TOPIC: X-RAY FILMS, INTENSIFYING SCREEN AND CASSETTE
🌟 IMPORTANT POINTS TO REMEMBER
🔹Direct action or non-screen film: It is also called wrapped or packet film which is sensitive primarily to X-ray photons.
🔹Indirect action or screen film: It is used in combination with an intensifying screen in a cassette.
🔹Periapical films: Films are available in size 0 (for children), size 1 (for anterior teeth in adults) and size 2 (for posterior teeth in adults).
🔹Occlusal films: These films are larger than periapical films used to take occlusal projections for detection of the lesions.
🔹Bitewing films: These films are used for the detection of proximal caries and alveolar bone loss.
🔹Extraoral films: These are used for taking all extraoral radiographs and used in combination with the intensifying screen.
🔹Duplicating film: These are single emulsion films.
🔹Slow-speed film: This type of film contains the small size of grains of silver halide.
🔹Fast-speed films: These films have larger grain sizes, and a coating of emulsion is present on both sides of the film. Due to this, these films require less exposure time as compared to other films.
🔹Hyperspeed G: This is the 800-speed film that reduces patient exposure.
🔹Single emulsion film: Emulsion is coated on only one side of the film. In this type, film is viewed from the emulsion side only.
🔹Double emulsion film: In this, the emulsion is coated on both sides. The film can be viewed from either side.
🔹Film packet: Film and its surrounding packaging are referred to as film packet. It contains an outer plastic wrapper, the film, a sheet of lead foil and a protective black paper.
🔹Lead foil: It is placed behind the film to prevent the amount of residual radiation that has passed through the film to continue into the patient’s tissues.
🔹Base: It is the transparent supporting material upon which the emulsion is coated. It is made of clear transparent cellulose triacetate or thin polyester plastic (polyethylene terephthalate).
🔹Adhesive: Between the emulsion and the base, there is a thin coating of the material called an adhesive layer to ensure uniform adhesion of the emulsion to the base.
🔹Emulsion: It is made up of silver halide crystals which are arranged parallel to the surface. The diameter is about 0.7–0.75 mm.
🔹Gelatin matrix: It is made of cattle bone and is porous to allow the processing chemicals to penetrate it.
🔹Gelatin supercoat: It acts as a protective layer and shields the emulsion from rough handling before exposure, scratching pressure and contamination during processing.
🔹Speed and sensitivity of film: It is defined as the amount of radiation required to produce a radiograph of adequate density.
🔹T-grain film: In 1994 Kodak Company introduced the newest E-speed film called Ekta speed film plus (E+). It uses flat or tubular grains or T grains in the emulsion.
🔹Non-screen films: These are used without intensifying the screen.
🔹Screen films: These are kept in a cassette between the intensifying screens.
🔹Extraoral film construction: The silver halide emulsion is designed to be sensitive primarily to light rather than to X-ray.
🔹Duplicating film: It is the type of film that is used to make an identical copy of an intraoral and an extraoral radiograph. It has emulsion only on one side of the film.
🔹Film storage: The optimum temperature for film storage is 50–70°F. Optimum humidity should be 30–50%.
🔹Intensifying screen: It consists of fluorescent phosphors, suspended in an inert transparent binder.
🔹Conduction band: Outermost electron positions are perturbed by interatomic forces which permit electrons to acquire sufficient energy to occupy one of these positions. The collective energy level corresponding to these positions is called the conduction band.
🔹Forbidden band: The energy levels of the inner electron below the conduction band are undisturbed by interatomic forces. The region between inner bands and conduction bands cannot be occupied and is called a disallowed or forbidden band.
🔹Fluorescence: If an electron, when released in the conduction band, immediately falls into the luminescent centre, the emission of light flows almost instantly after the action of exciting X-ray photons. This is called fluorescence.
🔹Phosphorescence: If the electron first falls in a trapping centre, light emission is delayed well after the source of activating X-rays has been removed. Luminescent materials that exhibit phosphorescence are almost undesirable in radiology as they may blur the image.
🔹Thermoluminescence: There are some materials that also emit visible radiation during and after irradiation by X-rays but only if heated up to a few hundred degrees centigrade.
🔹Protective coating: It is 15–25 mm in size. It is made up of plastic largely composed of cellulose compound which is mixed with polymer.
🔹Calcium tungstate: Calcium tungstate screens emit blue light and must be used with blue light–sensitive monochromatic film.
🔹Rare earth screen: Rare earth includes lanthanum (Z – 57), gadolinium (Z – 64), terbium (Z – 65) and thulium (Z – 69).
🔹Reflective layer: Between the luminescent layer and the base is a reflective layer of approximately 25 mm. It is made of a shiny substance such as magnesium oxide or titanium dioxide.
