A detailed description about CBCT in orthodontics in a very precise and simple language.

1. CBCT IN
ORTHODONTICS
PRESENTOR: DR. AKSHI
PG IST YEAR
DEPARTMENT OF ORTHODONTICS

2. CONTENTS
– Introduction
– Evolution
– Principles
– Components of image production
– Selection criteria
– Usage in dentistry
– Conclusion
– references

3. INTRODUCTION
– Cone beam computed tomography (CBCT) imaging is an inherently volumetric image capture
technology providing a data set from which digital images are reformatted and presented on a
display monitor.
– CBCT acquires data volumetrically providing 3D radiographic imaging for the assessment of the
dental and maxillofacial complex facilitating dental diagnosis.
– In orthodontics, 3D imaging can help unravel the complexity of dental and skeletal
malocclusions and improve diagnosis and treatment planning in specific case types
– There are 3 main processes in CBCT imaging : 1) image production
2) visualization
3) interpretation

4. EVOLUTION
– Discovery of x-rays by W.C.Roentgen – 1895
– DXIS , first dental digital panoramic x-rays system – 1995
– development of CT independently by Hounsfield and Cormack in the early 1970s
– Multislice CT (MSCT) or multirow detector CT (MDCT)
– Scanners were developed for craniofacial imaging in late 1990s.

6. PRINCIPLES OF CBCT
– CBCT imaging is performed using a rotating gantry or C –arm
supporting an x -ray source ,and reciprocating area detector.
– A divergent x-ray source, collimated as a cone or more
commonly a pyramid , is directed through the region of
interest (ROI) within the maxillofacial region, and the residual
attenuated photons strike the detector on the opposite side.
– On activation , data are acquired from a series of sequential
exposures as the gantry rotates around a fixed axis of rotation
centered within the patient’s ROI.

7. – Trajectory arc is ideally 360 ˚ but may vary form 180 ˚ to 720˚.
– During rotation , multiple sequential planar projection images are captured.
– These 2-D single projection images constitute the raw primary data and are individually referred
to as BASIS (images appear similar to ceph images except that each is slightly offset from the
next) , FRAME and RAW.
– CBCT exposure incorporates the entire ROI , only one rotational scan of the gantry is necessary
to acquire enough data for volumetric image construction.
– Cone beam geometry captures volumetric data with scan times ranging from less than 5 to
more than 30 seconds.

8. COMPONENTS OF IMAGE
PRODUCTION
1. X- ray generation
2. X – ray detection
3. Image reconstruction

9. X-RAY GENERATOR
– High voltage generator which provides incoming voltage and current to provide the x-ray tube
with the power needed to produce an x-ray beam of desired peak kilovoltage and current.

10. 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 transmitted beam , a process called as
AUTOMATIC EXPOSURE CONTROL .
– Exposure factors can be controlled manually or automatically :
• kVp : 60-90
• mA : 6-10
• Pulsed or continuous x-ray generation
- PRIMARY DETERMINANTS of patient exposure : PULSED X-RAY BEAM AND SIZE OF IMAGE FIELD.

11. X – RAY GENERATION
– PATIENT STABILISATION : patient sitting , standing or supine.
 Head is stabilized by combination of chin cup , bite fork or other head restraint mechanism.
- X-RAY GENERATOR : can be continuous or pulsed to coincide with the detector activation.
 Actual exposure time should be less than scanning time.
 This considerably reduces patient radiation dose.
 ALARA for CBCT should be adjusted on basis of patient’s size and specific diagnostic task.

13. EFFECTIVE
RADIATION DOSE

14. Methods to reduce radiation dose
– Smaller FOV
– High voltage and beam filtration
– Short exposure time
– Pulsed exposure
– Low resolution

15. – SCAN VOLUME (FOV) : dimensions primarily depends upon detector size, shape, beam
projection geometry and ability to collimate the beam.
– Desirable to limit the field size to the smallest volume that images the ROI.
– SCAN FACTORS : CBCT units are available providing fixed may be 360˚ or partial trajectory
arc or variable rotation angles.
• The speed with which individual images are acquired is called as FRAME RATE.
• Higher frame rate – more information is available to reconstruct the image and increases the
signal –to-noise ratio, producing images with less noise.
• But higher frame rates are usually accomplished with a longer scan time and hence higher
patient dose.

