2. ORTHODONTICS IS CHANGING?
ARE YOU?
3D imaging is quickly emerging as the standard of
care in orthodontics as new ultralow-dose CBCT
technology offers safer and more affordable
volumetric scanning than ever before.
The advantages of CBCT over traditional 2D imaging
are numerous.
3. DID YOU KNOW??
A PubMed search
using the key words
CBCT
or cone beam
computed
tomography and
orthodontics
generated 793
references published
The angle
orthodontist showed
134 reference
articles which
include
23 in 2013,
24 in 2014,
27 in 2015,
29 in 2016
AJO-DO showed 381
reference articles
which include
88 in 2013,
70 in 2014,
75 in 2015,
74 in 2016,
74 in 2017.
The pace of CBCT innovations and applications to orthodontics is reflected by the
rapidly expanding numbers and quality of publications on this topic.
5. WHY 3D?
A conventional X-ray image is basically a shadow.
Shadows give you an incomplete picture of an object's
shape.
This is the basic idea
of computer aided
tomography. In a CT
scan machine,
the X-ray beam
moves all around the
person, scanning
from hundreds of
different angles.
6. WHY 3D?
1. 3D treatment planning and the transverse dimension
2. Airway centered treatment from information not
available using 2D imaging
3. Improved pre-existing TMJ knowledge and avoiding
surprises during treatment
4. Mixed dentition and eruption guidance in 3D imaging
5. Visual Craniometric Analysis (VCA) – a new paradigm
in 3D Cephalometrics
7. OBJECTIVES
An overview of
the basic
technical
parameters
of image
acquisition
Rationale for
selection criteria
& indications of
CBCT in
orthodontics
8. CONTENTS
1. Introduction
2. Objective
3. Evolution
4. Computed tomography
5. Components of CBCT
6. Selection criteria
7. Use in orthodontics
8. Future of CBCT
9. Conclusion
10. references
9. INTRODUCTION
The introduction of cone-beam computed tomography
(CBCT) specifically dedicated to imaging the
maxillofacial region heralds a true paradigm shift from
a 2D to a 3D approach to data acquisition and image
reconstruction.
Interest in CBCT from all fields of dentistry is
unprecedented because it has created a revolution in
maxillofacial imaging, facilitating the transition of
dental diagnosis from 2D to 3D images.
10. EVOLUTIONdiscovery
of X-rays
by the
physicist
Wilhelm C
Röntgen
in 1895.
development
of CT
independentl
y by
Hounsfeld &
DXIS, the
first
dental
digital
panorami
c X-rays
system
1995
multislice
CT (MSCT)
or multirow
detector CT
(MDCT) in
scanners
were
developed
for
craniofacial
imaging in
the late
1990s.
11. COMPUTED TOMOGRAPHY
TOMOGRAPHY: Imaging of Layer/Slice
SLICE/CUT: The cross section portion of body which is scanned
for production of CT image.
The slice has width.
The width is determined by width of the x rays beam.
Think like looking into
the loaf of bread by
cutting into the thin
slices and then viewing
the slice individually.
13. HOW DOES CT WORK?
1. X-ray source and detector
mounted on a rotating
gantry.
2. During rotation, platform
will slowly move & the
receptor detects x rays
attenuated by the patient.
3. multiple images will be
captured during rotation.
4. “ raw data ” reconstructed
by a computer algorithm to
generate cross-sectional
images.
14. HOW DOES CBCT WORK?
1) A 3D cone beam is directed
through a central object onto a
detector.
2) After a single two-dimensional
projection is acquired by the
detector, the x-ray source and
detector rotate a small distance
around a trajectory arc.
3) At this second angular position
another basis projection image is
captured.
4) This sequence continues around
the
object for the entire 360 degrees
16. PATIENT POSITION
Imaging may be performed with the
patient seated, supine, or standing.
The patient’s head is positioned and
stabilized between the x-ray generator
and detector by a head holding
apparatus.
