Bending properties of rotary nickel-titanium instruments
`Edgar Scha¨fer, Prof Dr,a Anita Dzepina, Cand Med Dent,a and Gholamreza Danesh, Dr,b
`Mu¨nster, Germany
`WESTFA¨ LISCHE WILHELMS-UNIVERSITA¨ T MU¨ NSTER
`
`Objective. We sought to compare the bending properties of different rotary nickel-titanium instruments and to
`investigate the correlation between their bending moments and their cross-sectional surface areas.
`Study design. Resistance to bending was determined according to International Standards Organization publication
`3630-1. The sample size was 10 files for each type, taper, and size. The cross-sectional surface area of all instruments
`was determined by using scanning electron microscope photographs of the cross section. The images were scanned
`and the area was calculated by using special software. Data were analyzed by using analysis of variance and the
`Student t test and the Newman-Keuls test for all pairwise comparisons. The strength of the correlation between the
`bending moment and the cross-sectional area was determined by computing the Pearson product moment correlation.
`Results. Bending moments were significantly lower for ProFile and RaCe files than for all other files (P ⬍ .05). K3 files
`were significantly less flexible than all other instruments (P ⬍ .05). The correlation between stiffness and cross-
`sectional area was highly significant (r ⫽ 0.928; P ⬍ .0001).
`Conclusion. Nickel-titanium files with tapers greater than .04 should not be used for apical enlargement of curved
`canals because these files are considerably stiffer than are those with .02 or .04 tapers.
`(Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2003;96:757-63)
`
`In International Standards Organization (ISO) publica-
`tion 3630-1,1 as well as in the American National
`Standards Institute/American Dental Association Spec-
`ification Nos. 28 and 58,2,3 several mechanical require-
`ments for root canal instruments are listed (eg, resis-
`tance to bending). The resistance to bending of a root
`canal instrument is determined by fixing the instrument
`at its tip along a length of 3 mm and bending it. The
`bending moment at an angle of 45° is measured.1
`The resistance to bending of root canal instruments
`influences the results of instrumentation in curved ca-
`nals. Instruments with increased flexibility cause fewer
`undesirable changes in the shape of curved canals than
`those with greater resistance to bending. This increase
`in flexibility is achieved either by different design fea-
`tures of the instruments or by the use of nickel-titanium
`alloys.4-7
`The bending properties of endodontic hand instru-
`ments are mainly influenced by their cross-sectional
`design.4,5,7 Camps and Pertot5 showed that stainless
`steel instruments with a square cross section had sig-
`nificantly larger bending moments than files with a
`rhombus-shaped cross-sectional design, which had sig-
`
`aPoliklinik fu¨r Zahnerhaltung, Westfa¨lische Wilhelms-Universita¨t
`Mu¨nster, Germany.
`bPoliklinik fu¨r Kieferorthopa¨die, Westfa¨lische Wilhelms-Universita¨t
`Mu¨nster, Germany.
`Received for publication Dec 12, 2002; returned for revision Mar 3,
`2003; accepted for publication May 8, 2003.
`© 2003, Mosby, Inc. All rights reserved.
`1079-2104/2003/$30.00 ⫹ 0
`doi:10.1016/S1079-2104(03)00358-5
`
`nificantly higher bending moments than instruments
`with a triangular cross section. According to these
`researchers, there was an exponential relationship be-
`tween file size and bending moment.5 Camps et al4
`conducted a study on the relationship between file size
`and stiffness of nickel-titanium files and found that the
`square cross section K-Files had a significantly larger
`bending moment than the triangular cross section K-
`Files. Again, an exponential relationship between file
`size and bending moment was observed for triangular
`and square cross section K-Files.4 Scha¨fer and Tepel7
`used custom-made prototypes of endodontic stainless
`steel instruments characterized by 5 different cross-
`sectional shapes and 3 different numbers of flutes to
`investigate separately the relationship between the
`bending properties and the cross-sectional design on the
`one hand and the number of flutes on the other hand.
