Written by Ronald Perry, DMD, MS Thursday, 30 September 2004 19:00
While alginate is a good impression material, utilization can demand ideal, sometimes restricting conditions that require special handling. As a result, alginates can be time consuming and less than stable because of environmental humidity and temperature, working time, and mixing. They also can provide a very narrow window of opportunity for assistants to pour a model, after which the material cannot be reused. In busy practices, however, utilizing polyvinyl impression materials allows you the luxury of time—providing a whole new window of opportunity.
Polyvinyl impression materials can be poured the evening before without the fear of distortion and create very accurate impressions as an alternative to an alginate material. Laboratories often prefer polyvinyl impression materials over alginate because models are more accurate and they can pour multiple models within the same impression—unlike alginate, for which they have to stop, wrap up the impression materials, make sure it is in the correct bag, etc. Plus, they cannot reuse the same impression with alginate. With polyvinyl impression material, pouring multiple models from the same impression in the beginning, rather than duplicating models, enables the office to create backups and ensures that accuracy is not lost in translation.
Utilizing a polyvinyl impression material may be slightly more expensive than an alginate, but the benefits far outweigh the cost. The following case illustrates how the proper utilization of a polyvinyl impression material can play a key role in developing a satisfactory restoration.
A 25-year-old female presented for consultation, missing the upper right bicuspid and having previously been heavily restored with filling material. The patient had multiple root canals and chronic extensive bridgework. Based on the clinical exam and discussion with the patient, a 3-unit Lava bridge (3M ESPE) on teeth Nos. 4 to 6 and Cristobal and Cercon crowns (DENTSPLY) on teeth Nos. 15 and 18 were selected as the course of treatment for this case. We decided to take study models using Position Penta Quick Preliminary Impression Material (3M ESPE).
Using a polyvinyl impression material such as Position Penta Quick eliminates the “water factor” associated with alginate—you do not have to worry that the temperature of the water will affect the final setting time. Instead of having to mix powder and liquid, this polyvinyl impression material can be easily dispensed by utilizing an automix system such as the Pentamix mixing unit (3M ESPE). In our office, we simply place the material in the tray (Figures 1 and 2), set for 3 minutes, and have a final impression for study models, partial dentures, or any type of diagnostic indication. Furthermore, a mixing unit eliminates the potential for mishaps and reduces the bubbles and voids typically created by hand spatulating while using an alginate.
|Figure 1. Impression material is placed in tray.||Figure 2. Pentamix mixing unit ensures consistent loading.|
In terms of loading the tray, the Pentamix mixing unit is set at a specific ratio, improving consistency and accuracy of the impression. This leads to more consistent study models, which in turn results in a more accurate diagnostic evaluation, including aesthetics, function, etc. Assistants enjoy using the material because there is no waste of materials, no mess, and no more time spent on mixing. Not only does polyvinyl impression material set more quickly, but the taste of Position Penta Quick is more pleasant for the patient than alginate material.
Study models were fabricated using a properly fitting Directed Flow Impression Tray (3M ESPE). The assistant first selected the appropriate size tray to try in the patient’s mouth for a comfortable fit (Figure 3). Upper and lower impressions were taken. The impression tray was loaded east-to-west in short strokes to eliminate any potential for human error of incorporating bubbles and voids that could equate to a bad impression. Once loaded, the tray was placed into the patient’s mouth (Figure 4), gently pulling the cheeks over the impression tray to form all of the border molds. The impression was allowed to set for 3 to 4 minutes and gently snapped out of the patient’s mouth. The process was duplicated for the lower impression, and the patient was dismissed.
|Figure 3. The appropriate tray size for the patient is selected.||Figure 4. Tray is inserted into the patient’s mouth.|
The impressions (Figure 5) were then taken to the lab area, and during downtime later in the day, we were able to pull up the models and create duplicate sets of models by having 2 pours of lab stone (Yellowstone)—for use as a diagnostic for the office and laboratory—utilizing the same impression. The stone was vibrated, mixing the water and powder together to help the material settle into the impression (Figure 6). It usually requires about 15 to 20 minutes for the material to harden and set (although timing depends on the type of stone), at which point the assistant separates the impression from the stone. Once separated, we were left with 2 stone models and the original impression. The process can easily be repeated to create duplicates.
|Figure 5. Final impression.||Figure 6. Model is poured.|
Using the stone models, provisional restorations were fabricated to create a provisional shell to be relined in the patient’s mouth using Protemp 3 Garant Temporization Material (3M ESPE). A custom tray was created using Triad material (DENTSPLY Trubyte) to take a final impression with Impregum Penta Soft Impression Material (3M ESPE) and maintain the proper vertical dimension of the patient.
After fabricating the provisionals, we were able to evaluate occlusion, determine where to position teeth, and decide whether or not to change anything in the verticals. We also could perform evaluations that would help influence both the function and aesthetics of the final mock-up. Dimensions, bite, comfort, and aesthetics were maintained and reflected very similarly when placed in the patient’s mouth.
The second stone model was sent to Orfan Dental Laboratories (Walpole, Mass) along with other communication tools (photos, x-rays, etc) to create the bridges and single-unit crowns. The dentist and laboratory also utilized the ShadeVision shade matching system (X-Rite/Sullivan Schein) to gain the most accurate shades. The laboratory fabricated the restorations within a turnaround of 3 weeks. One month after the initial visit, the patient returned for cementation utilizing RelyX Unicem Self-Adhesive Resin Cement (3M ESPE).
Polyvinyl impression materials are examples of great advances in dental technology. Dentists, clinicians, patients, and laboratory technicians all benefit from using such materials. When substituting polyvinyl impression materials for alginate materials, mixing problems, work-time inefficiencies, and material instabilities can be eliminated.
In the clinical case presented, the dentist and dental assistant saved time, while our laboratory was able to fabricate the restorations easily and accurately. Further, the patient was provided with great-fitting and aesthetic final restorations.
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