(Courtesy Imaging Sciences International, Hatfield, Pa.)
17. X-RAY GENERATOR
High voltage generator which
modifies incoming voltage and
current to provide the x ray tube with
the power needed to produce an x
ray beam of desired peak kilovoltage
(kVp) and current (mA)
X ray tube
Anode
Cathode
tube envelop
tube housing
Collimator
18. X-RAY GENERATION
On some CBCT units both kVp and mA are automatically modulated
in near real time by a feedback mechanism detecting the intensity of
the transmitted beam, a process known generically as automatic
exposure control.
Exposure factors can be controlled manually or automatically
• KVp 60 to 90
• mA 6 to 10
• Pulsed or continuous x ray generation
Pulsed x-ray beam and size of the image field are the
primary determinants of patient exposure.
20. EFFECTIVE RADIATION DOSAGE
Comparison of effective radiation
doses from conventional 2D
radiography, CBCTs using pediatric
phantoms for dentoalveolar (small
and medium) and craniofacial
(large) FOVs, MSCT, and
background radiation.
Most of the radiation data are
provided in ranges and
medians (in parentheses).
21. EFFECTIVE RADIATION DOSAGE
Radiation risk in relation to age. This approach assumes a
multiplicative risk projection model averaged for the two genders.
In fact, the risk for females always is higher relatively than for
males.
22. SCAN FACTORS
The speed with which individual images are acquired
is called the frame rate.
With a higher frame rate, more information is
available to reconstruct the image; therefore, primary
reconstruction time is increased.
However, higher frame rates increase the signal-to-
noise ratio, producing images with less noise.
Note that higher frame rates are usually
accomplished with a longer scan time and
hence higher patient dose.
23. It is desirable to reduce CBCT scan times to as short
as possible to reduce motion artifact resulting from
subject movement.
Decreased scanning times may be achieved by
increasing the detector frame rate, reducing the
number of projections, or reducing the scan arc.
Average time may vary from 7-30 seconds.
It also varies if half a rotation or a full circle rotation is
used.
SCAN FACTORS
24. FIELD OF VIEW
The dimensions of the field of view depend on the
1. detector size and shape
2. beam projection geometry and the ability to
collimate or not.
Shape of the scan volume : cylinder or spherical.
Scanning of the entire craniofacial region is difficult
to incorporate into cone-beam design because of the
high cost of large area detectors.
25. FIELD OF VIEW
Large
show the roof of the
orbits and nasion
down to the hyoid
bone on a typical
adult
male.
Medium
capture the middle
of
the orbits down to
menton vertically
and from
condyle to condyle
horizontally.
Small
capture a user-
defined region,
usually equal to or
less than 10cm in
height.
28. The choice of the FOV is based on the diagnostic objectives for the imaging as determined
through a careful clinical assessment of the patient. The recommended FOV for specific
needs also is dependent on the size of the individual. Thus, if the image of the entire
craniofacial region is needed, it might entail using a large FOV for a child and an extended
FOV for an adult.
29. IMAGE DETECTION
Types of
detectors
image intensifier
tube/charge-coupled
device combination
flat-panel
imager
CCD based CBCT has a much higher spatial
resolution.
However, the image contrast & the noise level are
both worse than FP based CBCT system.
30. IMAGE DETECTION
The most common flat-panel configuration
consists of a cesium iodide scintillator applied to a
thin film transistor made of amorphous silicon.
A sensor which has smaller pixel size has better
resolution . One pixel can be 0.007 to 0.3mm size.
A sensor which has a higher bit rate, can identify
more areas of black and white .
31. MATRIX
The CT image is
represented as the
Matrix of the number.
A two dimensional
array of numbers
arranged in rows and
columns is called
Matrix.
Each number represent
the value of the image
at that location.
32. PIXEL
Each square in a matrix is called a
pixel.
Also known as picture element.
