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1. INSTRUMENT SEPERATION
AND ITS MANAGEMENT
PPAR
Dr.PRIYANKA IPPAR
SECOND YEAR PG
GUIDED BY:
Dr. RANA K. VARGHESE, PROFESSOR AND HOD.
Dr. MALWIKA SISODIYA, READER.
Dr. NAVEEN KUMAR GUPTA, READER.
Dr. ANITA CHANDRAKAR, SENIOR LECT.
Dr. CHANDRABHAN GENDLY, SENIOR LECT.

2. CONTENTS
 Introduction
 Prevalence and incidence
 Tooth factors
 Instrument factors
 Operator factors
 Patient factors
 Prevention
 Canal morphology
 Preparation instrument
 Flexural fatigue
 Torsional fatigue
 Instrumentation technique
 Torque

3. CONTENTS
 Speed
 Motor used
 Access cavity
 Cleaning and sterilization
 Re use
 Investigation technique
 Cross sectional design
 Thermal treatment
 Pre flaring
 Instrument sequence
 Instrument size
 Manufacturing process
 Management
 Success rate of each technique
 Associated complication
 Bypassing
 Leaving in situ
 Influence of canal infection on prognosis
 Conclusion
 References

4. INTRODUCTION :
 Separation of endodontic instruments within the root canal is an unfortunate
occurrence that may hinder root canal procedures and affect the outcome .
 Although many factors contribute to instrument separation , the exact mode of
separation is not fully understood. This reflects the complexity of the separation
process, the interaction of causal forces (torsional and bending), and contributing
factors.
 The composition and design of root canal instruments have been modified, with the
aim of achieving better performance and fewer undesirable complications including
instrument separation. Indeed, when a new instrument or system is introduced, it is
generally claimed by the manufacturer to be more efficient in preparing the root canal
and more resistant to separation.
 The advent of nickel-titanium (NiTi) alloys has not resulted in a lower incidence of
instrument separation ..

5.  Whereas separation rates of stainless steel (SS) instruments have been reported to
range between 0.25% and 6% (8–11), the separation rate of NiTi rotary instruments
has been reported to range between 1.3% and 10.0% (8, 9, 12–20).
 Even in experienced hands, this problem can still occur and frustrate both
practitioners and patients

6. PREVALANCE AND INCIDENCE OF
INSRUMENT FRACTURE
 The occurrence of intracanal instrument fracture is reported to range widely between
0.28% and 16.20%.In a 5-year retrospective study involving postgraduate students the
overall prevalence of instrument fracture among 1367 patients (2180 endodontic cases,
4897 root canals) during root canal preparation was found to be 1.83% (40/2180 cases)
 . Among 1682 instruments collected over 16 mo, the prevalence of fracture was 5% with
the lowest fracture rate being 3% for K3 (SybronEndo, Orange, CA, United States)
stainless steel (SS) hand instruments.
 In a student clinic, during a 10-year period (1997-2006) the overall incidence of
instrument fracture in 3854 root-filled teeth was 1.0% at the tooth level.
 Over 1 year, among 1235 patients (1403 teeth, 3181 canals) from a clinical practice, the
incidence of fracture for ProFile (Dentsply-Maillefer, Ballaigues, Switzerland), ProTaper
(Dentsply Maillefer), GTRotary (Dentsply Tulsa Dental Specialities, Tulsa, OK, United
States) and K3Endo (SybronEndo) nickeltitanium (NiTi) rotary files was 0.28%, 0.41%,
0.39% and 0.52%, respectively

7.  A 4-year retrospective study of 3706 ProFile instruments reported a fracture rate of
0.3%.
 In a large retrospective study, the incidence of Mtwo (VDW GmbH, Munich,
Germany) NiTi rotary instrument separation was 2.2% according to the number of
teeth (11306), and 1.0% according to the number of root canals (24108).
 In another 1-year study, the fracture incidence was 16.02% among 593 discarded
Mtwo instruments after clinical use. Over a 2-year period, 3543 canals were treated
during which 46 LightSpeed (LightSpeed Technology, Inc., San Antonio, TX,
United States) NiTi rotary instruments separated and were found to be non-
retrievable, resulting in a separation rate of 1.30%.
 A survey from Tehran reported that the most prevalent NiTi instrument failure fault
was “intra-canal file fracture” (88.5%) among all procedural faults.

12. FACTORS INFLUENCING REMOVAL OF
SEPERATED INSTRUMETS :
 TOOTH FACTORS :
 Tooth factors largely include anatomic factors that are dictated by the type of tooth, the
cross-sectional shape and diameter of the root canal, position of the fragment within the
root canal, location of the fragment with regard to root canal curvature, as well as the
radius and degree of root canal curvature. Removal of separated instruments is more
predictable in the following situations:
1. In maxillary teeth
2. In anterior teeth
3. When the fragment extends into the coronal third of the root canal
4. When the fragment is located before the root canal curvature,
5. When the instrument separates in straight or slightly curved root canals
 It is claimed that if one-third of the overall length of a separated instrument can be
exposed, then it is accessible for removal. Nevertheless, most NiTi instruments, because of
their flexibility, generally fracture more apically at or beyond the root canal curvature,
making their removal difficult

13.  The influence of anatomic factors can be explained in terms of visualization and
access , that is, the ability to see the separated segment, to obtain good access, and
to manipulate retrieval instruments/devices safely and effectively.
 In this context, 3 main factors are relevant: tooth type (posterior or anterior teeth,
mandibular or maxillary teeth), the fragment’s position in the root canal (coronal,
middle, and apical section), and the separated instrument–canal wall interface.
 For the latter, removal of a fragment is more predictable when a gap between the
fragment and root canal walls is present

14. SEPERATED INSTRUMENT FACTORS (Type
, Design and Length)
 It is generally believed that NiTi rotary instruments are more difficult to remove
compared with SS ones for the following reasons:
1. They tend to thread into root canal walls because of their rotary Movement.
2. They have greater tendencies to fracture repeatedly during removal procedures,
particularly when ultrasonics is used.
3. Clinical observation has revealed that fragments of NiTi instruments in curved root
canals tend to lie against the outer root canal wall and do not remain in the center of
the canal because of their flexibility
4. They usually fracture in short lengths, especially after torsional Failure ,the longer
the fragment, the higher the success rate of retrieval because longer fragments are
usually more coronally located

15.  The design of the separated instruments is also important, eg, removal of K-files is
easier and more successful than Hedstr€om files .
 The design of Hedstr€om files may contribute to their more challenging removal.
Compared with K-files, Hedstr€om files have larger helix angle, deeper flutes, and
greater positive rake angle .
 Another possible reason is that these features result in Hedstr€om files having greater
cutting efficiency than K-files, which may result in greater engagement in root canal
walls at the time when separation occurs.

16. OPERATOR FACTORS:
 Separation of an instrument is a frustrating incident that places the clinician under
stress and potential litigation , which may provoke him/her to attempt to remove the
fragment.
 However, one of the most important prerequisites for managing such cases is to
adopt a measured methodological approach with utmost patience on the part of the
operator.
 In addition, successful removal is a challenge that relies on knowledge, training,
familiarity with techniques and instruments, perseverance, and creativity . It is
important to stress that an experienced operator not only can remove the separated
instrument(s) but also does not sacrifice tooth tissue unnecessarily .
 If a clinician believes that he/she does not have the competence for successful
management, referring the patient to a specialist would be the preferred approach.

17. PATIENT FACTORS:
 Patient factors such as the extent of mouth opening, limitations in accessing the
tooth, time constraints, anxiety level, and motivation to retain teeth are important.
 By explaining and discussing the complexity of the procedures and their potential
complications with the patient before treatment, it may be possible to alleviate
many of the patient’s fears while earning ‘‘good will support’’ from the patient,
allowing the operator time to enable successful accomplishment of the task.

