Rotary Endodontic Instruments

Understanding the basic metallurgy, commonly used instruments and newly available rotary systems in the market enable us to better disinfect the root canal.

1. ROTARY ENDODONTIC INSTRUMENTS Guided by: Dr Hemant Vagarali Presented by: Dr Sahana Umesh

2. CONTENTS Introduction History Classification of endodontic instruments Why rotary instrumentation? Steel Rotary Instruments Characteristics Of NiTi Alloy Shape memory Super elasticity Strength Metallurgy of Nickel Titanium alloys

3. Advances in NiTi alloy Functioning of NiTi Rotary instruments Torsional stresses and fatigue Bending stresses Importance of the Section of the NiTi Rotary Instrument Endodontic Motors Life of Rotary NiTi Instrument NiTi rotary systems ProFile Hero K3

4. ProTaper GT files FlexMaster RaCe Quantec Recent NiTi systems ProTaper Next One Shape WaveOne XP Endo Shaper TruNatomy

5. Iatrogenic Mishaps and Safety Fracture of instruments Ledging Apical blockage Over-instrumentation Apical extrusion of debris Development of dentinal cracks Heat damage Perforation Conclusion References

6. Instruments play a very important role in the success of a root canal treatment therefore a basic knowledge of endodontic instruments is essential. Various endodontic instruments are used for cleaning and shaping of the root canal system, which ultimately determines the clinical outcome. Rotary systems have proved to be safer, quicker and more efficient over the conventional instruments. INTRODUCTION

7. 1733 - “ Le chirurgien dentiste ,” Pierre Fauchard described instruments for root canal preparation. The basic treatment technique at that time was cauterization of the pulp with heated instruments. 1838 - Edward Maynard - development of the first endodontic hand instrument. The first description of the use of rotary devices - Oltramare . HISTORY

8. 1889 - William H. Rollins developed the first endodontic handpiece for automated root canal preparation. This endodontic handpiece rotates at low speed of approximately 100 rpm and with a 360° rotation, similar to the motors used today for canal preparation with NiTi instruments.

9. 1928 - ‘ Cursor filing contra-angle ’ was developed by the Austrian company W&H(combined rotational and vertical motion of the file). 1958 – Racer handpiece (In 1958 W&H company start Marketing The Racer-hand piece in Europe and worked with a vertical file motion.) 

10. 1964 - Giromatic handpiece (a reciprocal 90º rotation). 1984 - Canal Finder was the first endodontic handpiece with a partially flexible motion. 1957 - Richman introduced Ultrasonics and sonics systems. Martin and Cunningham made ultrasonic devices popular in the 1970s.

11. First ultrasonic device was marketed in 1980. First sonic device in 1984. Electrosurgical devices and non-instrumental technique (NIT) by Lussi , using a vacuum pump for cleaning and filling of root canals seemed to be promising. The NIT was designed to clean the root canal system with intermitted positive and negative pressure and without any instrumentation or removal of root dentin. These techniques did not gain popularity or broader acceptance despite the innovative ideas.

12. 1988 - Instruments made from nickel-titanium (NiTi) were first described. Motors with a 360° rotation or with a reciprocal motion became popular again, making the use of NiTi more efficient. 2010 - SAF system was introduced.

13. CLASSIFICATION OF ENDODONTIC INSTRUMENTS - Grossman’s Endodontic Practice 14 th ed

14. Enhanced ability to collect and remove debris from the canal system. Better control for maintaining the central axis of the canal, reducing the incidence of ledging or perforating. Reduction in the time required for instrumenting the canal. WHY ROTARY INSTRUMENTATION?

15. The most commonly used low-speed rotary stainless steel instruments in endodontics are as follows: Gates-Glidden drills Flexogates Largo drills / Peeso Reamers LA Axxess burs Endo-Eze A.E.T. files ROTARY INSTRUMENTS

16. Characterized by a long shank and an elliptical extremity which is flame shaped with a “ guiding ” non cutting tip. Available in six sizes . Marked with circular notches on the part that attaches to the contra angled handpiece. Gates Burs is measured at the widest part of their elliptical portion GATES GLIDDEN DRILLS

17. Gates drills are available short version ~ overall length - 28 mm (shank length + active part of 15 mm) long version ~ overall length of 32 mm (shank length + active part of 19 mm) Gates-Glidden drills are designed with the weakest point at the start of the shank

18. Recommended speed – 800 rpm Gates # 1 and # 2 are very fragile and can fracture at the level of the tip, especially if the recommended rotational speed is exceeded and when they are subjected to bending stress. The blades of the Gates-Glidden drills do not have angles but flat cutting planes to reduce the aggressiveness and the tendency to screw in. They could be considered as the first example of the “ radial lands ” type of blades

19. The Gates drills must be used passively on withdrawal from the canal with a brush like circumferential movement Should always be preceded by preflaring of the canal using hand instruments Active use of the Gates Glidden drills is not recommended because they can lead to the formation of ledges and dangerous structural weakening that in the curved and thin canals can cause stripping.