20 and 60 µm
Size remain same whether it resides in
an intraoral device, the TFT screen, or
the II and solid-state combination
device.
33. VOXEL
The spatial resolution is determined by
individual volume elements called voxels.
The principle determinant of voxel size is the
pixel size of the detector.
Detectors with smaller pixel size capture fewer
x-ray photons per voxel and result in more
noise.
To balance it out a good scanner has higher
dosage of radiation.
34. GRAYSCALE
The ability of a CBCT scan to display differences in
attenuation.
related to the ability of the detector to detect subtle
contrast differences.
This parameter is called bit depth of the system and
determines the number of shades of grey available to
display the attenuation.
All current CBCT machines have 12 bit detectors and
are capable of identifying 4096 shades of gray .
35. GRAYSCALE
Examples of gray-scale
ramps representing distinct
gray levels from black to
white. Bit depth controls
the number of possible
gray levels in the image.
1bit - 2 shades of gray
2bits - 4 shades of gray
3bits – 8
4bits – 16
5bits – 32
8bits – 256
12bits(212) - 4096 shades
16bits - 65,536 shades of
gray
36. IMAGE RECONSTRUCTION
Once the basis projection frames have been acquired, it is necessary
to process these data to create the volumetric data set. This process is
called primary reconstruction.
a single cone-beam rotation produces 100 to more than 600 individual
projection frames, each with more than a million pixels with 12 to 16 bits
of data assigned to each pixel.
A conventional CT, cone-beam data reconstruction is performed by
personal computer – based rather than workstation platforms.
Projection data(acquisition
computer)
transferred by an Ethernet
connection
processing computer
(workstation)
38. DISPLAY
The volumetric data set is a compilation of all
available voxels.
for most CBCT devices, is presented to the clinician on
screen as secondary reconstructed images in three
orthogonal planes (axial, sagittal, and coronal)
39. DICOM FILE
Cbct produces two data products
The volumetric image data from the scan
Image report generated by the operator
All of these images are save in the DICOM (digital
imaging and communication in medicine) format.
This is the international standards organization –
referenced standard for all diagnostic imaging
Includes x ray, visible light images and ultrasound.
41. There remains some debate on which types of
orthodontic cases warrant a CBCT scan versus the use of
traditional two-dimensional (2D) projectional radiographs
(Halazonetis, 2012; Larson,2012 (Am J Orthod Dentofacial Orthop
2012;141:402-11)
Nevertheless there are certain benefits.
The 3D data derived from a CBCT scan can, in specific
situations, reduce ambiguity in diagnosis.
Treatment plans based on incomplete diagnostic data
can result in permanent damage to teeth including an
increased risk for decalcification, caries, and root
resorption (Motokawa et al.,2011 Orthod Waves-Jpn Ed 2011; 70(1): 21–31 ).
42. EVIDENCE-BASED
GUIDELINES
Fundamental to evidence-based guidelines development are
systematic reviews of the published literature.
Evidence supporting the use of cone-beam computed tomography in
orthodontics Olivier J.C. van Vlijmen, DDS and colleagues
JADA 2012;143(3):241-252 10.14219/jada.archive.2012.0148
¤ The authors found no high-quality evidence regarding the benefits
of CBCT use in orthodontics.
¤ Limited evidence shows that CBCT offers better diagnostic potential,
leads
to better treatment planning or results in better treatment outcome
than do conventional imaging modalities.
¤ Only the results of studies on airway diagnostics provided sound
scientific data suggesting that CBCT use has added value.
43. PATIENT SELECTION
CRITERIA
The choice of modality should be
based on research supported
clinical judgment as to whether
the examination is likely to
provide a clinical benefit for the
patient, in addition to an
assessment of the risk.
Guidelines for the use of CBCT in
orthodontics may be developed
with particular consideration to
the three-fold increased risk
associated with radiation
exposure to the largely pediatric
patient population.
