Endodontic Instruments Classification Notes

Endodontic Instruments Classification Notes

Although a variety of instruments used in general dentistry are applicable in endodontics, some special instruments are unique to endodontic purposes. The first endodontic file was made in the mid-1800s by Edward Maynard by notching round wires (earlier got from watch spring and then from piano wires).

In the early 1900s, a variety of tools like pathfinders, barbed broaches, reamers, files, etc. were available but there was little uniformity in quality control, the taper of canal or instrument, and filing materials in terms of size and shape. 1958 was the hallmark year in the history of endodontic instruments.

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The manufacturers came together and a consensus was made on instruments and obturation materials.

Then in 1959, the following standardization for instruments and obturating materials was made:

• The formula for diameter and taper for each instrument introduced
• Formulae for graduated increment in size from one instrument to another was developed

In 1968, Jack Jacklich of Loyola University formed a group with other dentists and performed endodontic therapy. Over a period of time, he found endodontic treatment using hand instruments a tedious process and development of “the scourge of digital hyperkeratosis.” All these problems led to many innovations in techniques and instruments.

In 1989, American National Standards Institute (ANSI) granted the approval of American Dental Association (ADA) specification No. 28 for endodontic instruments.

Endodontic Instruments Classification

Standardization Of Instruments Given By Ingle And Levine

Ingle and Levine using an electronic microcomparator found variations in the diameter and taper for the same size of the instrument. They suggested the following guidelines for instruments for having uniformity in instrument diameter and taper:

• Size: Instruments are numbered from 10 to 100. Each number should represent the diameter of the instrument in 100th of millimeter at the tip. For example, a No. 25 reamer shall have 0.25 mm at D1 and 0.57 mm (0.25 + 0.32) at D2. These sizes ensure a constant increase in taper, that is, 0.02 mm/mm of the instrument regardless of the size.
• There is an increase in 5 units up to size 60 and in 10 units till they are size 100. This has been revised to include numbers from 6 to 140
• Length: Instruments are available in the following lengths: 21, 25, 28, 30, and 40 mm. 21 mm length is commonly used for molars, 25 mm for anterior, 28 and 30 mm for canines, and 40 mm for endodontic implants
• Tip angle: Tip angle of an instrument should be 75 ± 15°
• Taper: The working blade shall begin at the tip (D1) and extend 16 mm up the shaft (D2). D2 should be 0.32 mm greater than D1, ensuring that there is a constant increase in taper, that is, 0.02 mm/mm of instrument
• Color coding: Instrument handles should be color coded for their easier recognition (Pink, gray, purple, white, yellow, red, blue, green, black, white, etc.)

Modifications from Ingle’s Standardization:

• An additional diameter measurement point at D3 is 3 mm from the tip of the cutting end of the instrument at D0 (earlier it was D1) and D2 was designated as D16
• Greater taper (GT) instruments (0.04, 0.06, 0.08, 0.10, 0.12) have also been made available.
• To maintain these standards, the American Association of Endodontists (AAE) recommended ADA and the United States Bureau of Standards to form a committee for the standardization of endodontic instruments.

History:

1750:             Fauchard recommended the removal of the pulp.
1850:             Wooden pegs for debriding pulp.
Early 1900:    Introduction of fies, reamers, etc.
1915:             Kerr company obtained a patent for their instruments.
1958:             Ingle and Levine standardization of endodontic instruments.
1964:             Introduction of romantic handpiece.
1975:             First potential application of NiTi alloys.
1976:             First approved specification for root canal instruments.
1988:             First use of NiTi in endodontics.
1989:             ANSI approved specification No. 28 for endodontic reamers and files.

Classifiation Of Endodontic Instruments

Grossman’s Classification According to Function

• Exploring: Smooth broaches and endodontic explorers (To locate canal orifices and determine patency of root canal)
• Debriding or extirpating: Barbed broaches (To extirpate the pulp and other foreign materials from the root canal)
• Cleaning and shaping: Reamers and fies (Used to shape the canal space)
• Obturating: Pluggers, spreaders, and lentulospirals (To pack gutta-percha points into the root canal space).

Endodontic Instruments Classification

Classification Based on Method of Use

• Group 1: Hand-operated endodontic instruments
  • Broaches and rasps
  • K-type reamers and files
  • Hedstroem files
• Group 2: Low-speed instruments with latch-type attachment
  • Gates-Glidden drills
  • Peeso reamers
• Group 3: Engine-driven instruments
  • Rotary NiTi instruments
  • Reciprocating instruments
• Group 4:
  • Sonics and ultrasonics.

Manufacturing of Hand Instruments:

A hand-operated instrument reamer or file begins as a round wire which is modified to form a tapered instrument with cutting edges. These are manufactured by two techniques:

• By machining the instrument directly on the lathe, for example, Hedstroem fie (H-fie), and NiTi instruments
• By fist grinding and then twisting. Here, the raw wire is ground into tapered geometric blanks, that is, square, triangular, or rhomboid. These blanks are then twisted counterclockwise to produce cutting edges.

Group 1 Hand-Operated Instruments

Broaches and Rasps:

Broaches and rasps were the earliest endodontic instruments used to extirpate pulp and debris from the canal.

Broach

Broach is of two types:

1. Barbed broach

• It is one of the oldest intracanal instruments with specifications by ANSI No. 63 and ISO No. 3630/1
• It has ADA specification No. 6
• Broach is a short-handled instrument meant for single use only
• It is made from round steel wire. The smooth surface of wire is notched to form barbs bent at an angle from its long axis
• Broaches are available in a variety of sizes, from triple extra fine to extra coarse
• Broach does not cut the dentin but can effectively be used to remove cotton or paper points which might have lodged in the canal

Broach Clinical Tips:

• Broach should not be inserted into the root canal unless the canal has been enlarged to a size No. 25 reamer/file
• Broach should not be forced apically into the canal, as its barbs get compressed by the canal wall. While removing, the barbs get embedded into dentin resulting in fracture of the instrument on applying pressure
• If the selected broach used is too narrow, it will not engage pulp tissue effectively
• If the broach is too wide, it may bind to canal walls and thus may fracture

Uses of barbed broach:

• Extirpation of entire pulp tissue
• Removal of cotton or paper points lodged in the canal
• Removal of necrotic debris and foreign material from the canal.

