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1. 105
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Original article
Magnetic resonance imaging artefacts and fixed
orthodontic attachments
Aurélien Beau*, Denis Bossard** and Sarah Gebeile-Chauty***
*Faculty of Odontology, Lyon, **Center for Medical Imaging Mermoz, Lyon, and ***Department of Orthodontics,
Faculty of Odontology, Lyon, France
Correspondence to: Aurélien Beau, Université d’Odontologie de Lyon, 11 rue Guillaum Paradin, 69008 Lyon, France. E-mail:
aurelien.beau@hotmail.fr
Summary
Background/Objectives: Orthodontic appliances are often removed before magnetic resonance
imaging (MRI) scans because they are known to produce artefacts.The purpose of this study was
to find the exact indications for removal of various fixed attachments when imaging four specific
areas of the head and neck.
Materials/Methods: Sixty patients requiring an MRI scan of the head for medical reasons
volunteered for this investigation. One of four different types of fixed attachments (stainless steel
brackets, titanium brackets, ceramic brackets with metal slots, and stainless steel retainers) were
assigned to a patient. Each patient had two scans at 1.5T: with an ‘empty wax jig’ and with a wax
jig including the attachment. Archwires were not investigated as they are easily removed before
a scan. Two radiologists evaluated the scans of each patient and each of the four areas under
investigation: maxillary sinus, oral cavity, temporomandibular joints, and posterior cerebral fossa.
Results: Stainless steel brackets always caused non-interpretability of all anatomic areas (100 per
cent). Titanium brackets, ceramic brackets with metal slots, and stainless steel retainers caused
artefact in the oral cavity only (for 20, 16.65, and 86.65 per cent of the subjects).
Conclusions/Implications: Our results show that ceramic brackets with metal slots and titanium
brackets do not always have to be removed before MRI scans of the head and neck, depending on
the area under investigation. Metal fixed retainers should only be removed if the oral cavity itself
is under investigation. Stainless steel brackets should always be removed before MRI scans of the
head and neck.
Introduction
Magnetic resonance imaging (MRI) has been used in medicine for
over 20 years; it is a non-invasive diagnostic tool that does not use
ionizing radiations. MRI is based on the signal of nuclear mag-
netic resonance emitted by the interaction of atomic nuclei that
possess spin with incident radiofrequency within a static magnetic
field (1).
However, the presence of metallic objects during MRI scans
can produce artefacts. An MRI artefact is defined by pixels that
do not faithfully represent the tissue components studied (2). The
dimensions of artefacts depend on the magnetic properties of the
metal that are divided according to their magnetic susceptibility
in three groups: paramagnetic, diamagnetic, and ferromagnetic
and also their shape, size, spatial orientation, and homogeneity
(3–5).
Orthodontists are frequently asked to remove fixed orthodontic
appliances for MRI scanning, particularly when looking for pathol-
ogy in the head and neck region. But debonding procedures, apart
from potentially damaging enamel, are time consuming, uncomfort-
able for the patient, and costly (6). Furthermore, orthodontic appli-
ances can be made in many different alloys, including some that have
never been tested and their compositions and designs keep evolving.
Finally, artefacts do not always interfere with the diagnosis since
they can affect areas that are not of interest.
European Journal of Orthodontics, 2015, 105–110
doi:10.1093/ejo/cju020
Advance Access publication 4 July 2014

2. The main purpose of our study was to determine which ortho-
dontic fixture should be removed by the orthodontist before an MRI
scan to prevent artefacts that could interfere with MRI images to
such a degree that diagnosis may be compromised. Artefacts created
by fixed appliances potentially affecting four defined anatomic areas
of the head and neck were assessed to give radiologists guidelines
when to recommend removal of fixed appliances before MRI scans
of the head and neck area are taken.
Materials and methods
The subjects selected for the present study were volunteer adult
patients referred for head and neck MRI examinations at the pri-
vate hospital Jean Mermoz, Lyon. Thirty-five men and 25 women—a
total of 60 subjects in ages ranging from 24 to 87 years (mean age,
55 years)—participated. All patients were given an informed consent
form explaining the purpose of the study. For each patient, one out
of four types of orthodontic fixtures were inserted into a wax jig
(Table 1); the type of appliance included was randomly assigned.
