operative instruments in conservative dentistry & endodontics
TRANSCRIPT
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Instruments in Operative Dentistry
Dr. Ashok Ayer
Assistant Professor
Department of Conservative Dentistry and Endodontics
College of Dental Surgery
B. P. Koirala Institute of Health Sciences, Dharan, Nepal
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Outline:
Hand Instruments
Introduction
Classification
Materials
Application
Techniques
Sharpening
Powered cutting equipments
Rotary cutting instruments
Cutting Mechanism
Hazards
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Introduction: G.V. Black
Nomenclature & numbering of hand instruments
1. Cutting instruments/ excavators
2. Noncutting
Designs of some early hand instruments
1728 – Pierre Fauchard invented the bow drill 1891 – Edward C Acheson –produced carborundum tools 1935 – W H Drendes - Diamond cutting instruments
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MATERIALS
CARBON STEEL:
HARDER THAN STAINLESS STEEL
MAINTAINED BETTER SHARPNESS
CORRODE IN MOIST CONDITIONSCarbon steel
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Stainless Steel
Preferred materials
Remains bright under most conditions
Loses keen edge during use much more
quickly
Chromium: corrosion resistance
Carbon: hardness
Stainless Steel
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TUNGSTEN CARBIDE
INSERTS OR BLADES TO PROVIDE MORE
DURABLE CUTTING EDGES (BRITTLE).
THEY MAY BE SOLDERED TO STEEL
HANDLES
SOME INSTRUMENTS ARE MADE WITH
CARBIDE TO PROVIDE MORE DURABLE
CUTTING EDGES.
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OTHER ALLOYS OF NICKEL, COBALT, OR
CHROMIUM ARE USED IN THE
MANUFACTURE OF HAND INSTRUMENTS.
THEY ARE RESTRICTED TO INSTRUMENTS OTHER THAN
THOSE FOR CUTTING TOOTH STRUCTURE
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Hardening and Tempering Heat
Treatments
Heat treatment Furnace
The hardening heat treatment hardens the
alloy, but it also makes it brittle, especially
when the carbon content is high.
Tempering heat treatment relieves strains and
increases toughness.
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Classification of Instruments:- by
SturdevantHAND
INSTRUMENT
cutting
excavators
ordinary
hatchets
hoes
Angle
formers
spoons
chisels
straight
curved
bin-angle
Enamel
hatchet
Gingival
margin trimmers
others
files
scalers
carvers
Non cutting
Amalgam
condensermirrors
explorers,
probes others
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ORDER
PURPOSE OF THE INSTRUMENT
E.G. EXCAVATOR, SCALER
SUB-ORDER
MANNER OF USE
E.G. PUSH, PULL
CLASS
FORM OF BLADE
E.G. HATCHET, CHISEL
ANGLE
NUMBER OF ANGLES IN THE SHANK: MONOANGLE, BIANGLE,
TRIPLE-ANGLE, QUADRANGLE
E.G. BIANGLED HATCHET EXCAVATOR,
According to G. V. Black
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Classification of Instruments:- by Charbeneau
Cutting instruments
Hand- hoes, chiesel etc
Rotary- burs, discs etc
Condensing instruments
Pluggers
Plastic instruments
Carvers, Burnishers
Finishing and polishing instruments
Discs, Strips
Isolation instruments
Cotton roll, Rubber dam
Miscellaneous-
Mirrors, Explorers
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CLASSIFICATION BY MARZOUK
EXPLORING
INSTRUMENTS
REMOVAL OF
TOOTH STRUCTURE
RESTORATION
OF TEETH
To dry
To illuminate
Retraction
Probes
Separators
Mixing
Plastic
Condensing
Burnishing
Carvers
Files
Knives
Finishing
& polishing
Hand cutting
Rotary cutting
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Design
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Blade
Working part of the instrument
Usually in the form of a bevel (acute angle) that
cuts into the tooth structure.
On non cutting instruments e.g. condensers the
part corresponding to the blade is called the nib or
face.
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Shank
Connect the handle to the working end of the instrument.
Normally smooth, round and tapered.
Mon-angle, bin-angle, triple angle
Balance is accomplished by designing the angle of the shank so
that the cutting edge of the blade must not be off axis by more
than 1-2 mm (Sturdevant’s)/2-3 mm (Summitt)
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Balance allows for the concentration of force onto
the blade without causing rotation of the
instrument.
