Jump start your impressions: tips for improving the impression-taking process.

Imagine you've just removed an impression tray from a patient's mouth, only to find that there is a void in a critical area, or that the teeth have contacted the tray, requiring the impression to be taken over. This obviously is not the outcome you anticipated, especially since you're behind schedule. Retaking the impression is going to put you even further behind, not to mention that the patient, who may have gagged through the procedure, won't be too pleased.

Whether you're taking a preliminary or a final impression, you want good, consistent results. But those results don't happen by accident. For instance, in a manufacturing environment, unexpected or less than satisfactory results can have devastating effects on the output of products. As a result, most manufacturers employ an ongoing review process called continuous quality improvement, in which each step of a procedure is analyzed for relevance, efficiency and overall effectiveness. Although we don't have a great deal of time to devote to this detailed process, it could be very helpful in improving techniques, which ultimately enhance productivity. So let's examine common impression techniques to determine if there are any steps that might improve the process.

The task that we will evaluate is taking a full arch impression for whitening trays, a common task delegated to dental assistants.

What steps are necessary to prepare the tray and impression material to the point of inserting the tray in the patient's mouth?

In most practices, impressions for study models or for whitening trays are taken with disposable or reusable perforated trays and alginate impression material. Reusable metal trays come in a variety of sizes, and several trays may need to be tried in the patient's mouth to determine the correct size. This is important both for patient comfort and the ability to record the appropriate structures in the mouth. Metal trays, and to some extent disposable trays, can be rather bulky and uncomfortable for the patient even without impression material. Perforated trays are used in most cases to lock the material into the tray, since adhesives are not used with alginate materials. The perforations may allow excess material to extrude from the tray and cause discomfort or gagging for the patient. In some cases, rope or beading wax may be used to prevent the impression material from extruding from the tray, or to add bulk to the palatal area of the upper tray if the patient has a high palate. Each additional step in the process of sizing and customizing the tray adds to the completion time necessary for the procedure.

Once the trays are selected and modified (if necessary), the material is mixed and placed in the tray using the mixing spatula. The recommended technique for loading the mandibular tray is to hold the tray in one hand, and with the opposite hand, place the spatula with material on the lingual side of the tray and scrape or wipe the material into the tray Once the tray is loaded, the tip of the spatula should be pressed down through the material to remove any air bubbles that may have been incorporated into the material, and could cause voids in the impression. It is important to smooth the surface of the material with room temperature water to provide a smoother surface to contact the teeth. The tray now is ready to be placed in the patient's mouth.

For a maxillary tray, it is recommended that the material be loaded from the posterior area of the tray. Place more material in the palatal area, and less at the rear of the tray, to prevent excess material from escaping when it is placed. When the tray is loaded, again press the tip of the spatula through the material to remove air bubbles, and smooth the surface with room temperature water. This tray now is ready to be placed in the mouth.

What if this procedure could be more comfortable for the patient, involve less preparation of materials and provide for increased accuracy of the impression?

These improvements can be accomplished by utilizing more advanced impression trays and new types of impression materials and mixing systems.

A new type of impression tray, the 3M ESPE Directed Flow Impression Tray, is a disposable tray that has been computer designed to enhance the fit for both arches. The tray utilizes a fleece strip to retain the impression material in place of adhesives or perforations (Photo 1).

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Fill the tray completely so that the retentive lips of the tray, along with the fleece strip, will prevent the material from pulling away from the sides. The strip also acts as a spacer to prevent teeth from contacting the tray after insertion.

The trays come in three sizes--small, medium and large for both arches, and can be used for preliminary and final full arch impressions (Photo 2). The maxillary tray has a built-in reservoir to catch excess material and prevent gagging. The characteristics of this tray make it more comfortable for the patient and can save steps in tray preparation.

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The next process improvement is utilizing 3M ESPE Position Penta[TM] Quick Impression Material. This is a vinyl polysiloxane (VPS) impression material that can be used in place of traditional alginate for preliminary impressions and study models. It is more accurate than alginate, has rigid physical properties, is less prone to tearing or damage after removal from the mouth, and does not require immediate pour-up. The material is similar to that used for final impressions, but modified for use as a preliminary impression material. It provides a much smoother surface, which produces better quality models for fabrication of whitening trays or for making temporary restorations if used as a matrix for provisional materials. When using this impression material, the seating technique is different compared to a traditional alginate material. Impressions made with Position Penta Quick impression material should be seated the same as a precision impression, where the tray is positioned, then slowly seated and held in place.

This impression material is designed to be mixed in the 3M ESPE Pentamix[TM] Mixing Unit. Using the Pentamix mixing unit makes mixing impression materials very fast and efficient--literally with the touch of a button. There is no air incorporated into the mix and the mix is completely homogeneous, resulting in more accurate impressions. Imagine no mixing bowls and spatulas to clean up after taking a preliminary impression. Imagine mixing the material with just one touch of a button, rather than squeezing an automix cartridge dispenser. The impression tray is filled automatically, directly from the mixing unit, making it much easier to fill the tray and less likely that air bubbles would become trapped in the material in the tray (Photo 3).

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Continuous improvement makes our jobs easier and provides a better patient experience. By making some changes in the process of taking impressions as described here, with improved tray design and a different type of impression material and mixing system we can achieve several desirable goals:

* we could eliminate discomfort for the patient

* save mixing and cleanup time

* produce a better end result.

Mary Govoni, CDA, RDA, RDH, MBA, has over 28 years of varied experience in the dental profession. She is the owner of Clinical Dynamics, a consulting company dedicated to the enhancement of the clinical and communication skills of dental teams, and past president of the ADAA. Ms. Govoni is a columnist for Dental Equipment & Materials. She can be reached at [e-mail].