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Table of Contents   
ORIGINAL RESEARCH  
Year : 2022  |  Volume : 33  |  Issue : 3  |  Page : 258-262
The effect of metallic dental restorations and implants in causing patient discomfort and artefacts during magnetic resonance imaging of the head and neck


1 Department of Prosthodontics, Government Dental College, Affiliated to Kerala University of Health Sciences, Kozhikode, Kerala, India
2 Department of Radiodiagnosis, Government Medical College, Affiliated to Kerala University of Health Sciences, Kozhikode, Kerala, India

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Date of Submission10-May-2021
Date of Decision12-Sep-2022
Date of Acceptance14-Sep-2022
Date of Web Publication17-Jan-2023
 

   Abstract 


Context: Patients with metallic dental objects in their oral cavity are often associated with discomfort or artefacts during magnetic resonance imaging (MRI) of the head and neck. Aim: This study was conducted to evaluate the effects of metallic dental objects in causing patient discomfort and artefacts during MRI of the head and neck region. Design: This is an observational study including 538 participants from various specialized MRI centres in Kozhikode. Methods and Material: MRI records of 538 participants who underwent head and neck MRI as a part of their medical treatment were collected. With the help of questionnaire and clinical examination, the type of metallic dental object in the patient's oral cavity was identified. After examining the MRI images, four categories of artefacts were established. In MRI brain, artefacts in three different sequences were also studied. Statistical Analysis Used: The significance of the difference between proportions was analysed by the Chi-square test. Results: Artefacts were found in 65 cases with metallic dental objects but none of the participants had experienced any kind of discomfort. The artefact formation significantly depended on the type of metallic dental restoration in the patient's oral cavity. Orthodontic braces and titanium bone plate created severe artefacts in head and neck MRI making interpretation almost impossible. In the MRI brain, diffusion-weighted imaging is most sensitive to artefact followed by fluid-attenuated inversion recovery. Conclusions: Artefacts were found in 65 cases with metallic dental restorations but none of the participants had experienced any kind of discomfort.

Keywords: Artefact, diffusion-weighted imaging, fluid-attenuated inversion recovery, magnetic resonance imaging

How to cite this article:
Ashok A, Ayyadanveettil P, Devarajan E, Thavakkara V, Latha N, Saraswathy A. The effect of metallic dental restorations and implants in causing patient discomfort and artefacts during magnetic resonance imaging of the head and neck. Indian J Dent Res 2022;33:258-62

How to cite this URL:
Ashok A, Ayyadanveettil P, Devarajan E, Thavakkara V, Latha N, Saraswathy A. The effect of metallic dental restorations and implants in causing patient discomfort and artefacts during magnetic resonance imaging of the head and neck. Indian J Dent Res [serial online] 2022 [cited 2023 Feb 5];33:258-62. Available from: https://www.ijdr.in/text.asp?2022/33/3/258/367880



   Introduction Top


Magnetic resonance imaging (MRI) of the head and neck region has become a promising aid in evaluating the pathologies of the brain and cervical spine.[1],[2] It uses a strong stationary magnetic field and radio waves rather than ionizing radiation.[3] Several studies reported that diagnosis with head and neck MRI is compromised to a certain extent, as it is prone to magnetic susceptibility artefacts caused by the presence of various metallic dental objects like crowns, fixed dental prostheses, implants and orthodontic appliances.[4],[5]

The degree to which the substances are magnetized when placed in a magnetic field depends on their magnetic susceptibility. The signal loss or image distortion occurs when there is a difference in the magnetic field strength at the interface between metallic dental objects and adjacent tissues, which often leads to artefact formation.[6]

Previous studies have shown that some unwanted effects like heat generation and mechanical displacement of dental materials may also result when the materials interact with the magnetic resonance imager.[7],[8],[9] However there has never been a report of a patient being seriously injured as a result of excessive heat development in a metallic, implanted device.[8],[9]

A greater number of patients are undergoing fixed restorative treatment, including fixed dental prostheses and implants for many years. Since the removal of a fixed prosthesis prior to MRI is a difficult task, a lot of studies were conducted to evaluate the compatibility of various dental materials with the magnetic field.[4],[5],[7] Hence purpose of this study was to find out, whether the presence of metallic dental objects in a patient's mouth causes any adverse effects for patients during imaging or in the diagnostic quality of MRI.