44. Clinical scenarios in which the use of CBCT may be indicated on the basis of research evidence or
case- or clinical judgment–based determination of the need for imaging. All three levels of indicators
require a careful consideration of the benefit-to-risk analyses prior to undertaking CBCT
45. FACTORS IN DEVELOPING
GUIDELINES
1.History and clinical examination
2.Benefits should outweigh risks
3.New information to aid the
patient
4.Not be repeated routinely
5.Diagnosis with lower
radiation imaging is
questionable
6.Thourough clinical
evaluation report should be
made
7.Should not be done for
soft tissue assessment
8.Use small volume doses where
you can
9.Resolution compatible with
adequate diagnosis yet low
radiation
10.Small FOV for dentoalveolar
regions and teeth
11.Avoiding the use of CBCT solely
to facilitate the placement of
orthodontic appliances such as
aligners and computer-bent wires.
46. RESEARCH EVIDENCE-BASED USE OF CBCT
Impacted and transposed teeth
Most common indications for CBCT imaging in
orthodontics.
CBCT has been shown to improve diagnosis and
contribute to modifications in treatment planning in
a significant number of subjects.
Walker et al., 2005; Haney et al., 2010; Katheria et al., 2010; Botticelli et al., 2011)
47. Depiction of impacted maxillary canines using a conventional 2D panorex (A) and 3D volumetric
rendering. The 3D images permit clear visualization of the location and relationships of the
impacted canines to adjacent structures, as well as the presence of any root resorption.
it facilitates treatment decisions, including determination of teeth to be extracted.if yes then the
optimal surgical approach, appropriate placement of attachments, and biomechanics planning.
48. RESEARCH EVIDENCE-BASED USE OF CBCT
Cleft lip and palate (CL/P)
valuable in determining the volume of the alveolar
defect and, therefore, the amount of bone needed for
grafting in CL/P patients
for determining the success of bone fill following
surgery (Oberoi et al., 2009;Shirota et al., 2010)
numbers, quality, and location of teeth in proximity to
the cleft site (Zhou et al., 2013),
The eruption status and path of canines in grafted cleft
sites (Oberoi et al., 2010)
49. 3D volumetric
reconstructions of
a patient with
bilateral CL/P are
useful in obtaining
detailed
information on
the
magnitude of the
defect and the
status and
position of teeth
at the defect site.
50. RESEARCH EVIDENCE-BASED USE OF CBCT
Orthognathic and craniofacial anomalies surgical
planning and implementation
CBCT combined with computer-aided surgical simulation (CASS) or
computer-aided Orthognathic surgery (CAOS) offers
refining diagnosis and optimizing treatment objectives in 3D
virtual treatment planning to improve surgical procedures and
outcomes.
51. Virtual surgical treatment planning for a patient to visualize and determine the
magnitude of maxillary and mandibular movements, as well as any complication
such as proximal segment interferences that may arise during surgery.
52. RESEARCH EVIDENCE-BASED USE OF CBCT
Asymmetry
3D CBCT imaging in the diagnosis and treatment
planning of asymmetries, where discrepancies often
manifest in all three planes of space.
When large differences exist between bilateral
structures, CBCT scans enable the use of a technique
called “mirroring”
In which the normal side is mirrored onto the
discrepant side so as to simulate and visualize the
desired end result, as well as to plan the surgery to
facilitate correction (Metzger et al., 2007)
53. Mirroring on a mid-sagittal plane for quantitation of mandibular asymmetry. A mid-
sagittal plane was defined for this patient based on Na, Ba, and ANS. The left ramus was
mirrored onto the right side using this plane.
54. Limitation of mirroring
Mirroring using mid-sagittal plane generates
inaccurate and
clinically irrelevant results for patients
1.cleft palate with facial features that affect the
midline position of the points (NA, ANS, Ba) used to
define this plane.
2.in patients with asymmetries involving the cranial
base, registration on the cranial base also results in
suboptimal results.