Instruments with long blades may required two or
three angles in the shank to bring the cutting edge
near to the long axis of the handle
Such shanks are termed contra angled.
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Handle/ Shaft
Serrated for better gripping and control of the
instrument.
a. Standard Stainless steel handle: Diameter 6.4 mm
approx.
b. Padded handles: Diameter 8mm approx.
c. Larger diameter handles: 9.5 mm
More ergonomic
Less likely to develop carpal tunnel syndrome
Occupy more space in instrument tray
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Handles are in conjunction with the shank
or it may be separable.
Separate type is known as cone-socket
handle and allows for replacement of several
working ends e.g. mirrors and condensers.
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cone-socket handle (mirror)
mirror
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Numeric formulas
Describing the dimensions and angle of the working end.
Three number formula
Four number formula:
Cutting edge is not perpendicular to the long axis of the
blade.
Gingival marginal trimmer
Angle former
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Instrument shank and
blade design
85
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Bevels
Most hand cutting instruments have on the end of the
blade a single bevel that forms the primary cutting edge.
Additional two secondary cutting edges that extend from
the primary cutting edge for the length of the blade.
Allows cutting in 3 directions; facial and lingual walls of
the proximal cavity
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Bibeveled instrument have two bevels that form the cutting edge;
e.g. hatched excavator
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Single beveled instrument such as spoonexcavator and gingival margin trimmer areused with lateral cutting movement.
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Enamel hatchet also as a single beveled instrument
used with direct cutting motion, a planning or
lateral cutting designated for right (R) and left (L) to
the instrument formula.
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The cutting edge is perpendicular to
the axis of the handle
e.g. binangle chisel.
Instrument with slight blade curvature
e.g.Wedelstaedt chisel.
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Hand cutting instrument
Excavators Chisels
Removal of caries and refinement of the
internal parts of the preparation.
Used primarily for cutting enamel.
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Excavators
1. Ordinary Hatchets
2. Hoes
3. Angle formers
4. Spoons
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Ordinary Hatchets
It has the cutting edge of the blade directed
In the same plane as that of the long axis of the handle
and
Is bibeveled.
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Used primarily on anterior teeth for
Preparing retentive areas and
Sharpening internal line angles, particularly in
preparations for direct gold restorations .
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Hoe excavators
Primary cutting edge of the blade perpendicular
to the axis of the handle
Planing tooth preparation walls and forming line
angles.
It is commonly used in Classes III and V
preparations for direct gold restorations.
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Hoes with longer and heavier blades, with the
shanks contra-angled.
For use on enamel or posterior teeth.
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The blade angle of the hoe: > 12.5 centigrades
The blade angle of chisel: ≤ 12.5 centigrades
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Angle former
It is mon-angled and has the primary cutting edge
at an angle (other than 90 degrees) to the blade.
It is available in pairs (right and left )
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Used primarily for sharpening line and point angles
and creating retentive features in dentin in
preparation for gold restorations
Also may be used in placing a bevel on enamel
margins
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Spoon excavators
Its blades are slightly curved, the shanks may be bin-angled
or triple-angled to facilitate accessibility.
Spoon excavators
discoid cleoid
The cutting edges are
circular
The cutting edges are
claw like.
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Left cutting and right cutting
Used mainly for removal of caries and refinement ofinternal opening in a cavity preparation
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bin-angled spoon
triple-angled spoon
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Cleoid spoon
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Discoid spoon
Discoid is disc shaped, with cutting edge around the blade
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Chisels:
Straight, Monoangle, Biangle, Wedelstaedt chisels
Enamel Hatchets
Gingival Marginal Trimmers
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Straight Chisel
The straight chisel has a straight shank and blade,
with the bevel on only one side.
Its primary edge is perpendicular to the axis of
the handle.
(12-7-0)
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The shank and blade of the chisel also may be
slightly curved (Wedelstaedt design)
11½-15-3
Biangled chisel
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Force used with chisels : straight thrust
The bin-angle and Wedelstaedt chisels:
Primary cutting edges in a plane perpendicular to theaxis of the handle.
Distal bevel or a mesial (reverse) bevel.
Used for cleaving undermined enamel and for shapingwalls.
Instrument with three cutting motion: vertical, right andleft.
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The blade with a distal bevel is designed to plane a
wall that faces the blade's inside surface
The blade with a mesial bevel is designed to
plane a wall that faces the blade's outside surface
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Enamel Hatchet
It is a chisel similar in design to the ordinary hatchet
excavator except that the blade is larger, heavier, and is
beveled on only one side
Cutting enamel
Right or Left cutting ends of the double- ended hatchet.
