In this step you’re essentially trimming back to the gingival margin, or more accurately, back to where the bulk-out wax ended on the gingival margin. If the wax margin is not well delineated it will be very difficult to determine how much needs to be trimmed off the shell. This first step in the trimming process should be done by orienting the acrylic bur perpendicularly to he axial wall along all the buccal and palatal surfaces. - See more at: http://www.speareducation.com/spear-review/2013/04/eggshell-provisionals-full-arch-cases-part-ii/#.U3cFjfl_ttw