Nickel titanium instruments for RCT

Question 1

What are traditional files made out of? What shape are they?

Answer 1

Stainless steel

Standard shape - ISO (International standards organisation)

Question 2

What is the taper on an instrument?

Answer 2

The amount by which the diameter of an instrument increases from tip to handle

Question 3

Taper on traditional files

Answer 3

Set taper of 2% (commonly referred to as ‘02 taper’

This means that for each mm from tip the diameter of file increases by 0.02mm

Question 4

Sizes of traditional files

Answer 4

 Traditional hand files are colour-coded and have a tip
size which increases in set increments
 Smallest tip size is 0.06mm (an 06 file) through
0.08, 0.10, 0.15 etc, etc
 The largest tip size is 1.40mm (a 140 file)
 All traditional files have cutting flutes 16mm long
 So due to the 2% taper, the final cutting part of the
instrument is 0.32mm wider than the tip (ie 16x0.02)

Question 5

Three main configurations of traditional files

Answer 5

K-files
Flexible K-files
Hedstrom files

Question 6

K-files shape

Answer 6

 Created by twisting a wire to produce cutting flutes

 Can be square or triangular in cross-section

Question 7

Flexible K-files shape and material

Answer 7

Similar to K-files but their cross-sectional design
enables them to be more flexible
 Can be made from stainless steel or nickel-titanium
(NiTi)

Question 8

Hedstrom files shape

Answer 8

 Made by grinding a tapered blank
 Round in cross-section with a series of cones with
cutting edges
 Very aggressive
(break quite easily, don’t use for apical prep)

Question 9

2 main ways in which traditional files are used

Answer 9

Watchwind-pull
Balanced force
(& circumferential technique)

Question 10

Watchwind-pull

Answer 10

 30 degree ‘watchwinding’ each way followed by a pulling
action
 Useful for both negotiating the canal and preparing the apical
third

Question 11

Balanced force method

Answer 11

 60 degree clockwise followed by 120 degree anti-clockwise
with apical pressure
 Fractures off dentine which has become lodged in the flutes
 Useful for preparing the apical third

Question 12

Disadvantages of traditional stainless steel files

Answer 12

 They have a tendency to produce canal
shapes which are narrow
 They become increasingly inflexible in the
larger sizes
 Root canals are rarely an 02 taper
 The traditional preparation techniques use a lot of instruments
 Must be used in a ‘reciprocating fashion – if
they are continually rotated they will fracture
 The push-pull action often used with traditional files has
a tendency to create ledges
 This action can also push debris into the canal causing blockages
 It takes a long time to prepare a canal with traditional files/ techniques

Question 13

Benefits of traditional stainless steel files

Answer 13

Good at negotiating canals and producing a glide-path

Question 14

Nickel titanium (NiTi)

Answer 14

 NiTi is a super-elastic metal alloy
 This property provides enhanced flexibility and shapememory
 This reduces the potential for canal-straightening
 It also allows files to be produced with greater-taper,
whilst still retaining elasticity

Question 15

Elastic deformation
Plastic deformation
Elastic modulus

Answer 15

Elastic: file can bend quite significantly and then will return to normal shape
Plastic: do not want to exceed file’s flexibility so it won’t go back to original shape
Modulus: NiTi is much higher

Question 16

Why is NiTi so flexible?

Answer 16

NiTi exists in 2 forms with different
properties
 Martensite
 Austenite
The application of outer stress causes martensite to form
When the stress is released the martensite transforms back into austenite and the material returns to its original shape
As a result, super-elastic NiTi can be strained several times more than ordinary metal alloys without plastic
deformation

Question 17

NiTi file design

Answer 17

 Due to elasticity of NiTi and connection between diameter & stiffness, NiTi files with 2 - 6x taper are possible
 NiTi files are designed to be used in continuous motion
 To produce NiTi files they cannot be twisted to shape, so therefore have to be machined – this increases the cost
 Most systems flatten, modify or shorten the cutting edges and vary the depth of groove, helical angle, pitch or taper to prevent the instrument from screwing and binding in the
canal wall
 The tips of NiTi files still conform to the ISO tip size
standard
 The tips are usually non-cutting, which allows the files to remain centred within the canal

Question 18

Main difference between different NiTI files

Answer 18

Presence or not of ‘radial lands’

• flat area which prevents file from locking into dentine - cutting occurs through planing (acting passively) action
• some systems do not having radial lands and are more aggressive, with sharp cutting edges (acting actively)

Question 19

The rake angle

Answer 19

 The rake angle is the angle between
the leading edge of the cutting tool and the surface being cut
 A rake angle can be negative, neutral or positive
 Most traditional endodontic instruments have a slightly
negative rake angle
 Most NiTi files have a slightly negative or neutral rake angle

Question 20

NiTi grooves

Answer 20

 The presence of grooves allows efficient removal of debris from the root canal
 Most studies show that NiTi (rotary) systems are more efficient at removing superficial debris
 They do however produce a thicker smear layer, particularly in the apical third

Question 21

Using NiTi files in practice

Answer 21

 Proper straight line access should initially be achieved
 The files are for canal enlargement, not canal negotiation
 Use a ‘crown-down’ technique
 If the canal is large enough and there is plenty of space e.g. a palatal root of an upper first molar, a
glide path is already present and working length
can be established straight away without coronal
two-thirds opening

Question 22

‘crown-down’ technique

Answer 22

 Hand files should therefore be used to create a glide path up to a minimum of size 15, but ideally size 20 K-file at 2/3
working length
 ‘Shapers’ are then used to open the canal up to this length
 Establish working length
 Establish glide path to full working length
 ‘Shapers’ then ‘finishers’ used to prepare canal to full working length
 Apex is gauged to determine size of final file

Question 23

What shape do NiTi files produce?