10-7-14
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Gingival margin trimmer
Blade is curved
Bevel for cutting edge: outside of the curve
Face of instrument: inside of the curve
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12½-100-7-1412½-75-7-14
Mesial Distal
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Cutting edge angle: 100 and 75 :
Inlay & Onlay preparations.
Cutting edge angle: 90 and 85 :
Amalgam preparations.
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Uses:
Beveling of the gingival margins of proximo-
occlusal preparations.
Beveling of the axio-pulpal line angle
Performing a gingival lock (reverse bevel), placed
on the gingival seat
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Usage of hand cutting instruments
Horizontal strokes:
Long axis of blade directed between 45 & 90
degree to the surface being planed or scraped
Vertical or chopping strokes:
Pulling stroke
Hoe: beveled end or distal bevel
Pushing stroke
Hoe: contrabeveled end or mesial bevel.
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The cutting edge of the hand instrument should
always be kept sharp as
Dull instruments may cause:
1. Loss of control.
2. More pain.
3. Prolonged time for the operative procedure.
4. Reduce the quality and precision of tooth
preparation.
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Stationary sharpening stone e.g. Arkansas
stone, silicon carbide.
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Mechanical sharpener; moves at low speed while
the instrument is held at the opposite angle and
supported by a rest i.e. easier and less time
consuming.
E.g. Rx Honing Machine
Mechanical sharpener
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Principles of Sharpening
Sharpen instruments only after they have been cleaned
& sterilized
Establish the proper bevel angle (usually 45 degree)
and the desired angle of the cutting edge to the blade.
Use light stroke pressure
Use a rest or guide whenever possible.
Remove as little metal as possible
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Non cutting Instruments
Diagnostic instruments
Mirror
Probe or explorer
Twizzer
Plastic instruments
Amalgam instruments
Condensers
Burnisher
Carver
Amalgam carrier
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MOUTH MIRROR
Most common sizes used are the No. 4 (⅞ inch diameter)
and No. 5. (15/16 inch diameter)
No. 2 (5/8 inch diameter): when working on posterior teeth
with a rubber dam.
For clarity, reflective surface on the external surface of the
glass: Front surface mirror.
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Uses for the mouth mirror. A, Indirect vision. B, Light reflection. C, Retraction. D, Tissue protection.
A
D
C
B
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Explorers
To feel tooth surface for irregularities
To determine the hardness of exposed dentin
1. Shepherd’s hook: No. 23
2. Cowhorn explorer: No. 2
3. No. 17: back action
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Tweezer/ cotton forceps:
Cotton forceps are used for picking up small items, cotton pellets
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Plastic filling Instruments
To carry and shape tooth colored restorative material: Composite resin and glass ionomer
For placing of base and lining material
Hard plastic or metal.
Composite placement instrument
Designed specifically for the placement of composite restorative materials.
Anodized aluminum
Teflon
Titanium nitride layer on instruments
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A: ash49 B:ash6 C:dycal applicator D:cement spatula.
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Amalgam Carriers
An instrument with a hollow cylinder that is filled with amalgam.
Sizes:
Mini: 1.5 mm diameter
Regular: 2.0 mm
Large: 2.5 mm
Jumbo: 3.0-3.5 mm
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Amalgam Condensers
Various Amalgam condensers
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Carvers
Hand instruments with a blade or nib used to contour the
surface of filling material in their plastic state, waxes,
models and patterns.
Hollenback carver (knifed edged- elongated- bibevelled)
Diamond (Frahm’s) carver : Bibevelled cutedge.
Ward’s ‘C’ carver
Discoid Cleoid
Interproximal carver
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Burnishers
Burnishing of the amalgam on the margins of the cavity,
Shaping metal matrix band to have more desirable contours for
restoration.
To bend cast gold restoration (inlay or onlay) near the margin of
the prepared cavity to narrow the gap between gold and the
tooth.
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Burnishers
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Disposable brush
Used with etching and bonding procedures associated with composite resins.
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Accessory Instruments
Scissors
Used for cutting dental dam material, retraction cord, and stainless steel crowns.
Crown and bridge scissors
Dappen Dish
Hold certain liquid dental materials during a procedure.
