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Is the metal in a Maryland Bridge MRI safe?

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Dr. Hall,
Is the metal used in a Maryland bridge M.R.I.safe?
– Kevin from the U.K.

Kevin,
You’re referring to the use of metals with magnetic properties that should be avoided around magnetic resonance imaging machines. There is an excellent article that discusses this issue on a blog called the MRI Metal Detector Blog, and I would refer anyone with more questions about this to that blog. There is another piece from the National Institutes of Health about the interactions between MRI and dental materials, but they offer no definitive conclusions—they only bring up the problem.

The metal in a Maryland Bridge is generally a non-precious dental alloy. It has to either have some beryllium in it or be tin plated. Neither of those metals has magnetic properties. But often the metal will have cobalt and/or nickel also, possibly a lot of cobalt or nickel, and both these metals do have magnetic properties. If that is the case, would the pull of the MRI machine be enough to dislodge the bridge? I doubt it, but I confess that I don’t know enough about the MRI machines to say for certain. I would refer the question to an MRI technician. To function in the mouth, a Maryland Bridge has to be designed and bonded so as to resist chewing forces, which are very heavy forces. If chewing won’t dislodge it, I doubt that an MRI machine would be able to. But Maryland Bridges can sometimes be done without proper designing to resist dislodging forces, which is why patients have problems with them falling out from time to time.

There are other types of dental work that also use these alloys. Crowns and bridges, as well as removable partial denture frameworks, can be made out of non-precious alloys (also called base metal alloys). Crowns and bridges, again, should be cemented very securely so that they resist chewing forces, and I have a hard time believing that a conventional crown or bridge could have an issue with MRI forces. A removable partial denture, however, is not fastened very securely, and if there is any cobalt or iron in the framework, my recommendation would be to remove the prosthesis before having an MRI.

– Dr. Hall

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About David A. Hall

Dr. David A. Hall was one of the first 40 accredited cosmetic dentists in the world. He practiced cosmetic dentistry in Iowa, and in 1990 earned his accreditation with the American Academy of Cosmetic Dentistry. He is now president of Infinity Dental Web, a company in Mesa, Arizona that does advanced internet marketing for dentists.

Is she allergic to the metal in her crowns?

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Dr. Hall,
I am 64 years old…had metal fused porcelain crowns (5 upper front teeth) placed 4 years ago. After countless dentist visits, a nightguard, a guard for my bottom teeth, tensing of the jaw, etc., I cannot stop grinding my teeth. I am constantly aware of these crowns with the sensations I feel in the roof of my mouth. Do you think that maybe I cannot tolerate the metal? Previous to these crowns, I had gold backed crowns for 42 years which I never had a grinding problem. I have no peace and I am ruining my bottom teeth. Could I be allergic to the metal? (only because it actually feels “itchy” at the roof of my mouth.)

– Mae in Pennsylvania

Mae,

I need a disclaimer because of not being able to examine you myself, but just going from what you are telling me, it sounds to me like you have two separate problems.

The itchy feeling around the metal backings to your new teeth could well be from a metal allergy. Here’s what I would do: Ask your dental office for information on the composition of the alloy used in the metal of your porcelain fused to metal crowns. The laboratory would have sent them what is called a “Identalloy” certificate, which lists all the metals in the alloy. If you see “Ni” among the metals listed – this stands for nickel, and nickel allergies are fairly common.

Are you sensitive to any metals in earrings, for example? Women who have nickel allergies need to wear hypoallergenic earrings, and they have to be careful with what metals are put in their mouth.

Let me explain these dental metal allergies. In the medical history that the dentist took before starting any treatment, he or she should have asked if you have any history of metal sensitivities, and if you have anything like that in your history, the dentist should have prescribed metals for use in your mouth that have no nickel in them. The problem is, those metals are more expensive than ones that do have nickel. There are three expense classifications of metals used in crown and bridge work. The highest is called “high noble.” The gold backing you used to have would be in this category. Other alloys have high platinum. This type of metal makes a finer margin and is more malleable, meaning that it can be made to fit the tooth the best. The second highest is called “noble.” These will have a higher silver content, but will have no nickel or beryllium, which are metals that can cause sensitivities in some patients. They are somewhat malleable and make a very nice fit to the tooth, but not as high quality as the high noble.