2. Smooth broach:

It is free of barbs. Previously it was used as a pathfinder, but at present flexible files are used for this.

Endodontic Instruments Classification

Rasp/Rat Tail Files:

• It has ADA specification No. 63
• Rasp has a similar design to barbed broach except in taper and barb size. Barb size is larger in broach than a rasp
• It is used to extirpate pulp tissue from canal space.

K-Type Reamers and Files:

Reamers and files are canal enlarging instruments, traditionally made from stainless steel and comprise of two basic designs, K-type instruments (K-files and K reamers) and the Hedstroem files. Since Kerr Manufacturing company was the first to produce them, these were also called K-type instruments.

These are made from rectangular or triangular blanks wires which are twisted to give the working end of the instruments a spiral form. These instruments may have different spirals, and cutting flutes.

Reamer:

• A reamer is used to ream the canals. It cuts by inserting into the canal, twisting clockwise one quarter to half turn, and then withdrawing, that is penetration, rotation, and retraction.
• Reamer has a triangular blank and a lesser number of flies than the file. The numbers of flutes in the reamer are 0.5–1/mm
• Though reamer has fewer numbers of flies than fie, cutting efficiency is the same as that of fies because more space between flies causes better removal of debris
• Reamer tends to remain self-centered in the canal resulting in less chances of canal transportation.

Files

K-File:

• It is triangular, square, or rhomboidal in cross-section, manufactured from stainless steel wire, which is grounded into the desired shape
• K-fie has 1.5–2.5 cutting blades per mm of their working end.
• Tighter twisting of the fie spirals increases the number of flies in fies (more than reamer)
• Triangular cross-sectioned fie shows superior cutting and increased flexibility than the file or reamer with a square blank
• The file is predominantly used with filing or rasping action in which there is little or no rotation in the root canal. It is placed in the root canal and pressure is exerted against the canal wall and the instrument is withdrawn while maintaining the pressure.

K-Flex File:

• It was seen that the square blank of the file results in a total decrease in the instrument flexibility. To maintain the shape and flexibility of this file, the K-flex file was introduced
• K-flux file is rhombus in cross-section having two acute angles and two obtuse angles
• Two acute angles increase the sharpness and cutting efficiency of the instrument.
• Two obtuse angles provide more space for debris removal
• Decrease in contact of the instrument with canal walls provides more space for irrigation
• It is used with filing and rasping motion

Endodontic Instruments Classification

Flexo File:

• It is similar to the K-flex file except that it has a triangular cross-section. This feature provides more flexibility and ability to resist fracture
• Tip of fie is modified to noncutting type
• It is more flexible but has lesser cutting efficiency.

Triple Flex File:

• It is made up of stainless steel and has a triangular cross-section
• It has more flutes than Reamer but lesser than K-fie
• The triangular cross-section provides better flexibility and cutting efficiency.

Flex-R File/Roane File:

• Flex-R fie is made by removing the sharp cutting edges from the tip of the instrument. A noncutting tip enables the instrument to traverse along the canal rather than gouge into it
• This design reduces ledge formation, canal transportation, and other procedural accidents when used with a balanced force technique
• Another feature of flux-R fie is the presence of triangular cross-section which provides it flexibility to be used in curved canals
• It is made up of NiTi and cuts during anti-clockwise rotary motion.

Hedstroem File (H-File):

•  H-fie has flies that resemble successively triangles set one on another
• It is made by cutting spiral grooves into round, tapered steel wire in the same manner as wood screws are made. This results in the formation of a sharp edge which cuts on removing strokes only
• H-fie cuts only when the instrument is withdrawn because its edges face the handle of the instrument
• When used in torquing motion, its edges can engage in the dentin of the root canal wall, causing H-files to fracture
• Rake angle and distance between the flutes are two main features which determine the working of the file. H-fie has a positive rake angle, that is, its cutting edge is turned in the same direction in which force is applied which makes it to dig the dentin, thus more aggressive in cutting
• H-file should be used to machine the straight canal because it is a strong and aggressive cutter. Since it lacks flexibility and is fragile in nature, the H-fie tends to fracture when used in torquing action

Endodontic Instruments Classification

Advantages of H-files:

• Better cutting efficiency
• Push debris coronally

Disadvantages of H-files

• Lack flexibility
• Tend to fracture
• Aggressive cutter

H-files Clinical Tips:

One should use Hedstroem fies in only one direction, i.e., retraction. It should not be used in torquing motion as it tends to fracture.

Modifiations in H-Files:

Safety Hedstroem File

• This file has a noncutting safety side along the length of the blade which reduces the chances of perforations
• The noncutting side is directed to the side of the canal where cutting is not required
• The noncutting side of the safety file prevents the lodging of the canals.

S-File:

• It is called an “S” file because of its cross-sectional shape
• S-fie is produced by grinding, which makes it stiffer than H-fie. This file is designed with two spirals for cutting blades, forming a double helix design
• S-file has good cutting efficiency in either filling or reaming action, thus this file can also be classified as a hybrid design

.

A-File:

• It’s a variant of H-fie
• Its cutting edges are at an acute angle to the long axis of the fie When used in curved canals, flies on the inner edge collapse, so no dentin is removed. On the outer edge, flies open, filing the dentin on the outer curvature.

