Dental Radiography: CBCT, Panoramic Imaging, Radiation Safety & Errors

What does CBCT stand for?

Cone-Beam Computed Technology.

What are some common uses of three-dimensional digital imaging?

Implant placement, airway and sinus evaluation, location of anatomic structures, and evaluating abnormalities.

What is the Field of View (FOV)?

The area or volume of tissue captured by the scan, determined by the size of the X-ray beam and detector area.

What is the axial plane?

A horizontal plane that divides the body or structure into superior (upper) and inferior (lower) parts.

What is the coronal plane?

A vertical plane that divides the body or structure into anterior (front) and posterior (back) parts.

What is the sagittal plane?

A vertical plane that divides the body or structure into right and left sides.

Why is it important for the dental professional interpreting the scan to be a board-certified oral and maxillofacial radiologist?

Because CBCT scans cover a large anatomical volume beyond just the teeth, requiring specialized training to identify pathology, incidental findings, and normal anatomical variants accurately.

What instructions should be given to the patient prior to the procedure?

Ask them to remove all metal objects (jewelry, glasses, hairpins, removable appliances) and instruct them to remain completely still during the scan.

What are the advantages of CBCT imaging?

Anatomically correct (no magnification), lower radiation dose than medical CT, easy to save and transport images.

What are the disadvantages of CBCT imaging?

Patient movement artifacts, high cost, and lack of adequate training for interpretation.

What does a 1:1 relationship with anatomy in cone-beam data mean?

It means there is no magnification or distortion, so measurements taken from the scan match the true physical size of the patient's anatomical structures.

What is the definition of the focal trough in panoramic imaging?

The focal trough is a predetermined, horse-shoe shaped, three-dimensional curved zone where structures are recorded clearly in focus.

What are some differences between intraoral and panoramic imaging?

Differences: Panoramic uses extraoral film/cassettes and a moving rotational X-ray source, whereas intraoral uses small film or digital sensors placed directly inside the mouth.

How should the panoramic unit be prepared for each patient?

Pre-clean and disinfect contact areas, place protective plastic barriers on surfaces touched by the patient, and remove/dispose of barriers and re-disinfect post-procedure.

How should the patient be prepared for panoramic imaging?

Explain the procedure, have them remove all metal objects, and place the panoramic lead apron high in front without a thyroid collar.

What are the correct guidelines for positioning the patient in the panoramic unit?

Align the vertical plane to the center of the forehead, the horizontal (Frankfort) plane parallel to the floor, and the anteroposterior plane aligned with the machine's specific canine landmark guide.

How are exposure factors determined for each patient?

Exposure factors (kVp, mA, time) vary and are selected based on the size and stature of the individual patient.

What additional instructions need to be given to the patient before panoramic exposure?

Swallow and press the entire tongue flat against the roof of the mouth, close lips around the bite-block, close eyes, and remain completely still.

What are common errors in patient preparation for panoramic procedures?

Leaving jewelry or removable appliances in place and failing to raise the tongue to the palate; avoided by thorough pre-procedural checks and patient coaching.

How is the panoramic image affected by a slumped cervical spine?

It appears as a wedge-shaped radiopacity in the center/midline of the image; corrected by having the patient stand or sit straight.

How is the panoramic image affected by a tilted or rotated midsagittal head plane?

Rotation causes one side's teeth to appear magnified/wider than the other side; corrected by centering the midsagittal plane vertically.

How is the panoramic image affected by a tilted vertical head plane?

Tilted up flattens/curves the occlusal plane and drops the hard palate; tilted down creates an exaggerated smile line and crowds mandibular incisors.

How is the panoramic image affected by the anteroposterior head plane being too far forward or back?

Too far forward makes anterior teeth look narrow and blurred; too far back makes anterior teeth look wide and magnified.

What are the results of improper exposure in panoramic imaging?

Overexposure results in a dark image; underexposure results in a light image. Corrected by adjusting kVp/mA or exposure time settings.

What film handling errors produce artifacts on panoramic radiographs?

Static electricity discharges, light leaks, and fingernail artifacts.

What specific x-ray photon interactions result in ionization of atoms?

Photoelectric effect and Compton effect.

What are the direct and indirect theories of radiation exposure?

Direct effect: X-ray photons directly damage cellular molecules. Indirect effect: X-ray photons interact with water molecules, producing free radicals that cause damage.

What are the definitions and units for quantifying radiation?

Exposure dose: Roentgen (R) or Coulombs/kg (C/kg); Absorbed dose: rad or Gray (Gy); Dose equivalent: rem or Sievert (Sv); Effective dose: Sieverts (Sv).

What factors influence radiation effects on human tissue?

Total dose, dose rate, amount of tissue exposed, cell sensitivity, Linear Energy Transfer (LET), age, and length of the latent period.

What are some examples of cells/tissues that are sensitive to the effects of radiation?

lymphoid tissue, bone marrow, reproductive cells, and intestinal epithelium.

What are some examples of cells/tissues that are resistant to the effects of radiation?

mature neurons, muscle cells, and mature bone/cartilage.

Arrange the following cells/tissues in order from most to least sensitive: neurons, connective tissue, salivary glands, bone marrow, muscle, and reproductive cells.

1. Bone marrow & Reproductive cells (Most sensitive) 2. Salivary glands 3. Connective tissue 4. Muscle & Neurons (Least sensitive)

What is the difference between somatic and genetic tissues?

