Does Magnetic Resonance Imaging (MRI) pose a threat for patients with embedded metal?
Dr. Ernie Lam provided the following commentary to the Globe and Mail article published on July 23rd, 2014: Heavy metal quandary; Tattoos, piercings, defibrillators, intrauterine devices – increasing metal use poses risks as magnetic resonance imaging gets stronger
In order for a material to interact with a magnetic field, the material needs to have a property known as ferromagnetism. Titanium is not ferromagnetic so should not interact with magnetic fields. Common materials that are ferromagnetic include iron, nickel, cobalt and alloys of these metals (including stainless steel), many of which are found in materials used in dentistry. These will disrupt local magnetic fields produced by the MR imaging system in the area, and may cause sizeable artifacts on the images.
What is the issue from a dental perspective?
If the alloy of titanium in an implant contains a ferromagnetic substance or if the alloy is part of the final coronal restoration (i.e. the crown or bridge), given the amount of ferromagnetic material (i.e. number of implants and their distribution in the jaws) and the type of imaging sequence used in the MR image acquisition, we will see variable degrees of artifact on the images that may potentially obscure an anatomical region of interest.
As magnetic fields become stronger, the interaction with a ferromagnetic substance may cause vibration and potentially dislodgement of the material which could be very dangerous in or around MR equipment. If you are imaging a leg and there is a stainless steel crown in the mouth, image artifacts are not an issue (although I am not sure about dislodgement). But, if a patient has fixed orthodontic appliances in place and the brain is to be imaged, then this can be a big issue!
What is the significance to dentists and their patients?
If a patient is being referred for an MRI of a body part close to the location of a ferromagnetic substance, artifacts can be produced on the images that may obscure the area; and therefore, make the imaging investigation suboptimal or potentially useless. And, if the MRI is necessary to make a particular diagnosis, then the artifact is troublesome.
Do you have any advice for dentists about what they should say to a patient who asks about the significance of dental implants, if they are going to have an MRI?
The dentist should know what the implant is made of (not “just titanium”) and what any crown or bridge attached to the said implant is made of. Dentists need to know what the components of any potential alloy may be, but also be kept in the loop as to what body part is being imaged so s/he can determine, if something needs to be done before imaging.
Dr. Ernie Lam is Professor in the Faculty of Dentistry at the University of Toronto. He is also Head of the Discipline of Oral and Maxillofacial Radiology and Director of the Oral and Maxillofacial Radiology Graduate Program.
Dr. Lam, thank you for your very informative article. Given the fact that most crowns are precious metals (gold, silver, platinum, palladium) and I do not use nickel or iron, it sounds like crowns/bridges should be fine during an MRI. I assume that all ceramic crowns should also be fine. Metal dentures–easily removed–are clearly a problem.
I was a bit surprised to see you say that implants are not 100% titanium. What else is in them?
The incorporation of trace amounts of metals can improve wear and durability of device made from a pure (i.e. 100%) metal element. While some dental implants are made from commercially pure titanium (i.e. 100%), others are made with titanium alloys that contain small amounts (around 5% each) of aluminum or vanadium; it depends on the implant system. The same, I believe, can be said for crowns made from precious metals. Although the precious metal may be the largest component of the alloy on a weight by weight or volume by volume basis, my recollection from my days as a dental student is that unless added metals are not incorporated, the durability of the a crown or a bridge may be suboptimal. But I would refer you to someone with more in-depth knowledge about biomaterials than me…
If you are restoring a tooth with a conventional crown made with a precious metal alloy, if there is a stainless steel pin in the underlying restoration there will be an artifact on the MR image. So just because you don’t “see metal” or it doesn’t look metallic doesn’t mean that something isn’t in there in trace amounts that can produce image artifacts.
The bottom line here is that you need to engage in a discussion, whether it is with the individuals from whom you purchase materials, who creates your crowns or bridges, and your (medical) colleagues who may be ordering MRI for your patients.
Dr lam
I found your article very interesting, thank you for sharing your knowledge in this matter, I am a dental technician and I made a two unit cantilever bridge for a patient over ten years ago and the metal I used has nickle , cobalt crom the patient is having a MRI scan on her neck and shoulder would this create an artifact or cause any harm to the patient ifvshe went ahead with the MRI scan looking forward to your reply best regards Colin Williams
Prof Lam,
Thank you for the informative article.
I would like to draw your attention to an article published in Dentomaxillofacial Radiology (2013) 42:20120271. You may wish to also alert your readers that even composites are not fully compatible with MRI. It depends on what the composite is made of.
Thanks for a great article. Implants are made of titanium grade 5 alloys nowadays and are claimed as MRI safe. Precious crowns are not 100 percent precious metal and are always added with alloys to give them strength. High noble content is around 60 percent in precious metal crown. Anyways I think a lot of research should still be done in this field .
Yes, Amay You are right. This field is growing now and research should still be done.