Unified:

• It is machined from round stainless steel wire by cutting two superficial grooves to produce flutes in a double helix design
• It resembles H-fie in appearance
• It is less efficient
• Less prone to fracture.

C+ File:

• C + fi e is made from specially treated stainless steel so have amazing stiffness and strength to be used for difficult and calcified canals. It has better buckling resistance than K-fie
• Twisted fie design provides greater strength
• It is available in sizes 8, 10, and 15 and in lengths 18, 21, and 25 mm.

Golden Medium File:

• Golden medium fie was described by Weine. It comes under intermediate files provided with half sizes between conventional instruments
• It is available in sizes from 12 to 37 like 12, 17, 22, 27, 32, and 37
• It is used for narrow canals since it provides a more gradual increase in size than conventional fies
• It is formed by cutting 1 mm from the tip of the instrument. In this way No. 10 file can be converted to No. 12 and Nos. 15–17 and so on.

Group 2 Low-Speed Instruments With Latch-Type Design

Gates-Glidden Drills:

• Traditional engine-driven instruments include GatesGlidden drills which have flame-shaped cutting points mounted on long thin shafts attached to a latch-type shank
• Flame head cuts laterally, therefore used with gentle, apically directed pressure. It has a safe tip to guard against perforations
• Gates-Glidden drills are available in a set from 1 to 6 with diameters from 0.5 to 1.5 mm
• Due to their design, Gates-Glidden drills are side-cutting instruments with safety tips
• They should be used in brushing strokes at the speed of 750–1,500 rpm
• The safety design of Gates-Glidden drills is that its weakest part lies at the junction of the shank and shaft of the instrument. If its cutting tip jams against the canal wall, fracture occurs at the junction of the shank and the shaft but not at the tip. This makes removal of a fractured drill from the canal by grasping with pliers easy
• GG drills can be used both in crown down as well as step back fashion.

Uses of Gates-Glidden Drills:

• For enlargement of root canal orifices
• For coronal flying during root canal preparation
• For removal of the lingual shoulder during access preparation of anterior teeth
• During retreatment cases or post-space preparation for removal of gutta-percha
• For preparing space while removal of separated instrument
• If used incorrectly, for example, using at high rpm, incorrect angle of insertion, or forceful drilling, GG drills can result in procedural accidents like perforations, instrument separation, etc.

Flexogates:

• Flexogates are modified Gates-Glidden drills. They are made up of NiTi and have a noncutting tip
• They are more flexible and used for apical preparation
• Flexogates can be rotated continuously in a handpiece through 360°
• These instruments have many advantages over traditional instruments in that they allow better debris removal because of continuous rotation and smoother and faster canal preparation with less clinician fatigue

Advantages of flexogates:

• Safe noncutting guiding tip
• Safety design, i.e., its breakage point is 16 mm from the tip, so once fractured, it can be easily retrieved
• Flexible so used in curved canals

Peeso Reamers :

• Peeso reamers are also stainless steel instruments like Gates-Glidden drills but they differ in that blades spread over a wide surface and their shape is cylindrical
• These are rotary instruments mainly used for post-space preparation
• They have safe-ended noncutting tip
• Their tip diameter varies from 0.7 to 1.7 mm
• They should be used in brushing motion.

Peeso Reamers Uses:

Peeso reamer is primarily used for post-space preparation when gutta-percha has to be removed from the obturated root canal.

Peeso Reamers Disadvantages:

• They do not follow the canal curvature and may cause perforation by cutting laterally
• They are stiff instruments
• They have to be used very carefully to avoid iatrogenic errors.

Peeso Reamers Clinical Tips:

Gates-Glidden drills and Peeso reamers are inflexible and aggressive cutting instruments. They should be used at a slow speed with contra-angled handpieces with extreme caution to prevent perforations and over instrumentation.

Group 3 Engine-Driven Instruments

NiTi Rotary Instruments

NiTi was developed by Buchler 60 years ago. NiTi is also known as the NiTinol (NiTi Naval Ordinance Laboratory in the US). In endodontics, commonly used NiTi alloys are 55 NiTinol (55% weight Ni and 45% Ti) and 60 NiTinol (60% weight of Ni, 40% Ti).

It was also called equiatomic NiTi alloy due to the 1:1 atomic ratio of nickel to titanium. NiTi alloys with equiatomic ratio possess superelasticity and shape memory effect due to the narrow solubility range of the NiTi phase at 500° or below.

The first use of NiTi in endodontics was reported in 1988 by Walia et al. when a 15 No. NiTi file was made from orthodontic wire and it showed superior flexibility and resistance to torsional fracture. This suggested the use of NiTi files in curved canals.

Superelasticity and shape memory of NiTi alloys is because of reversible stress-induced martensitic transformation, that is, the ability of NiTi alloy to undergo deformation at one temperature and then recover its original. Since this occurs at a narrow temperature change, no heating is necessary to cause the undeformed shape to recover. At high temperatures, a lattice of NiTi alloy is simple, referred as austenite or parent phase.

On cooling, transformation induced in alloy occurs by a shear type of process to a phase called martensitic phase. This causes a change in the physical properties of the alloy, giving rise to the shape memory effect. It has the structure of a closely packed hexagonal lattice. At this stage, unless external stress is applied, no macroscopic changes are seen.

This martensite shape can be deformed easily to a single orientation by a process called detwinning when there is a flipping-over type of shear. NiTi alloy is more ductile in the martensite phase than in the austenitic phase. This deformation can be reversed by heating the alloy. By heating, the alloy resumes the original structure/austenite phase.

This transition from austenitic to martensitic phase can also occur by application of stress which occurs during root canal preparation. In response to external stress, the austenitic phase changes to the martensite phase. The deformation which occurs below the transformation temperature range is reversible.

