hand instruments
TRANSCRIPT
HAND CUTTING INSTRUMENTS IN OPERATIVE DENTISTRY
CONTENTS• Introduction• Materials used in manufacturing hand
instruments• Instrument design• Balance and contrangling• Instrument nomenclature• Instrument formula• Single and double planed instrument• Direct and lateral cutting instrument• Bevels• Right and left instruments• Single and double ended instruments• Classification
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• Instrument grasps• Rests• Instrument sharpening• Instrument sterilization• Conclusion• References
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INTRODUCTION• The term “Instrument” refers to a tool or a
device used for specific purpose or work.• Instruments used in dentistry varied from the
time they came into existence. Some are still used today while some have been modified and some others have become obsolete.
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• Earlier, Removal and shaping of tooth structure was an essential part of restorative dentistry, was difficult and time consuming accomplished entirely by the use of hand instruments.
• The advent of modern high speed instruments has eliminated the need for many hand instruments. Nevertheless, certain hand instruments still remain an indispensable part in the performance of quality restorative dentistry.
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MATERIALS
• Hand cutting instruments are manufactured from two main materials:Carbon steel and stainless steelCarbon steel: Alloy of iron with small
percentages of carbon(0.5-1.5%) Other ingredients are manganese 0.2%,
silicone0.2%. Carbon steel is harder than stainless steel, but
when unprotected will corrode. It maintains the sharp edge under use, so is used for making blade and actual cutting edge of the instrument.
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• Stainless steel : iron chromium :12-30% carbon :0.15%• Chromic oxide – prevents corrosion..• Loses keen edge during use much more quickly
than does carbon steel.• Used for making the handle and the shank and
part of the blade.• To gain maximum benefits from carbon steel or
stainless steel ,they are subjected to Hardening and tempering heat treatments
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• Hardening heat treatment hardens the alloy, also making it brittle, if the C content is high.
• Tempering heat treatment relieves strains and increases toughness.
• Other materials used: Monel metal(Ni,Cu,Fe) Nichrome(Ni,Cr,Fe) Stellite(Co,Cr)
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INSTRUMENT DESIGN
Consists of 3 partsHandle ShankBlade
• For many non cutting instruments, the part corresponding to the blade is termed as NIB
• The end of the nib or the working surface is FACE
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SHAFT/HANDLE
• Available in various sizes and shapes, handles can be serrated to increase friction for hand gripping.
• A large, heavy handle is not always conducive
to delicate manipulation. Most handles are small in diameter and light.
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LONG HANDLES AND CONE SOCKETS
• Instruments are known as “long handled”,if the handle, shank and the blade are all made from single piece of steel.
• If the shank and blade or nib are separate from the handle and intended to be screwed into it,the instrument is called “cone socket” instrument.
• The advantage of cone socket instrument is that if the working part is broken, it may be replaced at less expense.
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THE SHANK
• Connects the shaft with the blade or working end of the instrument.It may have one or more angulation, to avoid the instrument having a tendency to twist in use when force is applied.
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BALANCE AND CONTRANGLING
• Enamel and dentin are hard substances to cut and require the generation of substantial forces at the tip of the instrument.
• To accomplish this ,hand instruments must be sharp and balanced. Balance allows for the concentration of force onto the blade without causing rotation of the instrument in the grasp. Sharpness concentrate the force onto a small area of the edge, producing a high stress.
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• The shanks of instruments have multiple angles to keep the working end of the instrument within 2 to 3mm of the long axis of the handle.
• A)The working end of the instrument is not close to the long axis of the handle and hence it is not balanced.
• B)The shank has 2 angles, so that the working end is brought near to (within 2 mm)the long axis of the handle.This provides balance for the instrument to facilitate control of the instrument during application of force. The instrument is said to be contrangled.
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• The instrument can be monangled, binangled, triple-angled and quadrangled.
• The length of the blade required is determined by the depth of the cavity and the blade angle is determined by the accessibility requirements.
