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Evolution of nickel–titanium instruments:
from past to future
Presented By : Dr. Arpit Viradiya
Guided By : Dr. Shubhprabh...
Introduction
• Up until the last decade of the past century,
endodontic instruments were manufactured
out of stainless-ste...
• As a result, when preparing a curved
root canal, restoring forces attempt
to return the instrument to its
original shape...
• NiTi instruments were introduced
over two decades ago and are proven
to be a valuable for root canal
therapy.
• NiTi ins...
• NiTi instruments have undergone a revolution
regarding different designs to produce an
instrument that cuts effectively ...
Design features of each
file generation
• The application of NiTi in
endodontics was first reported by
Walia et al. who us...
First-generation files
• The first rotary 0.02 taper NiTi instrument was
designed by Dr. John McSpadden and came to
market...
• In 1994, Dr. Johnson introduced a
line of files which became known as
the ProFile 0.04 tapered series.
• Their cross-sec...
• For this “classical” design, an unground space
remained next to each groove, providing the
so-called “radial land” area....
• This flat area prevents the file from locking in
the dentin, while cutting occurs through a
passive planing action.
• Dr...
• Other rotary file lines came along soon
afterwards, each with its advantages, such as
– The LightSpeed developed by Dr. ...
• LightSpeed was introduced as an
instrument differing from all others
because of its long, thin non-cutting
shaft and sho...
Second-generation files
• All first-generation NiTi rotary files had passive
cutting radial lands, fixed tapers over the
l...
• The critical distinctions of this generation of
instruments are that they have actively cutting
edges without radial lan...
• This generation of NiTi files includes the
ProTaper (Dentsply Tulsa) rotary files which,
unlike all other passive or act...
• The ProTaper system is based on a unique
concept and originally comprised just six
instruments: three shaping files and ...
• The first-generation rotary systems had
neutral or slightly negative rake angles.
• Several second generation systems we...
• The most obvious difference between the
Quantec and K3 models is the K3’s unique
cross-sectional design: a slightly posi...
• Unlike the Quantec, a two-flute file, the K3
features a third radial land to help prevent
threading-in.
• In the lateral...
• To discourage taper lock and the resultant
screw effect associated with both passive and
active fixed tapered NiTi cutti...
• The BioRaCe instruments undergo a finishing
treatment (electropolishing) after the
traditional grinding process to reduc...
• It has been suggested that the surface
condition of the NiTi instrument contributes
to fatigue resistance because most f...
• Attempts to enhance the surface of NiTi
instruments, resistance to cyclic fatigue, and
cutting efficiency have resulted ...
Third-generation files
• Improvements in NiTi metallurgy became the
hallmark of what may be identified as the third
genera...
• Since 2007, several new thermomechanical
processing and manufacturing technologies
have been developed in order to optim...
• M-wire was introduced in 2007.
• It is produced by applying a series of heat
treatments to NiTi wire blanks.
• M-wire in...
• The major difference between the Vortex and
the classical ProFile files lies in the non-landed
cross-section of the Vort...
• Vortex Blue instruments, new NiTi rotary
instruments made out of M-wire, show a
unique “blue color”, which is not seen i...
• The relatively hard titanium oxide surface
layer on the “Vortex Blue” instrument may
compensate for the loss of hardness...
• CM Wire is a novel NiTi alloy with flexible
properties that was introduced to endodontics
in 2010.
• CM NiTi files are m...
• HyFlex instruments have a triangular cross-
sectional design.
• Both the HyFlex and TYPHOON CM
instruments are made out ...
• In 2008, SybronEndo presented the first fluted
NiTi file manufactured by plastic deformation,
a process similar to the t...
• The instrument was named twisted file and
was first available with only no. 25 tip sizes in
tapers 0.04 up to 0.12.
• Ho...
• The design of K3 instruments was recently
updated by SybronEndo, and the system has
been available under the name of K3X...
• Numerous micropores with various diameters
can be seen on the surface of the instrument
flute on K3XF instruments.
• The...
Fourth-generation files
• The greatest number of commercially
available files that are utilized to shape root
canals are m...
• Initially, all reciprocating motors and related
handpieces rotated files in large equal angles
of 90° clockwise (CW) and...
• In 2008, Dr. Yared identified the precise
unequal CW/CCW angles that would enable a
single reciprocating 25/0.08 ProTape...
• In 2011, both WaveOne (Dentsply) and
Reciproc (VDW) were launched as single-file
shaping techniques.
