Operative dentistry aje qualtrough, jd satterthwaite la morrow, pa brunton

Hand instruments
Traditionally, hand files were manufactured by twisting square or 
triangular shafts of metal around their long axis. Recently, computer-
assisted machining has enabled the modification of existing file
geometries. The principal endodontic instruments are files.
Reamers
Reamers are made from stainless steel and are of square (smaller
sizes) or triangular (larger sizes) cross-section. The blank is twisted to
create an instrument with cutting flutes at predetermined intervals.
These instruments have the disadvantage in that they are relatively
inflexible and therefore are restricted to the shaping of canals of round
cross-section.
Files
A wide variety of hand files are available, these differ in their
configuration and mode of action. Below is a summary of the features
of the more common types of files.
Hedström files (Fig. 3.6)
• These are machined from a round tapered blank. A spiral groove 
is cut into the shank to produce a sharp blade. They are less flexible
than K-type instruments and only the smaller sizes may be pre-
curved owing to the risk of deformation or fracture.
• Cutting occurs during withdrawal of the file from the canal.
• Hedström files are very efficient in a planing action for removal of
dentine.
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Chapter 3
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Principles of endodontics


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• They should be inserted slowly with avoidance of rotation (except
for a slight rocking motion to aid negotiation).
• They should not be rotated anticlockwise.
• The files are used by withdrawal up each aspect of the root canal in
a circumferential filing motion.
K-type files (Fig. 3.6)
• These are probably the most widely used of the ‘classical’ designs
of root canal instrument.
• K-type files are formed by twisting a tapered steel wire of square 
or triangular cross-section. This method of manufacture results 
in work hardening and therefore produces a ‘springy’ instrument
with enhanced stiffness for insertion into narrow canals but it will
then elastically recoil against the canal wall. These instruments are
normally used with a filing action.
• K-type files are less aggressive in planing than the Hedström
design.
K-Flex files
• Their cross-sectional geometry is rhomboid to produce alternate
high and low flutes so the action is to cut and clean. The high flutes
cut and the low flutes allow space for dentinal shavings and more
efficient debris removal.
• This cross-sectional configuration results in a reduction in metal,
producing increased flexibility without a significant reduction in
strength.