The Crown Experiment 2007: Not in My Mouth!
Posted Apr 28, 2011, Published 2007-01-01
Identical impressions were sent anonymously to nine very different laboratories. The resulting crowns were evaluated by a panel of highly trained dentists and dental technologists. Every one of them resoundingly said: "I wouldn't want any of these in my mouth."
The evaluators--as well as LMT--were surprised by the disappointing quality of the nine crowns in our experiment, which earned an average score of only 4.3 on a scale of 0 to 10. Click here to see the average scores received by each crown in all categories. "These are amateurish crowns with no natural contours," said evaluator Fred Hornedo, Jr., MDT, manager of Acqua-Dent Dental Laboratory, Jamesburg, New Jersey. To see the crowns, click here.
Our evaluators also criticized the shallow anatomy, gray or too-bright shades and the poor staining and glazing. However, what concerned them most was that none of these crowns has an acceptable marginal fit when evaluated on the die. "Every unit is rotating or rocking," said Dr. Ira Zinner, who maintains a private practice in New York City and is a clinical professor at New York University College of Dentistry. "None of them have any bevels or closing angles to keep saliva out and prevent decay."
The technicians on our panel were especially bothered by what appeared to be a lack of pride in craftsmanship. "Why are we seeing such sloppy model work and presentations? It seems as though some of these technicians were just going through the motions," said evaluator Gail Broderick, MDT, laboratory director for Jason J. Kim Dental Laboratory, Great Neck, New York.
We opted to use a Dentiform model as our "patient" so that we could have nine crowns in our experiment without having to put a live patient through nine impressions. Our dentist-consultant modified the Dentiform so that it appeared more lifelike; he then prepared tooth #14 with a shoulder preparation. He took nine full-arch impressions of the Dentiform and sent each one to a different laboratory with a prescription for a low-gold PFM crown with a circumferential metal collar in shade A3.5. He requested light fissure staining on the occlusal and hand-articulated casts. We chose to prescribe a PFM unit since that is still the bread-and-butter work of most C&B departments and laboratories.
LMT chose six domestic labs--two small, two medium and two large--and three foreign labs. For the domestic crowns, our goal was to get samples from each of three broad regions of the U.S. We also wanted to cover a wide range of prices, so all of the crowns in our experiment are in the $60 to $190 range. The average turnaround time was 12 days.
Once the crowns arrived at LMT, all the casts, dies and crowns were marked with coordinating colors and assigned a letter so that the identities of the laboratories (as well as their size and location) would not be known to our evaluators.
We then brought the crowns to two prestigious east coast dental schools--New York University (NYU) and the University of Connecticut (UCONN)--to have them evaluated by a panel of technicians and dentists; one of the dentists is also a master dental technician. Click here to Meet the Evaluatorsand for commentary from Bill Mrazek. They were asked to rate each crown in nine categories: model and die prep, anatomy, contours, contacts/embrasures, occlusion, shade/vitality/enamel blend, stain and glaze, metal design/polish and the accuracy of fit on the die. (Because we wanted to eliminate the variable of impression-taking and focus solely on laboratory techniques, the fit of each crown on the Dentiform was not scored.) Our scoring system is based on a 0 to 10 scale, with 0 being "unacceptable" and 10 being "excellent."
LMT recognizes the limitations of this study and is not portraying it as a scientific experiment or implying that the work being evaluated here is necessarily representative of the entire industry. Rather, our experiment is a rare opportunity to get an inside look at the work being done in other laboratories, and to juxtapose it with the fees these labs are charging for their level of quality.
1. The lowest scores are for the accuracy of fit on the die. Even the first-place crown received a 4.0 on our 0 to 10 scale in that category; the average score for fit for all the crowns is only 3.5. Some evaluators commented that the type of shoulder prep used by the dentist who helped with our experiment may have inhibited a good fit, but others felt it is a real-world prep, similar to those often done by general dentists and that it has nice, clear margins. In the end, though, the real concern is each laboratory's inability to make a restoration that doesn't rock or rotate on the die. "No matter what the prep is like, these crowns should fit better than they do," said evaluator Mario Zerrillo, MDT, owner of Zerillo Dental Laboratory, Queens, NY.
2. The crowns that were fabricated outside of the United States are on par with the ones fabricated inside the country (the foreign crowns placed 5th, 6th and 7th among the nine restorations). In fact, the average overall score of our foreign crowns is 4.2 and the average for our domestic crowns is 4.4. While both of these scores reflect dissatisfaction among our evaluators, they show that the quality of the foreign crowns in our experiment is comparable to that of the domestic ones.
3. What surprises us most about the individual crowns is that the most expensive one in the group--in the $180 to $190 range--was rated to be the worst. Although the geographic area in which the laboratory is located tends to have higher prices, it was still shocking that--even on a bad day--a crown in this price range would rate 2.8 on a scale of 0 to 10.
4. Overall, our technician-evaluators gave scores that are an average of one point lower than the dentist-evaluators (3.6 compared to the average dentist score of 4.5). It's logical that the technicians--being professionals in dental prosthetics--would have a more technically critical perspective. Still, it's the dentist who is making the final decision about whether a restoration is suitable to be placed in a patient's mouth.
Although all of our dentist-evaluators said they would reject every crown if it was returned to them, some acknowledged there are dentists who would consider at least a few of these units to be clinically acceptable. And that's the reality: since quality is so subjective, what constitutes an acceptable crown is going to differ from one individual to another. That's evident even in the context of our experiment: the scores our evaluators gave Crown U in the stain and glaze category, for example, range from 1 (from a technician-evaluator) all the way to 9 (from a dentist-evaluator).
We believe that the laboratories involved in our experiment would be genuinely surprised by the scores they received. Of course, our evaluators didn't know the identities of the laboratories and, therefore, couldn't be swayed by their reputations or level of service. Instead, these crowns had to speak for themselves.
Although in the real world, your marketing, positioning and value-added service are part of the big picture, how would your product fare if it was judged on technical merit alone? In other words, if your work had to speak for itself, what would it say?
Editor's note: In the LMT Crown Challenge, LMT invited technicians to fabricate the same case as the one featured in our Crown Experiment. Like the restorations pictured, the crowns were evaluated by a panel of technicians and dentists and was featured in LMT. click here to see the article.
What concerned our evaluators most was that none of the crowns in our experiment has an acceptable marginal fit when evaluated on the die. Shown here are three crowns--(from l. to r.): Crown Z, Crown T and Crown R--that were among the worst of the lot. zopen.jpg topen.jpg r_open.jpg
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). s_broken.jpg sl.jpg
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