Rotary Files, generation and evolution, design advantages

Rotary files description

1. SEMINAR EVOLUTION OF NITI INSTRUMENTS Presented By- Dr Nayna Sharma Guided By- Dr Anurag Jain

2. Introduction - The epitome of an endodontic treatment should satisfy the bio-mechanical principles of cleaning and shaping of the root canal system which is influenced by type and efficiency of endodontic instruments used for the procedure. Hence there were advent of newer generations in endodontic files with several evolutions in terms of crystal characteristics or phase transformations (metallurgy) also surface treatment of endodontic instruments for improved mechanical properties

3. It appears to be necessary to select appropriate instruments for different cases due to the vastly prevalent complexities in the root canal morphology (curved canals, calcified canals, blunderbass canals). Therefore, a proper knowledge on the metallurgy of rotary instruments and its mechanical properties conclusively determines the treatment outcome. Hence there was development of rotary files with varying crystal characteristics intended in minimising the unanticipated errors (instrument separation, ledge, canal transportation) resulted by the use of conventional rotary instruments.

4. Lets Have A Look At The Evolution Of Endo Rotary Files, Since Their Inception

5. HISTORY- 1800- First Endodontic instruments – Barbed Broach by Edward Maynard 1852- Arthur recommended the use of small files for cleaning and shaping 1885- The Gates Glidden drill were introduced 1889- William H. Rollins developed the first endodontic hand piece fpr automated root canal preparation 1892- Oitramare – Fine needles with rectangular cross section mounted in dental handpieces

6. Materials for manufacturing of endodontic intruments – Carbon Steel Stainless Steel Nicket Titanium alloys

7. DESIGN FEATURES OF ROTARY FILE -

8. TIP – Tip is the element of the working part that performs the guiding function. The cutting part is the prime element of the working section, which has cutting blades that perform the enlargement of the root canal. A rotary cutting instrument may have a cutting or non-cutting tip. Cutting tip makes the file aggressive. Its advantage is that it can enter in narrow canals. If goes beyond apex, file with cutting tip results in elliptical tear at apex which is difficult to seal, whereas file with noncutting tip form concentric circle which can be sealed with gutta-percha

9. The tip might have a sharp or rounded configuration, depending on whether it appears – Active Passive TAPER – It signifies per millimeter increase in file diameter from the tip toward handle of file

10. Difference in minimum and maximum diameter can be reduced so that torque required for rotating larger instruments does not exceed the plastic limit of smaller instrument Traditional instrument used to have 2% taper but rotary endodontic files have 4%, 6%, 8%, 10%, or 12% taper. A zero taper or nearly parallel file can be used to enlarge the curved canals without undue file stress and pressing debris. File can be of constant taper but with varying tip diameter or constant tip size with graduating taper from 0.04 to 0.12. With graduating taper, only minimal part of the file engages the canal wall resulting in reduced resistance and thus less torque to run the file Protaper system has progressive taper which claims reduced torsional loading. GT series consists of GT 20, GT 30 and GT 40 with 10%, 8%, 6%, 4%. RaCe files are available from 15 to 60 sizes with taper of 10%, 8%, 6%, 4%, and 2%. Hero 642 consists of 12 files with varying tip sizes, tapers

11. BLADE - It is the working area of file It is the surface with the greatest diameter which follows the flute as it rotators

12. RAKE ANGLE - It is the angle formed by cutting edge and cross section taken perpendicular to long axis of the tooth. Cutting angle is angle formed by cutting edge and radius when file is sectioned perpendicular to the cutting edge It can be positive, neutral, or negative If angle formed by leading edge and surface to be cut is obtuse, rake angle is positive or cutting If angle formed by leading edge and surface to be cut is acute, rake angle is negative or scrapping

13. Positive rake angle cuts more efficiently than negative; it scrapes the canal wall. File with overly positive angle digs and gauges the canal and can result in instrument separation

14. FLUTE - It is a groove present on the working area of file to collect soft tissue and dentin chips removed from canal wall Effectiveness of flute depends upon depth, width, configuration, and surface finish

15. RADIAL LAND/MARGINAL WIDTH- It is the area between the flutes which projects axially from central axis, between flutes as far as the cutting edge It acts as a blade support, that is, amount of material supporting the blades Most of rotary files get their strength from material mass of core Peripheral strength is gained by increasing the width of radial land Profile and K3 have full radial lands, so they show superior peripheral strength. Increase in peripheral mass prevents propagation of cracks, reducing chances of separation. Protaper , Hero 642, RaCe do not have radial lands.