`According to their results, the prototypes with a rhom-
`bus-shaped cross-sectional design had less resistance to
`bending than the prototypes with other cross-sections.7
`The square cross section prototypes had significantly
`greater bending moments than did all other instru-
`ments.7
`In contrast to endodontic hand instruments, surpris-
`ingly little is known about the bending properties of
`continuously rotating nickel-titanium instruments. Pon-
`gione et al8 compared the bending properties of .06,
`.08, .10, and .12 tapered GT Rotary files (Dentsply
`Maillefer, Ballaigues, Switzerland) with those of .04
`and .06 tapered ProFiles (Dentsply Maillefer). The GT
`Rotary files were found to be less flexible than ProFile
`instruments.8 Calas et al9 conducted a study on the
`
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`758 Scha¨fer, Dzepina, and Danesh
`
`ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY
`December 2003
`
`Table I. Instruments used in this evaluation
`Instruments
`Manufacturers
`
`FlexMaster
`
`VDW (Munich, Germany)
`
`Hero 642
`
`Micro Me´ga (Geneva, Switzerland)
`
`K3
`
`ProFile
`
`RaCe
`
`Kerr (Orange, Calif)
`SybronEndo/Kerr
`Dentsply Maillefer (Ballaigues, Switzerland)
`
`FKG (La Chaux-de-Fonds, Switzerland)
`
`Tapers
`
`.02
`.04
`.06
`.02
`.04
`.06
`.04
`.06
`.04
`.06
`.04
`
`Sizes
`
`25, 30, 35
`25, 30, 35
`25, 30, 35
`25, 30, 35
`25, 30
`25, 30
`25, 30, 35
`25, 30, 35
`25, 30, 35
`25, 30, 35
`25, 30, 35
`
`bending properties of Hero (Micro Me´ga, Geneva,
`Switzerland), ProFile, and Quantec (Tycom, Irvine,
`Calif) instruments with tapers of .02, .04, and .06. Hero
`files were found to be stiffer than Quantec instruments.9
`The purpose of this study was to evaluate the bend-
`ing properties of 5 different rotary nickel-titanium in-
`struments with different tapers and sizes. Another goal
`of this investigation was to analyze the cross-sectional
`surface areas of these instruments to determine whether
`the cross-sectional surface area of rotary files can be
`seen as the predominant parameter affecting their bend-
`ing properties.
`
`MATERIAL AND METHODS
`All instruments tested in this study are listed in Table I.
`
`Composition of nickel-titanium alloy
`We performed x-ray energy-dispersive spectros-
`copy using a Philips PSEM-500 scanning electron
`microscope and an EDAX PV 9100 microscope
`(Philips Electronics N.V., Eindhoven, The Nether-
`lands) to analyze the composition of the nickel-
`titanium alloy used for the different instruments. One
`instrument of each type, taper, and size was used to
`quantitatively identify the chemical composition.
`The concentrations of the different elements are
`given in mass percentages.
`
`Measurement of file diameters
`The dimensional measurements used in this study
`were described in detail previously.10,11 Twelve instru-
`ments of each type, taper, and size were investigated,
`and the mean diameters and tapers were calculated. The
`measurements of diameters of files were performed
`with a measuring microscope accurate to 0.001 mm
`(UWM; Leitz, Wetzlar, Germany). The instruments
`were mounted in a special microscope attachment to
`secure their orientation. The instruments were mea-
`
`sured at 2 measuring points situated 3 mm and 13 mm
`from the tips. The taper of each file was calculated by
`using these 2 diameters.
`
`Resistance to bending
`Resistance to bending was determined with a testing
`apparatus corresponding to that mentioned in ISO pub-
`lication 3630-1.1 Before testing, each instrument’s han-
`dle was removed where it met the shaft. The tip of the
`instrument was inserted into a chuck to 3 mm, perpen-
`dicular to the axis of the geared motor running at a
`speed of 2 rpm in a clockwise motion. A torque meter
`(Dino Plot P6501a502; Novotechnik, Ostfildern, Ger-
`many) was attached to the machine. The torque meter
`was first adjusted to a 0 reading to measure the bending
`moment. The special bending device was then adjusted
`until it came into contact with the instrument. The
`bending moment was automatically measured in
`gramme centimetre (gcm) and continuously recorded
`on a XY Recorder (WX 4301; Watanabe Instruments,
`Tokyo, Japan).
