Classifiation Of Endodontic Instruments

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).

Read And Learn More: Endodontics Notes

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.