External walls should have 90째 Cavo surface angle.
Class II cavity preparation for extended carious lesion: Outline is determined by extent of caries, already present restoration with secondary caries. Gingival seat may be extended toward root surface. The width of gingival seat for premolar 1mm and molar 1-1.5mm. -
Depth of axial wall premolar 1.2mm; molar 1.8mm.
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Width of axial wall is not altered.
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Facial and lingual walls proximally more wider than initial class II preparation.
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Facio-gingival and linguo-gingival line angles are sharp.
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The width of isthmus is 1/3 of inter-cuspal distance.
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To prevent any injury to gingiva place triangular wedge in inter-dental area.
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The axial grooves are placed on facial and lingual walls as a secondary retention to prevent lateral displacement.
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If deep caries is there in axial wall it should be removed by spoon excavator and application of appropriate cavity liners.
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