Somatic cells are all the cells in the body except reproductive cells; damage affects only the exposed individual. Genetic cells carry hereditary information; damage can affect future generations.

What is the difference between the latent period of radiation and the cumulative effect of radiation?

The latent period is the time interval between radiation exposure and the first observable clinical sign of biological damage. The cumulative effect refers to the unrepairable additive nature of radiation injury over time with repeated exposures.

What are some everyday risks that are comparable to the risk of a radiographic examination?

Everyday activities carrying a similar low statistical risk include driving a car for a short distance, riding a bicycle, or smoking a very small number of cigarettes.

What are the basic requirements of the diagnostic radiation machine operator certificate rule and the x-ray machine inspection law?

Operators must possess proper credentialing/certification to legally expose patients, and X-ray equipment must undergo periodic state or local safety inspections.

What is leakage radiation?

any stray radiation escaping outward through the protective housing of the tubehead.

What is primary radiation?

Useful beam coming directly from the target of the X-ray tube

What is secondary radiation?

radiation that has been deflected from its path by interaction with matter

What is the ALARA principle and how does it pertain to radiation safety?

ALARA stands for 'As Low As Reasonably Achievable.' It mandates that every reasonable effort must be made to maintain radiation exposures to patients and operators as far below maximum limits as practical.

What are the radiation safety measures associated with the dental x-ray machine?

Built-in filtration, collimation, and long position-indicating devices (PIDs) constructed of lead-lined cylinders.

What are the radiation safety measures that reduce exposure to the dental patient?

Using digital sensors or fast-speed image receptors, rectangular collimation, proper exposure settings, patient lead aprons, and avoiding unnecessary retakes.

Why is it important to shield the patient during a radiographic procedure?

To protect radiosensitive tissues—specifically the thyroid gland and reproductive organs—from unnecessary scatter radiation.

What is the MPD and how does it influence the behavior of the dental radiation operator?

MPD stands for Maximum Permissible Dose—the maximum dose equivalent that a body is permitted to receive within a specific period with little expectation of significant bodily injury.

What are the radiation safety measures that the operator should practice for protection from occupational exposures?

Standing behind a protective barrier or wall, standing at the correct angle/distance away from the primary beam, and never holding a receptor or tubehead during exposure.

What are causes for unnecessary exposure to radiation?

Technical/operator errors leading to retakes, improper exposure settings, lack of proper collimation, and failure to use high-speed receptors.

What are the requirements for primary and secondary barriers?

Primary barriers require heavy shielding like lead sheets or thick concrete; secondary barriers require standard drywall or lesser thickness since scatter energy is much lower.

What is the purpose of wearing a personal occupational dosimeter?

To monitor and record the accumulation of occupational scatter radiation received by the dental worker.

How should the dosimeter be worn and when should it be analyzed?

Worn at waist or chest level outside of protective clothing during work hours; it should never be worn during personal medical/dental x-rays. 1-3 months

What are the ADA's recommendations for patient exposure to radiation?

Prescribing radiographs based on individual clinical needs following a comprehensive clinical examination.

Why is it important to get Informed Consent from the patient?

To ensure the patient understands the proposed diagnostic procedures, associated risks, and benefits.

What are the legal ramifications if a patient refuses exposure to radiation?

Document the refusal in the patient record, inform the dentist of the limitation this places on diagnosis, and have the patient sign a refusal waiver.

How can you tell the difference between a quality radiograph and one that has a technical or processing error?

A quality radiograph shows correct density, contrast, sharp outlines, proper anatomical coverage without distortion, whereas errors display artifacts, blurriness, or poor density.

What are the causes of image foreshortening and elongation? How do you correct these dimensional errors?

Foreshortening: Caused by excessive vertical angulation; correct by decreasing vertical angulation. Elongation: Caused by insufficient vertical angulation; correct by increasing vertical angulation.

What does an error in horizontal angulation do to the recorded images of the teeth? Why does this error render the image undiagnostic?

Incorrect horizontal angulation causes overlapping of adjacent tooth crowns and roots, making it impossible to evaluate interproximal bone levels.

How would you go about correcting cone cut errors?

Ensure the PID is properly aligned and center the central X-ray beam precisely over the receptor.

What are typical patient preparation errors that can occur during an intraoral radiographic procedure?

Leaving eyeglasses or partial dentures in place and incorrect lead apron/thyroid collar placement.

What does a collimator do?

Limits radiation from scattering and restricts the shape of it. 2.75in

What are bite wings used for?

Asses bone levels and how teeth meet

What is the maximum permissible dose for occupational workers?

5 rem/ year

What is ALATA?

As Low As Technologically Achievable

What is the filtration made out of?

Aluminum

What is the federal requirement for filtration in mm?

2.5mm

Which is a non-ionizing radiation?

Classic scattering

What is the purpose of a dosimeter?

Measure how much you’re being exposed

What do intraoral lead aprons have that extraoral aprons dont?

thyroid collar

What is radiation throughout your lifetime?

accumulative

What is foreshortening?

Anatomical structures become shorter of compressed

what is elongation?

Anatomical structures become longer

What is ionization?

The process by which high-energy radiation knocks orbital electrons out of atoms, leaving behind a positively charged atom and a free electron

What happens to tissues when rays pass through them?

When these rays pass through human tissue, they ionize atoms in cellular molecules, which can break chemical bonds or alter DNA