20. Uses of Gates-Glidden drills: Enlarge root canal orifices For coronal flaring during  root canal preparation For removal of lingual shoulder during access preparation of anterior teeth During retreatment cases or post-space preparation for removal of gutta-percha During instrument removal, for space preparation

21. Drux burs are designed similarly to the Gates-Glidden (GG) drill, but have a flexible shaft.

22. Flexogates are modified Gates - Gliddens. They are made up of NiTi and have noncutting tip . They are more flexible and used for apical preparation. Flexogates can rotate continuously in a handpiece through 360° These instruments have many advantages over the traditional instruments in that they allow increased debris removal because of continuous rotation, smoother and faster canal preparation with less clinician fatigue . FLEXOGATES

23. Largo drills or Peeso Reamers are steel instruments similar to the Gates-Glidden drills but differ in that the blades are spread over a wider surface and the shape is cylindrical. They should be used in brushing motion. Very useful in the preparation of the dowel space (post space) in canals already enlarged or in retreatments to speed up the removal of the obturation material. LARGO DRILLS / PEESO REAMERS

24. Designed by Dr. L.S. Buchanan Specifically designed to eliminate interferences in the pulp chamber and coronal one third of the canal. Available in 3 diameters: Small – min. diameter of 0.20 mm Medium – min. diameter of 0.35 mm Large – min. diameter of 0.45 mm LA AXXESS BURS

25. LA Axxess burs have a rounded guiding tip 12 mm length of flutes first 3 mm has a parabolic increase remaining 9 mm is characterized by a .06 taper

26. The particular design of this bur favors the penetration of the coronal one third of the canal while the blade with its double cutting spiral rapidly removes the pulp chamber and coronal interferences . Recommended rotational speed - 5,000 rpm.

27. Designed by F. Riitano. The Endo-Eze A.E.T. Files (Anatomical Endodontic Technology) consist of two types of instruments, the Shaping Files and the Apical Files Shaping Files – used with contra angled handpiece having alternate clockwise/counter-clockwise movement of 30° ENDO - EZE A.E.T FILES

28. Available in 4 lengths (19, 23, 27 and 30 mm) Shaping 1 ~ tip diameter of 0.10 mm and .025 taper Shaping 2 ~ tip diameter of 0.13 mm and .045 taper Shaping 3 ~ tip diameter 0.13 mm and .06 taper Shaper C ~ tip diameter 0.25 mm and taper .035 Shaping Files have blades that cut even with a lateral brushing movement Particularly indicated for the cleaning of canals with an irregular anatomy such as canals with an elliptical cross-section, C-Shaped etc.

29. Apical Files are hand instruments in steel characterized by a working part with limited length to allow a better tactile perception during the apical shaping. Apical Files are available in lengths of 19, 23, 27 and 30 mm and ISO diameters of 15 to 50. Taper of the working part is .02 up to diameter 25 and then increases to .025

30. Nickel Titanium Endodontic Instruments

31. NiTi alloy – W. H. Buehler (1960s) NiTiNOL – Ni ckel Ti tanium N aval O rdinance L aboratory Introduced into dentistry - Andreasen et al. (1971) - orthodontic wires. 1975 – Civjan & associates – 55-Nitinol (55% Ni by wt.); 60-Nitinol (60% Ni by wt.) They found that 60-Nitinol is corrosion resistant hence can be used for hand and rotary cutting instruments or files for operative dentistry, surgery, periodontics & endodontics. HISTORY OF NITI ALLOY

32. 1988 - First potential use in endodontics – Walia & associates. 1992 – Serene introduced new NiTi files to students in College of Dental Medicine at Medical University of South Carolina.

33. Shape Memory: By shape memory we mean the capacity of NiTi alloys to reacquire its initial shape through heating after strain. This property is utilized in orthodontics but not in endodontics. CHARACTERISTICS OF NITI ALLOY

34. Superelasticity: Elasticity – Property of bodies to deform by the action of external forces and once these external forces cease the ability to return to its original state. Elastic limit – Limit beyond which there is a component of plastic strain which can no longer be recouped by the elimination of external forces.

35. The stainless steel endodontic instrument presents a higher stiffness while the NiTi instrument is particularly compliant. The use of endodontic instruments in NiTi is particularly advantageous for shaping the canal system in harmony with the original anatomy

36. Strength: Walia et al. and Camps et al. have demonstrated that files in NiTi were much more resistant to clockwise and counter-clockwise torsional stress compared with files of equal size but in stainless steel. This elevated strength of the NiTi alloy has made it possible to manufacture rotary instruments that have greatly simplified the shaping of the root canal system.

37. The NiTi alloy used in root canal treatment contains approximately 56% (in wt ) of Nickel and 44% (in wt ) of Titanium . In some NiTi alloys, a small percentage (<2% in weight) of Ni can be substituted by cobalt. The resultant combination is a one-to-one atomic ratio ( equiatomic ) of the major components ( Ni:Ti ). This alloy has proved to be among the most biocompatible materials and it is extremely resistant to corrosion METALLURGY OF NiTi ALLOYS

38. NiTi belongs to the family of inter-metallic alloys. This means that NiTi alloy can exist in various crystallographic forms, with distinct phases and different mechanical properties: Austenitic phase Transformation phase Martensitic phase

39. AUSTENITIC PHASE (A): with body- centered cubic lattice. It’s the most stable phase. MARTENSITIC PHASE (M): with hexagonal compact lattice. It’s the most unstable and ductile phase. TRANSFORMATION PHASE (T): made up of series of intermediate phases which transform one into the other, causing a movement of the Ni and Ti atoms onto opposite and parallel crystalline levels; this doesn’t entail a variation of the crystallographic shape.

