After a tooth has been prepped for a crown or implants have replaced a tooth, a dental impression is taken to get an accurate reading of the tooth that now has a new shape.
Once an accurate impression is taken, a mold is made and the crown can be built from this mold.
An accurate dental impression must record ALL of the prepared tooth surfaces. If the gums are blocking the impression material from reaching the full tooth, a gingival “retraction” cord is used to temporarily move the gums out of the way. If the gums are
healthy, they get less in the way.

When gingival retraction cord is needed, the procedure is:

1. Ensure a dry and clean impression site with cotton rolls, and the saliva ejector as necessary.
2. Place the gingival retraction cord around the tooth.
3. Wait the appropriate time of 4 to 6 minutes.
4. Wash and dry the impression site.

Impression.

1. Syringe impression material carefully around the tooth.
2. Seat the impression tray immediately.
3. Wait 5 minutes until the impression material has set.
4. Remove the impression tray.
5. Remove the gingival retraction cord.

An accurate mold of the tooth is essential to make a well-fitting permanent crown.