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Howe Pliers
Also referred to as 110 pliers. Useful for holding items, for
carrying cotton products to and from the oral cavity,
removing the matrix band, and placing and removing the
wedge.
Guards
Interproximal wedges to protect soft tissues from contact
with sharp rotary cutting instruments.
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Preset restorative tray
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There are four grasps used with the hand
instruments:
Modified pen.
Inverted pen.
Palm and thumb.
Modified palm and thumb.
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M o d i f i e d p e n g r a s p
pen grasp Modified pen grasp
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Inverted pen grasp
If the hand is rotated so that the palm faces more toward
the operator.
Used in the lingual and labial surfaces of anterior teeth.
inverted pen grasp
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Palm and thumb grasp
The handle of the instrument is placed on the palm of the
hand and grasped by all the fingers while the thumb is free of
the instrument and rest on the nearby tooth of the same arch.
Preparing incisal retention in a class III preparation on a
maxillary incisor.
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Palm and thumb grasp
The same as in palm and thumb grasp but the
thumb is rested on the tooth being prepared.
Used in the upper arch.
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Powered cutting equipments
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CHARACTERISTICS:
SPEED
SURFACE FEET PER UNIT TIME OF CONTACT THAT THE TOOL
HAS WITH THE WORK TO BE CUT OR REVOLUTIONS PER
MINUTE
ACCORDING TO MARZOUK:
1. ULTRA LOW SPEED: 300-3000 RPM
2. LOW SPEED: 3000-6000 RPM
3. MEDIUM HIGH SPEED 20,000-45,000 RPM
4. HIGH SPEED 45,000-1,00,000 RPM
5. ULTRA HIGH SPEED > 1,00,000 RPM
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According to Charbenau:
1. Conventional or low speed: below 10,000 RPM
2. Increased or high speed: 10,000-1,50,000 RPM
3. Ultraspeed: above 1,50,000 RPM
According to Sturdevant:
1. Low or slow speeds: below 12,000 RPM
2. Medium/Intermediate speeds: 12,000 to 2,00,000 RPM
3. High/ Ultrahigh speeds: above 2,00,000 RPM
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Pressure: P=F/A
Low speed: 2-5 pounds of force
High speed: 1 pound of force
Ultra high speed: 1-4 ounces of force
Heat Production
Directly proportional to the Pressure, RPM, and
area of tooth in contact
113˚ F : Pulpitis & pulp necrosis.
130˚ F : Permanent damage of pulps.
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Brown et al: Temperature of dentin at a distance of
0.5 mm from a high speed bur cutting dry to be
245˚F (118˚C).
Even in non vital teeth, dry cutting at high speed
should be avoided, since the thermal stresses will
cause microfractures in the enamel. This could
contribute to marginal failure of the restoration.
Higher water velocity.
Clean head system
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Greater flow of water coolant is required to prevent clogging when diamonds are used under increased pressure.
42 psi is the optimal air pressure to achieve peak performance
Optic
Drive air
Spray water
Exhaust air
Spray air
Optic
Drive air
Spray water
Exhaust air
Spray air
6-pin
5-hole
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VIBRATION:
EQUIPMENT USED & THE SPEED OF ROTATION
EXCESSIVE VIBRATION: ANNOYANCE TO THE PATIENT,
OPERATOR FATIGUE AND RAPID WEAR OF INSTRUMENTS.
TORQUE:
ABILITY OF THE HAND PIECE TO WITHSTAND LATERAL
PRESSURE ON THE REVOLVING TOOL WITHOUT DECREASING
ITS SPEED OR REDUCING ITS CUTTING EFFICIENCY.
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Friction:
Occurs in the moving parts of the hand piece especially the
turbine.
Friction is reduced by equipping the hand piece with ball
bearings, needle bearings, glass and resin bearings.
Ceramic Ball Bearings:
40% lighter and 3 times harder than conventional
bearings, they offer an extended turbine life, reduced
operation noise, and less vibration.
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Handpieces:
Two basic types of handpieces, the straight handpieceand contra angle handpiece.
The straight is used more frequently for laboratorywork, while contra angle used in the oral cavity.
High speed techniques are generally preferred forcutting enamel and dentin.
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Penetration through enamel and extension of the
cavities outline are more efficient at high speed.
Small diameter burs should be used in the high
speed handpiece.
High speed generates considerable heat during
cutting, even with small diameter burs and should
be used with water coolant and high efficiency
evacuation
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Design:
This model is the choice for limited access or
when treating children.