   Subjects and Methods Top


An observational study was conducted from December 2018 to December 2020 in various specialized MRI centres in Kozhikode. This study protocol was approved by the Institutional Ethics committee of Government Dental College, Kozhikode (IEC no: 130/DCC/2018, dated 30-10-2018). A sample size of 538 participants who underwent head and neck MRI as a part of their medical treatment was included in this study. Findings were obtained by conducting an interview, intraoral examination and MRI Image analysis. A questionnaire was prepared to conduct an interview with the participants. Demographic information such as age, gender and socio-economic status was recorded. With the help of the questionnaire, details regarding the dental restorative treatment if any, and discomfort experienced by the patient during MRI were assessed.

An intraoral examination was done with the help of diagnostic instruments (mouth mirror and explorer). The participant's dental treatment status was assessed. Metallic dental objects such as amalgam restoration, metal/metal ceramic crowns and fixed dental prosthesis (FDP), titanium dental implants, titanium bone plate and orthodontic stainless-steel braces were identified in 73 participants. Any mucosal changes or evidence of movement or dislodgement of the restoration due to the interaction of the participant's restoration with the magnetic field were assessed.

MRI images of 538 participants were collected as DICOM files from the MRI centre. The picture archiving and communication system (PACS) was used to store the data. The images were analysed by two radiologists with a PACS DICOM viewer (RadiAnt DICOM Viewer 2020.2; Medixant Maciej Frankiewicz; Poland). The extent of the image distortion and its impact on diagnosis was evaluated. After MRI image analysis, four categories of artefacts were established according to the guidelines given by Hinshaw et al.[10] as, no artefacts, mild artefacts, moderate artefacts and severe artefacts. After the evaluation of the artefacts, the severity of artefacts and the diagnostic quality of each case were assessed.

Artefacts in three different sequences of MRI brain were also studied, which include standard sequence (T1 weighted imaging (T1WI) and T2 weighted imaging (T2WI)), fluid-attenuated inversion recovery (FLAIR) and diffusion-weighted imaging (DWI). The severity of artefacts in each sequence was compared to find out which sequence was more sensitive to the formation of artefacts.

Statistical analysis

Statistical analysis was done using Statistical Package for Social Sciences, 20.0 (IBM SPSS Statistics, v20.0; IBM Corporation) software. The significance of difference between proportions was analysed by Chi-square test.


   Results Top


Demographic data of the participants were recorded. It was found that out of 538 samples, metallic dental objects were found in 73 participants, and among them, artefacts were found in 65 (89.04%) cases. The number of cases with artefacts in the MRI brain was 32 out of 34 (94.1%) and in MRI spine was 33 out of 39 (84.6%). The difference observed was not significant (P = 0.19).

Most severe artefacts in both MRI brain and MRI spine are produced by orthodontic stainless-steel braces followed by titanium bone plate [Figure 1]. In subjects with amalgam restorations, mild artefacts were found in 58.82% of cases [Figure 2]a. In Titanium implant groups 6 patients had a single implant with a crown and 3 patients had 2 implants with splinted crowns, and all the cases exhibited mild artefacts [Figure 2]b.
Figure 1: Severe artefacts: (a) MRI brain with orthodontic braces, (b) MRI C-spine with orthodontic braces, (c) MRI C-spine with bone plate

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Figure 2: Mild artefacts: (a) MRI brain with amalgam, (b) MRI C-spine with dental implant

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Statistically significant differences (P < 0.001) were obtained [Table 1]. It was shown that the artefact formation significantly depends on the presence of metallic dental restoration in the patient's oral cavity.
Table 1: Severity of artefacts

