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How to Take PVS Impressions for Best Accuracy

PVS, also known as polyvinylsiloxanes or addition reaction silicones, were introduced in the 1970s as a more accurate and dimensionally stable material than condensation reaction silicones. PVS contain silicone-oxygen polymers as do the condensation reaction silicones, but PVS by-products of polymerization are consumed or added to the setting reaction. No by-products are released, therefore polymerization shrinkage is less. PVS are available as two-paste systems—once containing terminal silane hydrogen and the other containing terminal vinyl groups and a chloroplatinic acid catalyst. The result of mixing the two results in a highly cross-linked material with exceptional stability and better ability to recover from deformation.

For quality full-arch impressions, you need PVS putty, PVS light-body wash, and impression trays. Use only PVS impression material approved for PVS impressions, and be sure to wear vinyl, nitrile or powder-free latex gloves. Using equal amounts of putty, set the timer and mix. Putty is ready when it is uniform in color, without swirls (Figure 1). Roll the material into a hot-dog shape and load it into the impression tray. Press the putty against the tray, locking it into the perforations. Use your fingers to create a trough by pre-shaping or dimpling the putty to the arch shape,2 and build up the putty at the distal portion of the tray to contain the light-wash and to capture terminal molars (Figure 2). 

Place the tip of the light-wash against the putty and release the material into the tray. Firmly press the tip into the light-wash material to prevent bubbles (Figure 3). Dry the patient’s teeth, then insert the tray straight and evenly into the mouth, centering the tab to the patient’s nose (Figure 4). (Be sure you do not rock the tray.) Use a timer and follow the recommended setting time. When the recommended amount of time has passed, do a fingernail test on the impression material to make certain it is set, since PVS setting times can vary (Figure 5). After confirming that the material has set, remove the impression tray using a back-to-front motion, allowing the posterior seal to be broken first.2 Inspect the impression for defects. Once the impression has passed inspection, repeat the procedure for the opposing arch (Figure 6). Disinfect the impressions, and place them in a submission box for shipping (Figure 7). 

Best Practices

To get the best results, use the impression technique with which you are most comfortable. If there are deep undercuts, block them with wax before taking impressions (Figure 8). For patients with extreme gag reflex, sit the patient in a more upright to help avoid gagging. When inspecting impressions, look for defects such as air bubbles, double impression, missing anatomy, push-through, blended tooth and gingiva. Retake any impressions that contain these defects. 

References

 

  1. Tarnow, DP, Chu SJ, Kim, J. Aesthetic restorative dentistry: Principles and practice. Montage Media 2008; 239.
  2. Pitel, ML. Successful impression taking: First time. Every time. Heraeus Kulzer and UNC 2005  

 

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