Interpretation Basics of Cone Beam Computed Tomography. Группа авторов

is teeth that have been endodontically treated, as the filling material causes artifacts that obscure small fractures and create pseudo‐fracture lines (Figure 2.6).

Figure 2.3. (a) Coronal view showing localized vertical bone loss (white arrow) along the facial root surface of a mandible molar. (b) Axial view showing localized bone loss (white arrow) along the facial root surface of a mandible molar.

Figure 2.4. (a) Pantomograph showing impacted maxillary right canine. (b) Periapical radiographs showing impacted maxillary right first premolar and canine with a dentigerous cyst. (c) Cross‐sectional slices showing a vertical root fracture on the maxillary right second premolar (white arrow) and dentigerous cyst associated with impacted canine.

Figure 2.5. (a) Cross‐sectional slices showing a horizontal root fracture (white arrow). (b) Cross‐sectional slices showing a horizontal root fracture (white arrow).

Figure 2.6. Axial views showing artifact streaking from an endodontically treated tooth obscuring the root when evaluating for root fractures.

      The smallest root fracture that can be visualized on a CBCT scan is determined by the resolution/voxel size used. This is due to the Nyquist Theorem, which samples digitized information at 2 times the highest frequency. On a CBCT scan, this translates to the smallest root fracture visualized is twice the resolution/voxel size used. For example, if a resolution/voxel size of 0.2 mm is used, the smallest root fracture visible would be 0.4 mm.

      7 = Limited FOV CBCT should be considered when evaluating nonhealing previous endodontic treatment.

      8 = Limited FOV CBCT should be considered for nonsurgical retreatment.

      Surgical Retreatment

      9 = Limited FOV CBCT should be considered for presurgical treatment planning.

      Special Conditions

      10 = Limited FOV CBCT should be considered for implant treatment planning and placement.

      11 = Limited FOV CBCT should be considered for diagnosis and management after trauma.

12 = Limited FOV CBCT should be considered for localizing resorption (Figures 2.7 and 2.8).

Figure 2.7. Sagittal views showing the extent of invasive cervical resorption (white arrow) on the palatal root surface of a maxillary incisor.

Figure 2.8. Axial (A), coronal (C) and sagittal (S) views showing the extent of palatal root resorption (white arrow) of the maxillary right first molar.

      Outcome Assessment

      13 = Intraoral radiographs should be considered when evaluating healing post‐nonsurgical or surgical endodontic treatment if no clinical signs or symptoms are present.

      HOWEVER

14 = Limited FOV CBCT should be considered if it was used pretreatment to re‐evaluate the tooth endodontically treated (Figure 2.9).

Figure 2.9. (a) Rotated sagittal views showing a bone defect (white arrow) on the mesial of a mandibular molar. (b) Rotated sagittal views showing a bone defect (white arrow) on the mesial of a mandibular molar captured 6 months after (a) suggestive of a prominent marrow space.

Orthodontics

      The AAOMR published a paper in 2013 with recommendations regarding CBCT use in orthodontics. There are four main guidelines given.

      1 = Image appropriately according to the patient’s clinical condition.

Imaging should be based on a patient’s history, clinical examination, and presence of clinical findings where CBCT benefits outweigh risks. Avoid using a CBCT only for lateral cephalometric and panoramic views or when information can be obtained with nonionizing methods such as virtual models. When using CBCT, a FOV that captures only the region of interest should be used.

      2 = Assess the radiation dose risk.

      Consider the relative radiation level when assessing imaging risk over the course of orthodontic treatment. Explain risks and benefits to patients prior to imaging and document in patients records.

      3 = Minimize patient radiation exposure.

Take a CBCT with proper settings, a FOV that matches the region of interest, adult versus child setting, and appropriate voxel size. Use shielding when possible, but make sure that it is not captured in the FOV (Figure 2.10). If you have a CBCT unit in office, ensure the machine is continually calibrated.