`The sample size was 10 for each type, taper, and
`size in accordance with the instructions given by ISO
`publication 3630-1.1 Statistical analysis was per-
`formed with commercial software (MedCalc 5.0;
`MedCalc Software, Mariakerke, Belgium). Differ-
`ences between the instruments with respect to their
`bending moments were analyzed by using analysis of
`variance and the Student t test and the Newman-
`Keuls test for all pairwise comparisons (P ⬍ .05).
`The strength of the correlation between the bending
`moment and the measured area of the cross section
`was determined by computing the Pearson product
`moment correlation (r).
`
`Calculation of cross-sectional surface area
`The cross-sectional area of all instruments was de-
`termined by using photographs of the cross section.
`
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`ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY
`Volume 96, Number 6
`
`Scha¨fer, Dzepina, and Danesh 759
`
`Table II. Composition of rotary nickel-titanium instruments (the concentrations are given in mass percentages)
`Co ⫹ Cr
`Instruments
`Ni
`Ti
`Fe
`Al
`
`FlexMaster
`Hero
`K3
`ProFile
`RaCe
`
`55.28
`54.37
`54.55
`54.26
`55.25
`
`44.42
`45.32
`45.12
`45.42
`44.49
`
`0.03
`0.04
`0.04
`0.04
`0.03
`
`Max. 0.01
`Max. 0.01
`Max. 0.01
`Max. 0.01
`Max. 0.01
`
`0.24
`0.26
`0.27
`0.26
`0.21
`
`Ni, Nickel; Ti, titanium; Fe, iron; Al, aluminum; Co, cobalt; Cr, chromium.
`
`One instrument of each type, taper, and size was em-
`bedded in resin (Technovit 4000; Kulzer, Bad Hom-
`burg, Germany) and cut at the 3.0 mm working diam-
`eter with an ISOmet 11-1180 low-speed saw (Buehler,
`Lake Bluff, Ill). All samples were photographed by
`using a scanning electron microscope (Philips PSEM-
`500) at a magnification of 160⫻. Images were scanned
`at 600 dots per inch, and the cross-sectional surface
`area was calculated by using Scion Image for Windows
`software (public domain image-processing and analysis
`program; National Institutes of Health). The software
`automatically calculated the cross-sectional area (in
`square inches) with a relative error of 0.01%.
`
`RESULTS
`Composition of nickel-titanium alloy
`The compositions of the different instruments are
`listed in Table II. All instruments contained 55-Nitinol.
`The differences in composition obtained were all within
`the precision of measurements.
`
`Measurement of file diameters
`The results of the dimensional measurements are
`summarized in Table III. As can be seen in Table III,
`the diameter and taper of an instrument can often co-
`incide with a higher or lower file size or taper than
`intended. The most distinct deviation from the intended
`taper was in .06 tapered Hero size 25 files. In fact, the
`taper of these files was only 5.14%, not 6%. If a file
`measured outside the tolerance, in nearly all cases the
`mean D3 and D13 measurements were on the small side.
`
`Resistance to bending
`The bending moments (Figure) of all instruments
`tested are summarized in Table IV. Statistically, bend-
`ing moments were significantly lower for ProFile and
`RaCe instruments—withRaCe files being significantly
`lower than ProFile instruments—in all sizes and tapers
`than for the other files tested (P ⬍ .05). K3 files were
`significantly less flexible in all sizes and tapers than
`were the other instruments (P ⬍ .05).
`
`Cross-sectional surface area
`The results for the calculated cross-sectional areas
`are presented in Table IV. The Pearson product mo-
`ment correlation was calculated to examine the corre-
`lation between the bending moment of the instruments
`and the measured cross-sectional surface area. The cor-
`relation coefficient (r) was 0.928 (95% confidence in-
`terval for r: 0.853-0.966). The P value resulting from
`this test was P ⬍ .0001, which revealed a highly
`significant correlation between the bending moment
`and the cross-sectional area.
