C0083067x van T. Himel



Download 387.96 Kb.
Page3/5
Date conversion21.11.2016
Size387.96 Kb.
1   2   3   4   5




Low-Speed Rotary Instruments






Add to lightbox




   

Figure 8-26 Instrument tips arranged in order from cutting to noncutting. (Courtesy John T. McSpadden, Lookout Mountain, GA.)








Add to lightbox




   

Figure 8-27 RaCe instrument before and after electropolishing. (Courtesy John T. McSpadden, Lookout Mountain, GA.)






Many types of rotary instruments are used during endodontic procedures. In addition to regular burs adapted for endodontics, various types of root canal reamers are used to prepare the root canal or to place or remove root canal filling materials and to prepare the post space.




Burs




In addition to conventional burs, burs with extended shanks for low-speed contraangle handpieces (Fig. 8-28) are useful for providing good visibility during deep preparation of the pulp chamber. After access to the pulp chamber has been achieved, straight-line access to the initial point of curvature traditionally has been accomplished using rotary instruments such as Gates-Glidden burs and Peeso instruments. These reamers are available in a 32 mm length and a 28 mm length for posterior teeth (Fig. 8-29). Use of these instruments should be limited to the straight portion of the canal preparation. The risk of perforation with these instruments becomes a real possibility with attempts to instrument beyond the point of curvature or if the instruments are used to cut laterally. The risk of lateral cutting resulting in perforation is lower with Gates-Glidden burs than with the other instruments mentioned (Fig. 8-30). This risk is especially pronounced on the furcation sides of mesial roots of molars. Gates-Glidden instruments are also available in nickel-titanium (Fig. 8-31). The Peeso reamer is used mostly for post space preparation (Fig. 8-32).




Rotary Instruments for Canal Preparation




Components of a File




page 244



page 245






Add to lightbox




   

Figure 8-28 Various surgical length burs. The longer length of these burs allows a direct view. (From Johnson WT: Color atlas of endodontics, St. Louis, 2002, Saunders).








Add to lightbox




   

Figure 8-29 Gates-Glidden (GG) burs made of stainless steel. (From Johnson WT: Color atlas of endodontics, St. Louis, 2002, Saunders.)






To make the best use of files, the clinician should know the parts of each file and understand how variations in design affect instrumentation (Fig. 8-33 and 8-34). The taper usually is expressed as the amount the file diameter increases each millimeter along its working surface from the tip toward the file handle. For example, a size #25 file with a #.02 taper would have a 0.27 mm diameter 1 mm from the tip, a 0.29 mm diameter 2 mm from the tip, and a 0.31 mm diameter 3 mm from the tip. Some manufacturers express the taper in terms of percentage (e.g., a #.02 taper is a 2% taper). Historically, as an ISO standard, a file was fluted and tapered at 2% for 16 mm, but now files incorporate a wide variation of lengths and tapers of working surfaces. The ability to determine cross-sectional diameter at a given point on a file can help the clinician determine the file size in the point of curvature and the relative stress being placed on the instrument.






Add to lightbox




   

Figure 8-30 Working part of a GG bur made of stainless steel. Note the rounded safety tip and the lack of sharp cutting edges. The instrument has a marginal land for centering the drill in the canal and to allow safer machining of the canal walls.








Add to lightbox




page 245



page 246




   

Figure 8-31 Working part of a NiTi Gates-Glidden bur (Tulsa Dental Products, Tulsa, OK). Left, Small size; right, large size. Compare the design with that of the LightSpeed rotary instrument in Fig. 8-42.








Add to lightbox




   

Figure 8-32 Peeso reamer (Union Broach). Note the safety tip and guiding marginal lands on the machining surfaces.








Add to lightbox




   

Figure 8-33 Rotary ProFile NiTi instruments, sizes #3, #5, and #6 (Tulsa Dental Products). The instruments have marginal lands that guide the instrument in the center of the canals and around curvatures.








Add to lightbox




   

Figure 8-34 Components of an endodontic rotary instrument. (Courtesy John T. McSpadden, Lookout Mountain, GA.)






The flute of the file is the groove in the working surface used to collect soft tissue and dentin chips removed from the wall of the canal. The effectiveness of the flute depends on its depth, width, configuration, and surface finish. The surface with the greatest diameter that follows the groove (where the flute and land intersect) as it rotates forms the leading (cutting) edge, or the blade of the file. The cutting edge forms and deflects chips from the wall of the canal and severs or snags soft tissue. Its effectiveness depends on its angle of incidence and sharpness. If a surface projects axially from the central axis as far as the cutting edge between flutes, this surface is called the land (or sometimes the marginal width). The land reduces the tendency of the file to screw into the canal, reduces transportation of the canal, reduces the propagation of microcracks on its circumference, supports the cutting edge, and limits the depth of cut. Its position relative to the opposing cutting edge and its width determine its effectiveness. To reduce frictional resistance, some of the surface area of the land that rotates against the canal wall may be reduced to form the relief. The angle the cutting edge forms with the long axis of the file, called the helix angle, augers debris collected in the flute from the canal. This angle is important for determining which file technique to use (Fig. 8-35 and 8-36).




