Dental X-Ray Film Flashcards
What are dental films composed of?
- Film base
- Adhesive layer
- Film emulsion
- Protective layer
What is the film base composed of?
A 0.2 mm thick polyester plastic (will be the actual radiograph). This base provides strength and support and is constructed to withstand heat, moisture and chemical exposure
What is the purpose of the adhesive layer?
Covers both sides of the film base, attachment for the emulsion to the base
What is the film emulsion made up of? Why are these components important?
Silver halide crystals and gelatine. Silver halide crystals are important because they are sensitive to radiation or light and will absorb the radiation from the beam and store the energy from the radiation. Gelatine is important for suspending and dispersing all of the silver halide crystals
What is the protective layer and why is it important?
A thin coating over the emulsion to protect the emulsion during manipulation and processing
Were the silver halide crystals exposed if the image is light?
No
What is film speed?
Refers to the amount of radiation required to produce a radiograph of standard density. Determined by:
- Size of silver halide crystals
- Thickness of the emulsion
- Presence of special radiosensitive dyes
- Fast films require less radiation exposure because the film responds more quickly because the silver halide crystals in the emulsion are larger
What are the common types of film speeds nowadays and which is the fastest?
D, E, and F. F is the fastest
What is the quality of a dental radiograph determined by? What does this include?
Image characteristics. Includes:
- Proper density and contrast
- Sharpness with minimal magnification and distortion
What does radiolucent mean?
The part of a radiographic image that is dark, means the structure allowed for the passage of the x-ray beam and was likely not very dense
What does radiopaque mean?
The part of a radiographic image that is white, means the substance was likely too dense for the beam to pass through (absorbs or resists it) and therefore the silver halide crystals could not be energized
What are the two visual characteristics that influence diagnostic quality of radiographs?
Density and contrast
What is density?
The overall darkness or blackness of a dental radiograph, with the correct density, you will see black, white and gray
What is contrast?
The difference in degrees or shades of blackness between adjacent areas
What is the overall contrast determined by?
- Film contrast (inherent qualities of film and film processing)
- Subject contrast (characteristics of the subject that influence radiographic contrast)
What are the 3 geometric characteristics?
- Sharpness
- Magnification
- Distortion
What is sharpness?
The capability of an x-ray film to reproduce the distinct outlines of an object, how well the smallest details are reproduced on radiographs
What is the lack of image sharpness called?
Penumbra, all images have this
What are the 3 factors that influence image sharpness?
- Focal spot size (smaller focal spot = smaller penumbra determined by the manufacturer)
- Film composition (faster films have larger crystals which produce a less sharp image)
- Movement (patient moves themselves of the receptor)
What is magnification?
When the radiographic image appears larger than the actual object. Caused by divergence of the paths of x-ray beams.
How does the PID affect magnification? How close should the film be to the tooth to avoid magnification?
Longer PID and target-film distance results in rays being more parallel from the middle of the x-ray beam, striking the object rather than diverging rays. (Longer PID with film closer to tooth = less magnified image)
What is distortion? What causes distortion?
A variation in the true size and shape of the object being radiographed. Caused by unequal magnification of different parts of the same object because of improper film alignment or angulation of the x-ray beam
What are the influencing factors or distortion?
- Object-film alignment
- X-ray beam angulation
What is object-film alignment?
The object and film must be parallel to each other or there will be distortion. If the tooth is not parallel to the film, an angular relationship results
What is x-ray beam angulation?
X-ray beam must be directed perpendicular to the tooth and film to record the adjacent structures and their true shape
