Shape: Flat and perpendicular to long axis of tooth, so masticatory forces are transmitted to periodontium. A slight apical incline of enamel wall results when gingival seat is near to cervical portion of tooth. There is 0.5 mm clearance should be the there from adjacent teeth. In caries susceptible individual it is 0.75mm. Width: In premolars it is 0.6-0.8mm. Molars 0.8-1mm When placing gingival margin in cementum, the round tooth pick or triangular wedge is placed in gingival embrasure to protect underlying gingiva. Axial wall: Placement in dentin it should be parallel to long axis of tooth because - For convenience form. - To provide additional bulk of amalgam. - Retentive grooves can easily placed in dentin. Shape: Follow the contour of tooth (convex) or straight for increased resistance and retention. Length of axial wall from pulpal floor is 0.4-0.6mm Width is not uniform triangular shape apex towards occlusal and base towards gingival seat. Isthmus: Isthmus is junction between occlusal portion and proximal facial and lingual part of preparation.
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