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7/29/2019 14.Cl2 Amal.principles2.08
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CLASS II AMALGAM
Design Principles
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CLASS II
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Class II cavitated caries lesions
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opaque white haloes identify areas of
enamel undermining and decalcificationfrom within
Class II cavitated caries lesions
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radiographic appearance of
the Class II caries lesion
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A
E1 lesion
confined to outer
half of enamel
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B
E2 lesion
reaches into inner
half of enamel
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C
cavitated lesion
spreading radiolucency
at DEJ
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Primary Caries
D1E2
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Primary Caries
D1D2
D3
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Accepted Terminology
extending into proximal
extending gingivally
preparing a proximal box
Jargondropping a box
deepening cervically
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The Class II cavity prepared to receive amalgam has two parts
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the occlusal portion
design principles are the same as for the Class I cavity
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the proximal portion orproximal box
design principles will be presented now
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names of walls for the the occlusal portion of the Class II cavity
are similar to the Class I
Class IClass II
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DISTAL
WALL
LINGUAL WALL
BUCCAL WALL
MESIAL
WALL
DISTAL
WALL
LINGUAL WALL
BUCCAL WALL
Class I
Class II
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PULPAL FLOOR
PULPAL FLOOR
Class I
Class II
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names of walls for proximal portion of Class II cavity
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GINGIVAL SEAT
LINGUAL
WALL
BUCCAL
WALL
DISTAL WALL
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LINGUAL
WALL
BUCCAL
WALL
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LINGUAL
PROXIMAL
WALL
BUCCAL
PROXIMAL
WALL
BUCCAL
OCCLUSAL
WALL
LINGUAL
OCCLUSAL
WALL
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AXIAL
WALL
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names of line angles for proximal portion of Class II cavity
LINGUO-GINGIVAL
LINE ANGLE
AXIO-BUCCAL
LINE ANGLE
AXIO-PULPAL
LINE ANGLE
AXIO-LINGUAL
LINE ANGLE
AXIO-GINGIVAL
LINE ANGLE
BUCCO-GINGIVAL
LINE ANGLE
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names of cavosurface margins for proximal portion of Class II cavity
BUCCAL
PROXIMAL
CAVOSURFACE
MARGIN
LINGUAL
PROXIMAL
CAVOSURFACE
MARGIN
GINGIVAL
CAVOSURFACE MARGIN
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names of point angles for proximal portion of Class II cavity
AXIO-
BUCCO-
GINGIVAL
POINT ANGLE
AXIO-
LINGUO-GINGIVAL
POINT ANGLE
BUCCO-
GINGIVO-
CAVOSURFACE
POINT ANGLE
LINGUO-
GINGIVO-
CAVOSURFACE
POINT ANGLE
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PROXIMAL OUTLINE FORMPRINCIPLE
straight
B & L outlines near
parallel to long axis oftooth
gingival outlineperpendicular to long axis
of tooth
RATIONALE
conservative of toothstructure
resists forces of occlusion
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EXTENSION
a balance between
conservation of
tooth structure and
the need for access
and to removedefective tooth
structure
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PROXIMAL EXTENSIONPRINCIPLE encompasses carious
tissue
eliminatesunsupported enamel
encompassescontiguous fissures
encompassescontiguous
restorations
RATIONALE
eliminates infectedtissue
eliminates weakenedtooth structure
reduces risk ofsecondary caries
maximizes restorationlifespan
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PROXIMAL EXTENSION
PRINCIPLE
clears adjacent tooth by
0.5mm (0.3 - 0.65mm)
RATIONALE
access for matrix band
allows inspection ofrestoration margin
access for finishing
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PROXIMAL DEPTH
proximal depth is M-D dimension of proximal box
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PROXIMAL DEPTH