Rear-facing exhaust vents direct air flow away
from the surgical site for patient protection
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Commonly used couplings
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Zero Suck Back Technology
Prevents the intake of aerosol and other
particles when it is stopped.
Drive air flows into an Anti Suck Back
Diffuser (ASBD) within the capsule.
Air in the ASBD is pressurized through
centrifugal force created by the
impeller rotation.
Through the centrifugal force and
rotation of the impeller, air continues
to flow into the ASBD and remains
pressurized even after drive air is
stopped.
The pressurized air in the ASBD is
released to the outside at the
bottom of the head
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Low-Speed Handpiece
Design
Straight in appearance.
Standard length and “short.”
Speed ranges from 10,000 to 30,000 rotations per minute (rpm).
Operates the rotary instrument in either a forward or backward movement.
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Uses of the low-speed handpiece Intraoral Removal of soft decay and fine finishing of a
cavity preparation. Finishing and polishing of restorations. Coronal polishing and removal of stains.
Extraoral Trimming and contouring temporary crowns. Trimming and relining of removable partials and
dentures. Trimming and contouring of orthodontic
appliances.
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Low-Speed Attachments
Straight attachment receives a long-shank laboratory
bur, the contra-angle attachment, and the prophy
angle attachment.
Contra-angle attachment receives latch type rotary
instruments and mandrel.
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Prophylaxis Angle
Used during polishing procedures to hold the
prophy cup and bristle brush.
Two types
Plastic disposable “prophy” angle
Metal “prophy” angle
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High-Speed Handpiece
Cellular Glass Optics
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Uses of the high-speed handpiece
Removes decay.
Removes an old or faulty restoration.
Reduces the crown portion of the tooth for the preparation of a crown or bridge.
Prepares the outline and retention grooves for a new restoration.
Finishes or polishes a restoration.
Sections a tooth during a surgery.
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Ultrasonic Handpiece
Design
Attached to the dental unit.
Powered by electricity.
Attachments are similar in appearance to scaling instruments.
Delivers a pulsating spray of water.
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Uses of the ultrasonic handpiece
Removes calculus.
Removes stain.
Removes bonding materials from a tooth surfaceafter orthodontic appliances are removed.
Removes cement after orthodontic bands areremoved.
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Laser Handpiece
Design
Uses a laser light beam instead of rotaryinstruments.
The laser is conducted through a fiber-optic cable.
Resembles a standard handpiece.
Maintains a water-coolant system.
Maintains an air-coolant system
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Uses:Cauterizes soft tissue.Vaporizes decayed tooth structure.
Advantages:Usually painless.Patient usually does not require anesthesia.Proceed with procedure faster.
Disadvantage:Cannot be used on teeth with existing restorations.
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AIR-ABRASION HANDPIECE
Design
Small version of a sandblaster.
Compressed air at pressure of 7 to 11 atm (40
to 140 psi)
Produces a high-pressure delivery of aluminum
oxide particles (of 20 to 50 pm) through a small
probe.
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Uses:
Prepares teeth for sealants.
Removes external stains.
Class I through class VI preparations.
Endodontic access.
Crown margins.
Prepares a tooth surface for the cementation of a castrestoration, such as a crown or veneer.
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Disadvantages:
More effective on hard normal dentine than soft
dentine affected dentine
When using composite, the air abrasion doesn’t
provide the micromechanical roughness needs for
retention thus needs acid-etchant.
Loss of tactile sensation.
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Possible iatrogenic damage especially on thecementum and root dentine.
Can induce asthma –> thus needs high volume suction
Can’t remove amalgam restoration.
Can’t perform massive reduction for crown.
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Laboratory Handpiece
Design
Operates at speeds up to 20,000 rpm.
Uses laboratory burs.
Provides greater torque than handpieces used intraorally.
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Rotary instruments
Cutting Abrasive
Carbide burs
Made from
1- tungsten carbide
2- steel carbide
1- Diamond burs
2- Discs
3- Stones
4- Rubber wheels
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According to composition:
1. Steel burs
2. Tungsten Carbide burs
According to mode of attachment to handpiece
1. Latch type
2. Friction grip type
According to handpiece they are designed for;
1. Clockwise
2. Anticlockwise
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Rotary instruments consist of three parts :
1- shank
2- neck (shaft)
3- head
head shaft Shank
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Shank design
Long shank – used for straight hand piece (low speed)
Short latch shank – used for contra-angle (low speed)
Friction grip shank - used for high speed hand piece
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Dental Burs
A group of instruments that can turn on an axis with different
speed of rotation to perform different types of work.