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Participants with crown and FDP were divided according to the number of crowns or units of FDP per participant [Table 2]. They have shown a wide variation in the pattern of artefacts formation ranging from no artefacts to severe artefacts [Figure 3].
Table 2: Number of crowns per patient and its effect on severity of artefact

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Figure 3: Severity of artefacts in Crown and FDP group: (a) mild artefact due to single crown, (b) moderate artefact due to FDP, (c) Severe artefacts due to FDP

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Artefacts in three different sequences of MRI brain were also compared, which included standard sequences (T1WI and T2WI), FLAIR, and DWI. It was observed that DWI is most sensitive to artefact followed by FLAIR.

None of the participants had experienced any kind of discomfort like burning sensation, movement or dislodgement of the restoration, etc.


   Discussion Top


The present study evaluated the potential risks associated with head and neck MRI in participants with metallic dental objects, during a 2-year study period. Out of 73 participants with metallic dental objects, artefacts were found in 65 cases (89.04%). The number of cases with artefacts in the MRI brain was 32 out of 34 (94.1%) and in MRI spine was 33 out of 39 (84.6%). Statistical analysis has shown, no significant difference between the proportions (P = 0.19).

Artefacts were observed in 58.82% of cases with amalgam restoration, 97.1% of cases with crown and FDP, and whole cases (100%) with titanium dental implants, titanium bone plate and orthodontic stainless-steel braces. It was shown that the artefact formation significantly depends on the presence of metallic dental restoration in the patient's oral cavity (P < 0.001).

In subjects with amalgam restoration, 58.82% of cases produced mild artefacts and 41.18% of cases had no appreciable artefacts. Amalgam is an alloy of mercury with two or more different metals, in which silver is the most abundant component. Costa et al.[4] reported that, the amalgam will not produce any artefact due to the presence of non-ferromagnetic silver. Eggers et al.[5] also observed a lack of distortion of the image associated with amalgam restoration as they contain diamagnetic silver.

In this study, we have observed that only a mild artefact was observed in the scan of a subject with amalgam restoration, and it was located in the dentoalveolar region. This artefact did not have any influence on the image interpretation in both MRI brain and MRI spine since it was not present at the region of interest.

In cases with the titanium implant, 6 participants had single implant and 3 participants had double implants and both exhibited mild artefacts while imaging. Titanium implants contain traces of iron which is a ferromagnetic substance.[5] According to Eggers et al.[5] even traces of a ferromagnetic substance can cause a dropping out of the signal. So in this study, the artefacts observed in subjects with titanium implant is because of the presence of ferromagnetic iron. Smeets et al.[11] reported that titanium implants produced severe susceptibility artefacts. Duttenhoefer et al.[12] found that titanium implants produced strong magnetic field distortion whereas zirconia implants produced only minor distortions.

Beau et al.[13] reported that, in addition to the ferromagnetic property of titanium, the presence of traces of other elements contributes to the degradation of MRI images. Similar to amalgam restoration, artefacts due to dental implants were also not observed in the region of interest in the present study. In the case of a subject with a titanium bone plate, the artefact generated was severe and the diagnosis was compromised as it covers a larger area in the mandible.

Different magnitudes of artefact formation were seen in cases with crowns and fixed dental prosthesis, as there was variation in the number of crowns. Up to 2 units, the artefacts observed were mild (83.33% of cases). In subjects with 3–4 crown units, mild artefacts were found in 40% of cases and moderate artefacts were found in 60% of cases. In subjects with more than 4 units, moderate artefacts were found in 83.33% of cases and severe artefact were found in 16.67% of cases.

The dental casting alloys present in the metal or metal-ceramic crowns are mainly gold, cobalt, copper, chromium or titanium in variable amounts. Cobalt, gold and pure titanium are diamagnetic materials and chromium is paramagnetic.[14] Costa et al.[4] found that the dental crowns used in their study predominantly contained gold, which produced mild artefacts. Murakami et al.[15] reported that cobalt chromium alloy produced significantly larger artefact, followed by nickel-chromium alloy, titanium alloy and gold-palladium-silver alloy.

