Insight 75 — What Does a “Stretched” Dental Impression Mean? Why the Lab Says the Wash Has Stretched and Asks You to Re-Take the Impression

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Answer:

When the lab says the impression or the wash has “stretched”, what it means is that the impression material was taken out of the mouth before it had set completely. Material that has not yet set moves as it is removed and is deformed. The result is that the impression has not recorded the real shape of the tooth, and anything built on it no longer seats on the tooth. That is why the lab asks for the impression to be taken again.

Conventional impression taking is a very accurate method, provided its principles are respected. One of those principles is that we give the material time to set completely and do not take it out of the mouth too early.

How do we know the material has set?

One simple way to tell is the fingernail test. When you press a fingernail into the putty, no nail mark should remain and it should spring back quickly to its original state. If the nail mark stays or comes back slowly, the material has not set yet and you should not remove the impression.

The wash is the same: besides this test, it must not stick to the hand or the glove. If it sticks, it has not set yet.

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