`
`DISCUSSION
`Resistance to bending of root canal instruments de-
`pends on their metallurgic properties (eg, different al-
`loys) and their geometric shapes.4,5,7,12,13 Because
`meaningful data concerning the influence of different
`geometric shapes can be obtained only by comparing
`instruments made from the same alloy, the composition
`of the different nickel-titanium rotary instruments was
`investigated here. For all files, the resultant combina-
`tion was an equiatomic ratio of the major components
`nickel and titanium (Table II). The generic term for this
`alloy is 55-Nitinol.14
`Moreover, file dimensions may have a crucial effect
`on the bending properties of endodontic instruments.
`No international or national standards are currently
`available for rotary instruments with tapers greater than
`.02, so we decided to evaluate the diameters and result-
`ing tapers of the rotary nickel-titanium files on the basis
`of the ISO standard in publication 3630-1.1 In this
`standard, the diameter and taper of different types of
`instruments are carefully prescribed. According to the
`results obtained here (Table III), all .02 tapered files
`were within the ISO guidelines. In contrast, in the
`groups of .04 and .06 tapered files, the ProFiles and the
`Hero instruments had few sizes measuring outside the
`tolerance. These files were all on the small side. The .04
`tapered FlexMaster file size 30 was the only instrument
`that had a greater-than-allowed measurement at D3, but
`the D13 measurements were mostly within the accept-
`able range. The RaCe files had the most even measure-
`
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`
`760 Scha¨fer, Dzepina, and Danesh
`
`ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY
`December 2003
`
`Table III. Mean diameters (D3 and D13) and calculated tapers of all instruments (all values in mm)
`Diameters (mm)
`Acceptable range*
`
`Tapers
`
`Instruments
`
`Sizes
`
`.02
`
`.04
`
`.06
`
`FlexMaster
`Hero
`FlexMaster
`Hero
`FlexMaster
`Hero
`
`FlexMaster
`Hero
`K3
`ProFile
`RaCe
`FlexMaster
`Hero
`K3
`ProFile
`RaCe
`K3
`Profile
`RaCe
`
`FlexMaster
`Hero
`K3
`ProFile
`FlexMaster
`Hero
`K3
`ProFile
`FlexMaster
`K3
`ProFile
`
`25
`25
`30
`30
`35
`35
`
`25
`25
`25
`25
`25
`30
`30
`30
`30
`30
`35
`35
`35
`
`25
`25
`25
`25
`30
`30
`30
`30
`35
`35
`35
`
`*All values are in millimeters.
`
`D3
`0.294 ⫾ 0.011
`0.312 ⫾ 0.009
`0.353 ⫾ 0.005
`0.358 ⫾ 0.008
`0.400 ⫾ 0.004
`0.410 ⫾ 0.006
`0.355 ⫾ 0.003
`0.370 ⫾ 0.006
`0.360 ⫾ 0.004
`0.325 ⫾ 0.008
`0.369 ⫾ 0.012
`0.470 ⫾ 0.003
`0.400 ⫾ 0.008
`0.400 ⫾ 0.003
`0.384 ⫾ 0.004
`0.421 ⫾ 0.008
`0.458 ⫾ 0.003
`0.455 ⫾ 0.005
`0.465 ⫾ 0.013
`0.413 ⫾ 0.004