If a file is sectioned perpendicular to its long axis, the rake angle is the angle formed by the leading edge and the radius of the file. If the angle formed by the leading edge and the surface to be cut (its tangent) is obtuse, the rake angle is said to be positive or cutting. If the angle formed by the leading edge and the surface to be cut is acute, the rake angle is said to be negative or scraping (Fig. 8-37). However, the rake angle may not be the same as the cutting angle. The cutting angle, or the effective rake angle, is a better indication of a file's cutting ability and is determined by measuring the angle formed by the cutting (leading) edge and the radius when the file is sectioned perpendicular to the cutting edge. If the flutes of the file are symmetric, the rake angle and the cutting angle are essentially the same.




The pitch of the file is the distance between a point on the leading edge and the corresponding point on the adjacent leading edge; or, it may be the distance between corresponding points within which the pattern is not repeated. The smaller the pitch or the shorter the distance between corresponding points, the more spirals the file has and the greater the helix angle. Most files have a variable pitch, one that changes along the working surface. Because the diameter increases from the file tip toward the handle, the flute becomes proportionately deeper, resulting in a core taper that is different from the external taper.




page 246



page 247






Add to lightbox




   

Figure 8-35 Components of the ProTaper nickel-titanium rotary instrument (Dentsply-Tulsa Dental, Tulsa, OK). (Courtesy John T. McSpadden, Lookout Mountain, GA.)






The cutting angles, helix angles, and external and core tapers may vary along the working surface of the file, and the ratios of these quantities can vary between instruments of the same series. A change in any of these features can influence the file's effectiveness or its propensity for breakage as it progresses into the canal space and can explain why some files act uncharacteristically compared with other files in the same series. In one study, investigators using electric and air-driven handpieces with rotary nickel-titanium instruments found no significant difference in file distortion or breakage between the two handpieces at 150 revolutions per minute (rpm).38 Other researchers have shown that the ability to select precise rpm68 and torque95 settings affects the efficiency and durability of instruments. Determining a file's rpm level is more difficult with an air handpiece than with an electric handpiece. For this reason the clinician would be wise to use an electric handpiece when instrumenting with rotary files. The popularity of electric handpieces among clinicians appears to support the conclusion that regardless of the design used for rotary nickel-titanium instruments, an electric handpiece, rather than an air-driven handpiece, should be used because it allows precise speed control (Fig. 8-38).




Instrument Designs






Add to lightbox




   

Figure 8-36 Components of the Quantec nickel-titanium instrument (SybronEndo, Orange, CA). (Courtesy John T. McSpadden, Lookout Mountain, GA.)








Add to lightbox




page 247



page 248




   

Figure 8-37 Direction and action of the leading (cutting) edge. A negative angle (left) results in a scraping action, whereas a positive angle (right) results in a cutting action. Although cutting actions can be more efficient and require less force to enlarge a canal, a scraping action may have a smoother feel. The clinician erroneously may confuse smoothness with efficiency. However, applying excessive pressure to a cutting file could produce excessive torsion. (Arrows indicate the direction of the blade motion.) (Courtesy John T. McSpadden, Lookout Mountain, GA.)






Design changes are made in endodontic instruments to help prevent procedural errors, increase efficiency, and improve the quality of canal shaping. In many patients the apical canal is larger than the largest file used at working length; therefore, many design changes have been directed toward enabling the clinician to increase the size of the largest file used at working length.96,150 The following design components can be used to prevent excess stress on instruments.

  1. The difference between the file's minimum and maximum diameters can be reduced so that the torque required for rotating the larger diameter does not exceed the plastic limit of the smaller diameter.

  2. The space between the tip and the maximum diameter can be reduced so that the required torque does not exceed the ultimate strength of any part of the file.

  3. A zero taper or nearly parallel and fluted working portion of the file can be provided for curved canals so that the apical portion of the canal can be enlarged without undue file stress and compression of debris.

  4. The continuity of the blade engagement can be interrupted.

  5. The number of flute spirals can be eliminated or reduced to the smallest number necessary to prevent excessive torque, which results from the accumulation of debris.

  6. A means can be provided to complete the file function before the flutes fill with debris.

  7. Any land width can be minimized to reduce abrasion on the canal surface.

  8. The file can be given an asymmetric cross section to help maintain the central axis of the canal.

  9. The number of flutes with similar helix angles can be reduced. When helix angles are dissimilar, screwing-in forces are reduced; when flutes have no helix angles, screwing-in forces are eliminated.

