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Dear Dr. DiTolla,

My name is Robert McDonald, and I graduated from dental school in May 2013. I’m currently working for the Tennessee Department of Health in rural Dickson County. I try to read dental magazines to stay up to date because, frankly, at a state health department we do not utilize new and exciting techniques or materials due to the state budget and the limited scope of practice.

I just wanted to say that I really enjoyed your article about impressions entitled “The Good, The Bad and The Ugly” (Chairside® magazine, Vol. 9, Issue 2). I loved the respectable shout-out to the Two-Cord Impression Technique. Keep up the good work with your R&D team at Glidewell Laboratories; your contributions to dentistry are great!

– Robert M. McDonald, DDS
Dickson, Tennessee

Dear Robert,

Thank you so much for your kind words. I’m glad the magazine makes it out to your corner of the world. Much like how the PFM’s time as the king of indirect restorations has come and passed, I think the Two-Cord Impression Technique will one day have to turn its crown over, most likely to the inevitable generation of digital impressioning units that will be able to scan through saliva, blood and gingival tissues.

Thanks again,

– Mike

Dear Dr. DiTolla,

I was hoping you could advise me on how you solve extreme sensitivity underneath BruxZir® crowns. I have a 42-year-old male patient with extensive recession and large interproximal spacing. He has good oral hygiene and is not a perio surgical candidate. Due to extensive facial and palatal erosion, gum recession, and possibly abfraction, I recommended crown coverage to the gingiva. What would you suggest to alleviate some of his hot/cold sensitivity? Everything he eats or drinks has to be lukewarm.

– Kenneth V. Lee, DDS
Auburn, California

Dear Ken,

I have had patients much like the one you mentioned in your letter. Specifically, I have had patients where I have placed onlays on molars in an attempt to be conservative, only to have the tooth structure from the onlay margin to the gingival margin become very sensitive to temperature. As a result, I have ended up turning to full crowns in these situations, with the restorative margin placed slightly subgingival. I use Rella Christensen’s desensitization protocol, which places two one-minute coats of desensitizer on the tooth prior to cementation.

Hope that helps,

– Mike

Dear Dr. DiTolla,

I keep hearing and reading about how the PFM is as good as dead, and I agree. Occasionally, I have had to perform endo therapy on a previously crowned tooth. Most patients don’t seem to mind the occlusal being repaired with composite material as opposed to paying for an entirely new crown. This is accomplished fairly easily with a PFM. However, my question is: How will a BruxZir or an IPS e.max® (Ivoclar Vivadent; Amherst, N.Y.) crown respond to drilling? Will they crack and shatter? Or will they withstand the insult and continue to be serviceable after patching with composite?

– Jim Blanchard, DDS
Berryville, Arkansa

Dear Jim,

Well, concerning PFMs, I would agree that single units are dead, but bridges are not necessarily. Specifically for BruxZir bridges, we have a rule called the Rule of 27 that determines if the prep violates the material’s ability. So even now, there are cases where I might end up doing a PFM bridge.

As for how a BruxZir or e.max crown will respond to drilling? That’s a great question. Actually, Gordon and Rella Christensen at Clinicians Report are in the midst of doing research on this right now. The initial results from the SEMs look fantastic. As neither material has a layered ceramic on the outside of it, they do very well with an endo access hole. With PFMs, the vibration from the bur going through the porcelain causes them to chip and shatter. But with BruxZir Solid Zirconia especially, a zirconia-optimized diamond bur with a blue band on the shank goes through and comes out with no chipping whatsoever. IPS e.max has very small chips that are almost unnoticeable, way fewer than the number of fractures that we used to see with some PFMs. So BruxZir and e.max crowns are both easy to use and patch by comparison.


– Mike

Hey Dr. D,

My question is about the Hydraulic & Hydrophobic impression technique. Do you know anything about it? The video from Dentaltown® Magazine touts that no cord is necessary and the technique seems extremely easy. I haven’t had the courage to use it on my patients yet. Have you seen dentists use this technique with good success?

– Duy “Dewey” Nguyen, DDS
San Francisco, California

Hello Duy,

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.

– Mike

Chairside Magazine: Volume 10, Issue 1

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