The Effect of Cone Beam CT Voxel Size on the Identification of Vertical and Horizontal ... ·...

The Effect of Cone Beam CT Voxel Size on the Identification of Vertical and Horizontal Root Fractures:

An In-Vitro Study

by

Niloufar Amintavakoli

A thesis submitted in conformity with the requirements for the Degree of Master of Science in Oral and Maxillofacial Radiology

Discipline of Oral and Maxillofacial Radiology, Faculty of Dentistry University of Toronto

© Copyright by Niloufar Amintavakoli 2013

ii

The Effect of Cone Beam CT Voxel Size on the

Identification of Vertical and Horizontal Root Fractures:

An In-Vitro Study

Niloufar Amintavakoli

Master of Science in Oral and Maxillofacial Radiology

Discipline of Oral and Maxillofacial Radiology, Faculty of Dentistry

University of Toronto

2013

Abstract

Objective: The purpose of this study is to determine the relationship between cone beam CT

(CBCT) voxel size and tooth root fracture detection. Materials and Methods: Vertical and

horizontal root fractures were induced in a total of 30 teeth, and 15 teeth were left intact.

Teeth were imaged with projection digital radiography and the Kodak 9000 3D CBCT

system with a native voxel size of 76 μm. The CBCT voxels were then downsampled to 100

μm, 200 μm and 300 μm. Five blinded observers evaluated both sets of images with a 1

week washout interval between each set of observations. Results: CBCT outperformed the

projection images for fracture detection for all voxel sizes except 300 μm (p<0.05). No

significant differences were found between the different voxel sizes (p>0.05). Conclusion:

Although voxel size does not impact the interpretation of root fractures, in vitro, CBCT

outperformed projection imaging for voxel sizes less than 300 μm.

iii

Acknowledgments

I would like to express my sincere gratitude to my advisor Dr. Ernest Lam for his

support and guidance in all the time of research and writing of this thesis and also throughout

the three years of my graduate study.

A special thanks to my research committee members Drs. Pharoah and Basrani for

their constructive comments and encouragements.

My sincere thanks also goes to Drs Mariam Baghdady, Masoud Varshosaz, Catherine

Nolet-Levesque and Daniel Turgeon for their kindness in volunteering their time and

experience in this project.

Last but not the least, an extraordinary thanks to my parents, Farideh and Mohammad,

who are my life long teachers and my husband, Siamak, for his unconditional support and

encouragements.

iv

Table of Contents

Abstract .................................................................................................................................... ii

Acknowledgments .................................................................................................................. iii

Table of Contents .................................................................................................................... iv

List of Tables ........................................................................................................................... vi

List of Figures .......................................................................................................................... ix

List of Appendices .................................................................................................................... x

Chapter 1: Introduction .......................................................................................................... 1

1.1 Overview .................................................................................................................. 1

1.2 Vertical Root Fractures ............................................................................................ 2

1.3 Horizontal Root Fractures ........................................................................................ 4

1.4 Radiographic Features of Root Fractures ................................................................ 5

1.5 Cone Beam CT ......................................................................................................... 7

1.6 Cone Beam CT in the Diagnosis of Root Fractures in Non-Endodontically-

Treated Teeth .................................................................................................................... 11

1.7 Cone Beam CT in the Diagnosis of Root Fractures in Endodontically-Treated

Teeth ................................................................................................................................. 18

1.8 Statement of the Problem ....................................................................................... 26

1.9 Objectives and Hypotheses .................................................................................... 27

1.10 Null Hypotheses ................................................................................................... 27

Chapter 2: Methods and Materials ...................................................................................... 29

2.1 Sample Preparation ................................................................................................ 29

2.2 Image Acquisition .................................................................................................. 31

2.3 Image Evaluations .................................................................................................. 32

2.4 Projection Radiography Study ............................................................................... 33

2.5 Data Analysis ......................................................................................................... 35

2.6 Observers Agreement ............................................................................................. 35

Chapter 3: Results .................................................................................................................. 37

3.1 Diagnostic Test Results for CT Images ................................................................. 37

3.2 Comparison of Voxel Sizes and Fracture Detection .............................................. 43

v

3.3 Comparison of the Observers ................................................................................. 49

3.4 Comparison of Type of Tooth ................................................................................ 51

3.5 Comparison of Time .............................................................................................. 54

3.6 Diagnostic Test for Digital Periapical Images ....................................................... 55

3.7 Observers Agreement ............................................................................................. 55

Chapter 4: Discussion and Conclusion ................................................................................ 57

4.1 Overview ................................................................................................................ 57

4.2 Study Limitations ................................................................................................... 62

4.3 Future Directions ................................................................................................... 63

4.4 Clinical Implications and Conclusion .................................................................... 63

References ................................................................................................................................ 64

vi

List of Tables

Table 1.1: Summary of the results of in vitro studies of non-endodontically-treated teeth

using cone beam CT for the diagnosis of vertical root fractures. Where other manipulations

were performed (endodontic treatment or metal post placement), only the results of the non-

endodontically-treated teeth are summarized ..................................................................... 13-15

Table 1.2: Summary of the results of in vivo studies of non-endodontically-treated teeth using

cone beam CT for the diagnosis of horizontal root fractures. Where other manipulations were

performed (endodontic treatment or metal post placement), only the results of the non-

endodontically-treated teeth are summarized. .......................................................................... 17

Table 1.3: Summary of the results of in vitro studies of endodontically-treated teeth using

cone beam CT for the diagnosis of vertical root fractures. ................................................ 20-23

Table 1.4: Summary of the results of in vivo studies of endodontically-treated teeth using

cone beam CT for the diagnosis of vertical root fractures. ....................................................... 25

Table 3.1: Specificities, sensitivities, positive and negative predictive values for each

resolution and all root fractures for the cone beam CT images. .............................................. 37

Table 3.2 Areas under the receiver operator curves for different voxel resolutions and all root

fractures. .................................................................................................................................... 38


resolution and vertical root fractures for the cone beam CT images. ....................................... 39

Table 3.4: Areas under the receiver operator curves for different voxel resolutions and

vertical root fractures only. ....................................................................................................... 40


resolution and horizontal root fractures for the cone beam CT images. ................................... 41

Table 3.6: Area under the receiver operator curves for different voxel resolutions and

horizontal root fractures only. ................................................................................................... 42

Table 3.7: Comparison between each pair of voxel sizes in detection of all root fractures for

all observers. ............................................................................................................................ 43

vii

Table 3.8: Comparison of voxel sizes in detection of vertical root fractures only for all

observers. .................................................................................................................................. 44

Table 3.9: Comparison of voxel sizes in detection of vertical root fractures only in the oral

radiology graduate student group. ............................................................................................. 45


radiologist group. ...................................................................................................................... 46

Table 3.11: Comparison of voxel sizes in detection of horizontal root fractures only for all

observer groups. ........................................................................................................................ 47

Table 3.12: Comparison of voxel sizes in detection of horizontal root fractures only in the

oral radiology graduate student group. ..................................................................................... 48


oral radiologist group. .............................................................................................................. 49

Table 3.14: Comparison of oral radiology graduate students and oral radiologists in detection

of both types of fractures with each voxel size (df: 1/n: 150). ................................................. 50


of vertical fractures with each voxel size (df: 1/n: 150). .......................................................... 50


of horizontal fractures with each voxel size (df: 1/n: 150). ..................................................... 51

Table 3.17: Comparison of detection of root fractures between teeth in voxel size 76 µm

(df:1). ........................................................................................................................................ 51


(df:1), ....................................................................................................................................... 52


(df:1). ....................................................................................................................................... 52


(df:1). ....................................................................................................................................... 53

Table 3.21: Comparison of detection of root fractures between teeth in periapical radiographs

(df:1). ....................................................................................................................................... 53

viii

Table 3.22: Comparison of the mean time (seconds) spent by oral radiology graduate students

and oral radiologists in the detection of root fractures with each voxel size (df:223) .............. 54

Table 3.23: Comparison of each voxel size with periapical radiographs in detection of root

fractures (df:1/n:90). ................................................................................................................. 55

Table 3.24: Kappa values for the intra and inter observer agreement for each resolution and

periapical radiographs. .............................................................................................................. 56

ix

List of Figures

Figure 1.1: Complete and incomplete vertical tooth fracture patterns.

(adapted from Rivera et al.4). ...................................................................................................... 2

Figure 1.2: Schematic diagram of horizontal fractures (based on 33 fracture lines caused by

frontal impacts) (from Andreasen24

) ........................................................................................... 5

Figure 2.1: The bench vice used to induce vertical fractures .................................................. 30

Figure 2.2: Five teeth mounted in stone in the same manner as inside the mouth .................. 30

Figure 2.3: Samples were centered in the center of the field of view ...................................... 31

Figure 2.4: Bucco-lingual cross section slices of a molar with a vertical root fracture at voxel

sizes A) 76 μm, B) 100 μm, C) 200 μm, D) 300 μm ................................................................ 32

Figure 2.5: Bucco-lingual cross section slices of a molar with a horizontal root fracture at

voxel sizes A) 76 μm, B) 100 μm, C) 200 μm, D) 300 μm ...................................................... 32

Figure 2.6: Periapical images of a molar with a vertical root fracture (presented in figure 2.4)

with angulations of A) zero degrees and B) 15 degrees to the long axis of the tooth .............. 34

Figure 2.7: Periapical images of a central incisor with a horizontal root fracture (presented in

figure 2.5) with angulations of A) zero degrees and B) 15 degrees to the long axis of the

tooth .......................................................................................................................................... 34

Figure 3.1: ROC curves for all root fractures and all voxel resolutions .................................. 38

Figure 3.2: ROC curves for vertical root fractures only and all voxel resolutions .................. 40

Figure 3.3: ROC curves for horizontal root fractures only and all voxel resolutions .............. 42

x

List of Appendices

Appendix 1: Copy of the ethics approval of the research ........................................................ 72

Appendix 2: Consent Form for the observers .......................................................................... 73

Appendix 3: Tables of raw data ............................................................................................... 75

1

Chapter 1

1 Introduction

1.1 Overview

Tooth fractures represent splits or breaks in tooth structure that can involve the crown

and/or the root, enamel, dentin, cementum and/or pulp1, and numerous classification schemes

have been proposed over the years.2 Andreasen and Andreasen (1994) classified fractures into

5 subgroups based on the type(s) of tissue(s) involved, and complexity of the fracture pattern:

enamel fracture, uncomplicated enamel and dentin fracture, complicated enamel and dentin

fracture, crown and root fracture, and root fracture.3 In another scheme, Talim and Gohil

classified tooth fractures into those involving enamel (class 1), those involving enamel and

dentin without involving pulp (class 2), those involving enamel and dentin involving the pulp

(class 3), and those involving the roots (class 4). Walton looked specifically at longitudinal

tooth fractures, and classified these into 5 subgroups based on their extension: (1) craze lines,

(2) fractured cusp, (3) cracked tooth, (4) split tooth, and (5) vertical root fracture.4 (Figure 1.1)

Root fractures themselves have been further classified as being coronal, mid-root or apical

types based on their location, and/or vertical, horizontal or oblique.5 Furthermore, vertical root

fractures could involve the pulp or not, and horizontal root fractures could involve the

cervical, middle or apical thirds.2,6

Suffice it to say, there is a wide range and variability in the

way clinicians report fractures of teeth.

