niti Flashcards
What are traditional files made of?
SS
Follow a standard shape (ISO- international standards organisation)
Hedstrom and K files
Set taper of 2% (each mm increases by 0.02mm)
Smallest (06) largest (140)
Cutting flutes 16mm long
Final cutting part 0.32mm wider than tip
What are k files?
Created by twisting a wire to produce cutting flutes
Square/triangular in cross section
Flexible k files- SS/NiTi
What are hedstrom files?
Made by grinding a tapered blank
Round in cross section w a series of cones w cutting edges
V aggressive
How do you use k files?
Watch wind pull (30 degree, useful for creating glide path and preparing apical third)
Balanced force (60 degree clockwise then 120 degree anti-clockwise w apical pressure, fractures off dentine lodged in flutes, useful preparing apical third)
How do you use hedstrom files?
Up and down circumferentially in a passive canal
What are disadvantages of traditional files?
Produces narrow canals
Increasingly inflexible in larger sizes
Rarely a 02 taper
Techniques use a lot of instruments
Reciprocating fashion (continual rotation=fracture)
Push-pull creates ledges and pushes debris into canal
Takes a long time
What is NiTi?
Super elastic metal alloy
Enhanced flexibility and shape memory reduces potential for canal straightening
Allows files to have greater taper still w elasticity
Why is NiTi so flexible?
It exists in 2 forms (martensite and austenite)
Application of outer stress causes martensite to form
When stress is released it transforms back to austenite and to its original shapes
So can be strained several times more that ordinary metal alloys w/o plastic deformation
What is the NiTi file design?
2 to 6-fold taper
To be used in continuous motion
Can’t be twisted into shape (machined- more expensive)
Cutting edges can be flattened, modified, shortened
Can vary depth of groove, helical angle, pitch or taper
Tips of files still conform to ISO
Tips are non-cutting to allow files to remain centred
Can have radial lands
Rake angle slightly positive or neutral
Grooves can remove debris
Rotary are more efficient but produce thicker smear layer in apical third
What is a radial land?
A flat area which prevents the file from locking into the dentine- cutting occurs through a planing action
What is a rake angle?
Angle between the leading edge of the cutting tool and the surface being cut
Most traditional have a slightly negative
How do we use NiTi?
Straight line acccess
Files are for canal enlargement not negotiation
CROWN DOWN technique
Hand files to size 20
Shapers to open canal
Establish working length
Glide path to full WL
Shapers then finishers to full WL
Apex gauged
Can skip 2/3s if v wide canal
What shape does NiTi produce?
Profile (set taper)
Variable taper (upside down Eiffel Tower)- can use fewer files
System GT, ProTaper etc
What do ProTaper?
Variable taper
Triangular cross section
Active cutting blades
Blunt tip to centre file
S1- 12 tapers (coronal third)
S2- 9 tapers (middle third)
SX- shorter and 9 tapers
Fixed taper-
F1- 7% (20)
F2- 8% (25)
F3- 9% (30)
F4- 6% (40)
F5- 5% (50)
~apical third
What are contraindications for rotary?
Should be using w care (glide path created for rotary)
Tight/sclerosed canals
V curved canals
S-shaped canals
Apical hooks
Sharp elbows
If glide path can’t be formed
