Impression materials have certainly come a long way since the introduction of “modern” rubber base impression material. Rubber base impression materials were difficult and hard to use and foul-smelling. In the evolutionary course of impression material development we next moved to polyether and vinyl polysiloxane (VPS) materials. These materials were advantageous in that they were fast setting, easy to use, and accurate.
Certainly, accuracy and technique sensitivity, and stability are the benchmarks by which all impression materials are measured. In addition, there are other important qualities such as setting time, working time, tear resistance, taste, and flexibility to be considered when choosing an impression material. The primary function and design of any impression material is to transfer information from the clinician at chairside, to the laboratory technician who will fabricate the restorations. Consequently, the “best” clinician, with the most ideal preparation, in combination with the “best” technician, utilizing the finest porcelains, are at the mercy of the impression process.
Throughout time, dentists have listened to complaints from patients that the impression materials tasted bad, and took too long to set. Similar complaints of setting time, and difficulty in handling, were heard by the manufacturers from the dentist. Laboratory technicians complained about tearing at the critical margins and dimensional instability. This potentially resulted in friction between the technician, dentist, and ultimately the patient who had to endure yet another office visit to repeat an impression. Lost chair time, lab time, patient time and diminished patient confidence, all became “hostage” to the quality of the material used for the impression.
Arguments, with equal credibility, were made for both hydrophobic and hydrophilic materials. Manufacturers, recognized that there was a need to create a more viable material that would ultimately address these legitimate concerns. This “ideal” material would allow for a product to the patient, dentist and technician, which is aesthetic, functional and durable for an extended period. All of us are constantly bombarded with new materials. Ultimately, we must choose one with which we feel most comfortable, and is most tolerable for our patients. While there are only a limited amount of hydophillic materials (hydro-colloid and polyether) materials available, there is by contrast, a wide array of vinyl polysiloxanes available in the marketplace. In all cases, manufacturers have attempted to address the issues of bad taste, tearing at the margins, and smell that were often associated with the polysulfides and polyethers. So how do we go about selecting a material that will consistently work well?
Four key characteristics of an impression material that should be considered when selecting an impression material:
1. Ability to deal with fluid: Regardless of whether retraction cord or a laser is used to enhance the trough around the preparation, there may always be some residual moisture. The best material is one that is hydrophilic and therefore yields an accurate impression in a moist field.
2. Fast setting: An ideal material should be realtively fast setting, yet not have a short working time. Simply put, we want a material that will set in the patient’s mouth in a relatively short period of time, but not before we place it in the patient’s mouth.
3. Good tear strength and dimensional stability: We all agree that the VPS material should not tear at the margins and must be stable over a prolonged period of time. In doing so, the material must provide for an accurate depiction of the prepared area(s), while not being so rigid as to tear at the thinnest of margins when removed from the mouth. If a corrective wash is employed, the material should adhere to itself and not separate upon removal. The set impression should remain dimensionally stabile over an extended period, sufficient to allow for receipt, and use, by the laboratory. Ideally, the time between taking the impression and being poured by the laboratory should not exceed two weeks.
4. Easy to mix without slumping and taste good: The last three keys to a great material are that the material should be easy to mix (or available in auto-mix cartridges) while not slumping (i. e. be thixotropic), be neutral in taste, and be easy to use. As mentioned previously, most VPS materials have addressed these concerns. There should also be a variety of viscosities available in automix or bulk mix cartridge systems that allow for proper mixing ratios to insure perfect blending of the base and catalyst without cross contamination.
GC America (Alsip, IL) has successfully combined the accuracy of detail in a polyether with the ease of use associated with a VPS material in creating an impression material called Exa’lence VPES (Vinyl Polyether Silicone) (Fig. 1).
This new and innovative impression material is available in a variety of viscosities and setting times. Regardless of the setting time or viscosity you will get a consistent and accurate impression which will lead to an an execellent prosthethetic outcome (Fig. 2). Exa’lence VPES has the hydophilicity and wettabililty of a polyether yet handles like a VPS. You can safely use this material with any retraction cord system, with, or without hemostatic agents or astringents. One note though, if using ferric sulfate, you must thoroughly rinse the prepared tooth/teeth prior to taking the impression. The impression can, and should, safely be placed in a disinfecting solution prior to shipping to the laboratory.
Exa’lence VPES offers good color differentiation for that the lab can easily “read” the impression, and specifically the margins. Marginal detail is critical and the wash material, or light body flows easily into the sulcus to accurately record the margin. When it comes to tear strength, which is so critical, you will find that tear strength of Exa’lence VPES is four to six times greater than a conventional polyether thereby making it more forgiving and easier to use in the presence of undercuts. This VPES material is intrinsically hydophillic without surfactant additives, and has a very mild mint flavoring. The manufacture does suggest the use of a VPS tray adhesive material although I have successfully used the material without any adhesive. And finally, when it comes to cost, this material will generally be less costly than the more common polyethers currently on the market.
Another key reason to use Exa’lence is setting time. The Fast Set materials will be firmly set in only 90 seconds. In discussion with my colleagues around the world it has become apparent the roughly 80% of all crown and bridge impressions are single units. Clearly, we can all take a valid impression in this time and provide an efficient service for our patients in a comfortable manner. And, if speed is not important, or when impressing multiple units, Exa’lence Regular Set will set in only three minutes.
With either of these excellent materials, Exa’lence Regular Set or Fast Set, you will have the ability to mix and match materials to suit your technique. Whether using a single arch technique or a double arch (triple tray) technique you will have ample working time and a setting time that will yield a terrific impression.
There are so many impression materials available in today’s marketplace making it difficult to decide which material to select. Ultimately, we should and will select a material that works well in our hands, and is easy for the patient to tolerate. Now that decision may have gotten a whole lot easier with the combined VPS and polyether advantages found in Exa’lence VPES. Regardless of the materials selected, the bottom line is that a poor impression cannot lead to anything but a poor restoration. Therefore, in making the decision of which material to use, it is incumbent upon the dentist to make a selection after considering those factors discussed in this article.
The practitioner must be able to utilize a material that they can expect to enhance the result of the aesthetic, restorative procedure. Exa’lence VPES materials allow for a wide range of techniques, and a simplification of the impression process. All said, Exa’lence is faster, easier, and better!
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Dr. Glazer is an Attending Dentist at the Englewood Hospital (Englewood, NJ). He is the Deputy Chief Forensic Dental Consultant to the Office of Chief Medical Examiner, City of New York. He maintains a general practice in Fort Lee, NJ.
Oral Health welcomes this original article.
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Lost chair time, lab time, patient time and diminished patient confidence, all became “hostage” to the quality of the material used
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Manufacturers have attempted to address the issues of bad taste, tearing at the margins, and smell
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The practitioner must be able to utilize a material that they can expect to enhance the result of the aesthetic, restorative procedure
