CBCT IN ORTHODONTICS

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.


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.


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.


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.


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.


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

2. Accurate registration of cone-beam computed tomography scans to 3-dimensional facial Photographs, Kyung-Yen Nahm, Am J OrthodDentofacial Orthop 2014

3. Diagnostic accuracy of 2 cone-beam computed tomography protocols for detecting arthritic changes in temporomandibular joints , SumitYadav, Am J OrthodDentofacial Orthop 2015

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

6. Accuracy and reliability of cone-beam computed tomographymeasurements: Influence of head orientation ,Amr Ragab Et al ,AJODO 2011

7. Scarfe WC, Farmna AG, Sukovic P. Clinical applications of cone beamtomography in dental practice. J Can Dent Assoc. 2006;72:75–80.

8. Ludlow JB, Ivanovic M. Comparative dosimetry of dental CBCT devices and64-slice CT for oral and maxillofacial radiology. Oral Surg Oral Med OralPathol Oral Radiol Endod. 2008;106:106–114

REFERENCES

9. Jung, B.A., Wehrbein, H., Wagner, W., et al. (2012) Preoperative diagnostic for palatal implants: is CT or CBCT necessary? Clinical Implant Dentistry and Related Research, 14 (3), 400–405

10. Metzger, M.C., Hohlweg-Majert, B., Schon, R., et al. (2007)Verifcation of clinical precision after computer-aided reconstruction in craniomaxillofacial surgery. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontology, 104 (4), e1–e10.

11. Walker, L., Enciso, R., & Mah, J. (2005) Threedimensional localization of maxillary canines with cone-beam computed tomography. American Journal of Orthodontics and Dentofacial Orthopedics, 128 (4),418–423.

12. Oberoi, S., Chigurupati, R., Gill, P., et al. (2009) Volumetric assessment of secondary alveolar bone grafting using cone beam computed tomography. The Cleft Palate–Craniofacial Journal, 46 (5), 503–511.

13. Oberoi, S., Gill, P., Chigurupati, R., et al. (2010)Three-dimensional assessment of the eruption path of the canine in individuals with bone-grafted alveolar clefts using cone beam computed tomography.The Cleft Palate–Craniofacial Journal, 47 (5), 507–512

14. Zhou, W., Li, W., Lin, J., et al. (2013) Tooth lengths of the permanent upper incisors in patients with cleft lip and palate determined with cone beam computed tomography. Cleft Palate–Craniofacial Journal, 50 (1), 88–95

15. Shirota, T., Kurabayashi, H., Ogura, H., et al. (2010) Analysis of bone volume using computer simulation system for secondary bone graft in alveolar cleft. International Journal of Oral and Maxillofacial Surgery, 39 (9),904–908

16. Theodorakou, C., Walker, A., Horner, K., et al. (2012)Estimation of paediatric organ and effective doses from dental cone beam CT using anthropomorphicphantoms. British Journal of Radiology, 85 (1010),153–160

17. Okano, T., Harata, Y., Sugihara, Y., et al. (2009) Absorbed and effective doses from cone beam volumetric imaging for implant planning. Dentomaxillofacial Radiolology, 38, 79–85

18. Palomo, J.M., Rao, P.S., & Hans, M.G. (2008) Influence of CBCT exposure conditions on radiation dose. Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontology, 105 (6), 773–782

19. Ludlow, J.B., Davies-Ludlow, L.E., & White, S.C. (2008)Patient risk to common dental radiographic examinations: the impact of 2007 ICRP recommendationsregarding dose calculation. Journal of the American Dental Association, 139 (9), 1237–1243

20. Loubele, M., Jacobs, R., Maes, F., et al. (2005) Radiation dose vs. image quality for low-dose CT protocols of the head for maxillofacial surgery and oral implant planning. Radiation Protection Dosimetry, 117 (1–3),211–216

21. Garcia Silva, M.A., Wolf, U., Heinicke, F., et al. (2008a)Cone-beam computed tomography for routine orthodontic treatment planning: a radiation dose evaluation. American Journal of Orthodontics and Dentofacial Orthopedics, 133 (640), e1–e5

Education

CBCT IN ORTHODONTICS