LAMINAR FLOW II - More hints for the most accurate impressions you’ve ever taken

Also: How to make a backup impression that adds less than 60-seconds to any impression procedure

by Dr. Rod Kurthy
Mission Viejo, CA

“Yesterday I tried Mach-2® as the wash in the laminar impression technique as Dr. Rodger Kurthy described in his Parkell Today article. Neat! But I have a couple of questions.

I stumbled at first because the injected Mach-2 didn’t completely surround the prep. Also the Blu-Mousse® master impression seems to create more drags than I’m used to with my other material. Am I doing something wrong? Any suggestions?”

Kevin Greenway, DDS
Vinton, VA

Thanks for the great questions, Kevin.

Let me answer your Blu-Mousse question first. By “drags” I assume you’re referring to what I call “pulls” ... areas where the Blu-Mousse failed to flow around obstructions (I’ve circled one in figure 1.) Yes, I see drags in perhaps 20% of my Blu-Mousse impressions.

Before it sets, Blu-Mousse is fluffy. Sort of like Cool-Whip. That’s a big plus when you use sideless double-arch trays, because Blu-Mousse won’t slump or run during the impression procedure. But it also means it won’t flow into any areas that are shaded by anatomy during the insertion.*

If the drag isn’t at a critical location, I just ignore it. However, if it occurs by the teeth I’m restoring, I have to repair the defect. Otherwise, the impression won’t create a gasket around the prep. When I inject the Mach-2 wash it may flow out the drag instead of the escape hole.

To correct these flaws I first trim away any fins or undercuts on both sides of the impression that might interfere with complete reseating. I wash the impression, clean it with alcohol and dry it. Then I squirt a little Mach-2 into the offending area, reseat the impression and tell the patient to bite down firmly.

The excess material will flow all over the place, but that’s okay. Blu-Mousse is so stiff and Mach-2 is so runny that the primary impression will squish all the excess Mach-2 out at the border. So when you remove the impression, you’ll discover that the Mach-2 remains only in the defect (figure 2)

I understand from Dr. Gendusa that Parkell has developed a slower-setting Mach-2 specifically for folks who want more time when using the Laminar technique. But if you’re having problems with premature setting during the injection step, here are some suggestions to try before you switch to the slower material.

1) Make bigger holes. For some reason dentists tend to drill holes that are too small. I use a cone shaped diamond to create the mesial and distal perforations, but I enlarge them till they’re just slightly smaller than the size 1/8” bit.

2) Increase the diameter of the tip. The tips Parkell includes in the Mach-2 starter kit were originally designed to inject wash into a retracted sulcus. Their tiny orifice doesn’t allow the kind of flow you need for a laminar injection.

I clip off the end using scissors. Because the tip is cone-shaped, this creates a larger orifice. The plastic collapses when I cut it, so I use the point of the scissors to open up the hole.

3) Don’t be afraid to use significant hand pressure when you inject. You want a gushing flood of Mach-2 surging around the preparation and shooting out the exit hole. Think “Colorado River.” I use so much pressure during injection that I sometimes see Mach-2 oozing out under the primary impression. (Don’t worry though. The stiff Blu-Mousse will snap back and push all excess Mach-2 out at the border. (See figure 3.)

Incidentally, I heard of one dentist who experimented on a model before he inflicted the Laminar Technique on his patients. When he removed the impression he discovered that the Mach-2 wash had been injected into the tissue area. He asked what he was doing wrong. The answer is “Nothing.” The real problem was trying to impress a model. Remember, the whole idea of an injection step is to create a pressurized flow around the tooth. On a model, this pressure can actually raise the primary impression slightly so the wash flows under the Blu-Mousse and into the saddle and flange area. I always tell the patient to “bite down” before I inject. This will keep the impression firmly seated during the wash injection.

4) Inject both holes. First I inject the distal hole for 2 seconds (I count “One thousand one, two thousand two”.) Then I remove the tip from the hole and inject into the mesial hole for one second (“one thousand one.”)

Some Laminar aficionados use only a single wash injection, but I found that a double injection works better for me. When a tooth has a highly irregular circumference, a single injection may occasionally leave a void where the Mach-2 didn’t reach a concave surface. Voids are almost nonexistent when I inject both holes.

Incidentally, when you remove the tip from a hole, keep some pressure on the gun. This will prevent defects due to suck-back.

These hints really speed up the injection step. Even so, Mach-2 doesn’t allow much time to dawdle. If you’re still experiencing premature setting after trying these suggestions ... call Parkell and ask for the slower Mach-SLO™ . There’s also a slower two-minute version of Blu-Mousse.

A back-up impression adds less than a minute to any technique

I’ve incorporated a simple 3-unit back-up impression as a routine part of my laminar technique. But you could add this backup just as easily no matter what impression technique you use. It adds just 45-60 seconds to the entire procedure and provides insurance against a screw-up at the lab. For step-by-step illustrations

After I’ve taken my Blu-Mousse double-arch primary impression for the laminar impression and prepped the tooth, I pack the retraction cord.

The cord has to remain in place for about a minute. So immediately after I finish placing it, I express some Blu-Mousse Super-Fast directly from the gun onto the prep and proximal teeth. I build the material up about 5mm thick so after it sets it will be good and stiff.

By the time the Blu-Mousse has set, I’m ready to remove the cord. (Sometimes I don’t even have to pull it, because it comes out with the impression.)

I give the back-up impression to my assistant and proceed with the injection steps of the laminar impression. (Meanwhile she’s trimming, washing and drying my Blu-Mousse back-up.)

I remove the finished laminar impression and set it aside.

I inject Mach-2 into my back-up impression, seat it, and FORCE it down firmly for about 2 seconds. (Since the laminar impression was just removed, the tissue is still nicely retracted so I capture superb marginal detail.) Then I lighten up on the pressure and hold it in place for 20 seconds. I remove it after it’s been in mouth for at least 35 seconds.

And that’s it. This back-up adds less than a minute to the overall procedure. Do I need it? Hardly ever. But when something goes wrong at the lab, it sure is nice not to have to reschedule the patient, give another injection, pack cord and reimpress. To me, that insurance is worth way more than a 60-second investment.

* For example, if you seat the tray and then accidentally slide it first to the buccal, then to the lingual before finally centering it, you’ll discover drags on both sides of every tooth! That’s because when you slide the tray, you pull the Blu-Mousse away from the tooth surface, and because Blu-Mousse is so fluffy, it never flows back when you recenter the tray. As soon as I seat the tray, I gently place my hand against the cheek, which pushes the Blu-Mousse against the buccal surface. As a result most of my drags are on the lingual.

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