The characteristics of this work are either cutting , abrasive,
finishing or polishing.
Steel burs cut human dentin at low speeds, but dulls rapidly at
higher speeds or when cutting enamel
Steel necks bends easily causing vibration
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Carbide burs
Burs possess blades that shear (cut) toothstructure.
They are used for making preciseintracoronal preparation features such asplacing groove, and boxes.
Used for smoothing surface in enamel anddentin
They are not used for bulk reductionbecause to producing undulations on thetooth surface
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Shapes: Round Bur:
Initial entry into the tooth
Extension of the preparation
Retentive features and caries removal
Inverted cone bur Undercuts in the tooth preparation
Pear shaped bur Tooth preparation for amalgam, gold foil.
Straight fissure bur Tooth preparation for amalgam
Tapered fissure bur Tooth preparation for indirect restorations.
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Basic bur head shapes
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Regular –cut
Fine Cut
Coarse-cut
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Its used for highly smoothing of prepared surfaces of tooth
Because of its blades in a diagonal to the instrument shaft
Its have a torpedo shape
Twelve-fluted carbide bur
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Plain fissure bur
Its tapered and cylinder shape its used for placinggroove and boxes and they also used for finishing ofpreparation.
Groove seating
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Bur numbering systems
In the united states the burs have been traditionallydescribed in term of arbitrary i.e. numerical code
eg, 2 =1 mm diameter round bur,
34 = 0.8mm inverted,
57 = 1mm diameter straight fissure
Number 500 is added to indicate cross cutting
Number 900 is added to indicate end-cutting only
So no. 57 ,557 and 957 are all had the same head size
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Iso system(international standard organization)
FDI (Federation dentaire internationale)
Usually tend to use head shape name and size
(in tenth of a millimeter)
Eg. Round 010 = 1mm diameter
Straight fissure plain 010 = 1mm diameter
Inverted cone 008=0.8mm diameter
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Shapes & diameters of regular carbide burs used for tooth preparation
RoundBur size: 1/16 1/8 ¼ ½ 1 2 3 4 5 6 7 8 9 11
Diameter: 0.30 0.40 .50 .60 .80 1.0 1.2 1.4 1.6 1.8 2.1 2.3 2.5 3.1
Inverted coneBur size: 33½ 34 35 36 37 39 40
Diameter (mm): .6 .8 1.0 1.2 1.4 1.8 2.1
Straight Fissure:Bur size: 55½ 56 57 58 59 60
Diameter (mm): .60 .80 1.0 1.2 1.4 1.6
Straight fissure, round end:Bur size: 1156 1157 1158
Diameter (mm): .80 1.0 1.2
Tapered fissure:Bur size: 168 169 170 171
Diameter (mm): .80 .90 1.0 1.2
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Tapered fissure, rounded end
Bur size: 1169 1170 1171
Diameter (mm): .90 1.0 1.2
Pear:Bur size: 329 330 331 332
Diameter (mm): .60 .80 1.0 1.2
Long inverted cone, rounded corners (amalgam preparation)
Bur size: 245 246
Diameter (mm): .80 1.2
End-cutting:
Bur size: 956 957
Diameter (mm): .80 1.0
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Bur head design:
The number of blades on a bur is always even
Number of blades on an excavating bur may vary from 6 to8 t0 10.
Finishing bur: 12 to 40 blades
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Concentricity:
Measurement of the symmetry of the bur head.
Runout:
Test measuring the accuracy with which all blade tipspass through a single point when the instrument isrotated.
Average value of clinically acceptable run-out is about0.023 mm
Is the primary cause of vibration
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Bur blade design
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Rake angle:
Angle that the face of the bur tooth makes with the radial line.
Radial rake angle: radial line & the tooth face coincide.
Negative rake angle: blade face is leading the radial line Increases the life expectancy of the bur & provides for the most effective
performance in low and high speed ranges.
Positive rake angle:
Produce acute edge angle
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Edge angle:
In the range of 90˚ to provide strength to the blade &longevity of cutting efficiency of the bur.
Land: plane surface immediately following the cutting edge.
Flute/ Chip space:
Space between successive bur teeth or the blades of the bur.
Provides an exit for removal of the fractured matter andcreates a clearance angle.