R-phase:

It is an intermediate phase with a rhomboidal structure R phase possesses a lower shear modulus than the austenite or martensite phase, thus transformation strain for R phase. Transformation is less than other phases.

M-Wire:

It is produced by thermomechanical processing. It contains all three crystalline phases including deformed, microtwinned martensite, R-phase, and austenite. M-wire endodontic instruments like Profie GT-X, and Profie Vortex, and Controlled Memory files like Hyflx CM files are used in martensitic states and possess shape memory effects.

These files return to their original shape on autoclaving. The martensitic phase occurs at low temperatures and has a lower Young’s modulus (20–50 GPa) than the austenitic phase (40– 90 GPa). This means that martensite gets easily deformed at lower stress than austenite.

So martensitic phase is more flexible than the austenitic phase and reduces the risk of instrument fracture because, under high stress, it gets plastically deformed rather than the brake. So, much effort are put to develop the martensite phase for endodontic instruments.

Advantages of NiTi alloys:

• Shape memory
• Superelasticity
• Low modulus of elasticity
• Good resilience
• Corrosion resistance
• Softer than stainless steel

Disadvantages of NiTi files:

• Poor cutting efficiency
• NiTi files do not show signs of fatigue before they fracture
• Poor resistance to fracture as compared to stainless steel

Generations of motors:

• First generation: Motor without torque control
• Second generation: Motor with torque limit
• Third generation: Motor with simple torque control
• Fourth generation: Motor with apex locator and torque control

Characteristics/Properties of Rotary Instruments:

Tip Design:

• Rotary fie can have to cut (shaping Protaper files) or noncutting tip (ProFile, GT K3, Hero 642, RaCe, and finishing Protaper files)
• Cutting tip makes the fie aggressive. Its advantage is that it can enter in narrow canals. If goes beyond the apex, fie with a cutting tip results in an elliptical tear at the apex which is difficult to seal, whereas fie with a noncutting tip form a concentric circle which can be sealed with gutta-percha

Taper:

• It signifies per millimeter increase in file diameter from the tip toward the handle of the file. The difference in minimum and maximum diameter can be reduced so that the torque required for rotating larger instruments does not exceed the plastic limit of a smaller instrument
• The traditional instruments 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 fie stress and pressing debris.
• The 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 a minimal part of the fie engages the canal wall resulting in reduced resistance and thus less torque to run the file
• The Protaper system has a progressive taper which claims reduced torsional loading. GT series consists of GT 20, GT 30, and GT 40 with 10%, 8%, 6%, and 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

Blade:

• It is the working area of fie
• It is the surface with the greatest diameter which follows fate as it rotates.

Rake angle:

• It is the angle formed by the cutting edge and cross-section taken perpendicular to the long axis of the tooth. The cutting angle is the angle formed by the cutting edge and radius when fie is sectioned perpendicular to the cutting edge. It can be positive, neutral, or negative
• If the angle formed by the leading edge and surface to be cut is obtuse, the rake angle is positive or cutting
• If the angle formed by the leading edge and surface to be cut is acute, the rake angle is negative or scrapping
• A positive rake angle cuts more efficiently than a negative one; it scrapes the canal wall. File with an overly positive angle digs and gauges the canal and can result in instrument separation

Flute:

• It is a groove present on the working area of the fie to collect soft tissue and dentin chips removed from the canal wall
• The effectiveness of the flute depends upon depth, width, configuration, and surface finish

Radial land/marginal width:

• It is the area between the flutes which projects axially from the central axis, between flies as far as the cutting edge
• It acts as a blade support, that is, the amount of material supporting the blades
• Most of the rotary files get their strength from the material mass of the 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. An increase in peripheral mass prevents the propagation of cracks, reducing the chances of separation. Protaper, Hero 642, and RaCe do not have radial lands.

Relief:

• The surface area of land which is reduced to a certain extent to reduce frictional resistance.

Helical angle:

• It is the angle formed by the cutting edge with the long axis of the fie. 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 fie technique to use
• Variable helix angle causes better removal of debris and reduces the chances of screwing into the wall
• In K3 fie, there is an increase in helical angle from tip to handle, resulting in better debris removal
• Race has alternating helical design which reduces rotational torque

Pitch:

• It is the distance between a point on the leading edge and the corresponding point on the leading edge
• It shows a 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 screwed into the canal.

Generations Of Niti Rotary Files

First Generation NiTi Rotary Files

Profile System:

Profile system made by Tulsa Dental was one of the first commercially available NiTi instruments. This system was introduced by Dr. Johnson in 1944. Profile NiTi line includes Series 29, orifice shapers, Profile 0.02, 0.04, and 0.06, GT files, and ProTaper instruments Series 29 instruments, instead of increasing each fie by 0.05 between sizes, it was increased by 29%.

This system works well in small sizes but in bigger instruments. This much increase is not possible.

Profie 0.02, 0.04 and 0.06

• These have safe-ended noncutting tips with a negative rake angle (−20°) which makes them to cut dentin in scrapping motion. Profile instrument tends to pull debris out of the canal because of the presence of a 20° helical angle Recommended rotational speed for profiles
  is 150–300 rpm.
• The cross-section of the profile shows three U-shaped grooves with radial lands.
• The central parallel core present in the profile increases its flexibility.

Orifice Openers:

• They extend 19 mm below the head of the handpiece and have 10 mm of the cutting blade
• Series consists of six instruments which are safe-ended with increasing D0 diameters
• Used to prepare coronal two third of root canal system

Greater Taper Files (Steve Buchanan in 1994)

• GT files possess a U-shaped fie design with ISO tip sizes of 20, 30, and 40 and tapers of 0.04, 0.06, 0.08, 0.010 and 0.12
• Accessory GT files for use as orifice openers of 0.12 taper in ISO sizes of 35, 50, 70, and 90 are also available
• The maximum diameter of GT fie is 1 mm
• Recommended rotational speed for GT fie is 300 rpm
• The negative rake angle of the GT file makes it to scrape the dentin rather than cutting it.