`0.427 ⫾ 0.005
`0.423 ⫾ 0.005
`0.386 ⫾ 0.006
`0.470 ⫾ 0.004
`0.489 ⫾ 0.011
`0.479 ⫾ 0.004
`0.463 ⫾ 0.005
`0.515 ⫾ 0.004
`0.526 ⫾ 0.004
`0.510 ⫾ 0.007
`
`D13
`0.499 ⫾ 0.005
`0.513 ⫾ 0.006
`0.558 ⫾ 0.009
`0.573 ⫾ 0.005
`0.601 ⫾ 0.005
`0.612 ⫾ 0.008
`0.757 ⫾ 0.004
`0.776 ⫾ 0.010
`0.760 ⫾ 0.003
`0.722 ⫾ 0.006
`0.762 ⫾ 0.004
`0.800 ⫾ 0.002
`0.798 ⫾ 0.008
`0.810 ⫾ 0.006
`0.784 ⫾ 0.004
`0.807 ⫾ 0.012
`0.859 ⫾ 0.004
`0.859 ⫾ 0.005
`0.859 ⫾ 0.019
`1.023 ⫾ 0.004
`0.941 ⫾ 0.004
`1.023 ⫾ 0.004
`0.987 ⫾ 0.004
`1.084 ⫾ 0.007
`0.995 ⫾ 0.005
`1.078 ⫾ 0.003
`1.050 ⫾ 0.005
`1.119 ⫾ 0.003
`1.129 ⫾ 0.007
`1.113 ⫾ 0.008
`
`Tapers
`0.205 ⫾ 0.011
`0.201 ⫾ 0.011
`0.205 ⫾ 0.009
`0.215 ⫾ 0.013
`0.201 ⫾ 0.004
`0.202 ⫾ 0.001
`0.402 ⫾ 0.002
`0.406 ⫾ 0.007
`0.400 ⫾ 0.005
`0.397 ⫾ 0.007
`0.393 ⫾ 0.036
`0.397 ⫾ 0.001
`0.398 ⫾ 0.008
`0.410 ⫾ 0.006
`0.400 ⫾ 0.004
`0.386 ⫾ 0.007
`0.401 ⫾ 0.005
`0.404 ⫾ 0.002
`0.394 ⫾ 0.011
`0.610 ⫾ 0.010
`0.514 ⫾ 0.007
`0.600 ⫾ 0.004
`0.601 ⫾ 0.005
`0.614 ⫾ 0.006
`0.506 ⫾ 0.011
`0.599 ⫾ 0.005
`0.587 ⫾ 0.004
`0.604 ⫾ 0.003
`0.603 ⫾ 0.005
`0.603 ⫾ 0.007
`
`D3
`0.310 ⫾ 0.020
`
`D13
`0.510 ⫾ 0.020
`
`0.360 ⫾ 0.020
`
`0.560 ⫾ 0.020
`
`0.410 ⫾ 0.020
`
`0.610 ⫾ 0.020
`
`0.370 ⫾ 0.020
`
`0.770 ⫾ 0.020
`
`0.420 ⫾ 0.020
`
`0.820 ⫾ 0.020
`
`0.470 ⫾ 0.020
`
`0.870 ⫾ 0.020
`
`0.430 ⫾ 0.020
`
`1.030 ⫾ 0.020
`
`0.480 ⫾ 0.020
`
`1.080 ⫾ 0.020
`
`0.530 ⫾ 0.020
`
`1.130 ⫾ 0.020
`
`ments. However, these files were persistently on the
`small side of the acceptable tolerances, resulting in
`slightly smaller tapers than indicated. With respect to
`the mean taper of all files tested, the Hero files had
`large variations. Extreme recordings were obtained for
`Hero .06 tapered files sizes 25 and 30 (0.514 and 0.506,
`respectively).
`It was remarkable to find how poorly some types of
`instruments are conforming to the dimensions and
`tapers indicated by the manufacturer. These results are
`in good agreement with earlier findings concerning the
`standardization of endodontic hand instruments10,11
`and rotary nickel-titanium files.15 Until now, no ISO
`specification for endodontic instruments with a taper
`greater than the ISO standard .02 design has been
`available; moreover, it is obvious that there is a need
`for the development of international standards for size,
`taper, and acceptable tolerance limits of these rotary
`files. It can be assumed that the adoption of prescribed
`
`dimensions and tolerance limits may increase the effi-
`ciency of rotary instruments by reducing the undesir-
`able effects of overlapping sizes15 and may reduce the
`incidence of separation of rotary files. Certainly, this
`assumption warrants further investigation.
