EFFECTS OF ORTHODONTIC APPLIANCES ON DIAGNOSTIC … · 1.1 Orthodontic appliances and MRI 1 1.2 Current state of the literature on orthodontic appliances in MRI 3 1.3 Purpose and

EFFECTS OF ORTHODONTIC APPLIANCES ON

DIAGNOSTIC QUALITY OF MR IMAGES OF THE

HEAD

By

Dzmitry Zhylich

A thesis submitted in conformity with the requirements

for the degree of Master of Science (Orthodontics)

Graduate Department of Dentistry

University of Toronto

© Copyright by Dzmitry Zhylich, 2015

ii

EFFECTS OF ORTHODONTIC APPLIANCES ON DIAGNOSTIC QUALITY OF MR IMAGES OF THE

HEAD

Dzmitry Zhylich

MSc Degree, 2015

Discipline of Orthodontics, Faculty of Dentistry, University of Toronto

Toronto, Ontario, Canada

Abstract

Introduction: The influence of four common fixed orthodontic appliances on artifact formation and

diagnostic quality of head MR images produced by a 3 Tesla MR scanner was studied. Methods:

Stainless steel brackets, ceramic brackets, combination of ceramic brackets and steel molar tubes, and

multistranded steel mandibular lingual retainers were embedded into custom made Essix® trays for each

of 10 adult subjects. Head MR scans of nine regions were acquired for each subject wearing these trays.

Sagittal T1-weighted, axial T2-weighted, axial gradient-recalled, axial diffusion-weighted, non-contrast

axial MR angiography and axial fluid-attenuated inversion recovery MR sequences were included. Two

neuroradiologists evaluated image distortions and diagnostic qualities of the 13860 acquired images.

Results: Images were affected by appliance, head region and MR sequence. Conclusions: Head MR

images are differentially affected by the presence of orthodontic appliances. The appliance, region imaged

and MR sequence need consideration before imaging patients wearing different fixed orthodontic

appliances.

iii

Acknowledgments:

I would like to express my sincere gratitude to my primary supervisor Dr. Sunjay Suri for the

idea of the project and his great support and guidance through and through. I would also like to

thank my knowledgeable committee members: Dr. Bryan Tompson, Dr. Wendy Lou and Dr.

Andrea Doria for their advice and input during this study. I very much appreciate the work of the

radiologists Dr. Pradeep Krishnan and Prakash Muthusami who spent long hours reading

thousands of images as well as Dr. Manohar Shroff’s support and expertise.

My sincere thanks goes to very accommodating and professional MR technicians Ms. Tammy

Rayner-Kunopaski and Ms. Ruth Weiss.

I am very grateful to my patient colleagues who participated in the study.

Finally, I would like to thank my family, especially my wife Irina, son Antony and my mother

Safiya whose love and support gave me inspiration and strength to complete the project.

iv

Table of contents:

Chapter Page

1. Introduction 1

1.1 Orthodontic appliances and MRI 1

1.2 Current state of the literature on orthodontic appliances in MRI 3

1.3 Purpose and statement of the problem 4

1.4 Aims and objectives 4

1.5 Hypothesis 5

2. Materials and methods 6

2.1 Study sample 6

2.2 Consent 7

2.3 Appliances tested 7

2.4 Procedures 8

2.5 Pilot test 9

2.6 Main study 12

2.7 Statistical analysis 17

3. Results 18

3.1 Pilot test: assessment of MR image distortion produced by the Essix® tray 18

material

3.2 Main study: comparison of the distortion scores between different subjects 18

3.3 Comparison of the distortion scores between different anatomic regions 25

3.4 Comparison of the distortion scores between different MR sequences 31

v

3.5 Comparison of the distortion scores of different orthodontic appliances 37

3.6 Calculation of inter and intrarater agreements 71

4. Discussion 73

4.1 Scientific novelty of the study 74

4.2. Explanation of findings 76

4.3 Recommendations for clinical practice. 80

4.4 Strengths and limitations of the study 82

4.5 Recommendations for future studies 84

5. Conclusions 86

6. Bibliography 87

7. Appendices 91

7.1 University of Toronto Research Ethics Board approval 91

7.2 The Hospital for Sick Children Research Ethics Board approval 93

7.3 Invitation letter to subjects for participation 94

7.4 Research consent form 98

7.5 MRI screening form 108

7.6 Case Report Form 109

7.7 Randomized order of the appliances for 10 subjects 110

7.8 Representative sagittal and axial images for scores 1 to 5 111

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List of figures:

Figure Description Page

1. Appliances tested 13

2. Complete sets of maxillary and mandibular appliances 14

3. Flowchart of image acquisition 16

4. Mean distortion scores by the appliance type for each subject 20

5. Diagnostic scores for stainless steel brackets and tubes for each subject 21

6. Diagnostic scores for ceramic brackets for each subject 22

7. Diagnostic scores for ceramic brackets and stainless steel buccal tubes for each 23

subject

8. Diagnostic scores for ceramic brackets for each subject 24

9. Mean diagnostic scores for different appliances for each anatomic region 26

10. Diagnostic scores for stainless steel brackets and tubes for each anatomic region 27

11. Diagnostic scores for ceramic brackets for each anatomic region 28

12. Diagnostic scores for ceramic brackets and stainless steel buccal tubes for each 29

anatomic region

13. Diagnostic scores for lingual retainer for each anatomic region 30

14. Diagnostic scores of different appliances for each sequence 32

15. Diagnostic scores for stainless steel brackets and tubes for each MR sequence 33

16. Diagnostic scores for ceramic brackets for each MR sequence 34

17. Diagnostic scores for ceramic brackets and stainless steel tubes for each MR 35

sequence

18. Diagnostic scores for lingual retainer for each MR sequence 36

vii

19. Mean diagnostic scores for different anatomic regions according to the MR 39

sequence for the appliance type: stainless-steel brackets and buccal tubes

20. Diagnostic scores for stainless steel brackets and tubes for sagittal T1 sequence 40

according to anatomic regions

21. Diagnostic scores for stainless steel brackets and tubes for axial T2 sequence 41


22. Diagnostic scores for stainless steel brackets and tubes for axial gradient-recalled 42

sequence according to anatomic regions

23. Diagnostic scores for stainless steel brackets and tubes for axial diffusion-weighted 43


24. Diagnostic scores for stainless steel brackets and tubes for axial MRA sequence 44


25. Diagnostic scores for stainless steel brackets and tubes for axial FLAIR sequence 45


26. Mean diagnostic scores for different anatomic regions according to the MR sequence 47

for the appliance type: ceramic brackets

27. Diagnostic scores for ceramic brackets for sagittal T1 sequence according to 48

anatomic regions

28. Diagnostic scores for ceramic brackets for axial T2 sequence according to anatomic 49

regions

29. Diagnostic scores for ceramic brackets for axial gradient-recalled sequence 50


30. Diagnostic scores for ceramic brackets for axial diffusion-weighted sequence 51

viii


31. Diagnostic scores for ceramic brackets for axial MRA sequence according to 52

anatomic regions

32. Diagnostic scores for ceramic brackets for axial FLAIR sequence according to 53

anatomic regions


sequence for the appliance type: ceramic brackets and stainless steel buccal tubes

34. Diagnostic scores for ceramic brackets + steel buccal tubes for sagittal T1 56


35. Diagnostic scores for ceramic brackets + steel buccal tubes for axial T2 sequence 57


36. Diagnostic scores for ceramic brackets + steel buccal tubes for axial 58

gradient-recalled sequence according to anatomic regions

37. Diagnostic scores for ceramic brackets + steel buccal tubes for axial 59

diffusion-weighted sequence according to anatomic regions

38. Diagnostic scores for ceramic brackets + steel buccal tubes for axial MRA 60


39. Diagnostic scores for ceramic brackets + steel buccal tubes for axial FLAIR 61



sequence for the appliance type: lingual retainer

41. Diagnostic scores for lingual retainer for sagittal T1 sequence according to anatomic 64

regions

ix

42. Diagnostic scores for lingual retainer for axial T2 sequence according to anatomic 65

regions

43. Diagnostic scores for lingual retainer for axial gradient-recalled sequence according 66

to anatomic regions

44. Diagnostic scores for lingual retainer for axial diffusion-weighted sequence according

66

to anatomic regions

45. Diagnostic scores for lingual retainer for axial MRA sequence according to anatomic 68

regions

46. Diagnostic scores for lingual retainer for axial FLAIR sequence according to 69

anatomic regions

47. Approximate relative distances from the orthodontic appliances to the anatomic 77

regions of the head assessed in the study

x

List of tables:

Table Description Page

Table 1: Parameters of the MR sequences used 10

Table 2: Modified ROC (receiver operating characteristic) score system used for 11

MR image diagnostic quality determination

Table 3: Mean distortion scores with standard deviations (in brackets) by the 19

appliance type for each subject, overall mean distortion scores for each

appliance and pairwise comparisons with scores of ceramic brackets

Table 4: Mean distortion scores with standard deviations for different appliances 25

according to the anatomic regions

Table 5: Mean distortion scores with standard deviations for different appliances 31

according to the imaging sequence

Table 6: Mean diagnostic scores with standard deviations for different anatomic 38

regions according to the MR sequence for the appliance type: stainless steel

brackets and buccal tubes


regions according to the MR sequence for the appliance type: ceramic brackets


xi

regions according to the MR sequence for appliance type: ceramic brackets

and stainless steel buccal tubes


regions according to the MR sequence for appliance type: lingual retainer

Table 10: Intrarater agreements for reviewers 1 and 2 72

Table 11: Clinical recommendations for cranial MR imaging with 4 commonly 81

used orthodontic appliances and 6 common MR sequences

xii

List of abbreviations:

MRI: Magnetic Resonance Imaging

MR Magnetic Resonance

TMJ: Temporomandibular Joint

ECG: Electrocardiography

GRE: Gradient recalled

DWI: Diffusion-weighted

FLAIR: Fluid Attenuation Inversion Recovery

MRA: Magnetic Resonance Angiography

T: Tesla

RMO: Rocky Mountain Orthodontics

AO: American Orthodontics

SEMAC: Slice Encoding for Metal Artifact Correction

MAVRIC: Multiacquisition Variable Resonance Image Combination

SAR: Specific Absorption Rates

M: Metal

C: Ceramic

xiii

TMA: Titanium Molybdenum Alloy

C+M: Ceramic + Metal

LR: Lingual Retainer

N Number

ROC Receiver Operating Characteristic

1

CHAPTER 1.

Introduction

Magnetic resonance imaging (MRI) is a diagnostic modality widely used in medicine and

dentistry for soft tissue imaging. MRI is indispensable when investigating soft tissue tumors,

including those of the head and neck1, TMJ pathology

2, cardiovascular pathology

3, seizures

4 and

cerebral palsy.5 In addition, new applications for MR 3D hard tissue images are emerging.

6 MRI

offers several advantages. It offers the best resolution of soft tissues and does not involve

ionizing radiation.7 The number of MR scans that are conducted is steadily increasing each year.

