Note the preservation of all cusps, smooth-flowing outline with narrow isthmus and conservative dovetail forms. The green dots (left) and hatchet (right) indicate 0.5 mm "clearance" between the cavosurface margins and the adjacent tooth.
The resistance form criteria remain the same as Class I occlusal preprartions: Divergent proximal walls (mesial or distal) to protect the enamel ridge and minimum 1.5 mm measured at the marginal ridge providing at least 1.0 mm thickness of amalgam in all pits and fissures.
RESISTANCE FORM - Proximal Box
The axiopulpal line angle is rounded slightly to reduce stress concentration and increase bulk of amalgam between the occlusal and box portions. At the gingival cavosurface margin, the gingival wall is finished so that no unsupported enamel rods remain.