• In addition to balance, contrangling provides better access for instrumentation.
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THE BLADE
• It is that part of the instrument bearing the cutting edge. It begins at the angle where the shank is terminated. The blade ends in the cutting edge.
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CUTTING EDGE
• It is the working end of the instrument. It is usually in the form of a bevel with different shapes.
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THE CUTTING EDGE ANGLE
• It is defined as an angle between the margin of the cutting edge and the long axis of the shaft.
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THE BLADE ANGLE
• It is defined as the angle between the long axis of the blade and the long axis of the shaft.
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NOMENCLATURE
Dr. Black gave 4 classes in establishing a nomenclature for hand instruments.
1.ORDER-Purpose of the instrument. Eg: excavator2.SUBORDER-Position or manner of use. Eg: push,
pull3.CLASS-Form or design of working end. Eg:
hatchet4.SUBCLASS-The shape of the shank, monoangle,
binangle.
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• Naming the instrument usually moves from subclass to order.(4-1)
Eg: Binangle hatchet push excavator subclass class suborder order• The suborder is nonspecific and for practical
purpose is usually omitted.• Eg: Binangle hatchet excavator
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INSTRUMENT FORMULA
• Cutting instruments have formulas describing the dimensions and angles of the working end.These are placed on the handle using a code of three or four numbers separated by dashes or spaces.
• In a three numbered formula• The first number indicates the width of the
blade in tenths of a millimeter(0.1mm)• The second number indicates length of the
blade in millimeters
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• The third number indicates the blade angle. • 15- 8-12 binangle hatchet blade width1.5mm blade length 8mm blade angled 12°from the axis of handle or
shaft
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• When the primary cutting edge is at an angle other than 90°to the long axis of the blade,a 4th unit is added to the basic 3 unit formula.
• This number ,the cutting edge angle,represents the angle formed between the cutting edge and central axis of the shaft.
• It is placed in the second position of the 4 numbered formula.
• eg.,121/2-100-7-14 GMT
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SINGLE PLANE AND DOUBLE PLANE INSTRUMENT
• An instrument with the shank and the blade in the same plane is called as a single planed instrument. Even if they have 2 or 3 angles in the shank all are in the same plane.
• A single plane instrument could be laid on a table top so that all its angle coincide with the plane of the table eg.hatchet
• GMT with the curved blade is a double plane instrument, making an angle with the flat plane. The curved blade accentuates the lateral scraping ability of the instrument.
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DIRECT CUTTING AND LATERAL CUTTING INSTRUMENTS
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Direct cutting Lateral cutting
Force is applied in same plane as that of the blade and handle.
Force is applied at right angle to the plane of the blade and handle.
Usually single planed instrument are used.
All double planed instrument, contrangled are used.
Eg: straight chisel Eg: GMT
BEVELS
• Bevel is the angled surface of the cutting edge.• The principle of cutting instrument is to
concentrate forces on a very thin cross section at the cutting edge. Thinner the cross section, at the bevel, more pressure that is concentrated and the more efficient the instrument will be.
• They can be : Single beveledBibeveledTriple beveled, andCircumferentially beveled
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SINGLE BEVELED INSTRUMENT
• Instruments have a bevel on one side of the instrument.
• The instrument is held with the blade facing downward and away from the operator.
• If they are beveled on the side away from the shaft, they are called “distally beveled”
• Otherwise termed as “contra beveled” or “reverse beveled”
• If they are beveled on the side of the blade towards the shaft they are called “mesially beveled”
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• When these instrument have no angle in the shank, or an angle of 12° or less, they are used in push (direct cutting)motion and scraping motions(beveled to non beveled)
• If this angle in the shank exceeds 12°,the instrument could be used in pull(distally beveled) and push( mesially beveled) motions
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BIBEVELED INSTRUMENTS
• The blade of a bibeveled instrument has 2 bevels of equal dimension on the opposite side of the blade, placing the cutting edge in the centre.