For example, in the US, the estimated annual number MRI procedures is 26 million every year.8

An MR image is obtained by manipulating protons within the body by a very strong

magnetic field9. Metallic objects within the body including common orthodontic appliances can

produce artifacts on MR images, which are defined as distortions of signal intensity or voids that

do not have any anatomic basis in the plane being imaged.10

These artifacts are caused by a)

differences in magnetic susceptibility between the metallic object and the adjacent tissues

regions11

and b) by magnetic fields caused from eddy currents induced in the object by the

excitation radio frequency field or switched gradient fields.12,13

Artifacts caused by a metallic

object depend on the material of the object (its magnetic susceptibility and electric conductivity),

the object size, shape, orientation in magnetic field, and on the parameters of the MR scan.13

2

1.1 Orthodontic appliances and MRI

Costa et al. (2009)14

in a retrospective analysis of MR images in a university medical

center, revealed artifacts in 6% of all head scans and it was found that orthodontic appliances

produced 78% of all the artifacts. Fixed orthodontic treatment is relatively common and

increasingly prescribed for children and adults.15

It involves having orthodontic attachments

(braces) that are fixed in the patients’ mouth for the duration of treatment, which generally lasts

24-30 months.16

Orthodontic treatment is routinely followed by long-term retention to maintain

the treatment result. This usually includes a metallic wire that is fixed to the lingual surfaces of

the lower anterior teeth, and remains in situ for several years, even decades after the active

treatment with fixed appliances has been completed.17

Patients with fixed multibracket orthodontic appliances (braces) occasionally require MR

examinations of the head and neck region. While it is known that fixed multibracket orthodontic

appliances cause image artifacts on MR images, the extent and severity of image loss is not clear

from the literature. Consequently, to circumvent the problem of image artifacts caused by

orthodontic appliances, orthodontists are often requested to remove fixed orthodontic appliances

or fixed retainers before the planned MR scan, or orthodontic hardware is removed in emergency

rooms of the hospitals before an urgent MR examination.18,19

This increases the financial and

biological burdens since removal and later reinstallation of fixed orthodontic appliances is costly

and labor intensive.20

Debonding is also accompanied by risks of potential enamel loss21

,

tearouts21

and cracks.22

Because of the increase in orthodontic treatment utilization, the long-

term use of fixed lingual bonded metallic wire retainers and the ever rising utilization of MRI

each year, the problem of MR image loss from fixed orthodontic appliances is likely to become

even more significant in years to come.

3

1.2 Current state of the literature on orthodontic appliances in MRI

There have been a number of studies published on the subject of MRI artifacts produced

by dental materials. Lissac et al. (1991)23

found that precious alloys, dental ceramics, amalgams

and composite materials did not cause MR image distortion whereas titanium caused slight

image artifacts, and base alloys caused considerable artifacts. Abbaszadeh et al. (2000)24

found

that gold alloy and amalgam produced small artifacts while gold alloy produced large artifacts.

Although there are a number of studies that investigated artifacts on MR images of the head

caused by orthodontic appliances, the matter still remains controversial and unclear.14

Sadowsky

et al. (1988)9, Hinshaw et al. (1988)

25 found that artifacts caused by stainless steel bracket and

wires do cause some distortion of the MR image of the brain, but it still remains diagnostic. On

the other hand, a number of other studies confirmed that orthodontic appliances can render TMJ

and brain MR images undiagnostic.26,27

Some authors reported that titanium causes only minor

artifacts28-30

while other researchers stated the opposite.14,25

In addition, the effects of different

types of commonly used fixed orthodontic appliances on the MR image quality have not been

studied systematically. Elison et al. 26

undertook a structured investigation to study MR image

distortions caused by steel, ceramic, composite, and titanium brackets on images acquired using

an MR scanner with a 1.5 T magnet. Ceramic brackets without metal slot, composite and

titanium brackets were found not to have caused significant distortion on the MR images taken

with 1.5 Tesla strength scanner.19,26

In current practice of diagnostic imaging, 3 Tesla MR machines are becoming

increasingly popular because they offer better image resolution.26

Since the width of the artifact

4

depends on the strength of the magnetic field among other factors, an MRI compatible device

with a 1.5 T scanner might not be compatible with a 3T scanner.13,31,32

Elison et al 26

determined

that of the two types of steel commonly used in fixed orthodontic appliances, 18-8 stainless steel

did not cause deformation of the MRI image in vitro as opposed to type 17-4 stainless steel that

did. Although plastic and composite brackets might be compatible with MRI scanners, they have

several problems related to material performance such as bracket deformation under stress,

especially with torque expression, decreased wear resistance.33,34

These drawbacks have

prevented plastic and composite brackets from routine use in most clinical orthodontic practices.

1.3. Purpose and statement of the problem

Commonly used fixed orthodontic appliances cause image distortions of MR images of

the head and are therefore often required to be removed before the scanning is undertaken. The

effects of routine orthodontic appliances made of different types of materials on MRI artifact

formation, when used in a 3T MR scanner have not been studied in detail in a systematic manner

to elucidate the extent and severity of the artifact on the diagnostic quality of the MR images.

Consequently, there is a lack of consensus regarding the best practice protocols to be employed

for patients who need MR imaging during the period of their fixed orthodontic appliance

treatment or retention with fixed retainers.

5

1.4 Aims and Objectives

To investigate in-vivo, the influence of selected commonly used orthodontic appliances:

stainless steel brackets and molar buccal tubes, ceramic brackets, combination of ceramic

brackets and stainless steel molar buccal tubes, multistranded stainless steel lingual retainer on

the extent of artifact formation and the diagnostic quality of the MR images of the head obtained

by a 3 Tesla MR scanner using common MR image modalities.

1.5 Hypothesis

Commonly used stainless steel brackets, buccal tubes and lingual retainers cause

significant MR image distortion on 3T MR scanners to render the image nondiagnostic for MR

investigations of all the regions of the head.

6

CHAPTER 2

Materials and Methods

This clinical study assessed the influence of commonly used orthodontic appliances on

the extent of artifact formation and the diagnostic quality of the MR images of the head in a

sample of 10 adult volunteers. The study protocol, case report forms, patient consent forms and

the invitation letters were approved by the University of Toronto Research Ethics Board

(#30332, appendix 1) and the SickKids Research Ethics Board (#1000045973, appendix 2) prior

to commencing the study.

2.1 Study sample

10 healthy adult participants who were recruited from among staff and students and

patients at the Faculty of Dentistry, University of Toronto, and among staff at The Hospital for

Sick Children Toronto, through posting an invitation to participate (appendix 3) at prominent

sites in the Faculty of Dentistry, University of Toronto and in The Hospital for Sick Children:

Inclusion criteria:

Adults of both sexes who were informed about the purpose, benefits and risks of the

study and consented to participate.

Exclusion criteria:

1. Pregnant women.35

7

2. Individuals having metal objects in the body (e.g. aneurysm clips, pacemakers, fixed

orthodontic appliances, crowns and bridges, implants, amalgam restorations, traditional and

cosmetic tattoos etc).

3. Individuals who needed sedation before MRI.

4. Individuals wearing drug patches36

5. Individuals having any monitoring equipment (such as ECG leads or respiratory monitoring

leads) attached to their bodies.

2.2 Consent

An invitation letter (Appendix 3) describing the study and explaining its benefits and

risks and the compensation for participation were given to the volunteers. The informed consent

form (Appendix 4) was thoroughly reviewed with the participants. Informed consent was

obtained from each volunteer before the commencement of the study. There were 6 males and 4

females in the sample ages. Their median age was 29 years.

2.3 Appliances tested

a) Stainless steel brackets made of 17-4 and 18-8 stainless steel components brazed together with

silver alloy for all teeth erupted anterior to the first permanent molars, and bondable tubes for the

molars made of the same materials in both, maxillary and mandibular arches. (Mini Master®,

American Orthodontics, Sheboygan, WI)

8

b) Ceramic brackets for all teeth erupted anterior to the first permanent molars in both, maxillary

and mandibular arches, without any metal attachments for any teeth. (monocrystalline aluminum

oxide, Radiance®, American Orthodontics, Sheboygan, WI).

c) Ceramic brackets for all teeth erupted anterior to the first permanent molars in both, maxillary

and mandibular arches and with 18-8 stainless steel single piece bondable molar tubes for the

molars in both, maxillary and mandibular arches. (Radiance®, American Orthodontics,

Sheboygan, WI and FLI®, Rocky Mountain Orthodontics, Denver, CO).

d) Mandibular 18-8 stainless steel multistranded wire 3-3 retainer (Tri-Flex®, Rocky Mountain

Orthodontics, Denver, CO).

2.4 Procedures

The appliances listed above were placed in close contact with the subjects’ teeth, by

incorporating them into a clear 0.035’ Essix ACE® (GAC International, Bohemia, NY) retainer

in a manner similar to that used in indirect bracket bonding. This allowed the Essix® retainer to

be snapped on to the teeth for undertaking the tests in the MR scanner, obviating the need to

actually bond and debond these appliances for each subject. The Essix® material used in this

study has previously been used in MRI research26,27

and was reported not to have caused any

measurable MR image deformation in 1.5 and 0.5 Tesla MR scanners. To determine whether the

Essix® retainer causes any significant MR image deformation under the conditions of the current

study in a 3T MR scanner, a pilot test was done on one volunteer.

9

2.5 Pilot test

Maxillary and mandibular polyvinylsiloxane (Reflection®, Patterson Dental, Saint Paul,

MN) impressions (putty wash technique) were taken for one subject, and 4 sets of dental stone

models were poured from the impressions. Maxillary and mandibular Essix retainers were

fabricated on the models using Biostar® (Great Lakes Orthodontics, Tonawanda, NY) machine.

Similarly, the 4 appliances tested in the current study (listed in 2.3) were placed on the models

using indirect bonding with Transbond® (3M Unitek, Monrovia, CA). The appliances were

incorporated into the maxillary and mandibular Essix retainers that were made over them using

Biostar® machine. The retainers were checked for fit and comfort and adjusted as necessary.

Following this step, MR scans were acquired at the Hospital for Sick Children, Toronto. MR

scans were acquired for the volunteer in a 3T Siemens MAGNETOM® MRI machine (Siemens,

Erlangen, Germany) using a 12-channel head coil, with and without the Essix retainers, as well

as with 4 selected orthodontic appliances in random order, using the following sequences:

sagittal T1-weighted, axial T2–weighted, axial gradient-recalled, axial diffusion-weighted, non-

contrast axial magnetic resonance angiography (MRA), axial fluid attenuated inversion recovery

(FLAIR). The parameters of the above sequences are listed in Table 1.

10

Table 1. Parameters of the MR sequences used.

Sequence TR/TE

(msec)

Slice

thickness

(mm)

Gap

(mm)

Band

width

(Hz/Px)

Flip

angle

(degr.)

Matrix Scan

time

(min:sec)

Sagittal

T1-

weighted

1950.0/4.4 1.0 - 140 12 256x256 4:14

Axial

T2–

weighted

4500.0/83.0 3.5 - 219 120 256x256 1:54

Axial

gradient-

recalled

620.0/20.0 3.5 - 200 20 256x256 4:16

Axial

diffusion-

weighted

5000.0/93.0 4.0 - 1184 - 192x192 1:37

Axial

MRA

20.0/3.6 0.5 10 165 18 384x384 5:18

Axial

FLAIR

9000.0/88.0 3.5 - 271 120 256x256 3:56

TR-repetition time, TE-echo time, msec - milliseconds, Hz/Px-hertz/pixels, degr.-degrees, min :

sec-minutes : seconds, MRA-magnetic resonance angiography, FLAIR-fluid attenuation

inversion recovery.

The participant was screened before the scans (MRI screening form, Appendix 5), ear plugs were

provided to reduce the noise levels, and an emergency signaler was given to the participant.