Quantec File System:

• Quantec fie series were introduced in 1996 and are available in both safe cutting and noncutting tips with a standard size of 25 No. in 0.12, 0.10, 0.08, 0.06, 0.05, 0.04, 0.03, and 0.02 tapers. 0.02 tapered. Axes handles are 30% shorter than other files. Recommended speed is 340 rpm
• Files have reduced radial land which decreases the surface tension, contact area, and stress on the instrument
• Files have two flutes which increase the flute depth as compared to the three-flute design. This unique design minimizes its contact with the canal, thereby reducing the torque, providing greater space for debris removal, and reducing fie separation
• Quantec system utilizes the “graduated taper technique” to prepare a canal. It is thought that using a series of files of single taper results in decreases in efficiency as the larger instruments are used. This happens because more of the fie comes in contact with the dentinal wall which makes it more difficult to remove dentin.
• But in the graduated taper technique, restricted contact of the area increases the effiency of the instrument because now forces are concentrated on a smaller area.

HERO 642

• • HERO – High elasticity in rotation
  • 642 – 0.06, 0.04, and 0.02 tapers
• It was introduced by Daryl-Green
• HERO 642 (high elasticity in rotation, 0.06, 0.04, and 0.02 tapers) is used in at 300–600 rpm
• It has a tri helical Hedstrom design with a positive rake angle and sharp flutes. Cross section of HERO show geometrics similar to H fie without radial lands.
• Due to the progressively increasing distance between the flies, there is a reduced risk of binding the instrument in the root canal
• A larger central core provides extra strength and resistance to fracture.

Light Speed System :

• This system was introduced by Steve and Willian Wildely in 1990, now known as LS1
• Light speed system is an engine-driven endodontic instrument manufactured from nickel–titanium. This is so named because a “light” touch is needed as the “speed” of instrumentation is increased
• Light speed instrument is slender with a thin parallel shaft and has a noncutting tip with Gates-Glidden in configuration
• Recommended speed for use is 1,500–2,000 rpm
• These is available in sizes Nos. 20–140 including the half sizes, namely, 22.5, 27.5, 32.5. The half-sizes are also color-coded as full ones with the only difference in that half-size instruments have white or black rings on their handles
• The cutting head of the light speed system has three different geometric shapes:
  • Size 20–30 short noncutting tips at 75° cutting angle
  • Size 32.5 longer noncutting tip at 33° cutting angle
  • Size 35–140 longer noncutting tip with 21° cutting angle
• Cutting heads basically have three radial lands with spiral-shaped grooves in between.

Second Generation

Protaper Universal:

These were designed by Dr. Clif Ruddle, Dr. John West, and Dr. Pierre Machtou.

Features:

Progressive tapers:

This improves flexibility, and cutting efficiency, and reduces the number of recapitulations needed to achieve length. One of the benefits of a progressively tapered Shaping file is that each instrument engages a smaller zone of dentin which reduces torsional loads, fie fatigue, and the potential for breakage.

Convex triangular cross-section:

This feature reduces the contact area between the blade and dentin increases the cutting action and improves safety by decreasing the torsional load.

Helical angle and pitch:

Continuously changing the helical angle and pitch optimizes its cutting action, clears the debris out of the canal, and prevents screwing in of the instrument in the canal.

Variable tip diameters:

Variable D0 diameter allows fie to safely and efficiently follow the canal.

Modified guiding tip:

This allows each instrument to better follow the canal without damaging the root canal walls.

Short handles:

A short 12.5 mm handle improves access in posterior regions.

Shaping Files:

Finishing Files:

ProTaper Gold:

Developed with improved metallurgy, ProTaper Gold rotary files show the following features:

• Convex triangular cross-section and progressive taper
• Increased flexibility due to the advanced metallurgy process
• Greater resistance to cyclic fatigue so lesser chances of fire separation
• Shorter 11 mm handle
• The noncutting tip design allows each instrument to safely follow the canal while the small flat area on the tip enhances its ability to find its way through soft tissue and debris.

K 3 Rotary File System

Dr. John McSpadden in 2002 in North America introduced the K3 system.

• K 3 files are available in the taper of 0.02, 0.04, or 0.06 with ISO tip sizes. An Axxess handle design shortens the file by 5 mm without affecting its working length
• These files are flexible because of the presence of variable core diameter
• The cutting head shows three radial lands with relief behind two radial lands. Asymmetrically placed flutes make the K 3 system with superior canal tracking ability, add peripheral strength to K3 system, and prevent screwing into the canal
• Positive rake angle makes effctive cutting surface
• K 3 files are color-coded to differentiate various tip sizes and tapers
• Body shapers available in taper 0.08, 0.10, and 0.12, all with tip size 25 are used to prepare the coronal third of the canal.

Race Files (Reamers with Alternating Cutting Edges)

• Race has a safety tip and triangular cross-section. This file has two cutting edges, fist alternates with a second which has been placed at different angles. Alternating cutting edges help in reducing working time and decreasing operation torque. Noncutting safety tip helps in perfect control of the instrument
• It has variable pitch and helical angle which prevents the file from screwing into the canal
• Electrochemical treatment of these files provides better resistance to corrosion and metal fatigue.

Third Generation Files

TF Twisted Files:

These are the first flted NiTi files manufactured by plastic deformation. these are available in tip sizes from #25 to #50 and tapers from 0.04-.12.