This implies that patient specific methods may be
indicated for optimal localization and quantification of
mandibular
asymmetries.
55. CASE-BASED & CLINICAL JUDGMENT-BASED
USE OF CBCT
Root resorption
Detection of buccal or lingual root resorption by CBCT
that is not visualized by 2D radiographs could
differentiate pre- or in-treatment decisions made with
the two imaging modalities.
So the dilemma, in this scenario is how and when a
clinician would decide that a patient has undergone
buccal and/or lingual root resorption to justify taking
CBCT scan.
56. CASE-BASED & CLINICAL JUDGMENT-BASED
USE OF CBCT
Alveolar boundary conditions
Compromised pretreatment alveolar boundary
conditions may limit or interfere with the planned or
potential tooth movement, as well as the final desired
spatial position and angulation of the teeth.
Failure to diagnose compromised alveolar bone prior to
treatment and to involve this into the treatment plan
likely will lead to worsening of the problem during
orthodontic treatment.
57. Determination of anterior boundary conditions in a case with severely retroclined maxillary and
mandibular incisors using sagittal (A), axial (B) and coronal (C) multiplanar, and 3D volumetric (D
and E) reconstructions.
a severe Class II division 2 malocclusion presents with upper incisor roots that have
limited buccal bone support that could be placed into a better relationship with the bone
58. CASE-BASED & CLINICAL JUDGMENT-BASED
USE OF CBCT
TMJ degeneration, progressive bite
changes functional shifts, and responses
to therapy
Conventional 2D radiography of the TMJ including panoramic
radiographs and cephalograms do not provide an accurate
characterization of the joint because of distorted images with
superimposed structures.
CBCT imaging of entire joint spaces with visualization of osseous
hard tissue morphologic changes resulting from pathology and
adaptive processes allows for accurate detection and evaluation
of pathological changes.
59. Visualization of the TMJ in the axial (A), coronal (B), and sagittal (C) planes, as well as 3D volumetric
reconstructions here visualized from the buccal (D), medial (E), medio-inferior (F), and antero-
inferior (G).
in 3D can help in the identification of pathologic changes, including sclerosis, flattening,
erosions, osteophytes, abnormalities in joint spaces, and responses of the joint tissues to
60. THE FUTURE
Probably, Next iteration of digital invention into the field
of radio diagnosis will be the development in ARTIFICIAL
INTELLIGENCE based imaging diagnosis.
Artificial intelligence—the mimicking of human cognition
by computers—was once a fable in science fiction but is
becoming reality in medicine.
The combination of big data and artificial intelligence,
referred to by some as the fourth industrial revolution, will
change radiology and pathology along with other medical
specialties.
Adapting to Artificial Intelligence
JAMA. 2016;316(22):2353-2354. doi:10.1001/jama.2016.17438
61. FABRICATION OF STUDY
MODELS/APPLIANCES
Though intraoral scanners
have allowed us to restrain
from taking impressions.
CBCT scans can capture
and display the entire
dentoalveolar structure.
but currently lack the
spatial resolution required
for fabrication is
drawbacks.
unless the scan duration,
frame acquisition, and
radiation output of the
scan is increased.
62. CONCLUSION
This technique hugely expands the fields for
diagnosis and treatment possibilities, not to
forget many more research frontiers as well.
However CBCT should be used with careful
consideration ,it should not be used
deliberately where 2D imaging suffices.
63. REFERENCES
Cone Beam Computed Tomography in Orthodontics: Indications,
Insights, and Innovations ‘Sunil D. Kapila, BDS, MS, PhD’
White and Pharrow , oral radiology edition 6, 2009
European SEDENTEXCT guidelines for CBCT (2012)
ICRP – international commission on radiological protection 2007
publication
American academy of oral and maxillofacial radiology 2009
Prima Immagine Cone-Beam-1994-07-01-3" by Daniele Godi -Own work
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