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Indian Dental Academy: will be one of the most relevant and exciting training center with best faculty and flexible training programs for dental professionals who wish to advance in their dental practice,Offers certified courses in Dental implants,Orthodontics,Endodontics,Cosmetic Dentistry, Prosthetic Dentistry, Periodontics and General Dentistry.
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Introduction :
“Man has become the tool of their tools”.
Modern hand instruments, when properly used, produce beneficial results
that are advantageous to both the operator and the patients. It should be
noted that certain results can be satisfactorily achieved only with hand
instruments.
The standadization of the design of hand cutting instruments by the
manufactures has been helpful to the practioner. All the instruments are
identified by a nomenclature and number that describes the size, design and
common clinical usage.
The proficiency and quality of the clinical treatment depend on the
proper selection end use of the cutting instruments; therefore the
nomenclature and design of the operative instruments must be mastered and
adequate number of sharp and sterile instruments should be available for
each clinical procedure.
Metals used in the manufacture of hand instruments :
Carbon steel :
It is an alloy made by the addition of small percentage of carbon to
iron. It is capable of being hardened, softened and tempered. Two varieties
(i) Soft (ii) Hard. It is harder than stainless steel, but when unprotected, it
will rust and corrode. It maintains the been edge under use, so is used for
making blade and actual cutting edge of the instruments. Sterilization by
boiling water and steam under pressure (autoclave) will cause discoloration.
Dry heat can be used.
Stainless metals :
a) Stainless steel :
It is composed of carbon 6 – 10%; chromium 18% and iron 81 –
81.4%. It is extremely hard but requires very careful and precise heat
treatment during manufacture. The resistance to staining of these alloy is
attributed to the formation of a thin coating of transparent oxide on their
surface, therefore it must be kept highly polished at all times to prevent
corrosion. It looses a sharp edge on repeated usage easily as compared to
carbon steel so is used for handle, shank and part of blade.
b) Monel metal :
A natural alloy of nickel, copper and iron, Monel metal contains
approximately nickel 67%, copper 28% and iron 5%. It is markedly resistant
to acids and super heated system.
c) Nichrome :
Nichrome contains chiefly of nickel 60 – 80%, chromium 12 – 20%
and iron 0.26%. It can be subjected to high degree of temperature, doesnot
oxidize easily, and does not maintain a sharp edge.
d) Satellite :
This product is available in severed grades and consists chiefly of
cobalt 65 – 90%, chromium 10.35% with small quantities of tungsten,
molybdenum, iron or nickel. Its chief characteristics are hardness, strength,
density, high melting point, maintainance of cutting edge and resistance to
action of acids.
e) Tarno :
Is made of popular chromium alloy and is used for manipulation of
the cements.
DESIGN CHARACTERISTICS OF HAND CUTTING
INSTRUMENTS :
Parts : A hand instrument consist of the following essential parts.
Handle or shaft : It is mostly straight and octagonal in cross-section and
may be serrated to increase friction for hand gripping. They are available in
various sizes and shapes. Large, heavy handles are not conducive to delicate
manipulation; therefore most instrument handles small in diameter and light.
Most hand instrument handles are a continuation of the shank. If the hand
and blade are separate from the handle and intended to be screamed into it,
the instrument is known as a cone-socket instrument. The advantage with
this cone-socket instrument is that, if the working end is broken, it may be
easily replaced incurring less expense. The disadvantage is it tendency to
loosen at the joint.
Shank : It connects the shaft with the blade or working point. It is usually
tapers from its connection with the point shaft to where the blade begins.
Any angulation in the instruments can be placed at the junction of shaft and
shank.
Blade / Nib : The working end of cutting instrument is called the blade
whereas the working end of the non-cutting instruments such as condenser
is called a nib. The working surface or end of the nib is called a face. It
begins at the angle where the shaft is terminated.
Cutting edge : It is the working part of the instrument. It is usually in the
form of a bevel with different shapes.
Blade angle : It is defined as the angle between the long axis of the blade
and long axis of the shaft.
