Nickel Titanium Instruments for Root Canal Preparation

Question 1

What made up the traditional files?

Answer 1

SS - ISO shape

Question 2

Define taper

Answer 2

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

Question 3

What taper do traditional files have?

Answer 3

Have a set taper of 2%
= For each mm from the tip the diameter of the file increases by 0.02mm
The final cutting part of the instrument is 0.32mm wider than the tip

Question 4

What is the smallest tip size and largest for traditional files?

Answer 4

Smallest 0.06mm

Largest = 1.4mm

Question 5

What is the cutting flute length of traditional files>

Answer 5

16mm

Question 6

Traditional file configurations?

Answer 6

K files
- Square or triangular in cross section

Flexible K files

• Cross sectional design enables them to be more flexible
• S.S or NiTi

Hedstrom files

• Round in cross section with a series of cones with cutting edges
• Very aggressive

Question 7

How are traditional files used?

Answer 7

Watchwind-pull

• 30 degree watch winding each way followed by a pulling action
• Useful for negotiating the canal and preparing the apical 3rd

Balanced force

• 60 degree clockwise followed by 120 degree anticlockwise with apical pressure
• Fractures off dentine which has been lodged into flutes
• Useful for preparing the apical third

Question 8

Why are traditional files used?

Answer 8

Traditional files can be used very effectively to produce canal shaping during chemomechanical canal preparation
Used to negotiate the canals and produce a glide path

Question 9

Negatives of SS files?

Answer 9

Have a tendency to produce canal shapes which are too narrow
Become increasingly inflexible in the larger sizes
Root canals are rarely an o2 taper
Traditional preparation techniques use a lot of instruments
Must be used in a reciprocating fashion - if they are continually rotated they will fracture
Push pull action has a tendency to create ledges and pushes debris into the canal causes blockages

Question 10

NiTi file positives?

Answer 10

Super elastic metal alloy
= Enhances flexibility and shape memory
= Reduces potential for canal straightening
= Files produced with a greater taper whilst still retaining elasticity

Question 11

Why is NiTi so flexible?

Answer 11

NiTi exist in 2 forms with martensite and austenite properties
Application of outer stress = martensite forms
Stress released - martensite is transformed back to austenite and the material returns back to its original shape
= NiTi can be strained several times more than ordinary metal alloys without plastic deformation

Question 12

NiTi file taper design?

Answer 12

2 to 6 fold taper are possible due to elasticity and the connection between diameter and stiffness

Question 13

NiTi file general design?

Answer 13

Use in continuous motion
Cannot be twisted into shape = machined = more expensive
Systems modify the cutting edges to prevent the instrument from screwing and binding in the canal wall
Tips are usually non-cutting = files remain centred within the canal

Question 14

How do NiTi files differ?

Answer 14

Presence of radial lands or not
The rake angle
Presence of grooves

Question 15

What is a radial land?

What occurs when there is no radial land?

Answer 15

No radial land - more aggressive with sharp cutting edges, act actively
Radial land = flat area which prevents the file locking into dentine - cutting occurs through planing action (acting passively)

Question 16

What is the rake angle?

Answer 16

Angle between the leading edge of the cutting surface and the surface being cut
Neg, neural or positive
Most are slightly negative or neutral

Question 17

What does the presence of grooves allow on the file?

Answer 17

Efficient removal of debris from the root canal
NiTi rotary systems are more efficient at removing superficial debris
BUT produce a thicker smear layer, particularly in the apical 3rd

Question 18

How to use NiTi files in practice?

Answer 18

Achieve straight line access
Files are for canal enlargement, not canal negotiation
Use a crown-down technique
- Use hand files to create a glide path up to a minimum of size 15, but ideally size 20 K file at 2/3 working length
- Shapers used to open the canal at this length
- Establish working length
- Establish glide path to full working length
- Shapers then finishers used to prepare canal to FWL
Apex is gauged to determine size of final file

Question 19

What are NiTi files for?

Answer 19

Canal enlargement, not negotiation

Question 20

What can occur with NiTi files when a canal is large?

Answer 20

Large canal and plenty of space

A glide path already present and WL can be established straight away without coronal 2/3 opening

Question 21

NiTi file shape?

Answer 21

Initially variety of files with set taper - 04,06,08,10,12)
E.g. profile = set taper NiTi systems
Variable taper introduced = small at tip and gradually increased towards the shaft
Multi-tapered instruments produce a canal prep with varying amounts of taper but use fewer files

Question 22

Examples of NiTi systems?

Answer 22

System GT
ProTaper
Profile
RaCe

Question 23

Name the 6 files of ProTaper

Answer 23

3 shapers - SX, S1, S2

3 finishers - F1, F2, F3

Question 24

Protaper features?

Answer 24

Progressively tapered filed (variable taper)
Triangular cross section
Active cutting blades
Blunt tip to help the file remain centred on the canal

Question 25

Shaping file X?

Answer 25

Nine increasingly larger tapers
3.5-19% between D1 and D9
Fixed 2% taper between D10 and D14

Question 26

S1?

Answer 26

12 tapers from 2 percent to 11 percent between D1 and D14

Question 27

S2 features?

Answer 27

9 tapers - 4 percent to 11.5 percent between D1 and D14

Question 28

Protaper universal?

Answer 28

S1 and S2 can be used to shape the coronal and middle 3rd of the canal
Finishing files F1-F5 shape the apical part of the canal

Question 29

List the tip sizes of S1, S2, F, F2, F3

Answer 29

S1 = 0.17
S2 = 0.2
F1 = 0.2
F2 = 0.25
F3 = 0.3mm

Question 30

Contraindications for using rotary instruments?

Answer 30

Tight or sclerosed canals
Very curved canals
S-shaped canals
Apical hooks
Canals with sharp elbows
If glide path cannot be formed

Question 31

Advantages of NiTi techniques?

Answer 31

Less canal transportation
Flexible - better at preparing curved canals 
Good deep shape
Less debris extrusion
Faster than traditional files
Fewer files used
More predictable results

Question 32

Disadvantages of NiTi?

Answer 32

FRACTURE
Torsional failure due to unwinding of the file, usually due to too much apical pressure during instrumentation
Flexural fatigue from repeated flexing usually from use in overly curved canals
Torsional failure more common

Question 33

Precautions when using NiTi?

Answer 33

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 34

Newer developments - M wire?

Answer 34

Thermomechanical treatment
Lower elastic modulus = more flexibility
Higher fatigue resistane

Question 35

Newer developments - Single file technique?

Answer 35

Due to concerns over cost of files and decontamination
Use an M wire to reduce risk of distortion and fracture
Can reduce shaping of the canal time by 50%

Question 36

Newer developments - reciprocating action?

Answer 36

Rather than continuous 360 degree action
Reciprocating action is a clockwise action followed by an anti-clockwise motion = decrease risk of distortion and fracture
M wire used