A Dental Cone Beam Computed Tomography (CBCT) scan is a specialized X-ray procedure used when traditional two-dimensional dental images do not provide enough detail for complex treatment planning. This technology rotates a cone-shaped X-ray beam around the patient’s head, acquiring hundreds of views in a single rotation to create a three-dimensional (3D) digital volume of the teeth, jawbone, soft tissues, and nerve pathways. Visualizing these structures in 3D is necessary for procedures like dental implant placement, complex endodontics, and surgical planning for impacted teeth. While the CBCT offers a significant diagnostic advantage, the process involves exposure to ionizing radiation, leading to questions about the dose received.
Understanding Radiation Measurement Units
The concept of “effective dose” is the standard measure used in medical and dental imaging to quantify the risk from radiation exposure. Effective dose takes into account the amount of energy absorbed by the body and the specific sensitivity of different organs and tissues to radiation. This allows for a standardized comparison of the potential biological effect from different types of radiation exposure. The primary unit for expressing effective dose is the sievert (Sv). Because the doses in diagnostic imaging are quite small, smaller fractions are used: the millisievert (mSv) and the microsievert (\(\mu\)Sv). Most radiation doses encountered in dentistry are reported in microsieverts, which helps represent the very low levels of exposure more clearly.
Typical Radiation Dose from a Dental CBCT Scan
The actual radiation dose from a dental CBCT scan falls within a wide range, primarily depending on the size of the area being scanned and the equipment used. For a focused field of view (FOV), which targets a small area like a single tooth or a specific section of the jaw, the effective dose can be as low as 5 \(\mu\)Sv to 100 \(\mu\)Sv. These smaller scans are typically used for specific procedures like endodontic evaluation or assessment of a localized lesion. When the procedure requires a medium or large field of view to image the entire jaw or the maxillofacial region, the effective dose increases significantly. Large FOV scans, often required for orthognathic surgery planning or full-arch implant cases, can range from approximately 46 \(\mu\)Sv up to 1073 \(\mu\)Sv, with mean values clustering around 212 \(\mu\)Sv for adults. Modern CBCT machines frequently utilize low-dose protocols that aim to keep the exposure for limited FOV scans near the lower end of this spectrum.
Contextualizing the Dose Against Other Sources
Every person is continuously exposed to natural background radiation from cosmic rays, the earth, and even food, which averages about 3,650 \(\mu\)Sv (3.65 mSv) annually. A CBCT scan with a typical effective dose of 50 \(\mu\)Sv is equivalent to only about five to eleven days of this normal environmental exposure.
This dose is comparable to or slightly higher than other common dental X-rays. A standard panoramic X-ray, which captures the entire mouth in a single two-dimensional image, exposes the patient to an effective dose ranging from 9 \(\mu\)Sv to 30 \(\mu\)Sv. A full-mouth series of traditional intraoral X-rays, consisting of 18 separate images, can result in a cumulative effective dose of around 171 \(\mu\)Sv. A long-haul airplane flight, such as one across the United States, typically results in an exposure of about 40 \(\mu\)Sv.
The CBCT dose is substantially lower than that of a traditional medical CT scan, which uses a fan-shaped X-ray beam and requires a much higher dose to image the head or abdomen. A medical CT scan of the head or neck can easily exceed 1,000 \(\mu\)Sv. An abdominal CT can expose a patient to the equivalent of three years of natural background radiation. This comparison highlights that the dental CBCT is a low-dose imaging modality relative to its medical counterparts.
Factors Influencing Dose and Safety Protocols
The wide range of reported CBCT doses stems from several technical and patient-specific variables. The most significant factor is the Field of View (FOV) size, where scanning a smaller, focused area delivers a much lower dose than scanning the entire maxillofacial complex. Other technical factors include the machine manufacturer, the exposure settings selected by the operator (such as tube current and voltage), and the scan time. Larger patients may also require higher exposure settings to achieve a diagnostic quality image, contributing to dose variability.
Dental practitioners adhere to strict safety protocols to minimize patient exposure, guided by the principle of ALARA, or “As Low As Reasonably Achievable.” This means the lowest possible radiation dose is used while still ensuring the image is diagnostically acceptable for the clinical task at hand. Protocols include limiting the FOV to the smallest area necessary, utilizing low-dose settings when high-resolution is not required, and carefully positioning the patient to avoid the need for repeat scans. While lead aprons and thyroid collars are commonly used as protective shielding, the primary method of dose reduction involves optimizing these technical parameters.