diameters increase in 0.05mm increments up to size 60 file, and then by 0.1mm increments up to size 140. The diameter at the tip of the point is known as D0. The spiral cutting edge of the instrument must be at least 16mm along, and diameter at this point is D16. The file diameter increases at a rate of 0.02mm per running millimeter of length.

Color coding:

See the power point file

Restoring forces:

Any instrument action requires an engine. An endodontic file or reamers has two parts: the operators hand and the instrument shaft. The hand force engine is obvious, but the instrument engine is not. As instrument is curved, elastic forces develop internally. These forces attempt to return the instrument to its original shape and are responsible for straighten of the final canal shape. These internal elastic forces (called Restoring forces) act on the canal wall during preparation and influence the amount of dentin removed. They are particularly influncential at the junction of the instrument tip and its cutting edges. This junctional point is the most efficient cutting surface along an instrument. When activated by the restoring forces, it removes more tissue than can any other region of the file. Restoring forces are what power of the changes in canal shape as they act through the sharp surfaces of an instrument. Restoring forces are directly related to the metal composition of the instrument, the cross-sectional area of the instrument, and the angle of deflection. The greater the angle of deflection, the greater is the power. The larger the instrument, the larger is the cross-section and the greater the power. The more rigid the material the instrument is manufactured from, the greater is the power.



So, how can the dentist control this force?

  1. Radicular access minimizes the deflection of all subsequent instruments. This effectively increases the radius and decreases the arc of the canal curvature by allowing the instrument a straighter path to the apex, which generate a lesser restoring force along its cutting edges and tip.

  2. A triangular cross section is preferred, especially as apical preparation diameter increases beyond a No.25 file. Triangular reamers have a cross-sectional area or mass that is 37.5% less than that of a square file of the same standardized size. By using a specific method for calculating of restoring force of both instrument (reamer and file) of the same sizes, they found that the triangular file would be expected to develop only 62.5% as restoring force against the canal wall as square file assuming both were placed through the same curvature.

  3. Less rigid metals. Ni-Ti (Nickel-Titanium) instruments are presently being investigated and offer improved preparation accuracy as a result of reduced restoring force.

The two unique features of Ni-Ti K-files that are related to the endodontist are shape memory and super-elasticity. The crystal structure of Ni-Ti alloy is body-centered cubic lattice, which referred to as the austenite phase or parent phase. The transition from the austensitic to martensitic phase occurs during root canal preparation which caused stress-induced martensitic transformation, rather than slip as in St-St files. The occurrence of this phenomenon is due to the fact that the total atomic movement between adjacent plans in the atoms of Ni-Ti is less than a full inetratomic distance when based on normal atomic lattice arrangement which is termed “shape memory”.

The ratio of the increase in stress to level off to progressive deformation even if strain is added due to the martensitic transformation. This results in the so-called super-elasticity, a movement that is similar to slip deformation. The differences between the behaviors of Ni-Ti and St-St alloy can be seen in Figure.

The above, description of metallurgy of both instruments identifies the great flexibility of Ni-Ti files which were responsible for reduction of the force that applied the canal walls compared with more stiffer St-St files.

Power-Assisted Root Canal Instruments

Ultrasonic Instruments

The use of ultrasonic energy to prepare root canals was first described in the 1950s, although commercial production took another 20 years. The followings are some types of the ultrasonic instruments.



Cavi-Endo

This was the first ultrasonic unit specifically designed for endodontic use. The machine is a modified cavitron which contains an irrigant reservoir that supplies a continuous flow of sodium hypochlorite. As the file vibrates within the root canal (at 25 kHz) an acoustic streaming effect is set up within the irrigant.



Piezoelectric

These units are supplied with a multifunctional handpiece, into which different tips are fitted. This unit is additionally used for the location of calcified canals, removal of broken instruments, removal of cemented posts and for periradicular surgery. The ultrasonic energy is utilized to clean and shape root canals, remove debris, and disinfect all in one operation. This is accomplished in different ways. One is by vibratory motion of the instrument which is moved up and down in the root canal will, abrade the root canal walls. Cavitation and acoustic streaming are other properties of ultrasound. Cavitation is the formation of cavities in the liquid and their subsequent collapse, which is accomplished by intensive hydraulic shocks strong enough to destroy metal objects. Acoustic streaming is the rapid movement of fluid particles in vortex-like motion about a vibrating object.



Sonic Instruments

The Endo MM 1500 was developed as a sonic vibratory handpiece to be attached to the turbine line of a dental unit. The handpiece operates at a frequency of 1500 Hz and accepts specially designed Micro-Mega files.

Many type of hand and power assisted instruments, are available that claim to benefit one over the other, but the proceeding will be a receiving of the root canal preparation using St-St and Ni-Ti K-files hand instruments.

Rotary instruments

Gates-Glidden and Pesso Drills:  These burs cut well, are reliable, and are relatively inexpensive.  If they break, they break high up on the shaft next to the part that fits into the slow hand piece.  Because they break so high up on the shaft they are usually very easy to remove from the tooth.  Gates Gliddens and Peesos are not end-cutting.  There is a nipple at the end of these instruments that prevents them from cutting at their tip.  When the nipple engages the wall of a curved canal, the drill just spins and does not cut apically. Consequently, Gates Gliddens and Peesos will not perforate the canal in an apical plane.

The differences are:



  1.  The cutting head is much smaller on the Gates vs. the Peeso.

  2.  The shaft is thinner on the Gates vs. the Peeso

  3.  The diameters of the heads are different for the same number instrument.

    For example, the numbers on both the Gates and the Peeso are denoted by the number of circumferential grooves located on the shaft just below the cutout for the latch.  Not only are these instruments good for making post-holes but they are exceptionally good for preparing root canals in an easy and reliable manner.  They are especially good to use in a modified crown-down technique. . 
Both instruments are used for coronal third preparation and post space preparation and aid in removal of fractured instruments.








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