16. – It is desirable to reduce CBCT scan times to as short as possible to reduce motion artifact from
subject movement.
– Obtained by increasing the detector frame rate , reducing the number of projections and
reducing the scan arc.
– Avg. time = 7-30 sec

17. FIELD OF VIEW
– The dimensions of FOV depend on :
• Detector size and shape
• Beam projection geometry and ability to collimate
- Shape of scan volume : cylindrical or spherical

18. LARGE FOV – show roofs of the orbit and nasion
Down to hyoid bone
They have a height equal to or greater than 16 cm.
Entire dentofacial complex scan
MEDIUM FOV - middle of orbits down to menton vertically and from condyle to condyle horizontally.
SMALL FOV – a particular small segment , less than 20 cm in height

19. PROTOCOL FOR SELECTION
OF APPROPRIATE FOV

20. IMAGE DETECTION
– 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 – 0.3 mm
size.

21. MATRIX
– The CT image is represented as the matrix of the number.
– A 2D array of numbers arranged in rows and columns is called matrix.
– Each number represents the value of the image at that location.

22. PIXEL
– Each square in a matrix is called as pixel.
– Also k/a PICTURE element.
– Size : 20-60 micrometers.

23. VOXEL
– The spatial resolution is determined by individual volume elements called voxels.
– Principal determinant of voxel size : 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, a good scanner has higher dosage of radiation.

24. GRAYSCALE
– The ability of a CBCT scan to display differences
in attenuation.
– Related to the ability of detector to detect
subtle contrast differences.
– This parameter is called bit depth of the system
and determines the number of shades of gray
available to display the attenuation.
– All current CBCT machines have 12 bit
detectors and are capable of identifying 4096
shades of gray.

25. IMAGE RECONSTRUCTION
– Projection data (acquisition computer)
– Transferred by an ethernet connection
- Processing computer (workstation)

26. – ACQUISITION STAGE : It involves image collection and detector preprocessing for correction
of inherited defects.
– RECONSTRUCTION STAGE: the corrected images are converted into a special presentation
called as sinogram ( a composite image developed from multiple projection images.
– The final image is reconstructed from the sinogram with a filtered back projection algorithm for
volumetric data acquired by CBCT.

27. DISPLAY
– The volumetric data set is a compilation of all available voxels.
– For most CBCT devices , it is presented to the clinician on screen as secondary reconstructed
images in three orthogonal planes (axial , sagittal and coronal).

28. DICOM FILE
– Digital imaging and communication in medicine
– CBCT produces 2 data products :
o The volumetric image data from the scan
o Image report generated by the operator
- All the images are saved in the DICOM format.

30. EVIDENCE BASED
GUIDELINES
– Evidence supporting the use of CBCT in orthodontics Olivier J.C.van Vlijmen (2012)
 The authors found no high quality evidence regarding the benefits of CBCT use in orthodontics.
 Limited evidences show 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.

31. PATIENT
SELECTION
CRITERIA
Ref. CBCT in orthodontics: assessment of treatment outcomes and indications for its use,2015, British Institute of Radiology

33. 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) Thorough clinical evaluation report should be made
7) Should not be done for soft tissue assessment
8) Use small volume doses
9) Resolution compatible with adequate diagnosis
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

34. ADVANTAGES
– Rapid scan time – reduces motion artifacts
– Image accuracy
– Interactive display mode
– Multiplanar reformatting
– Comfortable and safe
– Better image with high resolution
– Beam limitation through collimation reduces and limits the radiation to the ROI
– Increased treatment efficiency
– Less radiation exposure
– Minimisation of unexpected issues and negative sequalae

35. DISADVANTAGES
– Scatter
– Artifacts
– Scan volume insufficiency
– Poor contrast resolution
– Soft tissue cannot be viewed

36. CBCT application –related to dental
specialty
– Missing teeth
– Impacted teeth
– Supernumerary teeth
– Root abnormalities
– Tooth size measurements
– Cysts , tumors
– Implant placement
– Expansion
– Facial trauma
– Craniofacial abnormalities

37. How to read CBCT ?

38. DENTAL DEVELOPMENT /
TOOTH MORPHOLOGIES
– CBCT can be used to evaluate developing arch length discrepancies.
– Small to medium FOV recommended
– Evaluation of :
• Presence and absence of unerupted teeth
• Tooth development
• Tooth position
• Bone loss, formation, depth, height and width
• Proximity of adjacent tooth

39. SUPERNUMERARY TOOTH
- CBCT - to precisely localize all supernumerary
teeth, many of which are unerupted or may be
impacted.
- to detail the morphology of the supernumerary
teeth.
- Information derived from CBCT images of
unerupted supernumerary teeth could facilitate
decisions on which of the teeth to retain,
determination of the retrievability of those teeth
and mapping the optimal surgical access to the
teeth.
Ref. CBCT in orthodontics: assessment of treatment outcomes and indications for
its use, 2015,British Institute of Radiology

40. ROOT ABNORMALITIES
– Root position and morphology are critical considerations for ideal orthodontic treatment for
two reasons:
(1) root position and parallelism - critical for an ideal stable occlusion
(2) external apical root resorption (EARR) - common adverse side effects of orthodontic
treatment.
– CBCT radiographs are valuable especially because they allow precise measurements of root
angulation and length before and after orthodontic treatment.