2

Figure 1.1: Incomplete and complete vertical tooth fracture patterns (adapted from

Rivera et al.4).

1.2 Vertical Root Fractures

A vertical root fracture is characterized by a cleavage plane that extends through the

long axis of the root, generally in an apical-coronal direction.7,8

Vertical root fractures can be

complete or incomplete; a complete fracture extends extends through the root structure and

involves both root surfaces and an incomplete fracture involves only one surface of the root.9

The prevalence of vertical root fractures has been reported to vary between 2% and 5% in

clinical studies of endodontically-treated teeth.10

The prevalence of vertical root fracture in the

extracted endodontically-treated teeth has been reported to be 10.9%.11

Recently, there has

been an increase in the prevalence of vertical root fractures being diagnosed, and this has been

ascribed to a decrease in the number of tooth extractions and improvements in the diagnosis of

the fractures.4

The etiologic factors contributing to vertical root fractures can be either non-iatrogenic

or iatrogenic. The loss of tooth structure as a result of previous pathosis and anatomical

variations of teeth are the primary non-iatrogenic factors predisposing teeth to vertical root

!!!!!!!!!!!!A!!!!!!!!!!!!!!!!!!!!B!!!!!!!!!!!!!!!!!!C!!!!!!!!!!!!!!!!D!!!!!!!!!!!!!!!!!!!!!!!E!

3

fractures. Changes in the dentinal tubules during aging and the gradual infill of the dentinal

tubules with minerals over time are the secondary non-iatrogenic cause of vertical root

fractures in teeth.10,12,13

Iatrogenic causes of vertical root fractures can be the result of loss of

tooth structure during endodontic treatment, the effects of chemicals or intra-canal

medications, and restorative procedures.12

The stress distribution in an endodontically-treated tooth is different from one that has

not been endodontically-treated. One of the factors that makes endodontically-treated teeth

more prone to fracture is the excessive removal of healthy tooth structure in curved and

narrow root canals during endodontic treatment.12

A discrepancy between the elastic moduli of

the post-crown system and tooth structure may change the distribution of stresses and strains

in the tooth, and this may predispose it to fracture.10

Furthermore, the loading angle of the

crown, type of material used in the core, features of the remaining tooth structure, shape and

diameter of the post, and the adhesion of the post to dentin are additional factors that may

predispose a tooth to fracture.12

Clinically, a tooth with a vertical fracture may display a wide range of signs and

symptoms including spontaneous pain, history of pain on biting, local swelling, sinus tract

formation, exacerbation of chronic inflammation, development of a periodontal pocket, and

sensitivity to percussion and palpation.9,14,15

Tamse et al. evaluated 92 extracted

endodontically-treated teeth with vertical root fracture, and pain (51%) and abscess (31%)

were the major complaints of the patients with vertical root fractures. The most common sign

of vertical root fracture was a deep periodontal pocket (67.4%), followed by sensitivity to

percussion, mobility, and fistula formation. The combination of both a deep pocket and fistula

formation was also reported in this series of patients.16

The presence of a sinus tract was

reported in 13% to 42% of the vertical root fracture cases, and these were usually located close

to the gingival margin of the osseous defect.9,10

The presence of two sinus tracts in both the

buccal and lingual cortices is another sign associated with vertical root fracture, and this may

be considered a pathognomonic feature of vertical root fractures.9,15

A periapical radiograph

made with gutta percha inserted into the area of the orifice may allow the sinus tract to be

traced to the location of the fracture.10,17

Also, periodontal pocket probing in vertical root

fractures is more localized compared to bone loss due to periodontal disease, which is more

4

generalized and can involve more than one surface of the tooth.9 Although definitive diagnosis

of vertical root fracture is made by direct visualization of the fracture, transillumination,

periodontal probing, staining, bite testing and radiographic examination are the most common

clinical procedures used to diagnose vertical root fractures.9,10,15

During surgical intervention,

an area of dehiscence or fenestration may be observed in the adjacent bone surface,18

and if

the overlying bone is intact, an apicectomy may be attempted to better visualize the fracture.9

The prognosis of vertical root fractures is usually poor, although this may depend on

the degree of separation of the fragments and involvement of the pulp.4 The release of bacteria

in the area and consequent destruction of the surrounding tissues make any treatment other

than extraction impossible, especially in single rooted teeth.9,17

In teeth with multiple roots,

hemi-section or root amputation in order to remove the fractured root is the treatment of

choice.4 In general, the prognosis of vertical root fractures in single root teeth is usually poor,

so an early, definitive diagnosis is important to reduce damage to the adjacent tissues.7,19

1.3 Horizontal Root Fractures

Horizontal root fractures are usually associated with acute trauma, and these fracture

planes are generally oriented orthogonally to the long axis of the tooth root (Figure 1.2).20

Horizontal fractures are most commonly seen in the middle third of the root, and in teeth with

completely formed roots and root apices.21

A horizontally fractured root may appear clinically

normal, although it may be extruded or its crown displaced. In the case of trauma, soft tissue

swelling may also be seen, and this may make the clinical evaluation of the area difficult.22

The degree of displacement of the fracture fragments is related to both severity of the injury

and the location of the fracture. The closer the fracture is to the crown, the greater is the

degree of tooth displacement.23

5

Figure 1.2: Schematic diagram of horizontal fractures (based on 33 fracture lines caused by

frontal impacts) (from Andreasen24

)

The treatment of horizontal root fractures depends on whether or not there is

communication of the fracture with the oral cavity. In the case of communication, the coronal

fragment should be extracted and the rest of the tooth can be either extruded or extracted. If

communication with the oral cavity is not present, reduction and alignment of the displaced

segments and stabilization can be done.21

The treatment may, however, be followed by pulp

necrosis, root canal calcification or obliteration, root resorption or fracture non-healing.21

Prognosis is usually influenced by different factors including age of the patient, stage of root

formation and closure of the apex, degree of dislocation of the coronal fragment, mobility of

the coronal and apical fragments, and distance between the fragments.25

A radiographic

evaluation is usually required for the follow-up as well as diagnosis.

1.4 Radiographic Features of Root Fractures

Radiography may not definitively identify a fractured root. Clinicians often base their

diagnoses on the patient’s clinical signs and symptoms, and on features identified on

6

conventional radiographs. The radiographic features of vertical root fracture are divided into

direct and indirect signs. The presence of a radiolucent line confined to and between the

fragments of a fractured root or root filling material, separation of root fragments, space

adjacent to a root filling or a post are direct radiographic features of root fracture.15,26

Without

the presence of separation of the tooth fragment, the direct diagnosis of fracture is generally

very difficult radiographically.10

A fracture line may not be visible on a conventional

radiograph if the x-ray beam does not pass through or is not aligned with the fracture plane.

Consequently, usually more than one periapical radiograph made at two or more different

horizontal angulations may be necessary to detect the radiolucent fracture line.10,27

The indirect radiographic features of vertical root fracture include localized widening

of the periodontal ligament space, and periapical or periradicular rarefaction.28

As well, there

may be periodontal bone loss adjacent to the fracture area in the early stages.10

The pattern of

bone resorption associated with a root fracture may show different appearances including

periapical radiolucency, isolated perilateral radiolucency, “halo” radiolucency, periodontal

radiolucency, vertical bone loss, and also bifurcation radiolucency.18,29,30

Tamse et al. in a

study of 49 extracted teeth with vertical root fracture found halo radiolucency (37%) and

periodontal radiolucency (29%) to be the most commonly associated signs of root fracture.29

Displacement of retrograde filling material into the surrounding tissue may also indicate the

presence of root fracture.10

There have been few studies evaluating the use of conventional and digital radiography

in the diagnosis of vertical root fracture. In a study with 60 extracted teeth, Tsesis et al.

reported specificities of 0.89 and 0.87 for film and digital radiography using a charge coupled

device, respectively, and sensitivities of 0.48 and 0.38, respectively. There was no significant

difference between these two modalities in their abilities to diagnose root fractures.31

The radiographic diagnosis of horizontal root fractures usually requires more than one

image. A radiographic follow up may also be required in the case of horizontal root fracture in

order to evaluate the consequences of treatment. Andreasen et al. stated that usually a

combination of an occlusal radiograph and a conventional periapical radiograph with

bisecting-the-angle technique is required for diagnosis of horizontal root fractures.32

The

7

occlusal radiograph is more reliable in diagnosis of oblique fractures in the apical and middle

third of the root and the periapical radiograph is a better diagnostic device in diagnosis of

horizontally angled coronal root fractures.21

The recommendation of the International

Association of Dental Traumatology is to obtain several radiographs in several angulations

based on the clinician’s judgment. This combination may include a periapical radiograph with

a 90˚ horizontal angle, occlusal view, and a periapical radiograph with lateral angulations from

the mesial or distal aspects of the tooth in question as well as a cone beam CT study in

complicated cases.22

As conventional radiographs are two-dimensional images of a three-dimensional

object, it may be difficult at times to detect radiographic features of fracture on these

images.33,34

Moreover, fracture detection may also be hindered by superimposition of adjacent

tissues, morphologic variations of tooth roots, magnification distortion, surrounding bone

density, x-ray angulation, and radiographic contrast.25,26,35

The inability of conventional two-dimensional imaging systems encouraged

researchers to find alternative ways to diagnose root fractures. Medical multidetector helical

computed tomography (CT) using a fan-shape x-ray beam has been used for this purpose.