proximal depth is M-D dimension of proximal box
Syn: axial depth
NOT pulpal depth
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PROXIMAL DEPTH
PRINCIPLE
0.5mm into dentin
1.25 - 1.5 mm measuredat level of gingival seat
RATIONALE
suf ficient bulk ofamalgam to preventfracture
maximum thickness ofdentin protecting pulp
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AXIAL WALL
PRINCIPLE
smooth
straight O-G, parallel tolong axis of tooth
parallels curvature of
tooth surface B-L
RATIONALE
optimize adapatationof amalgam to wall
uniform bulk ofamalgam to preventfracture
maximum pulpalprotection
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AXIO-PULPAL LINE ANGEL
PRINCIPLE
rounded or beveled
RATIONALE
reduces risk ofamalgam fracture
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GINGIVAL SEAT
PRINCIPLE
smooth, flat, straight
perpendicular to longaxis of tooth M-D & B-L
enamel planed at margin
RATIONALE
optimize adaptation ofamalgam to walls
resists forces of occlusion
elimination of friableenamel
A
A
A-A
plane margin enamel
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BUCCAL & LINGUAL WALLS
PRINCIPLE
smooth, straight G-O
wall nearest functionalcusp convergent 6 G-O
wall nearest non-
functional cusp parallelslong axis of tooth
RATIONALE
optimize adaptationof amalgam to walls
helps lock restoration intooth (retention)
preserves strength of
cusps (resistance form)
FC NFC
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tangent
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BUCCAL & LINGUAL WALLS
PRINCIPLE
angle with proximal
cavosurface 90-110(measured to tangent)
RATIONALE
optimizes strength ofboth amalgam and
enamel at margin
tangen
ttangent
90110
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the cavosurface angle is defined as the anglein metal at the margin of a restoration
9070
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BUCCAL & LINGUAL WALLS
PRINCIPLE
proximal cavosurface
angle is 70-90(measured to tangent)
RATIONALE
optimizes strength ofboth amalgam and
enamel at margin
9090 110
70
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PROXIMAL RETENTION GROOVES
PRINCIPLE
placed in B&L proximalwalls 0.5mm deep to DEJ
directed laterally, not pulpally extending from G seat to A-P
line angle
0.5mm deep gingivally,
fading away occlusally rounded cross-section
RATIONALE
provides mechanical lockagainst displacement
proximally prevents encroachment on
pulp
prevents undermining
enamel maximizes retention while
minimizing weakening oftooth
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CAVITY REFINEMENT
PRINCIPLE
internal line angles well-
defi
ned but not sharp
RATIONALE
maximizes amalgamresistance todislodgement
reduces stressconcentration & risk
of subsequent toothfracture
cusp fracture
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cuspfracture
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CAVITY REFINEMENT
PRINCIPLE
B-G and L-G line angles
have slight radius
RATIONALE
reduces stress
concentration & riskof subsequent tooth
fracture
dif fi
cult to condensethick amalgam into
sharp point angles
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CAVITY REFINEMENT
PRINCIPLE
cavosurface margins
well-defi
ned & well-supported
RATIONALE
easier to visualize &carve following
condensation optimize adaptation of
amalgam to margins
eliminates weak tooth
structure maximizes marginal
integrity
CAVOSURFACE MARGINS
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enamel
cavosurface marginunsupported, rough poorly defined
CAVOSURFACE MARGINS
tooth surface
CAVOSURFACE MARGINS
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amalgam enamel
cavosurface marginunsupported, rough poorly defined
CAVOSURFACE MARGINS
tooth surface
ditching
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ditching
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CLEANLINESSPRINCIPLE
cavity is free of debris
& moisture
RATIONALE
facilitates adaptation
of amalgam to the
cavity
improves physical
properties of the
restoration by
elimination of voids
& foreign material
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TISSUE PRESERVATIONPRINCIPLE
rubber dam intact
adjacent toothundamaged
gingival soft tissues
not undulytraumatized
RATIONALE
isolation important to
quality of result
prevention of post-
operative sensitivity,
inflammation, &
nidus for further
caries attack