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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 technician-evaluators 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. 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.
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, over-contoured 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 over-glazed. I gave a '0' to Crown S because it has cracks in the buccal and lingual surfaces of the porcelain. 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 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.
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?
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.
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