• Both files are ma...
• WaveOne represents a convergence of the
design features from the second and third
generation of files.
• coupled with a ...
• Strategically, after three CCW and CW cutting
cycles, the file will have rotated 360°, or one
complete circle.
• This no...
• The WaveOne technique is both a single-file
and single-use concept.
• Strategically, only one file is generally utilized...
• The Small 21/0.06 file has a fixed taper of 6%
over its active portion.
• The Primary 25/0.08 and the Large 40/0.08
Wave...
• From D1-D8, the WaveOne files have a
modified convex triangular cross-section,
whereas from D9-D16, these files have a
c...
• Reciproc instruments have a short shaft of 11
mm, enabling better access to molars
compared to many other instruments wh...
• The instruments are used at 10 cycles of
reciprocation per second, the equivalent of
approximately 300 rpm.
• The values...
• When the instrument rotates in the cutting
direction, it will advance in the canal and
engage dentin.
• When it rotates ...
• The self-adjusting file (ReDent-Nova)
represents a new approach in file design and
mode of operation.
• The file is a ho...
• The SAF system uses a
hollow reciprocating
instrument that allows for
simultaneous irrigation
throughout the
mechanical ...
• The instrument is used in a transline (in-and-
out) motion, and the abrasive surface of the
lattice threads promotes a u...
Fifth-generation files
• The fifth generation of shaping files has been
designed such that the center of mass and/or
the c...
• Like the progressively percentage tapered
design of any given ProTaper file, this offset
design serves to further minimi...
• Commercial examples of file brands that offer
variations of this technology are Revo-S
(Micro-Mega), One Shape (Micro-Me...
• ProTaper Next is the successor to the ProTaper
Universal system.
• There are five PTN files available, in different
leng...
• The PTN X1 and X2 files have both an
increasing and decreasing percentage tapered
design on a single file; whereas thePT...
• An offset design generates a traveling
mechanical wave of motion along the active
portion of a file.
• This swaggering e...
• Reduced engagement limits any undesirable
taper lock, the screw effect, and the torque on
any given file.
• An offset fi...
• The asymmetrical cross-section of the Revo-S
facilitates penetration by a “snake-like”
movement and is intended to reduc...
• The One Shape file from Micro-Mega
(Besançon, France) is the only single-file NiTi
instrument in continuous rotation for...
• The first zone presents a variable three-
cutting-edge design; the second, prior to the
transition, has a cross-section ...
Metallurgical and
mechanical properties
• NiTi “shape memory metal alloy” can exist in
two different temperature-dependent...
• This is important because several properties of
the two forms are notably different.
• Near equiatomic NiTi alloys conta...
• When the material is in its martensite form, it
is soft and ductile and can easily be deformed,
while austenitic NiTi is...
• To improve the fracture resistance of NiTi files,
manufacturers have either introduced new
alloys to manufacture NiTi fi...
• Enhancements in these areas of material
management have led to the development of
the new generation (3rd, 4th, and 5th
...
• The martensitic phase transformation has
excellent damping characteristics because of
the energy absorption characterist...
• The TF is a NiTi rotary file manufactured by
twisting when the metal is in the so-called R-
phase.
• The R-phase shows g...
• A reciprocating motion may decrease the
impact of cyclic fatigue on NiTi rotary
instrument life compared with rotational...
• Recent articles reported a higher cyclic fatigue
resistance of the reciprocating motion than
continuous rotation in inst...
Shaping properties : First- and
second-generation literature
• In a study using plastic blocks, the ProTaper
files created...
• The effect of Mtwo and ProTaper Universal
(PTU) on root canal geometry was compared
using micro-CT.
• The result showed ...
• Few results of in vitro experiments comparing
RaCe to other contemporary rotary systems
are available :
• canals in plas...
New generations (from 3rd to 5th
generations)
• The canal shaping properties of Hyflex CM,
TFs, and K3 rotary NiTi files w...
• Recently, in a comparison of GTX, Twisted File,
Revo-S, RaCe, Mtwo, and ProTaper Universal
systems on maxillary first pe...
• The shaping ability of NiTi instruments in
either continuous or reciprocating movements
was compared in plastic blocks.
...
• The shaping ability of WaveOne instruments
has been evaluated in plastic blocks and
extracted teeth.
• The WaveOne NiTi ...
• Bürklein et al. compared the shaping ability of
two reciprocating single-file systems (Reciproc
and WaveOne) with Mtwo a...