After the scout scans, alignment of the images was adjusted by the MRI technician according to

the accepted neuroanatomical landmarks. Since the orthodontic appliances were securely

embedded into the Essix appliance which was firmly retained on the subject’s teeth, there were

no special precautions taken regarding possible dislodgement of the appliances. No special

precautions were taken regarding possible heating of the appliances as previous studies found

appliance temperature changes clinically insignificant, within 1 degree.37

Resultant images were

analyzed by a panel of 2 neuroradiologists who were routinely assigned to read MR scans of the

11

brain and TMJ. The diagnostic value of the scans with and without Essix retainers was

determined using a modified ROC (receiver operating characteristic) score system described by

Elison et al26

(Table 2).

Table 2. Modified ROC (receiver operating characteristic) score system used for MR image

diagnostic quality determination.

Score Image appearance Diagnostic/Nondiagnostic

1 No distortion/Artifact Diagnostic

2 Minimal distortion/Artifact Diagnostic

3 Moderate distortion/Artifact Moderately diagnostic

4 Severe distortion Nondiagnostic

5 Complete obliteration Nondiagnostic

In this particular method of distortion classification, the score of 3 represents a cut-off for

clinical usability. This means that images with the score of 3 have moderate distortion/artifact,

but still can be used for diagnosis. To develop verbal definitions of each distortions score,

images acquired were discussed between the reviewers and another neuroradiologist, the head of

Diagnostic Imaging at The Hospital for Sick Children, Toronto to establish consensus in regard

to the definitions of the scores described in Table 2.

Nine regions of the head were assessed:

a) Base of the tongue

b) Hard palate

c) Body of the mandible

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d) Nasopharynx

e) Globes of the eyes

f) Pituitary gland

g) Frontal lobe

h) Temporal lobe

i) Brain stem

For the axial diffusion-weighted and axial gradient-recalled sequences, only brain regions of

frontal lobe, temporal lobe and brain stem were assessed as these sequences are routinely used

for assessment of the brain regions and inclusion of the other anatomic regions would have

resulted in artificially increased distortion scores for these sequences. No score was assigned to

the anatomic region if it was not included in the scan.

Whether a statistically significant difference existed in the diagnostic score of the scans with and

without Essix retainers was determined by using non-parametric Wilcoxon signed rank test.

2.6 Main study

Following the pilot test, maxillary and mandibular polyvinylsiloxane impressions were

taken for all the participants. 3 sets of dental stone models were poured from the impressions and

trimmed. Separating agent was applied on all the models. For each subject, the 4 appliances

listed in section 2.3 were placed on the models using indirect bonding with Transbond® (3M

Unitek, Monrovia, CA). One set of models was used to fabricate Essix trays with ceramic

brackets and separate Essix trays for the metal molar buccal tubes. This allowed using the same

trays with ceramic brackets as a separate appliance and in combination with metal buccal tubes.

13

The appliances were incorporated into the maxillary and mandibular Essix® retainers using

Biostar® machine. The retainers were checked for fit and comfort and adjusted if necessary. Fig.

1 demonstrates the appliances tested.

Fig.1. Appliances tested: a) Stainless steel brackets and buccal tubes; b) Ceramic brackets; c)

Ceramic brackets and stainless steel molar buccal tubes; d) Stainless steel mandibular lingual

retainer

a) b)

c) d)

14

Note: Only maxillary arch appliances are shown here for steel brackets and bucal tubes, ceramic

brackets, and the combination of ceramic brackets and steel molar buccal tubes. In the tests,

similar appliances were made for the maxillary and mandibular arches as shown in Fig.2.

Fig.2. Complete sets of maxillary and mandibular appliances: a) Stainless steel brackets and

buccal tubes; b) Ceramic brackets; c) Ceramic brackets and stainless steel molar buccal tubes;

a) b)

c)

15

MR scans were taken for the participants with a 3T MRI scanner using a head coil with

the appliances listed in 2.3 embedded into Essix trays, in random order using the following

sequences: sagittal T1-weighted, axial T2 –weighted, axial gradient-recalled (GRE), axial

diffusion-weighted (DWI), non-contrast axial magnetic resonance angiography (MRA), and axial

fluid attenuated inversion recovery (FLAIR).The parameters of the above sequences were the

same as in the pilot test. The total time each participant spent in the MR department of the

Hospital was around 2 hours. Resultant images were analyzed by the same 2 neuroradiologists

described in the pilot study, who were routinely assigned to read MR scans of the brain and TMJ.

The images of the subjects were reviewed randomly and not in sequence form 2 to 10.The nine

regions of the head described in the pilot study were assessed using the diagnostic score system

described earlier. For the diffusion-weighted and gradient-recalled sequences, only brain regions

of frontal lobe, temporal lobe and brain stem were assessed as these sequences are routinely used

for assessment of the brain regions and inclusion of the other anatomic regions would have

resulted in artificially increased distortion scores for these sequences. No score was assigned to

the anatomic region if it was not included in the scan. The data from the pilot test were included

in the final analysis of data from a total of 10 subjects (Case report form, Appendix 6). Figure 3

represents a flowchart of image acquisition.

16

Fig. 3 Flowchart of image acquisition (for 1 subject).

For intrarater reliability assessment, each radiologist was asked to re-evaluate 3 randomly

selected subjects.26

Reviewer 1 re-assessed subjects 9, 3, and 4. Reviewer 2 re-evaluated subjects

6, 2 and 9. The assignment of cases for re-evaluation was based on the computer-generated

random number allocation.

17

2.7 Statistical analysis

Statistical analysis was performed using SPSS 21 (SPSS , Chicago, Ill):The following tests were

used:

1. Kappa statistics for agreement within and between the raters. The diagnostic scores were

grouped: 1-3 were reassigned as 1 (diagnostic scan), 4-5 were assigned 2 (nondiagnostic

scan).26

2. Wilcoxon signed rank test for the differences between materials, anatomic sites, imaging

sequences with regard to the image distortion scale rating. This non-parametric test was

used because of the non-normal distribution of the distortion scores as was determined by

Shapiro-Wilk test.

A p value of less than 0.05 was chosen to indicate statistical significance.

18

CHAPTER 3

Results

3.1 Pilot test: assessment of MR image distortion produced by the Essix® tray

material

In the pilot test, mean diagnostic score for Essix® appliance was 1.89±1.382 (all

appliances, sequences and reviewers were included, 76 images were analyzed). Mean diagnostic

score for no appliance was 1.89±1.362 (all appliances, sequences and reviewers were included,

76 images were analyzed). There were no statistically significant differences between the

distortion scores for Essix® and no appliance (p=1.00, Wilcoxon Signed Rank test). Mean

diagnostic score for ceramic brackets was 1.82±1.382 (all appliances, sequences and reviewers

were included, 78 images were analyzed). There were no statistically significant differences

between the distortion scores for ceramic brackets and no appliance (p=1.00, Wilcoxon Signed

Rank test). Therefore, scans with no appliances were not performed for the subsequent subjects

to decrease the burden on the participants and redundant use of highly specialized equipment and

resources, and scores for ceramic brackets could arguably serve as a gold standard for

comparisons between different appliances.

Main study.

Examples of representative sagittal and axial images for scores 1 to 5 are given in Appendix 8

(frontal lobe of the brain was scored).

3.2 Comparison of the distortion scores between different subjects

Mean distortion scores of different appliances for each subject, overall mean distortion scores for

each appliance and pairwise comparisons with ceramic brackets are given in Table 3.

19

Table 3. Mean distortion scores with standard deviations (in parentheses) by the appliance type for each

subject, overall mean distortion scores for each appliance and pairwise comparisons with scores of

ceramic brackets (included all sequences, anatomic regions and reviewers).

Subject Stainless steel Ceramic Ceramic+Stainless steel Lingual Retainer

1

N for each appliance=66

Mean (SD)

2.61 (1.68)

Mean (SD)

1.39 (0.78)

Mean (SD)

2.09 (1.37)

Mean (SD)

1.67 (0.9)

2


2.89 (1.59) 1.59 (0.88) 2.18 (1.4) 1.85 (1.07)

3


2.68 (1.6) 1.7 (0.79) 2.32 (1.43) 1.74 (0.98)

4


2.97 (1.53) 1.89 (0.93) 2.52 (1.43) 1.86 (0.99)

5


2.65 (1.53) 1.67 (0.85) 2.29 (1.29) 1.82 (0.89)

6


2.73 (1.62) 1.58 (0.88) 2.38 (1.38) 1.91 (0.94)

7


2.8 (1.34) 1.59 (0.78) 2.34 (1.2) 2.08 (0.9)

8


2.88 (1.53) 1.6 (0.82) 2.42 (1.5) 1.92 (0.92)

9


2.94 (1.64) 2.12 (0.9) 2.35 (1.34) 2.03 (1.13)

10


3.17 (1.38) 2.3 (1.19) 2.71 (1.23) 1.94 (1.16)

Mean scores 2.83 (1.55) 1.74 (0.93) 2.36 (1.36) 1.88 (0.99)

Ceramic vs. other material (Z)*

-18.116 - -14.638 -6.763

P value*

<0.0001 - <0.0001 <0.0001

*Wilcoxon Signed Rank test. SD-standard deviation, N-number of images

20

There were statistically significant differences between the distortion scores for stainless

steel brackets and molar tubes, combination of ceramic brackets and stainless steel molar tubes,

and lingual retainer when compared to the distortion scores for ceramic brackets.

Fig 4 demonstrates a composite view of the mean distortion scores for different

appliances according to the subject. It can be noted that mean distortion scores for subject 10

were higher than for the rest of the subjects

Fig 4. Mean distortion scores by the appliance type for each subject.

21

Figures 5-8 (box plots) demonstrate diagnostic scores variability and the differences between the

diagnostic scores for each of the 10 subjects for a specific appliance. For all the following box

plots in the Results section, the bottom and top of each box represent the first and third quartiles

respectively. Middle band represents the median. Whiskers represent data within 1.5 times the

interquartile range. Dots represent data exceeding 1.5 times the interquartile range (outliers).

Stars represent data exceeding 3 times the interquartile range (extreme values).

Fig.5

22

For stainless steel brackets and tubes, almost all mean diagnostic scores were close to

nondiagnostic range between 2.5 and 3.0. Only for subject 10, the mean distortion score was

above 3.0 (3.17). Scores for all subjects showed high variability with the minimum of 1 and

maximum of 5.

Fig.6

For ceramic brackets, most of the mean scores were in the diagnostic range between 1.5 and 2.

Mean scores for subjects 9 and 10 were 2.12 and 2.3 respectively. Notably, scores for subjects 4,

9 and 10 were higher than for the rest of the subjects with greater variability and maximum

23

scores above 3.0. Scores for almost all the subjects included several outliers above 3.0. Scores

for subject 1 showed little variability and were uniformly 1 with the exception of 2 outliers.

Fig.7

Mean diagnostic scores for the combination of ceramic brackets and stainless steel buccal tubes

were almost uniformly between 2 and 2.5 with the mean score for subject 10 notably higher,

2.71. The scores variability was high for all subjects, with minimum of 1 and maximum of 5.

24

Fig.8

For the stainless steel mandibular lingual retainer, mean diagnostic scores for most subjects

showed fairly uniform distribution with median of 2 and interquartile range of 1 to 3.Subjects 1-3

had median scores of 1. All subjects with the exception of subjects 2 and 5 had upper quartile

scores bordering the non-diagnostic range.