18. PREVENTION OF INSTRUMENT FRACTURE
CANAL MORPHOLOGY
 It is important to assess the many variations in root and root-canal morphology before
initiating any endodontic treatment.Plotino et al stated that the shape of an artificial root
canal influenced the trajectory of the intracanal instrument.
 Differences in shape were reflected by the number of cycles to failure (NCF) measured
for the same instrument in different artificial root canals, and by the impact of the type of
canal on both the NCF and fragment length. Lopes et al indicated that significantly lower
NCF values were observed for instruments tested in canals with the smallest root
curvature radius, the longest arc and the arc located in the middle portion of the canal.
 Tzanetakis et al reported that the prevalence of instruments fractured in the apical third
(52.5%) was significantly higher when compared with the middle (27.5%) and coronal
(12.5%) thirds of the canals.

19.  Di Fiore et al found that instruments fractured in anterior teeth was 0.28%, in
premolars 1.56% and in molars 2.74%, which appeared to be related to the
increasingly complexity of canal morphology.
 Some 39.5% of fractured instruments were located in the mesiobuccal canals of
molars and 76.5% of the fragments were located apically.
 In conclusion, premolar and molar teeth, and the apical third of small-diameter and
curved canals in particular are prone to cause instrument fracture separation.

20. ROOT CANAL CURVATURE ANGLE
 The in vitro time to failure significantly decreased and the cyclic fatigue life
increased as the angles of root canal curvature increased. The abruptness of root
canal curvature negatively influenced the failure rate of rotary instruments
 Rotary FlexMaster instruments, with a cross-section similar to a triangle with
convex sides, are suitable for preparing curved root canals with the balanced-force
technique.
 Kim et al found that the “minimally invasive instrumentation” design of the Self-
Adjusting File (ReDent-Nova, Ra’anana, Israel) may produce minimal stress
concentrations in the apical root dentin during shaping of the curved canal

21.  Kitchens et al reported that increasing the angle (25°, 28° and 33.5°) at which the
ProFile instrument was rotated, decreased the number of rotations to fracture for
the 0.04- and 0.06-tapers.
 The 0.04-taper ProFile was more affected by an increase in the angle than the 0.06-
taper
 The greater the degree of root canal curvature, then the easier the instrument will
fracture. Apart from possible root canal transportation, Rotary FlexMaster,
LightSpeed and Self-Adjusting File instruments are suitable to prepare curved root
canals. However, the risk of any instrument fracturing increases with the severity of
canal curvature.

22. SCHNEIDER'S METHOD
 Using this method, a mid-point is marked on the file at the level of the canal
orifice.
 A straight line is drawn parallel to the image and that point is labeled as point A.
Another second point is marked where the flare starts to deviate that is labeled
point B.
 A third point is marked at the apical foramen and is termed point C and the angle
formed by the intersection of these lines is measured .
 If the angle is less than 5°, the canal is straight; if the angle is 5-20°, the canal is
moderately curved; and if the angle is greater than 20°, the canal is classified as a
severely curved canal

24. ROOT CANAL CURVATURE RADIUS:
 Radius of canal curvature was considered as the most significant factor in
determining the fatigue resistance of the files. As the radius decreased, then the
time to fracture also decreased.

25. PREPARATION INSTRUMENTS:
 The prevalence of SS hand and NiTi rotary instrument fractures by postgraduate
students was reported as 0.55% and 1.33%, respectively.
 SS instruments usually deform before they fracture, unlike NiTi instruments that
do not show visual signs of deformation before fracture. It was observed that SS
files had a significantly greater occurrence of failure in clockwise rotation, whereas
NiTi files had a significantly greater occurrence of failure in counterclockwise
rotation.
 Many studies have suggested that fatigue fracture and torsional fracture are two
major reasons for instrument separation.
 Plotino et al attributed the fracture of NiTi rotary instruments to cyclic flexural
fatigue or torsional failure, or a combination.

26.  Regarding the technique, light apical pressure, continuous axial movement
(pecking motion), and brief use inside the root canal are almost unanimously
recommended (Parashos and Messer 2006) in order to prevent torsional overload
and prolong the fatigue life (Sattapan et al. 2000a; Li et al. 2002; Rodrigues et al.
2011; Gambarra- Soares et al. 2013).

27. FLEXURAL FATIGUE
 Flexural fatigue occurs when the instrument continuously rotates freely in a curved
canal generating tension/compression cycles at the point of maximum flexure,
which eventually results in fracture.
 It is proposed that repeated tension-compression cycles caused by the rotation
within curved canals increases cyclic fatigue of the instrument over time.
 Flexural fatigue fracture occurs essentially due to overuse of the metal alloy, other
factors potentially contributing to metal fatigue include corrosion and changes
caused by thermal expansion and contraction.

28. TORSIONAL FRACTURE
 Torsional fracture occurs when the instrument (generally the tip) becomes locked in
the canal while the file shank continues to rotate.
 Subsequently fracture of the file occurs when the elastic limit of the alloy is
exceeded. Instruments that fracture as a result of torsional overload, reveal
evidence of plastic deformation such as unwinding, straightening and twisting
 Certain studies reported that the majority of instruments fractured due to flexural
fatigue thereby implying that overuse was the most significant mechanism of
failure. It was theorised that once a microcrack was initiated (fatigue-crack growth
rates are higher in NiTi alloys than in other metals of similar strength) it can
propagate quickly causing catastrophic failure.

29.  Conversely other studies classified torsional fracture as the dominant mode of
fracture suggesting that torsional failure was the result of using excessive apical
force during instrumentation or excessive curvature of the canal. Generally,
torsional failure of instruments decreases and flexural failure increases as the size of
the instrument increases.

30. SIGNIFICANCE OF INSTRUMENTATION TECHNIQUE
 A crown-down instrumentation technique (enlarging the coronal aspect of the canal
before apical preparation) and creation of a manual glide path (preparing the canals
manually with a SS file to working length before rotary NiTi instrumentation) has
been proposed to reduce the frequency of instrument fracture.
 These techniques aid in reducing instrument ‘taper lock’ or ‘instrument jamming’
which is associated with torsional fracture.
 Crown-down instrumentation reduces torsional stresses generated particularly in the
smaller instruments and a glide path limits the level of torque on the instrument
thereby protecting against shear fracture

31. TORQUE
 Torque is a less straight forward parameter than rotational speed. It is a measure of the
turning force applied to the instrument in order for the instrument to overcome
friction and continue rotating.
 Since electric motors strive to maintain a constant rotational speed, the torque applied
to the instrument can vary continuously depending on friction, which is, in turn,
determined by the contact area between the instrument blades and dentin and the
handling of the instrument.
 The contact area is mainly affected by the size, taper, and cross-sectional shape of
both the instrument and the root canal; a wider contact area increases friction, so
higher torque is necessary in order for a larger instrument to rotate inside a narrow
root canal (Kobayashi et al. 1997, Sattapan et al. 2000a).

32.  For instance, the contact area increases considerably when instruments of the same
taper but of progressively larger size are used consecutively in the same root canal;
every subsequent instrument after the first one is subjected to excessive friction and
requires much higher driving torque to rotate (a situation called “taper lock”) that
could lead to a torsional failure
 Torque control electric motors allow the operator to determine a maximum torque
value to be applied to the instrument during rotation; upon exceeding this value, the
motor stops and usually reverses the rotation (auto-reverse) to disengage the
instrument from dentin. Obviously, different torque limits should be used for each
instrument,according to the manufacturer’s recommendations

33.  Torque-controlled electric motors are generally recommended for use with rotary
NiTi systems. An in vitro study has demonstrated that torque controlled motors,
which perform below the elastic limit of the file, reduce instrument fracture due to
torsional overload.
 However, clinical studies did not demonstrate any significant difference in failure of
Profile NiTi instruments used with high or low torque motors.Another clinical study
investigated three torque control levels (high, moderate and low) during NiTi canal
preparation and reported that if the operator was inexperienced fracture rates
decreased with a low torque-controlled motor.
 Nevertheless, this study observed no difference when experienced operators used a
high or moderate torque-controlled motor.
 The use of torque control has been questioned by one study which suggested that
rotary NiTi instruments function better at higher torque and that frequent
engagement of the auto-reverse function carries a risk of torsional fatigue and
failure.