Youssefzadeh et al., in an in vivo study, in the evaluation of 42 teeth suspected of vertical root

fracture imaged with medical CT, reported specificity and sensitivity to be 100% and 70%,

respectively. These workers also reported that medical CT was superior to conventional

images in the diagnosis of root fractures.36

The limitation of this study is that all the fractures

were displaced; incomplete and non-displaced fractures, which are more difficult to diagnose,

were not examined.37

Recently, clinicians have turned to cone beam CT to evaluate tooth

fractures because of rapid acquisition time, lower relative patient radiation dose, a more

highly-collimated x-ray beam, and higher image resolution with cone beam CT.38

1.5 Cone Beam CT

Cone beam CT is a three-dimensional imaging modality in which a cone-shaped x-ray

beam rotates around the patient’s head.33,39

The three-dimensional nature of cone beam CT is

reported to result in better visualization of both direct and indirect radiographic signs of root

8

fracture.33,40

The divergent cone-shaped x-ray beam is directed through the area of interest and

the attenuated beam is detected. During the single rotation of the x-ray source and detector

around a fixed fulcrum, multiple planar “basis” projection images are acquired of the field of

view.33,38,41

Three-dimensional image volumes are made up of volume elements or voxels, as

the smallest elements of these images. The size of each voxel is determined by its height,

width and thickness. A cone beam CT voxel is isotropic, meaning its height, width and

thickness are all equal.42

The voxel sizes of different cone beam CT systems vary from 0.076

mm (76 μm) to 0.40 mm (400 m), and this value is what determines the spatial resolution of

a cone beam CT system; the smaller the voxel size, the higher the spatial resolution.33,38,41

Choosing the optimal voxel resolution in cone beam CT is task-specific.33

Liedka et al. in their

in vitro study evaluating 60 human mandibular incisors with simulated external root resorption

reported that a voxel resolution of 0.30 mm is the optimal voxel resolution for diagnosis.43

In

another in vitro study, Bauman et al. used 24 extracted human maxillary molars and scanned

them at four voxel resolutions with the iCAT Classic (Imaging Sciences International,

Hatfield, PA, USA). Five endodontic postgraduate students and two endodontic staff then

evaluated 96 videos generated from horizontal images of these studies.44

They reported that

detection of the mesio-buccal canal in the maxillary molars increased from 60.1% to 93.3% by

decreasing voxel size from 0.40 mm to 0.125 mm. Amongst the many cone beam CT systems

available on the market, the Kodak 9000 3D (Carestream, Rochester, NY, USA) has the

highest reported native spatial resolution (76 μm).33

Michetti et al., using a Kodak 9000 3D

(Carestream, Rochester, NY, USA) to explore root canal anatomy, scanned nine extracted

teeth (14 canals) and then compared the outlined canals with the canals obtained using areas

and Feret’s diameters from histologic sections. These researchers reported strong to very

strong correlations between the cone beam reconstructions and the histologic sections for

canal diameter (r=0.890) and area (r=0.928).45

The spatial resolution of periapical radiographs is determined by the size of the pixel in

digital imaging systems, or the size and number of the silver halide crystals in the

conventional imaging systems. In a study of comparison of 18 different x-ray detectors used in

dentistry, Farman et al. reported that the pixel size of x-ray detectors currently used in

dentistry varies between 18.5 to 40 μm, which is smaller compared with the smallest voxel

9

size available with cone beam CT.46

In comparison, the size of the silver halide crystal is even

smaller than the smallest pixel size available, varying between 1.0 to 1.8 μm.47

Variations in

the sizes of imaging elements result in spatial resolutions of between 5 and more than 20 line

pairs per millimeter.38,46,47

Minimizing radiation risk injury is a primary concern when choosing the type of

imaging to perform. The effective dose of cone beam CT scans is affected by several factors

including the imaging parameters used (kVp, mA), whether x-ray beam emission is pulsed or

continuous, the amount, type, and shape of x-ray beam filtration, the number of basis images

required to create the volume, and the size of the field of view.33

One way that radiation risk

can be quantified for different modalities is by examining effective radiation dose from

different imaging modalities.33

The range of effective doses to the mandible and maxillae in

medical CT scans based on a combination of both maxillae and mandible scans and hyoid to

skull base scans is 1320 to 3324 μSv (mandible) and 1031 to 1420 μSv (maxillae).41

By

limiting the volume of tissue imaged, the effective radiation dose can decrease substantially.

For these smaller field-of-view cone beam CT units, effective radiation doses have been

reported to vary between 5.3 to 488 μSv depending on the imaging site and system.33

For

example, Ludlow calculated the lowest dose from the Kodak 9000 3D system (Carestream,

Rochester, NY, USA) to be 5.3 Sv in the anterior maxilla, and a higher effective dose was

calculated for the Planmeca Promax 3D (Planmeca OY, Helsinki, Finland). 48

Scattering of the x-ray beam is a drawback of cone beam CT systems. Scatter radiation

refers to the askew radiation which degrades the image quality by increasing image noise and

decreasing the image contrast, and increases patient radiation without a concomitant patient

benefit.38,49

Because medical CT beams are collimated in a fan shape rather than a cone shape,

the amount of scattered radiation is lower compared to the cone beam CT systems. The ratio

of scatter to primary radiation can be as high as 3 in large field of view cone beam CT scans,

however, this ratio is 0.2 for multidetector medical CT systems.49

Other factors that contribute

to the quality of the images are contrast-to-noise ratio and signal-to-noise ratios. Daly et al in

their study showed that contrast to noise ratio increases as the square root of dose and voxel

size, decreases as the inverse of the reconstruction filter relative cutoff frequency.50

Signal to

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10

noise ratio represents the ratio of the signal to background noise. Increasing the number of

projection data and frame rate increases the signal to noise ratio. 38

As well as scatter radiation, CT image-related artifacts can also affect the quality of

images. These artifacts can be classified being patient-related, scanner-related, those specific

to the cone beam CT system used and x-ray beam-related.33,38

Patient-related artifacts may be

related to the presence of high attenuation materials such as gutta percha or metallic

restorations, including crowns.30

Metal objects can degrade the quality of CT images by

creating alternating radiopaque and radiolucent “bright tracks” that can overlap the tooth root

and mimic root fractures.51

Since the restoration of endodontically-treated teeth often requires

the insertion of a metallic intra-canal post, the presence of such artifacts is one of the major

limitations of cone beam CT in diagnosis of root fractures.40

Partial volume averaging is a machine-related artifact that is a feature of both medical

fan beam and cone beam CT systems. This artifact occurs when the voxel size is greater than

the size of an object being imaged. In the resultant image, the voxel represents a weighted

average of the densities of the different tissues contained within that voxel. Therefore, if the

object is smaller than the size of the voxel, the numerical value of the voxel will represent an

average of the portion of the voxel filled by the object and whatever other material is

contained within the voxel. By using systems with smaller voxel sizes, the potential of partial

volume averaging is less.38,52

Studies focusing on the application of cone beam CT to diagnose root fractures began

appearing in the literature in 2009. These studies evaluated the role of cone beam CT scan in

both endodontically and non-endodontically-treated teeth. Despite the reported higher

specificity and sensitivity of cone beam CT compared to conventional radiography for the

detection of root fractures, the limitations of cone beam CT may include an increased radiation

dose, the presence of image artifacts, and the lower spatial resolution compared to periapical

radiographs.33,39

11

1.6 Cone Beam CT in the Diagnosis of Root Fractures in Non-Endodontically-Treated Teeth

Hassan et al. investigated vertical root fractures in an in vitro model using teeth

fractured with a hammer and tapered chisel inserted into the root canal space. This study of

root filled and non-filled teeth was performed using an i-CAT cone beam CT system (Imaging

Sciences, Hatfield, PA, USA) with voxel size of 0.25 mm. They reported the specificity and

sensitivity of cone beam CT in the absence of root filling material to be 97.5% and 80.0%,

respectively. Furthermore, cone beam CT had significantly higher sensitivity (79.4%) but not

specificity compared with periapical radiographs (37.1%).40

In a similar study, Varshosaz et

al. used the Promax 3D (Planmeca, Helsinki, Finland) operating at a voxel size of 0.30 mm,

and found that the area under the receiver operator curve (ROC) to be 0.91.35

Using a small

voxel size of 0.16 mm, Valizadeh et al. reported an area under the ROC curve of 0.74, and

detection specificity of 76.9% and sensitivity of 66.7%.53

Kambungton et al. used the

Veraviewepocs 3D (Morita Mfg. Corp., Kyoto, Japan), a system with an even smaller voxel

size of 0.125 mm. These workers found the mean areas under the ROC curves for cone beam

CT to be 0.81 compared with film (0.80) and a digital sensor (0.77); there were no

statistically-significant differences between the 3 modalities.54

In a more extensive in vitro study of voxel size effects, Ozer used the Imaging

Sciences International i-CAT (Imaging Sciences, Hatfield, PA, USA) and observed no

significant differences in specificities and sensitivities between the different voxel sizes they

investigated, but reported higher positive likelihood ratios for 0.125 mm and 0.20 mm voxel

sizes compared with 0.30 mm and 0.40 mm voxel sizes.42

Da Silveira et al. used the same

cone beam CT system and studied non-root filled teeth, root filled and teeth containing a metal

post in an in vitro study at three different voxel sizes (0.20 mm, 0.30 mm, 0.40 mm).

Conventional radiography performed equally well to cone beam CT images acquired at 0.20

mm and 0.30 mm voxel resolutions of teeth that were not endodontically-treated; the

calculated values of specificity, sensitivity, and accuracy (true positives and true negatives)

were all similar.55

Khedmat et al. compared the diagnostic ability of digital radiography, multidetector

medical CT and cone beam CT in the diagnosis of vertical root fracture in both the absence

12

and presence of gutta percha. Using a system with a smaller 0.16 mm voxel resolution

(Planmeca Promax 3D, Roselle, IL, USA), these workers reported cone beam CT specificity

and sensitivity to be 88% and 92%. The specificity and accuracy of cone beam CT was

significantly higher than digital radiography and medical CT. There were, however, no

significant differences among the sensitivities of the three modalities.56

13

Table 1.1: Summary of the results of in vitro studies of non-endodontically-treated teeth using cone beam CT for the diagnosis of

vertical root fractures. Where other manipulations were performed (endodontic treatment or metal post placement), only the results of

the non-endodontically-treated teeth are summarized.

Study Sample Cone beam CT imaging system Results

Hassan et al., 200940

80 extracted teeth (40

premolars and 40 molars)

placed in dry human

mandible.

i-CAT, 0.25 mm voxel size. Specificity: 97.5%

Sensitivity: 80.0%

Varshosaz et al., 201035

100 single-rooted teeth placed

in dry human mandible.

Promax 3D, 0.30 mm voxel size. ROC curve area: 0.91

Valizadeh et al., 201153

120 extracted single-rooted

teeth placed in acrylic blocks.

NewTom 3G, 0.16 mm voxel size. Specificity: 76.9%

Sensitivity: 66.7%

Ozer, 201142

60 extracted maxillary

premolar teeth placed in dry

human mandible.

i-CAT, 0.125 mm, 0.20 mm, 0.30

mm, 0.40 mm voxel sizes.

0.125 mm voxel size

Specificity: 96%

Sensitivity: 98%

Accuracy: 97%

0.20 mm voxel size

Specificity: 96%

Sensitivity: 97%

Accuracy: 96%

14

0.30 mm voxel size

Specificity: 93%

Sensitivity: 93%

Accuracy: 93%

0.40 mm voxel size

Specificity: 93%

Sensitivity: 91%

Accuracy: 92%

Da Silveira et al., 201355



i-CAT, 0.20 mm, 0.30 mm and

0.40 mm voxel sizes.

0.20 mm voxel

Specificity: 100%

Sensitivity: 97%

Accuracy: 98%

0.30 mm voxel

Specificity: 97%

Sensitivity: 87%

Accuracy: 92%

0.40 mm voxel

Specificity: 80%

Sensitivity: 76%

Accuracy: 77%

15

Kambungton et al.,

201254


teeth placed in dry human

mandible.

