Dental Radiography Basics

Radiology - X-Ray Films

• Radiograph: An image of an object using X-rays, instead of light.
• Dental X-ray film: A recording medium for X-ray images of objects.
• X-ray film types:
  • Intra oral X-ray film
  • Extra oral X-ray film
• Intra oral X-ray film composition:
  • Sensitized emulsion on both sides of a transparent base (cellulose acetate).
  • Base provides structural support and flexibility.
  • Emulsion is the material that interacts with light/X-rays to form the image; it contains a mixture of silver halides (mostly silver bromide) suspended in gelatin, sensitive to both light and X-rays.
• Intra oral film wrapping: Opaque material prevents light from reaching the film, as light can activate the silver halide crystals. A thin sheet of lead is often placed behind the film to prevent secondary radiation from reaching it.
• Intra oral film types (A-Type I):
  • Periapical films examine tooth apices, crowns, and surrounding bone.
  • Available in different sizes (0, 1, 2) based on size; size 0 is for small children, and size 2 is the standard for adults.
• Intra oral film types (B-Type II):
  • Bitewing films.
  • Used to detect interproximal caries (cavities between teeth) and alveolar bone height between adjacent teeth.
  • Often includes a projection from the middle of the film for the patient to bite onto.
  • Different sizes (0, 1, 2, and 2.3 or 3.4) are available
• Intra oral film speed:
  • Speed relates to the sensitivity of silver halide crystals to X-rays.
  • Faster speed requires less radiation due to larger crystals; slower speed requires more radiation due to smaller crystals.
  • Film speed is classfied alphabetically from A to F, increasing sensitivity from slow to fast.
  • Film speed D and above is suitable for oral intraoral radiography (Faster).
• Extra oral film types:
  • Screen film (more sensitive to light and more specifically blue light).
  • Non-screen film (more sensitive to X-rays than light). -Increased thickness in non-screen films. -Non-screen films require lower exposure time compared to screen films. -Sizes: 5x7 and 8x10 inches.

Film Properties

• Density: The degree of blackness on a processed film; measured by light transmission. Typically ranges from 0.25 to 2 in diagnostic radiographs.
• Sensitometry: The relationship between film exposure and resulting blackness (post-processing). Sensitiometry involves measuring this with a densitometer and presenting a characteristic curve which shows the correlation.
• Contrast: The difference in film density between light and dark areas.
  • Low contrast: many shades of gray, with gradual transitions.
  • High contrast: few shades of gray, with abrupt transitions.

Factors affecting film characteristics (details, density, and contrast)

• Exposure time/intensity: Increasing time/intensity increases density.
• Kilovoltage (kV): Increasing kV increases density.
• Milliamperes (mA): Increasing mA increases density.
• Developing time: Increasing time increases density.
• Distance: Increasing distance decreases density.
• Kilovoltage: Increasing kV increases contrast.
• Processing solution temperature: Higher temperature decreases contrast.
• Focal spot size: Smaller focal spot size produces sharper images.
• Film grain size: Smaller film grain size produces sharper images.
• Movement during exposure: Causes blurring, reducing image sharpness (details).
• Object-film and target-object distances: Closer objects-film distance and farther target-object distance results in sharper images.
• Film-screen contact: Poor contact reduces sharpness.

Darkroom Considerations

• Darkroom size: Depends on the type and amount of films used, the number of radiographers and processing tanks.
• Darkroom location: Should be easily accessible but away from areas where exposure to light is possible, and where temperature is consistent.
• Safe-lights: Should contain safe-light filters to prevent fogging the film. A red warning light should be visible to indicate safe-lighting is on.
• Film storage: Protect films from humidity and heat.