`We examined the bending properties of rotary nick-
`el-titanium instruments in light of the specifications in
`the ISO 3630-1 publication1; however, no maximum
`values were prescribed in this standard for files with a
`taper greater than the ISO standard .02 design. ISO
`maximum values for K-Files are 120 gcm (size 25), 150
`gcm (size 30), and 190 gcm (size 35). The stiffness test
`revealed that the bending moments for all instruments
`were well below these maximum values (Table IV). For
`tapers of .04 and .06, the K3 files, sizes 25, 30, and 35,
`were significantly stiffer than all other files of the same
`taper and size (P ⬍ .05). In contrast, independent of the
`taper and size tested, ProFile and RaCe instruments
`were found to be significantly more flexible than the
`
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`
`ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY
`Volume 96, Number 6
`
`Scha¨fer, Dzepina, and Danesh 761
`
`Figure. The relationship between stiffness and cross-sectional area of rotary nickel-titanium instruments. The left axis indicates
`the mean bending moments in gcm, whereas the right axis depicts the calculated cross-sectional surface area in square inches at
`a magnification of 160⫻. A, FlexMaster instruments. B, ProFile instruments. C, Hero instruments. D, K3 instruments. E, RaCe
`instruments.
`
`other instruments (P ⬍ .05; Table IV), with RaCe files
`being significantly more flexible than ProFile instru-
`ments. These results corroborate those of previous stud-
`ies.8,9
`The low bending moments of all instruments tested
`are indicative that these files are extremely flexible,
`which is clinically very desirable. Because of their
`flexibility, the load on the cutting edges in a curved
`canal is reduced, which in turn reduces stress on the
`instrument and the possibility of fracture.12 In addition,
`
`this superior flexibility reduces the risk of canal trans-
`portation during the enlargement of curved canals.
`However, in previous studies, it has been observed that
`some rotary nickel-titanium files created slight canal
`transportation toward the outer aspect of the curvature
`in the apical region of root canals.16-18 Obviously, this
`canal transportation may be attributable to root canal
`preparation with instruments of greater taper, because
`these are considerably stiffer than are those of .02 or .04
`tapers (Figure). Thus, manufacturers should be aware
`
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`
`762 Scha¨fer, Dzepina, and Danesh
`
`ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY
`December 2003
`
`Table IV. Resistance to bending and area of cross section for evaluated instruments
`Resistance to bending (in gcm)
`
`Significance*
`P ⫽ .176†
`
`P ⬍ .0001†
`
`P ⫽ .057†
`
`a
`a
`
`b
`b
`
`c
`c
`
`Tapers
`
`Instruments
`
`Sizes
`
`Means
`
`.02
`
`.04
`
`.06
`
`FlexMaster
`Hero
`FlexMaster
`Hero
`FlexMaster
`Hero
`
`FlexMaster
`Hero
`K3
`ProFile
`RaCe
`FlexMaster
`Hero
`K3
`ProFile
`RaCe
`K3
`ProFile
`RaCe
`
`FlexMaster
`Hero
`K3
`ProFile
`FlexMaster
`Hero
`K3
`ProFile
`FlexMaster
`K3
`ProFile
`
`25
`25
`30
`30
`35
`35
`
`25
`25
`25
`25
`25
`30
`30
`30
`30
`30
`35
`35
`35
`
`25
`25
`25
`25
`30
`30
`30
`30
`35
`35
`35
`
`15.64
`14.11
`25.22
`31.34
`37.25
`41.14
`
`33.29
`34.75
`46.50
`25.09
`17.58
`52.68
`51.43
`77.14
`45.87
`24.74
`116.62
`65.33
`36.75
`
`66.51
`73.25
`92.16
`46.07
`85.97
`113.01
`139.90
`67.41
`127.05
`139.56
`100.78
`
`SDs
`
`2.66
`2.69
`1.78
`2.23
`3.76
`5.55
`
`5.91
`6.22
`4.15
`3.80
`2.20
`6.61
`6.36
`3.53
`4.34
`2.64
`11.51
`6.17
`3.76
`
`6.57
`4.89
`8.02
`5.03
`4.76
`13.56
`8.28
`5.84
`1.56
`11.98
`6.36
`
`Minimum
`
`Maximum
`
`10.84
`10.01
`22.52
`28.37
`31.79
`31.69
`
`23.35
`27.52
`40.04
`20.02
`15.01
`44.20
`37.53
`70.89
`39.19
`21.68
`96.74
`53.37
`30.86
`
`60.05
`65.05
`75.89
`39.19
`80.06
`87.57
`127.60
`56.71
`122.59
`113.42
`91.74
`
`21.68
`17.51
`27.52
`35.86
`46.70
`50.04
`
`40.87
`46.70
`54.21
`30.86
`21.68
`65.05
`58.38
`82.56
`52.54
`30.02
`134.27
`73.39
`44.20
`
`80.06
`80.89
`103.42
`55.04
`95.57
`137.61
`151.78
`75.04
`128.44
`155.96
`111.76
`
`*Means with the same letter are not significantly different (P ⬎ .05; Student–Newman-Keuls tests).
