Two-cord technique for impressions

March 1, 2006
To perform the highest quality restorative dentistry possible, it goes without saying that there should not be much bleeding present at the preparation or seat appointment.

To perform the highest quality restorative dentistry possible, it goes without saying that there should not be much bleeding present at the preparation or seat appointment. At each of these appointments, bleeding typically is a sign of iatrogenic dentistry, or bad treatment planning on the dentist’s part.

At the prep appointment, there is always potential for bleeding since we are using a high-speed handpiece and a diamond bur near the gingival tissues. Lacerating the tissues will make preparation more difficult, especially as we finalize the margin of the preparation. It also poses a problem because we are not sure how the tissue will heal, and whether or not it will recede from the margin.

When it comes to taking impressions, bleeding can compromise ideal results. The two most popular impression materials for final crown and bridge impressions are polyvinyl siloxanes (addition reaction silicones) and polyether materials. By nature, polyvinyls are hydrophobic, and additives are introduced into the material to make it somewhat more hydrophilic. This hydrophilicity applies to water only; saliva and blood do not count.

Polyethers, on the other hand, are naturally hydrophilic, but they still do not perform well in the presence of blood or saliva. With either class of impression material, the cleaner and drier the field, the better the impression. This is why I use the two-cord technique to take impressions.

I have found the two-cord technique is the most predictable method to prevent bleeding. The first cord, a 00 Ultrapak cord from Ultradent, is placed as soon as the contacts are broken. The ends are cut flush so the entire cord will remain subgingival throughout the preparation sequence. This first cord retracts the tissue about 0.5 millimeter. This allows you to drop the margin of your preparation to the new gingival level.

When the cord is removed and the tissue has returned to its original height, this new margin position will be just slightly subgingival. This occurs even though the bur never was taken subgingival, which leads to lacerated tissue. Because the first cord stays in place for the entire preparation, there is no medication or styptic agents used on this cord.

After finishing the preparation, the second cord is placed on top of the first cord. The second cord is an Ultrapak 2E cord from Ultradent. This cord provides ample retraction for the final impression material. For certain clinical situations, such as areas of gingival recession, it is not possible to get a 2E cord on top of the other cord. In this instance, a size 1 cord might be more desirable. While the patient is biting down, this cord is left in place for eight to 10 minutes with an anatomic Comprecap (Coltène/Whaledent) placed on top of it.

When the eight to 10 minutes have elapsed, the Comprecap and top cord are removed. This leaves an open, dry sulcus in which to express the syringe material. You should not see any bleeding at this point because the 00 cord is still in place against the base of the sulcus. In a typical one-cord technique, one cord is placed. When it is pulled five minutes later, the bleeding starts. It is important to remember that no matter how healthy someone’s free gingival margin looks, there is always inflammation at the base of the pocket. The two-cord technique addresses the tendency for bleeding by keeping the bottom cord on top of the inflamed tissue.

In fact, the bottom cord can remain until the temporary crowns have been cemented. Then the cords can be pulled to ensure that no excess temporary cement has been left in a sulcus or an embrasure. Excess temporary cement in either location can lead to gingival recession while the permanent crowns are being made.

A dental assistant can make the provisionals, making sure that the gingival embrasures are completely open on the temps. The patient is advised about the black triangles on the temps, and is told that they will not be on the final restorations. You do not want to create any papillary recession due to overcontoured temps. You won’t notice this until the seat appointment. While the crowns will fit fine, there will be some exposed margin due to recession. You will see the junction line between the crown and the tooth.

There are times where bleeding gingiva is simply unavoidable. For these times, I use Ultradent’s ViscoStat Clear. Previously, I preferred ViscoStat, but I stopped using it because of the way it interacted with the Ultrapak retraction cord, turning the gingiva purple. ViscoStat Clear remains clear throughout the entire process, and works well to stop unnecessary minor bleeding.

Dr. Michael DiTolla is the Director of Clinical Research and Education at Glidewell Laboratories in Newport Beach, Calif. He lectures nationwide on both restorative and cosmetic dentistry. He also teaches hands-on courses on digital photography and digital image-editing for the entire team. Dr. DiTolla has several clinical programs available on DVD through Glidewell. For more information on this article, or to receive a free copy of one of Dr. DiTolla’s clinical DVDs, e-mail him at [email protected].

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