The unique features of these files are:

1. R-phase heat treatment technology is used to optimize the molecular phase which increases fie flexibility and resistance to cyclic fatigue.
2. Twisted design, not ground; twisting helps preserve grain structure and reduces the formation of microfractures, making the file even more durable. Grinding weakens the metal’s structure at the molecular level and creates microfractures on the metal’s surface.
3. A proprietary surface conditioning treatment of the fie.

Fourth-Generation Reciprocating Instruments

Reciprocation is defined as repetitive back-and-forth motion and it has been clinically utilized to use stainless steel fies since 1958. In rotation, NiTi files require less inward pressure and take the debris out of the canal, whereas reciprocation mimics manual filing. These instruments result in less debris removal because of pecking motion and can result in debris extrusion.

Advantages of reciprocating motion:

• Less binding of the instrument leads to canals so less torsional stress.
• Decreased risk of instrument separation
• Less flexural stress due to a reduction in a number of cycles within the root canal.

Disadvantages of reciprocating motion:

• An increased amount of debris extrusion during the instrumentation procedure.
• Causes cracks in dentin due to reciprocating instrumentation technique.

WaveOne NiTi File System:

It is a single-use, single-fie system to shape the root canal completely from start to finish. It works in a similar but reverse “balanced force” action moving in a back-and-forth “reciprocal motion.” There is three files in the WaveOne single-file reciprocating system, available in lengths of 21, 25, and 31 mm.

There are used at a speed of 300 rpm with a torque of 5 N cm. These work with a reverse cutting action. They have a modified convex triangular cross-section at the tip end. These work with a reverse cutting action.

They have a modified convex triangular cross-section (Fig. 13.53) at the tip end.

• WaveOne small fie has a tip size of ISO 21 with a taper of 6%. It is used in fie canals
• WaveOne primary fie has tip size of ISO 25 with the taper of 8% that reduces toward the coronal end
• WaveOne large fie tip size of ISO 40 with the taper of 8%. It is used in large canals

WaveOne Gold:

WaveOne Gold incorporates the metallurgical advancements of Gold wire, improving flexibility by 80% over of WaveOne. It has a parallelogram-shaped cross-section, which helps in improving cutting effiency and debris removal within the canal. It’s variable taper helps it to perform better in smaller and narrower canal anatomy. Tip sizes match ISO Numbers 020, 025, 035 and 045

Self-Adjusting File:

The Self-Adjusting File is a hollow Nickel–Titanium latticelike cylinder that scrubs the canal walls by vertical vibrations. Its hollow shape allows for the continuous flow of irrigant through its lumen to achieve superior disinfection. It is available in lengths 21, 25, and 31 mm and two diameters 1.5 and 2.0 mm.

It is used at 5,000 vertical vibrations per minute. Its abrasive surface acts similarly as sandpaper by scrubbing uniformly and gradually enlarging the root canal circumferentially. The slow, low-torque rotation occurs when the SAF is not engaged with the canal walls, allowing circular repositioning throughout the process.

TF Adaptive file system:

TF adaptive fie works as rotary under normal conditions but changes to reciprocation when stress is increased on fie. these features allow better resistance to cyclic fatigue with higher durability.

Available in different sizes; for small canals as 20/0.04, 25/0.06, and 35/0.04, and for medium to large-sized canals as 25/0.08, 36/0.06, and 50/0.04.

Fifth Generation Instruments

Revo-S:

Revo-S has snake-like movement inside the canal. It has an asymmetrical cross-section which provides more flexibility and less stress on the instrument. It works in a cyclic way (3C concept); cutting, clearance, and cleaning at rotation speeds ranging between 250 and 400 rpm. It consists of three instruments: SC1, SC2, and SU.

Protaper Next:

Features:

Shortens the shaping time; high cutting effiency reduces
the shaping time.

Swaggering Effect: Protaper Next’s innovative off centered rectangular cross section gives the fie a snake-like “swaggering” movement as it moves through the root canal. This helps in better removal of debris and canal tracking

M-WIRE NiTi improves fie flexibility, greater resistance to cyclic fatigue, and cutting effiency.

Scoutrace Files

• ScoutRace is a sequence of three instruments with .02 taper and with ISO sizes of 10, 15 and 20
• These are used at 600–800 rpm
• These have extreme flexibility due to 0.02 taper, rounded safety tip for precise guiding, alternating cutting edges to avoid screwing-in effect, sharp edges for best cutting efficiency, and electrochemical polishing for better resistance to torsion and fatigue

Group 4 Sonics And Ultrasonics In Endodontics

The ultrasonic instrument was first used in dentistry for tooth preparation with an abrasive slurry. Though it showed low cutting effiency, it had many advantages like improved visualization, a conservative approach, and selective cutting. The concept of using ultrasonics in endodontics was suggested by Richman in 1957.

The pioneering research on endodontics was done by Cunningham and Martin in early 1980. Endodontics is a device which imparts sinusoidal vibration of high intensity to a root canal instrument.

Sonic Handpiece

• Sonic instruments rely on a passage of pressurized air through the instrument handpiece for use operating at 3–6 kHz. Its handpiece is attached to a normal airline, so it uses compressed airline at a pressure of 0.4 MPa (already available in dental unit setup as its source of power)
• It has an adjustable ring to give an oscillating range of 1,500–3,000 cps
• There are two options for irrigating the root canal while using sonic handpieces. Either the waterline of the dental units can be attached to the sonic handpiece or the water can be cut of and the dental assistant can introduce
• sodium hypochlorite from a syringe:
• Sonic handpiece uses the following types of files:
  • Helio sonic (Trio sonic)
  • Shaper sonic
  • Rispi sonic
• All these instruments have safe-ended noncutting tip 1.5–2 mm in length. The sizes for these instruments range from 15 to 40
• The instrument oscillates outside the canal which is converted into vibrational up-and-down movement in the root canal. Sonic instruments are used in step down technique
• To permit the insertion of No. 15 sonic fie, the canal should be initially prepared with conventional hand fies (No. 20). Sonic fie begins its rasping action 1.5–2.0 mm from the apical stop. This length is called as sonic length
• When sonic fie is operated without any constraint, it sets up circular motion characterized by true vertical or longitudinal movement.