34. SPEED
 The widespread adoption of electric motors has occurred in parallel with the
prevalence of the low-speed low-torque instrumentation concept (Gambarini
2001b).
 Manufacturers of rotary NiTi files recommend a specific rotational speed, usually
in the range from 250 to 600 revolutions per minute (rpm), but its effect on
instrument failure is controversial; several studies have found no influence on
instrument fracture (Pruett et al. 1997, Yared et al. 2002, Zelada et al. 2002, Herold
et al. 2007, Kitchens et al. 2007), while others have reported an increase in
fractures with increasing speed (Li et al. 2002, Martın et al. 2003).

35. ELECTRIC VS AIR DRIVEN HANDPIECES
 Interestingly when comparing air-driven and electric handpieces, no difference in
instrument fracture rate was reported.
 However, clinical logic dictates that an electric motor would ensure delivery of a
constant speed; whereas air driven instruments would subject the instrument to
surges in pressure and lack of speed and control, creating a more fracture-prone
situation.
 It is worth noting that all manufacturers of NiTi instruments currently recommend
that the rotary files are used in a speed controlled electric motor.

36. ACCESS CAVITY
 The definition of an “adequate” access cavity has undergone several changes
throughout the years.
 A completed access cavity should still allow unobstructed visual access to all root
canals and act as a funnel to guide the instruments into the canal, straight to the
apex, or to the point of first curvature (Peters 2008).
 Interference by the cavity walls or by unremoved dentin shoulders in the coronal
third of the root canal can increase the stress imposed on the instruments during
preparation by increasing the number and severity of curvatures that must be
negotiated (iatrogenic S curve) (Roda and Gettleman 2016); this could lead to
instrument failure .
 Conversely, expanding the access cavity beyond the confines of the pulp chamber
could also hinder the entrance of files into the root canals and lead to accidental
bending of the tips.

39. EFFECT OF CLEANING AND STERLIZATION
 The literature, regarding the impact of sterilisation on NiTi instruments, appears
contradictory.
 A number of studies report that subsequent to multiple sterilisation/ autoclave cycles,
NiTi instruments exhibit evidence of crack initiation and propagation and an increase
in depth of surface irregularities, furthermore, a decrease in cutting efficiency has
been demonstrated.
 However, the deleterious effects of heat sterilisation on the mechanical properties of
NiTi files have been disputed with other studies concluding that it does not
significantly affect the fracture incidence of NiTi instruments.
 Nonetheless, the evidence appears clearer in relation to recently developed files that
are twisted rather than machined, with a recent study reporting a decreased cyclic
fatigue resistance subsequent to multiple heat sterilisation cycles.

40.  Interestingly, the sterilisation process has been reported to have positive effects on
the fatigue life of NiTi files by reversing the stress-induced martensite state back to
the parent austenite phase.
 However, generally the temperatures required to achieve these positive
characteristics are unlikely to be achieved in practice.
 It has been postulated that the corrosive effect of the root canal irrigant sodium
hypochlorite (NaOCl) may have a negative impact on the mechanical properties of
NiTi instruments.
 However, it has also been argued that NaOCl is unlikely to result in pitting or cause
crevice corrosion of NiTi instruments and therefore its use did not increase the
prevalence of fracture or the number of revolutions to cause flexural fatigue of NiTi
instruments

41. RE USE
 All endodontic instruments should be carefully examined under magnification prior
to reuse for signs of wear. Regarding SS instruments, any shiny marks, uneven
spacing between the flutes, areas of unwinding, sharp bending, or any other kind of
permanent distortion or corrosion are indications of excessive fatigue and should
serve as warnings of impending fracture; any such instruments should be discarded.
 Similar deformations of NiTi instruments should also be regarded as a signal to
discard them .
 However, their original shape can be more complex or asymmetric and may
include flutes with reverse direction combined with straight areas, varying helical
angles or pitch, and off-center cross section (Peters et al. 2016); these features
should not be confused with indications of impending fracture

42.  In addition, instruments made of the so-called “controlled memory” alloy may
normally undergo some unwinding during use, and this should only be considered
an indication to discard the instrument if rewinding in the opposite direction appears
or the file does not regain its original shape upon heat treatment (Coltene Endo
2014).
 Therefore, the clinician must bear in mind the original shape of the instrument and
any specific guidelines by the manufacturer in order to identify correctly which
instruments should be discarded.
 Still, NiTi instruments may commonly fracture even without any visible
deformation (Sattapan et al. 2000b; Martın et al. 2003; Peng et al. 2005; Shen et al.
2006, 2009).
 Examination under high magnification has also revealed dentin debris embedded
into machining grooves or surface cracks of used instruments (Fig. 2.17) (Zinelis
and Margelos 2002; Alapati et al. 2004), and it has been hypothesized that this
debris may accelerate crack propagation (Alapati et al. 2004).

43.  Instruments need to be cleaned and sterilized before their first use (unless they are
delivered by the manufacturer in sealed presterilized packages) and also before
every reuse; the effect of this process on instrument failure is still controversial.
 Several studies state that NiTi instrument failure is influenced more by the manner
in which they are used rather than how many times they are used.
 However, regardless of the manner in which files are used, NiTi rotary files
undergo a reduced flexural fatigue resistance with repeated usage and the torque
necessary to induce failure of a previously used instrument is significantly lower
when compared with new instruments.
 Surprisingly, no correlation has been established clinically between the number of
uses and the frequency of file fracture.

45. INSTRUMENT FRACTURE INVESTIGATION TECHNIQUES
 Fracture studies are generally based on a low powered lateral microscopic
examination of the fractured file.
 Reliability of this technique has been questioned as, although it enables detection of
plastic deformation, it does not reveal the actual mechanism involved in the fracture
process.
 It has been suggested that a fractographic examination is necessary to identify
features on the fracture surface that would indicate the origin and propagation of the
crack which ultimately leads to a fracture. Additionally, scanning electron
microscopy (SEM) of fracture surfaces has been employed experimentally in vitro;
however, the application of SEM analysis may be limited after in vivo file use, due to
excessive distortion of the fractured file surface.
 In conclusion, the clinical relevance of in vitro investigations is generally
undermined by the lack of standardisation of testing methods.

46.  Indeed, it was concluded in a recent review of cyclic fatigue testing that
methodological variation altered the fatigue behaviour of the tested instruments,
thereby influencing the study results.
 The authors further suggested that it was difficult to assess clinical relevance of
studies which test one factor in isolation for example, cyclic fatigue, as this differs
from the in vivo fracture situation where a series of factors act simultaneously.

47. CROSS SECTIONAL DIMENSIONS AND DESIGN FEATURES
 Cross-sectional area
Rotary files are manufactured with different cross-sectional designs; for example: Convex
triangle-ProTaper, Wave One, Triple U-Profile, Equilateral triangle-Race, S-type-M-two,
Reciproc, and Rectangular–ProTaper Next
 Inner core and CSA: More the core and CSA, more is the TR but less is the CFR.This is the
reason for improved fracture resistance of ProTapers than profiles in narrow canals
 Cross-sectional design: Instrument separation occurs in the decreasing order with the following
cross sections
 Square > rectangular > triangular and slender rectangular triangle
 S-shaped, H-file fracture more compared to triangular cross section
 Alloy type: With the same cross section, M-wire alloy resists fracture better than conventional
alloy
Cyclic fatigue resistance (CFR), torsional resistance (TR), superelasticity (SE), shape memory (SM).