40. Each crystalline phase exists in a specific temperature interval. The transition from one phase to the other is possible only within a temperature range including those at the beginning and at the end of transformation.

41. T.T.R

42. Such phase changes can also be induced by the application of deformation states, as it happens with NiTi endodontic instruments during their work inside the root canals NiTi alloys are characterized by a stress- distortion diagram which is divided into three distinct portions

43. Aim of this study : To compare the effect of hand instruments and rotary nickel titanium on the extent of straightening of curved root canals. Preoperative and postoperative radiographs were taken of each tooth using customized bite blocks Conclusion: This clinical study indicates that FlexMaster (NiTi) instruments prepared curved canals more rapidly and with only minimal straightening compared to hand staninless steel instruments

44. M-wire NiTi - Developed by Dentsply Tulsa Dental Specialties (Tulsa, OK, USA) Advantage: This material has greater flexibility and an increased resistance to cyclic fatigue when compared to traditional NiTi alloys R-phase NiTi – Developed by SybronEndo (Orange, CA, USA) Advantage: Files have reduced stiffness and more fracture resistance compared to standard NiTi files. Controlled-Memory (CM) NiTi Advantage: Files have superior cyclic fatigue resistance and increased torque strength over traditional NiTi files. ADVANCES IN NiTi ALLOYS

45. Its important to know the functioning of the NiTi rotary instruments during the shaping of the canal system. The states of stress to which the NiTi rotary instrument is cyclically subjected are responsible for the strain (deterioration). The strain is determined by two principal types of stresses: bending stress and torsional stress . FUNCTIONING OF NiTi ROTARY INSTRUMENTS

46. Torsional stress Torsional stresses of elevated intensity rapidly causes fracture of the instrument. It happens in three situations: 1) when a large surface of the instrument rubs excessively against the canal walls (taper lock) 2) when the instrument tip is larger than the canal section to be shaped 3) when the operator exerts excessive pressure on the handpiece

47. Large contact surface The larger the blade-dentine contact surface the higher the torque required to allow the rotation of the instrument and therefore the cutting of the dentine An elevated torsional stress is stored in the alloy, rapidly reducing the life of the instrument If the torque values necessary to make the instrument rotate exceed the values of the maximum torque moment that the instrument can endure, the instrument distorts and fractures

48. To avoid these limitations, NiTi rotary instruments with greater taper must be utilized with the crown-down technique. Blum et al. have demonstrated that the NiTi rotary instruments are subjected to lower stress levels if utilized with the crown-down technique rather than if utilized with the step-back technique. Cutting ability of the instrument is also more efficient with the crown-down technique.

49. Accumulation of dentinal debris between the blades of the instrument can increase the surface contact between canal wall and instrument thereby increasing the torsional stress. The operator must become aware of when the speed with which the NiTi rotary instrument advances inside the canal starts to diminish, this is a sign of an excessive accumulation of debris between the blades. Hence its important to clean the blades after every passage into the canal.

50. Instrument tip and canal width Vast majority of rotary NiTi instruments with greater taper have a non cutting / moderately cutting tip. This is to prevent the formation of ledges, false paths or apical foramen transport.

51. If these tips encounters a canal or a canal portion with a smaller cross-section, the tip advances with great difficulty. Torsional stress increases enormously and if the tip binds and the gearing of the motor is higher than the maximum torque that the instrument can withstand, it immediately undergoes plastic strain and fractures. Essential to manually create a glide path for the tip of the greater taper NiTi rotary instrument that will have to be utilized in complex canals.

52. Conclusion: The manual pre-flaring avoided subjecting the tip of the S1 to torsion while trying to make a path in a canal with a very small cross-section. In this way one created a guide path for the tip of the NiTi rotary instrument thereby enormously reducing the torsional stress that the instrument experiences and in so doing increases its life span six fold.

53. Excessive manual pressure on the handpiece An excessive manual pressure on the handpiece causes a notable increase in the friction between the instrument and the canal wall. Consequently very high torsional stresses are generated which could immediately cause the fracture of the instrument.

54. Bending stresses These are the main causes of strain and they depend on the original anatomy of the canal which forces the instrument to bend as it passes through it. Pruett et al. have demonstrated that the curve radius, the bend angle and the largeness of the instrument are the factors responsible for the fractures due to bending fatigue. If one imagines a stationary rotary instrument inside a curved canal it follows that it will be subjected to two different types of stresses:

55. – compression stress on the internal surface of the curve – tensile stress on the external surfaces of the curve. There will be continuous passing from tension to compression, from compression to tension and so on. Hence the alloy will be continuously subjected to stress of the opposite type. Therefore it is important to never stop inside a curved canal with the instrument in motion.

56. IMPORTANCE OF THE SECTION OF THE NiTi ROTARY INSTRUMENT The ideal NiTi rotary instrument should be sufficiently compliant to be able to create a centrifugal shaping of the canal and to be sufficiently resistant to withstand the torsional and bending stresses. The ability to cut the dentine is determined by the shape of the blade. Berutti et al. have analyzed the mechanical behaviors of two sections, the ProFile (U File) and the ProTaper (convex triangular section) through the method of finite element analysis.