25

3.3 Comparison of the distortion scores between different anatomic regions

Table 4. Mean distortion scores with standard deviations (in parentheses) for different appliances

according to the anatomic regions (all subjects, MR sequences, reviewers were included).

Anatomic region Stainless steel Ceramic Ceramic + Stainless

steel

Lingual Retainer

Base of the tongue

N for each

appliance=19

Mean (SD)

4.84 (0.38)

Mean (SD)

2.20 (0.89)

Mean (SD)

4.26 (0.45)

Mean (SD)

3.00 (0.69)

Body of the mandible

N for each

appliance=20

4.90 (0.31) 2.24 (0.89) 4.74 (0.45) 2.90 (0.72)

Hard palate

N for each

appliance=20

5.00 2.50 (0.83) 4.21 (0.54) 3.85 (0.81)

Nasopharynx

N for each

appliance=80

2.04 (1.05) 1.41 (0.63) 1.84 (0.93) 1.56 (0.63)

Globes of the eyes

N for each

appliance=80

3.35 (1.31) 1.85 (0.84) 2.36 (1.15) 1.99 (0.84)

Pituitary gland

N for each

appliance=80

1.96 (0.85) 1.39 (0.65) 1.66 (0.69) 1.47 (0.65)

Frontal lobe

N for each

appliance=120

2.91 (1.50) 1.78 (0.95) 2.25 (1.27) 1.87 (0.93)

Temporal lobe

N for each

appliance=120

2.83 (1.51) 1.93 (1.14) 2.46 (1.41) 1.93 (1.08)

Brain stem

N for each

appliance=120

2.49 (1.71) 1.61 (0.91) 2.21 (1.46) 1.60 (0.85)

SD-standard deviation, N-number of images

26

Fig. 9 Mean diagnostic scores for different appliances for each anatomic region.

It can be noted that there is a general trend for the regions farther from the teeth and orthodontic

appliances to have lower diagnostic scores although it is also apparent that images for certain

tissues are more significantly affected then others despite their relatively greater distance from

the appliances compared to other regions.

Figures 10-13 (box plots) demonstrate the distortion scores for each appliance according to

anatomic region.

27

Fig.10

For stainless steel brackets and tubes, scores for intraoral regions of base of the tongue, hard

palate and body of the mandible were uniformly 5 (complete image obliteration) with the

exception of several outliers. Mean distortion scores for nasopharynx, pituitary gland and brain

stem were in the diagnostic range. Frontal lobe and temporal lobe received mean scores close to

the non-diagnostic range. Globes of the eyes had the mean score above 3. Variability of the

scores for nasopharynx, temporal lobe, frontal lobe, and brain stem was high with the lower

quartile being below 3 and upper quartile above 3.

28

Fig.11

Mean diagnostic scores for ceramic brackets for all anatomic regions were in the diagnostic

range. Scores for intraoral regions of base of the tongue, body of the mandible, hard palate, as

well as for frontal and temporal lobes showed high variability with the upper quartile bordering

the non-diagnostic range.

29

Fig. 12

For the combination of ceramic brackets and 18-8 stainless steel buccal tubes, intraoral regions

of the base of the tongue, body of the mandible, and hard palate received high scores between 4

and 5, in the non-diagnostic range. The other regions received mean scores below 3 (the cut off

for diagnostic image). Scores for nasopharynx, globes of the eyes, frontal and temporal lobes had

high variability with the median scores of 2 and the maximum scores being in the non-diagnostic

range. Frontal, temporal lobes and brain stem had an interquartile range from 1 to 4.

30

Fig. 13

For lingual retainer, mean scores for intraoral regions of base of the tongue and body of the

mandible were close to 3. Hard palate received scores in the non-diagnostic range. For the rest of

the regions, the mean scores were below 3 with the scores for globes of the eyes, frontal lobe,

and temporal lobe showing high variability with the upper quartile bordering the non-diagnostic

range.

31

3.4 Comparison of the distortion scores between different MR sequences

For axial gradient-recall and axial diffusion-weighted sequences, only the brain regions

of frontal lobe, temporal lobe and brain stem were assessed because these sequences are

routinely used for assessment of the brain regions and inclusion of the other anatomic regions

would have resulted in artificially increased distortion scores for these sequences.

Table 5 and Fig.14 illustrate mean diagnostic scores for different appliances according to the

imaging sequence.

Table 5. Mean distortion scores with standard deviations (in parentheses) for different appliances

according to the imaging sequence (all subjects, anatomic regions, and reviewers were included).

MR sequence Metal Ceramic Ceramic + Metal Lingual Retainer

Sagittal T1


3.66 (1.23) 1.82 (0.85) 3.10 (1.22) 2.30 (1.03)

Axial T2


2.08 (1.00) 1.40 (0.64) 1.63 (0.77) 1.44 (0.65)

Axial GRE


4.68 (0.47) 3.10 (0.68) 4.05 (0.50) 3.03 (0.49)

Axial DWI


4.83 (0.38) 2.93 (0.52) 4.08 (0.66) 3.02 (0.50)

Axial MRA


1.33 (0.55) 1.18 (0.51) 1.25 (0.49) 1.15 (0.42)

Axial FLAIR


1.93 (1.00) 1.26 (0.59) 1.40 (0.63) 1.28 (0.57)

N-number of images, SD-standard deviation, GRE-gradient recalled, DWI-diffusion-weighted,

MRA-magnetic resonance angiography, FLAIR-fluid attenuation inversion recovery

32

Fig.14.Mean diagnostic scores of different appliances for each sequence.

Figures 15-18 (box plots) demonstrate diagnostic scores and their variability for different

appliances according to the MR sequence.

33

Fig.15

For stainless steel brackets and tubes, mean diagnostic scores for sagittal T1, axial diffusion-

weighted, axial gradient-recalled sequences were above 3 (non-diagnostic). Scores for T1

sequence showed significant variability with interquartile range of 3 to 5. Mean scores for the

34

axial T2, axial FLAIR and axial MRA sequences were in the diagnostic range with the upper

quartile for T2 and FLAIR sequences bordering the non-diagnostic range.

Fig.16

35

For ceramic brackets, scores for the axial diffusion-weighted and axial gradient-recalled

sequences were uniformly 3 with the exception of several outliers. For the rest of the sequences,

the scores were in the diagnostic range.

Fig.17

36

For the combination appliance, the scores for axial diffusion-weighted (DWI) and axial gradient-

recalled (GRE) sequences were in the non-diagnostic range. For sagittal T1 sequence, the

diagnostic scores were symmetrically distributed with the median of 3 and interquartile range

from 2 to 4. The scores for axial T2, axial MRA and axial FLAIR sequences were below 3

(diagnostic).

Fig. 18

37

For lingual retainer, scores for axial DWI and axial GRE sequences were uniformly 3 with the

exception of several outliers. For sagittal T1 sequence, the scores showed variability with

interquartile range from 2 to 3 and median of 2. For the rest of the sequences, the scores were in

the diagnostic range with scores for MRA and FLAIR sequences uniformly 1, with the exception

of several outliers.

3.5 Comparison of the distortion scores of different orthodontic appliances

Table 6 and Fig.19 demonstrate mean diagnostic scores for different anatomic regions according

to the imaging sequence for stainless steel brackets and tubes.

38

Table 6. Mean diagnostic scores with standard deviations (in parentheses) for different anatomic regions

according to the MR sequence for the appliance type: stainless steel brackets and buccal tubes (included

all subjects and reviewers).

Anatomic region Sag.T1 Axial T2 Axial

GRE

Axial

DWI

Axial

MRA

Axial

FLAIR

Base of the tongue

N=19

4.84

(0.38)

- - - - -


N=20

4.90

(0.31)

- - - - -

Hard palate

N=20

5.00 - - - - -

Nasopharynx

N for each

sequence=20

3.30

(0.57)

1.75

(0.79)

- - 1.35 (0.59) 1.75 (0.97)

Globes of the eyes

N for each

sequence=20

4.65

(0.49)

3.80

(0.52)

- - 1.45 (0.69) 3.50 (0.61)

Pituitary gland

N for each

sequence=20

2.70

(0.93)

1.95

(0.51)

- - 1.45 (0.69) 1.75 (0.72)

Frontal lobe

N for each

sequence=20

3.00

(0.32)

2.10

(0.45)

4.75

(0.44)

4.75

(0.44)

1.15 (0.37) 1.7 (0.73)

Temporal lobe

N for each

sequence=20

2.70

(0.57)

1.80

(0.62)

4.60

(0.50)

4.90

(0.31)

1.35 (0.49) 1.65 (0.59)

Brain stem

N for each

sequence=20

1.95

(0.67)

1.05

(0.22)

4.70

(0.47)

4.85

(0.37)

1.20 (0.41) 1.20 (0.41)



39

Fig.19 Mean diagnostic scores for different anatomic regions according to the MR sequence for

the appliance type: stainless steel brackets and buccal tubes.

Distribution and variability of the scores for stainless steel brackets and tubes for each sequence

according to the anatomic region are shown in the box plots below (figures 20-25).

40

Fig. 20

For stainless steel brackets and tubes in T1 sequence, diagnostic scores for intraoral regions were

almost uniformly 5 with the exception of several outliers. Mean diagnostic scores for the rest of

the regions were in or close to non-diagnostic range with one notable exception: brain stem

(1.96). Scores for pituitary gland showed greatest variability of 1 to 4 with a median of 3 and

interquartile range from 2 to 3.

41

Fig. 21

For T2 sequence, only globes of the eyes had a mean score above 3, the rest of the regions

received scores in the diagnostic range. Scores for nasopharynx and temporal lobe showed

significant variability with a range from 1 to 3.

42

Fig. 22

43

Fig. 23

For axial gradient-recalled and axial diffusion-weighted sequences, the scores for stainless steel

brackets and tubes were uniformly above 3, between 4 and 5.

44

Fig. 24

For MRA sequence, stainless steel brackets and tubes received low scores with a median of 1 for

all regions. Scores for nasopharynx, globes of the eyes, and pituitary gland showed significant

variability, and the ranged from 1 to 3.

45

Fig.25

For axial FLAIR sequence, stainless steel brackets and tubes received scores in the diagnostic

range with the exception of globes of the eyes (mean score 3.5). Scores for nasopharynx showed

significant variability, with a range from 1 to 4, median of 1 and interquartile range from 1 to

2.5.

Table 7 and Fig. 26 demonstrate mean diagnostic scores for ceramic brackets for different

sequences and regions.

46

Table 7. Mean diagnostic scores with standard deviations (in parentheses) for different anatomic

regions according to the MR sequence for the appliance type: ceramic brackets (included all

subjects and reviewers).

Anatomic region Sag.T1 Axial T2 Axial GRE Axial DWI Axial MRA Axial FLAIR

Base of the tongue

N=20

2.20 (0.89) - - - - -


N=20

2.30 (0.86) 1 - - - -

Hard palate

N=20

2.50 (0.83) - - - - -

Nasopharynx

N for each sequence=20

1.80 (0.83) 1.35 (0.59) - - 1.15 (0.37) 1.35 (0.49)

Globes of the eyes


1.95 (0.83) 2.35 (0.59) - - 1.25 (0.55) 1.85 (0.99)

Pituitary gland


1.65 (0.67) 1.4 (0.60) - - 1.20 (0.7) 1.30 (0.57)

Frontal lobe


1.40 (0.68) 1.20 (0.41) 3.05 (0.39) 2.90 (0.31) 1.10 (0.31) 1.05 (0.22)

Temporal lobe


1.50 (0.61) 1.15 (0.37) 3.45 (0.69) 3.20 (0.52) 1.30 (0.73) 1.00

Brain stem


1.10 (0.31) 1.00 2.80 (0.79) 2.70 (0.57) 1.05 (0.22) 1.00


MRA-magnetic resonance angiography, FLAIR-fluid attenuation inversion recovery.