48.  Different cross sections along the length of an instrument improve the fracture resistance;
for example: One shape and WaveOne
 Asymmetric cross sections of ProTaper Next and Revo-S also reduce screwing in and
breakage
 Protaper universal files (F2, F3, F4, F5) are made more flexible by incorporating an
additional groove in the middle of side of convex triangular cross section
 Tip
In general, NiTi rotary instruments are designed with noncutting tips to prevent ledging,
torsional failure, and fracture.
 Booster tip is a lead tip, that is incorporated in XPendoShaper. The lead section enters
canal ensuring fit into the pre-established glide path.
 There are no cutting flutes on this section (¼ mm) where as the next ¼ mm has 6 cutting
flutes, which shapes canal to #25/.02 to #60/.02 instrument.
 The repeated use of the shaper prepares the canal to a taper size consistent with the
intracanal dentinal anatomy and hardness.

49. Taper
 Taper is increase in the diameter of file per mm increase in length. Fixed taper files
cause excessive screwing in and taper lock than graduating or variable taper files.
 An instrument with larger taper and tip diameter is more likely to fracture in a canal
with more acute and coronally located curvature
Pitch
 It refers to the number of flutes per unit length of the file. More the flutes on the file,
lesser the pitch and more is the fracture resistance of the file.
 Hence, it is recommended to use a file with smaller pitch (more flutes) for both
curved and straight canals.
RADIAL LAND:
 Radial land is a surface that projects axially from the central axis between the flutes, it
as far as the cutting edges.

50.  Increased width of land increases the peripheral strength and canal-centering ability,
but induces stresses due to increased contact with the canal wall causing fracture.To
balance these properties, K3 is designed with two recessed and one full land:
ProTaper and Race lack radial lands
Rake angle
 It is the angle formed by the cutting edge and cross-section taken perpendicular to
the long axis of the instrument.
 Slight positive rake angle is recommended to for both good cutting action and
reduced screwing in; for example: K3.
Helical angle
 Helical angle is the angle that the cutting edge makes with the long axis of the file.
Varying the helical angle through the working part has been shown to reduce the
screwing in tendency; for example; in K3, helical angle is increased from tip to the
handle. In Race, alternate helical design reduces the torque

51. THERMAL TREATMENT OF ALLOYS:
 R-Phase Alloys
R-phase alloys have more flexibility, TR and CFR than conventional alloys with the
same geometry, in both dry and aqueous environments, and also when used in
reciprocating motion.However, they have low TR than M-wire alloys.
 M-Wire Alloys
They are produced by a series of heat treatment and annealing cycles which endow them
superior strength due to stable nanocrystalline martensitic structure.
 Controlled Memory Alloys
Unlike conventional rotary files, controlled memory files do not exhibit SM, and hence
do not straighten the canal or cause ledging Instruments with low transformation
temperature exhibit (Hero, K3) higher maximum torque and resist fracture better than
instruments with high transformation temperature (Endowave, Profile, and ProTaper

52.  Alloys With Gold Thermal Treatment
Files are subjected to a temperature of 370°C–510°C for 10–60 min depending on
the size and taper of files. Files exhibit two-stage transformation behavior and high
Af temperature of 50°C; for example ProTaper Gold.In WaveOne Gold, a constant
strain of 3–15 kg is applied at a temperature of 410°C–440°C. After machining, the
working portion is again heat treated at 120°C–260°C.
 Maxwire Alloys (Martensite-Austenite Electropolish Flex) Alloys
This new technology allows the file XPendoShaper to attain martensitic phase
when cooled (20°C) and austenitic phase at body temperature (37°C). At austenitic
phase, it has a snake-like shape adapting to the canal irregularities, reducing stress
on the file.

53.  Electric discharge machining technology
 Electric discharge machining (EDM) technology is a noncontact thermal erosion
process in which electric sparks are used to melt and vaporize the top layer of NiTi
alloy, reducing the surface defects.
 This increases the fracture resistance of files.After cutting, cleaning is done
ultrasonically in an acid bath. Then, they are heat treated at 300°C–600°C for 10 min,
5 h before and after the cleaning; for example: HyFlex ® EDM
 Blue phase treatment
In this, the surface of a NiTi alloy is treated with titanium oxide by proprietary
manufacturing process, which increases the surface hardness, wear resistance, cutting
efficiency and flexibility of the file; for example: Vortex Blue and Reciproc Blue

54.  T-Wire Alloys
The proprietary heat treatment claims to increase the flexibility and fracture
resistance by 40%; for example: 2 shape files, it has two rotary files TS1 and TS2.
The instruments regain their original shape after each use.Thermally treated alloys
have low modulus of elasticity (20–40 GPa) than conventional (40–90 GPa) alloys
and resist fracture better under stress.
 Surface treatment of nickel–titanium alloys
 Rotary files are subjected to various surface treatments to improve their properties .
Implantation of Argon ion increases the fatigue resistance.
 Nitrogen ion implantation has negative effect on fatigue resistance. Thermal
nitridation at 250°C has shown more fatigue resistance because at 300°C the
superelastic behavior is lost.
 Deep dry cryogenic treatment of 24 h, at −185°C, provides adequate time for
transformation of retained austenite to martensite, improving the fatigue life.

55.  Electropolished instruments have more number of cycles to fracture than that of
nonpolished instruments. However, it does not prevent the development of
microcracks on the instrument surface

56. INSTRUMENT SEQUENCE
 It is essential that the instrumentation sequence of a specific technique is not
neglected.
 A sequence including various tapers is safer compared to a single taper
use.Although it requires a greater number of instruments to prepare canals, each
file will undergo less stress and consequently a greater life span.
 The concept of hybrid instrumentation has been recently introduced.
 It is believed that a combination of fi les of different systems and the use of
different instrumentation techniques to manage individual clinical situations can
reduce the risk of fi le separation

57. PRE FLARING
 It is accepted that provision of a glide path should facilitate the work of subsequent
instruments which can smoothly clean and shape root canals.
 Prefl aring of root canal with hand files was reported to allow a signifi cantly greater
number of uses of rotary files before fracture occurred.
 There are two main advantages when initial manual prefl aring is established.
 Firstly, torsional stress is drastically reduced because the canal width becomes at
least equal to the diameter of the tip of the instrument is used.
 Secondly, prefl aring creates an understanding of the root canal anatomy and allows
a glide path for the instrument tip.

58. INSTRUMENT SIZE
 A higher incidence of fracture and distortion in smaller NiTi instruments has been
recorded in a number of in vitro studies.
 Certain investigators have concluded that smaller instruments are more susceptible
to torsional failure than larger instruments and have recommended that small files
(eg 0.04 taper ProFile size 20) should be considered as a single use instrument,
such is the likelihood of distortion.
 Conversely, a large clinical cohort study reported the greatest number of
instrument failures occurred when using the larger diameter files, suggesting that
larger stiffer files experienced greater stress during use.
 Clinically, logic would suggest that smaller files are more susceptible to distortion
as they are the principal files involved in negotiation and initial instrumentation of
the root canal system.

60. MANUFACTURING PROCESS
 Traditionally, NiTi endodontic files are ‘machined’ from a blank NiTi alloy wire during
manufacture.
 The process has been shown to create an irregular surface characterised by grooves,
pits, multiple cracks and metal rollover with the frequency of such irregularities
increasing proportionally with the taper of the instrument.
 The manufacturing process itself leads to work hardening of rotary NiTi instruments,
creating brittle areas. These surface imperfections may act as a centre of stress
concentration, initiating crack formation during clinical use.
 In general, surface defects affect the ultimate strength of the material and have a major
bearing on the fatigue resistance of the instrument.
 As a result manufacturers have endeavoured to improve the mechanical properties of
the files by modifying the surface or alloy microstructure during the manufacturing
process.