Veraviewpocs 3D, 0.125 mm

voxel

ROC curve area: 0.81

Khedmat et al., 201256



Promax 3D, 0.30 mm voxel Specificity: 88%

Sensitivity: 92%

Accuracy: 90%

16

Finally, in an in vivo study, Wang et al. investigated vertical root fractures in 86 teeth

with the 3D Accuitomo 80 (J. Morita, Kyoto, Japan) that uses a voxel size of 0.125 mm. The

fractures were also confirmed by surgery. These workers reported specificity and sensitivity of

94.7% and 97%, respectively, for cone beam CT, and 100.0% and 26.3%, respectively, for

periapical radiographs. 14

Only a few studies have investigated the specificity and sensitivity of cone beam CT in

the diagnosis of horizontal root fractures. Kamburoğlu et al. used the 3D Accuitomo 80 (0.08

mm voxel size) (J. Morita, Kyoto, Japan) and compared these images with intraoral

radiographs in an in vitro study. They failed to report any significant differences between the

reported specificities, however, they reported significant differences in the sensitivities of the

two methods.34

A similar study by Avsever et al. compared two different cone beam CT

systems (the 3D Accuitomo 170 cone beam CT [J. Morita, Kyoto, Japan] and the NewTom 3G

cone beam CT [QR SLR, Verona, Italy]) with the VistaScan photostimulable phosphor system

(Dürr Dental GmbH & Co. KG, Germany), a charge couple device sensor (Trophy Radiologie

Inc., Paris, France) and conventional film (Kodak Insight Film, Eastman Kodak Co.,

Rochester, NY). They reported that the specificity and sensitivity of the 3D Accuitomo 170

cone beam CT (97% and 94%, respectively) were higher than the NewTom 3G cone beam CT,

as well as the digital image detectors and conventional film.25

Iikubo et al. also reported higher

sensitivity with limited field-of-view cone beam CT incorporating a 0.117 mm voxel size

compared with intraoral radiography or multidetector helical CT at slice thicknesses of 0.63

mm and 1.25 mm in a study on 28 maxillary anterior teeth.20

17

Table 1.2: Summary of the results of in vivo studies of non-endodontically-treated teeth using cone beam CT for the diagnosis of

horizontal root fractures. Where other manipulations were performed (endodontic treatment or metal post placement), only the results

of the non-endodontically-treated teeth are summarized.

Study Sample Cone beam CT imaging system Result

Kamburoğlu et al.,

200934

36 incisor teeth placed in dry

human maxillae.

Accuitomo 80, 0.08 mm voxel Specificity: 97%

Sensitivity: 92%

Iikubo et al., 200920

28 maxillary anterior teeth

with 13 fractured placed in 7

beagle dogs’ maxillae.

PSR-9000N Dental CT, 0.117 mm

voxel

Specificity: 91%

Sensitivity: 96%

Accuracy: 93%

Avsever et al., 201325

82 extracted human

maxillary incisors with 31

fractured placed in dry

human maxillae.

Accuitomo 170, 0.08 mm voxel

NewTom 3G, 0.18 mm voxel

3D Accuitomo

Specificity: 97%

Sensitivity: 94%

Accuracy: 93%

NewTom 3G

Specificity: 89%

Sensitivity: 89%

Accuracy: 87%

18

1.7 Cone Beam CT in the Diagnosis of Root Fractures in Endodontically-Treated Teeth

Since root fractures are most commonly seen in endodontically-treated teeth and the

presence of root canal filling material and posts are sources of artifact in cone beam CT

images, it is reasonable to evaluate the efficacy of cone beam CT scan in diagnosis of root

fractures in endodontically treated teeth.

Khedmat et al. in an in vitro study found that in the presence of gutta percha, the

specificity of dental radiography (100%) and multidetector medical CT (88%) were

significantly higher than cone beam CT (64%). However, there were no significant differences

between the sensitivities of these modalities in the presence of gutta-percha. The accuracy of

multidetector medical CT (78%) for the detection of vertical root fractures was significantly

higher than that of cone beam CT (72%) and digital radiography (64%). Furthermore, these

workers showed that the accuracy, specificity and sensitivity of cone beam CT was

significantly reduced in the presence of gutta-percha although gutta-percha had no effect on

accuracy, specificity and sensitivity of multidetector medical CT.56

Hassan et al. imaged 80 extracted teeth for vertical root fractures in root canal filled

teeth using the i-CAT cone beam CT system (Imaging Sciences, Hatfield, PA, USA) with

voxel size of 0.25 mm, and reported a specificity and sensitivity of 87.5% and 78.8%,

respectively.40

Mello et al. evaluated the effect of the presence of cast-gold posts and gutta

percha on the diagnostic ability of cone beam CT to identify vertical root fractures with two

different voxel sizes. They reported the 0.20 mm voxel resolution showed greater sensitivity

(82%) than a 0.30 mm voxel size (51%) for fracture detection, but concluded that although

cast-gold posts and gutta percha decreased the overall diagnostic ability of cone beam CT, this

was not statistically significant.19

In another in vitro study, Hassan et al. compared five different cone beam CT systems:

the NewTom 3G (QR SLR, Verona, Italy), the i-CAT (Imaging Sciences, Hatfield, PA, USA),

the Galileos 3D (Sirona Germany, Bensheim, Germany), the Scanora 3D (Soredex, Tuusula,

Finland), and the 3D Accuitomo (J. Morita, Kyoto, Japan) for detection of vertical root

fractures in teeth in both the absence and presence of gutta percha. The voxel sizes varied

19

from 0.20 to 0.30 mm with the lowest being the NewTom 3G and Scanora 3D (0.20 mm). The

authors reported significant differences between different systems, and greater accuracy of

axial slices to detect the vertical root fractures. The i-CAT imaging system (0.25 mm) resulted

in the highest overall specificity and sensitivity. They argued that field-of-view size or voxel

size differences explained the variation in the results.57

Da Silveira et al. showed in teeth with

root canal treatment and a post that the sensitivity was higher when 0.20 mm voxel size was

used. The specificity and sensitivity reported for 0.20 mm voxel size in the presence of root

canal treatment was 97% and 93%, respectively. These values were 83% and 80% in presence

of metallic post with the same voxel size.55

Recently, Ferreira et al. evaluated 59 teeth for the detection of vertical root fracture in

the presence of fiber-resin or titanium posts In an in vitro study. They imaged the teeth before

and after producing the fractures using two different cone beam systems with flat panel image

detectors; the i-CAT Next Generation (Imaging Sciences, Hatfield, PA, USA) and Scanora 3D

(Soredex, Tuusula, Finland). They reported a significant higher sensitivity for diagnosis of

fracture in the roots with fiber-resin posts using the i-CAT system (85%) compared to of the

metal post.58

20

Table 1.3: Summary of the results of in vitro studies of endodontically-treated teeth using cone beam CT for the diagnosis of vertical

root fractures.

Study Sample Cone beam CT imaging system Results


80 extracted teeth (40 premolars

and 40 molars) with root canal

treatment placed in dry human

mandible.

i-CAT, 0.25 mm voxel Specificity: 87.5%

Sensitivity: 78.8%

Melo et al., 201019

180 single-rooted teeth with

presence of gutta percha (GP) and

metallic post (MP) placed in dry human skull.

i-CAT, 0.20 mm or 0.30 mm

voxel sizes

0.20 mm voxel (GP)

Specificity: 73%

Sensitivity: 93%

0.30 mm voxel size (GP)

Specificity: 70%

Sensitivity: 47%

0.20 mm voxel size (MP)

Specificity: 66%

Sensitivity: 70%

0.30 mm voxel size (MP)

Specificity: 63%

Sensitivity: 53%

21


80 extracted teeth (40 premolars

and 40 molars) with root canal

treatment placed in posterior region

of dry human mandible.

NewTom 3G, 0.20 mm voxel

i-CAT, 0.25 mm voxel

Galileos 3D, 0.30 mm voxel

Scanora 3D, 0.20 mm voxel

3D Accuitomo, 0.25 mm voxel

NewTom 3G

Specificity: 95%

Sensitivity: 30.4%

Accuracy: 62.7%

i-CAT

Specificity: 91.3%

Sensitivity: 77.5%

Accuracy: 84.4%

Galileos 3D

Specificity: 85%

Sensitivity: 18.8%

Accuracy: 53.8%

Scanora 3D

Specificity: 85%

Sensitivity: 57.5%

Accuracy: 71.3%

3D Accuitomo

Specificity: 90.7%

Sensitivity: 48.1%

22

Accuracy: 69.4%

Da Silveira et al.,

201355

60 extracted single-rooted teeth

with presence of gutta percha (GP)

or metallic post (MP) placed in

acrylic blocks.

i-CAT, 0.20, 0.30 and 0.40 mm

voxel sizes.

0.20 mm voxel

Specificity (GP): 93%

Sensitivity (GP): 97%

Accuracy (GP): 95%

Specificity (MP): 80%

Sensitivity (MP): 83%

Accuracy (MP): 82%

0.30 mm voxel



Accuracy (GP): 70%



Accuracy (MP): 68%

0.40 mm voxel



Accuracy (GP): 65%



23

Accuracy (MP): 57%

Khedmat et al., 201256

100 extracted single-rooted teeth

placed in acrylic blocks.

Promax 3D, 0.16 mm voxel Specificity (GP): 64%


Accuracy (GP): 72%

Ferreira et al., 201258

59 extracted maxillary first

premolars with fiber-resin (FR) or

titanium (T) posts placed in acrylic

blocks.

i-CAT, 0.125 mm voxel

Scanora 3D, 0.133 mm voxel

i-CAT

Specificity (FR): 74%

Sensitivity (FR): 85%

Accuracy (FR): 78%

Specificity (T): 75%

Sensitivity (T): 72%

Accuracy (T): 73%

Scanora 3D

Specificity (FR): 71%

Sensitivity (FR): 73%

Accuracy (FR): 71%

Specificity (T): 76%

Sensitivity (T): 73%

Accuracy (T): 74%

24

In in vivo studies, the role of cone beam CT was evaluated in the diagnosis of vertical

root fractures in endodontically-treated teeth. Edlund et al. investigated the presence of

vertical root fracture in 33 teeth in 29 patients with clinical signs and symptoms suspicious of

vertical root fracture with either the i-CAT (Imaging Sciences, Hatfield, PA, USA) unit or the

3D Accuitomo unit (J. Morita, Kyoto, Japan). The radiologic findings were then correlated

with surgical exploration. This study reported specificity and sensitivity of 75% and 88%,

respectively.59

In another study, Metska et al. evaluated 39 endodontically-treated teeth with

the clinical and radiographic signs and symptoms of vertical root fracture with two cone beam

CT systems. Twenty-five teeth were scanned with a NewTom 3G (QR SLR, Verona, Italy)

with voxel size of 0.20 mm and fourteen were scanned with a 3D Accuitomo (J. Morita,

Kyoto, Japan) with voxel size of 0.08 mm. The NewTom 3G has an image intensifier/charge

coupled device detector and a voxel size of 0.20 mm, and the 3D Accuitomo 170 incorporates

a flat panel detector and a voxel size of 0.08 mm. The specificity and sensitivity reported for

the 3D Accuitomo was 80% and 100%, respectively, and 56% and 75% for the NewTom 3G.