41. – CBCT- extracted panoramic radiographs and is defined as the angle formed by the tooth’s long
axis and the occlusal plane.

42. DILACERATED ROOTS

43. ROOT RESORPTION

44. IMPACTED AND
TRANSPOSED
TEETH
– Most common indication for CBCT in
orthodontics
– enhances the ability to localize impacted
tooth accurately, evaluate their
proximity to other teeth and structures,
determine the follicle size and the
presence of pathology, estimate space
conditions, assess resorption of adjacent
teeth, assist in planning surgical access
and bond placement, and aid in defining
optimal direction for extrusion of these
teeth into the oral cavity.

46. CLEFT LIP AND PALATE
– CBCT may provide more precise information on the numbers, quality and location of teeth in
proximity of the cleft site, eruption status and path of teeth in grafted cleft sites and diagnosing
for implant placement.
– In determining the volume of alveolar defect and therefore, the amount of bone needed for
grafting in patients.
– To determine the success of bone filling after surgery

48. ORTHOGNATHIC AND
CRANIOFACIAL
ANOMALIES SURGICAL
PLANNING
– CBCT combined with computer aided surgical simulation or computer aided
orthognathic surgery offers :
 Refining diagnosis and optimizing treatment objectives in 3D
 Virtual treatment planning to improve surgical procedures and outcomes
 Pre-operative assessment of bone support of the dentition and interdental
spacing for interdental osteotomies ideally is performed with CBCT imaging,
assessment helps to eliminate parallax errors, visualize variations in root
anatomy such as dilacerations, and determine the pre-operative position and
course of the inferior alveolar nerve, which can be useful for planning slight
variations in the position of the sagittal split osteotomy to help minimize injury
to the nerve.
 Post-operative assessment with 3D imaging allows a high-resolution
determination of osteotomies and fixation that are essential in implementing
process.

50. ASYMMETRY
– 3D CBCT imaging in the diagnosis and treatment planning of asymmetries , where discrepancies
often manifest in all three planes.
– When large differences exist between bilateral structures , use of MIRRORING technique is
enabled.
– In this tech. the normal side is mirrored onto the discrepant side so as to simulate and visualize
the desired end result.
– CBCT also helps in diagnosing and treatment planning of craniofacial anomalies such as
hemifacial microsomia, cleidocranial dysplasia, and ectodermal dysplasia.
– advantage of CBCT imaging with CFA patients is the increased anatomic detail and
measurement accuracy, which is critical for orthodontic and surgical treatment planning. Digital
3D images can be used to map the distances and directions of dental and skeletal movements
precisely that are needed to optimize the treatment outcome.

51. HEMIFACIAL MICROSOMIA

52. ALVEOLAR BOUNDARY
CONDITION
– Alveolar boundary conditions are the
depth, height and morphology of alveolar
bone relative to tooth root dimensions,
angulation and spatial position.
– Compromised or limited 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.

54. TMJ DEGENERATION, PROGRESSIVE BITE
CHANGES, FUNCTIONAL SHIFTS, AND
RESPONSES TO THERAPY
– CBCT images the entire joint with visualization of minor to overt osseous hard tissue
morphologic changes and congruency of bone surfaces that define the joint space resulting
from pathology and adaptive processes and allows for accurate detection and evaluation of
pathological changes.
– Radiographic signs of bony changes associated with TMJ arthritis include irregular and possibly
thickened cortical outlines (sclerosis), erosions, osteophyte formation, subchondral cysts, and
flattening and narrowing of the joint space .

56. TADs – planning and placement
– When placing an endosseous orthodontic TAD, the objective is to anchor the miniscrew
securely in the surrounding bone and to avoid any damage to adjacent anatomical structures.
– CBCT technology allows an exact visual identification of the location, shape, and divergence of
the mesial and distal dental roots, the floor of the maxillary sinus, and the buccal and lingual
wall of the alveolar process.
– Generally, a small FOV, high resolution scan is recommended for placement of TADs.

57. CONCLUSION
– This technique expands the fields for diagnosis and treatment possibilities.
– However , CBCT should be used with careful consideration , it should not be used deliberately
where 2D imaging suffices.

58. REFERENCES
– Cone beam computed tomography in orthodontics : indications , insights and innovations –
Sunil D . Kapila, BDS, MS. PhD
– White and Pharrow , oral radiology
– European Sedentexct guidelines for CBCT - 2012