• Eg: Hatchet• Cut by being pushed in the
direction of the long axis of the blade.
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TRIPLE BEVELED INSTRUMENTS
• Beveling the blade laterally, together with the end, forms three distinct cutting edges. Other than the 1°cutting edge, two additional cutting edges called the 2°cutting edges, extend from the primary edge for the length of the blade.
• This type of beveling increases the cutting potential of small, single planed instruments.
• Eg- chisel, angle former.
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CIRCUMFERENTIALLY BEVELLED INSTRUMENTS
• The blade of the cutting instrument is beveled at all peripheries and is usually are double planed instruments.
Eg: Spoon excavator.
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RIGHT AND LEFT INSTRUMENTS
• Direct cutting instruments are made either right or left by placing a bevel on one side of the blade.
• If the instrument is held with the cutting edge down and pointing away from the operator and the bevel is on the Right side, it will be a “Right” sided instrument
• If the bevel is on the Left, it is the “Left” sided instrument
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• Lateral cutting instruments are made left and right by having the curve or angle, which is at right angle to the principal plane(shaft plane),either on the right or on the left.
• Holding the instrument with its blade down and cutting edge pointing away, the instrument having that curve of the blade directed to the right is right instrument and vice versa for the left.
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• Identifying rings on the shaft, identifies Right of the pair.
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SINGLE AND DOUBLE ENDED INSTRUMENTS
• Instruments are available with blades and shanks on both ends of the handle.
• Such instruments are double ended. The right instrument of the pair is on one end of the handle and the left instrument is on the other end.
• Single ended instrument are safer to use, but double ended instruments are more efficient because they reduce instrument exchange.
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CLASSIFICATION
According to Marzouk: Instruments for operative dentistry procedures can be generally classified as
• Those used for exploration• Those used for removal of tooth structure. • Those used for restoration of teeth.
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I. Those used for exploration
A) Dry the area on the tooth:This necessitates the use of an
• Air syringe.• Pair of tweezers (pliers)• Cotton pellets to dry the tooth. • Cotton rolls – to isolate the area around the tooth.
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B) Illuminate the area : A source of light could be either an overhead fixture supplying non-reflecting light or an intra-canal light. They can be Battery operated lights. Built in lights attached to dental unit. Light attached to mirror or hand piece.
• Light can be introduced directly or indirectly by reflecting it on the field via a mirror.
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C) To retract the soft tissues: The hand mirror is used to move the tongue
and cheek away. Blunt plastic instruments may help in
retraction. Tongue depressor or retractors are
sometimes helpful for this procedure.
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D) To probe the potential lesion:
Explorers are used for this purpose. These are 4 types of explorers.
Straight explorer. Right angled explorerArch explorer Interproximal explorer.
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II) Those used for tooth structure removal:
Hand cutting instruments. Rotary cutting and abrasive instruments. Ultrasonic instruments
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III) Those used for restoring:– Mixing instruments– Spatulas– Plastic instruments– Condensing instruments– Burnishing instruments– Carvers– Files– Knives– Finishing and polishing instruments.
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According to Charbeneau: Operative instruments can be conveniently classified into 6 categories.
I. Cutting instruments– Hand
HatchetsChiselsExcavatorsOthers
– Rotary Burs Stones Disks Others
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II. Condensing instruments - Pluggers
Hand Mechanical
III. Plastic instrumentsSpatulasCarversBurnishersPacking instruments
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IV. Finishing and polishing instruments• Hand
Orange wood sticks Polishing points Finishing strips
• Rotary Finishing burs Mounted brushes Mounted stones Rubber cups Impregnated disks and wheels
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V. Isolation instruments• Rubber dam frame• Clamps, forceps, punch• Saliva ejector• Cotton roll holder• Evacuating tips and equipment
VI. Miscellaneous instruments• Mouth mirrors• Explorers• Probes• Scissors• Pliers• Others
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EXCAVATORS• For excavation and removal of carious
dentin and for the shaping of internal parts of cavity preparation.