They postulated that these differences were attributed by three factors: the quality of the scans,

the presence of metal artifacts, and the experience of observers.30

Also Wang et al. in a study

of evaluation of 49 endodontically-treated teeth with signs and symptoms of root fracture and

using 3D Accuitomo 80 (J. Morita, Kyoto, Japan) with voxel size of 0.125 mm reported

specificity and sensitivity of 100% and 71.4%, respectively. The diagnosis was then confirmed

by surgical intervention as a part of the treatment such as extraction, amputation or root-end

resection.14

25

Table 1.4: Summary of the results of in vivo studies of endodontically-treated teeth using cone beam CT for the diagnosis of vertical

root fractures.

Study Sample Cone beam CT imaging system Gold standard Results

Edlund et al.,

201159

33 teeth in 29 patients

with clinical signs and

symptoms suspicious of

vertical root fracture.

i-CAT, 0.125 mm voxel or


Endodontic

surgery

Specificity: 75%

Sensitivity: 88%

Accuracy: 84%

Wang et al., 2011 14

49 teeth with clinical

signs and symptoms

suspicious of vertical

root fracture

3D Accuitomo, 0.125 mm voxel Surgical

intervention

Specificity: 100%

Sensitivity: 71.4%

Metska et al.,

201230

39 teeth from 39 patients

with clinical and

radiographic signs and

symptoms suspicious of

vertical root fracture.


or NewTom 3G, 0.20 mm voxel

Orthograde

retreatment,

endodontic

microsurgery,

or extraction of

the tooth

3D Accuitomo

Specificity: 80%

Sensitivity: 100%

Accuracy: 93%

NewTom 3G

Specificity: 56%

Sensitivity: 75%

Accuracy: 68%

26

In the only study that evaluated teeth for horizontal root fractures in the presence of

intra-canal metallic posts, Costa et al. using the PaX Uni3D (Vatech, Suwon, Korea) with a

voxel size of 0.20 mm reported a significant reduction of both specificity and sensitivity of

cone beam CT. The specificity of horizontal root fracture detection in absence and presence of

intra-canal metallic post ranged from 60% to 95% and 45% to 85%, respectively. They also

reported sensitivity ranges of 65% to 85% in the absence of metallic posts with three different

observers. When a metallic post was present, sensitivity significantly decreased to between

40% and 65%. 51

Bernardes et al. conducted a study of 20 patients of endodontically-treated teeth with

suspected root fractures using the 3D Accuitomo (J. Morita, Kyoto, Japan). Only 15 out of 18

root fractures were symptomatic. These workers found root fractures in 18 cases while

conventional periapical radiographs showed the presence of such fractures in only 8 cases,

although the types of fracture were not specified. A significant weakness of this study was that

the radiologic findings were not confirmed surgically.39

1.8 Statement of the Problem

While there have been several publications related to the identification of root fractures

using cone beam CT, many of the variables in these studies have been poorly controlled.

Some studies have been performed in vitro and others, in vivo, and some studies have had

anatomical correlation, while others have not. In some studies, the methods used to induce the

fractures (e.g., chisel and hammer, disc and hammer) were not be reliable, resulting in

fragmentation of tooth material and loss of some particles. In some studies, images of different

voxel sizes were used as well as systems with different image receptors and field-of-view

sizes. Some studies incorporated teeth that have been endodontically-treated or have had metal

posts inserted. In some studies, images were evaluated by radiologists, in some by

endodontists and in some by a combination of both.

Coupled with a more precise method for inducing predictable fractures, our study was

designed to compare the specificity, sensitivity, and positive and negative predictive values of

projection digital intra-oral radiography with cone beam CT images acquired using four

27

different voxel sizes in the detection of vertical and horizontal root fractures using the same

set of radiologic phantoms and the same imaging system.

1.9 Objectives and Hypotheses

The primary objective of this study is to determine if voxel size affects the detection of

vertical and horizontal root fractures on cone beam CT images.

The secondary objectives are:

1. To calculate the specificity, sensitivity, and positive and negative predictive

values of different resolutions of cone beam CT scan in detection of vertical

and horizontal root fractures.

2. To determine if the detection of root fracture is influenced by the level of

experience of the observers.

3. To determine if the detection of root fractures is influenced by the type of the

tooth.

4. To compare the cone beam CT of different resolutions with projection

periapical images made using a complementary metal-oxide

semiconductor (CMOS) detector for the identification of root fractures.

1.10 Null Hypotheses

Our primary hypothesis was that there are no differences between different voxel sizes

for detection of horizontal or vertical root fractures using cone beam CT.

The secondary hypotheses of this study are:

1. There are no differences in specificity, sensitivity, and positive and negative

predictive values of cone beam CT images made with lower voxel size and

cone beam CT studies with higher voxel sizes.

2. There are no differences between observers with different levels of experience

in their abilities to detect root fractures.

28

3. There are no differences in root fracture detection between different teeth

imaged with cone beam CT.

4. There are no differences in root fracture detection between a complementary

metal-oxide semiconductor (CMOS) detector and cone beam CT scans made

with different voxel sizes.

29

Chapter 2

2 Methods and Materials

2.1 Sample Preparation

This study has been approved by the Health Sciences Research Ethics Board of

university of Toronto. Forty-five intact, extracted human teeth were used in this study, of

which there were 9 incisors, 18 premolars and 18 molars. The teeth were stored in 1%

formalin solution after extraction. Teeth with gross caries or restorations were not used. The

teeth were also evaluated for the presence of a root fracture with a disclosing agent, methylene

blue (Vista-Blue, Vista Dental Products, Racine, WI). The teeth were then randomly divided

into three groups of 15 teeth each. Vertical root fractures were induced in one group of 15

teeth, horizontal root fractures were induced in a second group, and 15 teeth were left intact.

A sample size calculation was performed addressing the primary objective of

examining the ability of cone beam CT to detect root fractures.43

The targeted significance

level of the test was 0.05 with a minimum 90% power. A sample size of 30 fractured teeth and

15 non-fractured achieves 99% power to detect a difference of 0.217 between the area under

curve under the null hypothesis and the area under curve under the alternative hypothesis

using a two-sided z-tests.

To induce vertical root fractures, a “bench vice” was used to apply a force along the

long axis of the tooth (Figure 2.1). The vertical root fractures were incomplete and in the cases

where the forces result in a complete separation of the two fragments, the tooth was discarded.

To induce horizontal root fractures, the teeth were fractured manually. So that the fragments

could be placed into the tooth block, the fragments of the horizontally-fractured teeth were

then glued back together in their original relationship with Advanced Instant Glue (Elmer’s

products, Toronto, ON, CA).

30

Figure 2.1: The bench vice used to induce vertical fractures

The disclosing dye, methylene blue (Vista-Blue, Vista Dental Products, Racine, WI),

was used to trace the fractures induced by the fracture methods. The teeth were also checked

for the presence of more than one fracture, and the teeth with more than one fracture were

discarded.

All the teeth were then covered with a 0.5 to 1 mm layer of rose wax in order to mimic

the periodontal ligament space radiographically, and also to produce the image contrast

between tooth structure and surrounding stone. The teeth were then randomly divided into 9

groups of 5 teeth, with each group consisting of one incisor, two premolars and two molars.

The teeth were then fixed in a straight line in a box filled with stone (Microstone Golden,

Whip Mix Corp, Louisville, KY) (Figure 2.2).

Figure 2.2: Five teeth mounted in stone in the same manner as inside the mouth.

31

2.2 Image Acquisition

Each group of teeth was then scanned with the Kodak 9000 3D cone beam CT system

(Carestream, Rochester, NY, USA) operating at 65 kVp and 2.5 mA at the native voxel size of

76 μm. The samples were positioned on the edentulous chin rest with the central line being

centered on the sample. (Figure 2.3)

Figure 2.3: Samples were centered in the center of the field of view.

The raw images were then downsampled to voxel sizes of 100, 200, and 300 μm. The

downsampling was performed using the Kodak Dental Imaging software (Carestream,

Rochester, NY, USA) (Figures 2.4 and 2.5). These voxel sizes were chosen based on the

available downsampling options in the Kodak Dental Imaging software.

32

A B C D

Figure 2.4: Bucco-lingual cross sectional slices of a molar with a vertical root fracture at

voxel sizes A) 76 μm; B) 100 μm; C) 200 μm; and D) 300μm.

A B C D

Figure 2.5: Bucco-lingual cross sectional slices of an incisor with a horizontal root fracture at

voxel sizes A) 76 μm; B) 100 μm; C) 200 μm; and D) 300 μm.

2.3 Image Evaluation

The images were anonymized using OsiriX software (Version 3, Pixmeo SARL,

Geneva, Switzerland) and were coded on the basis of the sequence of each observation

session. The sequences of the images were randomized for each observer using Microsoft

Excel software (Microsoft Corp., Redmond, WA, USA).

33

A total of five observers were used for this study. Two second year oral radiology

graduate students, one non-certified oral radiologist with 18 years experience and two certified

oral radiologists, one with 19 years experience and one with 5 years experience, reviewed the

randomized images at weekly intervals over a four week period with a one week washout

period between each group of observations. The observers were blinded to the presence or

absence of a fracture, and voxel size (resolution). The images were reviewed using In Vivo 5.2

software (Anatomage, San Jose, CA, USA.) under dimly-lit lighting conditions using the same

Dell (Dell Corporation, Round Rock, TX, USA) 23” UltraSharp monitor. The observers were

free to manipulate the images using contrast and brightness settings, and zoom in the software.

The observers were asked to record the absence or presence of a fracture in each tooth.

If a fracture was seen, observers were asked to determine if it was vertical or horizontal. A

fracture was considered vertical if it was angled at less than 45 degrees relative to the long

axis of the tooth. A fracture was considered to be horizontal if the angle of the fracture was

greater than 45 degrees relative to the long axis of the tooth. The observers were also asked to

provide a level of confidence from one to 10, with one representing the lowest and 10

representing the highest level of confidence for all teeth. And finally, observers were asked to

record the amount of the time they spent on each tooth making a determination.

2.4 Projection Radiography Study

To take full advantage of the experimental material, 90 periapical images were

obtained from the samples using the CDR digital sensor (Schick Technologies Inc., Long

Island City, NY, USA) with the pixel size of 40 μm. The exposures were made using a

Progeny Preva intra oral x-ray system (Progeny, A Midmark Company, Lincolnshire, IL,

USA) operating at 65 kVp and 5 mA with a focus-to-object distance of 15 centimeter and

focal spot size of 0.4 mm. The exposure time chosen for the incisors and premolars was 0.4

sec and the exposure time for the molars was 0.5 sec. Two periapical images were made of

each tooth from two different angulations; one at zero degrees and a second at 15 degrees to

the long axis of the tooth (Figures 2.6 and 2.7). In order to increase the quality of the

34

periapical images, the thickness of the stone was reduced to 15 mm by trimming 9 mm of

thickness.

A B

Figure 2.6: Periapical images of a molar with a vertical root fracture (presented in Figure 2.4)

with angulations of A) zero degrees; and B) 15 degrees to the long axis of the

tooth.

A B

Figure 2.7: Periapical images of a central incisor with a horizontal root fracture (presented in

Figure 2.5) with angulations of A) zero degrees; and B) 15 degrees to the long

axis of the tooth.