47

Fig 26 Mean diagnostic scores for different anatomic regions according to the MR sequence for

the appliance type: ceramic brackets.

For the axial T2-weighted sequence, hard palate was not included in the scan.

Distribution and variability of the scores for ceramic brackets for each sequence according to the

anatomic region can be seen in box plots in figures 27-32.

48

Fig. 27

For sagittal T1 sequence, ceramic brackets received mean diagnostic scores below 3 for all

regions. However, the scores for intraoral regions of base of the tongue, body of the mandible,

and hard palate had a large variability from 1 to 4 with the upper quartile bordering 3.

49

Fig.28

For axial T2 sequence, diagnostic scores for most of the regions were in the diagnostic range,

and were clustered around 1. The highest scores were received by globes of the eyes with median

of 2 and intrequartile range of 2 to 3. Scores for nasopharynx and pituitary gland showed

significant variability and ranged from 1 to 3.

50

Fig. 29

For axial gradient-recalled sequence, ceramic brackets received scores of 3 for frontal lobe with

the exception of 3 outliers. Temporal lobe scans received a median score of 3.0 with a range of 2

to 5 and interquartile range of 3 to 4. Brain stem scans had scores with a median of 3 and

interquartile range of 2 to 3.

51

Fig. 30

For axial diffusion-weighted sequence, ceramic brackets received diagnostic scores of 3 for

frontal lobe. Temporal lobe received a median score of 3 with a range from 3 to 4. Scores for

brain stem had significant variability with a median of 3, range from 2 to 4, and interquartile

range from 2 to 3.

52

Fig.31

Scores for axial MRA sequence for ceramic brackets were uniformly 1 for all regions with the

exception of several outliers.

53

Fig.32

For axial FLAIR sequence, ceramic brackets received scores in the diagnostic range for all

regions. Median scores were 1, scores for globes of eyes showed significant variability with the

range of 1 to 3.

Mean diagnostic scores with standard deviations (in brackets) for combination of ceramic

brackets and steel molar buccal tubes for all the regions and sequences are given in Table 8 and

illustrated in Fig.33.

54

Table 8. Mean diagnostic scores with standard deviations for different anatomic regions

according to the MR sequence for the appliance type: ceramic brackets and stainless steel molar

buccal tubes (included all subjects and reviewers).


Base of the tongue

N =20

4.26 (0.45) - - - - -


N =20

4.74 (0.45) - - - - -

Hard palate

N =20

4.21 (0.54) - - - - -

Nasopharynx

N for each sequence =20

3.10 (0.45) 1.50 (0.69) 1.30 (0.57) 1.45 (0.61)

Globes of the eyes


3.60 (0.75) 2.65 (0.81) 1.25 (0.44) 1.95 (0.94)

Pituitary gland


2.20 (0.7) 1.70 (0.57) 1.35 (0.67) 1.40 (0.50)

Frontal lobe


2.00 (0.65) 1.45 (0.61) 4.10 (0.31) 3.60 (0.5) 1.10 (0.31) 1.25 (0.44)

Temporal lobe


2.25 (0.72) 1.40 (0.5) 4.15 (0.49) 4.30 (0.66) 1.40 (0.5) 1.25 (0.44)

Brain stem


1.70 (0.66) 1.10 (031) 3.90 (0.64) 4.35 (0.49) 1.10 (0.31) 1.10 (0.31)



55

Fig 33. Mean diagnostic scores for different anatomic regions according to the MR sequence for

the appliance type: ceramic brackets and stainless steel buccal tubes (combination appliance).

Distribution and variability of the scores for ceramic brackets and stainless steel buccal tubes for

each sequence according to the anatomic region is illustrated in box plots in figures 34-39.

56

Fig.34

For sagittal T1 sequence, the combination of ceramic brackets and stainless steel molar buccal

tubes received scores in the diagnostic range for brain regions. For temporal lobe, 25% of the

scores were in the non-diagnostic range The rest of the regions had scores in the non-diagnostic

range

57

Fig. 35

For axial T2 sequence, the combination appliance received scores below 3 for brain regions and

nasopharynx. The mean score for the globes of the eyes was 2.65. The scores for the globes

showed significant variability with the range for 2 to 4 and interquartile range from 2 to 3.

58

Fig.36

59

Fig. 37

For axial gradient-recalled and axial diffusion-weighted sequences, the combination of ceramic

brackets and stainless steel buccal tubes received scores above, 3 in the non-diagnostic range.

60

Fig 38

The combination appliance received diagnostic scores for axial MRA sequence for all the

regions with medians of 1 and scores generally ranging from 1 to 2 with a few outliers.

61

Fig 39

For FLAIR sequence, ceramic brackets+stainless steel buccal molar tubes received scores in the

diagnostic range for all regions. Scores for nasopharynx and globes of the eyes showed the

greatest variability with a range from 1 to 3 and medians of 1 and 2, respectively.

62

Table 9 and Fig.40 show mean diagnostic scores for lingual retainer for all anatomic regions and

sequences.

Table 9. Mean diagnostic scores with standard deviations for different anatomic regions

according to the MR sequence for the appliance type: lingual retainer (included all subjects and

reviewers).


Base of the tongue

N=20

3.00 (0.69) - - - - -


N=20

2.90 (0.72) - - - - -

Hard palate

N=20

3.85 (0.81) - - - - -

Nasopharynx


2.35 (0.81) 1.40 (0.5) - - 1.15 (0.37) 1.35 (0.49)

Globes of the eyes


2.35 (0.67) 2.47 (0.61) - - 1.30 (0.57) 1.85 (0.93)

Pituitary gland


1.85 (0.67) 1.45 (0.51) - - 1.10 (0.45) 1.35 (0.49)

Frontal lobe


1.60 (0.60) 1.30 (0.47) 3.05 (0.22) 3.05 (0.22) 1.10 (0.31) 1.10 (0.31)

Temporal lobe


1.75 (0.75) 1.05 (0.22) 3.35 (0.49) 3.25 (0.44) 1.15 (0.49) 1.05 (0.22)

Brain stem


1.10 (0.31) 1.00 2.70 (0.47) 2.70 (0.57) 1.10 (0.31) 1.00



63

Fig 40. Mean diagnostic scores for different anatomic regions according to the MR sequence for

the appliance type: lingual retainer.

Distribution and variability of the scores for lingual retainer for each sequence according to the

anatomic region are illustrated in figures 41-46.

64

Fig.41

For sagittal T1 sequence, mean scores for intraoral regions were above 3 (non-diagnostic). The

rest of the anatomic regions received mean scores in the diagnostic range. The scores for

nasopharynx and globes of the eyes showed significant variability with medians of 2, range from

1 to 4 and interquartile range from 2 to 3.

65

Fig.42

For mandibular stainless steel lingual retainer, the mean scores for T2 sequence were in the

diagnostic range for all anatomic regions. For globes of the eyes, the median score was 2, range

was from 2 to 4, and interquartile range was from 2 to 3.

66

Fig.43

67

Fig.44

For axial gradient-recalled and axial diffusion-weighted sequences, lingual retainer received

scores of 3 for frontal lobe with little variability. Scores for temporal lobe had median of 3, range

from 3 to 4. Brain stem received the scores with median of 3, and the interquartile range from 2

to 3.

68

Fig.45

For the lingual retainer, the scores for MRA sequence were in the diagnostic range in all

anatomic regions with median scores of 1. Only scores for globes of the eyes showed significant

variability. The interquartile range was between 1 and 2.

69

Fig.46

All anatomic regions for FLAIR sequence received scores below 3. The scores for globes of the

eyes showed greatest variability with median of 1.5 and range from 1 to 3.

70

In the pilot test, there were no statistically significant differences between the distortion

scores of ceramic brackets and no appliance. Therefore, scores of ceramic brackets could

arguably serve as a gold standard to compare other appliances to. Distortion scores for ceramic

brackets for axial T1, axial T2, axial MRA and axial FLAIR sequences were in the diagnostic

range. For these sequences, a diagnostic score cut off of 3 was used to determine the diagnostic

usability of the MR images for steel brackets and tubes, the combination appliance, and lingual

retainer. For GRE and DWI sequences, diagnostic scores for ceramic brackets were close to, or

slightly above 3. For GRE and DWI sequences, the diagnostic scores for stainless steel brackets

and tubes and the combination appliance were much higher than those of ceramic brackets

(between 4 and 5). Only for lingual retainer, the diagnostic scores for GRE and DWI sequences

were close to, or slightly above 3, similar to the scores of ceramic brackets. Mean diagnostic

scores for lingual retainer for axial GRE and axial DWI sequences were 3.03±0.49 and

3.00±0.49, respectively (60 images were analyzed, all regions and reviewers were included).

Mean diagnostic scores for ceramic brackets for axial GRE and axial DWI sequences were

3.10±0.68 and 2.93±0.52, respectively (60 images were analyzed, all regions and reviewers were

included). To determine whether there were statistically significant differences between the

diagnostic scores for ceramic brackets and lingual retainer for GRE and DWI sequences,

Wilcoxon signed ranks tests were performed. There were no statistically significant differences

in the diagnostic scores between lingual retainer and ceramic brackets for axial gradient-recalled

sequence (p=0.822) and for axial diffusion-weighted sequence (p=0.204).

For axial diffusion-weighted and axial gradient recalled sequences, the distortion scores

were in close or slightly above 3 even with no appliances. The scores for non-contrast axial

magnetic resonance angiography (MRA), axial fluid attenuated inversion recovery (FLAIR), and

71

axial T2-weighted sequences were found to be below 3 (diagnostic) in all the appliances and

regions with the exception of globes of the eyes for metal brackets and tubes in T2 and FLAIR

sequences. Stainless steel brackets and buccal tubes rendered images nondiagnostic in 3 Tesla

cranial MRI for sagittal T1-weighted, axial gradient-recalled, and axial diffusion-weighted

sequences. Ceramic brackets showed minimal MR image distortion in all anatomic regions. The

combination of ceramic brackets and metal buccal tubes caused image distortions with the scores

above 3.0 for axial gradient-recalled and axial diffusion-weighted sequences. For sagittal T1

scan, the combined appliance received nondiagnostic scores in oral, pharyngeal regions of the

head and globes of the eyes. Brain regions had diagnostic scores. Multistranded stainless steel

mandibular lingual retainer received scores above 3.0 for axial gradient-recalled and axial

diffusion-weighted sequence. However, there were no statistically significant differences

between the scores of lingual retainer and the control appliance (ceramic brackets). For sagittal

T1-weighted sequence, the scores were in the nondiagnostic range for oral and pharyngeal

regions of the cranial MRI. Brain regions remained diagnostic.

3.6 Calculation of intra and interrater agreements

Interrater agreement was calculated using unweighted Kappa statistics. The scores were

categorized into two groups. Group 1 included scores of 1-3 (diagnostic scans), group 2 included

scores above 3 (non-diagnostic).26

Because the diagnostic score definitions were developed

based on the raters’ collective discussion of the images of subject 1, kappa was calculated for the

images of subjects 2-10 excluding subject 1 to avoid artificially increased value for the interrater

72

agreement. A total of 1181 scores per each reviewer were used to calculate the interrater

agreement.

