1. technology and computing

FROM the ARCHIVES
Laboratory Procedure
How To Process a Mach-2 Laminar Impression
®
Bonding agents for the befuddled, the confused, the technique-challenged, and everyone else –
By Rod Kurthy, D.M.D., and Paula Kim, C.D.T.
O
Introduction (Dr. Kurthy)
ver the past two years I’ve
authored several articles
concerning the Laminar
Impression Technique.
In a nutshell …
Before tooth preparation, I take a preliminary impression using Super-Fast BluMousse® in a sideless double-arch tray.
After the teeth have been prepped, 2 holes
are drilled one mesial and one distal to
each prep. The impression is reseated and
a flowable wash is injected into the holes.
I learned about the Laminar Impression
from its creator, Dr. Gary Schoenrock
(Perrysburg, OH). At first I was highly
skeptical. I couldn’t believe any technique
that used disposable double-arch trays
could produce 1st-class crowns. Boy, was
I ever mistaken! Not only was the fit as
good or better than I’d previously been
getting, but the time required to impress a
typical patient dropped substantially.
My contribution to the Laminar Technique was the use of a very flowable,
extremely hard-setting material (Mach-2®
“die silicone”) for the injection-step.
When intercuspation is good, much of
the side-to-side strength of an impression
comes from the wash material - not the
Blu-Mousse. In my judgment, a traditional
light-body wash produces an impression
that’s too flexible. It’s prone to distortion
either from “snap-back” when removed
from the mouth or from mishandling at
the lab.
When I switched to Mach-2 for the injection wash, the crown adjustments went
from “rare” ... to “nonexistent”, and the
margins became so good I couldn’t even
feel them with a hand instrument.*
For more info about the Mach-2 variation
of the Laminar Technique, see Parkell
Special Report #28 or visit Parkell’s
website (www.parkell.com).
Almost as gratifying as the improvement in my crowns is the feedback I’ve
received from other dentists who’ve read
my articles. They’re reporting exactly the
same results I’ve experienced.
(And this from a technique that slashes 10
minutes or more off the typical impression
procedure!)
However, a few dentists have reported
some initial resistance from their laboratory. Sometimes the technician has been
burned by other double-arch techniques.
Even experienced laminar technicians
can be perplexed by that super-stiff wash,
because it requires a number of changes to
the traditional laminar lab technique.
So I thought it might be helpful if I asked
Paula Kim, CDT (owner - Aspen Dental
Laboratory), to describe how she and her
crew fabricate a crown using one of our
impressions.
This article follows a single case from
impression, through fabrication and the
postinsertion radiograph ... documenting
each step of the process. We’re not proposing that this is the only way to handle
a Mach-2 laminar impression ... but it’s
a technique that works consistently well
for us.
Incidentally, here in California, qualified
Extended-Functions RDAs (or “EFRDA”s) can legally take impressions. So
this laminar impression was taken by my
very-talented assistant, Manuela “Nellie”
Vargas. She did everything from packing
the cord to injecting the Mach-2.
As I’ve mentioned in prior articles, I
always make a small 3-unit trayless impression as a backup. I hardly ever need it,
but it’s good insurance in case something
horrible happens at the lab. Besides, since
the tissue is already retracted, the backup
adds only a minute to the total procedure.
(If you’re interested in the back-up technique, ask for Parkell Impression Newsletter #14 or see the step-by-step illustrated
(Fig. 1) Here’s what Dr. Kurthy sends to the lab:
A standard workorder ... the laminar working
impression ... plus the trayless backup.
technique at Parkell’s website –
(www.parkell.com)
The Laboratory Technique
(Paula Kim, C.D.T.)
Traditional Laminar Impressions are
extremely accurate, but they share one
thing with other double-arch techniques.
They must be handled with kid gloves
in the laboratory to avoid distortion (See
sidebar page 3).
From the technician’s point of view,
one of the nice things about the Mach-2
modification to the laminar technique
is the increased strength. Dr. Kurthy’s
Laminar impressions are substantially
more robust than most impressions taken
with a conventional flexible wash.
This permits us to process the model more
like a traditional quadrant impression.