The paired image files were saved in .jpg format and then exported into a PowerPoint®

(Microsoft Corp., Redmond, WA, USA) file. Both 0 degree and 15 degree images of each

35

tooth were presented in the same .pdf (Adobe Corp., San Jose, CA, USA) image. The same

five evaluators evaluated the images in the same way that they did for the cone beam CT

study.

2.5 Data Analysis

Statistical analysis was performed using the SPSS Statistics software, version 21.0

(IBM SPSS, Chicago, Il, USA). Specificity, sensitivity, positive predictive value and negative

predictive value were calculated for the vertical and horizontal root fracture group, and for the

2 groups, combined. Specificity and sensitivity are measurements of binary tests; Specificity

shows the part of true negatives and sensitivity indicates the part of true positives which have

been correctly identified by the test . A positive predictive value represents the proportion of

subjects with positive results and a negative predictive value represents the proportion of

subjects with negative results which are correctly diagnosed.

Receiver operating characteristic (ROC) curves were generated for each resolution,

and for the fractures together as a group, and separately (vertical and horizontal). In a ROC

curve, sensitivity is plotted as function of 100 - specificity. McNemar’s test was used to

determine if there were statistically significant differences between voxel sizes for the

detection of fractures as a group, and separately (vertical and horizontal). Also, a Chi-square

test was used to determine if there were differences between the observer groups in the

detection of fractures. An independent sample t-test was used to compare the time spent by

each observer group in detection of the fractures. Finally, a Chi-square test was also used to

compare the results of periapical radiographs with each voxel size.

2.6 Observers Agreement

In order to evaluate the intra-observer agreement, one of the observers volunteered to

review a subset of the images the second time. Eight cone beam CT studies and 10 periapical

images were randomly chosen to review by this observer. Microsoft Excel (Microsoft Corp.,

36

Redmond, WA, USA) software was used to randomize the images. For the periapical images,

the first 10 image pairs were chosen after randomization for this purpose. For the cone beam

CT studies, two scans was chosen for each voxel size. Kappa (κ) test was used to measure the

intra-observer agreement as well as the inter-observer agreement. The inter-observer

agreement was measured using the average of the values of Kappa (κ) for pairs of observers. 60

37

Chapter 3

3 Results

3.1 Diagnostic Test Results for CT Images

The results of the specificity, sensitivity, positive predictive value and negative

predictive value of each resolution of all observers and for all fractures are provided in Table

3.1, and the receiver operating characteristic (ROC) curves of each resolution are provided in

Figure 3.1. The areas under the ROC curves are shown in Table 3.2. Higher specificity,

sensitivity, and positive and negative predictive values were found for the 100 µm voxel size

and for the area under the 100 m voxel size ROC curve.

Table 3.1 Specificities, sensitivities, positive and negative predictive values for each :

resolution and all root fractures for the cone beam CT images.

Voxel Size

Test Results

76 µm

100 µm

200 µm

300 µm

Specificity 70.7% 76.0% 70.7% 74.7%

Sensitivity 64.7% 66.0% 62.7% 54.0%

Positive Predictive Value 81.5% 84.6% 81.0% 81.0%

Negative Predictive Value 50.0% 52.8% 48.6% 44.8%

38

Figure 3.1: ROC curves for all root fractures and all voxel resolutions.

Table 3.2 Areas under the receiver operator curves for different voxel resolutions and all root :

fractures.

Area Under Curve

76 µm 0.565

100 µm 0.593

200 µm 0.557

300 µm 0.558

39


predictive value of each resolution of all observers and vertical fractures are provided in Table

3.3, and the receiver operating characteristic (ROC) curves of each resolution are provided in

Figures 3.2. The area under curve is provided in Table 3.4 associated with Figure 3.2.

Higher specificity, sensitivity, and positive and negative predictive values were found

for the 100 µm voxel size and for the area under the 100 m voxel size ROC curve. 200 m

voxel size also showed higher specificity.

Table 3.3 Specificities, sensitivities, positive and negative predictive values for each .

resolution and vertical root fractures for the cone beam CT images.

Voxel Size

Test Results

76 µm

100 µm

200 µm

300 µm

Specificity 70.6% 76.0% 70.6% 74.6%

Sensitivity 64.0% 66.7% 61.3% 50.7%



40

Figure 3.2: ROC curves for vertical root fractures only and all voxel resolutions.

Table 3.4 Areas under the receiver operator curves for different voxel resolutions and vertical :

root fractures only.

Area Under Curve

76 µm 0.609

100 µm 0.629

200 µm 0.598

300 µm 0.607

41


predictive value of each resolution of all observers and horizontal fractures are provided in

Table 3.5, and the receiver operating characteristic (ROC) curves of each resolution are

provided in Figures 3.3. The area under curve is provided in Table 3.6 associated with Figure

3.3. Higher specificity and positive predictive value were found for the 100 m voxel sizes,

higher sensitivity was found for 76 m, and higher negative predictive value was found for

100 m and 76 m. The area under the 100 m voxel size ROC curve was also highest

amongst the different voxel sizes.

Table 3.5 Specificities, sensitivities, positive and negative predictive values for each .

resolution and horizontal root fractures for the cone beam CT images.

Voxel Size

Test Results

76 µm

100 µm

200 µm

300 µm

Specificity 70.6% 76.0% 70.6% 74.6%

Sensitivity 45.3% 41.3% 44.0% 29.3%



42

Figure 3.3: ROC curves for horizontal root fractures only and all voxel resolutions.

Table 3.6 Area under the receiver operator curves for different voxel resolutions and :

horizontal root fractures only.

Area Under Curve

76 µm 0.520

100 µm 0.558

200 µm 0.515

300 µm 0.510

43

3.2 Comparison of Voxel Sizes and Fracture Detection

McNemar’s test was performed to determine if there is any significant difference

between the voxel sizes in the detection of root fractures. The test failed to indicate a

significant difference between the voxel sizes (see Table 3.7). Voxel size had no impact on

fracture detection.

Table 3.7: Comparison between each pair of voxel sizes in detection of all root fractures for

all observers.

Voxel Size p value

76 µm vs. 100 µm 1.000

76 µm vs. 200 µm 0.453

76 µm vs. 300 µm 0.146

100 µm vs. 200 µm 0.754

100 µm vs. 300 µm 0.180

200 µm vs. 300 µm 0.581

McNemar’s test was performed to determine if there is any significant difference

between the voxel sizes in the detection of horizontal and vertical root fractures. The test

failed to indicate a significant difference between the voxel sizes (see Tables 3.8 and 3.11).

44

A Chi-square test was performed to compare the abilities to detect vertical and

horizontal root fractures. This test showed that the detection of vertical root fractures was

significantly better than the detection of horizontal root fractures (p<0.001).

Table 3.8: Comparison of voxel sizes in detection of vertical root fractures only for all

observers.

Voxel Size p value

76 µm vs.100 µm 1.000

76 µm vs. 200 µm 1.000

76 µm vs. 300 µm 0.125

100 µm vs. 200 µm 1.000

100 µm vs. 300 µm 0.250

200 µm vs. 300 µm 0.250

Using McNemar’s tests, a significant difference was indicated between the voxel sizes

of 100 µm and 300 µm in the graduate student group (p value<0.05) in detection of vertical

root fractures (Tables 3.9, 3.10).

45


radiology graduate student group.

Voxel Size p value

76 µm vs.100 µm 0.629

76 µm vs. 200 µm 0.442

76 µm vs. 300 µm 0.189

100 µm vs. 200 µm 0.832

100 µm vs. 300 µm 0.041*

200 µm vs. 300 µm 1.000

*

p value <0.05

46


radiologist group.

Voxel Size p value

76µm vs.100µm 0.791

76µm vs. 200µm 0.424

76µm vs. 300µm 0.092

100µm vs. 200µm 0.774

100µm vs. 300µm 0.180

200µm vs. 300µm 0.549

47

Table 3.11 : Comparison of voxel sizes in detection of horizontal root fractures only for all

observer groups.

Voxel Size p value

76µm vs.100µm 0.688

76µm vs. 200µm 0.250

76µm vs. 300µm 0.344

100µm vs. 200µm 1.000

100µm vs. 300µm 0.754

200µm vs. 300µm 1.000

McNemar’s tests showed that there was no significant difference between voxel size in

the detection of horizontal root fractures by either oral radiology graduate students or oral

(Tables 3.12, 3.13). radiologists

48

Table 3.12 : Comparison of voxel sizes in detection of horizontal root fractures only in the

oral radiology graduate student group.

Voxel Size p value

76µm vs.100µm 0.481

76µm vs. 200µm 1.000

76µm vs. 300µm 0.728

100µm vs. 200µm 0.711

100µm vs. 300µm 1.000

200µm vs. 300µm 0.856

49


oral radiologist group.

Voxel Size p value

76µm vs.100µm 0.607

76µm vs. 200µm 0.481

76µm vs. 300µm 0.064

100µm vs. 200µm 1.000

100µm vs. 300µm 0.210

200µm vs. 300µm 0.359

3.3 Comparison of the Observers

The results of comparison of oral radiology graduate students and oral radiologists in

the detection of both types of fractures, and then vertical and horizontal fractures separately,

are reported in Tables 3.14, 3.15 and 3.16, respectively.

Oral radiologists detected all fractures at 300 m voxel resolution more effectively

than the oral radiology graduate students. For vertical fractures, oral radiologists outperformed

oral radiology residents at 76 m, 200 m and 300 m voxel sizes. For horizontal fractures

there was no difference between the two groups.

50


of both types of fractures with each voxel size (df: 1/n: 150).

Voxel Size Chi Square value p value

76 µm 2.025 0.155

100 µm 1.468 0.226

200 µm 0.146 0.699

300 µm 7.242 0.007*

* p value <0.05


of vertical fractures with each voxel size (df: 1/n: 150).


76 µm 6.916 0.009*

100 µm 0.087 0.768

200 µm 3.882 0.049*

300 µm 8.781 0.003*

* p value <0.05

51


of horizontal fractures with each voxel size (df: 1/n: 150).


76 µm 1.331 0.249

100 µm 0.543 0.461

200 µm 3.357 0.067

300 µm 1.977 0.160

3.4 Comparison of Type of Tooth

The result of comparisons of diagnostic efficacy of fractures based on the tooth type

(incisor, molar and premolar) is presented in the Tables 3.17, 3.18, 3.19, 3.20, and 3.21. There

were no differences in fracture detection based on tooth type.


(df:1).

Voxel Size Chi Square value p value n

Incisors vs. Premolars 0.386 0.535

27

Incisors vs. Molars 0.089 0.766 27

Premolars vs. Molars 0.148 0.700

36

52


(df:1).


Incisors vs. Premolars 3.068 0.080 27


Premolars vs. Molars 0.131 0.717 36


(df:1).





53


(df:1).

Voxel size Chi Square value p value n

Incisors vs. Premolars 1.918 0.166

27


Premolars vs. Molars 1.870 0.171

36

Table 3.21: Comparison of detection of root fractures between teeth in periapical radiographs

(df:1).

