ENDODONTIC INSTRUMENTS

1. Endodontic instruments

2. Broaches
• Barbed broaches are produced in a variety of sizes and
color codes
• Manufactured by cutting sharp, coronally angulated
barbs into metal wire blanks
• Broaches are intended to remove vital pulp from root
canals, and in cases of mild inflammation, they work well
for severing pulp at the constriction level in toto
• Use of broaches has declined since the advent of nickel-
titanium rotary shaping instruments, but broaching
occasionally may be useful for expediting procedures and
removing materials (e.g., cotton pellets or absorbent
points) from canals

4. K-Files
• K-files were manufactured by twisting
square or triangular metal blanks along
their long axis, producing partly horizontal
cutting blades
• Noncutting tips, also called Batt tips, are
created by grinding and smoothing the
apical end of the instrument
• NiTi K-files are extremely flexible and are
especially useful for apical enlargement in
severe apical curves
• They can be precurved, but only with
strong overbending; this subjects the file
to excess strain and should be done
carefully
• Because of their flexibility, the smaller NiTi
files (sizes up to #25) are of limited use

5. • ISO-normed K and Hedström files are available in
different lengths (21, 25, and 31 mm), but all have a
16-mm-long section of cutting flutes
• The cross-sectional diameter at the first rake angle
of any file is labeled D0
• The point 1 mm coronal to D0 is D1, the point 2
mm coronal to D0 is D2, and so on up to D16
• The D16 point is the largest diameter of an ISO-
normed instrument
• Each file derives its numeric name from the
diameter at D0 and is assigned a specific color code

6. Taper 0.02 mm/mm
Length of working part 16 mm
15 20 25 30 35 40 Normed instrument tip sizes

7. • Another aspect of ISO files is the standard
taper of 0.32 mm over 16 mm of cutting
blades, or 0.02 mm increase in diameter per
millimeter of length (#.02 taper)
• The tip size increases by 0.05 mm for file sizes
#10 to #60; for sizes #60 to #140, the absolute
increase is 0.1 mm

8. Hedstroem Files
• Hedström files are milled from round,
stainless steel blanks
• They are very efficient for translational
strokes but rotational
• Working movements are strongly
discouraged because of the possibility
of fracture
• Hedström files up to size #25 can be
efficiently used to relocate canal
orifices and, with adequate filing
strokes, to remove overhangs
• On the other hand, overzealous filing
can lead to considerable thinning of
the radicular wall and strip
perforations
• As with stainless steel K-files,
Hedström files are single-use
instruments

9. c
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10. Gates-Glidden Drills
• GG instruments are manufactured in a set and
numbered 1 to 6 (with corresponding diameters
of 0.5 to 1.5 mm); the number of rings on the
shank identifies the specific drill size
• GG instruments are available in various lengths
and made by several manufacturers
• Each instrument has a long, thin shaft with
parallel walls and a short cutting head

12. • GG drills are side-cutting instruments with
safety tips; they can be used to cut dentin as
they are withdrawn from the canal (i.e., on
the outstroke)
• GG instruments should be used only in the
straight portions of the canal, and they should
be used serially and passively

13. • Two procedural sequences have been
proposed: with the step-down technique, the
clinician starts with a large drill and progresses
to smaller ones; conversely, with the step-
back technique, the clinician starts with a
small drill and progresses to larger ones
• GG instruments are inexpensive, safe, and
clinically beneficial tools

14. • High revolutions per minute (rpm), excessive
pressure, an incorrect angle of insertion, and
the use of GG instruments to aggressively drill
into canals have resulted in mishaps such as
strip perforation
• Cyclic fatigue may cause GG instruments to
fracture when used in curved canal areas, and
the short cutting heads may fracture with high
torsional loads

15. • Gates-Glidden drills may be used safely and to
their fullest potential at 750 to 1500 rpm
• As with nickel-titanium rotary instruments, GG
drills work best when used in electric gear
reduction hand pieces rather than with air
motors

16. Nickel-Titanium Rotary Instruments
• Manufactured by a grinding process, although
some are produced by laser etching and others
by plastic deformation under heating
• Surface quality is important because cracks that
arise from superficial defects play important
role in instrument fracture
• NiTi instruments may have characteristic
imperfections such as milling marks, metal
flashes, or rollover

17. • Thermal process introduced in the
manufactureof NiTi instruments.
• This process is believed to respect the grain
structure of the material better and does not
introduce milling marks or other surface
irregularities

18. • Surface irregularities may also provide access to
corrosive substances, most notably sodium
hypochlorite (NaOCl)
• Some studies have suggested that chloride
corrosion may lead to micropitting and possibly
subsequent fracture in NiTi instruments
• Corrosion of NiTi instruments used in the clinical
setting, therefore, might not significantly
contribute to fracture except when the
instruments are immersed in warmed NaOCl for
longer than 60 minutes

19. Different NiTi rotary systems used
• LightSpeed and LightSpeed LSX Instruments
• GT and GTX Files
• HERO 642, Hero Shaper
• ProTaper Universal
• K3
• FlexMaster
• RaCe, Bio Race
• EndoSequence
• Twisted File

20. Fracture Mechanisms
• Instruments used in rotary motion break in
two distinct modes
– Torsional: Torsional fracture occurs when an
instrument tip is locked in a canal while the shank
continues to rotate, thereby exerting enough
torque to fracture the tip
– Flexural: flexural fracture occurs when the cyclic
loading leads to metal fatigue