Interrater kappa was 0.761, 95% CI=0.712-0.81 (p<0.0001) (substantial agreement,

Landis and Koch interpretation).

Inrarater agreement was calculated for each reviewer after they independently re-scored 3

randomly selected subjects26

(Table 10). Reviewer 1 re-scored images for subjects 3, 4, and 9;

reviewer 2 re-scored images for subjects 6, 2, and 9. Inrarater agreement calculation for reviewer

1 was based on 398 repeated scores; intrarater agreement calculation for reviewer 2 was based on

394 repeated scores.

Table 10. Intrarater agreements for reviewers 1 and 2.

Kappa SE p Lower

CI

Upper CI

Reviewer 1 0.559 0.051 <0.0001 0.459 0.659

Reviewer 2 0.667 0.048 <0.0001 0.573 0.761

SE-standard error, CI-confidence interval.

Intrarater agreement was moderate for reviewer 1 and substantial for reviewer 2.

73

CHAPTER 4

Discussion

MRI is a diagnostic modality increasingly used for a vast variety of medical conditions.

Among them, there are tumors, epilepsy, cardiovascular abnormalities, headaches, TMJ

pathology, multiple sclerosis etc. Management of these conditions often requires multiple

periodic MR examinations. With the ever increasing utilization of MRI and orthodontic

treatment, especially by adults, and ubiquitous use of fixed retainers after orthodontic treatment,

it seems very likely that every orthodontic provider will sooner or later face the problem of fixed

orthodontic appliances potentially interfering with MR examination in their orthodontic patients.

Therefore, it is important to have clear best practice protocols for patients who need MR imaging

during the period of their fixed orthodontic appliances treatment or retention with fixed retainers.

Currently, there is a lack of consensus regarding best practices for imaging patients with fixed

orthodontic appliances in MR scanners. The issue of artifacts produced by dental materials on

MR images of the head have been addressed in a number of studies. Sadowsky et al. (1988)9

investigated in-vitro and in-vivo the influence of stainless steel orthodontic appliances on cranial

MR images produced by a 0.5 Tesla MR scanner and came to the conclusion that only archwires

should be removed before cranial MRI; brackets and bands can be left in place. On the other

hand, Lissac et al. (1992)38

found that dental appliances made of non-precious metals caused

significant disturbances in the cranial MR images produced by a 0.5 Tesla scanner and need to

be removed before the scan. These findings were confirmed by the studies of Masumi et al.

(1993)39

using 0.1 Tesla MR scanner, and Elison et al. (2008)26

using 1.5 Tesla MR scanner.

Artifact intensity is directly proportional to the strength of magnetic field.13,40

Additional

difficulty in summarizing the available data comes from the fact that unambiguous classification

74

of dental material MR compatibility based on material properties only without specification of

MRI parameters and the device geometry is impossible.13

4.1 Scientific novelty of the study.

To our knowledge, this study is the first systematic investigation to analyze the effects of

orthodontic appliances on cranial MR scans made with a 3 Tesla magnet. 3 Tesla MR scanners

are becoming a standard of care in the field of clinical MRI because they offer better image

resolution.13

Since the intensity of the artifact is directly proportional to the strength of the

magnetic field , an MRI compatible device with a 0.5 or 1.5 Tesla scanner might potentially

render image non-diagnostic in a 3Tesla scanner.13,31,32

In addition, the study looked into artifact formation caused by molar tubes made of

austenitic non-magnetic 18-8 stainless steel in addition to orthodontic brackets and tubes made of

magnetic 17-4 stainless steel brazed to 18-8 stainless steel bases. Elisson et al 26

found that of the

two types of steel commonly used in fabrication of fixed orthodontic appliances, 18-8 stainless

steel did not cause deformation of the MR image in vitro on a phantom grid as opposed to the

17-4 type stainless steel that did. They predicted that orthodontic appliances made entirely of 18-

8 steel would not compromise the quality of cranial MR scans. However, in the current study,

buccal tubes which were made of only austenitic 18-8 stainless steel as a single piece via metal

injection molding did cause significant distortion of cranial MR scans. It can possibly be

explained by several factors. Firstly, it is possible that buccal tubes made of austenitic 18-8 steel

could undergo stress-induced martensitic transformation caused by cold working or slow

cooling.41

This can increase magnetic susceptibility of the attachment and thus, artifact

75

formation. Secondly, apart from the material magnetic susceptibility, artifact size is also

dependent on the material electric conductivity.13

Therefore, even non-magnetic metallic objects

can create sizable artifacts in MR images.

Next, MR artifacts caused by one of the most common types of fixed lingual retainers

were studied systematically in vivo for the first time to the best of our knowledge. Fixed lingual

wires, especially in the mandibular arch, are now a universally-accepted means of long-term

retention after orthodontic treatment, and can remain attached to the teeth for many years, after

treatment completion. With the ever-increasing utilization of orthodontic treatment and MRI,

fixed lingual retainers are likely to be the most frequent problem encountered in MR imaging of

patients with orthodontic appliances. Shalish et al. (2015)40

investigated artifacts produced by

two common types of lingual retainer wires in the MR images of a dry skull immersed in a

gadolinium contrast agent. The images were acquired by 1.5 Tesla and 3 Tesla MR scanners. The

investigators found that stainless steel lingual retainers did not have to be removed before the

MR scans unless the region of interest was near the retainer. However, dry skull does not allow

for a representation of soft tissues of the face and brain tissues for which MRI is most commonly

used. Results of the current study support those of Shalish et al. (2015). It was found that

mandibular stainless steel lingual retainer did not cause significant distortion of the cranial MR

images with the exception of the intraoral regions in the close proximity to the retainer.

Finally, a systematic investigation of the two frequently used MR sequences (FLAIR and

MRA) with fixed orthodontic appliances was undertaken for the first time, to the best of our

knowledge. Fluid-attenuation inversion recovery (FLAIR) is a special sequence with long T1 to

remove the effects of fluid from the resultant images. This sequence is particularly useful in the

detection of subtle changes at the periphery of the hemispheres and in the periventricular region

76

close to CSF. The usefulness of FLAIR sequences has been established in diseases of the central

nervous system such as infarction, multiple sclerosis, subarachnoid haemorrhage, head injuries

etc.42

Non-contrast axial magnetic resonance angiography also known as time of flight

angiography (TOF) is an MRI technique to visualize flow within vessels, without the need to

administer contrast.43

It is useful in diagnosis of vascular stenosis, occlusions, most often in

atherosclerosis, as well as aneurysms and other vascular abnormalities. The current study

suggests that none of the appliances we tested produced significant artifacts on brain MR images

using axial FLAIR and axial MRA sequences. Therefore, none of the appliances, including

stainless steel brackets and molar tubes, may need to be removed before the brain MR scans

using these sequences.

4.2. Explanation of findings

There was individual variability in the distortion scores depending on the study subject.

Subjects 7, 9, and 10 showed mean distortion scores higher the other participants for all the

appliances used. It can be explained by possible motion artifacts caused by the subjects’ physical

movement during image acquisition. Another possible explanation may be individual’s unique

tissue susceptibility which may be dependent on the tissue anatomy (different lipid-water

interfaces, air-bone interfaces), vascularity, chemical composition.44

The results of this study are

similar to the findings of Elison et al. (2008)26

where the researchers found individual variations

in the distortion scores of images of different subjects.

Mean distortion scores for different anatomic regions demonstrated a general trend of

reduction in the image distortion with the increasing distance from the orthodontic appliance.

http://radiopaedia.org/articles/lacunar-infarct

http://radiopaedia.org/articles/multiple-sclerosis

http://radiopaedia.org/articles/subarachnoid-haemorrhage

77

These findings are in accordance to the results of previously done studies. 9,26

However, some

anatomic regions demonstrated mean distortion scores higher than the regions more distant from

the appliances. For example, globes of the eyes demonstrated significantly higher distortion

scores than nasopharynx for all appliances. A possible explanation to this phenomenon can be

organ movement as well as unique tissue interfaces in a particular anatomic area. Approximate

relative distances from the appliances to the anatomic regions assessed in this study can be seen

in Fig.47.

Fig.47 Approximate relative distances from the orthodontic appliances to the anatomic regions of

the head assessed in the study.

78

In 3 Tesla cranial MRI, axial gradient-recalled and axial diffusion-weighted sequences

received scores close to, or in the nondiagnostic range even with no appliances. These results

coincide with the data from the previously done study by Elison et al.26

where in 1.5 Tesla MRI,

mean distortion scores for axial gradient-recalled and axial diffusion-weighted sequences were

close to, or in the non-diagnostic range. The distortion scores for axial diffusion-weighted

sequence in this study were higher for all the appliances compared to the scores in the study by

Elison et al. This difference in the results can possibly be explained by the strength of the

magnetic field, which is one of the main factors determining the artifact size, and which was

twice as strong in our study compared to Elison et al.26

High distortion scores for axial gradient-

recalled and axial diffusion-weighted sequences can be explained by the nature of these

sequences (use of strong gradient pulses, eddy currents, rapid switching of strong gradient pulses

and thus, high sensitivity to artifacts due to metallic objects, bone/air interface, and movement).45

Gradient-recalled and diffusion-weighted sequences are routinely used to evaluate brain regions.

Therefore, we included only brain regions of frontal lobe, temporal lobe and brain stem into the

assessment for these two sequences to avoid artificially increased scores due to inclusion of other

regions.

The intrarater agreement was based on the reviewer 1 independently re-scoring images of

3 randomly selected subjects (398 repeated scores, about 132 scores per each subject), and

reviewer 2 independently re-scoring images of 3 randomly selected subjects (394 repeated

scores, about 131 scores per each subject). The intrarater agreement was moderate for reviewer 1

(kappa=0.059, 95% CI=0.459-0.659) and substantial for reviewer 2 (0.667, 95% CI=0.573-

0.761). The interrater agreement was based on the image scores of subjects 2-10 (a total of 1181

scores per reviewer) because the diagnostic score definitions were developed based on the raters’

79

collective discussion of the images of subject 1. The interrater agreement was substantial (0.761,

95% CI=0.712-0.81).

The scores for non-contrast axial magnetic resonance angiography (MRA), axial fluid

attenuated inversion recovery (FLAIR), and axial T2-weighted sequences were found to be

below 3 (diagnostic) in all the appliances and regions with the exception of globes of the eyes for

metal brackets and tubes in T2 and FLAIR sequences. High scores for the globes of the eyes

could be explained by eye movement.46

If brain is the area of interest, none of the four

appliances need removal before imaging with axial T2-weighted, axial MRA and axial FLAIR

sequences according to the data from our sample. MRA and FLAIR sequences were

systematically studied for the first time. The results for axial T2-weighted sequence are in

accordance with the findings of Elison et al.26

, where the researchers found mean distortion

scores for axial T2 sequence to be the lowest from all the used sequences, and in the diagnostic

range even for stainless steel brackets and buccal tubes (although the distortion scores for this

appliance were close to the non-diagnostic range). However, Elison et al. concluded that stainless

steel brackets needed to be removed before the axial T2 cranial MR scans even if the region of

interest was brain. The difference in the recommendations regarding axial T2 sequence

compared to the current study can be explained by the fact that the researchers in the study by

Elison et al. calculated mean distortion score for axial T2 sequence with stainless steel brackets

and tubes for all anatomic regions which does not allow for assessment of each anatomic region

separately. In our sample, intraoral regions of base of the tongue, body of the mandible and hard

palate were not included in axial T2 sequence, globes of the eyes received scores in the

nondiagnostic range, nasopharynx and brain regions received scores around 2, in the diagnostic

range, for stainless steel brackets and molar tubes.