Advantages of Sonic Instruments:

• Better shaping of the canal as compared to ultrasonic preparation
• Due to constant irrigation, lesser chances of debris extrusion beyond the apex
• Produces clean canals free of smear layer and debris

Disadvantages of Sonic Instruments:

• Walls of prepared canals are rough
• The chances of transportation are more in curved canals.

Ultrasonic Handpiece:

• Ultrasonic endodontics is based on a system in which sound as an energy source (20–42 kHz) causes three-dimensional activation of a file in the surrounding medium. Ultrasound energy can be produced by magnetostriction; it converts electromagnetic energy into mechanical energy or piezoelectricity principle.
• In this, crystal is used which changes dimension when an electric charge is applied, therefore, the electric current generates a wave in the crystals. This crystal deformation is converted to mechanical oscillation with no production of heat
• Ultrasonic systems involve a power source to which an endodontic fie (K file) is attached with a holder and an adapter. Before a size 15 can be freely used with ultrasonics, the canal must be enlarged with hand instruments to a size Nos. 30–40 fie Irrigants are emitted from cords on the power source and travel down the file into the canal to be energized by the vibrations

Advantages of Ultrasonics:

• Clean canals free of smear layer and debris
• Enhanced action of NaOCl because of increased temperature and ultrasonic energy.

The disadvantage of Ultrasonics:

Causes transportation of root canal if used carelessly.

Mechanism of Action/Biophysics:

• Cavitation

Cavitation is defined as the growth and subsequent violent collapse of a small gas field with pre-existing inhomogeneity in the bulk fluid. When a vibrating object is immersed in a fluid, oscillations cause a local increase (compression) or decrease (rarefaction) in fluid pressure. During the rarefaction phase, at a certain pressure amplitude, the liquid fails under acoustic stress and form cavitation bubbles.

During the next positive pressure phase, these vapor-filled cavities implosively collapse resulting in shock waves. Cavitation has been shown useful in the removal of deposits in scaling procedure, but during its use in root canal regarding the cavitation phenomenon, the following points are to be considered:

• • The threshold power setting at which this phenomenon occurs is beyond the range that is normally used for the endodontic purpose
  • Cavitation depends on the free displacement amplitude of the fie. During root canal therapy, when fie movement is restricted, this phenomenon is impossible to achieve.

Acoustic streaming;

Acoustic streaming is defined as the generation of time-independent, steady, unidirectional circulation of fluid in the vicinity of a small vibrating object. This flow of the liquid has a small velocity, of the order of a few centimeters per second, but because of the small dimensions involved the rate of change of velocity is high.

This results in the production of large hydrodynamic shear stress around the fire, which are more than capable of disrupting most biological material.

Uses of Endodontics:

Access enhancement:

The use of round or tapered ultrasonically activated diamond-coated tips has been shown to produce smoother shapes of access cavities.

Orifie location:

Ultrasonic instruments are very useful for the removal of chamber calcifications, troughing for canals in the isthmus, and locating the canal orifices.

Irrigation:

Endosonics results in the activation of the irrigating solution in the canal by cavitation and acoustic streaming. This combined with the oscillation of the instrument results in cleaner canals.

Sealer placement:

Sealer is placed using an ultrasonic fie which runs without fluid coolant.

Gutta-percha obturation:

Moreno first suggested the technique of plasticizing gutta-percha in the canal with endodontics. Gutta-percha gets plasticized due to friction being generated. Final vertical compaction is done with hand or finger pluggers.

MTA (Mineral Trioxide Aggregate) placement:

Low-powered ultrasonics can be used to vibrate the material into position with no voids.

Endodontic retreatment:

• Intraradicular postremoval:

Ultrasonics help in the removal of the post by activating tip of the ultrasonic instrument against the metal post. The ultrasound energy transfers to the post and breaks down the luting cement resulting in the loosening of the post

• Gutta-percha removal:

Endosonics alone or with solvent helps in removing gutta-percha from canals

• Silverpoint removal:

Krell introduced a conservative approach for the removal of silver points. In this, a fie H-fie is placed into the canal alongside the silver point. The file is then activated by the ultrasonic tip and slowly withdrawn. Ultrasonics with copious irrigation along with gentle up and down strokes is quite effctive in the removal of silver points, separated files, burs tips, etc.

Instrument Deformation And Breakage

An unfortunate thing about NiTi instruments is that their breakage can occur without any visible sign of unwinding or permanent deformation, that is, visual examination is not a reliable method for evaluation of any NiTi instrument. There are two modes of rotary instrument separation, namely, torsional fracture and flexural fracture.

Torsional Fracture:

A torsional fracture occurs when the torque limit is exceeded. Term torque is used for forces which act in a rotational manner. According to Marzouk, torque is the ability of the handpiece to withstand lateral pressure on a revolving tool without reducing its speed or cutting effiency. The amount of torque is related to the mass of the instrument, canal radius, and apical force when worked in the canal.

As the instrument moves apically, the torque increases because of the increased contact area between the fie and canal wall. Theoretically, an instrument used with high torque is very active, but the chances of deformation and separation increase with high torque. Thus, as the fie advances further into the canal, pressure should be reduced to decrease torque.

Depending on the manufacturer and condition of the handpiece, each handpiece has a different degree of effctiveness depending upon the torque values.

Role of Handpiece:

Handpiece is a device for holding instruments, transmitting power to them, and positioning them intraorally. Both speed and torque in a handpiece can be modified by the incorporation of a gear system. Various types of gear systems can be incorporated in the handpiece but the gearing is limited by the need to maintain the drive concentrically through the handpiece and the head.