61. ELECTROPOLISHING
 Electropolishing alters the surface composition of the NiTi file creating a
homogeneous oxide layer, with an associated reduction in surface defects and stress,
which it is claimed results in enhanced NiTi corrosion resistance and fracture
resistance.
 Commercially available file systems include BioRace™ and RaCe™ (FKG Dentaire,
La Chaux-de-fonds, Switzerland).
 Certain studies specifically reported a significantly improved resistance to flexural
fatigue and improved torsional properties after electropolishing;
 however, this has not been universally demonstrated.Interestingly, it was also shown
that the improved surface composition of NiTi after electropolishing rendered the
instrument more resistant to the effects of sodium hypochlorite solution (NaOCl).

62.  However, the positive effects of electropolishing are inconsistent and appear to alter
in magnitude with factors such as instrument design, type and particularly cross-
sectional area.

63. ION IMPLANTATION
 The implantation of argon, boron or nitrogen into manufactured files has been
investigated in an attempt to improve surface characteristics of NiTi instruments
and thereby enhance mechanical properties such as flexibility, surface hardness,
and cyclic fatigue resistance.
 Ion implantation has demonstrated promise in improving the mechanical
characteristics of certain NiTi files in vitro, however, these techniques are
experimental, not cost effective and currently not implemented by file
manufacturers

64. TWISTING OF FILES
 Originally, due to the shape-memory characteristics of NiTi rotary instruments, it
was deemed necessary to machine these instruments to create the desired taper, flute
design and cutting edge and other features.
 Recent technological advancements have enabled twisting of NiTi alloys (Twisted
file™ [TF] SybronEndo, Orange, CA, USA) by a process of heating and cooling
raw NiTi wire in the austenite crystalline structure and then modifying it into a
different phase of crystalline structure (R-phase).
 It has been reported that the properties and structure of R-phase NiTi are superior to
traditional machined NiTi files due to optimisation of the grain structure, as grinding
is believed to create microfractures on the metal surface.
 In an attempt to further enhance the mechanical features of the file, TFs undergo a
proprietary process (Deox) in which surface impurities and the oxidation layer is
removed.

65.  Ground and twisted files have been compared in vitro where it was reported that
TFs exhibited increased torsional resisitance, flexibility and strength compared to
ground files.
 A separate study corroborated the significantly higher resistance of TFs compared
with selected, but not all ground files.
 Other evidence contradicts the reported mechanical benefits of twisting NiTi
alloys demonstrating that TF files actually had the lowest resistance to torsional
fracture when compared with several other commercially available ground files.

66. ADVANCEMENTS IN MACHINED FILES
 Recent developments in alloy technology include M-Wire (Dentsply-Tulsa Dental
Specialities, Tulsa, OK, USA). M-Wire is a variant of NiTi, composed of SE508
Nitinol, that has undergone heat treatments and drawing of the wire under a specified
tension producing a material described as ‘partially in the martensitic and the
premartensitic R-phase while still maintaining a pseudoelastic state.
 WaveOne™ (Dentsply Maillefer, Ballaigues, Switzerland) is an example of a new
file system availing of this technology. Several studies have reported a significantly
increased resistance to cyclic fatigue with M-Wire compared with conventionally
ground NiTi rotary files.
 However, one study reported that files manufactured from M-Wire showed no
difference in cyclic fatigue resistance when compared with those produced from
conventional grinding while also finding that TFs (SybronEndo, Orange, CA, USA)
demonstrated significantly more resistance to cyclic fatigue than ground files.

67.  However, it is perhaps worth noting that several of these studies were undertaken
by commercial representatives of companies and this highlights the need for
investigation of new technologies to be carried out by independent groups.

68. HEAT TREATMENT (POST-MACHINING/
POST-TWISTING)
 This process has recently been heralded as potentially offering the most promising
technological developments in NiTi alloy metallurgy.
 It is theorised that the use of appropriate heat treatment – transforming the alloy
into a slightly altered crystalline phase structure – to achieve microstructure
control, may be used as a cost effective method of creating rotary NiTi instruments
with superior flexibility and fatigue resistance.
 Heat treatment strongly affects superelasticity and shape memory characteristics82
resulting in the development of instruments that have no memory or a ‘controlled
memory’ (for example, HyFLEX™ CM; Coltène/Whaledent, Inc., Cuyahoga Falls,
OH, USA) with claims of increased fatig ue resistance

69.  The new HyFlex EDM files constitute the 5th generation root canal files. HyFlex
EDM NiTi files have completely new properties due to their innovative
manufacturing process using electric discharge machining.
 Workpieces are machined in the EDM manufacturing process by generating a
potential between the workpiece and the tool.
 The sparks generated in this process cause the surface of the material to melt and
evaporate. This creates the unique surface of the new Niti files and makes the
HyFlex EDM files stronger and more fracture resistant.
 This entirely unique combination of flexibility and fracture resistance makes it
possible to reduce the number of files required for cleaning and shaping during root
canal treatments without having to compromise preservation of the root canal
anatomy.

70. PREVENTION:
• Ensure adequate training and proficiency in the NiTi system of choice before clinical use by
practicing on extracted teeth or resin blocks
• Create a manual glide path (K-file, size 10–15° or NiTi pathfiles™ (Dentsply Maillefer,
Ballaigues) to ensure unimpeded access to the root canal, before use of greater taper NiTi
files
• Employ a crown-down instrumentation technique to ensure straight-line access to the root
canal
• Use an electric speed and torque-controlled motor at the manufacturer’s recommended settings
• The NiTi files should be used in constant motion using gentle pressure to avoid placing
excessive torsional forces on the instrument
• Avoid triggering or disable the auto-reverse mode or disable the auto-reverse feature on the
motor, as it increases the risk of torsional fatigue

71. • If not obligated to adopt a single-use file policy consider adopting a personal policy
to prevent overuse of files. Files used in particular challenging root morphology
should be considered for early replacement or discard
• Use of rotary files in abruptly curved or dilacerated canals should be avoided.

73. CHEMICAL SOLVENTS
 The use of EDTA has been suggested as a method of softening root canal wall
dentin around separated instruments, facilitating the placement of files for the
removal of the fragment .
 Other chemicals such as iodine trichloride, nitric acid, hydrochloric acid, sulfuric
acid, crystals of iodine, iron chloride solution, nitrohydrochloric acid, and
potassium iodide solutions have historically been used to achieve intentional
corrosion of metal objects .
 However, for obvious reasons, such as irritating the periapical tissue, they are no
longer in use.

74. MINI FORCEPS
 In the presence of sufficient space within the root canal system, an instrument
separated in a more coronal portion of the root canal can be grasped and removed
by using forceps such as Steiglitz forceps (Union Broach, York, PA), Peet silver
point forceps (Silvermans, New York, NY), or Endo Forceps (Roydent, Johnson
City, TN).