The wax jig, about 0.4 inches in thickness, had an arch shape and
contained either a metal wire extended from canine to canine (rep-
resenting a mandibular fixed retainer) or 24 stainless steel, ceramic,
or titanium brackets (arranged in two rows representing upper and
lower fixed appliances from first molar to first molar). Each patient
underwent two successive MRI scans: the first was for diagnostic
purposes and served as control (no appliance); during the second
one, the patient was asked to bite on the selected wax sample.
Neither the patient nor the examiner knew the content of the par-
ticular sample.
All MRI scans were undertaken on a 1.5 T system (Siemens
Avanto: Siemens AG, Erlangen, Germany) with the following param-
eters: T2 Blade SPAIR (spectral selection attenuated inversion recov-
ery) Transverse, slice thickness of 3.5 mm, matrix size of 256 × 256,
field of view 240 × 240, TR 4200 ms, TE 131 ms. For each scan, 20
slices were obtained, archived, and analysed later.
All images were evaluated independently by two experienced
radiologists (Denis Bossard, Jean-François Dugor). For each
patient, both scans were compared, and the examiners had to
determine whether the second image was interpretable specifi-
cally assessing four specific anatomic areas of the head: maxil-
lary sinus, oral cavity, temporomandibular joints, and posterior
cerebral fossa. The image of an area was considered non-inter-
pretable if at least a part of the area was distorted or subject to
a black artefact. If any artefact existed on the first scan due to
pre-existing dental restorations, the examiners had to determine
if this artefact was exacerbated on the second scan. The scans of
20 patients were re-evaluated 2 weeks later by the two radiolo-
gists to assess intra- and inter-examiner reliability.
Results
The percentages of images with artefacts by type of appliance and
anatomic area are shown in Table 2. Stainless steel brackets caused
non-interpretability of all four anatomic areas in all 15 patients (100
per cent). Titanium brackets caused no artefact for 12 patients out
of 15 (80 per cent), and artefacts located in the oral cavity only for
3 patients. Ceramic brackets with metal slots caused no artefact for
12 patients (for the first examiner)/13 patients (for the second exam-
iner) out of 15 (83.35 per cent mean) and artefacts located in the
oral cavity for 3 (for the first examiner)/2 (for the second examiner)
patients. Stainless steel retainers caused no artefact for 2 patients out
of 15 (13.35 per cent) and artefacts located in the oral cavity only for
13 patients (86.65 per cent).
The artefacts caused by stainless steel brackets consisted in a
large area of deformation, circled by a ring of low signal (Figure 1).
The absence of artefact made the wax jig clearly visible (Figure 2).
The artefacts caused by titanium and ceramic brackets consisted in
small areas of low signal, located in the anterior part of the oral cav-
ity, close to the appliance (Figure 3). The artefacts caused by stainless
steel retainers were larger and contained both deformation and low
signal areas (Figure 4).
Cohen’s kappa and Siegel’s kappa were measured. Kappa
(Cohen) = 0.986003, Z = 44.1331, P = 0; Kappa (Siegel) = 0.971604,
Z = 13.3476, P = 0. Both kappa coefficients were larger than 0.80,
which reveals almost perfect agreement between examiners.
Diagnostic re-evaluation of 20 patients showed identical results.
Table 1. The four types of appliances used for the study.