Cutting edge angle : It is defined as an angle between the margins of the
cutting edge and long axis of the shaft.
INSTRUMENT NOMENCLATURE :
Dr. G.V. Black established a nomenclature for hand instruments,
similar to the biological classification.
1. Order : Purpose of instrument
Eg : excavator or sealer.
2. Suborder : Position or manner of use
Eg : Push, pull
3. Class : From of working end,
Eg : hatchet, chisel.
4. Subclass : Shape of shank
Eg : Monoangle or binangle.
Naming usually moves rom 4 to 1.
INSTRUMENT FORMULA :
Dr. G.V. Black gave an instrument formula that describes the
dimension and angulation of the hand instruments.
The basic formula consists of three units whose measurements are
based upon the metric system.
The 1st figure represents : the width of the blade in tenths of the
millimeter.
The 2nd figure represents : Length of the blade in millimeters.
The 3rd figure represents : Angle which the blade forms with the long
axis of the handle. This angle is expressed in 100th of a circle or centigrades.
These three measurements are sufficient for describing a great
percentage of instruments. However for instruments with their cutting edge
at on angle. Other than a right angle to the long axis of the blade, a fourth
unit, cutting edge angle is added to the basic three unit formula. This
additional number represents the angle formed between the cutting edge and
the long axis of the handle. It is placed in the second position of the formula,
i.e., before the length of the blade for example, a gingival marginal trimmer
has a 4 unit formula.
INSTRUMENT DESIGN :
1. Direct Cutting Instrument :
It is the instrument that force is applied in the same plane as that of
blade and handle. It is called ‘single-planed’ instrument. It may have 2 or
more curve/angle in shank but all are in same plane to handle. It is used as
direct and lateral cutting instrument.
2. Lateral Cutting Instrument :
Are those in which force is applied at a right angle to plane of blade
and handle. They are called ‘Double-planed’ instrument. They have
curve/angle right angled to handle. It is used in only lateral cutting.
3. Contra angling :
To gain access shank 1 or more bends to angle of blade relative to
handle. Its extent depends on length of the blade. So the working point is
moved out of line with the axis of handle. If this occur more than 3 mm
from handle, the instrument is out of balance in lateral cutting motions and
force required to control rotating of instrument. So 1 or more angels given
in shank to keep working point within 3 mm. Principle is called contra
angling length of the blade determined by depth of cavity. Blade angle
determined by accessibility. So greater angle for posterior teeth and incisal
portion of the anterior teeth.
4. Right and left instruments :
Instruments are made right/light by placing bevel on one side of
blade. If the cutting edge down pointing away from operator and bevel on
right side, it is right instruments. If bevel on left side, it is left instrument.
Single planed instrument for direct cutting, the non-beveled side of blade
should be in contact with wall being shaved. For lateral cutting acts, move
instrument in scraping action from beveled side to non-bebelled side of the
blade. in lateral cutting instrument, blade down, cutting edge away, the
instrument have curve directed to right, is right instrument and if the
instrument having curve directed to left is left instrument.
5. Single bevelled instrument :
These are all single planed instrument. Cutting edge right angle to
long axis of shaft. They are designed like carpenter chisel. If the bevel on
the blade away from shaft – distal. If the bevel on blade towards shaft.
Mesial. When these type of instrument have no angle in shank or an angle of
120 or less, they are used in push (direct cutting) or scraping motion
(bevelled to non-bevelled side). If this exceed 120 instrument used in pull
motion (distal, beveled) and push motion (mesially beveled).
6. Bibevelled instruments :
Hatchets and straight chisels – bibevelled. Blade equally beveled both
sides and they are cut by pushing them in the direction of long axis of blade.
7. Triple bevelled instrument :
Bevelling blade laterally together with ends – 3 edges. Mostly single
planed instrument and small one are tripe beveled. This has additional
cutting potential.
8. Circumferentially bevelled :
Occur in double planed instrument. Blade bevelled at all peripheries.
9. Single ended and double ended instrument :
Double ended – Mesial, distal, right, left in same handle. Single
ended – only one specific function.