57. The distribution of torsion stresses in ProTaper section were regular and uniform , while in the ProFile section caused high stress peaks were evidenced at the base of the blade grooves and their distribution was heterogeneous Even with bending stresses , ProTaper section under equal loading reached lower stress levels which were homogeneously distributed over all the surfaces compared to the ProFile section . ProFile rotary instruments ProTaper rotary instruments

58. The characteristics of the NiTi alloy depend on its strongly non linear behaviour. The most performatory phase for the work of the NiTi rotary instrument is the transformation phase, where one sees the super elastic characteristic. To avoid an excessive and dangerous damage due to cyclic stresses in the NiTi rotary instrument, the alloy should work within this security phase. The first devices utilized were air driven. They were mounted on dental units replacing the turbines ENDODONTIC MOTORS

59. They were soon abandoned because the variations in the air pressure caused the instrument to have dangerous variations of rotational speed. Then we had electric motors dedicated to NiTi rotary instruments, able to maintain a perfectly constant rotational instrument speed. In order to do this, the torque utilized was quite high. This sometimes brought about such high stresses that breakages of the rotary NiTi instruments occurred inside the canal.

60. To avoid fractures as much as possible, in recent years highly sophisticated endodontic motors have been introduced on the market, with which it possible to control the speed as well as the maximum torque. Endodontic motor Tecnika Vision (ATR and Sirona) Endodontic motor DTC ( Aseptico , USA)

61. To keep the speed constant, the torque varies continuously depending on the cutting difficulty and the instruments progression. These latest generation endodontic motors are made up of a control system that drives the electric motor which has a contra-angle reduction handpiece attached to its shaft. The control system is able to store a large amount of data, thereby allowing the operator to utilize many different NiTi rotary instrument systems.

62. When the maximum torque value preset by the operator has been reached the motor will reverse the rotation and the instrument turning anti-clockwise, will automatically exit the canal. Endodontic motor DentaPort (J. Morita Corp) Endodontic motor X-Smart (Dentsply Maillefer )

63. LIFE OF THE NITI ROTARY INSTRUMENT The obligatory questions frequently asked are: How long do these instruments last? How many canals are we able to shape?

64. The criteria that will influence the life of the instrument: Original canal anatomy Mechanical characteristics of the NiTi rotary instruments Rotational speed and maximum torque values when using NiTi rotary instruments Characteristics of the work carried out by the NiTi rotary instruments Operator ability

65. Original anatomy of the canal: Yared has shown that the longevity of the instrument is strictly correlated to the number of rotations it makes inside the canal. The more complex the anatomy is, the more wear there is in terms of increased fatigue damage and therefore the life of the instrument is reduced. Therefore the curve radius and angle of the canal which the instrument has to shape is determinant in the cyclic fatigue of the instrument.

66. The cutting ability of the NiTi instrument tip is not generically very efficient in curved canals. This causes an immediate increase in the torsional stress that the instrument accumulates when it must advance in those canal sections. This is easily detectable by the immediate increase of the torque values The torque variations can be seen on a digital and acoustic indicator. This again highlights the importance of a manual preshaping which prevents the engagement of the NiTi rotary instrument tip against the canal walls, in this way drastically reducing the torsional stress.

67. Mechanical characteristics of the selected instruments: Theoretically to optimize the use of NiTi rotary instruments and to avoid fractures the instrument should be subjected to low levels of stress. The more the section is able to withstand high levels of torsional stress the more it is resistant. The more the section has a low bending moment, the more compliant it is and therefore able to respect the original canal anatomy. The capability of an instrument to resist the stress and at the same moment to respect the curvature of the canal is therefore a compromise between the torsional and bending characteristics of its section.

68. Instruments with the same characteristics have different mechanical behaviours in relation to their size. If the instrument has a small caliber, it has reduced strength capabilities to torsional stress, if on the contrary it is big, it is more prone to fracture because of bending stress.

69. Therefore think of small instruments having low strength to torsional stress and large instruments having low strength to bending stress in final phases of shaping. For example, a canal with extreme curvature should be prepared with an instrument of reduced taper as they are more resistant to cyclic fatigue. If a canal that is extremely narrow and calcified is to be prepared it is necessary to carry out an adequate manual preshaping to reduce the torsional stress.

70. The instrument which presents the slightest sign of plastic strain (increase/decrease of the spiral gaps) should be eliminated immediately to avoid intracanal fractures.

71. Rotational speed and maximum torque values for NiTi rotary instruments: Rotational speed - should be constant Maximum torque - should be less than the torque value necessary to cause plastic strain It is therefore essential to use an electric motor that allows one to set the rotational speed and maximum torque value to be used according to the recommendation of the manufacturer for the particular rotary NiTi rotary instruments

72. Characteristics of the work carried out by the NiTi rotary instruments There are two factors which influence the work of the instrument: the section of the working part directly involved with the cutting the depth at which the instrument carries out its work within the canal. The smaller the working portion of the instrument directly involved with cutting the dentine, the lower the torsional stresses.

