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.