• The use of Reciproc and WaveOne files
resulted in significantly shorter preparation
times than the other two file system...
Reduction of intracanal bacteria
• The eradication of a microbial infection is
accomplished mainly through mechanical
inst...
• Indeed, it is important to note that no
difference in the effectiveness of bacterial
removal has been found between hand...
• Dalton et al. sampled root canals irrigated
with saline solution before, during, and after
instrumentation and then cult...
• Their result was confirmed by Siqueira et al. in
a study showing that instrumentation
combined with saline irrigation me...
• Siqueira et al. compared the capability of SAF
and rotary NiTi instrumentation with irrigation
to eliminate Enterococcus...
• Recently, Lin et al. found that hand and rotary
files techniques were equally effective in
removing bacteria from the ma...
• The SAF removed significantly more bacteria
from the groove than the rotary and hand
files.
Clinical use
• Instrument fracture is a potentially serious
mishap that can complicate and compromise the
endodontic treat...
• The incidence of SE NiTi instrument fracture in
clinical practice for files used multiple times
has varied from 0.05% to...
• Operator proficiency is an important
consideration when evaluating the propensity
of instrument failure.
• The operator’...
• A clinical study on HyFlex NiTi instruments
found that none of the 468 HyFlex
instruments fractured during instrumentati...
• Although multiple clinical uses of NiTi rotary
files may be one of the causes of instrument
breakages and deformations, ...
Conclusions
• New endodontic files for root canal
instrumentation are continually added to the
armamentarium, and older sy...
• Since then the focus has shifted to new
manufacturing processes (thermomechanical
treatment and R-phase) and different u...
• Ultimately, clinical experience, handling
properties, safety, and case outcomes will
decide the fate of a particular des...
•Thank You
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Evolution of nickel–titanium

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This presentation describes about evolution of nitinol (NiTi), its properties, manufacturing, metallurgy and various rotary systems in the field of endodontics.

Published in: Health & Medicine

Evolution of nickel–titanium

  1. 1. Evolution of nickel–titanium instruments: from past to future Presented By : Dr. Arpit Viradiya Guided By : Dr. Shubhprabhat Gupta
  2. 2. Introduction • Up until the last decade of the past century, endodontic instruments were manufactured out of stainless-steel. • Stainless-steel files have an inherent stiffness that increases as the instrument size increases.
  3. 3. • As a result, when preparing a curved root canal, restoring forces attempt to return the instrument to its original shape, especially when the operator uses a filing motion. • Therefore, in curved canals, steel instruments must be pre-curved for use, which effectively prevents them from being used in a rotary motion.
  4. 4. • NiTi instruments were introduced over two decades ago and are proven to be a valuable for root canal therapy. • NiTi instruments are highly flexible and elastic. • NiTi rotary shaping files have nearly eliminated the iatrogenic instrumentation complications that are often connected to endodontic steel instruments.
  5. 5. • NiTi instruments have undergone a revolution regarding different designs to produce an instrument that cuts effectively while exhibiting resistance to fracture even in the most challenging anatomical confines. • One should always bear in mind that all file systems have benefits and weaknesses.
  6. 6. Design features of each file generation • The application of NiTi in endodontics was first reported by Walia et al. who used nitinol orthodontic wire to fabricate intracanal files. • By the 1990s, the first commercially available NiTi rotary files had come to market. • Most NiTi rotary files have rounded non-cutting tips that serve as a guide in the canal.
  7. 7. First-generation files • The first rotary 0.02 taper NiTi instrument was designed by Dr. John McSpadden and came to market in 1992. • Although these instruments began to change how dentists viewed instrumentation, there were problems associated with file breakage.
  8. 8. • In 1994, Dr. Johnson introduced a line of files which became known as the ProFile 0.04 tapered series. • Their cross-sectional shapes were made by machining three equally spaced U-shaped grooves around the shaft of a tapered NiTi wire.
  9. 9. • For this “classical” design, an unground space remained next to each groove, providing the so-called “radial land” area. Radial Land U shaped groove
  10. 10. • This flat area prevents the file from locking in the dentin, while cutting occurs through a passive planing action. • Dr. Johnson broke the tradition of ISO 0.02 tapered files by making these more tapered files, and together with Dr. McSpadden, the two are generally regarded as the fathers of NiTi rotary files.
  11. 11. • Other rotary file lines came along soon afterwards, each with its advantages, such as – The LightSpeed developed by Dr. Steve Senia and Dr. William Wildey, – The Quantec developed by Dr. John McSpadden, – And the Greater Taper files developed by Dr. Steve Buchanan.