80

4.3 Recommendations for clinical practice.

Stainless steel brackets and buccal tubes rendered images nondiagnostic in 3 Tesla cranial

MRI for sagittal T1-weighted, axial gradient-recalled, and axial diffusion-weighted sequences.

Therefore, it is suggested in the current study that stainless steel brackets and tubes should be

removed before imaging with these sequences. Ceramic brackets did not cause significant image

distortions in 3 Tesla cranial MRI. Even though the scores for ceramic brackets for axial

gradient-recalled and axial diffusion-weighted sequences were close to, or in the nondiagnostic

range, they were not statistically significantly different from the distortion scores for the cranial

images with no appliances. Therefore, ceramic brackets may not need to be removed before the

imaging with all the used sequences. The combination of ceramic brackets and metal buccal

tubes had scores in the nondiagnostic range for axial gradient-recalled and axial diffusion-

weighted sequences, thus buccal tubes should be removed before these scans. For cranial sagittal

T1 scan, the combined appliance received scores in the nondiagnostic range for oral, pharyngeal

regions of the head and globes of the eyes. Brain regions remained diagnostic. Therefore, metal

buccal tubes may not need to be removed before 3 Tesla T1 sagittal brain scans. Multistranded

stainless steel lingual retainer received scores above 3 (nondiagnostic) for axial gradient-recalled

and axial diffusion-weighted sequences. However, they were not statistically significantly

different from the scores of the control appliance (ceramic brackets). In sagittal T1-weighted

sequence, the scores of the oral and pharyngeal regions of the cranial MRI were above 3.0, but

the brain regions remained diagnostic. Therefore, for brain imaging, an orthodontic lingual

retainer made from 18-8 stainless steel multistranded wire may not need to be removed for

imaging with any of the used sequences. Clinical recommendations from this study are

summarized in Table 11.

81

Table 11. Clinical recommendations for cranial MR imaging with 4 commonly used

orthodontic appliances and 6 common MR sequences.

Bas

e o

f th

e

ton

gu

e

Bo

dy

of

the

man

dib

le

Har

d p

alat

e

Nas

op

har

ynx

Glo

bes

of

the

eyes

Pit

uit

ary

gla

nd

Fro

nta

l lo

be

Tem

po

ral

lob

e

Bra

in s

tem

Sagittal

T1

M M M M M M M M M

C C C C C C C C C

C+M C+M C+M C+M C+M C+M C+M C+M C+M

LR LR LR LR LR LR LR LR LR

Axial

T2

M M M M M M

C C C C C C C

C+M C+M C+M C+M C+M C+M

LR LR LR LR LR LR

Axial

GRE

M M M

C C C

C+M C+M C+M

LR LR LR

Axial

DWI

M M M

C C C

C+M C+M C+M

LR LR LR

Axial

MRA

M M M M M M

C C C C C C


LR LR LR LR LR LR

Axial

FLAIR

M M M M M M

C C C C C C


LR LR LR LR LR LR

M represents stainless steel brackets and molar tubes, C represents ceramic brackets,

C+M represents combination of ceramic brackets and stainless steel molar buccal tubes, LR

represents stainless steel lingual retainer. Red color of the cell indicates that the appliance should

be removed before the imaging. Green color of the cell indicates that removal of the appliance is

not necessary before the imaging. Yellow color of the cell indicates that 25% or fewer images

received a score of 4 (nondiagnostic) although the majority of scores were in the diagnostic

range; thus removal of the appliances could be considered based on the individual assessment of

the case by the prescribing physician/radiologist. Empty cell indicates that the anatomic region is

either not included in the MR scan, or not assessed. GRE-gradient recalled, DWI –diffusion-

weighted, MRA-magnetic resonance angiography, FLAIR-fluid attenuation inversion recovery.

82

It seems prudent for an orthodontist to pay close attention to the patient’s medical history

pertaining to the current or potential need for MRI. Questions regarding previous MRI

examinations, conditions such as seizures, TMJ disorders, tumors, cerebral palsy, cardiovascular

abnormalities, , multiple sclerosis, autism etc. may positively influence the practitioner’s

appliance choice to potentially reduce patient’s and practice burden.

MR imaging of patients with metal appliances causes some potential safety concerns.

One potential risk is rapid movement of the metal objects in the magnetic field. In this study,

orthodontic appliances were securely embedded into the rigid Essix retainers which were firmly

attached to the teeth. Previously conducted studies using same methods of appliance fixation did

not find any perceivable movement of orthodontic appliances during image acquisition.26,27

Therefore, in this study, no special precautions were taken in regard to the potential appliance

movement. MR imaging of patients with metal appliances poses another potential risk of

appliance overheating during image acquisition. However, changes in the temperature of

orthodontic appliances were found to be clinically insignificant, within 1 degree.37

None of the

participants in this study had any discomfort during the procedure.

4.4 Strengths and limitations of the study

Development of a scientific basis for the clinical protocol of MR imaging of patients with

fixed orthodontic appliances in 3 Tesla MR scanners should be considered the strength of this

study. Also, comparison of artifact formation by molar buccal tubes made of different types of

steel is of high clinical relevance. Despite advances in material science and presence of

alternatives to stainless steel brackets such as ceramic, titanium and composite brackets which

83

were found not to cause significant artifacts in 1.5Tesla MRI 26

, stainless steel brackets remain

most frequently used ones. Although plastic and composite brackets might be compatible with

MRI scanners, they have several problems related to material performance such as bracket

deformation under stress, especially with torque expression, decreased wear resistance.33,34

These

drawbacks have prevented plastic and composite brackets from routine use in most clinical

orthodontic practices. In addition, inclusion of a multistranded stainless steel lingual retainer into

the study added to its strength because of potentially frequent presence of this appliance in MRI

subjects.

The study has, however, a few limitations. Firstly, with 4 different appliances and 6 MR

sequences for each appliance, the study sample size is small. This study found individual

variability in the distortion scores depending on the study subject. The influence of the study

subject on the distortion scores could not be investigated fully because of the small sample size.

In addition, limited sample size creates interdependence of the data, thus multiple statistical tests

performed on the same small number of subjects pose a risk of a Type I error. Intrarrater

agreement calculation was based on each reviewer independently repeating close to 400 scores.

However these scores were from scans of only 3 randomly selected subjects, thus creating data

interdependence. In this study, all the statistical differences found were highly significant

(p<0.0001). This increases confidence in the data obtained. Increasing the sample size would

have increased the statistical power of the study and decreased the risks associated with data

interdependence. However, significant increase of the sample size was cost-prohibitive in this

study due to the high cost of MR scans and appliances. The sample size of 10 seems to be the

largest in the in-vivo studies26,27

published on the topic of MRI and dental appliances presumably

because of high MRI and material costs.

84

Secondly, there is a great variety of brackets including self-ligating brackets on the

market made of different combinations of materials and with the aid of various technological

processes e.g. metal injection molding, casting, milling, brazing etc. All of the above variables

influence magnetic susceptibility of the final product and thus, its MRI compatibility.13,41

It

would certainly be unrealistic to test every bracket on the market, and the only possible way

would be to generalize MR compatibility of different bracket systems by grouping them

according to the material combination and the technological processes involved. Keeping these

limitations in perspective, we chose to investigate the most commonly used fixed orthodontic

appliances and MR sequences. Taking in account high cost of MRI and orthodontic appliances,

we elected not to include archwires into the study because they can be relatively easily and

quickly removed from the patients’ mouths before the MR scans Therefore, archwires do not

pose as significant a clinical problem in MRI as do bonded orthodontic appliances.

4.5 Recommendations for future studies

It would be beneficial to study more appliance types such as titanium or cobalt-chromium

(no-nickel) brackets and buccal tubes, different types of archwires and lingual retainer wires (e.g.

gold retention chains, titanium molybdenum alloy (TMA), wires, metal bands to determine their

MR compatibility at 3Tesla. It also seems very useful to study surgical fixation screws and plates

in head MRI as these appliances remain permanently embedded into the tissues after

maxillofacial surgery and are rarely removed. Apparently, this potential investigation would

have to be retrospective considering invasive nature of surgery.

85

In addition, the influence of commonly used orthodontic appliances on

temporomandibular joint images in 3 Tesla MRI needs to be systematically investigated. Not

only is MRI a gold standard for TMJ imaging in patients with TMJ pathology, but fixed

orthodontic appliances are also frequently used in such patients as treatment of a significant

proportion of these patients includes orthodontics and orthognathic surgery.27

Finally, new MRI modalities are emerging which are specifically designed to suppress

metal artifacts.47,48

Two new sequences were used in recent descriptive pilot studies to suppress

metal artifacts in imaging patients with metal implants of the hip joints and spine in 1.5 and 3

Tesla MRI. Slice encoding for metal artifact correction (SEMAC) and multiacquisition variable

resonance image combination (MAVRIC) showed promising results compared to traditional MR

sequences. The slice-encoding for metal artifact correction (SEMAC) technique is based on two-

dimensional multi-slice spin-echo imaging, and uses additional slice-encodings to deal

with the through-plane distortion. SEMAC corrects artifacts via encoding of each excited slice

against metal-induced field inhomogeneities.48

The multiacquisition variable resonance image

combination (MAVRIC) technique is based on the three-dimensional acquisition, and acquires

multiple images with different center of excitation frequency to deal with a broad field

perturbation.49

Prospective studies using head MR imaging in patients with orthodontic

appliances acquired with SEMAC and MAVRIC sequences compared to traditional MR imaging

would be of great clinical value.

86

CHAPTER 5

Conclusions

The hypothesis: “commonly used stainless steel brackets, buccal tubes and lingual

retainers cause significant MR image distortion on 3T MR scanners to render the image

nondiagnostic for MR investigations of all the regions of the head” was rejected because this in-

vivo investigation revealed that head MR images in different regions were differentially affected by

the presence of orthodontic appliances.

1. Ceramic brackets caused minimal MR image distortions in 3 Tesla head MRI.

2. Multistranded stainless steel lingual retainer did not cause significant image distortions in MR

images of the brain with any of the used sequences.

3. None of the 4 appliances we tested caused significant image distortions in 3 Tesla brain MRI

using non-contrast axial magnetic resonance angiography (MRA), axial fluid attenuated

inversion recovery (FlAIR), and axial T2-weighted sequences.

4. Stainless steel brackets and buccal tubes rendered images nondiagnostic in 3 Tesla head MRI

for sagittal T1-weighted, axial gradient-recalled, and axial diffusion-weighted sequences.

5. The combination of ceramic brackets and metal buccal tubes rendered images nondiagnostic

for axial gradient-recalled and axial diffusion-weighted sequences. For sagittal T1 head scan,

buccal tubes rendered images of oral, pharyngeal regions of the head and globes of the eyes non-

diagnostic. T1 sagittal brain scans remained diagnostic with this appliance.

