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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, SENIO R 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.

8. 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

9. 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

10. 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: 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

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

16. 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

17. 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.

18. 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

19. 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.

20. 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.

21. 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).

22. 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.

23. 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.

24. 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.

25. 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

26. 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).

27. 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

28. 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.

29. 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).

30. 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.

31. 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.

32. 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.

33. 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

34. 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

35. 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).

36. 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.

37. 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.

38. 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.

39. 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 ).

40. 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.

41. 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.

42. 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

43. 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

44. 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.

45. 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

46. 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.

47. 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

48. 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

49. 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.

50. 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.

51. 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.

52. 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 ).

53. 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.

54. 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

55. 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.

56. Ground and twisted files have been compared i n 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.

57. 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.

58. 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.

59. 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

60. 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.

61. 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

62. • 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.

63. MANAGEMENT

64. 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.

65. 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).

66. 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

67. 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

68. 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

69. 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

70. 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.

71. 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.

72. 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.

73. 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

74. 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.

75. 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.

76. 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.

77. 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.

78. 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.

79. 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.

80. 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

81. 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

82. 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

83. 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..

84. 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

85. 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.

86. 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

87. 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

88. 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

89. 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.

90. 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.

91. 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 .

92. 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

93. 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.

94. 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.

95. 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.

96. 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

97. 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.

98. 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

99. 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

100. 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.

101. 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

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