  12. 12. • LightSpeed was introduced as an instrument differing from all others because of its long, thin non-cutting shaft and short anterior cutting part. • The files are used for apical preparation and do not cut over most of the canal length because of the existence of a smooth small diameter shaft that also enhances the flexibility of the instrument.
  13. 13. Second-generation files • All first-generation NiTi rotary files had passive cutting radial lands, fixed tapers over the length of their working parts, and required a considerable number of files to achieve preparation objectives. • By the end of the 1990s, the next generation of NiTi rotary files came to market.
  14. 14. • The critical distinctions of this generation of instruments are that they have actively cutting edges without radial lands and fewer instruments are required to fully prepare a canal. • The angle between the cutting blade and the longitudinal axis of the instrument is lower than in first-generation files, which greatly reduces the tendency for a screwing effect during use.
  15. 15. • This generation of NiTi files includes the ProTaper (Dentsply Tulsa) rotary files which, unlike all other passive or active NiTi cutting instruments, have multiple tapers of increasing and decreasing size on a single file.
  16. 16. • The ProTaper system is based on a unique concept and originally comprised just six instruments: three shaping files and three finishing files. • The ProTaper Universal set is now complemented by two larger finishing files and a set designed for re-treatment procedures. • The cross-section of finishing files F3, F4, and F5 is slightly relieved for increased flexibility.
  17. 17. • The first-generation rotary systems had neutral or slightly negative rake angles. • Several second generation systems were designed with positive rake angles, which gave them greater cutting efficiency. [e.g. K3 SybronEndo] Positive Rake angle Negative Rake angle
  18. 18. • The most obvious difference between the Quantec and K3 models is the K3’s unique cross-sectional design: a slightly positive rake angle for greater cutting efficiency, wide radial lands, and a peripheral blade relief for reduced friction.
  19. 19. • Unlike the Quantec, a two-flute file, the K3 features a third radial land to help prevent threading-in. • In the lateral aspect, the K3 has a variable pitch and variable core diameter, which makes the file stronger close to its apical tip.
  20. 20. • To discourage taper lock and the resultant screw effect associated with both passive and active fixed tapered NiTi cutting instruments, EndoSequence and BioRaCe provide files with alternating contact points. • Although this feature is intended to mitigate a taper lock, these files still have a fixed taper over their active portions.
  21. 21. • The BioRaCe instruments undergo a finishing treatment (electropolishing) after the traditional grinding process to reduce the surface defects and improve the mechanical properties of the instruments.
  22. 22. • It has been suggested that the surface condition of the NiTi instrument contributes to fatigue resistance because most fatigue failures nucleate from the surface, especially in the presence of high stress amplitude or surface defects • During this period, manufacturers began to focus on other methods to increase the resistance to file separation.
  23. 23. • Attempts to enhance the surface of NiTi instruments, resistance to cyclic fatigue, and cutting efficiency have resulted in a variety of strategies including ion implantation and electropolishing. Comparison of electropolished file with a nonelectropolished instrument
  24. 24. Third-generation files • Improvements in NiTi metallurgy became the hallmark of what may be identified as the third generation of mechanical shaping files. • Heat treatment is one of the most fundamental approaches toward adjusting the transition temperatures of NiTi alloys and affecting the fatigue resistance of NiTi endodontic files.
  25. 25. • Since 2007, several new thermomechanical processing and manufacturing technologies have been developed in order to optimize the microstructure of NiTi alloys. • Recently, several new thermomechanically processed endodontic NiTi files such as the HyFlex CM, K3XF, ProFile GT Series X, Vortex Blue and Twisted Files have been introduced.
  26. 26. • M-wire was introduced in 2007. • It is produced by applying a series of heat treatments to NiTi wire blanks. • M-wire instruments include Dentsply’s ProFile GT Series X, ProFile Vortex, and Vortex Blue. • The design principles of GT & GT Series X instruments are same. • The main differences are the use of M-wire for GTX, and a different approach to instrument usage.
  27. 27. • The major difference between the Vortex and the classical ProFile files lies in the non-landed cross-section of the Vortex files, whereas the tip sizes and tapers are similar in both files. • Manufactured out of M-wire, the ProFile Vortex also has a varying helical angle to counteract the tendency of the non-landed files to thread into the root canal.