🔹Base of the screen: It is 1 mm or 250 mm thick, and is made up of high-grade cardboard polyester or metal.
🔹Rinn Snap-A-Ray film holder: It is a plastic film holder that can be used in both anterior and posterior regions.
🔹Bite-blocks: Film is inserted into the slot in the wooden bite-block on one end, and the patient is asked to bite in the slot at the other end of the bite-block.
🔹Haemostat: It was designed by Dr. G Fitzgerald of the University of California. The serration of this haemostat runs lengthwise rather than across the beak (which is present in the case of a surgical haemostat).
🔹Rinn XCP instrument: It consists of bite-blocks (these are used to retain the film packet by means of tension created by semi-flexible plastic backing), a stainless steel rod (it is used to align the X-ray cone with the film) and locator ring (it is made for sliding into a rod to establish alignment of the cone and rectangular-shaped extension cone with the film; it also prevents cone cutting).
🔹Beam aligning holders: They are usually PID. These holders align the fixed angle of the central ray to the film.
🔹Cassette: It is a lightproof holder that contains the screen and the film. It usually consists of a lightproof aluminium or carbon fibre container with the radiographic film sandwiched tightly between two intensifying screens.
📌 MULTIPLE CHOICE QUESTIONS (MCQs)
1. The type of film that is used in combination with an intensifying screen is
a. Occlusal film
b. Periapical film
c. Extraoral film
d. Bitewing film
💡Answer: c
2. Single emulsion films are used in
a. Periapical radiography
b. Duplicating film
c. Bitewing radiography
d. Occlusal radiography
💡Answer: b
3. Lesser exposure time is required in which type of films?
a. Slow-speed film
b. Fast-speed film
c. Both a and b
d. Extraoral films
💡Answer: b
4. C-speed film is a type of
a. Slow-speed film
b. Fast-speed film
c. Hyperspeed G
d. None of the above
💡Answer: a
5. Dimensions of size 2 film are
a. 24 × 40 mm
b. 31 × 41 mm
c. 57 × 76 mm
d. 22 × 35 mm
💡Answer: b
6. Lead foil is used in X-ray film packets to
a. Protect the film from light
b. Prevent contamination from saliva
c. Prevent scattered radiation
d. All of the above
💡Answer: c
7. Polyester is preferred as a base because it is
a. More resistant to wrapping with age
b. Stronger than triacetate
c. Non-inflammable as compared to cellulose nitrate base
d. All of the above
💡Answer : d
8. The ideal thickness of the base used in X-ray film is
a. 0.5 mm
b. 0.2 mm
c. 1.0 mm
d. 0.7 mm
💡Answer: b
9. Emulsion in X-ray film is sensitive to
a. X-rays
b. Static electricity
c. Visible light
d. All of the above
💡Answer : d
10. The average diameter of silver grains in emulsion is about
a. 0.7–0.75 mm
b. 0.5–1.0 mm
c. 2.0–2.5 mm
d. 1.0–1.5 mm
💡Answer: a
11. Which constituent is added to emulsion in order to increase sensitivity?
a. Silver iodide
b. Gold
c. Sulphur
d. Both a and b
💡Answer : d
12. The factor that affects film speed is
a. Size of crystal
b. Shape of grains
c. Thickness of emulsion
d. All of the above
💡Answer : d
13. The average size of a film used in panoramic radiography is
a. 5 × 7 in.
b. 6 × 12 in.
c. 8 × 10 in.
d. 10 × 12 in.
💡Answer: b
14. The total thickness of the intensifying screen is about
a. 380 mm
b. 430 mm
c. 250 mm
d. 450 mm
💡Answer: a
15. Advantages of intensifying film include
a. Reduced patient dose
b. Less development time of film
c. More sensitivity to film
d. All of the above
💡Answer : d
16. The ideal thickness of the phosphorus layer in the intensifying screen is about
a. 40–100 mm
b. 50–60 mm
c. 100–120 mm
d. 40–60 mm
💡Answer: a
17. The type of film-holding device used in patients with hypersensitive gag reflex is
a. Haemostat
b. Bite-blocks
c. Rinn Snap-A-Ray film holder
d. Rinn XCP instrument
💡Answer: c
18. The type of cassette used in panoramic radiography is
a. Rigid cassette
b. Flexible cassette
c. Gridded cassette
d. Both a and b
💡Answer : d
19. Phosphor material used in intensifying screen is
a. Calcium tungstate
b. Titanium dioxide
c. Gadolinium and lanthanum
d. Both a and c
💡Answer : d
20. The most common type of intensifying screen film used in panoramic and cephalometric radiography is
a. Ultraviolet light
b. Greenlight
c. Blue light
d. Red light
💡Answer: b