Nickel Titanium Instruments for Root Canal Preparation Flashcards
What made up the traditional files?
SS - ISO shape
Define taper
Amount by which the diameter of an instrument increases from tip to handle
What taper do traditional files have?
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
What is the smallest tip size and largest for traditional files?
Smallest 0.06mm
Largest = 1.4mm
What is the cutting flute length of traditional files>
16mm
Traditional file configurations?
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
How are traditional files used?
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
Why are traditional files used?
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
Negatives of SS files?
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
NiTi file positives?
Super elastic metal alloy
= Enhances flexibility and shape memory
= Reduces potential for canal straightening
= Files produced with a greater taper whilst still retaining elasticity
Why is NiTi so flexible?
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
NiTi file taper design?
2 to 6 fold taper are possible due to elasticity and the connection between diameter and stiffness
NiTi file general design?
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
How do NiTi files differ?
Presence of radial lands or not
The rake angle
Presence of grooves
What is a radial land?
What occurs when there is no radial land?
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)
What is the rake angle?
Angle between the leading edge of the cutting surface and the surface being cut
Neg, neural or positive
Most are slightly negative or neutral
What does the presence of grooves allow on the file?
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
How to use NiTi files in practice?
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
What are NiTi files for?
Canal enlargement, not negotiation
What can occur with NiTi files when a canal is large?
Large canal and plenty of space
A glide path already present and WL can be established straight away without coronal 2/3 opening
NiTi file shape?
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
Examples of NiTi systems?
System GT
ProTaper
Profile
RaCe
Name the 6 files of ProTaper
3 shapers - SX, S1, S2
3 finishers - F1, F2, F3
Protaper features?
Progressively tapered filed (variable taper)
Triangular cross section
Active cutting blades
Blunt tip to help the file remain centred on the canal
Shaping file X?
Nine increasingly larger tapers
3.5-19% between D1 and D9
Fixed 2% taper between D10 and D14
S1?
12 tapers from 2 percent to 11 percent between D1 and D14
S2 features?
9 tapers - 4 percent to 11.5 percent between D1 and D14
Protaper universal?
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
List the tip sizes of S1, S2, F, F2, F3
S1 = 0.17 S2 = 0.2 F1 = 0.2 F2 = 0.25 F3 = 0.3mm
Contraindications for using rotary instruments?
Tight or sclerosed canals Very curved canals S-shaped canals Apical hooks Canals with sharp elbows If glide path cannot be formed
Advantages of NiTi techniques?
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
Disadvantages of NiTi?
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
Precautions when using NiTi?
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
Newer developments - M wire?
Thermomechanical treatment
Lower elastic modulus = more flexibility
Higher fatigue resistane
Newer developments - Single file technique?
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%
Newer developments - reciprocating action?
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
