Impression Pearls: Obtaining Successful and Predictable Indirect Restorative Outcomes

By Jeffrey Bonk on January 20, 2021

Preparing teeth properly for indirect restorations is critical for creating an acceptable outcome that satisfies the Esthetic, Function, Structure, Biology (EFSB) requirements. Obtaining accurate and predictable impressions is an integral part of the restorative process. In today's world, impressions may be obtained either through digital technology or a more traditional analog technique.

Whatever the method, the marginal fit is a key parameter for a successful outcome. The digital world has advanced tremendously regarding its application in restorative dentistry.

The digital approach is certainly efficient and effective but just like the analog technique, success depends upon obtaining clear preparation margins. This article is aimed at providing a few “impression pearls” to help bring predictability to the capture of restoratively prepared tooth structure.

Pearl 1 – Cotton wisps

Whether impressions are obtained through digital or analog means, clear capture of the preparation margins is imperative for restoration success. There is more forgiveness in the analog capture world than in a digital scan.

Digitally speaking, if the scanner recording tip (or eye) cannot “see” the marginal area (with approximately 0.5 mm separation between tooth structure and tissue), significant inaccuracy and unreadability are expected. All tissue interference must be removed to digitally capture margins precisely. If tissue overhangs the marginal area, or if crevicular fluid or hemorrhage is present, a clear capture is improbable.

This is not as much an issue in the analog world. In using a polyvinyl or silicone impression technique, the injection and flow of the material may deflect the fluid. Additionally, if the impeding interferences are not diverted, the impinging tissue will be captured within the impression. This tissue obstacle will be trimmed away from the margin at the time of master die stone manufacture. No matter which technique (i.e., analog or digital) is applied, tissue and fluid control lead to greater impression predictability.

Tissue retraction cord is mandatory with subgingival margins. The most common approach for most dentists is to use a two-cord technique. Using this method, the tooth is prepared for the gingival margin. The first cord is placed to retract the tissue and allow for sub-gingival tooth preparation.

Subsequently, a second cord is placed on top of the first to control fluid and physically deflect the tissue. The superior cord is removed just before the impression process. Although the technique yields predictable margin capture, the two-cord placement may injure or insult the tissue biologic width dimensions and result in potential tissue recession.

As an alternative to placing two cords, cotton wisps dipped in Hemodent (a buffered aluminum chloride liquid from Premier Dental) may be gently placed over the first cord. The cotton wisps offer the opportunity to use a varied thickness dimension. Pulling cotton fibers from a cotton roll results in an amalgamation of fiber size. One end of the wisp may be only a few fibers in thickness. The opposite end may include greater consistency.

By using gentle pressure in placing the wisp, and utilizing the chemical action of the Hemodent, tissue retraction becomes adequate and less traumatic. The results are improved marginal visualization and attainment.

Jeffrey Bonk, D.D.S., is a member of Spear Resident Faculty. For full article click here

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