TYPES
A) HATCHET EXCAVATORS 3-2-28• Single planed, bibeveled instrument.• Mode of use: Pull or push in direction of the
blade• Use: Anterior teeth-retentive areas,
sharpening the internal line angle, direct gold restoration in posterior teeth.
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B). Hoe Excavator 4½ -1½ - 22• Single planed instrument• Primary cutting edge
perpendicular to axis of handle
• 4 possible movements: vertical, push(pull), right & left
Uses:• Remove harder residual caries
as well as form the internal parts of cavity
• Cutting mesial & distal walls of premolars & molars
• Class III & class V preparation for direct gold restoration
• Shanks contrangled for heavier & longer blades
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C) Spoon Excavator 8-6-12 ;13-8-12• Cutting edge has semicircular
circumferential bevel & is sharpened to thin edge
• Curve of the blade makes it lateral cutting instrument
• Double planed instrument with right and left cutting movements
• Paired instrument with the curve of one blade directed from right to left & other from L-R
• Instrument of choice for removal of carious dentin
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Spoon excavators• Triple angled discoid
spoon• Binangle spoon or
regular spoon or banana spoon
• Binangle discoid spoon
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D) Discoid Excavator(disc like)10-2-12
• Double planed instrument with R or L cutting movements
• Blade is disc shaped, with the cutting edge extending around the periphery except where it is joined to the shank
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E) Cleoid Excavator(claw like) 20-2-12• Double planed with lateral cutting movements• Blade resembles claw, hence the name
“CLEOID”Uses:• Excavating decay in areas of difficult access • Carving amalgam & wax
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CHISELS• Chisels are instruments designed for planning or
cleaving enamel & dentin• Characterized by a blade that terminates in a cutting
edge formed by one sided bevel.• Cutting edge is at right angle to the shaft.• Chisels are angled for better access.• 4 types-
straight chisel monoangled chisel binangled chisel triple angled chisel
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STRAIGHT CHISEL:12 – 7- 0 -straight blade in line with the shank &
blade, -bevel on one side
-primary edge is perpendicular to axis of handle
-single planed instrumentUSE: to remove unsupported enamel rods in a single thrust movement
MODE OF USE: with the bevel facing away from the cavity, the instrument is used in push motion
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MONOANGLED CHISEL: 10 – 7- 8• single planed,• single angle in the shank,• mesially or distally bevelled.BINANGLED CHISEL:• 2 angles in the shank,• mesially or distally bevelled• Cleave or split undermined enamel.TRIPLE ANGLED CHISEL:• singled planed instrument, • 3 angles in the shank, • flattens pulpal floor,• mesially or distally bevelled
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WEDELSTAEDT CHISEL:15-10-3;20-10-3
• Similar to straight chisel with a slight vertical curvature in the shank (the blade does not make a real angle with the shaft).
• Beveled on one side.• If bevel is on the side toward the curvature of shank-
mesially bevelled.• If bevel is on the side away from the shank-distally
bevelled.
• Primary cutting edge in a plane perpendicular to the axis of the handle.
USE : Cleaving undermined enamel and for shaping walls.• Mesially bevelled:push motion• Distally bevelled:pull motion
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SPECIAL FORMS OF CHISELSEnamel hatchet 10-7-14• Hatchet is different from chisel with the
cutting edge parallel or in the same plane as the shaft.
• Single planed instrument. • The shank may have one or more angles.• They are paired, right and left. • Are used for planing or cleaving enamel &
dentin walls during cavity preparation.
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• Certain hatchets are “bi-bevelled”. The blade has two bevels of equal dimension placing the cutting edge in the centre. This type of hatchet is single ended.
• Used to refine line and point angles in varied forms of cavity preparation.
• Their blade lengths are short & are used in anterior teeth, where dimensions are small.