IMPORTANT: Careful trimming of
both the impression and the excess stone
is critical to processing a Mach-2 Laminar Impression. Some technicians have
difficulty creating multiple pours from a
* To learn more about the Laminar Technique in general see Dr. Schoenrock’s Video. MDEG 6920 Springvalley Dr. Suite 103, Holland OH 43528, 419866-1238, FAX 419-866-1907. Or go to the “Tech Articles” section of www.parkell.com
© 2011 Parkell, Inc. • Toll Free: 1-800-243-7446 • Visit www.parkell.com • Email: [email protected]
1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
(Fig. 2) The first step is to carefully inspect the impression to be certain that Dr. Kuthy didn’t screw up (Kidding). Notice there is virtually no Mach-2
wash outside the prep area. This is important. If a film of wash covers the proximal teeth, don’t even bother pouring the model. That film indicates
that the pressure of laminar injection caused the bite to open slightly and the patient did not return to centric before the Mach-2 set. A crown made
using that impression will be high. (Fig. 3) We then carefully trim the impression. This makes it easier to handle. But more important, after the excess
Blu-Mousse is trimmed, the model will be much easier to remove without damaging either model or impression (Fig. 4 & 5) We box the impression
and pour. When the stone has partially set, we use a lab knife to remove the overpour. We do this for the same reason we trimmed the excess BluMousse: to prevent lock-on. Remember, in the Mach-2 laminar technique the impression is almost as hard as the stone. (If it locks on, you’re going to
have to cut the impression off to avoid breaking teeth.) (Fig. 6) After the stone has completely set, we carefully remove the model. Despite this care,
the rigid Mach-2 may tear in the thin proximal areas. Don’t worry. This won’t pose a problem. This is our working model. (Fig. 7) The working model
base is trimmed, drilled and pinned.
Fig. 8
Fig. 9
Fig. 10
Fig. 11
Fig. 12
Fig. 13
(Fig. 8) The opposing side of the impression is poured in exactly the same fashion. (The excess stone is trimmed when partially set, etc., etc.) (Fig. 9)
The bases of the upper and lower working models are poured ... (Fig. 10) The models trimmed ... (Fig. 11) … and the die separated and ditched.
(Fig. 12) We can use either the working model or the solid model for articulation. In this case we used the pinned working model. (Fig. 13) We apply
a moderate coat of die spacer (Kerr), taking care to keep it short of the margin.
Fig. 14
Fig. 15
Fig. 16
(Fig. 14) The models are carefully placed back into the impression for articulation ... and mounted using the laminar impression for registration. (At
this stage it may be necessary to trim interproximally to facilitate reseating.) The type of articulator we use isn’t determined by the impression technique, so that’s the dentist’s call. (Fig. 15) The pattern is waxed ... (Fig. 16) …cast ...and the coping is fitted to the die.
2
Enjoy this article? Visit our article archive to download other free technique articles.
And what if the dentist uses
a flexible wash? by Paula Kim, CDT
Here’s how to process a laminar impression if the dentist doesn’t use Mach-2 for
the injection.
Except for the meticulous care we
take during trimming, our lab technique
for a Mach-2 Laminar Impression is
almost identical to our standard model
procedure.
However, if a conventional light-body
material is substituted for the Mach-2
injection step, the impression will be more
prone to distortion during pouring and
handling.* Here the lab should use a
different technique. Most of these hints
were first printed by Dr. Schoenrock in the
Interface Newsletter (May/June ‘94).**
• Pour the counter side of the impression
first.
The stone reinforces the impression so
the die-side can be manipulated with
less chance of distortion.
(Fig. 17 & 18) Our ceramist builds and fires the
porcelain. (Fig. 19) We seat the crown on our
proximal check model to confirm the contacts
... and on the model from the back-up impression to confirm the margins (shown here). If the
crown fabricated from one impression fits the
model from another impression – we can pretty
much guarantee that it will fit in the mouth.
The crown plus all the models are sent to Dr.
Kurthy. (The articulated models are always still
mounted on the articulator.) (Fig. 20) At the
cementation appointment, the crown slides
home without adjustment. (Fig. 21) The post
cementation radiograph shows the kind of
marginal fit that’s typical with this Mach-2 Laminar technique.
• Pour both sides of the impression and
articulate before removing the models
from the impression.
This is recommended procedure for most
double-arch impressions ... and it’s the
rule most frequently ignored by labs.
That’s because it means setting their
pin heads in unset stone using the old
“bobby-pin” technique.
If you simply MUST drill dowel pin holes,
pour your working model - VERY carefully
remove it - then pour a second model
which you leave in the impression for
articulation.
There are two downsides to this approach.
(1) You may distort the flexible impression
when removing the first impression. (2)
Your working model won’t be articulated.
As a result, during fabrication you’ll have
to repeatedly switch back and forth
between the working model and the
articulated model.
Dr. Schoenrock makes other good
recommendations which don’t specifically apply to the laminar technique (e.g.
Trim dies carefully and harden them
with cyanoacrylate, never alter casts,
always return cases mounted on the
articulator, etc.)