The lowest category is called “base metal.” These are very stiff alloys and tend to be cast with small gaps between the metal and the tooth, so they don’t fit quite as well and they aren’t malleable at all. They will have some nickel in them and sometimes some beryllium.

Your new crowns may have also disrupted your bite. The metal sensitivity shouldn’t be causing you to grind your teeth, But if you had crowns on five front teeth, that has a strong impact on your bite and your bite could be thrown off to where it is making you want to grind your teeth. If this is happening to you, I would wear a nightguard every night until the bite is adjusted to where you don’t grind any more.

A particular problem if you have porcelain crowns on your front teeth that don’t have a full metal backing is that the porcelain on the upper teeth is highly abrasive to your lower teeth, and you will gradually wear down your lower front teeth. So I would get this fixed.

Dr. Hall

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About David A. Hall

Dr. David A. Hall was one of the first 40 accredited cosmetic dentists in the world. He practiced cosmetic dentistry in Iowa, and in 1990 earned his accreditation with the American Academy of Cosmetic Dentistry. He is now president of Infinity Dental Web, a company in Mesa, Arizona that does advanced internet marketing for dentists.

Allergic to the Metal in her Crowns

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This is a follow-up e-mail from Carolyn in New Jersey. She asked about the types of metals that are used in porcelain-fused-to-metal crowns.

Dr. Hall,
Thank you very much for your informative answer.

At this point, my last concern is aesthetics. I seem to be reacting to a metal in my porcelain-fused-to-metal crowns. (Tongue inflammation where the tongue touches the metal parts of my crowns, inflammation in the skin on the lips and around the mouth, and general facial inflammation).

I saw the metal shell underneath each of these porcelain crowns just before they were placed in my mouth. I hadn’t been informed, first, that such a metal shell could or would exist under the porcelain, so there was no time to halt the procedure in order to seriously question the makeup of that shell. It was rough, grainy, and very dull silver-colored. I suppose this is the “black” that is now appearing near the gums. I’m guessing this would have to be a “base” metal. It certainly wasn’t “shiny.” More like the lowest grade of industrial steel.

In addition, I’d asked for a gold surface on top of some of the the porcelain crowns. I had no metal in my mouth prior to this and my goal was to have only gold, if any metal at all. I have a TMJ problem so a forgiving metal was needed on some surfaces.

Understanding completely that there is no “pure gold” for the mouth and that all gold comes as an alloy, I still cannot believe that these surfaces on top of the porcelain crowns are actually gold. They are quite dark silver now, “hot” to my tongue, they burn my tongue, and now the tongue is swollen in those places. I do have an all-gold crown, in the back of my mouth, to compare these dark silver metal surfaces to. The all-gold crown looks, feels, and acts like gold. It’s beautiful and feels good. These “gold” surfaces on top of the porcelain-fused-to-metal crowns, however, look and feel so dark and so hot. I’m suspecting an electrogalvanic reaction between the upper metallic surfaces and the baser metals at the gumline.

I’d questioned the gold content of these upper surfaces (because they looked silver) and received the answer that the colors can be different due to the fact that the gold comes as an alloy. But “this degree of different” is really strange. If my white gold ring began to look this way, I’d take it back to the jeweler for a refund.

So I’m trying to gather intelligent background information, independently, on what I might have received in my mouth that is causing my mouth and tongue to burn, and my facial/lip skin to become so inflamed with scaly red patches around the mouth. I realize that no one but my dentist can give me the chemical composition for sure. I just wanted to have a ballpark idea of what might be happening to me before I approached him on this.

In general terms in the profession: Is it possible for a patient who has paid in full for such crowns to go back, a mere two or three years later, and receive from the lab the exact metallic composition of each crown that they produced for me?

Any further information on any of these points would be greatly appreciated. I understand completely that only my dentist can give me the “bottom line” on my own case. I’m just looking for accurate ballpark info so that I do not permit myself to be led astray.

Does the black at the gumline, therefore, give evidence of a “base metal” having been used for the metal shell under the porcelain crown?

Thank you.
Carolyn

Carolyn,
No, the black line at the gumline doesn’t give any clue as to what metal you have in the crowns, nor does the rough appearance of the metal on the inside of the crown (it is left rough to be more retentive – a shiny surface would slip off the tooth more easily). But your sensitivity gives a strong clue. I would give at least 95% odds, based on your reactions, that nickel was used in your crown, as that is the metal that usually provokes this kind of reaction. That is one of the base metals.

