The completed cavity design showing the typical cusp cover for the disto-lingual cusp. Note the limited extension to the buccal of the disto-buccal cusp. There is no need to extend beyond the totally demineralised enamel – that is, extension for prevention is not justified. A short length of mylar strip has been contoured and placed to act as a matrix. It is lightly supported by a wooden wedge ready for placement of the glass-ionomer.