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Clearance angle:
Angle between the back of the blade and the tooth surface.
If a land is present on the bur:
1. Primary clearance angle: the angle the land will make with work.
2. Secondary clearance angle: the angle between the back of the bur
tooth and work.
3. Radial clearance angle: is formed when the back surface of the bur
tooth is curved.
Provides clearance between the work & the cutting edge to prevent
the tooth back from rubbing on the work.
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Abrasive instruments
Head consists of small angular particles of hard substance
embedded in a soft binder (ceramic, metal, shellac,
rubber).
Diamond abrasives
Other abrasives –Silicon carbide (carborundum),
aluminium oxide, garnet, quartz, pumice, cuttlebone.
Deposited by Electroplating, sintering or microbrazing.
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These are made from diamond chips bonded to blanks(heads). Diamonds used for grinding enamel anddentin surfaces
Diamond burs may divided according to :
1- coarseness ( medium grit - fine grit )
2- shape
Diamond stones
Medium grit
Fine grit
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Diamond particle size:
1) Coarse: 125~150 um
2) Medium: 88~125 um
3) Fine: 60~74 um
4) Very fine:38~44 um
Diamond instruments consists of three parts:
A metal blank,
The powdered diamond abrasive
A metallic bonding material that holds the
diamond powder onto the blank
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Color coding:
Coarse: 120-150µ
Standard: 106-125µ
Fine: 53-63µ
Extra- fine: 20-30µ
TF: Taper flat end; TR: Taper round end; TC: Taper conicalend; FO: Flame Ogival end; SF: Straight flat end; SO:Straight Ogival end; BR: Ball round; WR: wheel round edge;
Green
Blue
Red
Yellow
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Discs, Mandrel, Stones, and Wheels
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Moulded abrasive instrument –
Manufactured by pressing a uniform mixture of abrasive
and matrix around roughened end of shank,
Points and stones; finishing & polishing
Coated abrasive instrument –
Disks that have a thin layer of abrasive cemented to a
flexible backing.
surface contouring, finishing
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SmartPrep Instruments
SmartPrep Instruments (Smart Bur, Polymer Bur)
Medical polymer that has the ability to remove decayed dentine
while keeping the healthy dentin.
Its hardness is less than healthy dentine while harder than the
carious dentin.
Ability to self-limit(selectively)
It will only cut what is carious and if it’s in contact with
healthy dentin the bur will only wear away (when extensive
force isn’t used).
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Advantages:
Conservative Minimal to none disease transfer (because its singleuse only). No need for Local Anesthesia. For Students to start with first clinical cases.
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Disadvantages:
Single-patient-use = Expensive.
Technique sensitive ( too much pressure and you will cut the healthy dentine)
The bur breaks down when it touches enamel.
It can sometimes leave large amounts of decayed tissue (use caries dye to locate the left amount.
Access should be done by a different type of bur that can penetrate the enamel.
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Cutting Mechanisms
Bladed Cutting:
Brittle fracture: crack production, by tensile loading.
High speed cutting, especially of enamel
Ductile fracture: plastic deformation, by shear.
Low speed cutting.
Abrasive Cutting:
Diamonds are most efficient when used to cut
brittle materials, are superior to burs for removal of
the dental enamel.
Burs are generally preferred for cutting ductile
materials such as dentin.
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CUTTING RECOMMENDATIONS
Use of contra-angled handpiece, air-water spray
for cooling, high operating speed (above 200,000
rpm), light pressure.
Carbide burs are better for end- cutting, produce
lower heat, and have more blade edges per diameter
for cutting.
Diamonds are more effective than burs for both
intracoronal & extracoronal tooth preparations,
beveling enamel margins on tooth preparation, &
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CHEMO-MECHANICAL CARIES REMOVAL
Carisolv (Chemo‐mechanical caries removal )
Composition:
0.5% sodium hypochlorite and 0.1 M amino acids “Glutamine, leucine and lycine”
This is a technique used to remove caries and decay with minimal invasive techniques. Hypochlorite: dissolves the decayed dentine
Amino acid: buffering solution to prevent damage to the healthy tissue.
[The amino acid and hypochlorite will react with the denaturedCollagen Tissue of dentine (Infected dentine) making soft and easilyremoved with hand instruments.]
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Advantages:
Less anesthesia is used
Useful for children, dental‐phobic patients.
Useful for removing root or coronal caries in easily accessible areas.
