Chairside Magazine Volume 2, Issue 1 - Glidewell Dental Labs

LMT Technical Strategies Columnist Bill Mrazek, CDT, asks:
WHERE ARE WE HEADED?
Crown S lost points during evaluation because it was returned
on a broken model (left photo) and because there are cracks in
the porcelain on the buccal and lingual surfaces (right photo).
When the fine folks at LMT asked if I would offer a
“real-world” perspective on the restorations in their
crown experiment, I agreed without hesitation. I felt I
had a pretty good grasp of the “levels” of restorations being
produced in our profession. I’ve been a dental technician
for 30 years and a CDT for almost 28 years. I’ve presented
numerous lectures and clinics and written articles for over
15 years. Many of us have looked to Willi Geller, Asami
Tanaka, Lee Culp and others for inspiration, guidance and
education—and continue to learn from them—in an attempt to
continually raise the level of our restorations.
As we know, there remains a range of acceptability in what
we produce. That is not to say that high quality restorations
are not being delivered on a daily basis; they certainly are.
There are also restorations being delivered that are not as
detailed; as accurately fitting; or as anatomically, functionally,
gnathologically or esthetically correct that still fall within that
range of acceptability. Then there are those that should not
be delivered at all. But, in most businesses, there is a market
for everything. Unfortunately, as evidenced from this study,
restorative dentistry is no exception.
First, let me say that my comments are not directed at
specific laboratories, since I do not know where the
restorations were fabricated. I evaluated each crown in the
same categories used by the other dentist- and technicianevaluators
(see Meet the Evaluators on page 36) and used
the same 0 to 10 scale. I looked at each crown three times,
on three different days, to make sure that I was being fair
and consistent. I’ve arranged my observations based on the
judging categories:
Model and die prep (my scores range from 0 to 7.5): Crown
S received a zero because the model was returned badly
broken, as if dropped from a second-floor window (see photo
on page 32). Crown T received the highest score because it
uses one-piece double pins and the model work is neat and
clean. Most of the cases use simple plastic articulators, which
are common, but they allow no protrusive movement and only
limited excursive movements.
In most businesses, there’s a market for everything.
Unfortunately, as evidenced from this study,
restorative dentistry is no exception.
Anatomy (my scores range from 2 to 8): Only Crown T
includes a Cusp of Carabelli, even though there clearly is one
on the 1st molar on the opposite side of the arch.
Contours (my scores range from 5 to 7.5): Almost all units
exhibit a square, boxy, overcontoured shape.
Contacts/embrasures (my scores range from 0 to 8): I gave
two crowns a zero—Crown W and Crown Z—because they
have both mesial and distal open contacts. Crown R and
Crown V have one open contact; the others have varying
degrees of contact, from point to concave design.
Occlusion (my scores range from 2 to 8): Crown R was
totally out of occlusion; the others exhibited good centric
contact, but most had lateral interferences.
Shade/vitality/enamel blend (my scores range from 0 to 9):
Most of the samples are too high in value, the chroma varies
from crown to crown and, the lower scoring units—such as
Crown S and Crown Z—don’t represent the requested A3.5
shade at all.
Stain and glaze (my scores range from 0 to 9): Most of the
restorations have a poor and unrealistic-appearing application
of occlusal stain, and some appear overglazed. I gave a
‘0’ to Crown S because it has cracks in the buccal and lingual
surfaces of the porcelain (see photo on opposite page). Crown
W earned a ‘9’ because it is the only one with surface texture.
Metal design/polish (my scores range from 0 to 9): Crown
Z earned the ‘0’ since it did not follow the Rx request for a
metal collar. The highest scores were given to those crowns
that exhibit the narrowest collar at the buccal margin (such as
Crown U).
Accuracy of fit on die (my scores range from 0 to 9): I gave
seven of the nine crowns scores of 2 or less; four of them
received a ‘0’! (The two that fit the best—Crown X and Crown
Y—earned a 9 and 7.5, respectively). To me, this is the most
amazing aspect of the experiment, as the prep is ideal and has
margins that could be read in the dark. Some of the crowns
fit very loosely on the die, others have open margins, short
margins, or over-extended margins that could be easily seen
without any form of magnification!
Final analysis: In my estimation, the clinical acceptability of
Crown X and Crown Y is questionable; the remaining crowns
are, without a doubt, undeliverable.
In all fairness, nine samples don’t constitute an accurate
representation of the work being done by the entire dental
laboratory profession. But doesn’t it seem reasonable to
expect that there would be at least some higher scores than
we see here? Obviously, the laboratories in this experiment
Nine samples don’t constitute an accurate
representation of the work being done by the entire
profession. But doesn’t it seem reasonable to expect
that there would be at least some higher scores?
sent back a product that they felt was an acceptable
restoration. If these restorations are accurate representations
of what they produce on a regular basis, it means their
products are being accepted and delivered on a regular
basis.
My greatest concern is not directed at those laboratories in
the experiment, but actually at the level of acceptance that
apparently exists in our profession—a level of acceptance
that is a shared responsibility between the dentist and the
laboratory.
Crown
Model &
Die Prep
Anatomy Contours Contacts/
Embrasures
I truly hope that restorative dentistry can remain a respectable
profession rather than becoming strictly a “business
arrangement” between the dentist and laboratory, primarily
based on price and turnaround time. Once we reach that point,
our restorations are nothing more than a manufactured commodity.
Ultimately, it is up to each of us to determine where
we are headed. In what direction do you want to go? Í
Occlusion
Shade/
Vitality
Bill Mrazek, CDT, is the owner of Mrazek
Prosthodontics, Ltd. and Mrazek Consulting
Services in Naperville, Illinois. LMT is grateful
to Bill for lending his creative input during
brainstorming for this experiment, as well as
for his technical expertise during its planning
and execution.
AVERAGE SCORES RECEIVED BY EACH CROWN IN ALL CATEGORIES
Stain &
Glaze
Metal
Design/
Polish
Accuracy
of Fit
on Die
CROWN R 3.9 1.5 2.9 2.0 1.8 2.8 3.6 4.5 1.5
CROWN S 3.5 4.9 4.5 6.0 5.7 5.1 5.6 6.6 2.6
CROWN T 4.5 5.1 5.0 4.6 4.7 5.4 6.2 6.3 1.5
CROWN U 2.3 2.7 3.0 4.7 3.9 3.6 5.1 3.6 1.9
CROWN V 5.9 5.7 6.0 6.4 5.8 7.0 6.6 6.7 4.0
CROWN W 5.9 4.6 4.5 4.3 5.2 4.4 4.4 5.0 4.3
CROWN X 5.2 3.5 3.1 3.9 3.6 4.0 4.1 5.0 6.7
CROWN Y 4.6 4.5 3.6 3.7 3.2 4.3 4.6 5.0 6.2
CROWN Z 3.4 4.2 4.1 2.7 4.2 4.8 5.6 2.5 3.2
LMT’s Crown Experiment 2007 LMT’s Crown Experiment 2007