16. RELIEF - Surface area of land which is reduced to a certain extent to reduce frictional resistance.

17. HELICAL ANGLE- It is the angle formed by cutting edge with the long axis of the file. File with constant helical angle results in inefficient removal of debris and is susceptible to “screwing in” forces This angle is important for determining which file technique to use Variable helix angle causes better removal of debris and reduces the chances of screwing into the wall • In K3 file, there is increase in helical angle from tip to handle, resulting in better debris removal RaCe has alternating helical design which reduces rotational torque

18. PITCH- It is the distance between point on leading edge and corresponding point on leading edge It shows number of threads per unit length. File with constant helical angles and pitch tend to screw in the file, whereas file with variable pitch and helical angle reduces the sense of being screwing into the canal

19. CARBON STEEL- Rigidity increases with increased size Less resistant to breakage by bending and twisting The instruments are easily corroded Low cost

20. STAINLESS STEEL- Greater flexibility than their carbon steel counterparts Greater resistance to fracturing by twisting Less sharper than carbon steel Resistant to corrosion

21. NICKEL TITANIUM ALLOYS - Long before the advent of NiTi files into dentistry, endodontic instruments used to clean and shape root canals were made up of carbon steel and stainlesssteel which were less flexible and produced procedural errors which were overcome by the introduction of NiTi instruments

22. NiTi alloy was first developed by W. F. Buehler, a metallurgist in 1960s, with unique properties of super-elasticity and shape memory which did not confine to normal metallurgic properties of alloys Introduced in dentistry by Andearson in 1972 It was Harmeet Walia who first fabricated an endodontic file from a NiTi arch wire in 1988. Since then, NiTi alloy has become an inevitable part of endodontics Over the past three decades, the nickel–titanium ( NiTi ) rotary instruments have highly improved the quality of the cleaning and shaping of the root canals.

23. NiTi : metallurgical structure and phases Nickel and titanium are transitional metals. Transitional metals or elements are those that have properties of both metals and non- metals. NiTi alloys are usually equiatomic in nature usually with a 1:1 atomic ration. Majority of endodontic instruments approximately contain about 55% of nickel and 45% of titanium by weight

24. The unique features of NiTi instruments are its superelasticity and shape memory property which usually arises due its microstructural phase transformation. NiTi can have 3 different forms: Austenite, Martensite and R-phase (intermediate phase). The character and relative proportions of which determine the mechanical properties of the metal. The “Parent phase” or “Austenite phase” has a body centered cubic lattice structure that only occurs at high temperature and low stress exhibiting a strong and rigid characteristic

25. The “Daughter phase” or “Martensitic phase” has a face centred cubic lattice structure that occurs at low temperature and high stress exhibiting a soft and ductile characteristic

26. Structure of NiTI -

27. Austenite PHASE - A crystal structure of Niti Alloy at high temperature ranges (100.c ) is a stable , body- centred cubic lattice which is referred to as the austenite phase or parent phase

28. MARTENSITE PHASE - At low temperatures, NiTi spontaneously transforms to a more complicated monoclinic crystal structure known as Martensite phase Martensite’s crystal structure known as monoclinic (closely packed hexagonal lattice) has the unique ability to limited deformation in some ways without breaking atomic bonds this type of deformation is known as Twinning

29. AUSTENITE – Hard , firm Inelastic Resembles titanium Simple structure MARTENSITE – Soft Elastic Complex Structure

30. The super-elasticity property of NiTi alloy is induced due to transformation from the stable austenitic to stress induced unstable martensite which tends to reverts back to its original shape on unloading (stress induced property). Whereas, the shape memory property of NiTi alloy is induced due to a transformation from a stable austenite to a stable martensite phase (martensitic re-orientation) which is a specified heat-controlled property and will not regain its original shape on unloading. This allows the alloy to remember its original shape and retain to it when heated above its transition temperature

31. Properties- When NiTi instrument is used, it undergoes a stress strain behaviour and this stress-strain behaviour best depicts the variations in the crystal configurations of the alloy which is responsible for their unique properties. When introduced into a root canal, there occurs an initial elastic deformation of NiTi instrument followed by a transformation from austenite phase to a martensite phase. After transformation, the instrument undergoes a state of both elastic and plastic deformation.

32. On ceasing instrumentation, the sequence of events is reversed, there occurs a decrease in elastic strain, followed by transformation of martensite to austenite structure. Finally, as bending movement decreases the elastic strain reduces to zero. But a small amount of permanent angular deformation remains in instrument because a permanent deformation is induced during use of NiTi instrument which does not occur in cases of any other alloys. Other alloys may undergo permanent deformation and will not revert back to its original shape unlike NiTi alloy due to its super-elasticity property

33. Most of the NiTi instruments used for cleaning and shaping of root canals were heat treated during manufacturing and remain in a stable austenitic structure at both room and body temperature. When they are introduced into the canals, it produces a stress induced martensitic structure (unstable) and once the stress is relieved and when the instrument is back to room temperature, it reverts back to austenitic structure. This phenomenon is called shape memory property. In general this mechanism of reversible transformation between austenitic and martensitic structures in NiTi which is of clinical significance

34. When stressed or upon cooling of NiTi the austenitic phase can transform into two phases namely, martensitic phase or an intermediate phase between the austenite to martensitic transformation called the R-phase, which has a rhombohedral crystal structure.