1. Omniarch® (GAC) stainless steel brackets
Carbon Silicone Manganese Phosphorus Sulphur Nickel Chrome Copper Niobium Iron
<0.07% <1% <1% <0.04% <0.03% 3–5% 15–17.5% 3–5% 0.15–0.45% Other
2. TitaniumOrthos® (Ormodent) titanium brackets
Alloy UNS No. Cr Ti
N/A N/A <0.1% >99.0%
3. Clarity® (3M) ceramic brackets with metal slot
Transparent polycrystalline alumina Alumina grains
Stainless steel support
(contains nickel)
Marking ink
soluble in water
>90% <5% <5% <1%
4. Bond-a-braid® (American Ortho) stainless steel retainers
Cobalt Silicone Manganese Aluminium Molybdenum Nickel Chrome Copper Tungsten Iron
0–5% 0–5% 0–2% 0–2% 0–4% 8–12% 15–20% 0–4% 0–4% 65–75
European Journal of Orthodontics, 2015, Vol. 37, No. 1106

3. Discussion
Few studies showed the effect of metal fixtures used in orthodontics
on MRI scans and the results obtained from studies using prostho-
dontic materials (7–11) cannot be transferred to orthodontics because
of the different shapes and metal composition of the appliances.
Existing studies evaluating orthodontic appliances (12–14) are nei-
ther particularly comprehensive nor comparable in terms of materials
and situations investigated. Moreover, several studies are in vitro and
the effects of the different materials investigated are not consistent.
Our study did not investigate temperature changes and displace-
ment forces induced by magnetic fields on orthodontic appliances,
Table 2. Percentages of images with artefacts by type of appliance and anatomic area.
Stainless steel
brackets
Titanium
brackets
Ceramic brackets
with metal slots
Stainless steel
retainers
Oral cavity 100% 20% 16.65% 86.65%
Maxillary sinus 100% 0% 0% 0%
Temporomandibular joints 100% 0% 0% 0%
Posterior cerebral fossa 100% 0% 0% 0%
Figure 1. Example of artefacts caused by stainless steel brackets. All areas
under investigation were affected.
Figure 2. No artefact shown.The dark area in the oral cavity corresponds to
the wax sample. Being magnetically neutral, it sends no information to the
device and thus has the same contrast as air.
Figure 3. An example of artefacts caused by either titanium or ceramic
brackets (with metal slot).
Figure 4. Example of artefacts caused by a stainless steel retainer, affecting
the oral cavity only.
A. Beau et al. 107

4. which have already been shown respectively negligible (15) and
should not be problematic for as long as the bonding and attachment
of the different elements are checked before the MRI scan (16, 17).
Our study focused on bonded appliances for which removal
procedures could potentially damage enamel, are time consum-
ing, uncomfortable for the patient, and costly. We did not include
archwires or removable appliances in our study; these can be easily
removed before an MRI examination without causing any of the
above-mentioned unwanted effects (13, 18).
Apart from the stainless steel brackets, we chose contemporary
orthodontic materials that have either not been tested extensively
(titanium) or had, to our knowledge, not been investigated before
(fixed retainers, ceramic brackets with metal slots). For each type
of appliance, a single brand was chosen: even if slight variations
between manufacturers exist, components and shapes are fairly sim-
ilar and the evaluation methods used in our study would not have
been able to differentiate between those. We hence considered our
sample as reasonably representative for each type of appliance. We
chose Clarity brackets to represent ceramic brackets containing a
metal slot. We chose not to use self-ligating ceramic brackets because
shape and composition are quite similar to ceramic brackets with a
metal slot, so we would expect similar results in terms of artefacts.
All samples were embedded in single use wax sticks because wax
is magnetically neutral, economical, easy to prepare, adaptable to
the arch shape and size of each patient, and allows an easy fitting
and removal.
An in vivo design was chosen to resemble a clinical scenario best
in terms of materials used and anatomical areas investigated.
The study was undertaken using a 1.5 T MRI scanner (Siemens
Avanto: Siemens AG, Erlangen, Germany) because a magnetic field
of this strength is commonly used in radiology. The sequence we
used was representative for the pathologies usually investigated in
the head and neck area. Most MRI examinations use axial slices in
T2-weighted sequence, which is most likely to produce artefacts and
it was used for that reason.
We decided to include 60 patients as artefacts are known to
vary between patients (12). Sixty may seem to be a small sample
compared to other epidemiological studies but for this study, it was
deemed satisfactory because of the good intra- and inter-examiner
reproducibility.