-fixed tapers

Answer 23

 Initially, NiTi systems used a variety of files with different taper (fixed taper of 04, 06,08,10,12)
 After coronal access and creation of a glide path the different files (with different taper) were used to achieve a gradually tapering preparation, with a wider taper coronally with decreasing taper towards the apex

Question 24

What shape do NiTi files produce?

-variable taper

Answer 24

Following fixed tapers, the concept of ‘variable taper’ was
introduced
 Files no longer had one set taper, but varied the
amount of taper, starting small at the tip of the file and gradually increasing towards the shaft
 This file design is sometimes referred to as the ‘upside down Eiffel Tower’
 Produce a canal preparation with varying amounts of taper, but using fewer files

Question 25

NiTi systems on the market

Answer 25

 System GT
 ProTaper (used in the hospital)
 Profile
 RaCe
 K3
 Quantec
 FlexiMaster

Question 26

ProTaper system

Answer 26

The main ProTaper system uses six files:
 3 ‘shapers’ (SX, S1, S2)
-do what gates glidden do
 3 ‘finishers’ (F1, F2, F3) 
ProTaper uses progressively tapered
files (variable taper)
It has a triangular cross-section
It has active cutting blades
It has a blunt tip to help the file remain centred on the canal

Question 27

SX file

Answer 27

Variable taper

Increasingly larger tapers

Question 28

S1 file

Answer 28

Variable taper
-12 taper from 2% to 11%
Shapes the coronal third

Question 29

S2 file

Answer 29

Variable taper
-nine taper from 4% to 11.5%
Shapes the middle third of the canal

Question 30

Finishing files

Answer 30

These do step-back technique
Fixed taper
Shape the apical part of the canal
7%, 8% and 9%
F1: 20
F2: 25
F3: 30
(they'res also F4 [40], and F5 [50])

Question 31

Protaper for hand use

Answer 31

SX, S1 and S2

Question 32

Contra-indications for using rotary

Answer 32

 ‘Tight’ or sclerosed canals
 Very curved canals
 S-shaped canals
 Apical hooks
 Canals with sharp ‘elbows’
 If a Glide Path cannot be formed

Question 33

X-Smart

Answer 33

Safety
-precise and controlled speed
-torque control and autoreverse
Ergonomy
-no foot pedal
-works on batteries
-micro-head (access)

Question 34

Advantages of NiTi techniques

Answer 34

 Less canal transportation
 Flexible, therefore better at preparing curved canals
 Good ‘deep shape’
 Less debris extrusion
 Faster than traditional files
 Fewer files used
 More predictable results

Question 35

Torque

Answer 35

Amount of resistance motor will allow before the handpiece will stop going

Question 36

Disadvantages of NiTi - fracture

Answer 36

 Torsional failure is caused by ‘unwinding’ of the file, usually as a result of using too much apical force during instrumentation.
 Flexural fatigue results from repeated flexing usually from use in overly-curved canals.
 Torsional failures are more common than flexural failures

Question 37

Precautions when using NiTi

Answer 37

 Always have a glide path
 Work instruments to light resistance and never
force them
 Light ‘pecking’ action
 Do not engage tight curves
 Discard when signs of stress occur

Question 38

M-wire

Answer 38

Newer development
 Proprietary thermomechanical treatment
 Lower elastic modulus and therefore more flexibilty
 Higher fatigue resistance due to more efficient superelastic behaviour
 Studies suggest that endodontic instruments made with this wire are more flexible and fatigue resistant than those made with conventionally processed NiTi wires

Question 39

Single-file technique

Answer 39

Newer development
 Due to concerns over cost of files and decontamination a single file system was developed
 This followed a study which showed successful outcomes with the use of a ProTaper F2 file only in the preparation of root canals in vitro
 These systems use M-wire to reduce the risk of distortion and fracture
 Can reduce shaping of the canal time by up to 50%

Question 40

Reciprocating action

Answer 40

Newer development
 Systems have recently been developed which use a reciprocating action rather than continuous 360 degree action
 Reciprocating action is a clockwise motion (eg144 degrees) followed by an
anti-clockwise motion (eg 72 degrees)
 The reciprocating action is reported to reduce the risk of distortion and fracture
 M-wire is used
 One system (WaveOne) uses one file, with a choice of three depending on the
size of the canal