class i [lecture by dr.wedad etman @amcofam]
TRANSCRIPT
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Class I lesion affects
�The pit and fissures of posterior teeth Surfaces involved are:Surfaces involved are:
–Occlusal surfaces of premolars & molars
–Occlusal 2/3 of the facial & lingual surfaces of molars
� Palatal surfaces of maxillary incisors
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Spread of pit &fissure caries in
enamel & dentin
In enamelCone shape
Base towards DEJ
& apex toward the surface& apex toward the surface
In dentin (Spreads more rapidly than enamel)
Cone shape
Base towards DEJ
& apex towards the pulp
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Class I could be :• Simple occlusal cavity S.O.C
• Compound class I (two surfaces)
* Occluso buccal O.B.C
* Occluso lingual or palatal O.L.C /O.P.C
• Complex class I (more than two surfaces)
* occluso bucco lingual O.B.L.C
• Buccal pit
• Paltal pit in anterior
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CLASS I SIMPLE OCCLUSAL CAVITY
(OCCLUSAL SURFACE ONLY)
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Outline form
Varies in shape according to theVaries in shape according to the
number of cusps
and orientation of pits ad fissures
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Resistance form is obtained by
• Outline placed equidistance from the defective pits ,fissures on smooth ,soundtooth structure
• Sufficient width to include the defects, • Sufficient width to include the defects,
pits & fissures and permit insertion of small condenser for placement of amalgam
But otherwise as narrow as possible
(preservation of tooth structure)
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Extension for prevention
Black suggested that it was necessary to
• remove additional tooth structure to gain access
Resistance
• remove additional tooth structure to gain access
& visibility
• extend the cavity to self-cleansing areas to
AVOID RECURENT CARIES
Black’s cavity width
1/3 intercuspal distance
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CONSERVATIVE APPROACHE
Introduction of amalgams with better properties
& the use of smaller instruments
Resistance
� Cavity width (faciolingual width)
,/- intercuspal distance
(not more than ,-,./ mm)
No extension for prevention
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A Conservative cavity preparation
• Saves tooth structure
Minimize pulpal irritation
Resistance
• Minimize pulpal irritation
• Strong tooth structure,
marginal integrity &
restoration longevity
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� Outline should consist of smooth
curves on occlusal surface
(no sharp line angles)
Resistance
To avoid stress concentration
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• Box form (mortis form)
* flat floor
* definite line & point angles
Resistance
Distribution of force
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• Cavosurface margin is 90° butt joint
• Remove any undermined enamel (enamel
supported with dentin)
Resistance
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• Depth * 0.5mm below DEJ (cavity in dentin)
* The whole cavity depth is about
1.5 - 2 mm
from cavity margin to pulpal floor
Resistance
from cavity margin to pulpal floor
Pulpal floor
D
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�Minimal extension into the marginal ridge (only enough to remove the defect) without removing dentinal support
� Mesial & distal walls
* divergent occlusally(≥≥≥≥ 10°) to follow
Resistance
* divergent occlusally(≥≥≥≥ 10°) to follow
the direction of enamel rods & prevent undermining of the marginal ridge
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• Join weekend ridge between two cavities (<0.5 mm apart)
Resistance
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Retention form
Is obtained through
• Converging Buccal and lingual walls occlusally (undercut)
• Parallelism of the walls
• Griping action of dentin
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Extra means of retention
Grooves
Retention
Prepared at the line angle between floor of the cavity & its walls with
a ¼ round bur
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• Establishing RESISTANCE & RETENTION
(depth & width of the cavity)
gives adequate convenience
Convenience form
gives adequate convenience
to instrumentation ,removal of
decay & insertion of the
restoration
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If there is spot of caries
remaining in the cavity
Infected carious dentin should be removed by:
• Excavators (spoon or discoid) • Excavators (spoon or discoid)
soft caries
• Large carbide Rose head at low speed
hard caries
* Until the tooth structure feels hard & firm
* lesion is lighter in color
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The removal of carious dentin should not affect resistance form
Create a flat floor peripheral
to the excavated area
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Compound class I
cavity cavity
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It involves two surfaces
• Occlusal surface
• Buccal or Lingual grooves OF molars
Compound class I
• Buccal or Lingual grooves OF molars
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� Occlusal box follows the same principles for class I simple occlusal cavity
� After preparing the occlusal cavity
* #245 bur is held ⊥ to the pulpal floor &
parallel to the long axis of the tooth crown
Cavity preparation
parallel to the long axis of the tooth crown
* moved towards the buccal/lingual
direction along the fissure maintaining uniform depth until the bur reaches the buccal/lingual surface
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• The step is prepared keeping the bur parallel to the buccal/ lingual surface of the corresponding groove
So The axial wall will follow the contour of
the buccal/lingual surface at a the buccal/lingual surface at a
uniform depth of 0.5mm inside
the DEJ (0.2mm is permissible)
• Axiopulpal line angle is
rounded
Resistance
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• Extend the lingual box gingivally to terminate at the buccal/lingual groove creating a flat gingival seat for
…………. Resistance …………. Resistance
• Gingival wall meets the tooth surface at 90°& the axial wall makes an obtuse angle with the pulpal floor ……………..Resistance
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• Mesial & distal walls of the B/L BOX are made parallel to each other with slight occlusal convergence ………………………………..Retention
• Mesial & distal walls are butt joint with the cavity margins………………… Resistancecavity margins………………… Resistance
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Pit & fissure on facial or lingual surface
only(buccal pit /paltalpit)
• Shape varies (oval –round-oblong) depending
upon the extent of caries
• Walls continually joined & slightly convergent • Walls continually joined & slightly convergent
towards the cavosurface margin
• Axial wall follows the contour of the
buccal/lingual surface