  28. 28. • Vortex Blue instruments, new NiTi rotary instruments made out of M-wire, show a unique “blue color”, which is not seen in traditional superelastic (SE) NiTi instruments. • The “blue-color” oxide surface layer of Vortex Blue files is a result of the difference in manufacturing process.
  29. 29. • The relatively hard titanium oxide surface layer on the “Vortex Blue” instrument may compensate for the loss of hardness compared with “Vortex M-wire” by improving the cutting efficiency and wear resistance.
  30. 30. • CM Wire is a novel NiTi alloy with flexible properties that was introduced to endodontics in 2010. • CM NiTi files are manufactured using a special thermomechanical process that controls the memory of the material, making the files extremely flexible but without the shape memory of other NiTi files.
  31. 31. • HyFlex instruments have a triangular cross- sectional design. • Both the HyFlex and TYPHOON CM instruments are made out of CM Wire. • They exhibit a lower percent by weight of nickel (52 Ni %wt) than the common 54.5–57 Ni %wt of the great majority of commercially available SE NiTi rotary instruments.
  32. 32. • In 2008, SybronEndo presented the first fluted NiTi file manufactured by plastic deformation, a process similar to the twisting process that is used to produce the majority of stainless-steel K-files and reamers. • According to the manufacturer, a thermal process allows twisting during a phase transformation into the so-called R-phase of NiTi.
  33. 33. • The instrument was named twisted file and was first available with only no. 25 tip sizes in tapers 0.04 up to 0.12. • However, instruments with tip sizes no. 30, 35, and 40 were recently added.
  34. 34. • The design of K3 instruments was recently updated by SybronEndo, and the system has been available under the name of K3XF since 2011. • K3 and K3XF instruments are identical in shape and differ only in that K3XF instruments undergo post-machining heat treatment.
  35. 35. • Numerous micropores with various diameters can be seen on the surface of the instrument flute on K3XF instruments. • These small pores do not contribute to the failure, but serve as a local stress/strain discontinuity from which the crack nucleates. K3XF K3 K3XF K3 K3XF K3
  36. 36. Fourth-generation files • The greatest number of commercially available files that are utilized to shape root canals are manufactured out of NiTi and are mechanically driven in continuous rotation. • However, reciprocation, defined as any repetitive back-and-forth motion, has been clinically utilized to drive stainless-steel files since 1958.
  37. 37. • Initially, all reciprocating motors and related handpieces rotated files in large equal angles of 90° clockwise (CW) and counterclockwise (CCW) rotation. • Over time, virtually all reciprocating systems in the marketplace began to utilize smaller, yet equal, angles of CW/CCW rotation. • Currently, the M4 (SybronEndo), Endo-Eze AET (Ultradent), and Endo-Express (Essential Dental Systems) are examples of reciprocating systems that utilize small, equal 30° angles of CW/CCW rotation.
  38. 38. • In 2008, Dr. Yared identified the precise unequal CW/CCW angles that would enable a single reciprocating 25/0.08 ProTaper file to optimally shape virtually any canal. • Although this specific reciprocation technique stimulated considerable interest, this ProTaper F2 file was never designed to be used in this manner.
  39. 39. • In 2011, both WaveOne (Dentsply) and Reciproc (VDW) were launched as single-file shaping techniques. • Both files are made out of M-wire. • Innovation in reciprocation technology led to a fourth generation of instruments for shaping canals. • Clinical experience and future studies will determine whether this generation has fulfilled the promise of the long hoped-for single-file technique.
  40. 40. • WaveOne represents a convergence of the design features from the second and third generation of files. • coupled with a reciprocating motor that drives any given file at unequal bidirectional angles. • The CCW(150) engaging angle is five times the CW (30) disengaging angle and is designed to be less than the elastic limit of the file.
  41. 41. • Strategically, after three CCW and CW cutting cycles, the file will have rotated 360°, or one complete circle. • This novel reciprocating movement allows a file to progress more readily, cut efficiently, and removes debris effectively out of the canal.
  42. 42. • The WaveOne technique is both a single-file and single-use concept. • Strategically, only one file is generally utilized to fully shape virtually any given canal. • However, there are three WaveOne files available to address a wide range of endodontic anatomy commonly encountered in practice. • The three WaveOne instruments are termed Small (yellow 21/0.06), Primary (red 25/0.08), and Large (black 40/0.08).