Voxel size Chi Square value p value n




54

3.5 Comparisons of Time

The mean time spent on each tooth in detection of the root fracture for voxel sizes 76

µm, 100 µm, 200 µm, and 300 µm was 90.1, 85. 6, 91.0 and 84.1 seconds, respectively. The

independent sample T-test indicated that the mean time spent by the oral radiology graduate

students evaluating 300 µm voxel size (99.9 ± 124.0 sec) was significantly higher than the

mean time spent by oral radiologists (73.6 ± 66.2 sec). This was significant to p<0.05.

However, there was no significant difference between time spent on each tooth by the oral

radiology graduate students and oral radiologists in detection of root fractures with any other

voxel sizes (Table 3.22).

Table 3.22: Comparison of the mean time (seconds) spent by oral radiology graduate students

and oral radiologists in the detection of root fractures with each voxel size

(df:223).

Voxel Size Mean SD p value

Oral

Radiology

graduate

students

Oral

Radiologists

Oral

Radiology

graduate

students

Oral

Radiologists

76µm 97.8 84.9 97.1 91.5 0.312

100µm 96.64 78.2 116.5 84.1 0.169

200µm 86.68 93.9 84.7 94.6 0.560

300µm 99.87 73.6 124.0 66.2 0.040*

*p value< 0.05

55

3.6 Diagnostic Test for Digital Periapical Images

Significant difference was observed between observers’ abilities to detect fractures on

periapical radiographs compared to voxel sizes of 76 µm, 100 µm, and 200 µm (p < 0.05).

These results are summarized in Table 3.23.

Table 3.23: Comparison of each voxel size with periapical radiographs in detection of root

fractures (df:1/n:90).


Periapical radiographs vs. 76 µm 4.630 0.031*



Periapical radiographs vs. 300 µm 2.217 0.136

*p value< 0.05

3.7 Observers Agreement

The results of intra and inter observer agreement are provided in the table 3.24. The

strength of the Kappa (κ) values was interpreted using the guidelines provided by Landis and

Koch (<0.00, poor; 0.00 to 0.20, slight; 0.21 to 0.40, fair; 0.41 to 0.60, moderate; 0.61 to 0.80,

substantial; 0.81 to 1.00, almost perfect).59

56

Table 3.24: Kappa values for the intra and inter observer agreement for each resolution and

periapical radiographs.

Imaging Type Inter-Observer Intra-Observer

Kappa (κ) Interpretation Kappa (κ) Interpretation

All cone beam CT 0.3 Fair 0.62 Substantial

76 µm 0.4 Fair 0.49 Moderate

100 µm 0.33 Fair 0.56 Moderate

200 µm 0.34 Fair 0.7 Substantial

300 µm 0.23 Fair 0.69 Substantial

Periapical 0.44 Moderate 0.7 Substantial

57

Chapter 4

4 Discussion

4.1 Overview

There have been multiple studies evaluating the role of cone beam CT in the detection

of root fractures, yet there has been little or no general consistency in the methodologies.

Some studies have been performed using in vitro models and others have involved patients.

Some studies have examined only vertical or horizontal fractures, and some have examined

endodontically-treated teeth while others have examined teeth with metal posts in place.

Some have used smaller field-of-view cone beam CT systems with small voxel sizes while

others have used larger field-of-view systems with larger voxel sizes. The number of different

variables in these studies has made the body of literature on this topic very confusing.

The literature evaluating tooth fractures using cone beam CT has reported wide ranges

of results. The specificity and sensitivity of cone beam CT for the detection of vertical root

fractures varies from 56% to 100% and 18.8% to 100%. By comparison, the specificity and

sensitivity for horizontal root fractures varies from 45% to 97% and 40% to 94%. These

variations suggest that there are multiple factors that may be involved in the accuracy of

diagnosis of root fractures with cone beam CT. These factors can be classified into factors

related to the cone beam CT system itself, observer experience, and factors related to the

patient. Although it is not possible to control every variable, we have attempted, in the present

study, to control as many as possible so that direct comparisons can be made.

The production of cone beam CT images involves four stages: 1) acquisition; 2) image

detection; 3) image reconstruction; and 4) image display. 38

The factors involved in each of

these stages may influence the quality of the cone beam CT volume and rendered images.

Each cone beam CT system has its own set of unique features including the type of the

detector, native voxel size field-of-view, and operating parameters (kVp and mA).

Two types of image detectors are used in cone beam CT systems to acquire the images;

the image intensifier tube/charge couple device detector and the flat-panel detector.57

Miles et

58

al. stated that the quality of images of cone beam CT systems with flat-panel detectors is

higher than those with image intensifier tube/charge couple device due to higher x-ray photon

collection efficiency. This is reported to be 50% for the image intensifier/charge couple device

detector and 98% for flat-panel detectors.61

The detector used in Kodak 9000 3D is also

amorphous flat panel.

Another factor involved in the reported higher performance of imaging systems is the

voxel size of the image detector. Hassan et al. evaluated vertical root fractures using 5 cone

beam CT systems, and reported a significantly higher sensitivity with i-CAT (Imaging

Sciences, Hatfield, PA, USA) (77.5%) and Scanora 3D (Soredex, Tuusula, Finland) (57.5%)

in comparison to the three other systems evaluated. In both systems, the detector type used

was flat-panel.57

The voxel size used for the i-CAT in their study was 0.25 mm and the voxel

size for the Scanora 3D was 0.20 mm. The voxel size used for the NewTom 3G system (QR

SLR, Verona, Italy) in this same study was also 0.20 mm (detector type for the NewTom 3G

system is a flat-panel detector). Since the overall sensitivity of this system (30.4%) is lower in

comparison to the two other systems, there may be other internal or external factors (including

the number of the basis projections, data reconstruction algorithms and machine-specific

artifacts).51

In this same study, only the Galileos 3D system (Sirona Germany, Bensheim,

Germany) showed significantly better diagnosis efficacy in detecting fractures between

endodontically-treated and non-treated teeth, suggesting that this system may be more capable

of artifact suppression.

In the present study, we used the same Kodak 9000 3D system for all of our cone beam

CT acquisitions, which operates at a native voxel resolution of 76 m. We were then able to

downsample the native resolution images to images of lower resolution using the imaging

system’s own software without affecting the positions of the phantoms. Our results agree with

the work of Ozer42

, who found higher specificity and sensitivity with voxel sizes 0.125 and

0.20 mm. In our study, we found higher specificity and sensitivity of fracture detection with a

voxel size of 0.10 mm. In another study evaluating the effect of voxel size in detection of

stimulated external root resorption with different sizes, Liedke et al.43

did not find any

differences between voxel sizes of 0.20, 0.30 and 0.40 mm. These workers considered the size

0.30 mm voxel size to be the most effective for the diagnosis of external root resorption

59

because both diagnostic performance and patient radiation dose were balanced. Unlike our

study, both the Ozer and Liedke results were based on different acquisitions with different

acquisition times for the same phantom which could potentially confound their results. In the

only study evaluating the effect of different cone beam CT exposure parameter on the

accuracy of the cone beam CT images, Vandenberghe et al. found that exposure time and

voxel size have a significant role in differentiation of cortical borders and transition with

surrounding soft tissue in the jaw bone models.62

This may also influence the result of

the previous studies evaluating the role of voxel size in detection of root fractures,

since they used different exposure time.

The specificities, sensitivities, and positive and negative predictive values we reported

are within the ranges reported in previous studies.14,34,40,53,55,57

These results agree with the

results from previous studies. We did, however, find that the 100 µm voxel size performed

better than the others; even the smaller 76 m size. Although the use of smaller voxel sizes

result in higher resolution images, less “blurring” of the image and less potential for volume

averaging, smaller voxel sizes increase image noise and contribute to a reduction of the

contrast-to-noise ratio.50

With a marginally larger voxel size, there may be less noise

degradation of image quality, and this may reduce the difficulty of fracture detection. The

variation between higher specificity and sensitivity in our study in comparison with other

studies may be attributed, in part, to the method used to induce the fractures in our study;

Factors including the degree of separation of fragments and loss of some tooth particles may

play role in detection of root fractures. In the present study, we tried to keep the loss of tooth

particles as low as possible. That the treatment of teeth with root fracture can vary between

endodontic treatment and extraction, the higher specificity of cone beam CT is an important

outcome.

In the present study, we also compared the ability of detection of root fractures using

cone beam CT with periapical radiographs made at two angulations. The detection of root

fractures with voxel sizes 76 µm, 100 µm and 200 µm was significantly better than periapical

radiographs (p<0.05). No significant difference was observed in the detection of root fractures

between periapical radiographs and a voxel size of 300 µm. These results show that the

elimination of superimposition of adjacent structure including the surrounding material (e.g.

60

stone and bone) and other roots in three-dimensional images, manipulation of the images and

changing the angle of the image slice to align with possible fractures are some of the factors

that may play a major role in detection of root fracture. However, this is not the only factor

having a role in the detection of root fractures. Others who have compared cone beam CT with

periapical radiographs have also reported significant differences between fracture

detection.14,20,25,34

On the other hand, Silveira et al. in their study did not find any statistical

difference among the images in diagnosis of vertical root fractures. In their study, they

compared i-CAT (Imaging Sciences, Hatfield, PA, USA) images made with two voxel sizes

0.20 mm and 0.30 mm with images made using ANSI D speed films made using three

different horizontal angulations. They did not provide any specific reason for lack of

difference in their study.54

In the present study, the efficacy of detection of vertical root fractures was

significantly better than the detection of horizontal root fractures (p<0.001). This could be

due, in part, to the methods to create the tooth block phantoms. For horizontal root fractures,

the exact matching fragments had to be glued together in order to enable us to place them in

the stone without the 2 fragments separating from one another. Consequently, this made the

separation of the horizontal fracture fragments similar to cracks, making fracture detection

more challenging. This is the same method used by Ozer to induce cracks in his study

evaluating the effect of thickness of fracture lines in their diagnosis by cone beam CT scan.63

In the teeth with vertical root fractures, glue was not used because these fragments did not

separate when placed into the stone. The significant difference between the detection of

vertical and horizontal root fractures underpins the importance of the effect of separation on

the ability to detect fractures.

No significant differences were observed in detection of root fractures between

different types of teeth. We hypothesized that detection of root fractures in multi-rooted teeth

is more difficult because of superimposition of other roots on the fracture line. This, however,

was not the case, likely because the tomographic method abrogated any potential for

superimposition.

61

We achieved fair inter-observer agreement in detection of root fractures with cone

beam CT scan and moderate inter-observer agreement in detection of fractures with periapical

radiographs. The higher inter-observer with periapical radiographs can be attributed to greater

familiarity of the observers with two-dimensional images and also the different level of

experience between the observers. The intra-observer agreement of cone beam CT studies and

periapical radiographs was moderate to substantial, which can be contributed to the level of

experience of the observer who did the second session of the observations.