75. BROACH AND COTTON
 If the separated fragment is a barbed broach and not tightly wedged in the root
canal, another small barbed broach with a small piece of cotton roll twisted around
it can be inserted inside the root canal to engage the fragment; then the whole
assembly is withdrawn

76. WIRE LOOPS
 A wire loop can be formed by passing the 2 free ends of a 0.14-mm wire through a
25-gauge injection needle from the open end until they slide out of the hub end. By
using a small mosquito hemostat, the wire loop can be tightened around the upper
free part of the fragment, and then the whole assembly can be withdrawn from the
root canal.
 The loop can be either small circular or long elliptical in shape, according to canal
size and the location of the fragment. This technique can be used to retrieve objects
that are not tightly bound in the root canal

78. HYPODERMIC SURGICAL NEEDLES
 The beveled tip of a hypodermic needle can be shortened to cut a groove around the
coronal part of the fragment by rotating the needle under light apical pressure .
 The needle size should allow its lumen to entirely encase the coronal tip of the fragment ,
which guides the needle tip while cutting so as to remove the minimum amount of dentin .
 Counterclockwise rotation may enhance removal of instruments with right-hand threads
and vice versa. The needle’s cutting edges should not be blunt; hence, it is time-saving to
use as many new needles as required. The groove (trough) around the fragment can also
be prepared by using thin ultrasonic tips or trephine burs.
 To remove the fragment, a cyanoacrylate glue or strong dental cement (eg,
polycarboxylate) can be inserted into the hypodermic needle, and then (when set) the
complex (needle-adhesive-fragment) can be pulled out delicately in a clockwise or
counterclockwise rotational movement

79.  Roughening the smooth lumen by small burs can enhance the bond . In cases in which
glue cannot be used, a Hedstr€om file can be pushed in a clockwise turning motion
through the needle to wedge the upper part of the fragment and the needle’s inner wall
.
 With good interlocking between the fragment and the Hedstr€om file, both can then
be gently pulled out of the root canal. Because they are not flexible, needles cannot be
used in curved canals.
 Although there is no evidence on its effectiveness as a primary retrieval method,
Suter et al reported successful removal of 10 of 11 fragments (91%) by using tubes
and Hedstr€om files as a second technique in cases where the primary one, ultrasonic
vibration, was unsuccessful.
 Clinicians should train before using such a technique on clinical cases; otherwise,
complications may occur

81. BRAIDING OF ENDODONTIC FILES
 A Hedstr€om or K-type file(s) can be inserted into the root canal to engage with the
fragment and then withdrawn. This method can be effective when the fragment is
positioned deeply in the canal and not visible and the clinician is relying on tactile
sense, or the fragment is loose but cannot be retrieved by using other means.
 The largest possible size of files should be used with caution because of the
possibility of separation of the braided files.

82. MASSERANN INSTRUMENTS
 The Masserann kit (Micro-Mega, Besanc¸on, France) consists of 14 hollow cutting-end
trephine burs (sizes 11–24) ranging in diameter from 1.1–2.4 mm and 2 extractors (tubes
into which a plunger can be advanced).
 The trephines (burs) are used in a counterclockwise fashion to prepare a groove (trough)
around the coronal portion of the fragment. When inserted into the groove and tightening
the screw, the free part of the fragment is locked between the plunger and the internal
embossment.
 The relatively large diameters of extractors (1.2 and 1.5 mm) require removal of a
considerable amount of dentin, which may weaken the root and lead to perforation or
postoperative root fracture.
 This largely restricts the use of Masserann instruments to anterior teeth . However, by
creating a wider space between the tube and plunger inside the tubular extractor, it can be
used in the straight portion of canals of posterior teeth . This also increases retention
while gripping the firmly wedged separated instrument.

83. EXTRACTORS:
 The concept behind the Masserann technique has been further developed, and new
extractors have been introduced. The Endo- Extractor system (Roydent) has 3
extractors of different sizes and colors (red 80, yellow 50, and white 30).
 Each extractor has its corresponding trephine bur that prepares a groove around the
separated instrument. The Cancellier Extractor Kit (SybronEndo, Orange, CA)
contains 4 extractors with outside diameters of 0.50, 0.60, 0.70, and 0.80 mm. The
Instrument Removal System (Dentsply Tulsa Dental, Tulsa, OK) contains 3
extractors.
 The black extractor has an outside diameter of 1 mm and is used in the coronal one-
third of larger root canals. The red and yellow extractors (0.80 and 0.60 mm,
respectively) are used in narrower canals . Recently, new systems have been
introduced into the market. The Endo Rescue (Komet/Brasseler, Savannah, GA)
consists mainly of a center drill called Pointier that excavates dentin coronal to the
fragment and trephine burs that rotate in a counterclockwise direction to remove the
fragment.

86.  These instruments are available in 2 sizes, 090 (red) and 070 (yellow).
 The Meitrac Endo Safety System (Hager and Meisinger GmbH, Neuss, Germany) is
another new system that has 3 sizes of tubes. Although some extractors (eg,
Instrument Removal System) can go partially around a curve, trephine burs should
only be used in the straight part of the root canal.
 Especially when adhesives are used, extractors can effectively remove a separated
fragment that is already loosened. However, caution should be exercised not to use
too much adhesive that could inadvertently block a root canal.
 More importantly, overenlargement of root canals may predispose to a ledge, root
perforation, or root fracture

87. CANAL FINDER SYSTEM
 The original Canal Finder System (FaSociete Endo Technique, Marseille, France)
consisted of a handpiece and specially designed files . The system produces a vertical
movement with maximum amplitude of 1–2 mm that decreases when the speed
increases.
 It effectively assists in bypassing a fragment, but caution should be exercised not to
perforate the root or apically extrude the fragment, especially in curved root canals.
 The flutes of the file can mechanically engage with the separated fragment, and with
the vertical vibration, the fragment can be loosened or even retrieved .
 In a clinical study that used the Canal Finder System as the primary retrieval
technique, a 68% overall success rate was reported . This system has been recently
replaced by the EndoPuls system (EndoTechnic, San Diego, CA) in which SS files are
used in vertical reciprocation and a passive ¼ turn motion.

89. ULTRA SONICS
 Ultrasonic instruments have a contra-angled design with alloy tips of different lengths
and sizes to enable use in different parts of the root canal . Most ultrasonic instruments
have an SS core coated entirely with diamond or zirconium nitride; therefore, the
instrument abrades along its sides in addition to its tip.
 By contrast, the titanium-based tips have a smooth surface (uncoated) and can cut only
at their tip. Although companies claim that these tips are flexible and can penetrate into
curved root canals, blind trephining of dentin may lead to undesirable consequences.
 A staging platform is prepared around the most coronal aspect of the fragment by using
modified Gates Glidden burs (no. 2–4) or ultrasonic tips . The Gates Glidden bur is
modified by grinding the bur perpendicular to its long axis at its maximum cross-
sectional diameter.
 The platform is kept centered to allow better visualization of the fragment and the
surrounding dentin root-canal walls; therefore, equal amounts of dentin around the
fragment are preserved, minimizing the risk of root perforation.

90.  The ultrasonic tip is activated at lower power settings, so it trephines dentin in a
counterclockwise motion around a fragment with right-hand threads and vice versa.
 With this trephining action and the vibration being transmitted to the fragment, the
latter often begins to loosen and then ‘‘jumps’’ out of the root canal. Other root canal
orifices in the tooth, when present, should be blocked with cotton pellets to prevent
the entry of the loose fragment.
 If little care is taken and excessive pressure on the ultrasonic tip is applied, the
vibration may push the fragment apically or the ultrasonic tip may fracture, leading
to a more complicated scenario.
 Also, to prevent separation of the ultrasonic tip, it is important to avoid unnecessary
stress by only activating it when in contact with root tissue (Yoshitsugu Terauchi,
personal communication, September 2011).
 K-type or Hedstr€om files can be alternatives to ultrasonic tips . The activated file
should be of a tip size that enables trephination of dentin around the fragment.

91.  However, files that are too small should not be used because they are themselves
prone to separation.
 Also, a spreader can be modified to a less tapered and smaller tip-sized instrument
that can be activated to trephine deeply around a fragment .
 Success rates for fragment removal by using ultrasonics in clinical trials have
ranged from 67% by Nagai et al to 88% and 95% reported recently by Cuje et al
and Fu et al , respectively.

