Blocking Out Undercuts for Impressions
By Dr. Lee Ann Brady
One of the great things about VPS impression material is the rigidity. Without this the impressions would have inaccuracies that made seating restorations very challenging. The other side of this is the difficulty at removing a full arch VPS impression when there are undercuts. The material tends to flow into the space of the gingival embrasures and can meet connect when entering from both buccal and lingual. This material can make removing the tray from the patients mouth extremely difficult.
In these moments the patient’s eyes are getting very wide and you are trying to remain calm and reassure them that the impression will come out. Learning to check for open embrasures and undercuts can prevent a tense moment and a panicked patient. Once we have identified these areas the next challenge is to prevent the impression material from getting in to them. Wax has been used for this purpose for years, but can be challenging to handle and does not like to stay where you put it.
Recently I have started to use Teflon tape for this purpose. I thoroughly dry the embrasure and using a cotton pliers pack the Teflon tape into the space. It sticks to itself and forms a custom shape to the embrasure and is tucked in, so it stays in place. Most of the time the Teflon tape comes out inside the impression and I leave it in place and send the impression on to the lab. If the impression was for diagnostics I cut away the Teflon tape under magnification before we pour the model.