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Dr. Menni to sez
Hey Mo, learn’m ‘bout
dental tools today!
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- Thomas Carlyle
Man is a tool using animal.Nowhere do you find him without tools;
Without tools he is nothing, with tools he is all.
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2 Lectures
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used in dentistry
hand rotary
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Dr. A. F. Peete
St. George, SC
late 19th century
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Single-ended
Double-ended
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Carbon 1.0 - 1.2%
Manganese 0.2%
Silicon 0.2%
Iron 98.4 - 98.6%
Carbon 0.6 - 1.0%
Chromium 18%
Iron 81 - 81.4%*
1930’s
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Chisel of stainless steel with carbide insert
to produce the cutting edge.
Carbide - an intermetallic compoundof carbon and another material
“ Tungsten” carbide - used in cutting instruments (blades)
“ Silicon” carbide - used as abrasives
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Annealing
Hardening
Tempering
- 3 basic & sequential steps
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Annealing reduces the steel to its extreme degree of softness. The
metal is heated to a dull redness and cooled slowly. A greater degree
of softness is produced by excluding the atmosphere by covering it
and allowing it to cool slowly. Annealing relieves strains and makes
the metal as ductile as possible for machining and shaping.
Main Entry: duc·tile
Pronunciation: ' d&k- t &l , - "t I l
Function: adjective
Etymology: Middle French & Latin; Middle French, from Latin ductilis, from duc
1 : capable of being drawn out or hammered thin <ductile iron>
2 : easily led or influenced
3 : capable of being fashioned into a new form
synonym see PLASTIC
-duc·til·i·ty /"d&k- ' t i - l &- tE/ noun
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The metal is then hardened to its limit by heating it to a full cherry-red color
which allows the carbon to freely migrate through-out the piece
and plunging it immediately into cold water. In this state it is extremelybrittle. The more carbon present, the harder and more brittle it becomes.
Note: Gold casting alloy is hardened by slow bench
cool ing and annelled (softened) by quenching a hot
casting in water.
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The relief of strains produced by the hardening process to an
extent needed for a particular tool (varies). Tempered steel is less brittle.
This is accomplished by reheating to a lower temperature (than for
hardening) and plunging it into cold water, oil, or mercury.
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Temperature abuse of hand instrumentswill alter the original properties of the alloy
and make the instrument unserviceable
for the intended purpose.
Don’t flame a cutting/carving instrument becauseyou will destroy its cutting ability and toughness.
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4 Parts Of A Hand Cutt ing Instrument
Handle (shaft)
Shank
Blade (or nib)
Cutting Edge (or “face” in the case of a nib)
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blade
(nib)shank handle
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Face (2)
Secondary
Cutting edge
SecondaryCutting
edge
side
bevel
endbevel
primary
cuttingedge
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Likewise with a spoon excavator !
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The Good, the Bad and the Ugly:
Proper and Improper End Bevels
Cutting edge
Angle of the bevel
inefficient efficient
and
durableefficient
but
not durable
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- a small pointed or projecting part
… but without a blade or cutting edge
Examples in instruments we use:
• amalgam condensers• burnishers
• plastic instruments
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Straight - no angle
Monangle - one angle
Binangle - two angles
Triple angle - three angles
curved
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15-8-12
G.V. Black’s Instrument Numbering Formula
Enamel Hatchet: 15-8-12
15 = width of blade
(tenths of mm.)
8 = length of blade
(mm)
12 = angle of blade
from long axisof handle
centigrade !
He’s Watching Yo
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Astronomical scaleCentigrade scale
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Measuring
Angle of cutting edge
Measuring
Angle of blade
14°
Instruments with four numbers
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15 - - 8 - 12
Instruments with four numbers
Primary cutting edge is
NOT 90° to blade.
Angle of primary cutting edge (centigrade °)
placed in second position.
95
margin trimmers & angle formers
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distal margin trimmer
Mesial Margin Trimmerless than
90° more than
90°
mesial margin tr immer
80
90
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Unsupported enamel
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c. 20°
Margin Trimmer In Action
Explorer 23-17
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p
“ E P k”
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“ Exam Pack”
mirror
explorer
perio probe
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Cone Socket Front-Surface Mirror
EVIL RearSurfaceMirrors
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EVIL Rear Surface Mirrors
Spoon Excavator
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Spoon Excavator
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Binangle Chisel
“2 angles”1
2
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Curved Chisel (Wedelstaedt)
Wh t i it?
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What is it?
1 2
3
Triple Angle Hoe
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…fair material for testing.!
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Palm & Thumb
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with finger rest !
with f inger rest ! uh-oh!
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Questions about hand instruments
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