Chapter 38: Foundations of Radiography, Radiographic Equipment, and Radiation Safety

Introduction to Radiography:

  • Allows dentists to see conditions not visible in the oral cavity

  • Exposure to radiation has the potential to cause biologic changes

  • DA must have an understanding of radiation; minimizes exposure to patient and operator


Uses of Dental Images:

  1. Detects dental caries early

  2. Identifies bone loss early

  3. Locates abnormalities in hard and soft tissues

  4. Evaluates growth and development

  5. Provide information during dental procedures

  6. Document patient’s condition

Discovery of X-Radiation:

  • Wilhelm Conrad Roentgen: physicist; discovered the x-ray (Nov. 8, 1895)

    • Roentgen Rays: what x-rays were referred as

    • 1901: Awarded the first ever physics Nobel Prize

Pioneers in Dental Radiography:

  • Otto Walkhoff: first dental radiograph

  • Dr. C. Edmund Kells: first practical use of radiographs in dentistry (1896)

Radiation Physics:

  • Atom: composition of nucleus and orbiting electrons

    • Electrons remain stable unless disturbed; x-rays can disturb

  • Nucleus: composed of protons and neutrons

    • Protons: carries positive electrical charges

    • Neutrons: carries no electrical charges

    • Dental x-rays don’t affect the nucleus; only changes direction/scatters

  • Electrons: tiny, negatively charged particles; orbits nucleus

    • Electron Shell: orbit path of electron; contains specific # of electrons

    • Maintained in orbit by electron-binding energy

  • Ionization: x-ray photons collide with electrons; pushes an electron out of orbit and produces an ion

    • Photon: minute bundle of energy with no weight/mass

Properties of X-Rays:

  • X-Rays: form of energy that can penetrate matter

  • Electromagnetic Radiation: made up of photons that travel through space at the speed of light in a straight line in a wavelike motion

    • Shorter the wavelength, greater its energy

  • Electromagnetic Energy:

    • Travels through space in transverse waves

    • Short wavelengths, high frequency = more energy

    • Long wavelengths, low frequency = less energy

  • Dental radiographs need short wavelengths or hard radiation

    • Hard Radiation: high frequency, high energy, and high penetrating power

    • Soft Radiation: low energy, low frequency, and low penetrating power

      • Unsuitable for exposing dental radiographs

Types of Radiation:

  • Primary Radiation: from central beam of x-ray tubehead

    • High energy, short wavelength, travels in straight line

    • Useful x-ray; produces diagnostic image on film

  • Secondary Radiation: x-radiation from primary beam interacting with matter

    • Waves turn into longer wavelengths; less energy and diagnostic x-ray

  • Scatter Radiation: secondary radiation; when beam deflects from path by interaction with matter

    • Scatters in all directions; most serious danger to operator

      • Operator must be at least 6 feet from patient or behind a structural shielding

  • Leakage Radiation: escapes in all directions from tube/tubehead

    • Check machines for leakage; cannot use till problem is fixed

    • Not useful for diagnostic x-rays

    • Long wavelengths cause harm

X-Ray Production:

  1. X-ray machine is plugged into outlet and turned on; electric current enters control panel and travels through tubehead

  • Travels from control panel to tubehead through electrical wires in extension arm

  • Travels through step-down transformer to cathode filament

    • Filament circuit heats the tungsten filament in the cathode portion

    • Causes thermionic emission; releases electrons

  1. Exposure button activates high-voltage circuit

  • Electrons accelerate across tube to anode

  1. Less than 1% is converted to x-rays; 99% lost as heat

  • Heat is carried away and absorbed

  • X-rays travel through unleaded glass window, tubehead seal, and aluminum filter

    • Aluminum Filter: removes longer-wavelength x-rays

  1. X-rays travel through collimator, lead-lined PID, and exits at end of PID

Interactions of X-Rays with Matter:

  • No interaction

  • Photoelectric Effect

    • Ex. light shines on metal; electrons eject from the surface

  • Compton Scatter

    • Ex. x-rays scattered on material with x-increase in wavelength

  • Coherent Scatter

    • Ex. photon bounces off atom and has low-energy radiation

Radiolucent and Radiopaque Characteristics:

  • Radiolucent Structures: x-rays pass through

    • Appear dark or black on radiograph

  • Radiopaque: x-rays cannot pass through

    • Appear white or light gray on radiograph

Characteristics of X-Ray Beam:

  • Quality: energy or penetrating ability

  • Quantity: number of x-rays produced

  • Intensity: combination of quantity and quality

X-Radiation: 3 characteristics determine sharpness/detail of x-ray

  • Contrast: contrast of an image; difference between shades of gray

    • Influenced by kilovoltage (kVp)