  43. 43. • The Small 21/0.06 file has a fixed taper of 6% over its active portion. • The Primary 25/0.08 and the Large 40/0.08 WaveOne files have fixed tapers of 8% from D1-D3, whereas from D4-D16, they have a unique progressively decreasing percentage tapered design. • The design feature of the WaveOne files is that they have a reverse helix and two distinct cross-sections along the length of their active portions.
  44. 44. • From D1-D8, the WaveOne files have a modified convex triangular cross-section, whereas from D9-D16, these files have a convex triangular cross-section. • The WaveOne files have non-cutting modified guiding tips, which enable these files to safely progress through virtually any secured canal.
  45. 45. • Reciproc instruments have a short shaft of 11 mm, enabling better access to molars compared to many other instruments which have a shaft of 13 mm or longer. • The design of the cross-section is S-shaped.
  46. 46. • The instruments are used at 10 cycles of reciprocation per second, the equivalent of approximately 300 rpm. • The values of the CW and CCW rotations are different.
  47. 47. • When the instrument rotates in the cutting direction, it will advance in the canal and engage dentin. • When it rotates in the opposite direction (smaller rotation), the instrument will immediately disengage. • The end result, related to the degree of CW and CCW rotations, is an advancement of the instrument in the canal without the risk of a screwing effect.
  48. 48. • The self-adjusting file (ReDent-Nova) represents a new approach in file design and mode of operation. • The file is a hollow device, designed as a cylinder of thin-walled, delicate NiTi lattice with a lightly abrasive surface.
  49. 49. • The SAF system uses a hollow reciprocating instrument that allows for simultaneous irrigation throughout the mechanical preparation. • When inserted into the root canal, the manufacturer claims that the SAF is capable of adapting itself to the canal shape three-dimensionally.
  50. 50. • The instrument is used in a transline (in-and- out) motion, and the abrasive surface of the lattice threads promotes a uniform removal of dentin. • An initial glide path is established with a #20 K-file to allow the insertion of the SAF file
  51. 51. Fifth-generation files • The fifth generation of shaping files has been designed such that the center of mass and/or the center of rotation are offset. • In rotation, the files that have an offset design produce a mechanical wave of motion that travels along the active length of the file.
  52. 52. • Like the progressively percentage tapered design of any given ProTaper file, this offset design serves to further minimize the engagement between the file and dentin.
  53. 53. • Commercial examples of file brands that offer variations of this technology are Revo-S (Micro-Mega), One Shape (Micro-Mega), and ProTaper Next (Dentsply). • PTN files are the convergence of three significant design features, including various tapers on a single file, M-wire technology, and the fifth generation of continual improvement, the offset design.
  54. 54. • ProTaper Next is the successor to the ProTaper Universal system. • There are five PTN files available, in different lengths, for shaping canals: X1 (17/0.04), X2 (25/0.06), X3 (30/0.07), X4 (40/0.06), and X5 (50/ 0.06). • The tapers shown above indicate the taper of the tip region of each file and are not fixed over the active portion of any given PTN file.
  55. 55. • The PTN X1 and X2 files have both an increasing and decreasing percentage tapered design on a single file; whereas thePTNX3, X4, and X5 files have a fixed taper from D1-D3, then a decreasing percentage tapered design over the rest of their active portions.
  56. 56. • An offset design generates a traveling mechanical wave of motion along the active portion of a file. • This swaggering effect serves to minimize the engagement between the file and dentin compared to the action of a fixed tapered file with a centered mass of rotation.
  57. 57. • Reduced engagement limits any undesirable taper lock, the screw effect, and the torque on any given file. • An offset file design may also decrease the probability of laterally compacting the debris and blocking the root canal system anatomy.
  58. 58. • The asymmetrical cross-section of the Revo-S facilitates penetration by a “snake-like” movement and is intended to reduce torsional stress on the instrument. • The manufacturer claims that this sequence has a cutting, debris elimination, and cleaning cycle which optimizes the root canal cleaning by improving the upward removal of the generated dentin debris.
  59. 59. • The One Shape file from Micro-Mega (Besançon, France) is the only single-file NiTi instrument in continuous rotation for root canal preparations. • The One Shape instrument presents a variable cross-section along the blade which has an optimal cutting action in three zones of the canal.
  60. 60. • The first zone presents a variable three- cutting-edge design; the second, prior to the transition, has a cross-section that progressively changes from three to two cutting edges; and the last (coronal) has two cutting edges.
  61. 61. Metallurgical and mechanical properties • NiTi “shape memory metal alloy” can exist in two different temperature-dependent crystal structures called martensite (lower temperature or daughter phase) and austenite (higher temperature or parent phase). • The crystal lattice structure can be altered by either temperature or stress.
