CBCT: Three-Dimensional Imaging of the Jaws

Cone beam computed tomography produces a three-dimensional volume of your jaws, teeth and surrounding structures, which can then be examined slice by slice in any plane. It is the most significant advance in dental diagnosis of the past thirty years.

It is also not a routine image. It carries a higher radiation dose than a standard X-ray, and it is taken when a specific question needs a three-dimensional answer.

How it differs from a normal X-ray

A conventional dental radiograph is a shadow: a three-dimensional object flattened onto a two-dimensional surface. Structures superimpose on one another, a curved root may be foreshortened, and the geometry is distorted in ways that vary across the image.

A cone beam scanner rotates around your head, capturing hundreds of images from different angles, and reconstructs them into a volume of data. That volume can be sliced in any direction and, critically, is dimensionally accurate: a measurement made on the scan corresponds to a real distance in your jaw.

It differs from medical CT in using a cone-shaped beam and a single rotation, which makes it faster, smaller, cheaper and considerably lower in dose, while producing better resolution for hard tissue in the jaws. It is poorer than medical CT at distinguishing soft tissues, which is a deliberate trade.

When it genuinely changes the plan

Implant planning is the most common indication. It shows the width and height of available bone, its density, the exact path of the inferior alveolar nerve in the lower jaw, and the position and floor of the sinus in the upper jaw. From that data, an implant position can be planned virtually and a surgical guide printed so the implant goes exactly where the final tooth needs it.

Endodontics is the other major use. It reveals extra canals that do not appear on a flat image, identifies the cause of a persistent infection after treatment, locates root fractures, and shows the true extent of a lesion at the root tip. For a tooth that has failed previous root canal treatment, it frequently provides the answer directly.

Also: impacted teeth, particularly wisdom teeth sitting close to the nerve and impacted canines whose exact position determines the orthodontic approach; jaw pathology such as cysts and tumors; temporomandibular joint assessment; facial trauma; and airway analysis in sleep apnea evaluation.

Dose, and the case for restraint

A dental cone beam scan delivers substantially more radiation than a single intraoral X-ray, though considerably less than a medical CT of the same region. The exact figure varies widely with the machine, the field of view and the resolution selected, which is itself an important point: a small field of view covering two teeth carries a fraction of the dose of a full craniofacial scan.

The professional consensus is clear and worth stating plainly. Cone beam imaging should never be used as a routine screening tool or taken on every new patient. It is justified when the diagnostic question cannot be answered with lower-dose imaging and when the answer will change what is done.

Where it is indicated, the smallest field of view that answers the question is used, and the resolution is matched to the task. Children and adolescents warrant particular care.

Having the scan, and reading it

The scan itself is easy. You sit or stand with your head in a support while the arm rotates around you, typically for ten to forty seconds. Nothing goes in your mouth and nothing touches you. The main requirement is staying still, since movement blurs the reconstruction.

Afterward the volume is reviewed on screen, and you can be shown the relevant slices. Seeing the actual bone available where an implant is planned, or the extra canal in a tooth that has kept hurting, makes the treatment plan concrete in a way a description does not.

One responsibility comes with a three-dimensional image: it includes structures beyond the teeth, and anything unexpected in that volume needs to be evaluated, sometimes by a radiologist. If a scan has been recommended for you, ask what question it is meant to answer. Call Cedar Creek Dentistry in Portland.

Questions about your own care? The team at The Best Dentist In Portland, Oregon is happy to help — call us at (503) 646-1811.

This article is for general information only and is not medical advice.