Orthodontic braces are made up of austenitic stainless steel and contain nickel (8%) and chromium (18%). Nickel and Iron are ferromagnetic materials.[14] Costa et al.[4] found that, since orthodontic appliances are employed in both upper and lower jaws, a large area of image distortion occurs, making the interpretation almost impossible.

Debonding of the braces prior to MRI scanning results in loss of enamel and are usually time-consuming, uncomfortable for the patient and not economical. Wylezinska et al.[16] reported that stainless steel brackets caused the most severe distortion on MRI images. Cross et al.[17] reported that the plane of imaging can be altered to avoid the artefacts formation by avoiding the location of metal devices. Beau et al.[13] recommended removal of the stainless-steel brackets prior to MRI scan since the extensive image distortion rendered the image interpretation almost impossible.

In the present study artefacts in three different sequences (Standard sequences (T1WI and T2WI), FLAIR and DWI) of brain MRI were compared. It was observed that DWI is most sensitive to artefact by FLAIR. According to Bryll et al.[18] the type of imaging sequence has a significant influence on artefact formation. They found that the artefacts observed in fast spin echo T2 (FSE T2) were smaller than those that appeared in FLAIR sequences. Katarzyna Krupa et al.[19] found that FLAIR and DWI are very sensitive to magnetic susceptibility artefacts.

Among 538 participants, none of the participants had experienced any kind of discomforts like burning due to excessive heat development and movement or dislodgement of the restorations. Previous studies have shown that the temperature changes associated with magnetic resonance imaging of a patient with metallic dental objects were minimal.[8],[9] Dempsey et al.[8] reported that only minor temperature change if any, has occurred around the biomedical implants.

American Society for Testing and Materials (ASTM F2052-06) has given standard testing methods to determine the displacement force induced by the magnetic field. If the deflection angle is less than 45°, the risk imposed will be negligible and is similar to the risk imposed by the gravitational force.[20] According to Hasegawa et al.[7] the angular deflections were greater than 90° for magnetic dental attachments during 3T magnetic resonance imaging with a deflection force ranging from 0.03–0.3 N. However the displacement of the prosthesis can be prevented by the dental luting cement, having a retentive force of 48–150 N. Braces should be checked for its bond strength prior to the scanning, and if it is firmly bonded to the tooth surface, it will be safe in the magnetic field.[7],[13]

Limitations of the present study that may affect the results include; since the patients were unaware of the chemical composition of the dental restorations, we could not distinguish which component contributed to the artefact in this study. The MRI acquisition parameters were different in each case since the participants had undergone MRI for various reasons. Different radiographers used different protocols to reduce the magnetic susceptibility artefacts, which might have influenced the findings obtained in this study. The type of dental materials and their influence on MRI interpretation of different regions could not be studied. Hence more multicentre studies are required so that a larger number of participants, a different region of imaging and different imaging protocols can be incorporated.


   Conclusion Top


Within the limitations of the study, following conclusions were drawn. Among 538 participants who underwent head and neck MRI, 73 cases had metallic dental objects and artefacts were found in 65 cases. The artefact formation significantly depended on the type of metallic dental restoration in the patient's oral cavity. Orthodontic braces and titanium bone plate created severe artefacts in head and neck MRI, making interpretation almost impossible. DWI and FLAIR are more sensitive to artefact formation as compared to the standard sequences (T1WI and T2WI) in MRI brain. None of the participants had experienced any kind of discomforts like dislodgement of the restoration or burning sensation etc.

Acknowledgement

The authors are grateful to Dr. Biju George (Assistant Professor, Government Medical College, Kozhikode) who has helped in the statistical analysis of this study, and Ms. Aswathi and Mr. Rajeevan (Radiographers) who have provided the technical assistance and helped with the data collection.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Correspondence Address:
Dr. Aiswarya Ashok
Department of Prosthodontics, Government Dental College, Kozhikode - 673008, Kerala
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijdr.ijdr_430_21

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