And to answer your previous question, yes, the dentist should retain documentation of what alloy was used and its composition. The dental laboratory is required to send to the dentist what is called an identalloy certificate that lists the composition of the alloy that was used, and the dentist is required to retain this. The dentist bears responsibility for insuring that you don’t have this kind of reaction. Do you have any history of metal allergies, such as a reaction to any metals in earrings? We always asked whether people had any reaction to metals, and flagged the charts of those patients who had metal sensitivities, so I would know when to avoid base metals. Although we got to where we simply didn’t use them on anybody because of the risks involved, except for Medicaid patients, where the government specified that they wanted us to use base metals, because they were cheaper. If your dentist didn’t ask you this, then he or she is responsible for this and should make it right with you.
Dr. Hall

Dr. Hall,
Again, thanks so much. I very much appreciate your insight and your time.

The one overwhelming thing known about me by the dentist and his staff is my multiple chemical sensitivity. That reality looms larger than my name, at this point. I have been my dentist’s “chemical education,” with all the difficulties and humorous moments that implies.

Although mercury made me miserable (all those teeth fell apart and the mercury was incidentally removed before these metal-shelled crowns were installed) I never had a nickel allergy to report! I supposed now I will.

Carolyn

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About David A. Hall

Dr. David A. Hall was one of the first 40 accredited cosmetic dentists in the world. He practiced cosmetic dentistry in Iowa, and in 1990 earned his accreditation with the American Academy of Cosmetic Dentistry. He is now president of Infinity Dental Web, a company in Mesa, Arizona that does advanced internet marketing for dentists.

What metals are in porcelain fused to metal crowns?

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Dr. Hall,
I have 6 porcelain-fused-to-metal crowns. I have two questions:

1) What are the usual metals contained in the metal shell?

2) Is the metal shell the thing that begins to show at the gumline, causing the black lines? (I have those black lines.)

Thank you for your information.
– Carolyn from New Jersey

Carolyn,
There are two basic types of metals that are used in porcelain-fused-to-metal crowns – precious or noble metals and base metals. Noble metals used are gold, platinum, and palladium. Base metals would be chromium and nickel. Dentists will classify these crowns as porcelain fused to high noble, porcelain fused to noble, or porcelain fused to base metal.

The noble metals have less tendency to corrode, provoke less sensitivity, and are made to a more accurate fit.

The metal can show at the gumline, and this is what causes the dark, sometimes it’s even black, line at the gumline. Dentists may try to hide this under the gum, but after several years, sometimes the gum recedes and this line is visible anyway. The dentist may ask the dental lab to cut back the metal at this front part of the gumline and leave this margin all in porcelain. This is called a porcelain butt margin. The dentist will pay an extra fee for this – about $30 to $40, and they generally pass this on to the patient. While this makes this line more subdued, it will usually still be present. The reason is that there is still a lot of opaquer that has to be used in the crown to mask the metal. The contrast between the opaque crown and the natural tooth structure makes it difficult to blend colors here, and creates the effect of the dark line.

Patients generally prefer the all-porcelain crowns, which will eliminate any dark line. And the general natural translucency of the crown without any metal is much more natural-looking. But be careful. I would never ask a dentist who is more comfortable doing a porcelain-fused-to metal crown to do an all-porcelain crown. Dentists who are good at all-porcelain crowns will far prefer them for front teeth. If your dentist suggests a porcelain fused to metal crown for a front tooth and you are concerned about the esthetics so that you want all-porcelain, take that as a signal that you are in the wrong practice. This dentist places a low priority on esthetics and if you try to nudge them out of their comfort zone, the results could be disastrous.
Dr. Hall

Follow-up – in a subsequent e-mail exchange, it came out that Carolyn is probably allergic to the metal in her porcelain fused to metal crowns. Read the posting on dental metal allergy.

About David A. Hall

Dr. David A. Hall was one of the first 40 accredited cosmetic dentists in the world. He practiced cosmetic dentistry in Iowa, and in 1990 earned his accreditation with the American Academy of Cosmetic Dentistry. He is now president of Infinity Dental Web, a company in Mesa, Arizona that does advanced internet marketing for dentists.

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