H&H Impressions

H&H or Hydraulic and Hydrophobic impressions are avoided by some labs due to the difficulty the material causes during model work. Here at Two Ocean Dental Lab we appreciate these impressions for the accuracy that they afford. Accurate impressions mean fewer remakes, which is well worth a little extra time and care in the model room. Principles behind the H&H technique have to do with a very high durometer material forcing the low durometer material into the sulcus using hydraulic pressure. In other words materials like Blue Bite have very little flex, so in a two part impression the light body material is forced around the prep and slightly subgingival. This simple mechanical principle captures accurate impressions with little distortion when done correctly. There are a few things to keep in mind when using this impression technique: First make sure your materials are correct. Vinyl polysiloxane material for the primary impression must have a high durometer hardness of at least 85, and the secondary material must have a low durometer hardness below 50. Second you need to remove undercuts in the initial impression because this material will not flex enough to allow the tray to fully seat otherwise. This does not need to be fancy, just look into the impression and break off any spots that may cause an interference. Third the materials used must be hydrophobic and compatible. Everyone has a favorite impression technique, as well as a reason for using it. As a technician I only know what I like about these impressions from my work in the lab. If anyone would like to share a trick or tip that works for them please contact me. I will be happy to include it in the Blog, and of course I will give you full credit.