• 4 potential cutting movements- vertical, push, pull & either right or left lateral cutting.
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GINGIVAL MARGIN TRIMMER• GMT is a modified hatchet. • The cutting edge makes an angle other right
angle with the axis of the blade.• Blade of GMT is curved & is a double planed
instrument with lateral cutting action.• They are paired instruments • Single beveled instrument, either Mesially or
distally beveled.
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• They are double ended, paired instruments.
• A Mesial and a distal GMT,each with a Right and Left blade at their ends.
• If the acute angle of the cutting edge is nearer to the shaft,it is a mesial GMT and vise versa.
• Holding the instrument with its blade down and cutting edge pointing away,the instrument having that curve of the blade directed to the right is a right instrument and vise versa.
• GMT takes the 4 numbered formula:12- 95- 10- 1212 ½ - 100 – 7 – 1412 ½ - 75 – 7 – 14
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• When the second number in the formula is 90-100, the pair is used as distal GMT.
• 85-75 : mesial GMT.• 100 & 75 pairs are used for inlay/onlay
preparations with steep gingival bevels.• 90 & 85 pairs are for amalgam
preparations with gingival enamel bevels that decline gingivally only slightly.
USES:• Roundening of axio-pulpal line angle of
tooth surface preparation.• Forming sharp angles in internal parts of
cavity preparation.
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ANGLE FORMER
• 12-85-5-8 ; 8-80-3-9• The cutting edge is sharpened
at an angle to the axis of the blade.
• The angle of cutting edge to the blade axis is usually 80-85º
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USES:
• To accentuate line & point angle in the internal outline form in cavities for cohesive gold to establish retention form.
• The action of instrument is essentially lateral scrapping.
• Blade of the angle former is beveled on the sides as well as the end to form 3 cutting edges.
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OFFSET HATCHET
• Similar to regular hatchet except that the whole blade is rotated quarter turn forward or backward around its long axis.
• Single planed instrument.• Right or left.• Used to create and shape specific
angulations for cavity walls especially in areas of difficult access.
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TRIANGULAR CHISEL
• Blade is triangular in shape with the base of the blade away from the shaft.
• It has terminal cutting edge like a straight chisel.
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MOUTH MRROR • Clear & distinct vision
• Quite unique
• To see obscure areas
• Reflects operating light
• Mirrors come in different size
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USES OF THE MOUTH MIRROR
• INDIRECT VISION – when the operator uses a mirror to view area of the oral cavity not seen with direct vision.
• REFLECTION OF LIGHT – illumination of an area being examined or treated.
• RETRACTION – when the cheeks or tongue are retracted for better visibility and for protection of the tissues.
• TRANSILLUMINATION – Reflection of light through the tooth surface to detect fractures.
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• Plane or regular surface mirrors have reflective surfaces(silver coatings) on the backs of the glass. This gives the image a “ghost image” as the light reflects from the glass and the silver layer.
• Front surface mirrors have reflective coatings (rhodium) on top of the glass. This coating eliminates the “ghost image”; it reflects only once to give a clear view free of distortion.
• Concave surface mirrors magnify the image.
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INSTRUMENT GRASPS
• A proper instrument grasp is essential for performing operative procedures.
• It provides control of the instrument, allowing precise adaptation and flexibility of motion.
• Prevents muscle fatigue, while allowing application of controlled pressure to the instrument.
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MODIFIED PEN GRASP• Pads of the thumb,index, and
the middle fingers contact the instrument.
• The tip of the ring finger and the little finger rest on the nearby tooth surface of the same arch as a rest.
• The pad of the middle finger is placed near the topside of the instrument, generating the cutting pressure.
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INVERTED PEN GRASP
• The finger positions are the same as for the modified pen grasp. However, the hand is rotated so that the palm faces more toward the operator.
• This grasp is used mostly for tooth preparations utilizing the lingual approach on anterior teeth.