MRI is a non-ionizing imaging technique and is not known to
cause short-term side effects. However, there are important safety
concerns to consider before performing an MRI scan: pacemakers
malfunction, artificial limbs heating up, and skin irritation due to skin
tattoos have all been encountered (19, 20). No contrast media was
used for this study. All volunteers who presented with medical indica-
tions for a head and neck MRI scans were consented accordingly.
The first scan was used as a reference in our study. Evaluation was
based on clinical criteria (interpretable or non-interpretable image)
unlike other studies that measured size of the artefact (9, 21, 22) or
pixel density (1).To standardize results, we defined the term non-inter-
pretable as an artefact covering ‘part of the area under investigation’;
i.e. one of the four anatomical areas. Artefacts, caused by dental resto-
rations, were detected by the first diagnostic scan and these were taken
into account when interpreting the scan that included the appliances.
The results of our investigation confirmed that stainless steel
causes artefacts, a finding that previous authors already described
(9, 22–26).
Stainless steel brackets rendered the MRI scans diagnostically
unusable in all cases. The amount of ferromagnetic metal plays an
Figure 5. Indications for the radiologist when to recommend removal of fixed appliances before magnetic resonance imaging scans of the head and neck area are taken.
European Journal of Orthodontics, 2015, Vol. 37, No. 1108

5. important factor in degradation of image quality: although stainless
steel retainers caused artefacts in 86.6 per cent of scans, this affected
the oral cavity only; indeed in the residual 13.3 per cent of scans,
no artefact was present at all. Ceramic brackets with stainless steel
inserts also caused only localized artefacts in 13.3 per cent of scans.
Our results are consistent with other authors who noted that the
size of the artefact partly depends on volume and shape of the metal
object in the scan (1).
A number of authors showed that titanium does not generally
cause artefacts (26–28). This can be explained by the small quanti-
ties used (1). However, in 20 per cent of scans, very localized arte-
facts appear in the oral cavity. This confirms that titanium is able to
produce artefacts, and this has been reported before (1, 9, 22, 29–
31). Titanium itself has ferromagnetic properties but the presence
of traces of other metals could also explain the ability to degrade
MRI images. The titanium brackets used in our study contained less
than 0.1 per cent of chromium, which is ferromagnetic. Some of the
authors above found the artefacts on MRI scans caused by titanium
significant, while we did not. This can be explained by the different
quantities of titanium used in other studies: Lissac (9) used a tita-
nium block of 9 × 9 × 1 mm in size and found a spherical deformation
doubling the size of the sample; many other authors use titanium
screws or implants (22, 29–31) and the results of those investigations
are not transferable to orthodontics due to the amount and concen-
tration of titanium in one anatomical area.
The image distortion caused by stainless steel brackets rendered
all of our MRI scans non-diagnostic for all anatomical areas inves-
tigated. We therefore recommend that stainless steel brackets are
always removed before MRI scan of the head and neck region is
undertaken. Only 10 per cent of our patients required an MRI scan of
the oral cavity for diagnostic purposes. Removal of fixed appliances
containing titanium brackets, ceramic brackets with metal slots, or
metal fixed retainers is only indicated for this small cohort of patients.
Conclusions
1. Ceramic brackets with a metal slot and titanium brackets caused
either very limited or no artefacts on MRI images. These ortho-
dontic fixtures will only have to be removed if the area under
investigation is close to the fixed appliances, i.e. in the oral cavity.
2. Fixed retainers containing steel cause poor image quality in the area
of the oral cavity only and only need to be removed ahead of an
MRI scan if the area under investigation is within the oral cavity.
3. Stainless steel brackets caused extensive artefacts, rendering the
images for all areas investigated here uninterpretable in all cases
and should therefore always be removed before MRI images of
the head and neck area are taken (Figure 5).
Acknowledgements
The authors would like to thank Dr Jean-François Dugor for his kind par-
ticipation, Mrs Marie-Paule Gustin-Paultre for the statistical analysis, Mrs
Barbara Schaff and Mrs Josiane De Volder for their help with translation.
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