Radiology Basics Dental Assistant Registration Course Click the play (arrow) button to advance to the next slide.

Discovery of the X-Ray William Conrad Roentgen discovered x-rays in 1895 by using a glass vacuum tube with an electrical circuit connected to each end. The stream of electrons traveled from the cathode end to the anode end. Also in 1895, Dr. Otto Walkoff was the first to use the x-ray to take the first dental radiograph. In 1896, Dr. C. Edmund Kells took the first intraoral radiograph and Dr. William Rollins, the inventor of the first dental x-ray unit, reported effects of radiation exposure. In 1913, Dr. William Coolidge invented the hot cathode x-ray tube. Victor X-Ray Corporation, later known as General Electric Corporation, developed a dental x-ray machine known as the Coolidge tube.

Radiation Production Thermionic emission occurs as the filament is heated by electricity, sending electrons through the tube. Electrons travel from cathode to anode The X-ray is produced at the exact moment the electrons collide.

Dental X-Ray Film Halide crystals suspended in gelatin store energy when exposed to x-rays, thus forming a black mark on the film. There are several speeds used by dentists; D-speed (Ultraspeed), E-speed, (Ektaspeed), and F-speed (InSight). Five basic sizes are used in intraoral x-rays, depending on the size of the patient’s oral cavity and the area to be radiographed. Film is placed in the intraoral film packet, which is sealed in plastic wrap and backed with lead foil. Dental film should be stored carefully to prevent exposure to stray radiation.

Digital Radiography Projected to replace conventional film exposure completely. Allows dentist to take an intraoral or extraoral radiograph and display on computer screen without exposing or processing dental film. The image can be digitized, enhanced, printed, stored, or sent to another office by fax or modem. Term “image” is used when speaking of – not “radiograph” or “x- ray” Pixels are the dots that make up an image; the more pixels, the higher the resolution and sharper the image. A computer can display over 200 shades of gray, although humans can detect only 32. The computer software can enhance these shades for better comparison and evaluation from the dentist.

Direct Digital Imaging Sensor is placed in the patient’s mouth and exposed to x-rays. It is then transmitted to the computer almost immediately.

Indirect Digital Imaging Scanner digitized the image and then sends to the computer. Indirect is not used as much in dentistry because the quality of the image is inferior to a direct digital image; however, this technique does offer a means to digitize existing x-rays for storage. Storage phosphor: Second type of indirect digital imaging system. Wireless that uses coated plates instead of sensors to record the image; which must be cleared between each use and sterilized. They are placed on a high-speed scanner and sent to the computer

Computed Tomography (CT) Used to plan implant surgery and to locate and define lesions associated with oral cavity. Patient is placed in unit, where the radiation and image detector rotates around them; then information is sent to a computer and image displayed on screen. Magnetic resonance imaging (MRI) Mainly used to diagnose TMJ disease. Ability to look at soft tissues with very little risk to the patient. Electromagnetic radiation instead of ionizing.

Components of the Dental X-Ray Unit The dental assistant should understand the components that make up the dental x-ray unit. Settings, adjustments, and selections of milliamperage, kilovoltage, and the electric timer are made on the control panel. The amount or quantity of electrons is determined by the milliamperage. The quality or penetrating power of the central beam is determined by kilovoltage (KV). The higher the KV, the greater the penetrating power of the x-rays, and therefore, less exposure time is necessary.

Components of the Dental X-Ray Unit The electronic timer controls the total time rays flow from the x-ray tube. It is located in a safe area outside the room or behind a lead barrier to keep the operator safe. The amount of radiation exposure a patient receives is determined by milliamperage seconds (mAs). Contrast is indicated on an x-ray by differing shades of gray. The degree of darkness on an x-ray is referred to as density, and is affected by distance to the x-ray tube, patient tissue thickness, and amount of radiation reaching the film.

Components of the Dental X-Ray Unit The arm assembly is a flexible extension attached to the x-ray room wall that enables the operator to position the unit as needed. The x-ray vacuum and the step-up (high voltage) and step-down (low voltage) transformers are located in the tubehead. X-rays travel through the x-ray tube to a metal filter, known as an inherent filter, which separates hard and soft x-rays. Hard x-rays, called the central beam, pass through the collimator, a lead disc used to filter out weaker x- rays.

References Dental Assisting: A Comprehensive Approach, Phinney, D.J., Halstead, J.H. (3rd. Ed.) Thomson /Delmar Learning,2008 Dental Radiography: Principles & Techniques, 3rd Ed; Iannucci & Howerton, Elsevier, St. Louis, 2006