As far as impression techniques go, the H&H method is about as controversial as they come. Having practiced inside of a laboratory for the last 12 years, I can tell you that when the technique is mentioned to any technician or manager out on the floor, they just roll their eyes because they see a higher remake percentage with it. Our remedy for this is to put a couple of extra coats of die spacer on the die, because otherwise they’re undersized.
Dr. Jeffrey Hoos and J. Morita USA came up with the technique to match one of their proprietary impression materials, Blue Velvet® (J. Morita USA, Inc.; Irvine, Calif.). They say that once it sets, when the impression goes back in the mouth, it will permanently deform rather than rebounding.
To help you understand the importance of that statement better, here are the steps for the technique: After preparing the tooth, you’ll take a double-arch impression tray and put the Blue Velvet material on both sides and have the patient bite down. Essentially, we’re going to get an impression of the opposing arch and most of the preparation down to about the free gingival margin, and register the bite. We pick up the subgingival margins in the second half of this.
After the first material has fully set, we have the patient open again. Making sure the tray stays on the opposing arch, rinse and dry the prep and the inside of the impression, and then reline it with the second material, Flexi-Velvet® (J. Morita USA, Inc.). Express the low-viscosity vinyl polysiloxane material into the preparation itself, and not along the entire tray. The patient then closes back into that, biting tightly. This motion creates a hydraulic chamber, where the low-viscosity VPS is going to be driven down into the sulcus.
You can see how the original impression material might want to expand a little bit because it already fits snuggly against the tooth. According to J. Morita, other bite registration materials rebound afterward. So if you were going to try it, I’d recommend using the J. Morita impression materials to get off on the right foot.
If you were to ask a dentist about their views on the H&H impression technique, most will say, “Yeah, I use it. I love it. It’s great.” I can tell you, though, from talking to lab technicians and lab managers (not just at Glidewell, but at other labs as well) that they somewhat wish dentists wouldn’t do it. And that’s because it typically means higher remakes.
It’s one of those impression techniques where it takes some coordination between you and the lab.