73. Berutti et al. have verified how many endodontic simulators the instruments of the ProTaper System S1, S2, F1, F2 utilized in sequence were able to shape before breaking. These were the results: S1: 59 endodontic simulators before breaking. S2: 48 endodontic simulators before breaking. F1: 23 endodontic simulators before breaking. F2: 11 endodontic simulators before breaking

74. A further important fact that emerged from this study is that if the instruments of the ProTaper System work with a lower torque, they have a considerably shorted life. The following results were obtained using the Tecnika ATR endodontic motor: S2: torque 20%, speed 300 rpm = 28 simulators before breaking. S2: torque 80%, speed 300 rpm = 48 simulators before breaking. F1: torque 28%, speed 300 rpm = 8 simulators before breaking. F1: torque 100%, speed 300 rpm = 23 simulators before breaking. F2: torque 40%, speed 300 rpm = 4 simulators before breaking F2: torque 100%, speed 300 rpm = 11 simulators before breaking.

75. This notable and constant difference in the life of the tested ProTaper System instruments resulted from the frequent insertion of the auto reverse of the endodontic motor when the utilizable torque was low.

76. Operator ability It has been demonstrated that the experience of the operator is decisive in preventing the fracture of the NiTi rotary instruments inside the canal. An inexperienced operator probably exercises an excessive apical pressure during the use of the NiTi rotary instruments. This brings about excessive friction of the instrument blades against the canal walls.

77. Berutti et al. studied the relationship that exists between the experience of the operator and the time required to shape the canals The experienced operator is able to shape more canals because the average working time with each instrument is inferior to that of an inexperienced operator. This causes an unnecessary stress overload which the instrument accumulated during the excessive amount of time spent rotating in the canals.

78. PART II

79. RECAP… Introduction History Classification of endodontic instruments Why rotary instrumentation? Steel Rotary Instruments Characteristics and Metallurgy Of NiTi Alloy Advances in NiTi alloy Functioning of NiTi Rotary instruments under Torsional Bending stresses Importance of the Section of the NiTi Rotary Instrument Endodontic Motors Life of Rotary NiTi Instrument

80. Speed Range – 300 to 30,000 rpm Speed Range – 120 to 800 rpm

81. Speed Range – 0 to 800 rpm X – Smart Plus Endo Motor Speed Range – 250 to 1200 rpm

82. Assess case difficulty Provide adequate access Prepare with hand files up to size #20 prior to rotary use Use light touch and low rpm Proceed with crown-down sequence Replace rotary instruments frequently The “Golden Rules” for NiTi Rotary Preparation American Association of Endodontists 2008

83. NITI ROTARY SYSTEMS Ingle 7 th edition

84. Grossman 14 th edition

85. ProFile System: Introduced by Dr. W. Ben Johnson in 1994 C.S – Triangular U shape Taper – 2% to 8% Recommended speed – 150 to 350 rpm

86. ProFiles are obtained by micromachining three parallel furrows on a nickel titanium wire The surfaces of the wire between the furrows are not sharpened so that in cross-section the instrument has a design defined as a “triple U” with blades characterized by flat cutting surfaces called “radial lands” Triple U design - increased flexibility The “radial lands” blades of the ProFiles are not efficient in lateral cutting. The low cutting capacity and their flexibility make the ProFiles particularly useful in the shaping of curved canals, reducing the risk of apical tears and transportation.

87. GT System: By Dr. S. Buchanan C.S – Taper – 4% to 12% Recommended speed – 300 to 500 rpm

88. The Rotary GT Files present a non cutting tip, a prefixed tip diameter and a prefixed maximum flute diameter (MFD), multiple tapers and a blade length inversely proportional to the taper. Blade direction is clockwise in the Rotary GT and counter-clockwise in the Hand GT The clockwise direction of the blades and the radial cutting planes are fundamental because they make it possible to use the Rotary GT in continual clockwise rotation without screw in.

89. Rotary GT Files are at present available in 4 principal series, each one of which comprises 4 instruments: GT 20 Series comprises 4 instruments with a 0.20 mm tip diameter and tapers of .04, .06, .08 and .10

90. GT 30 Series comprises 4 instruments with a 0.30 mm tip diameter and tapers of .04. .06, .08 and .10

91. GT 40 Series comprises 4 instruments with a 0.40 mm tip diameter and tapers of .04, .06, .08 and .10

92. GT Accessory comprises 3 instruments with a taper of .12 and a tip diameter respectively of 0.50, 0.70 and 0.90 mm

93. Lightspeed instruments: By Dr. S. Senia C.S – Recommended speed – initially 1000 to 2000 rpm later manufacturer recommended lesser speed No. of files – 20

94. Very similar to the GG drills with a long shaft and a working part in the shape of a very short flame. The long and thin shaft ensures that the LightSpeed has an elevated flexibility but at the same time it diminishes torque stress resistance For this reason LightSpeed instruments are made with a point of separation at 18 mm from the tip, in order to facilitate their removal incase of intracanal fracture. LightSpeed instruments available in the 21, 25 and 31 mm lengths, must be used from the smallest to the largest in a stepback sequence with a typical pecking movement

95. ProTaper System: C.S – 6 instruments of 2 groups with 3 instruments each: Shapers with the marking SX, S1 and S2 and Finishers with the marking F1, F2 and F3 Taper – 2% to 19% Recommended speed – 250 to 350 rpm