35. THE R- PHASE - The R-Phase is essentially a rhomboidal distortion of the cubic austenite phase The R-Phase it is an intermediate transition between austenite and martensite The R- Phase often appearing during cooling before martensite then giving way to martensite upon further cooling. Similarly, it can be observed during heating prior to reversion to austenite or my be completely absent

36. Twisting NiTi wire is only possible in R-Phase Youngs modulus is lower than austenite, thus the instrument made from R-Phase is more flexible R-Phase shows good super elasticity.

37. The temperature that induces conversion from twinned martensite to austenitic structure is termed a s transformation temperature. There is specific transformation temperature for start and finish of each phase of NiTi alloy. Usually, transformation temperature range of NiTi is well below or close to body temperature. And transformation temperature influences the use of NiTi alloy in its different properties. If the austenitic transformation temperature is less than the body temperature, it produces the super-elastic effect of the NiTi alloy. But if the body temperature is less than the martensitic transformation temperature it produces the shape memory property of NiTi alloy.

38. Alloy microstructure of NiTi instruments CONVENTIONAL NITI- Conventional NiTi instruments remain in a stable austenite phase but on instrumentation it produces a stress induced martensite phase which is unstable which tend to straighten during preparation leading to canal transportation. They are usually manufactured by milling or grinding process tends to acquire surface imperfections or irregularities, milling marks or metal flash which remain vulnerable for crack propagation and ultimately fracture of the NiTi instrument. Hence various studies aimed in improving the surface characteristics by thermomechanical treatments which may significantly alter the material properties

39. M-WIRE- M-Wire (Martensitic wire), introduced in 2007 by Dentsply, is produced by applying a series of heat treatments to NiTi wire blanks. Here the austenite finish temperature ( Af ) is higher (40-50oC) than normal which gives rise to the phase composition of austenite with small amounts of R-phase and martensite that render the instrument more super elastic than conventional NiTi instrument. Advantageous property is that these instruments need less stress for their martensitic transformation than the conventional NiTi instrument. They exhibit greater resistance to cyclic fatigue. Instruments with Mwith technology include ProFile Vortex, ProFile GT Series X, ProTaper Next

40. R-PHASE- The R-phase was developed by Sybron Endo in 2008. R-phase is an intermediate phase (rhombohedral structure) that can form during forward transformation from martensite to austenite on heating and reverse transformation from austenite to martensite on cooling. The phase composition of R-phase is purely austenite. It exhibits unique characteristics of low elastic modulus with less transformation strain which will require only less stress to produce plastic deformation in R-phase . Hence NiTi during manufacturing process the alloy will be brought to its R-phase for easy twisting or grinding and then back to the stable austenite phase. An instrument made from the R-phase wire would be more flexible . Instruments with R-phase technology are Twisted file, Twisted file Adaptive, K3XF

41. CM WIRE- Controlled Memory (CM) wire was introduced in 2010. This novel NiTi alloy was found to have properties that controlled the memory making the files extremely flexible. The phase composition of CM wire is completely made of martensite. Exhibits only shape memory property but not super elasticity at body or root canal temperature. But will exhibit super elastic property if it undergoes sterilization cycles. The major advantage is that, no canal transportation occurs unlike conventional NiTi instruments, CM wire lacks super-elasticity property hence it tends to adapt to the canal morphology and they do not fully straighten during preparation of curved canals. Instruments with CM Wire technology are Hyflex CM, Hyflex EDM, Protaper Gold, Waveone Gold, Vortex Blue, Reciproc Blue, V-taper 2H

42. MaxWire - Max wire- Martensite Austenite electro polish file X, introduced by FKG Dentaire in 2015 is the most recent advancement in thermomechanical treated files. This is the first endodontic NiTi alloy that has both shape memory and super-elasticity effect in clinical application. These instruments are straight at room temperature and exhibit a shape memory effect when inserted into the root canal (M-phase to Aphase ) and possess super-elasticity during preparation. Instruments made of MaxWire are XP-endo Shaper and XP-endo Finisher

43. Generations - FIRST GENERATION This category of NiTi rotary instruments were first introduced to the market during the mid‑1990s. The most important characteristic of the first‑generation NiTi rotary files is having passive cutting radial lands along with fixed 0.04–0.06 tapers over the full working lengths. The main important NiTi rotary instruments within this category are LightSpeed Endodontics (1992), Profile‑Dentsply (1993), Quantec‑SybronEndo (1996), and GT system‑Dentsply (1998).

