How to get a perfect impression in adverse conditions By: Robert Margeas, DDS

• Accuracy in all phases of treatment.
• The preparation must be clean and free of debris.
• The sulcus must be free of blood, saliva, and medicaments that will cause distortion.
• The impression material must be accurate and stable, exhibit high tear strength, and perform well in a moist environment.

An in-depth knowledge of available materials and clinically proven techniques can simplify these everyday procedures. Whether you are treating a single tooth or several teeth, the techniques described will enable you to overcome any clinical challenge, avoid costly remakes, and increase your profitability.

Selecting impression materials
Vinyl polysiloxane impression materials have the best dimensional stability and elastic recovery and are the most accurate of all available impression materials. The impression material you choose should be easy to use and should match your personal handling preferences. Your impression material should also match the technique and impression tray you select for each case.

The key to the ideal impression requires not only great products, but also good tissue management and a good impression technique, especially in adverse conditions.

Good tissue management
Periodontal tissue management is one of the most important phases of the impression procedure. In an ideal situation, the tissue would be in immaculate condition. This would mean no bleeding, exudate, or periodontal problems. But this just isn’t the case in most dental practices. Most patients have either fractured a tooth subgingivally, or perhaps the decay is below the gumline, requiring you to take the margins subgingival. Anytime you are required to take preparations below the free gingival margin, you can cause bleeding that may be difficult to control. This can affect the accuracy of your impressions and the final restoration.

The case that follows will demonstrate how to control hemostasis and cleanse the preparation prior to impressioning. It will also illustrate how important material and impression tray selection can be in obtaining accurate impression results.

Placing retraction cord and achieving hemostasis
When the tooth preparation is complete, tissue retraction should be done in a manner that minimizes tissue trauma. When tissue is healthy and no bleeding occurs from the preparation stage, it is crucial to use a very small, memory-free retraction cord (First String, Clinician’s Choice™). Tissue health is best maintained by not disrupting the connective tissue as you place the cord. When the epithelial attachment and subsequently the connective tissue is violated, bleeding is induced and long-term tissue recession can occur. So, take care when packing retraction cord; lightly tease the cord into the sulcus.

If there is severe bleeding, as shown in Figure 1, achieve hemostasis, or reappoint the patient after proper temporization. In this case, Tissue Goo (Clinician’s Choice), an excellent hemostatic agent, was selected because it is less aggressive than other hemostaic agents and is delivered in a gel that provides lubrication for easy cord placement. Inject Tissue Goo around the sulcus (Fig. 2) and allow it to pool for several seconds. Retraction cord placement becomes easier when packed directly through the Tissue Goo, then allowed to remain in place for approximately 5 minutes (Fig. 3). Rinse away Tissue Goo, and observe the tissue for hemostasis. Notice that Tissue Goo does not discolor the tissue (Fig. 4). Rinse the site prior to prep cleansing, cord removal, and syringing the impression material. After tissue retraction and hemostasis is achieved, examine the preparation for any debris or hemorrhagic by-products around the margins. The air/water syringe often does not remove these.

Figure 1		Figure 2		Figure 3
Figure 4		Figure 5		Figure 6

Cleaning the preparation
Proper care must be taken when cleaning the preparation. If an aluminum chloride or ferric sulphate hemostatic agent is used and not properly cleansed, the impression material may not set. Often, residual hemostatic agent, monomer from temporary fabrication, or hand piece oil can interfere with obtaining a good impression. This debris can be quickly removed with Detail (Clinician’s Choice), by syringing it around the entire tooth preparation and scrubbing for 10 seconds (Fig. 5). Detail contains EDTA, which lifts debris and contaminants off the preparation surface in just seconds. The result is a perfectly cleansed preparation site. Rinse Detail thoroughly (3 seconds) and air dry the preparation (Fig. 6).

A good impression technique
In this case a double cord technique was used. The top cord is removed prior to taking the impression, while the primary cord is left in the sulcus. Syringe Affinity Light Body HF High Flow (Clinician’s Choice) around the preparation margins, keeping the mixing tip submerged and moving forward to avoid air entrapment. During this process, the material is injected around the tooth twice, also to help to avoid air entrapment (Fig. 7). A gentle stream of air further directs the material into the sulcus and gently coats the tooth. Be sure to inject enough light body to completely cover the preparation and even adjacent teeth (Fig. 8).

While you are injecting the light body around the preparation, have your assistant syringe Affinity InFlex into the Quad-Tray™ (both Clinician’s Choice). InFlex is a unique, ultra-rigid tray material developed specifically for the Quad-Tray technique or dual arch technique. The Quad-Tray is the preferred tray for this single crown technique due to its rigidity, low sidewalls, and wide arch structure (Fig. 9). These features prevent distortion during placement and removal of the tray. To provide added support once cured, build excess InFlex around the preparation areas within the tray (Fig. 10).

Figure 7		Figure 8		Figure 9
Figure 10		Figure 11		Figure 12
Figure 13

Insert the tray into the patient’s mouth and remind him/her to fully close, without excess clenching pressure (Fig. 11). One of the most common mistakes made during the impression procedure is taking the impression under compression. Whether due to excess clenching by the patient or excessive pressure by the dentist or assistant holding the impression tray in place, the clinical result will be a missed margin or excessive occlusal adjustment during insertion of the final prosthesis. The impression material itself can rebound once pressure is taken away. Therefore, the best impression is taken under passive conditions.

Affinity impression material cures in less than 3 minutes, allowing far less opportunity for distortion to occur. And the patient also benefits from this short intraoral cure time. At 3 minutes, remove the impression, opposing side first to prevent possible tearing of the impression material. Upon inspection, you’ll notice the clean easy-to-read margins of the impression (Fig. 12). Also, the Affinity InFlex tray material does not overdisplace the light body, which means the entire preparation is captured in light body, yet it cures to a very rigid 78 durometer. Figure 13 shows the final, perfect impression.

Conclusion
The tissue management and impressioning phases of successful fixed prosthodontic procedures can be achieved consistently when you combine predictable products with clinically proven techniques.

For further information on Clinician’s Choice products referenced in this article, please contact Clinician’s Choice at 1-800-265-3444 or by fax at 1-800-719-3292.

Dr. Margeas received both his dental and AEGD degrees from the University of Iowa, where he currently serves as Adjunct Professor in the Department of Operative Dentistry. He has published several articles, and since 1999 has been a clinical instructor at the Center for Esthetic Excellence®, Chicago, IL. Dr. Margeas is board certified by the American Board of Operative Dentistry and is a Fellow of the Academy of General Dentistry (AGD). He maintains a private practice devoted to esthetic dentistry in Des Moines, IA.