  10. Positive cutting angles can be incorporated to enhance the efficiency of canal enlargement.

  11. Blades can be made appendages or projections from the file shaft rather than ground into the shaft.

  12. Channels can be cut along the long axis of the file to facilitate its removal if it breaks.






Add to lightbox




   

Figure 8-38 A high-torque, low-rpm electric handpiece. (Courtesy Dentsply-Tulsa Dental.)






ProFile and ProFile GT






Add to lightbox




   

Figure 8-39 Rotary ProFile NiTi instruments, size #3 (Dentsply-Tulsa Dental).






ProFile rotary nickel-titanium instruments (Dentsply-Tulsa Dental, Tulsa, OK) are available in sizes with a #.02, #.04, #.06, or #.08 taper (Fig. 8-39). These instruments are distinguished by their trihelical, symmetric U-shaped flutes separated by lands (Figs. 8-40, 8-41, and 8-42). The blades have slightly negative rake angles. The ProFile and ProFile GT have essentially the same cross-sectional configuration. The ProFile has a 16 mm working length; in contrast, the length of each taper of the ProFile GT varies as a result of having the same tip sizes and maximum diameters. The ProFile GT has slightly more spirals at the tip portion of the instrument and slightly fewer at the handle portion. The ProFile GT series does not include #.02 tapers. As with most systems using a large taper, the instrument becomes rather stiff before the apical preparation has been sufficiently enlarged.96,150 This puts limitations on the use of this instrument in narrow, curved root canals. ProFile GT instruments are divided into three primary size families (#20, #30, and #40) based on the tip size. Each series has four tapers (#.04, #.06, #.08, and #.10. The largest taper is also available in sizes #35, #50, and #70.




LightSpeed




page 248



page 249






Add to lightbox




   

Figure 8-40 Rotary ProFile NiTi instruments, size #5 (Tulsa Dental Products). Note the instruments' wide marginal land (arrows).








Add to lightbox






Add to lightbox




   

Figure 8-41 Microphotograph of ground cross section of ProFile/ProFile GT instruments (Tulsa Dental Products), showing the triple helix configuration. A, ProFile #45 with #.04 taper. Note the symmetric U-grooves and the three lands. B, ProFile GT #20 with #.10 taper. The cross section is similar to that of the ProFile, but the U-grooves are less clear.






The LightSpeed instrument (LightSpeed Technology, San Antonio, TX) has essentially the same cross-sectional design as the ProFile and ProFile GT. However, it has a unique, short, flame-shaped working portion and a reduced-diameter shaft similar to that of a Gates-Glidden drill. The long, unspiraled shaft provides good flexibility around canal curves. The minimal working surface requires higher rotation speeds (1000 to 2000 rpm) compared with other files. The tip has a long, noncutting pilot portion (Fig. 8-42). The LightSpeed instrument comes in sizes #020 to #140. It also includes "half" sizes (e.g., #022.5, #027.5) up to #060. In the smaller sizes the head is less well defined (Fig. 8-43). The design has been shown to vary with the instrument size.180 The manufacturer recently proposed that these instruments be used in a hybrid technique. Other instruments presented in this chapter would be used to shape the coronal segments of the root canal, and a limited number of LightSpeed instruments would be used to enlarge the apical segment. This suggestion is based on reports that larger-than-normal apical preparation sizes can be obtained with these instruments without compromising remaining dentin thickness in the more coronal segments of the canal.339 This capability takes on greater importance because increasing the size of the apical preparation has been shown to be directly related to the clinician's ability to disinfect the critical segment of the infected canal.266 In one study, a combination of tapered rotary and LightSpeed instruments was used in 40 patients; the study showed that instrumentation to apical preparation sizes larger than those typically used (60 for molars and 80 for cuspids and premolars) more effectively removes culturable bacteria from canals.49




Quantec






Add to lightbox




   

Figure 8-42 LightSpeed rotary NiTi instruments, size #90 (LightSpeed Technologies, San Antonio, TX). The instrument head and radial lands are well defined.








Add to lightbox




   

Figure 8-43 LightSpeed rotary NiTi instruments, size #20 (LightSpeed Technologies). The working head is slightly larger than the shaft, and the radial lands are poorly defined.






The Quantec instrument (SybronEndo, Orange, CA) has double helical, asymmetric flutes separated by lands, the width of which is reduced by a relief. The Quantec also has positive cutting blades on the working portion. The lands of the instrument are said to enhance the instrument's strength (Fig. 8-44). The Quantec file is available with two tip designs, a cutting tip (Fig. 8-45) and a safety cutting tip. Instruments come in #.02, #.03, #.04, #.05, #.06, #.08, #.10, and #.12 taper. The instruments are available in #.02 taper in sizes #15 to #60.




