The following pictures depict the sequence of burs we recommend that you use to finish a preparation quickly. While patient is getting numb, take a quick look at the clearance you will need to reach proper material thickness. Once the quadrant is isolated with isolite and optragate, take an occlusal router bur and create a trough to gain the proper depth. Follow that with a flat disk, and you can quickly reduce the occlusal height.
A shoulder bur of .8 mm thickness can help you reduce the interproximal areas as well as the buccal and lingual margin lines. Before finishing the prep, place hemostatic agent like expasyl in the sulcus and place retraction cord. while it is setting, check your reduction. If you need more space, now is the time to reduce some more.
Once you have adequate clearance, retraction, and hemostatis, you can readily image and find your margins in the CAD software