*References 99, 202, 205, 212, 252, 253, 282, and 283.
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Figure 9-22 Deformation of endodontic instruments manufactured from nickel-titanium alloy. A and B, Intact and plastically deformed ProFile instruments (arrows indicates areas of permanent deformation). C, ProFile instrument placed on a mirror to illustrate elastic behavior.
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Figure 9-23 Design features of a LightSpeed instrument. A, Lateral view. (SEM, ×50.) B, Cross section. (SEM, ×200.) C, Lateral view. D, Design specifications.
The ProFile system was introduced by Dr. Ben Johnson in 1994. In contrast to the LightSpeed, with its thin, flexible shaft, the ProFile has an increased taper compared with conventional hand instruments. The ProFile first was sold as a series of 29 hand instruments in #.02 taper, but it soon became available in #.04 and #.06 conicity (see Fig. 9-24). The tips of the ProFile Series 29 rotary instruments (Dentsply-Tulsa) had a constant proportion of diameter increments (29%). Because of the nonstandardized diameters, obturation was performed with nonstandardized gutta-percha cones, using either lateral compaction or thermoplastic obturation of gutta-percha (see Chapter 10). Later, another ProFile series (Dentsply Maillefer) was developed and marketed in Europe. This version featured tip sizes similar to those of ISO-normed instruments. This set was believed to better accommodate standardized gutta-percha cones, which are predominantly used in Europe. Subsequently, instruments with even greater tapers and 19 mm lengths were introduced, and recently a #.02 variant was added (see Fig. 9-24).
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Figure 9-24 Design features of a ProFile instrument. A, Lateral view. (SEM, ×50.) B, Cross section (SEM, ×200.) C, Lateral view. D, Design specifications. *Note that ProFile tip sizes do not always correspond to ISO sizes; for example, an instrument designated size #25 in fact has a somewhat smaller tip diameter.
Cross sections of a ProFile instrument show a U-shape design with radial lands and a parallel central core. Lateral views show a 20-degree helix angle, a constant pitch, and bullet-shaped, noncutting tips. Together with a neutral or slightly negative rake angle, this configuration ensures a reaming or scraping action on dentin rather than cutting. Also, debris is transported coronally and is effectively removed from the root canals.
The recommended rotational speed for ProFile instruments is 150 to 300 rpm, and to ensure a constant rpm level, the preferred means is electrical motors with gear reduction rather than air-driven motors.
ProFile instruments shaped canals without major preparation errors in a number of in vitro investigations.* A slight improvement in canal shape was noted when size #.04 and #.06 tapered instruments were used in an alternating fashion.44 Loss of working length did not exceed 0.5 mm44-46,285,286 and was not affected by the use of size #.06 instruments.44
The Greater Taper file, or GT file (Fig. 9-25), was introduced by Dr. Buchanan in 1994. This instrument also incorporates the U-file design. The GT system was first produced as a set of four hand-operated files and later as engine-driven files. The instruments came in four tapers (#.06, #.08, #.10, and #.12), and the maximum diameter of the working part was 1 mm. This decreased the length of the cutting flutes and increased the taper. The instruments had a variable pitch and an increasing number of flutes in progression to the tip; the apical instrument diameter was 0.2 mm. Instrument tips were noncutting and rounded.
The GT set subsequently was modified to accommodate a wider range of apical sizes. The current set includes instruments of three apical diameters: 0.2, 0.3, and 0.4 mm (Fig. 9-25). The tapers also were modified and now are available in #.04, #.06, #.08 and #.10. In addition, accessory files with a #.12 taper are available in sizes #35, #50, #70, and #90. The maximum diameter in these files is 1.5 mm, similar to that of a #6 GG. The recommended rotational speed for GT files is 350 rpm, and the instrument should be used with minimal apical force to avoid fracture of the tip.
*References 44-46, 147, 202, 205, 284, and 285.
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Figure 9-25 Design features of a GT-file. A, Lateral view. (SEM, ×50.) B, Cross section. (SEM, ×200.) C, Lateral view. D, Design specifications.
Studies on GT files found that the prepared shape stayed centered and was achieved with few procedural errors.100,121,206,210,331 μCT comparisons showed that GT files machined statistically similar canal wall areas compared with ProFile and LightSpeed preparations.206 These walls were homogeneously machined and smooth.191,331
First-generation rotary systems had neutral or slightly negative rake angles. Second-generation systems were designed with positive rake angles, which gave them greater cutting efficiency. HERO instruments (MicroMega, Besançon, France) are an example of a second-generation system.
Cross sections of a HERO instrument show geometries similar to those of an H-file without radial lands (Fig. 9-26). Tapers of #.02, #.04, and #.06 are available in sizes ranging from #20 to #45. The instruments are relatively flexible (the acronym HERO stands for high elasticity in rotation) but maintain an even distribution of force into the cutting areas.296,297 HERO instruments have a progressive flute pitch and a noncutting, passive tip, similar to other NiTi rotary systems. The instruments are coded by handle color.
Research with HERO files indicates a shaping potential similar to that of the FlexMaster127 (Dentsply VDW, Munich) and the ProFile,97 although in one study the HERO induced more changes in cross-sectional anatomy.105 HERO instruments also were found to cause some aberrations when used in simulated canals with acute curves282 but were safer than Quantec SC instruments (Analytic Endodontics, Orange, CA).130
The ProTaper system is based on a unique concept and comprises just six instruments, three shaping files and three finishing files. These instruments were designed by Dr. Cliff Ruddle, Dr. John West, and Dr. Pierre Machtou. The cross section of the ProTaper shows a modified K-type file with sharp cutting edges and no radial lands (Fig. 9-27); this creates a stable core and sufficient flexibility for the smaller files. The cross section of finishing file F3 is slightly relieved for increased flexibility. The unique design factor is the varying tapers along the instruments' long axes. The three shaping files have tapers that increase coronally, and the reverse pattern is seen in the three finishing files.
Shaping files #1 and #2 have tip diameters of 0.185 mm and 0.2 mm, respectively, 14 mm long cutting blades, and partially active tips. The diameters of these files at D14 are 1.2 and 1.1 mm, respectively. The finishing files (F1, F2, and F3) have tip diameters of 0.2, 0.25, and 0.3 mm, respectively, between D0 and D3, and the tapers are 0.07, 0.08, and 0.09, respectively. The finishing files have noncutting tips.
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Figure 9-26 Design features of a HERO instrument. A, Lateral view. (SEM, ×50.) B, Cross section. (SEM, ×200.) C, Lateral view. D, Design specifications.
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Figure 9-27 Design features of a ProTaper instrument. A, Lateral view. (SEM, ×50.) B, Cross section. (SEM, ×200.) C, Lateral view. D, Design specifications.
The convex triangular cross section of ProTaper instruments reduces the contact areas between the file and the dentin. The greater cutting efficiency inherent in this design has been safely improved by balancing the pitch and helix angle, preventing the instruments from inadvertently screwing into the canal. The instruments are coded by colored rings on the handles. ProTaper instruments can be used in gear reduction electrical handpieces at 300 rpm in accordance with universally recognized guidelines.
In a study using plastic blocks, the ProTaper created acceptable shapes quicker than GT rotary, ProFile, and Quantec instruments331 but also created somewhat more aberrations. In a comparison of ProTaper and K3 instruments (SybronEndo, Glendora, CA), Bergmans et al30 found few differences, with the exception of some transportation by the ProTaper into the furcation region. A study using μCT showed that the ProTaper created consistent shapes in constricted canals without obvious preparation errors, although wide canals may be insufficiently prepared with this system.205