96. Important structural characteristics of the ProTapers are: robust triangular cross-section with convex sides to increase the metal mass of the central core resistance of the instruments cutting blades with cutting angles (there are no radial lands) variable helical angle & variable pitch (distance between spirals) to reduce the risk of screw in and aid the removal of debris multiple increase in tapers towards the handle of the shapers (so as to increase the flexibility in the apical third) and decrease towards the handle in the Finishers (so as to enlarge the apical preparation without making the coronal third of the instrument too rigid)

97. K3 System: Dr John McSpadden in 2002 C.S – Taper – 2% to 6% Recommended speed - 300 to 350 rpm Files used at a rotational speed of 350 rpm were more likely to fracture than those used at 250 rpm and than those used at 150 rpm (contrary to manufacturers recommendations)

98. FlexMaster System: C.S – Taper – 2% to 11% Recommended rpm – 300rpm

99. RaCe System: C.S – Taper – 2% to 10% Recommended rpm – 600 to 800 rpm All instruments, except an orifice shaper, are used to working length: .05/15 (non-cutting tip) and .04/25 (cutting tip) working in the most apical area; .06/25 (noncutting tip) working in the middle and coronal third, 04/30 and .04/40 (cutting tips), working apically

100. Quantec System: C.S – Taper – 2% to 12% Recommended rpm – 300 to 250 rpm The Quantec File is designed to enhance the balance of the cutting actions on each wall of canal curvatures. Incorporating cutting edges having unequal efficiencies causes cutting to occur on the canal wall opposite the pressure surface. By using alternate cutting efficiency throughout the canal, transportation of the central axis in curved canals is reduced

101. Mtwo System: Mtwo was one of the first NiTi systems with instruments designed as Hedstrom files. C.S – All files of the set (04/10, 05/15, .06/20, .05/30, .04/35, .04/40) are used to working length with the largest instrument in size being .04/40. Two additional sets .04/45, .04/50, .04/60 and .06/30, .06/35, and .06/40 are completing the system. If thermoplastic obturation is used, a final .07/25 instrument is also available.

102. Hero 642: Hero 642’s are mechanical instruments derived from the Helifiles Taper – 2% to 6% Generally Hero are used in a crown down sequence based on the reduction of the taper (6-4-2) and/or of the diameters. Recommended rpm - 300 to 600 rpm

103. Characterized by: a triple helix cross-section with three positive rake angles; there are no radial cutting tiers as in the ProFile and Quantec instruments, but there are cutting angles as in the ISO instruments even though they have a different inclination; a higher “ residual core” inside the blades which increases the resistance to torsional loads diminishing the risk of fracture; a progressive sequence of the blades to reduce the tendency to screw in; three tapers which permit the reduction of the contact surfaces between the blades and the canal walls; a tip that remains centered in the canal and which does not normally come into contact with the canal walls.

104. Hero Shaper: Hero Shaper are instruments which are derived directly from the 642 Hero. Hero Shaper differs from the 642 Hero : rake angle (helical angle) of the blades is variable and increases from the tip towards the handle, pitch (distance between two spirals) increases with the taper of the instruments, shorter handle allows an easier access to the posterior teeth the tip is completely inactive and self guiding

105. Hero Shaper series comprises three instruments with a taper of .06 (20, 25 and 30) and three instruments with a taper of .04 (20, 25 and 30), available in lengths 21, 25 and 29 mm. Recommended speed - 300 to 600 rpm

106. ProTaper Gold System: C.S – • Increased Flexibility • Greater Resistance to Cyclic Fatigue • Shorter 11 mm Handle • Preferred Over ProTaper Universal

107. Hyflex CM System: Controlled Memory NiTi Proprietary Thermo mechanical Treatment Retain Shape After Bending Regains shape after Sterilization Superior canal tracking Ability 300 % more resistant to Cyclic fatigue than Conventional NiTi Taper- 0.04,0.06 Size - #15- #60 Speed – 500 rpm Torque – 2 N.cm

108. HyFlex EDM One File System:

109. • Up to 700% higher fracture resistance • Unique hardened surface • Less filing required for treatment success Electrical Discharge Machining - Innovative manufacturing process uses spark erosion to harden the surface of the NiTi file, resulting in superior fracture resistance and improved cutting efficiency

110. ProTaper Next: C.S – Swaggering Effect- ProTaper Next’s innovative off - centered rectangular cross section gives the file a snake-like “swaggering” movement as it moves through the root canal. The off - centered cross section and the unique design of the file generate enlarged space for debris hauling. Recommended speed – 300 rpm

111. Intended for initial endodontic treatments, Revo-S innovates with only 3 instruments. Its asymmetrical section initiates a snake-like movement of the instrument inside the canal. High performance and simple to use, this sequence is adapted for most root canal anatomies. Revo – S System:

112. Sequence of 3 instruments with asymmetrical cross-section. The instrument works in a cyclic way (3C Concept): 1) Cutting 2) Clearance (debris elimination) 3) Cleaning Recommended speed - 250 - 400 rpm Snake like movement inside the canal

113. One Shape System: MicroMega innovation - : the instrument presents a variable cross-section along the blade Works in continuous Rotation Variable Pitch Continuously Changing Cross section Anti Breakage Control-File Unwinds on use OneShape

114. One Shape principle: 3 different cross-section zones. The first zone presents a variable 3-cutting-edge design. The second, prior to the transition, has a cross-section that progressively changes from 3 to 2 cutting edges. The last (coronal) is provided with 2 cutting edges.