      • Higher kVp, more penetrating x-rays, lower radiation dose, decreases image contrast

  • Density: overall blackness or darkness of an image

    • Influenced by milliamperage (mA)

      • Milliamperage: controls temperature of cathode filament; how many electrons get produced/released

        • More electrons produced, more x-rays emitted, better quality/intensity of image

    • Other Factors Influencing Density:

      • Distance, developing time/temperature, patient body size

  • Intensity: number and energy of photons

    • Affected by time and distance

Geometric Characteristics: affect quality of radiograph

  • Sharpness: detail, resolution, definition

  • Distortion: disproportionate change in size

    • Caused by excessive/insufficient vertical angulation

  • Magnification: proportionate enlargement

Dental X-Ray Machine:

  • Tubehead: metal housing; contains x-ray tube that produces dental x-rays

    • Metal Housing: body of tubehead; filled with insulating oil

    • Tubehead Seal: leaded glass/aluminum; keeps oil in tubehead and filters x-ray beam

    • X-Ray Tube: glass; where x-rays are produced

      • Heart of x-ray generating system

      • 6 inches long, 1 inch in diameter

  • Position Indicator Device (PID): aims the x-ray beam

    • Open End of PID: placed against patient’s face

    • Cylindrical or Rectangular

  • Extension Arm: encloses wire between tubehead and control panel

    • Positions tubehead

  • Control Panel:

    • Master switch, indicator light, selector buttons, exposure button

Radiation Effects:

  • Ionization: harmful effect of x-rays in human beings

    • Amount of x-radiation in dental is small

    • Entire x-ray area is considered a radiation hazard

  • Critical Organs: skin, thyroid gland, lens of the eye, bone marrow

  • Causes biologic changes (chemicals, cells, tissues, and organs)

    • Latent Period: period between direct exposure and development of biological effects

  • Cumulative Effects: effects of exposure increase every time the individual is exposed

    • Tissues: some damage occurs; can repair but never to original state

  • Acute Radiation: large dose of radiation absorbed in a short period

  • Chronic Radiation: small amounts of radiation absorbed repeatedly over a long period

  • Genetic Effects:

    • Genetic Cells: reproductive cells

    • May not involve primary individual exposed

    • Cannot be repaired; is passed to future generations

  • Somatic Effects:

    • All other cells in the body

    • Damage remained with primary individual; not passed to future generations

Radiation Measurement:

  • Traditional/Standard System: older system

  • Systeme Internationale (SI): newer system

  • Maximum Permissible Dose: 5000 mrem (5.0 rem) per year for occupationally exposed individuals

    • Carries little change of injury

    • Strive for 0; adhere to strict protection practices

  • Daily Radiation Exposure:

    • Natural Radiation: earth, sun, atmosphere

    • Artificial Radiation: x-rays, televisions, air travel, tobacco, smoke alarms, cell phones

Radiation Safety:

  • ALARA: As Low As Reasonably Achievable

    • Using the least amount of radiation possible!!

Dentist’s Responsibilities for Dental Imaging:

  1. Prescribe: take images when required for diagnostic purposes

  2. Ensure: all radiographic equipment is properly installed and in safe working condition

  3. Provide: shielding to protect staff/patients

  4. Require: properly train and supervise individuals taking radiographs

  5. Obey: follow state radiographic licensing requirements/rules

  6. Participate: informed consent

Protective Devices:

  • Tubehead: aluminum filters, lead collimators, PIDs

  • State/Federal regulating agencies check equipment regularly

  • Repair faulty/malfunctioning equipment immediately

  • Radiation Monitoring:

    • Film Badge

    • Pocket Dosimeter

    • Thermoluminescent/TLD

Patient Protection:

  • Lead Apron and Thyroid Collar: must be on patients for all exposures regardless of age, sex, or number of images

    • Covers patient from neck to lap

Fast-Speed Film:

  • Requires less exposure to produce a quality radiograph

  • Most effective method of reducing exposure to x-radiation

  • Film Speed: amount of radiation required to obtain the image

    • Larger silver bromide crystals, faster film

Image Receptor-Holding Devices:

  • Keeps patient’s hands and fingers from being exposed to x-radiation

  • Keeps film/receptor in stable position

Exposure Factor:

  • Adjust kVp, mA, and time setting

  • 70 to 90 kVp keeps patient exposure to a minimum

X-Rays During Pregnancy:

  • Does not need to be altered

  • Lead apron is used; radiation in pelvic region is nearly zero


Pediatric Patients:

  • Seat in parent’s lap in dental chair if they cannot cooperate

  • Parent can hold film/sensor in place; cover parent/child in lead apron