In order to improve diagnosis using cone beam CT images, the clinician must be

familiar with the three dimensional display of anatomy and image manipulation.58

Our results

indicated that there was no significant difference in detection of both types of root fractures

between oral radiology graduate students and oral radiologists at any voxel sizes except for

300 µm. Although we did not find any significant difference in detection of horizontal root

fracture between the two observer groups we did find a significant difference in detection of

vertical root fractures at all voxel sizes except for 100 µm for both groups. To date, there has

been no previous study evaluating the effect of experience on the diagnosis of root fractures.

The mean time spent on each tooth in detection of root fractures by the oral radiology

graduate students was significantly higher than the mean time spent by the oral radiologist

group with a voxel size of 300 µm. The significant difference between the time spent by these

two groups shows the importance of the role of level of experience in the pace of detection of

root fractures, particularly at higher voxel sizes. In this study, oral radiologists had five years

or more experience.

Clinically, fractures without displacement of the fragment are difficult to diagnose;

consequently the diagnosis of this type of fracture may rely to a greater degree on clinical

observations.5,22,58

Ozer in his study evaluated the efficacy of cone beam CT in the diagnosis

of cracked teeth, with 0.20 mm and 0.40 mm fracture thicknesses. Although he did not find

any significant difference in the diagnostic ability of cone beam CT scan to detect fractures

under either condition, the separation of vertical root fracture fragments was inversely related

to the accuracy of cone beam CT in diagnosing them.63

The significantly better result in the

62

detection of the vertical root fractures as well as the methods we used in preparation of the

vertical and horizontal root fractures is a confirmation of this finding.

Although we did not find any significant difference in detection of root fractures with

different voxel sizes, there are other factors which should be considered when deciding the

type of the cone beam CT machine in diagnosis of root fractures. These factors include dose to

the patient and cone beam CT system availability. There is a large variation in radiation dose

received by the patient with different cone beam CT scan systems. It has been reported that

the radiation exposure reduces as the voxel size reduces.19

There is wide variation in effective radiation dose with different types of cone beam

CT systems. Factors that contribute to this variation include the imaging parameters used

(kVp, mAs), a pulsed versus continuous beam, the amount, type, and shape of the beam

filtration, the number of basis images created, field-of-view size and voxel size.33

Lower voxel

resolution acquisitions require less scanning time, and this decreases patient radiation dose as

well.43

Thus, not only was the highest performance observed with a voxel size of 100 µm in

our study, but the fact that the radiation exposure was comparably lower indicate that it may

be the best voxel size to use in detection of root fractures, balancing the risks and benefits

associated with that.

4.2 Study Limitations

One of the limitations of this study is that fractures induced in vitro may be different

from the fractures encountered clinically. The most challenging cases to diagnose clinically

are those without displacement of the fracture fragments. By the nature of the study design, no

considerations were given to the contributions of indirect signs of fracture that could

potentially be evaluated in an intact biological system. For example, useful indirect

information that could suggest fracture might include changes to the periodontal ligament

space, the presence of areas of rarefying osteitis developing at the site of fracture or at the

tooth root apex, the development of a fistula, changes to the position of the coronal fragment

in the dental arches, and changes to the response of the tooth to temperature or percussion, to

63

name a few. Also, the density of the surrounding stone may not be exactly same as the density

of bone and soft tissue together and it may show different absorption in compared to real

situation. Due to time restrictions, only one of the observers were able to review the images

for the second time to calculate the intra-observer agreement.

4.3 Future Directions

Future studies should focus objectively evaluating image quality of different voxel

resolution images, and relate this to the diagnostic efficacy of fracture detection. Although we

used a very small native voxel size, high resolution images compromise image signal-to-noise.

Although this may be difficult to mimic in an in vitro study, thought could be given to

designing a model of tooth fracture where fragments could be displaced linearly or at variable

angles to on another. Conducting a prospective clinical study, but with anatomical verification

of fracture, using an image evaluation protocol similar to the one used in this study could also

be performed. Finally, a future study may also determine the influence of indirect signs of

fractures on fracture detection rates.

4.4 Clinical Implications and Conclusions

With recent advances in cone beam CT technology as well as the increasing

availability of different types of cone beam CT systems, small field-of-view high resolution

imaging systems like the one used in these experiments is becoming more popular among

dentists. Our study suggests that for the detection of root fractures, the 100 µm voxel size may

be the most optimal for this task balancing image noise and contrast. However, lack of

statistically significant differences between different voxel sizes in detection of root fractures

encourages the clinicians to consider other factors such as radiation dose in their decision.

64

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Appendix 1

Copy of the ethics approval of the research

73

Appendix 2

Consent Form for the observers

Title

The effect of the voxel size on the identification of vertical and horizontal root fractures by cone beam computed tomography in an in-vitro study.

Introduction

The aim of this study is to determine the effects of the voxel size on the identification of vertical and horizontal root fractures by cone beam CT scan in an in vitro study.

Study Procedure

If you agree, you will be asked to participate in four sessions, each one week apart, for evaluation of the cone beam CT studies. In each session, you will review nine series of images; each series contains five teeth, some of which have a fracture and some that do not. You will be asked to decide if the fracture is present or not, and in the cases that the fracture is present you will be ask to classify that as a vertical type or horizontal type. You will be asked to record the time after evaluation of each tooth. The estimated time for each session is 5 hours.

Benefits and Risks

There are no known risks to you from participating in this study. The results do not reflect your academic or professional abilities.

Subject Rights

Your participation in this study is voluntary. You may withdraw from the study at any time without penalty. If you are a graduate student, your refusal or withdrawal from the study will not affect any academic evaluations. You will be provided with an email address if you need to ask questions about the study at any time.

Confidentiality

All information collected about you and your observations in this study will be confidential. No individual information will be disclosed. The data will be securely stored. No one will have access to these data except the primary investigator. Ten years after completion of the study, all information will be destroyed. Researchers will use the results of this study to write scientific papers and present at scientific conferences.

Contact

74

Dr. Niloufar Amintavakoli is the principal investigator under the supervision of Dr. Ernest Lam ([email protected]). If you need any further information about the study, you can contact Dr. Niloufar Amintavakoli by email at ([email protected]).

Consent Agreement

I acknowledge that the procedures of this study have been explained to me clearly. I had the opportunity to ask questions, and any questions were answered to my satisfaction. I am aware that I may ask further questions at any point. I have been provided with contact information for the research supervisor of this study. I am aware that my participation is voluntarily. I can withdraw from the study at any time. In addition, my participation or withdrawal will not affect my academic evaluation.

A I agree to participate

B. Disagree to participate

C. Name (please print): ________________________

D. Signature: __________________________

E. Date: ___________________

75

Appendix 3: Tables of Raw Data

Appendix Table 1: Specificity, sensitivity, false positive and false negative for resolution 76

µm and all root fractures for the cone beam CT images.

76 µm voxel size Total

No fracture With fracture

Gold standard No fracture Count 53

70.7%

22

29.3%

75

100% % within Gold

With fracture Count 53

35.3%

97

64.7%

150

100% % within Gold

Total Count 106 119 225

% within Gold 47.1% 52.9% 100%






76.0%

18

24.0%

75

100% % within Gold


34.0%

99

66.0%

150

100% % within Gold


% within Gold 48.0% 52.0% 100%

76






70.7%

22

29.3%

75

100% % within Gold


37.3%

94

62.7%

150

100% % within Gold


% within Gold 48.4% 51.6% 100%






74.4%

19

25.3%

75

100% % within Gold


46.0%

81

54.0%

150

100% % within Gold


% within Gold 55.6% 44.4% 100%

77

Appendix Table 5: Positive predictive value and negative predictive for resolution 76 µm and

all root fractures for the cone beam CT images.


No fracture

With fracture

Gold standard

No fracture Count 53

50.0%

22

18.5%

75

33.3% % within 76 µm voxel size

With fracture

Count 53

50.0%

97

81.5%

150



% within 76 µm voxel size 100% 100% 100%

Appendix Table 6: Positive predictive value and negative predictive for resolution 100 µm

and all root fractures for the cone beam CT images.


No fracture

With fracture

Gold standard


52.8%

18

15.4%

75


With fracture

Count 51

47.2%

99

84.6%

150




78




No fracture

With fracture

Gold standard


48.6%

22

19.0%

75


With fracture

Count 56

51.4%

94

81.0%

150







No fracture

With fracture

Gold standard


44.8%

19

19.0%

75


With fracture

Count 69

55.2%

81

81.0%

150




79


µm and vertical root fractures for the cone beam CT images.




70.6%

22

29.3%

75

100% % within Gold


36.0%

48

64.0%

75

100% % within Gold


% within Gold 53.3% 46.7% 100%

Appendix Table 10: Specificity, sensitivity, false positive and false negative for resolution

100 µm and vertical root fractures for the cone beam CT images.




76%

18

24%

75

100% % within Gold


33.3%

50

66.7%

75

100% % within Gold


% within Gold 54.6% 45.4% 100%

80




No fracture

With fracture

Gold standard


70.6%

22

29.4%

75

100% % within Gold

With fracture

Count 29

38.7%

46

61.3%

75

100% % within Gold


% within Gold 54.6% 45.4% 100%






74.6%

19

25.4%

75

100% % within Gold


49.3%

38

50.7%

75

100% % within Gold


% within Gold 62% 38% 100%

81


and vertical root fractures for the cone beam CT images.


No fracture

With fracture

Gold standard


66.2%

22

31.5%

75

50% % within 76 µm voxel size

With fracture

Count 27

33.8%

48

68.5%

75







No fracture

With fracture

Gold standard


69.5%

18

26.5%

75


With fracture

Count 25

30.5%

50

73.5%

75




82




No fracture

With fracture

Gold standard


64.6%

22

32.3%

75


With fracture

Count 29

35.4%

46

67.7%

75







No fracture

With fracture

Gold standard


60.2%

19

33.3%

75


With fracture

Count 37

39.8%

38

66.7%

75




83


µm and horizontal root fractures for the cone beam CT images.




70.6%

22

29.4%

75

100% % within Gold


54.7%

34

45.3%

75

100% % within Gold


% within Gold 62.6% 37.4% 100%


100 µm and horizontal root fractures for the cone beam CT images.




76.0%

18

24%

75

100% % within Gold


58.7%

31

41.3%

75

100% % within Gold


% within Gold 67.3% 32.7% 100%

84






70.6%

22

29.4%

75

100% % within Gold


56%

33

44%

75

100% % within Gold


% within Gold 63.3% 36.7% 100%






74.6%

19

25.4%

75

100% % within Gold


70.7%

22

29.3%

75

100% % within Gold


% within Gold 72.6% 27.4% 100%

85


and horizontal root fractures for the cone beam CT images.


No fracture

With fracture

Gold standard


56.4%

22

39.3%

75


With fracture

Count 41

43.6%

34

60.7%

75







No fracture

With fracture

Gold standard


56.4%

18

36.7%

75


With fracture

Count 44

43.6%

31

63.3%

75




86




No fracture

With fracture

Gold standard


55.8%

22

40.0%

75


With fracture

Count 42

44.8%

33

60.0%

75







No fracture

With fracture

Gold standard


51.4%

19

46.3%

75


With fracture

Count 53

48.6%

22

53.7%

75




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