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Class I lesion affects
�The pit and fissures of posterior teethSurfaces 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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CLASS ISIMPLE OCCLUSAL CAVITY(��� $�% �$&'%�( �) *�
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Resistance formis obtained by
• Outline placed equidistance from thedefective pits ,fissures on smooth ,soundtooth structure
• Sufficient width to include the defects,• Sufficient width to include the defects,pits & fissures and permit insertion of smallcondenser for placement of amalgam
But otherwise as narrow as possible(preservation of tooth structure)
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 toAVOID RECURENT CARIES
Black’s cavity width1/3 intercuspal distance
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Resistance
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No extension for prevention
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Resistance
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� Outline should consist of smoothcurves on occlusal surface
(no sharp line angles)
Resistance
To avoid stress concentration
• Box form (mortis form)* flat floor* definite line & point angles
Resistance
Distribution of force
• Cavosurface margin is 90° butt joint• Remove any undermined enamel (enamel
supported with dentin)
Resistance
• Depth* 0.5mm below DEJ (cavity in dentin)* The whole cavity depth is about
1.5 - 2 mmfrom cavity margin to pulpal floor
Resistance
from cavity margin to pulpal floor
Pulpal floorD
�Minimal extension into the marginalridge (only enough to remove thedefect) without removing dentinalsupport
� Mesial & distal walls* di t l ll ( 10°) t f ll
Resistance
* divergent occlusally(≥≥≥≥ 10°) to followthe direction of enamel rods &prevent undermining of the marginalridge
• Join weekend ridge between twocavities (<0.5 mm apart)
Resistance
Retention formIs obtained through
• Converging Buccal and lingual wallsocclusally (undercut)
• Parallelism of the walls• Griping action of dentin
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Retention
Prepared at the line angle betweenfloor of the cavity & its walls with
a ¼ round bur
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Convenience form
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Infected carious dentin should be removedby:
• Excavators (spoon or discoid)( p )soft caries
• Large carbide Rose head at low speedhard caries
* Until the tooth structure feels hard &firm* lesion is lighter in color
The removal of carious dentin should notaffect resistance form
Create a flat floor peripheralto the excavated area
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Compound class I
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� Occlusal box follows the same principles forclass 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 maintaininguniform depth until the bur reaches thebuccal/lingual surface
• The step is prepared keeping the burparallel to the buccal/ lingual surfaceof the corresponding groove
So The axial wall will follow the contour ofthe buccal/lingual surface at athe buccal/lingual surface at auniform depth of 0.5mm inside
the DEJ (0.2mm is permissible)• Axiopulpal line angle is
roundedResistance
• Extend the lingual box gingivally toterminate at the buccal/lingual groovecreating a flat gingival seat for
…………. Resistance• Gingival wall meets the tooth surface at 90°
& the axial wall makes an obtuse angle withthe pulpal floor ……………..Resistance
• Mesial & distal walls of the B/L BOXare made parallel to each other withslight occlusal convergence………………………………..Retention
• Mesial & distal walls are butt joint with thecavity margins………………… Resistancecavity margins………………… Resistance
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