Instrument of cavity preparation• High speed small round bur,fissure bur,inverted cone bur.(carbide or diamond)• Low speed round bur.(carbide)• Hand cutting instrument
Step of amalgam cavity preparation• In shallow cavity,outline form design should be considered first.• In deep cavity,convinience form and remove of deepest part of carious dentin must perform before any other step of cavity prepared.
Cavity preparation(I)• Cavity depth 1.5 mm or beneath DEJ 0.2 mm.• Isthmus width equal 1/3-1/4 B-L cusp width.• Cavity width should less than ½ of B-L cusp width.• Buccal-lingual converge and mesial-distal diverge.• Marginal ridge should preserve of 1.6 mm.• Pulpal wall parallel to occlusal plane.• Not involved oblique and transverse ridge, if it is unnecessary.
Criteria of carious dentin removed• Remove unminerized dentin with excavater or low speed round bur.• Tiny white powder without stagnation on bur surface.• Light reflect over dentin surface.
Cavity preparation(II)• Trunket cone in proximal box.• In Class II cavity , proximal clearance 0.2 mm, gingival clearance 0.5 mm. Reverse curve in buccal surface.• Axiopulpal line angle should be rounded or bevel, gingival line angle beveled.• Gingival wall width should be 0.8-1.2 mm.