Whatever you see in your mirror is what the scanner is going to pick up. You want to be able to see .5mm sub-marginal.

Often we receive digital impressions that have not had an adequate job of tissue and moisture control. While the margin is visible, it is not clearly definable. Impression material will hydraulically force tissue and moisture out of the way and travel sub-marginal. Your pre-impression techniques for digital impression must accommodate that same sub-marginal requirement visually.

When sufficient separation between the soft tissue and the margin is not achieved, it can be immediately seen with the first scan.

The most effective way to gain a clear digital scan is to prepare a supragingival margin. However, this is not always possible as often clinical needs dictate subgingival margins.

When subgingival margins are present these retraction strategies work well:

• Use a soft-tissue laser to remove unhealthy inflamed bleeding tissue and tissue that is impinging on the margin.
• Packing cord is an effective means to get the isolation you need, though it does take up some of the space that you need to get a clear visual submarginal.
• Using retraction paste such as Espasyl, Traxodent, or 3M Espe Astringent can give you the cleanest line of sight, and usually have hemostatic properties, thus controlling the problem of bleeding.

It is best to moderate to heavy chamfer and polish your prep. The chamfer margins allow the milling process to produce the most intimately-fitting crown. Avoid feather edge margins, especially when they are deep subgingival.