* And if the dentist ever sends a laminar impression with the primary impression taken using
conventional heavy-body PVS (NOT Blu-Mousse
or something approaching it), SEND IT BACK. Or
at least make it clear that you will not assume
responsibility for the fit.
** Midwest Dental Evaluation Group. INTERFACE. 6:33, May/June, 94.
Interface $51 per year. MDEG 6920 Springvalley
Dr. Suite 103, Holland OH 43528, 419-866-1238,
FAX 419-866-1907
Blu-Mousse impression without damaging either the impression or the model. I
suspect they’re not adequately trimming.
I’m a big fan of Dr. Kurthy’s 3-unit
backup impression, and I encourage my
other accounts to emulate his technique.
Things can happen at even the most
careful lab that damage the primary
impression. If this occurs, having a
small backup impression eliminates
the need to contact the dentist and have
the patient rescheduled simply to take
another impression. As you’ll see, we’ve
incorporated the backup impression
into our standard technique for
Dr. Kurthy’s cases, and it’s improved
our fit-checking ability.
Ideally, our C&B technique requires
three models – at minimum, two models.
1) A working model
2) A solid model to check the proximal
contacts, and
3) Another solid model to confirm the
marginal fit.
© 2011 Parkell, Inc. • Toll Free: 1-800-243-7446 • Visit www.parkell.com • Email: [email protected]
In a pinch you can use one model to confirm both the contacts and the margin.
Do NOT under any circumstances
modify the proximal check model. At
the cementation appointment we want
the crown to slide home. Any modification of the proximal teeth on the second
model will jeopardize the fit.
The first two models are poured using
the laminar impression. To allow an
extra degree of certainty, we pour the
third model using Dr. Kurthy’s backup impression. (If a crown fabricated
on a model from one impression fits a
check-model from another impression,
we can be virtually certain it will fit in
the mouth.)
Because the Mach-2 laminar impression
produces such an accurate model, the
purpose of this spacer is solely to create
space for the cement. It is NOT
to compensate for sloppy fit. One coat
is sufficient.
3
Note From Dr. Rod: This may upset the congregations of the various
Occlusion Churches, but my preference concerning articulators is
very simple.
If the occlusion is normal (as it was in this case), either a plastic or metal articulator will
serve nicely for a single crown. In fact, I actually prefer plastic because it lets me flex the
models a bit to detect any high spots.
If the occlusion is less-than-ideal, I always insist on metal articulators.
Conclusion (Dr Kurthy)
And that’s pretty much it.
At the cementation appointment, the crown drops home with zero adjustments (Figure
20.) Very, very occasionally I may do some minor tweaking of the occlusion. But in
approximately 2000 crowns I’ve impressed using the Mach-2 Laminar Technique, I have
NEVER had a redo. Not one. In fact, of those 2000 crowns only 3 (three!) have required
any internal adjustment at all in order to persuade them to seat.
The seating radiograph (Fig. 21) shows the kind of fit I’m talking about.
I’m fortunate. I have a fabulous expanded duty-assistant and a terrific lab. I readily admit
that they make my life a lot easier. But I attribute much of my C&B success to the laminar technique I learned from Dr. Gary Schoenrock, plus the super fluid, super hardsetting
Mach-2 wash I’m now using. And as I already mentioned, I’m not alone. Other dentists
who’ve tried this technique have reported similar success.
ABOUT the AUTHORS:
Dr. Rod Kurthy
Dr. Kurthy maintains a full-time practice in
Mission Viejo, CA. He has authored numerous articles concerning clinical dentistry and
dental marketing – and recently published
a handbook on how to attract only the
best kind of new patient – “The No-Coupon
Marketable Dentist” (available at
www.newpatientsinc.com)
Paula Kim, CDT
Paula Kim, CDT owns and operates Aspen
Dental Laboratory in Anaheim, CA. A graduate of DTI in Orange county California, Ms.
Kim has more than 15 years experience in
the dental industry. Before opening her own
laboratory, Ms. Kim worked in several labs
on the East and West Coasts - and served as
Manager of High-Tech at Glidewell
Laboratories She reportedly has a number
of accounts successfully using the laminar
impression technique.
Ms. Kim can be contacted at Aspen Dental
Laboratory, 4081 E. La Palma Ave. - Suite G,
Anaheim, CA 92807 714-632-5159,
[email protected]
Not bad for an impression technique that requires less than 6 minutes start-to-finish.
(For detailed information concerning the Mach-2 Laminar Impression Technique - ask for
Parkell Special Report #48 or visit the Parkell web site, www.parkell.com.)
4
Enjoy this article? Visit our article archive to download other free technique articles.