93. FILE REMOVAL SYSTEM
 This system has been developed by Terauchi et al , and it is claimed that the
amount of dentin removed is minimal. It involves 3 sequential steps that use
specially designed instruments .
 In step 1, 2 low-speed burs (28 mm long) are used. The Cutting Bur A, with a
diameter of 0.5 mm and a pilot tip, is used to enlarge the root canal. The Cutting
Bur B has a cylinder-shaped tip and a 0.45-mm diameter, so it removes dentin
around the coronal part of the fragment.
 Both burs are flexible, so they can be used in curved canals. They can loosen or
even remove the fragment because they are used in a counterclockwise motion. If
this fails; step 2 is attempted. In step 2, an ultrasonic tip (30 0.2 mm) is used to
prepare a groove around the separated fragment (at least 0.7 mm deep).
 This usually loosens the fragment or even removes it. Otherwise, step 3 is carried
out. In step 3, to mechanically engage the fragment and pull it out of the root canal,
a file removal device of 2 sections is used.

94.  One part consists of a head connected to a disposable tube (0.45 mm in diameter),
with a loop made of NiTi wire (0.08 mm) projecting from it. The second part is a
brass body equipped with a sliding handle on the side that holds the wire of the
head attachment
 When the handle is moved downward, it fastens the loop and vice versa . This
system has been effective in laboratory studies and in some clinical cases of
instruments separated in the apical part of the root canal when a relatively short
retrieval time was reported . However, this system has not been introduced into the
market yet.

96. SOFTENED GUTTA PERCAH
 Rahimi and Parashos reported a novel, but simple, technique to remove loose
fragments located in the apical third of the root canal by using softened gutta-
percha (GP) points.
 SS Hedstr€om files #8, #10, and #15 are initially used to partially bypass the
fragment and to check that it is loose. Then, the apical 2–3 mm of a size 40, 0.04
taper GP point, or different size and taper according to the canal accommodating
the fragment, is dipped in chloroform for approximately 30 seconds.
 The softened GP is then inserted to the maximum extent into the canal and is
allowed to harden for approximately 3 minutes. The GP point and the Hfragment
can be then removed by using a delicate clockwise and counterclockwise pulling
action. This conservative technique may assist in removal of loose fragments that
are not easily accessible while using other removal techniques

97. LASER IRRADIATION
 The Nd:YAG laser has been tested recently in laboratory studies for removal of
separated instruments .
 It is claimed that minimum amounts of dentin are removed, reducing the risk of root
fracture. In addition, fragments can be removed in a relatively short time (less than 5
minutes) in 2 ways: the laser melts the dentin around the fragment and then H-files
are used to bypass and then remove it, and the fragment is melted by the laser.
 However, there are several concerns with this concept: the probability of root
perforation in curved root canals or thin roots, and the temperature rise on the external
root surface (up to 27C), with the potential of periodontal tissue damage .
 Also, heat generated within the root canal can carbonize or even burn dentin, which
in turn may disturb the close contact or bond between the filling materials and root
canal walls

98.  Although promising results indicate that many of these concerns can be
circumvented , vaporization of the separated instrument has yet to be achieved, as
was hoped many years ago

99. DISSOLUTION OF FRAGMENT VIA ELECTRO CHEMICAL
PROCESS
 Ormiga et al introduced and tested a new concept that is based on electrochemical-
induced dissolution of metal. Two electrodes are immersed in electrolyte; one acts as
a cathode and the other as an anode.
 The contact between the separated file and the anode as well as an adequate
electrochemical potential difference between the anode and cathode electrodes results
in the release of metallic ions to the solution, consequently causing progressive
dissolution of the fragment inside the root canal.
 The tips of #20 K3 rotary files were exposed to sodium floride and sodium chloride
solution for 8, 17, and 25 minutes and until the total consumption of the immersed
portion (6 mm). Optical microscopy analysis revealed a progressive consumption of
the immersed portion of the files with increasing polarization time.
 Importantly, the results presented evidence that this method is feasible..

100.  Despite its limitations (long time required for complete fragment dissolution and
the limited root canal space to accommodate the electrodes), results are promising
and suggest the need for further studies to develop the technique before it is
adopted clinically

102. SUCCESS RATE OF EACH TECHNIQUE
 The devices, techniques, and methods described here vary in their effectiveness, cost,
and mechanism of action.
 Whereas the Masserann kit, for example, has a reported success rate of between
48%–55% , H€ulsmann and Schinkel reported an overall success rate of 68%,
including instruments that had been bypassed, with the Canal Finder System
technique.
 Alomairy reported a 60% success rate by using the Instrument Removal System in
ex vivo study. Higher success rates have been achieved since the introduction of
ultrasonics: 79% by Nagai et al , 91% by Nehme , 88% by Fu et al , and 95% by Cuje
et al .
 The innovative combination of dental operating microscope with ultrasonics
(microsonics) has also contributed to higher success rates.

103.  Cuje et al and Suter et al attributed the higher success rates in their reports (95%
and 87%), compared with 69% reported by H€ulsmann and Schinkel, to the use of
the dental operating microscope, which has been considered as a prerequisite for
successful removal of separated instruments.
 A protocol combining different techniques and methods in sequential steps also can
increase the success rate

104. COMPLICATIONS ASSOCIATED WITH
REMOVAL OF SEPARATED INSTRUMENTS
 A variety of complications may be associated with removal of separate instruments.
Ledge formation is common and usually prevents preparing and filling root canal
system to the desired length .
 Ledges are also potential areas of stress concentration that may contribute to
vertical root fracture . With the aid of magnification, ledges can be reduced or even
removed by inserting a rotary file with greater taper or a precurved hand file and
applying an axial filing movement with 1- to 2-mm amplitude.
 If the ledge is apically located and a straight-line access exists, a flexible rotary
instrument can be inserted, the ledge bypassed, and the instrument used to smooth
the ledge by using an outward brushing movement

105.  Nevertheless, great care should be exercised when attempting to deal with a ledge
that is close to the root canal terminus because it may lead to excessive reduction of
the remaining wall thickness and root perforation.
 Instruments used for removal may themselves separate and complicate treatment
further. This is more likely to occur when the fragment is removed by braided
Hedstr€om files or K-files or ultrasonics .
 Such a complication can be avoided; for example, ultrasonic tips should be used
without irrigation to maintain constant vision, and more importantly, they should be
activated at a low power setting. This reduces heat generated within the root canal
and, therefore, lowers the risk of secondary separation of the fragment itself or the
ultrasonic tip.
 In addition, it minimizes the risk of heat generated on the external root surface and
its damaging effect on periodontal tissues . In this respect, incorporating an air flow
function into the ultrasonic handpiece is advantageous . Nevertheless, activating
ultrasonic tips for prolonged periods can cause severe periodontal tissue damage and
may result in tooth loss

106.  Preparation of straight-line access to visualize the fragment is an essential step when
attempting fragment retrieval.Most methods and techniques require additional
preparation of the root canal, depending on the technique used.
 When ultrasonics is used, it is recommended to prepare the staging platform by
using modified Gates Glidden burs. Consequently, this considerable loss of dentin
may be of concern .
 The deeper the separated instrument within the root canal, the greater the amount of
prepared root substrate, and the weaker the root .
 Another consequence of excessive root canal preparation is root perforation
(stripping), especially when preparing the staging platform. Even when a clinician
tries to bypass a fragment or a ledge by using hand files, root perforation is still
possible, especially in curved root canals or when the roots are thin.
 Therefore, great care and caution should be exercised, particularly on root canal
walls near the furcation area.

107.  Extrusion of the fragment apically or even beyond the root apex is a complication
that usually results from excessive pressure applied on instruments used for
removal or from the vibration of ultrasonic instruments, particularly if applied to its
end surface rather than around its periphery.
 Once again, a careful approach can reduce the risk of such an undesirable event.

