<prompt> While preparing the proximal box, the mesiodistal width of the ditch should be:0.8 mm ; two thirds in dentin and one third at the expense of enamel0.8 mm ; one third in dentin and two thirds at the expense of enamel0.8 mm ; full depth in dentin0.8 mm ; full depth in enamel  <response>: Proximal BoxIf the bur is allowed to cut only dentin, the resulting axial wall would be too deep. The mesiodistal width of the ditch should be 0.8 mm the tip diameter of the bur and prepared approximately two thirds 0.5 mm at the expense of dentin and one third 0.3 mm at the expense of enamel.Sturdevant operative dentistry 7th Edition, Page No:e99 