cbct in orthodontics
TRANSCRIPT
Dr.S.K.Pandit
CBCT
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.
DID YOU KNOW??
A PubMed search
using the key words
CBCT
or cone beam
computed
tomography and
orthodontics
generated 793
references published
in English in last 5
The angle
orthodontist showed
134 reference
articles which
include
23 in 2013,
24 in 2014,
27 in 2015,
29 in 2016
31 in 2017.
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.
WHY 3D?
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 ofdifferent angles.
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
OBJECTIVES
An overview of
the basic
technical
parameters
of image
acquisition
Rationale for
selection criteria
& indications of
CBCT in
orthodontics
CONTENTS
1. Introduction2. Objective3. Evolution4. Computed tomography5. Components of CBCT6. Selection criteria7. Use in orthodontics8. Future of CBCT9. Conclusion10. references
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 inmaxillofacial imaging, facilitating the transition of dental diagnosis from 2D to 3D images.
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
CBCT
scanners
were
developed
for
craniofacial
imaging in
the late
1990s.
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.
COMPUTED TOMOGRAPHY
X-ray beam
geometry
Fan
beam
Cone
beam
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.
HOW DOES CBCT WORK?
1) A 3D cone beam is directed through a central object onto a detector.
2) After a single two-dimensionalprojection 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 theobject for the entire 360 degrees (full trajectory) or partial trajectory.
COMPONENTS TO CBCT IMAGE ACQUISITION
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.)
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
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.
Radiation Dosage
European SEDENTEXCT guideline for CBCT(2012)
EFFECTIVE RADIATION DOSAGE
Comparison of effective radiation doses from conventional 2D radiography, CBCTs using pediatricphantoms for dentoalveolar (small and medium) and craniofacial (large) FOVs, MSCT, and background radiation.
Most of the radiation data are provided in ranges andmedians (in parentheses).
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.
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.
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
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.
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.
FIELD OF VIEW
PROTOCOL FOR THE SELECTION OF APPROPRIATE FOV
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.
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.
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 .
MATRIX
The CT image is represented as the Matrix of the number.
A two dimensional array of numbersarranged in rows and columns is called Matrix.
Each number represent the value of the image at that location.
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.
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.
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 .
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 gray2bits - 4 shades of gray3bits – 84bits – 165bits – 328bits – 25612bits(212) - 4096 shades16bits - 65,536 shades of gray
IMAGE RECONSTRUCTION
Once the basis projection frames have been acquired, it is necessaryto process these data to create the volumetric data set. This process iscalled 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)
RECONSTRUCTION PROCESS
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)
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.
DOES THE DIAGNOSTIC TASK REALLY REQUIRE
CBCT?
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 ).
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, leadsto 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.
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.
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
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 lowerradiation imaging is questionable
6.Thourough clinicalevaluation 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.
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)
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.
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 cleftsites (Oberoi et al., 2010)
3D volumetric reconstructions of a patient with bilateral CL/P are useful in obtaining detailed information on themagnitude of the defect and the status and position of teeth at the defect site.
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.
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.
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)
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.
Limitation of mirroring
Mirroring using mid-sagittal plane generates inaccurate andclinically 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 cranialbase, registration on the cranial base also results insuboptimal results.
This implies that patient specific methods may be indicated for optimal localization and quantification of mandibularasymmetries.
CASE-BASED & CLINICAL JUDGMENT-BASEDUSE 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.
CASE-BASED & CLINICAL JUDGMENT-BASEDUSE 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.
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 through lingual root torque.
CASE-BASED & CLINICAL JUDGMENT-BASEDUSE 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.
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 therapy.
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
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.
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.
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
REFERENCES
1. Hatcher DC -Operational principles of cone beam computedtomography JADA oct 2010
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4. Impact of cone-beam computed tomography on orthodontic diagnosis and treatmentplanning, Ryan J et al Am J OrthodDentofacial Orthop 2013
5. Comparison of transverse analysis
between posteroanteriorcephalogram and cone-beam computed tomography by KyungMin Lee et al , Angle Orthod. 2014
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REFERENCES
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