Specialized Dental Imaging

• A Digital volume tomography

  CONE BEAM COMPUTED TOMOGRAPHY (CBCT)
• Cone beam volumetric imaging

  CONE BEAM COMPUTED TOMOGRAPHY (CBCT)
• Field of view (FOV) variations

  • Small, limited/dento-alveolar (approx. 4 cm3)

  • Medium/maxillofacial (approx. 8 cm3)

  • Large/craniofacial – includes cranial base (with/without skull vault)
• Indications of CBCT in Developing Dentition

  • Localization of an unerupted tooth

  • Assessment of external resorption in relation unerupted teeth

  • Localized assessment of an impacted tooth

  • Assessment of cleft palate

  • Planning complex orthodontic/surgical management of maxillofacial skeletal abnormalities
• CBCT for developing Dentition is generally not indicated for:

  • Planning the placement of temporary anchorage in orthodontics

  • Routine orthodontic diagnosis
• CBCT Indications for Restoring Dentition

  • Assessment of periodontal infra-bony defects and furcation lesions

  • Periapical assessment

  • Assessment of root canal anatomy in multi-rooted teeth

  • Planning surgical endodontic procedures

  • Endodontic treatment complicated by resorption lesions, endo-perio lesions, perforations and atypical pulp anatomy

  • Assessment of dental trauma (suspected root fracture)
• CBCT for restoring dentition is generally not indicated for:

  • Diagnosing dental caries

  • Routine imaging of periodontal support

  • Routine diagnosis of periapical disease

  • routin assessment of root canal anatomy
• CBCT indications for Surgical Applications

  • Assessment of lower 3rd molars
  • Assessment of unerupted teeth
  • Cross-sectional imaging prior to implant placement
  • Assessment of pathological lesions affecting the jaws (cysts, tumors, giant cell lesions, osseous dysplasias)
  • Assessment of facial fractures where soft tissue detail is not required
  • Planning orthognathic surgery to obtain 3D datasets of the craniofacial skeleton
  • Assessment of the bony elements of the TMJ
  • Assessment of the bony walls of the maxillary antra
• Employs a cone-shaped x-ray beam and a special detector (ex. image intensifier linked to a CCD)

  CBCT SURGICAL APPLICATION
• 3 stages of the scanning/image creation: in CBCT

  1. Data acquisition
  2. Primary reconstruction
  3. Secondary/multiplanar reconstruction
• Stage with 180/270/360-degree rotation


  Stage 1- data Acquisition
• Stage with Approx. 5-40 seconds long

  Stage 1- data acquisition
• Stage with Field of view (FOV) – cylindrical/spherical volume


  Stage 1- Data acquisition
• Stage that Caught in 1 cycle/scan


  Stage 1- Data acquisition
• Stage which Computer divides the volume into tiny cubes (“voxels”) and calculates the x-ray absorption in each voxel


  stage 2-Primary Reconstruction
• equivalent of voxel

  Voxel = 0.076 mm3-0.4 mm3
• A stage where Each voxel is allocated a number, then a color from the grey scale from black through to white


  Stage 2- Primary Reconstruction
• Stage: 1 scan=100M voxels


  Stage 2-Primay Reconstruction
• Stage with Overall image resolution of hard tissues is generally very good, but spatial resolution is not so compared to 2D imaging

  Stage 2- Primary reconstruction
• Stage: Smaller voxel size potentially increases the spatial resolution, but also increases the radiation dose


  Stage 2- Primary Reconstruction
• Stage: Computer software then allows the operator to select voxels in 3 planes – sagittal, coronal, axial


  Stage 3- Secondary/Multiplanar Reconstruction
• Stage: Software allows these image data sets to be scrolled through in real time

  Stage 3- Secondary/multiplanar reconsruction
• Stage: Possible to reconstruct cross-sectional (transaxial) images of any part of the jaw


  Stage 3- Secondary/Multiplanar Reconstruction
• Stage: Produce volume rendered/surface rendered images

  Stage 3- Secondary/multiplanar reconstruction
• Techniques and position in CBCT

  • Positioning techniques vary from one machine to another

  • Written protocols should be provided (patient positioning, exposure parameters, volume size)
• Patient preparation in CBCT

  • Remove any earring, jewelry, hair pins, glasses, dentures, orthodontic appliances

  • Procedure and equipment movements should be explained to reassure patients

  • Remaining stationary throughout the scan must be emphasized
• Equipment in CBCT: Smallest volume needed to answer the clinical question
• Equipment in CBCT: Optimal exposure factors selected to satisfy the diagnostic requirements of the exam
• Equipment in CBCT:Optimal reconstructed voxel size should be selected
• Equipment in CBCT: Some machines have a “quick scan” - reduces the number of projections taken = reduced dose
• Patient positioning in CBCT: Use manufacturer’s guidelines to ensure the correct region of interest is captured “Scout” view”
• Patient positioning in CBCT: Immobilization chin cups and head straps used to prevent any patient movement
• Patient Positioning in CBCT: No need for routine use of protective lead apron
• Patient positioning in CBCT: No need for routine use of protective thyroid collar (thyroid gland does not normally lie in the primary beam); consider its use particularly in children
• Effective dose varies, depending on factors such as:

  • Exposure factors (Kv, mA, time of exposure)

  • Volume size (FOV)

  • Type of equipment used

  • Part of the jaw/maxillofacial skeleton being imaged
• Typically, doses are lower than medical CT, but higher than conventional dental radiography
• Some new CBCT units produce very small FOV, high resolution images with doses equivalent to a few periapical radiographs
• Advantages of CBCT

  • Multi-planar reformatting and data manipulation, allowing anatomy or pathologic conditions to be viewed in different planes

  • Lower radiation dose than medical CT

  • Geometrically accurate images

  • Very good spatial resolution

  • Fast scanning time

  • Compatible with implant and cephalometric planning software
• Disadvantages of CBCT

  • Patient has to remain absolutely stationary throughout the scan to avoid movement artifacts

  • Soft tissues not imaged in detail

  • Computer constructed panoramic type images are not directly comparable with conventional panoramic radiographs

  • Radiodense objects (ex. Restorations, root filling materials) can produce beam hardening artifacts (streak/star artifacts)
• Assessment of Image Quality: No errors or minimal errors in either patient preparation, exposure, positioning or image reconstruction and of sufficient image quality to answer clinical question

  Grade 1- Diagnostically Accepted