Torque control motors allow the setting of torque produced by the motor. In low torque control motors, torque values set on the motor are less than the value of torque at the deformation and separation of the instruments. Whereas in high torque motors, torque value is higher as compared to torque at deformation and separation of the rotary instruments.

During root canal preparation, all the instruments are subjected to different levels of torque. If the torque level is equal or greater than the torque at deformation, the instrument will deform or separate. Thus, with low torque control motors, the motor will stop rotating and may even reverse the direction of rotation when the instrument is subjected to a torque level equal to the torque value set at the motor.

By this, instrument failure can be avoided. In high-torque motors, instruments may deform or separate before the torque value of the motor is achieved. So, we can say that torque control is an important factor to reduce NiTi fracture.

Flexural Fracture:

When an instrument rotates in a curve, it gets compressed on the inner side of a curve and stretched on the outer side of the curve. With every 180° of rotation, the instrument flexes and stretches again and again resulting in cyclic fatigue and subsequent fracture of the instrument.

In large-size fields because of more metal mass, more of tensile and compressive forces occur resulting in early fatigue of the instrument. Elastic and fracture limits of NiTi rotary instruments are dependent on the design, size, and taper of the instrument. This to prevent instrument deformation and fracture, the right torque value for each instrument should be calculated.

Sotokowa’s classification of instrument damage:

• Type 1: Bent instrument
• Type 2: Straightening of twisted flutes
• Type 3: Peeling of metal at blade edges
• Type 4: Clockwise twist (partial)
• Type 5: Cracking of instrument along its long axis
• Type 6: Full fracture of instrument

Prevention of Breakage of Instruments when using Nickel–Titanium Rotary Instruments

• Use only torque-controlled electric handpieces for rotary instruments
• A proper glide path must be established before using rotary files, that is, getting the canal to at least size 15 before using them
• Use crown down method for canal preparation. By this apical curves can be negotiated safely
• Frequent cleaning of flies should be done as it reduces the chances that debris will enter the microfractures and result in the propagation of the original fracture and finally the separation
• Do not force the file apically against resistance. The file should be moved smoothly with 1–2 mm deep increments relative to the previous instrument
• Canals should be well lubricated and irrigated to reduce friction between the instrument and dentinal walls
• Dentin mud collected in the canal increases the risk of fracture, it should be cleared of by frequent irrigation
• Discard a fie if it is bent, stretched, or has a shiny spot
• Do not use rotary nickel–titanium files to true working length especially in teeth with S-shaped canals, canals with multiple and sharp curves, and if there is difficult access of orifice because it can place stresses on the instrument which will cross the breaking torque value. In such cases, the apical portion of the canal should be prepared by hand fies
• A fie should be considered disposable when
  • It has been used in curved canals
  • Despite an excellent glide path, it does not cut dentin properly

Two things can be done to reduce the risk of NiTi fracture:

1. Examine the file every time before placing it into the canal
2. Bend the file to at least an 80° angle, every time before placing it into the canal, to see if it will fracture

Instruments Used For Filling Root Canals

Spreaders and pluggers are used to compact the guttapercha into the root canal during obturation. In 1990, ISO/ADA Endodontic Standardization Committee recommended the size of 15–45 for spreaders and 15–140 for pluggers.

Hand Spreader:

• It is made from stainless steel and is designed to facilitate the placement of accessory gutta-percha points around the master cone during the lateral compaction technique
• Hand spreader does not have a standardized size and shape
• It is not used routinely because excessive pressure may cause a fracture of the root.

Finger Spreader

• They are shorter in length which allows them to afford a great degree of tactile sense and allows them to rotate freely around their axis
• They are standardized and color-coded to match the size of gutta-percha points
• They can be manufactured from stainless steel or nickel-titanium
• Stainless steel spreaders may pose difficulty in penetration in curved canals and may cause wedging and root fracture if forced during compaction. They also produce great stress while compaction
• NiTi spreaders are recently introduced spreaders which can penetrate curved canals and produce less stress during compaction. But they may bend under pressure during compaction.
• So, we can say that combination of both types of spreaders, that is, stainless steel and NiTi, is recommended for compaction of gutta-percha, NiTi spreaders in the apical area and stainless steel in the coronal part of the root canal

Hand Plugger:

• The hand plugger has a diameter larger than the spreader and have a blunt end
• It is used to compact the warm gutta-percha vertically and laterally into the root canal
• It is also be used to carry small segments of gutta-percha into the canal during the sectional filing technique
• Calcium hydroxide or MTA-like materials may also be packed into the canals using a hand plugger

Finger Pluggers :

They are used for vertical compaction of gutta-percha. They apply controlled pressure while compaction and have more tactile sensitivity than hand pluggers. Care should be taken with spreaders and pluggers while compacting the gutta-percha in canals.

They should be cleaned prior to their insertion into the canal; otherwise, the set sealer from the previous insertion may roughen their surface and may pull the cone outside the canal rather than packing it. Also, one should discard the instrument when it has become bent or screwed to avoid instrument separation while compaction.

Lentulo Spiral

• Lentulo spirals are used for applying sealer to the root canal walls before obturation
• Available in lengths of 17, 21, and 25 mm
• It has left-handed screw threading so that the sealer flows down to the tip when rotated in low speed.

Endodontic Instruments Conclusion

Since ages, many areas offer many exciting research possibilities to further increase the performance of endodontic instruments by increasing flexibility, bending, and torsional strength of files without compromising the cutting efficiency.

In the case of rotary NiTi instruments, the use of the right speed and torque are stressed for controlled instrumentation. One should not use rotary NiTi files overenthusiastically without a complete understanding of the physical and mechanical properties of NiTi instruments.