Class I Cavity Preparation for Amalgam [Compatibility Mode]
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Transcript of Class I Cavity Preparation for Amalgam [Compatibility Mode]
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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)
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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 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
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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 mmfrom cavity margin to pulpal floor
Resistance
from cavity margin to pulpal floor
Pulpal floorD
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�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
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• Join weekend ridge between twocavities (<0.5 mm apart)
Resistance
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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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• (��������� &(���0%)�( + &(0()0��)
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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
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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
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• 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
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• 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
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• 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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