sinus as it varies as he travels anteroposteriorly fig2 furthermore the surgeon approximates the mesial anterior extent in a coronal apical direction as well as the distal posterior extent in a coronal apical direction the surgeon also approximates the occlusal outline of the osteotomy as it connects the mesial and distal anterior and posterior walls of the osteotomy fig6 more importantly the surgeon must then determine the depth laterally along the z axis of the osteotomy within his outline fig3 so as to penetrate up to the schneiderian membrane this lateral depth varies as the surgeon moves along the x y plane along the outline form the methodology traditionally available is the surgeon 39 s view of the color of the bone as it changes as he approaches the piercing of the lateral wall and sees the grey schneiderian membrane after the surgeon has cut the outline form of the osteotomy and penetrated the lateral wall of the sinus fig7 the surgeon begins to elevate the membrane from the floor of the sinus and graft bone in the site rarely does the surgeon place his osteotomy exactly on the floor of the sinus the coronal border and along the exact anterior border of the sinus therefore the surgeon must maneuver the instruments as to separate the membrane from the sinus floor and anterior and posterior walls as there is inevitably a shelf of bone to negotiate to assist the surgeon in visualizing the outline of the sinus in three dimensions a patient can have a ct scan e g.