87

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APPENDICES

Appendix 1. University of Toronto Research Ethics Board approval

92

93

Appendix 2: The Hospital for Sick Children Toronto Research Ethics Board approval

94

Appendix 3: Invitation letter to subjects for participation

Version: Sep 3 2014

FACULTY OF DENTISTRY, UNIVERSITY OF TORONTO

124 Edward Street, Toronto, Ontario M5G 1G6

HOSPITAL FOR SICK CHILDREN, TORONTO

555 University Avenue, Toronto Ontario M5G 1X8

CANADA

Title of the Project:

Effects of orthodontic appliances on diagnostic quality of MR images of the head.

Dear

You are invited to participate in a clinical research study being conducted at the Faculty

of Dentistry, University of Toronto and the Hospital for Sick Children, Toronto. The aim of the

study is to investigate the influence of commonly used orthodontic braces and appliance parts on

magnetic resonance images (MRI) frequently used in hospitals to diagnose different medical

95

conditions. MRI has been used in medicine for more than 30 years and has not been shown to

have deleterious effects on humans.

The study will involve your MR imaging with removable braces. First, you will have two

appointments in the Orthodontic Clinic, Faculty of Dentistry, University of Toronto which will

last about 30 and 15 minutes respectively. In the first appointment, orthodontic impressions of

your upper and lower teeth will be taken. In the second visit, the Essix retainer trays with the

appliances embedded in them will be tried on your teeth to check for their fit. After that, you will

be taken to the MRI section of the department of Diagnostic Imaging at the Hospital for Sick

Children where your MR scans will be made. It will take about 2 hours. Your total time spent

will be around 2hours and 45 minutes.

Your participating in this study will provide information that will be useful for MR

imaging of the patients with braces. You will always retain the right to withdraw your consent to

participate in the study at any time.

If you agree to participate in this study, you will help to improve understanding of MR

imaging of the patients with braces. You will also be compensated $ 75 for the participation at

the end of the MRI acquisition.

Thank you in advance for your participation in the study.

96

The study is being conducted by Dr Dzmitry Zhylich as a part of his Masters project at the

Faculty of Dentistry, University of Toronto under primary supervision of Dr Sunjay Suri,

Associate Professor of Discipline of Orthodontics.

Co-investigators:

Dr. Andrea Doria, Chief of Research, Radiologist, Department of Diagnostic Imaging The

Hospital for Sick Children, Associate Professor, Co-Director of Research, Department of

Medical Imaging, University of Toronto

Dr. Bryan Tompson,Head, Division of Orthodontics, Department of Dentistry The Hospital

for Sick Children, Discipline Head, Orthodontics Faculty of Dentistry, University of Toronto

Dr. Wendy Lou

Head, Division of Biostatistics, Dalla Lana School of Public Health


Ms. Tammy Rayner-Kunopaski

MRI Technologist, Department of Diagnostic Imaging,

The Hospital for Sick Children

Feel free to contact Dr Zhylich for any questions or concerns by telephone at 416-979-

4750 ext 3039 or via e-mail: [email protected] or his supervisor, Dr Suri by

97

telephone at 416 979 4924 ext 4397 at the Discipline of Orthodontics, Faculty of Dentistry,

University of Toronto, 124 Edward Street, Toronto M5G 1G6.

98

Appendix 4. Research Consent Form

Version: Sep 10 2014

Appendix 2 : Consent Form.

Research Consent Form

Title of Research Project:

Effects of orthodontic appliances on diagnostic quality of MR images of the head

Investigators:

99

1. Principal Investigator:

Dr Sunjay Suri,

Staff Orthodontist, Department of Dentistry


Associate Professor

Discipline of Orthodontics, Faculty of Dentistry, University of Toronto

Telephone 416-979-4924 ext 4397

e-mail: [email protected]

2. Co-investigator 1.

Dr. Dzmitry Zhylich

Graduate MSc. Student

Discipline of Orthodontics, Faculty of Dentistry, University of Toronto.

Telephone 416-979-4750 ext 3039



Dr. Andrea Doria

Chief of Research, Radiologist, Department of Diagnostic Imaging


Associate Professor, Co-Director of Research, Department of Medical Imaging,


Telephone 416-813-6079

100



Dr. Bryan Tompson

Head, Division of Orthodontics, Department of Dentistry


Discipline Head, Orthodontics

Faculty of Dentistry, University of Toronto

Telephone 416-979-4924 ext.4396



Dr. Wendy Lou

Head, Division of Biostatistics, Dalla Lana School of Public Health


Telephone 416-946-7804


6. Co-investigator 5

Ms. Tammy Rayner-Kunopaski

MRI Technologist, Department of Diagnostic Imaging,


Telephone: 416-813-6060

101


Purpose of the Research:

The aim of the study is to investigate the influence of commonly used orthodontic braces and

appliance parts on magnetic resonance images (MRI) frequently used in hospitals to diagnose

different medical conditions. We wish to make your MR images with different removable

braces. Your participating in this study will provide information that will be useful for MR

imaging of the patients with braces.

Description of the Research:

The study will involve your MR imaging with removable braces. First, you will have two

appointments in the Orthodontic Clinic, Faculty of Dentistry, University of Toronto which will last

about 30 and 15 minutes respectively. In the first appointment, orthodontic impressions of your

upper and lower teeth will be taken. In the second visit, the Essix retainer trays with the appliances

embedded in them will be tried on your teeth to check for their fit. After that, you will be taken to

the MRI section of the department of Diagnostic Imaging at the Hospital for Sick Children where

your MR scans will be made. It will take about 2 hours. Your total time spent will be around 2hours

and 45 minutes

Potential Harms:

We know of no harm that taking part in this study could cause you.

102

Potential Discomforts or Inconvenience:

Potential Discomforts or Inconveniences include the length of MRI acquisition, participation in 3

visits, potential discomfort of dental impressions (although these are very routine and are not known

to cause any significant level of discomfort or inconvenience). Increase in skin temperature during 3

Tesla MRI scanning of the head has been described in the literature to be insignificant (within 0.5

degrees), with no discomfort reported. The use of imaging at 3 Tesla MRI scanners is common

practice in Canada, scanners are commercially available and have Health Canada approval. The 3T

MRI machines have Specific Absorption Rates set which do not allow the sequences to go beyond

FDA approved limits and the SAR values for all such sequences are much below allowed limits.

Also the sequences described in the proposal are those which are used routinely in clinical practice.

However, if you feel any discomfort or a significant rise in temperature during MR scanning, please

notify the MRI technician immediately, and further tests on the material that led to the rise in

temperature will be terminated.

Potential Benefits:

To individual subjects:

A better understanding of the MR imaging of the patients with braces will result from the study. This

will reduce the financial and biological burden and risks associated with removal and reinstallation

of braces for orthodontic patients needing MRI. Considering orthodontic treatment is very common

103

today, the results of this study will potentially benefit you if you need to have MRI concurrently with

braces in your future life.

There may be a possibility of incidental findings on your MRI of which you will be fully informed.

The results of the research will be available to the public in the University of Toronto Faculty of

Dentistry Library. A short summary of the study findings will additionally be provided to you.

To society:

A better understanding of the MR imaging of the patients with fixed braces will result from the

study. This will reduce the financial and biological burden and risks associated with removal and

reinstallation of the fixed braces for the orthodontic patients needing MRI which is a major

limitation under existing conditions.

Confidentiality:

We will respect your privacy. No information about who you are will be given to anyone or be

published without your permission, unless required by law. For example, the law could make us give

information about you if a child has been abused, if you have an illness that could spread to others, if

you or someone else talks about suicide (killing themselves), or if the court orders us to give them

the study papers.

104

The data produced from this study will be stored in a secure, locked location. Only members of the

research team (and maybe those individuals described above) will have access to the data. This could

include external research team members. Following completion of the research study the data will be

kept as long as required then destroyed as required by Sick Kids policy. Published study results will

not reveal your identity.

Reimbursement:

If you agree to participate in this study, you will help to provide information that will be useful for

MR imaging of the patients with braces. We will also provide you with some compensation, $ 75 in

recognition of your time and effort after the completion of the MR imaging.

Participation:

It is your choice to take part in this study. You can stop at any time. The care you get at Sick Kids or

at the Faculty of Dentistry, University of Toronto will not be affected in any way by whether you

take part in this study.

New information that we get while we are doing this study may affect your decision to take part in

this study. If this happens, we will tell you about this new information. And we will ask you again if

you still want to be in the study.

105

If you become ill or are harmed because of study participation, we will treat you for free. Your

signing this consent form does not interfere with your legal rights in any way. The staff of the study,

any people who gave money for the study, or the hospital are still responsible, legally and

professionally, for what they do.

Sponsorship:

The sponsors/funders of this research are:

1) Principal investigator Dr. Sunjay Suri, Department of Orthodontics, Faculty of Dentistry,

University of Toronto.

2) Department of Orthodontics, Faculty of Dentistry, University of Toronto

3) Companies donating braces for the study

Conflict of Interest:

I, and the other research team members have no conflict of interest to declare.

Consent :

By signing this form, I agree that:

1) You have explained this study to me. You have answered all my questions.

106

2) You have explained the possible harms and benefits (if any) of this study.

3) I know what I could do instead of taking part in this study. I understand that I have the right not

to take part in the study and the right to stop at any time. My decision about taking part in the study

will not affect my health care at Sick Kids.

4) I am free now, and in the future, to ask questions about the study.

5) I have been told that my medical records will be kept private except as described to me.

6) I understand that no information about who I am will be given to anyone or be published without

first asking my permission.

7) I agree, or consent, to take part in this study.

_________________________________

Printed Name of Subject & Age Subject’s signature & date

_________ _________________________________

Printed Name of person who explained consent Signature of Person who explained consent & date

107

_______________________________________ __________________________________

Printed Witness’ name (if the subject/legal guardian Witness’ signature & date

does not read English)

If you have any questions about this study, please Dr.Dzmitry Zhylich at 416-979-4750 ext.3039

If you have questions about your rights as a subject in a study or injuries during a study, please call

the Research Ethics Manager at 416-813-5718.

108

Appendix 5. MRI screening form.

109

Appendix 6. Case Report Form for the study: “Effects of orthodontic appliances on

diagnostic quality of MR images of the head. Version: Sep 3 2014

110

Appendix 7. Randomized order of the appliances for 10 subjects.

N Appliance sequence MRI Date

1 1-metal (M)

2-ceramic (C)

3-ceramic+metal(C+M)

4-lingual retainer (LR)

5-Essix (E)

6-No appliance (N)

14.10.2014

2 1-M

2-C

3-C+M

4-LR

14.10.2014

3 1-M

2-C

3-C+M

4-LR

14.10.2014

4 1-C

2-LR

3-M

4-C+M

1.12.2014

5 1-LR

2-M

3-C

4-C+M

2.12.2014

6 1-C

2-C+M

3-M

4-LR

3.12.2014

7 1-C

2-LR

3-M

4-C+M

4.12.2014

8 1-C+M

2-M

3-LR

4-C

11.12.2014

9 1-C

2-M

3-C+M

4-LR

19.12.2014

10 1-C

2-LR

3-M

4-C+M

23.12.2014

Appendix 8. Representative sagittal and axial images for scores 1 to 5 (frontal lobe of the brain was scored). Sa

gitt

al im

ages

(T1

)

Sco

re

1 2 3 4 5

Axi

al im

ages

Axial T2 Axial DWI Axial DWI Axial DWI Axial DWI

DWI-diffusion-weighted sequence.

Documents

EFFECTS OF ORTHODONTIC APPLIANCES ON DIAGNOSTIC … · 1.1 Orthodontic appliances and MRI 1 1.2 Current state of the literature on orthodontic appliances in MRI 3 1.3 Purpose and