NiTi instruments for root canal preparation

Question 1

Taper of file

Answer 1

Amount by which diameter of an instrument increases from tip to handle
2%
Every mm from tip, diameter increases by 0.02mm

Question 2

Tip sizes
Length
Smallest
Largest

Answer 2

Increase in set increments
16mm long
Smallest - 0.06mm
Largest 1.40mm

Question 3

Three types of traditional

Answer 3

K-files

Flexible k-files - SS or NiTi

Hedstrom files - will break in narrow canals or using fine prep

Question 4

2 methods of use of traditional files

Answer 4

Watchwind pull

• 30 degree winding each way and then pulling
• negotiating canal and preparing apical 1/3

Balanced force

• 60 degree clockwise followed by 120 degree AC with apical pressure
• fractures off dentine lodged in flutes
• apical 1/3

Question 5

Advantages of traditional

Answer 5

Traditional files still fulfil and essential role in endo
Can be used very effectively to produce satisfactory canal shaping during chemomechanical canal prep
- Essential to negotiate canals and produce glide path

Question 6

Disadvantages of traditional

Answer 6

• 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 7

NiTi - properties

Answer 7

Super elastic alloy
Enhanced flexibility and shape memory
Reduces chance of canal straightening
Allows files to be created with greater taper whilst retaining elastic modulus

Question 8

Why is NiTi so flexible

Answer 8

MArtenite/Austenite forms
Forms martensite when outer stress applied
Transforms back to austenite when stress is released
Super elastic NiTi can be strained several times more without deformation

Question 9

NiTi file design

Rake angle
Most have

Presence of grooves allows
Will generally follow canal because

Disadvantages of NiTi file

Answer 9

Angle between the leading edge of the cutting tool and the surface being cut 
Rake angle can be -ve, +ve or neutral 
Most have slightly -ve angle
Efficient removal of debris 
from the root canal 
Non-cutting edge

Produce thicker smear layer in apical area
Non-cutting edge
May or may not have radial lands - absence means more likely to get stuck

Question 10

Using files in practice

Which technique should be utilised

Answer 10

Files are for canal ENLARGEMENT not negotiation

Crown DOWN technique

Question 11

If canal has plenty of space and glide path already present

Answer 11

WL can be established without opening 2/3

Question 12

Shape produced by NiTi files

Answer 12

Gradually tapering prep with wider coronal and decreasing taper towards apex

Question 13

ProTaper

Answer 13

6 files
3 shaping - SX S1 S2 - CORONAL 2/3
3 finishers - F1, F2, F3 - STEPBACK

Question 14

Properties of Protaper and mechanism

Answer 14

Progressively tapered files
Triangular cross section
Active cutting blades
Blunt tip to help file remain centred

Question 15

Function of shaping files

Answer 15

Shape coronal and middle third of canal

Question 16

Contraindications for using rotary

Answer 16

Tight/sclerosed canals
Very curved canals
S shaped canals
Apical hooks
Canals with sharp bends 
If a glidepath cannot be formed

Question 17

Advantages of NiTi techniques

Answer 17

Less canal transportation
Flexible 
Good deep shape
Less debris extrusion 
Faster
Fewer files used
More predictable

Question 18

Disadvantages of NiTi - fracture

Answer 18

Torsional failure - UNWINDING of file due to too much force
Flexural fatigue repeated flexing usually from overly curved canals
Torsional more common than flexural

Question 19

Crown Down technique

Answer 19

Hand files 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’ - S1, S2, SX are then used to open the canal up to this length
Establish working length
Establish glide path to full working length
‘Finishers’ used to prepare canal to full working length (STEPBACK)
 Apex is gauged to determine size of final file

Question 20

If canal is large enough and there is plenty of space

Answer 20

Glide path is already present and so WL can be established without opening coronal 2/3

Question 21

Advantages of X-Smart Rotary

Answer 21

Precise and controlled speed
Torque control 
Ergonomic 
Works on batteries 
Microhead