  62. 62. • This is important because several properties of the two forms are notably different. • Near equiatomic NiTi alloys contain three microstructural phases (i.e. austenite, martensite, and R-phase), the character and relative proportions of which determine the mechanical properties of the metal.
  63. 63. • When the material is in its martensite form, it is soft and ductile and can easily be deformed, while austenitic NiTi is quite strong and hard. • The conventional SE NiTi file (1st and 2rd generation) has an austenite structure at room and body temperatures. • It is well known that the nature of the alloy and the manufacturing process greatly affect the mechanical behavior of the instrument.
  64. 64. • To improve the fracture resistance of NiTi files, manufacturers have either introduced new alloys to manufacture NiTi files or developed new manufacturing processes. • Recently, a series of thermomechanical processing procedures has been developed with the objective of producing SE NiTi wire blanks that contain the substantially stable martensite phase under clinical conditions.
  65. 65. • Enhancements in these areas of material management have led to the development of the new generation (3rd, 4th, and 5th generation) of endodontic NiTi instruments. • NiTi files with thermal processing (e.g. CM Wire and M-wire) contain a mixture of austenite and martensite conditions at body temperature. • The martensitic phase of NiTi has some unique properties that have made it an ideal material for many applications.
  66. 66. • The martensitic phase transformation has excellent damping characteristics because of the energy absorption characteristics of its twinned phase structure. • In addition, the martensitic form of NiTi has an excellent fatigue resistance.
  67. 67. • The TF is a NiTi rotary file manufactured by twisting when the metal is in the so-called R- phase. • The R-phase shows good superelasticity and shape memory effects; • its Young’s modulus is typically lower than that of austenite. • Thus, an instrument made out of R-phase wire would be more flexible. • Also, the stress hysteresis is smaller for TFs than for ground files
  68. 68. • A reciprocating motion may decrease the impact of cyclic fatigue on NiTi rotary instrument life compared with rotational motion. • It has been postulated that the increased fatigue resistance occurs because of the release of reaction stresses built up in the material by reversing the rotational direction.
  69. 69. • Recent articles reported a higher cyclic fatigue resistance of the reciprocating motion than continuous rotation in instruments specifically designed to be used in a reciprocal motion as well as in those manufactured for continuous rotation use.
  70. 70. Shaping properties : First- and second-generation literature • In a study using plastic blocks, the ProTaper files created acceptable shapes more quickly than GT, ProFile, and Quantec instruments, but they also created more aberrations. • In a comparison of ProTaper and K3 instruments, Bergmans et al found few differences, with the exception of some transportation by the ProTaper into the furcation region.
  71. 71. • The effect of Mtwo and ProTaper Universal (PTU) on root canal geometry was compared using micro-CT. • The result showed that PTU produced greater transportation at the apical third. • The shaping ability of K3 files in vitro seems to be similar to that of the ProTaper and superior to that achieved with hand instruments.
  72. 72. • Few results of in vitro experiments comparing RaCe to other contemporary rotary systems are available : • canals in plastic blocks and in extracted teeth were prepared by the RaCe with less transportation from the original curvature occurred than with the ProTaper.
  73. 73. New generations (from 3rd to 5th generations) • The canal shaping properties of Hyflex CM, TFs, and K3 rotary NiTi files were described by using micro-CT in maxillary first molars. • The TFs system produced significantly less transportation than the K3 system in the apical third of canals. • No significant difference in apical transportation was found between TFs and Hyflex CM instruments.
  74. 74. • Recently, in a comparison of GTX, Twisted File, Revo-S, RaCe, Mtwo, and ProTaper Universal systems on maxillary first permanent molars, Celik et al. found that there was no significant difference between NiTi rotary system groups at any level except for 2.5 mm from the working length. • At this level, the ProTaper Universal system caused more canal transportation than the other files tested.
  75. 75. • The shaping ability of NiTi instruments in either continuous or reciprocating movements was compared in plastic blocks. • The results showed that in the most apical third of the canal, the continuous rotation group produced a greater enlargement of the canal than the reciprocating group. • In the apical third, the continuous rotation group displayed significantly greater enlargement of the canal at the external side.
  76. 76. • The shaping ability of WaveOne instruments has been evaluated in plastic blocks and extracted teeth. • The WaveOne NiTi Primary reciprocating single file maintained the original canal anatomy better, with less modification of the canal curvature than the ProTaper system up to F2.