`†Comparison of 2 means (t test).
`
`Cross-sectional
`areas (in2 ⫻ 10⫺7)
`
`875.0
`746.1
`1144.5
`941.4
`1460.9
`1218.7
`
`1117.2
`1242.2
`1382.8
`761.7
`742.2
`1363.3
`1492.2
`1648.4
`1230.5
`878.9
`2363.3
`1785.2
`1089.8
`
`1722.7
`1769.5
`1613.3
`1367.2
`2226.6
`2410.2
`2089.8
`1859.4
`2781.3
`2261.7
`2035.2
`
`of the bending properties of the different types of rotary
`nickel-titanium instruments when recommending an in-
`strumentation sequence for the enlargement of severely
`curved canals.
`As expected, a highly significant correlation between
`stiffness and cross-sectional area was detected (P ⬍
`.0001). These results indicate that the cross-sectional
`configuration seems to be the predominant factor af-
`fecting the bending properties of rotary nickel-titanium
`instruments. This corroborates findings obtained when
`comparing the bending properties of custom-made pro-
`totypes of endodontic hand instruments with 5 different
`cross-sectional shapes.7 Moreover, the results of our
`study are also in good agreement with previously re-
`ported data from mathematical modeling calcula-
`tions.19,20 Turpin et al20 calculated the cross-sectional
`surface areas of triple-helix (eg, Hero files) and triple-U
`files (eg, ProFile) and compared bending stresses in
`
`these 2 instruments. For identical working diameters,
`the area of the triple-helix cross section was found to be
`approximately 30% greater than that of the triple-U
`file,20 a finding in agreement with those of the current
`study (Table IV). Because of the more massive struc-
`ture of the triple-helix file, this instrument was found to
`be less flexible than the triple-U instrument.20 Again,
`these mathematical modeling data are in good agree-
`ment with the results of the present experimental study.
`
`REFERENCES
`1. International Organization for Standardization ISO 3630-1. Den-
`tal
`root-canal
`instruments—Part 1: files,
`reamers, barbed
`broaches, rasps, paste carriers, explorers and cotton broaches.
`Switzerland:
`International Organization for Standardization;
`1992.
`2. Council of Dental Materials and Devices. ANSI/ADA Specifi-
`cation No. 28 for Root Canal Files and Reamers. Type K. J Am
`Dent Assoc 1982;104:506.
`3. Council of Dental Materials and Devices. ANSI/ADA Specifi-
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`US ENDODONTICS, LLC., Petitioner
`
`

`
`ORAL SURGERY ORAL MEDICINE ORAL PATHOLOGY
`Volume 96, Number 6
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`Scha¨fer, Dzepina, and Danesh 763
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`Reprint requests:
`Edgar Scha¨fer, Prof. Dr. Med. Dent.
`Poliklinik fu¨r Zahnerhaltung
`Waldeyerstr. 30
`D-48149 Mu¨nster, Germany
`eschaef@uni-muenster.de
`
`7 of 7
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`IPR2015-00632 - Ex. 1021
`US ENDODONTICS, LLC., Petitioner