Balance :
Balance allows for the concentration of force on to the blade without
causing rotation of instrument in the grasps. Balance accomplished by
designing angles of shank so that cutting edge lies within the projected axis
of the handle and nearly coincide with projected axis of handle. For optimal
antirotational design the blade edge must not be off axis by more than 1 – 2
mm.
Sharpness :
Sharpness concentrates the force into a small area of the edge
producing a high stress.
1. Chisels :
These are instruments designed after ordinary carpenter’s tools and
are intended for planning and cleaning. These are characterized by a blade
that terminates in a cutting edge formed by a one sided bevel. Cutting edge
of a chisel is at right angle to the shaft.
There are following types of chisels available
a. Straight chisel : These have a straight blade in line with the handle
and shank. The cutting edge is on one side only.
b. Mon angle chisels : In these, the blade is placed at on angle to the
shaft. It may be mesially (standard) or distally (Reverse) bevelled.
c. Binangle chisels : These have two angles between the shaft and the
blade. It may be mesially or distally bevelled.
d. Triple – angle chisels : These have three angles in the shank and are
usually used to flatten pulpal floor. It may also be mesially or distally
bevelled.
2. Excavators :
They are used for excavation and removal of caries and sharpening or
refinement of the internal parts of the cavity preparation.
Types :
a. Hatchet : A chisel – bladed instrument with a cutting edge in the
plane of the instrument is termed a hatchet. If the blade of a hatchet is at
perpendicular angles to the shaft, the cutting edge would be parallel to
the shaft. These are poised i.e. R & L, with an indented ring on the shank
or shaft of the right instrument. Certain hatchets are bibevelled also with
the cutting edge in the centre.
Application : These are used for delicate cutting within the preparation
especially in incisors.
b. Hoe excavators : A hoe is a descriptive term gives to a form of chisel
in which the angle of the blade more nearly approaches a right angle i.e.
25 centigrade. It is a single planed instrument, which can be distally
bevelled or mesially bevelled and used with pull motion.
Application : These are used for cutting mesial and distal walls of
premolars and molars.
Both hatchets and hoes are used to remove harder varieties of caries
as well as to give form to the internal parts of the cavity preparation.
c. Spoon excavators : In these, the cutting angle is ground to a semi-
circular circumferential bevel and sharpened to a thin edge. These are
available in pairs with the blade of one curved to the right, and the blade
of the other curved to the left. The spoon excavators all double-planed
instruments with right or left cutting movement only.
Application : Used for removal of decayed dentin.
d. Cleoid (claw like) excavator : It is similar to the spoon excavator,
except that the blade resembles a claw, hence the name ‘cleoid’. It is
used in carving amalgam and excavating decay from areas of difficult
access.
3. Special forms of chisels :
These are designed to perform specific functions.
a. Enamel hatchet :
These are used for splitting or clearing undermined enamel in
proximal cavities and on buccal and lingual walls where it is not possible to
use a chisel. The smaller sizes are primarily used in anterior teeth and larger
sizes are mainly used in posterior teeth.
b. Gingival marginal trimmer (G.M.T) : It is a (used for
forming sharp angles in internal parts of preparation) modified form of
hatchet. Two distinct modifications of the basic hatchet design are noted
as :
i) Cutting edge of a hatchet is at a perpendicular angle
to the axis of blade while cutting edge of a gingival margin trimmer is
at an angle other than a perpendicular angle to the axis of the blade
(so a 4 unit formula).
ii) Hatchet has a straight blade, the blade of a G.M.T is
curved.
iii) Hatchet is a single plane instrument while G.M.T
with curved blade is a double plane instrument, so is primarily a
lateral cutting instrument. It is paired with right and left sided bevels.