115. WaveOne: Wave One file system from Dentsply Maillefer is a singleuse , single­file system to shape the root canal completely from start to finish. Available in lengths of 21, 25 and 31 mm.

116. Wave One small file Used in fine canals. Tip size is ISO 21 Continuous taper of 6% Wave One primary file Used in most of the canals. Tip size is ISO 25 An apical taper of 8% that reduces towards the coronal end. Wave One large file Used in large canals. Tip size is ISO 40. Apical taper of 8% that reduces towards the coronal end.

117. Reciproc : The Reciproc instrument series possesses many similarities to the WaveOne set of instruments. But differs mainly in the cross sectional design and as well as the sizes of the three instruments available. WaveOne instruments are based on the ProTaper The Reciproc instruments are based on Mtwo. R25 (size: 25/0.08) for smaller canals R40 (size: 40/0.06) for medium canal R50 (size: 50/0.06) for larger canals

118. Self Adjusting File (SAF): This was the first system developed based on this concept and comprised a single instrument. Introduced by Zvi Metzger. Concept The file three dimensionally adapts both longitudinally and along the cross-section of the root canal system and this is its most characteristic feature. This results in a uniform cutting

119. Design Designed to be used as single-use files. SAF system consisted of a hollow compressible NiTi lattice with a thin-walled pointed cylinder 1.5 or 2.0 mm in diameter. It operated with a modified vibrating handpiece generating 3,000–5,000 vibrations/min at an amplitude of 0.4 mm. Another advantage of the system was the feature of continuous irrigation by a silicon tube to the irrigation hub on the file.

120. Twisted File Adaptive File System: TF Adaptive file system Automatically adapts and changes the file motion based upon the stress placed on the instrument while in use. Advantage “Rotary when you want it, Reciprocation when you need it”

121. XP Endo Shaper and Finisher: XP-Endo Shaper instrument is a rotary snake-shaped instrument made of a proprietary alloy Due to this alloy, the file has an ability to change its shape according to the temperature. When cooled, in its martensitic phase, the file stands straight with a size #30 and an initial taper of 0.01. However, when introduced to body temperature, it changes to its austenitic phase assuming a snake shape that can achieve a final minimum canal preparation of 30/0.04 when using this instrument alone

122. XP-Endo Finisher is an anatomical finishing file that consists of a small-core-size (tip size 25 and nontapered ) rotary NiTi instrument. When submitted to body temperatures, it changes to its austenitic phase (A-phase) assuming a spoon shape of 1.5 mm depth in the final 10 mm of its length. According to the manufacturer, when the instrument is placed inside the canal in the rotation mode, the A-phase shape allows the files to access and clean areas that other instruments might not have reached, without damaging dentin or altering the original canal shape.

123. TruNatomy System: By Dr. George Bruder and Dr. Ove Peters. Acc. to manufacturer TruNatomy offers: • Smooth feeling during preparation • Improved performance and efficacy • More space for debridement and debris removal • Respect of the natural tooth anatomy • Preserve tooth structure

124. Operates at a higher speed with less torque (Recommended speed – 500 rpm, torque – 1.5N) With just 2 cutting edges, it encounters less resistance and thus requires less applied pressure, ensuring precision with increased ease of use Thermal treatment provides greater flexibility with improved fatigue resistance

125. TruNatomy Shaping Files are available in three different sizes and lengths (21mm, 25mm & 31 mm) While the TruNatomy Prime shaping file is appropriate for most cases, two additional shaping files, the TruNatomy Small and the TruNatomy Medium , are available to address both smaller and larger canals. Manufacturer claims the clinician will experience a fluid transition between the TruNatomy Shaping Files.

126. IATROGENIC MISHAPS Damage to the apical foramen: When the curved canal is deviated from the original long axis it is often associated with loss of the apical stop. Clinically, it may result in mechanical irritation of the periapical tissues and increase the risk of extruding irrigation solutions, debris and root canal filling materials.

127. Perforation: This procedural error represents a communication between the root canal space and the external root surface. It may be caused from use of instruments with sharp cutting tips in reaming or rotary working motions. In many instances, a perforation will be located at the apical part toward the outer side of the canal.

128. Strip perforation: In contrast to perforation located at the apical part of the canal, strip perforation results from over-preparation along the inner side of the curvature in the middle or coronal third of the canal. Strip perforations mainly occur in mesial roots of mandibular molars at the furcal aspect, also know as the “danger zone”

129. Elbow-formation: The typical picture of canal transportation is over-preparation along the outer side of the curvature at the apical part and along the inner side more coronally. The elbow-formation usually occurs between two areas of excessive dentin removal and a narrow portion of the canal. Usually, the elbow is located at the point of maximum curvature. The clinically relevant adverse effects of this procedural errors are insufficient debridement and obturation of the canal part located apically to the elbow-formation

130. Zip: The curved part of the canal adopts an elliptical or “teardrop” shape at the apical end point. This is caused because the axis of the curved canal is deviated towards the outer aspect and inadvertently more dentin is removed from the outer side. Due to this irregular cross-sectional shape, the quality of canal obturation is markedly reduced when employing the cold lateral compaction technique.

