When it is necessary to place casting margins subgingivally, it is important that they not violate the biologic width. A technique utilizing nonmedicated retraction cord during preparation is described which has several advantages. It results in bloodless, trauma-free tooth preparation and concealment of the metal margin without biologic width impingement or gingival recession. A resilient, unattached gingival margin free of inflammation is critical for the success of this technique. The physical and chemical properties of healthy gingival collagen and ground substance are briefly discussed along with the disadvantages of using this technique in the presence of gingival inflammation.