44. Several researches showed that all first‑generation rotary instruments created smooth root canal walls which centered in the middle and caused low procedural errors. The main deficiency of this generation of NiTi rotary instruments was requiring numerous files to achieve these goals and complexity

45. SECOND GENERATION - The second generation of NiTi rotary files was introduced into the market in 2001. These instruments had active cutting edges with greater cutting efficiency, so the number of instruments required to achieve complete cleaning and shaping was almost less in comparison with the previous generation. Notable systems in this generation are ProTaper Universal‑Dentsply, K3‑SybronEndo, Mtwo ‑VDW, Hero Shaper‑Micro‑Mega, I Race, and I Race Plus‑FKG Dentaire .

46. Several studies have also approved the efficiency of these systems in fast preparation and also preserving the original shape of canals even in curved and calcified challenging cases although some researchers have reported some degrees of canal transportations along with tendency for breakage while usage

47. THIRD GENERATION - It was in late 2007 that the manufacturers started to apply the heating and cooling technologies on NiTi alloys to improve the safety of these instruments, especially in the curved root canals. In making third generation of the NiTi rotary files, the manufacturers have highly focused on metallurgic properties of the NiTi alloy using heating and cooling procedures on wires which results in reduction of the cyclic fatigue of the files and also reduction of the separation risk of the instruments which is highly demanded by the practitioners. Applying M‑wire and R‑phase technologies and electrical discharge methods make instruments with high memory shapes and low risk of separation

48. K3 XF Files‑ SybronEndo , Profile GTX Series–Dentsply, controlled memory (CM) Files ( HyFlex CM)– Coltene , and Vortex Blue (Dentsply Tulsa) are notable files in this group which have been exposed to heat treatments to increase flexibility and safety. The CM property helps the instrument to save the shape of the canal when it is moved out of the canal. Flex files ( NeoEndo ) files have been predisposed to gold thermal treatment which increases their cutting efficiency along with cyclic fatigue resistance

49. FOURTH GENERATION - Reciprocation which is described as any repetitive back and forth or up and down motion is another philosophy in canal preparation which was first introduced by Blanc, a French dentist, in the late 1950s. Instead of full rotation, the reciprocating NiTi rotary instruments have movements in which clockwise and counterclockwise degrees of rotation are quite equal. The reciprocation theory of canal preparation has led to development of the fourth generation of NiTi rotary instruments.

50. The use of a single file technique to achieve a thorough cleaning and shaping goals at this phase was another success which was also derived from the reciprocating philosophy in cleaning and shaping the root canal systems Many studies have shown that the Wave One and the One Shape single‑file systems can efficiently reduce the bacterial number in the root canal along with preserving the original shape of it. Wave One‑Dentsply, self‑adjusting file (SAF)‑ ReDent Nova, and Reciproc ‑VDW are featured instruments of fourth generation

51. FIFTH GENERATION - In this generation, the efficiency of canal shaping has been improved by offsetting the center of rotation. The offset designed files produce a mechanical wave of motion that distributes along the full length of the NiTi file which improves cutting and removing the debris in comparison with a centered mass rotating instrument. Furthermore, this offset design reduces the taper lock or the screwing effect which causes instrument separation. HyFlex /electrical discharge machining (EDM)‑ Coltene , Revo ‑S‑Micro‑Mega, One Shape Micro‑Mega, and ProTaper Next‑Dentsply are important files of the fifth generation

52. Despite the reciprocating philosophy based of the fourth generation, the Revo ‑S and the One Shape systems of the fifth generation, both manufactured by the Micro‑Mega Company, offer proper root canal shaping by continuous clockwise rotation of the instruments inside the root canal system. One Shape which is just a single number 25/0.06. Taper instrument with asymmetrical cross section along the entire blade has variable cross section and longer pitch. Using the glide path, instrument is optional in One Shape instrumentation strategy. Micro‑Mega also offers optional using apical finishing files. These sterile single‑use NiTi ‑finishing files are used after root canal shaping with One Shape in order to enlarge the root canal diameter

53. The Revo ‑S NiTi rotary system also manufactured by Micro‑Mega simplifies and optimizes the cleaning and shaping of the root canals with only three NiTi instruments. The asymmetric cross section of the Revo ‑S facilitates penetration by a snake‑like movement and offers a root canal shaping adopted to the biological and ergonomic imperatives