131. Ledging: A ledge is a platform created at the beginning of the outer side of the curvature that hinders the instruments from reaching the working length. Usually, ledge formations are located in the middle or apical part of root canals.

132. Canal Straightening: The extent of apical canal transportation can be classified as follows: Type I: minor movement of the position of the apical foramen, resulting in only slight iatrogenic relocation. Type II: moderate movement of the physiologic position of the foramen, resulting in a considerable iatrogenic relocation on the external root surface. Type III: the physiologic position of the root canal is severely moved, resulting in a relevant iatrogenic relocation of the physiologic foramen.

133. Prevention of Canal Transportation and Ledging The access cavity should be prepared so that unrestricted access of the instruments to the apical foramen is available A glide path should be created prior to canal preparation. When using stainless steel hand instruments (e.g., Pilot instruments) for canal scouting, the tactile feedback provides relevant information regarding the consistency of the canal content, possible blockages (e.g., root canal branches) and radiographically unseen curvatures. Severely curved canals should be prepared using engine driven NiTi instruments having non-cutting tips.

134. When using NiTi hand instruments, preference should be given to the balanced-force technique. Instruments should not be forced into the root canal. Skipping instrument sizes should be avoided. Frequent recapitulation of the canal using small hand instruments is recommended. Copious irrigation should be carried out during canal preparation to avoid any blockage of the canal lumen. Instruments should never be used in dry canals.

135. Apical Extrusion of Debris: Avoiding extrusion of some debris during root canal preparation is virtually impossible. During root canal preparation, necrotic or vital pulp tissue, dentin chips, microorganisms, irrigants and in the case of retreatment even certain filling materials may be extruded into the periapical tissues. Most common consequences of apical debris extrusion are post-operative pain and interappointment flare-ups

136. When comparing different hand preparation techniques to engine-driven rotary preparation, it has been reported that hand preparation techniques using crown-down approach, or employing cervical flaring, were associated with less debris extrusion than techniques involving a linear manual filing motion. On the other hand, some studies reported that, when properly used, rotary engine driven preparation does not produce significant debris extrusion. Currently, the use of any types of instrument or preparation technique is associated with some debris extrusion.

137. Fracture of Instruments: The fracture of endodontic instruments is not an uncommon mishap during root canal preparation. It may occur in 1%–6% of cases for stainless steel instruments and approximately 0.4%–3.7% for rotary NiTi instruments Basically, there are two modes of fracture: cyclic fracture and torsional fracture. Cyclic fracture occurs when an instrument is used for too long. Unfortunately many manufacturers focus on the number of canals treated rather than the duration.

138. A single torturous canal may, often, require a duration exceeding that of several non-complicated root canals. Torsional fracture occurs when the tip of an instrument is firmly engaged inside the root canal and the motor continues to rotate. The torque will exceed the elastic limit and the instrument will separate. Single overload of NiTi instruments has been identified as a major reason of fractures. It can also occur when the flutes of an instrument are packed with dentinal debris thereby increasing the torque above a critical limit.

139. The following factors were associated with file fracture: • Frequency of use • Number of rotations • Preflaring and preenlarging • Angle of the curvature • Radius of the curvature Non-contributing factors are: • Torque • Sterilization Controversial factors: • Rotational speed • Operator’s experience

140. CONCLUSION From a biological perspective, root canal treatment is directed toward the elimination of micro-organisms from the root canal system and the prevention of reinfection. Over the last few years endodontics has undergone a complete revolution with the introduction of the NiTi alloy from the manufacture of initial manual to rotary endodontic instruments. Technological advances in the form of rotary NiTi instruments has led to a dramatic improvement in the ability to shape root canals with potentially fewer procedural complications.

141. The extraordinary characteristics of NiTi alloy has made it possible to manufacture rotary instruments with double, triple and quadruple taper compared to the traditional manual instruments. This has made it possible to achieve perfect shaping with the use of very few instruments in a short period of time. In this mechanistic age it will always be the operator with his choices and his manual dexterity, that will know how to make the difference.

142. Ingle’s Endodontics – 7 th edition Endodontics Vol II – Arnold Castellucci Grossman’s endodontic practice – 14 th edition Textbook of endodontics – Nisha Garg & Amit Garg Schäfer E, Schulz- Bongert U, Tulus G. Comparison of hand stainless steel and nickel titanium rotary instrumentation: a clinical study. Journal of endodontics. 2004 Jun 1;30(6):432-5. Berutti E, Negro AR, Lendini M, Pasqualini D. Influence of manual preflaring and torque on the failure rate of ProTaper rotary instruments. Journal of Endodontics. 2004 Apr 1;30(4):228-30. REFERENCES

143. Brochures – ProFile ProTaper ProTaper Next ProTaper Gold GT System K3 Quantec RaCe Hero FlexMaster Mtwo HyFlex CM HyFlex EDM Revo – S OneShape WaveOne Reciproc Self adjusting files XP EndoShaper & Finisher TruNatomy