This chapter summarises the prescription of the various imaging techniques in relation to the more common conditions/clinical situations encountered in dentistry. An introduction to the key responsibilities and principles involved in radiological interpretation is also included.
Abbreviations: IOR – intraoral radiography; OPG – panoramic radiographs; CBCT – cone beam computed tomography; MDCT –multidetector (multislice) computed tomography; MRI – magnetic resonance imaging.
PRESCIPTION OF THE OPTIMAL IMAGING TECHNIQUE – A SUMMARY:
The various imaging techniques, including the associated radiation dose levels delivered, have been discussed in the preceding chapters. The following summarises the indications in relation to the conditions and clinical scenarios which are more commonly encountered in dentistry:
• Bitewing radiographs remain the optimal technique – the limitations, especially in relation to sensitivity, are noted and clinical correlation is essential.
• OPGs are considered inadequate – caries cannot be fully excluded.
• CBCT is associated with increased sensitivity, but decreased specificity. Artefact related to restorations is another limitation.
• OPG provides a good overview. The associated limitations compared to the IOR are recognised.
• IOR demonstrates periodontal bone levels and root morphology, but is less accurate than CBCT and MDCT. Limited sensitivity in relation to vertical defects and furcations have also been demonstrated.
• CBCT and MDCT provide 3D information, which allows for more accurate diagnosis and treatment planning. Could be considered for cases with moderate to severe periodontal disease.
Periapical inflammatory disease:
• A periapical radiograph and clinical findings are sufficient for most cases. • OPG is less sensitive for detecting periapical lesions.
• CBCT and MDCT are more sensitive, should be considered in cases with contradictory findings or non-specific/unresolved pain.
• In rare instances, MRI can be considered where the clinical suspicion for periapical inflammatory lesion is high, but this is not demonstrated with MDCT/CBCT.
Other conditions affecting the jaws:
• For example, cysts, tumours, osteomyelitis, etc.
• MDCT is usually the technique of choice. CBCT may suffice for some lesions.
• Dentoalveolar inflammatory disease is a common cause – clinical findings combined with IOR and/or OPG are sufficient for diagnosis in most cases.
• Dentoalveolar inflammatory lesions contributing to orofacial pain cannot be fully excluded with IOR and OPG. • MDCT or CBCT should be considered if the cause of pain is not identified clinically and with 2D imaging.
• Volumetric imaging should be considered if other causes for the orofacial pain is suspected, e.g. sinus disease.
• MRI should be considered if diagnosis is not made following volumetric imaging.
• IOR and OPG may be useful for initial assessment.
• Pre-implant MDCT or CBCT must be considered.
• MRI may be used to identify the location of the inferior alveolar nerve where the mandibular canal borders are not demonstrated with MDCT or CBCT.
Dental extractions/exposure procedures:
• IOR and OPG are appropriate for most cases.
• Volumetric imaging could be considered for more complicated cases or where the tooth is potentially in close relationship to significant anatomic structures, e.g. the mandibular canal.
• Third molar and related morphology including the relationships with the mandibular canal are better demonstrated with volumetric imaging. The indication for CBCT or MDCT is based upon clinical parameters, potential intra-surgical implications and the OPG appearances.
• Ultra-low dose CBCT should be considered for impacted/ectopic canines.
• PA radiographs with different horizontal and vertical angulations has been recommended.
• CBCT and MDCT should be considered where 2D imaging is inconclusive, for complex/severe cases of dentoalveolar trauma and where jaw fractures are suspected. MDCT is the technique of choice for more involved facial bone fractures.
• OPGs are inadequate – sinus disease cannot be fully excluded with this technique.
• Volumetric imaging (particularly MDCT) is recommended for the assessment of sinus disease.
• OPGs are inadequate – arthropathy cannot be fully excluded with this technique.
• MDCT is optimal for the evaluation of the bony structures. MDCT also demonstrates the soft tissues and the articular disc may be visualised.
• CBCT demonstrates the bony structures – image degradation related to beam hardening must be considered.
• MRI is optimal for the evaluation of the soft tissues related to the TMJs. MRI is also optimal in the evaluation for effusion, synovitis and marrow oedema. Bony structures are also demonstrated although the lower spatial resolution is recognised.
Soft tissue lesions:
• CBCT does not demonstrate the soft tissues sufficiently well.
• MDCT or MRI could be considered. Ultrasound may be useful, especially for more superficial lesions.
All structures included in any imaging must be appropriately evaluated. The practitioner presiding over the radiologic study is responsible for the thorough interpretation of the entire image, not only the region of interest. Should the entirety of the lesion not be included in the initial scan, preliminary interpretation should still be carried out, which can be useful in deciding the optimal imaging technique for further evaluation. Studies have demonstrated the challenges that dentists encounter in relation to the interpretation of OPGs and CBCT scans.
Volumetric data requires a different level of knowledge and skill for interpretation. Several authors recommend that CBCT scans should be interpreted by persons with sufficient advanced training.
The following publications introduce the key principles of radiologic interpretation:
Koong B. The basic principles of radiological interpretation. Aust Dent J. 2012;57 Suppl 1:33–9. Koong B. Diagnostic imaging of the periodontal and implant patient. In Lang PL & Lindhe J (eds.), Clinical periodontology and implant dentistry (6th edition., 574-608). UK: Wiley Blackwell
Some of the key points, based upon these two publications, are summarised:
• Radiologic anatomy: An in-depth knowledge of anatomy and their normal variants is critical. Knowledge of the appearances of all normal structures will aid in identifying the presence of pathology.
• Pathology: Knowledge of the pathology which may occur in all regions included in the field of view or scan, as well as the radiologic appearances of these lesions, is obviously of importance.
• Imaging modality: Understanding the strengths and limitations of the various imaging techniques impacts on the interpretation of the studies. Examples include the tomographic nature of OPGs and beam hardening seen in CBCT scans.
• Viewing conditions: The lighting conditions and display quality of the monitor can have a significant influence on the accuracy of the radiologic interpretation. This was covered in Chapter 1 of this series.
Identifying the presence of disease
• A methodical approach during evaluation of the entire image or dataset is critical.
• The interrogation of volumetric data requires a different skill set to that for plain 2D films.
Radiologic evaluation of a lesion(s)
An algorithm should be followed to identify the relevant radiologic features. Below is an example:
2. Shape and contour
4. Internal appearances
5. Adjacent anatomical structures
Lesions will not always present classically, nor will they necessarily demonstrate all the typical features. As a result, it is necessary to weigh the identified features. For example, a lucency at the apex of a tooth is often inflammatory in nature. However, a malignant lesion may also present as a lucent lesion apically and weight must be given to the marginal appearances.
As advances in diagnostic imaging continue, it is increasingly essential that clinicians remain up-to-date in order to prescribe the optimal radiological test for their patients. The practitioner presiding over the radiologic study is responsible for the examination in its entirety and should ensure that it is interpreted by appropriately skilled persons.
Published on March 15, 2021Back