G.M.T. is used for creating a proper bevel at the gingival floor. It is
also used for trimming the margins of various walls of cavity, preparation.
c. Angle former : It is a modified form of chisel. In this
instrument, the primary cutting edge is sharpened at a angle to the axis of
the blade. The angle of cutting edge to the blade axis is usually 80-850 (4
unit formula). Blade of the angle former is bevelled on the sides also, to
form three cutting edges. The acute cutting angle being directed to the
right or left makes the angle former a paired instrument. Right of the pair
is identified by an indented ring. It is a single planed instrument.
It is used to accentual line and point angles in the internal outline
form. It is frequently used in cavity preparation for cohesive gold to
establish retention form.
d. Wedelstaedt chisel : It is like a straight chisel, but with a slight
vertical curvature in its shank. It is bevelled on one side only which can
be placed mesially or distally.
It is used for cleaving undermined enamel and for shaping walls.
4. Miscellaneous :
a. Dental probes : Various types of probes are available, these
can be straight, curved or graduated (used in periodontology).
b. Knives : Nibs of these instruments carry knife edges faces on
one of their sides only the knives known as finishing knives, amalgam
knives are made in various sizes and shapes.
They are used for trimming off excess filling material on the gingival,
facial or lingual margins of a proximal restoration or trimming and
contouring the surface of a class V restorations.
c. Knives for specific purposes :
Wilson’s knife : In this nib is in a plane at perpendicular angle to that of the
shaft, so that it can be introduced interproximally for use.
Stein’s knife : It has a trapezoidal nib and is used mainly for direct gold
restorations for continuous and margination.
Files :
Nib in files can be foot-shaped, hatchet shaped or parallelogram
shaped with serrations of the serrations are directed away from the handle, it
is a push file, and if the serrations are directed towards the handle, it is a
pull file.
These are used for smoothening of margins; if knives and carvers are
not sufficient to produce the requisite caw surface margins at the gingival
and, files can be used to achieve above said requisite.
INSTRUMENT GRASPS :
It is more than just a manner of holding the instrument and must be
taken quite seriously otherwise bad habits may be acquired that result in loss
of operating efficiency and accumulation of unnecessary strain on the
operator.
Fundamentally, there are four grasps used with hand instruments.
1. Pen grasp : It is similar to the method of holding a pen, except
that the pulps of the thumbs, 1st and 2nd fingers contact the instrument,
while the tip of the 3rd and 4th fingers are placed on the adjoining teeth (as
rests).
The position of 2nd finger is important for good control and thrust to
the instrument. This way, due to greater length of the 2nd finger, the
application point for the force will be near the working point of the
instrument.
2. Inverted pen grasp : This is similar to the pen grasp, but the
hand is rotated so that the palm is facing upwards. It is usually used in
upper teeth. Not used two frequently, but on certain occasions,
depending on the area of operation, type of instrument used and position
of the point and operator, modifications of the inverted pen grasps are
used.
3. Palm and thumb grasp : It is similar to the method of holding
a knife, when cutting a piece of wood. The handle is placed in the palm
of the hand and grasped by the four fingers, while the thumb rests on an
area other than that being operated on. A supporting rest provided by
thumb is necessary because distal control is somewhat insufficient. This
grasp is used when the thumb must rest at some point distant from the
operating site. It may be used on maxillary teeth particularly the right
side, when working form the right rear chair position.
Conclusion :
It has to be remembered that rotary instruments are for gross
reduction, but refinement is brought about best by hand cutting instruments.
Thus with this vision of hand cutting instruments let's strive towards
precision in operative dentistry.
CONTENTS
INTRODUCTION
METALS USED IN THE MANUFACTURE OF HAND
INSTRUMENTS
DESIGN CHARACTERISTICS OF HAND CUTTING
INSTRUMENTS
INSTRUMENT NOMENCLATURE
INSTRUMENT FORMULA
INSTRUMENT DESIGN
INSTRUMENT GRASPS
CONCLUSION
OHP FORMAT OF SEMINAR
COLLEGE OF DENTAL SCIENCES
DEPARTMENT OF CONSERVATIVE DENTISTRY AND
ENDODONTICS
SEMINAR
ON
HAND CUTTING INSTRUMENTS
PRESENTED BY :
Dr. Siddheswaran V.