Cone Beam CT, & Why Sometimes Do We Order It?

Cone Beam CT (Computed Tomography) has been developed in recent years for use in dental & maxillofacial regions and its slowly establishing itself as the imaging modality of choice in certain clinical situations. It allows clinicians to get a 3D image reconstruction of the 2D image. Thus allows a better and accurate radiographic interpretation.

Considerable controversy exists for the use of CBCT. Some authorities claim that CBCT should be used on routine basis for dental and maxillofacial examinations. Others claim that it should only be used when conventional panoramic radiography is not sufficient for proper examination of the patient.

Some of the indications of CBCT are:

  1. Localized assessment of an impacted tooth
  2. Assessment of cleft palate
  3. When planning Apicoectomy or surgical endodontics
  4. Assessment of Maxillofacial Trauma
  5. Assessment of the relationship of the wisdom teeth to the inferior alveolar nerve
  6. Implant Surgery
  • Guidelines For Taking a Cone Beam CT

The following guidelines will help the clinician in preparing the equipment and the patient prior to taking a CBCT.

Patient Preparation

  1. Patients should be asked to remove any earrings, dentures, jewelry, hair pins, & glasses.
  2. The patient should be informed and reassured about how the machine will move and emphasize on the importance to remain still without movement.

Equipment Preparation

  1. Use the radiation volume necessary to answer the clinical question required. Thus minimizing radiation dose and enhancing image quality.
  2. Optimal Exposure factors should be selected to satisfy the diagnostic requirement of the examination.
  3. Optimal reconstructed voxel size should be selected.
  4. Use the “Quick Scan” feature, if available & when it satisfies the diagnostic requirement.

Patient Positioning

  1. The patient should be positioned according to the manufacturer instructions.
  2. There is no need for routine use of lead apron and/or thyroid collar.

The following case is an example of why dentists order a Cone Beam CT scan that I have noticed in my practice.

A  female patient was complaining of a broken right wisdom tooth. She has visited a couple of dental clinics and none of them agreed to extract it. They were all afraid due to its close proximity to the lower nerve of the jaw (Inferior Alveolar Nerve). The patient here was informed of the possibility of the risk of nerve paresthesia or complete total loss of sensation on the right side of the jaw.

She was informed to do a CBCT to detect how close it is to the inferior alveolar nerve. On CBCT however, a thin bone appeared between the root of the tooth and the nerve thereby separating it. In addition an apical inflammation was also noted very clearly. Thanks to advantage of a CBCT for giving us a  3D image that in no way would we get it with a normal panoramic radiograph.

The treatment was still preferred to do the extraction surgically to minimize the stress on the nerve and for better prognosis.

Reference: Essentials of Dental Radiography & Radiology by Eric Whites, & Nicholas Drage

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