K3




Similar in concept to the Quantec, the K3 instrument (SybronEndo) has three asymmetric flutes separated by lands. A safety tip is incorporated into the design (Fig. 8-46). This instrument has the most positive cutting angles of the instruments currently available and is considered among the most resistant to fracture because of its cross-sectional geometry (Fig. 8-47). The instrument is available in #.02, #.04, and #.06 tapers. A series of body shapers in #.08, #.10, and #.12 is available and has become a common component of most instrument sets.




Hero 642




page 249



page 250






Add to lightbox




   

Figure 8-44 Quantec rotary NiTi instrument, size #10 with a #.02 taper (Analytic Endodontics, Orange, CA). Note the double land that characterizes the Quantec instrument. The higher marginal land (wide white bar) machines the root canal; the lower reduced peripheral surface (double white bars) contributes to peripheral strength. Note the sharp, blunt tip.








Add to lightbox




   

Figure 8-45 Quantec rotary NiTi orifice opener #1 with #.06 taper (Analytic Endodontics). Note the blunt, sharp tip of the instrument.






The Hero 642 (MicroMega, Geneva) has trihelical, sharp flutes resembling a Hedström design (Fig. 8-48). The blades are followed by recessive lands that do not extend axially to the circumference, which is designed to reduce stress. Consequently, the recommended rotation speed is 500 to 600 rpm. The Hero 642 has a large central core that resembles that of the K3. This instrument is available in sizes #20 to #45. All sizes are available in #.02 taper, and sizes #20, #25, and #30 also are available in #.04 and #.06 taper.




RaCe




The RaCe instrument (Brasseler, Savannah, GA, and FKG Dentaire, La-Chaux-de-Fonds, Switzerland) incorporates alternating nonspiraled and spiraled segments along its working length to minimize torsion of engagement and torsion resulting from screwing-in forces (thus its name, Reamer with Alternating Cutting Edges). In one study these instruments were found to do an excellent job of removing debris while maintaining the original canal curvature in extracted teeth.244




Sequence




Resembling a K-reamer, the Sequence file (Brasseler, FKG Dentaire) has a slight corkscrew configuration with variable pitch and helix angles. This design reduces the amount of force with which some parts of the blades become engaged in the canal wall. These instruments are available in #.04 and #.06 taper. The tip design is said to be noncutting, with the first blade positioned 1 mm from the tip.




EZ-Fill Safesider






Add to lightbox




   

Figure 8-46 K3 instrument with safety tip. (Courtesy John T. McSpadden, Lookout Mountain, GA.)








Add to lightbox




page 250



page 251




   

Figure 8-47 Comparison of the manufacturers' illustrated cross-sectional design (left) with the actual cross-sectional shape at different levels on the working surface, at 1 mm, 6 mm, and 14 mm from the file tip (right). The photographs of sections at D1 and D6 were taken in the direction toward the tip ends; the sections of D14 appear as mirror images because these were directed toward the handle ends.








Add to lightbox




   

Figure 8-48 Scanning electron microscopic (SEM) image of the Hero 642. Note the positive rake and the similarity to a trihelix Hedström file. (Courtesy MICRO-MEGA, Besancon, France.)






EZ-Fill SafeSider instruments (Essential Dental Systems, South Hackensack, NJ) are said to be designed around the principle that when fewer blades engage the canal walls, less stress is placed on the instrument. The EZ-Fill SafeSider is a series of noncircular, uninterrupted flat-sided instruments. Stainless steel SafeSiders (sizes #15 through #40) are made with relieved twisted wires and have a D-shaped cross section. The newest instruments in the series are made of nickel-titanium. These instruments have been reported to reduce dentinal engagement and consequently the resistance of the instruments in the canal, shortening the time required for canal preparation compared with conventional instruments.203




Oscillating/Reciprocating Files




The Giromatic handpiece, a rotary instrument in use since 1969, delivers 3000 quarter-turn reciprocating movements per minute. Rasps and barbed broaches are most often used in Giromatic handpieces, but K-type and H-type instruments also can be used. The Endo-Eze file system (Ultradent, South Jordan, Utah) is a recently introduced addition for Giromatic handpieces. The set has four instruments, which are designed to clean the middle third of the canal. The sizes and tapers are 0.10 # 0.025 taper, 0.13 # 0.35 taper, 0.13 # 0.45 taper and 0.13 # 0.06 taper The use of hand stainless steel instruments is suggested for the apical third of the canal.
1   2   3   4   5


The database is protected by copyright ©dentisty.org 2016
send message

    Main page