108. BYPASSING THE SEPERATED INSTRUMENT
 The ultimate goal of management of separated instruments is not only to retrieve the
fragment but also to preserve the integrity of the tooth. With the associated
complications, bypassing a fragment located deep in the root canal or beyond the
root canal curvature, if possible, may be the appropriate treatment option.
 To some extent, this fulfills the objective of root canal treatment: proper cleaning and
shaping of the root canal system followed by good filling.
 Thus, bypassing the separated instrument has been categorized as a successful
approach , especially because there have been no clinical studies comparing the
treatment outcome of bypassing fragments and removing them.
 However, it is possible that a false channel parallel to the original root canal can be
created when a clinician attempts to bypass the fragment, which in turn can lead to a
root perforation .

109.  Therefore, bypassing is best carried out under high magnification by using hand files
and radiographic checks to avoid such complications.
 Also, ledge formations, secondary separation of instruments, pushing the fragment
apically, and complete fragment extrusion are complications that should be
anticipated and managed. Attempting to bypass the fragment, partially or completely,
minimizes the contact between the fragment and root canal walls and may even
dislodge it.
 In addition, it provides enough space to introduce instruments such as ultrasonic tips
alongside the fragment.
 Therefore, bypassing can be considered as an initial step toward a successful removal,
because in most cases once bypassed, the fragment can be removed

111. LEAVING THE FRAGMENT IN- SITU
 If a separated instrument cannot be removed or bypassed, referral of the patient to a
specialist who is more experienced and equipped to handle such cases is generally
the preferred option.
 Otherwise, cleaning, shaping, and filling the root canal system to the level of the
fragment are the only alternative conservative approach. This may be especially
applicable if the separation occurs toward the final stages of root canal preparation
or the fragment is located in the apical third beyond a severely curved root canal .
 Patients with separated instruments left inside their teeth, however, should be
recalled for regular clinical and radiographic examination. If post-treatment
diseases develop, surgical approaches can be discussed with the patient and be
considered accordingly.

113. SURGICAL MANAGEMENT OF SEPERATED
INSTRUMENTS
 When conservative management of a separated instrument fails and clinical and/or
radiographic follow-up indicates presence of disease, surgical intervention may be
warranted if the tooth is to be retained.
 In addition, because of the evidence of adverse impact of periapical lesions on root
canal treatment outcome, a surgical approach can be considered as the optimum
management choice if the fragment is inaccessible and a periapical lesion is present
at the time of instrument separation.
 However, some cases are not amenable to surgery because of the location of the
surgical area and vital anatomic structures. Surgical management includes apical
surgery, intentional replantation, root amputation, or hemisection.
 These different options and approaches should be discussed with the patient, and a
suitable treatment plan devised.

114.  When root-end resection is performed, a separated fragment located in the apical root
section is removed as a part of the procedure.
 Otherwise, if the fragment is located in the middle or coronal part of the root canal,
the root-end cavity can be prepared and sealed with a root-end filling without
fragment removal. In both instances, elimination of bacteria and infected tissue as
well as providing an excellent coronal and apical seal of the root canal system are
essential.
 Several materials including zinc oxide–eugenol cement, intermediate restorative
material, glass ionomer cements, amalgam, and mineral trioxide aggregate cement
have been used as root-end filling materials.
 Although there are many laboratory studies comparing the properties of different
root-end filling materials, little information from well-designed, long-term follow-up
clinical trials is available.

115.  A recent meta-analysis study concluded that mineral trioxide aggregate is better
than amalgam but similar to intermediate restorative material.
 Nevertheless, it can be said that important innovations such as surgical ultrasonic
tips, dental operating microscopes, and biocompatible root end filling materials
have contributed to a better outcome for endodontic surgery

117. INFLUENCE OF CANAL INFECTION ON
PROGNOSIS
 The clinical situation (absence or presence of infection) and the time of instrument
fracture during treatment can significantly influence prognosis and the approach to
management.
 It is preferable to remove the fragment and pursue treatment under ideal conditions,
but this is not always possible.
 The risks of removal should be balanced against benefits as weakening of the tooth
or perforation during instrument removal may be more detrimental than the
fragment of instrument.

118. VITAL PULPECTOMY
 In this situation, the canal is virtually sterile, the objective of treatment is to remove
all pulp tissue, shape, disinfect and fill the canal, sealing the access to prevent re-
contamination.
 This treatment must be performed under rubber dam, free of saliva, with sterile
instruments and the use of an antibacterial irrigant. The obturation should ideally be
completed in the same session, providing that sufficient time is available to avoid the
possibility of contamination between visits.
 If an instrument fractures during the shaping process, then a radiograph should be
taken to establish its position. If the location precludes easy removal or bypass, then
treatment should be concluded in the same visit, including root canal filling and
coronal seal.
 If the canal system has never been contaminated, the presence of the retained
fragment should have no influence on the prognosis

119. INFECTED CANALS
 When the root canal system is infected with bacteria, the objective of treatment is to
obtain complete disinfection, and prevent re-infection with an appropriate endodontic
and coronal seal.
 If the fracture occurs at the end of instrumentation, and disinfection has already been
obtained, then the canal should be sealed conventionally, by embedding the fragment
in the filling material.
 In this case, the prognosis is reasonable. If, on the other hand, the fracture occurs
early in treatment, then there will have been little opportunity to disinfect the root
canal system.
 The anatomy beyond the instrument may become inaccessible to further
instrumentation and irrigation. Infection in this part of the canal will therefore remain
and may be directly responsible for failure

120. RETREATMENT
 This problem is comparable with the above, the objectives of treatment are the
same; specifically, disinfection of the root canal system and prevention of its re-
infection.
 The presence of an apical radiolucency confirms infection of the canal;
nevertheless the absence of a lesion should not be regarded as a guarantee of
sterility.
 During retreatment, the root canal system should be considered as contaminated
and the presence of a retained instrument fragment may prevent access to the apical
third of the canal, thus compromising disinfection.
 If the instrument can be removed or bypassed, treatment objectives can be achieved
with a success rate equivalent to conventional retreatment.

121. CONCLUSION
 Guidelines for management of intracanal separated instruments should be based on
the highest level of clinical evidence; however, this has yet to be formulated.
 The decision on management should consider the following: constraints of the root
canal accommodating the fragment, the stage of root canal instrumentation at
which the instrument separated, the expertise of the clinician, armamentaria
available, possible associated complications, the strategic importance of the tooth
involved, and the presence/or absence of periapical pathosis.
 Clinical experience and understanding of these influencing factors as well as the
ability to make a balanced decision are essential

122. REFERENCES
1 McGuigan MB, Louca C, Duncan HF. Clinical decision-making after endodontic
instrument fracture. Br Dent J. 2013 Apr;214(8):395–400.
2 McGuigan MB, Louca C, Duncan HF. Endodontic instrument fracture: causes and
prevention. Br Dent J. 2013 Apr;214(7):341–8.
3 Boutsioukis C, Lambrianidis T. Factors Affecting Intracanal Instrument Fracture. In:
Lambrianidis T, editor. Management of Fractured Endodontic Instruments [Internet].
Cham: Springer International Publishing; 2018 [cited 2018 Oct 29]. p. 31–60. Available
from: http://link.springer.com/10.1007/978-3-319-60651-4_2
4 Madarati AA, Watts DC, Qualtrough AJE. Factors contributing to the separation of
endodontic files. Br Dent J. 2008 Mar;204(5):241–5.
5 Simon S, Machtou P, Tomson P, Adams N, Lumley P. Influence of Fractured Instruments
on the Success Rate of Endodontic Treatment. Dent Update. 2008 Apr 2;35(3):172–9.

123. 6 Madarati AA, Hunter MJ, Dummer PMH. Management of Intracanal Separated
Instruments. J Endod. 2013 May;39(5):569–81.
7 Tang W-R. Prevention and management of fractured instruments in endodontic
treatment. World J Surg Proced. 2015;5(1):82.
8 COHEN
9 INGLE