Removes the smear layer and doesn’t affect the bond strength of the adhesive materials.
No histological effect on the pulp even with direct contact.
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Ozone treatment Ozone gas has a high oxidation potential and is
effective against bacteria, viruses, fungi, and protozoa.
Capacity to stimulate blood circulation, platelets, and immune response.
Ozone is used in dentistry in gaseous, ozonated water and as ozonated oils
Ozone has been proven to halt root caries and alsoreverse lesions (pit and fissure carious lesions) byallowing the natural remineralisation process to proceed.
Remineralised lesions are known to be more resistant tofurther dissolution than sound tooth surfaces.
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Disruption of the protected ecological niche of the micro-flora allows remineralisation from the saliva.
Intracanal irrigants in endodontic treatment.
Treatment of alveolitis, avascular osteonecrosis of the jaw,and herpes virus infection.
Inhibits plaque formation: periodontal surgical andmaintenance phase.
Used in dental unit water line to disinfect water.
Advantage of ozone therapy is it is an atraumatic,biologically based treatment.
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O3 delivered from the HealOzone unit:(2100 ppm O3, 615 ml/min) through a handpiece with a silicone cup that sealed thetooth.
Once sealed, the device automaticallydelivered the O3 for the treatment groupfor 10 seconds followed by 10 secondsvacuum.
Recall:
After one and three months.Prophylaxis of teeth Re-examination using the DIAGNOdent® and ECM readings. Ozone treatment repeat on each of these two recall visits.
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HAZARDS WITH CUTTING INSTRUMENTS
PULPAL PRECAUTIONS:
MECHANICAL VIBRATION, HEAT, DESICCATION, LOSS OF
DENTINAL TUBULE FLUID, AND OR TRANSECTION OF
ODONTOBLASTIC PROCESSES.
PULPAL SEQUELAE (RECOVERY OR NECROSIS) TAKE FROM 2 WEEKS
TO 6 MONTHS OR LONGER, DEPENDING UPON EXTENT AND
DEGREE OF TRAUMA.
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The remaining tissue is effective in protecting the pulp
in proportion to the square of its thickness.
Steel burs produce more heat than carbide burs because
of inefficient cutting.
Dull instruments will plug debris, do not cut efficiently
and result in heat production.
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When used without coolants, diamond instruments
generate more damaging heat than carbide burs.
Air alone as coolant: much lower heat capacity than
water, desiccates dentin, damage odontoblasts.
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Soft tissue precautions: Lips, tongue and cheeks of the patient.
Good access and visibility.
Isolation of the operating site: rubber dam, retraction type salivaejector tip.
Wait for the instrument to stop or extremely careful while removing thehandpiece from the mouth.
Large disc
Sudden reflex by the patients.
Hand excavators: soft caries removal in the deep preparation may leadto mechanical pulp exposure: round bur at low speed.
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Eye Precautions
Airborne particles, old restorations, tooth structure,
bacteria, debris.
Strong high volume evacuation.
Ear Precautions:
Loud noise: mental and physical distress, increase accident
proneness, reduce overall eficiency.
Noise level in excess of 75 db, 1000 to 8000 cps(frequency)
may cause hearing damage.
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Inhalation Precautions
Amalgams or composites produce submicron particles and
vapor.
Alveolar irritation and tissue reactions.
During cutting or polishing: thermal decomposition of
polymeric restorative materials (sealants, acrylic resins,
composites) : Monomers.
Mask : do not filter either mercury or monomer vapors
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Conclusion:
The removal and shaping of the tooth structure are
essential aspects of restorative dentistry. Modern high
speed instruments has eliminated the need of many
hand instruments, but hand cutting instruments are
still important for finishing many tooth preparations
and thus they remain as an essential part of the
armamentarium for quality restorative dentistry.
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References:
1. Sturdevant’s Art & Science of Operative Dentistry :4th edition
2. Fundamentals of Operative Dentistry; James B. Summitt; 3rd edition.
3. Operative Dentistry of Modern Theory and Practice: M K Marzouk
4. Black GV. A work on Operative Dentistry. Chicago: Medico-Dental Publishing, 1908
5. Dental Hand Instruments, 2003: Elsevier Science (USA). ISBN 0-7216-9770-4
6. Fundamentals of Tooth Preparation: Shillingburg
7. Journal of Interdisciplinary Dentistry / Jul-Dec 2011 / Vol-1 / Issue-2
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