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PALM AND THUMB GRASP
• The handle is placed in the palm of the hand and grasped by all the fingers, while the thumb is free of the instrument and serves as rest.
• Limitation in tactile sensitivity and flexibility of the instrument
• Used in anterior region and used for sharpening instruments.
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MODIFIED PALM AND THUMB GRASP
• The handle of the instrument is held between the pads of the four fingers pressing it against the palm, as well as the pad and 1st joint of the thumb.
• Greater ease of instrument movement and more control against slippage.
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RESTS• Finger rest or fulcrum is essential for
the controlled movement of an instrument.
• It is the point of support from which the hand moves to activate the instrument and also provides control and prevents injury to the soft tissues from an instrument which inadvertently slips.
• Closer the rest areas are to the operating tooth, more reliable they are.
• Neither soft tissue rests nor distant hard tissue rests afford reliable control.
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• Modified pen grasp and inverted pen grasp: ring and little finger on tooth/teeth of same arch
• Palm and thumb grasp: Tip of thumb on the same
tooth/adjacent tooth. Rests can be established on the
opposite quadrant.
• Indirect rest :Operating hand rests on the opposite hand, which rests on stable oral structure.
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SHARPENING HAND INSTRUMENTS
• “No man has ever yet become a good and efficient dentist until after he has learned to keep his cutting instruments sharp”—G.V.Black
• As said above, selecting and using the proper instrument mean little if the instrument is not sharp.
• Instruments are dulled by repeated contact with tooth tissues and by frequent sterilization. Use of instruments with dull cutting edges cause more pain, prolong working time,reduce quality and preciseness in cavity preparation and also make control difficult. Therefore it is essential that all cutting instruments be sharp.
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• Sharpening is done by reducing the bulk of the metal at the cutting edge, following the original configuration of the bevel.
• There are many types of sharpening instruments which include : stationary oil stones e.g.Arkansas stones mechanical sharpener diamond hone stones used in handpiece
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PRINCIPLES OF SHARPENING
1)Sharpen instruments only after they have been cleaned and sterilized.
2)Establish the proper bevel angle (usually 45 degrees) and the desired angle of the cutting edge to the blade before placing the instrument against the stone, and maintain these angles while sharpening.
3)Use a light stroke or pressure against the stone to minimize frictional heat.
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4) Use a rest or guide whenever possible.
5) Remove as little metal from the blade as possible.
6) Lightly hone the unbeveled side of the blade after sharpening, to remove the fine bur that may be created.
7) After sharpening, resterilize the instrument along with other items on the instrument tray setup.
8) Keep the sharpening stones clean and free of metal cuttings.
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STERILIZATION OF HAND CUTTING INSTRUMENT
• Sterilization can be accomplished by autoclaving, dry heat procedures, ethylene oxide equipment and chemical vapor sterilizers.
• Boiling and chemical solutions only disinfect the instruments.
• Sterilizing carbon steel instruments by methods other than dry heat, causes discolouration, rust, and corrosion.
• High heat in dry heat procedures, may reduce the hardness of the alloy, reducing the instrument to retain a sharp cutting edge.
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• Boiling water or autoclave methods of sterilization do not produce discolouration of stainless steel instruments. However prolonged immersion in cold disinfectant solutions may cause rust.
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CONCLUSION
• Modern hand instruments, when used, produce beneficial results for both the operator and the patient. It should be noted that some of these results can be satisfactorily achieved only with hand instruments.
• To perform the intricate and detailed procedures associated the dentist must have a complete knowledge of the purpose, availability and application of the instruments required.
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REFERENCE
• Operative dentistry: Modern theory and practice – MA Marzouk, I Edition.
• The art and science of operative dentistry – Sturdevent, IV Edition.
• Principles and practice of Operative Dentistry – Charbenaeu.
• Delmar's dental assisting: a comprehensive approach - Donna J. Phinney, Judy H. Halstead
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