  77. 77. • Bürklein et al. compared the shaping ability of two reciprocating single-file systems (Reciproc and WaveOne) with Mtwo and ProTaper rotary instruments during the preparation of curved root canals in extracted teeth. • The results showed that both single-file systems maintained root canal curvature well and were safe.
  78. 78. • The use of Reciproc and WaveOne files resulted in significantly shorter preparation times than the other two file systems, which are used in continuous rotation
  79. 79. Reduction of intracanal bacteria • The eradication of a microbial infection is accomplished mainly through mechanical instrumentation and chemical irrigation. • With the advent of NiTi rotary systems, perhaps too much credit has been given to these systems as being the solution to overcome the challenges of root canal disinfection.
  80. 80. • Indeed, it is important to note that no difference in the effectiveness of bacterial removal has been found between hand and rotary instruments.
  81. 81. • Dalton et al. sampled root canals irrigated with saline solution before, during, and after instrumentation and then cultivated and counted colony-forming units. • They found that using instrumentation without an antimicrobial irrigant reduced the number of bacteria regardless of whether NiTi rotary or stainless-steel hand instrumentation was used. • However, neither technique achieve bacteriafree canals.
  82. 82. • Their result was confirmed by Siqueira et al. in a study showing that instrumentation combined with saline irrigation mechanically removed more than 90% of bacteria in the root canal. • Siqueira et al. compared the capability of SAF and rotary NiTi instrumentation with irrigation to eliminate Enterococcus faecalis populations from root canals of extracted human teeth.
  83. 83. • Siqueira et al. compared the capability of SAF and rotary NiTi instrumentation with irrigation to eliminate Enterococcus faecalis populations from root canals of extracted human teeth. • Results showed that the preparation of long oval canals with the SAF was significantly more effective than rotary NiTi instrumentation in reducing intracanal E. faecalis counts.
  84. 84. • Recently, Lin et al. found that hand and rotary files techniques were equally effective in removing bacteria from the main canal, although both were unable to achieve complete elimination of the microbes. • However, it appeared that the rotary files were capable of achieving better removal of biofilm bacteria within the apical groove than the hand files.
  85. 85. • The SAF removed significantly more bacteria from the groove than the rotary and hand files.
  86. 86. Clinical use • Instrument fracture is a potentially serious mishap that can complicate and compromise the endodontic treatment outcome, especially if the fragment prevents access to the apical part of an infected root canal. • NiTi rotary files are available in a variety of designs, each with features that affect the manner in which they engage and cut dentin and the stress that may be generated within the file.
  87. 87. • The incidence of SE NiTi instrument fracture in clinical practice for files used multiple times has varied from 0.05% to 39%. • The reasons for the fracture of NiTi instruments may be complex and multifactorial; • The most important reasons may be operator- related (such as skill, experience, instrumentation technique, method of use), instrument design, bulk material properties, and root canal anatomy.
  88. 88. • Operator proficiency is an important consideration when evaluating the propensity of instrument failure. • The operator’s ability to sense and resist the binding or “locking” tendency is a skill that can be obtained only with experience. • That is, judgment error or inadvertent misuse by the operator may be more important than the number of uses in causing the breakage of the instrument in the canal.
  89. 89. • A clinical study on HyFlex NiTi instruments found that none of the 468 HyFlex instruments fractured during instrumentation of three teeth by each file. • Only 3.4% (16 of 468) of the instruments revealed plastic deformation.
  90. 90. • Although multiple clinical uses of NiTi rotary files may be one of the causes of instrument breakages and deformations, some studies have found that a brand-new SE NiTi instrument may also fail at first use.
  91. 91. Conclusions • New endodontic files for root canal instrumentation are continually added to the armamentarium, and older systems are updated. • First-generation NiTi rotary files relied much on the superelasticity of the metal, while in instrument design the emphasis was on maximized safety (e.g. radial lands) rather than cutting effectiveness.
  92. 92. • Since then the focus has shifted to new manufacturing processes (thermomechanical treatment and R-phase) and different unique features such as a variable cross-section along the length of theactive portion of the file. • Many variables and physical properties influence the clinical performance of NiTi rotaries.
  93. 93. • Ultimately, clinical experience, handling properties, safety, and case outcomes will decide the fate of a particular design. • In the future, new instruments should fulfill the three tenets for shaping canals: safety, effectiveness, and simplicity. • Research will be needed to validate the performance and benefits of each new system.
  94. 94. •Thank You

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