The document summarizes the process of radiographic film processing and the darkroom equipment used. It discusses: 1. How a latent image is formed on the film when exposed to x-rays and the chemical components involved. 2. The steps of film processing - developing the latent image into a visible one using developer solutions, fixing the image using fixer, and washing the film. 3. The components and purpose of developer and fixer solutions, and factors like temperature, time and replenishment that are important in processing. 4. Darkroom requirements like safelighting, manual processing tanks, timers and drying racks used to process films.

2. RADIOGRAPHIC PROCESSING AND DARK
ROOM
Presented by:
Pragy Mallik
Roll no:21
Bds 2nd batch

3. Formation of the latent image
 When a beam of photons exits an object and exposes an x-ray film, it
chemically changes the photosensitive silver halide crystals in the film
emulsion.
 These chemically altered silver bromide crystals constitute latent image on
the film.

4.  Silver bromide crystal in the emulsion of an x-ray film contains mostly silver and
bromide ions in a crystal lattice. There are also free interstitial silver ions and areas
of trace chemicals that form sensitivity sites.
 Exposure of the crystal to photons in an x-ray beam results in release of electrons,
usually by interaction of the photon with a bromide ion. When electrons reach a
sensitivity site, they impart a negative charge to this region
 Free interstitial silver ions (positive charge) are attracted to the negatively charged
sensitivity site.
 Silver ions after reaching sensitivity site, acquire an electron and become neutral
silver atoms. These silver atoms now constitute a latent image site. The collection
of latent image sites over the entire film constitute the latent image.

6. Film processing
 Film processing refers to a series of steps that produce a visible permanent
image on a dental radiographs.
Aims
• To convert latent image (invisible) on the film to a visible image.
• To preserve the image so that it is permanent and doesn’t disappear from
a radiograph.

7. Processing solutions
Procedure:
i. Immerse exposed film in developer
ii. Rinse developer off film in water bath
iii. Immerse film in fixer
iv. Wash film in water bath to remove fixer
v. Dry film and mount for viewing

9. Developing solutions
 Developer reduces all silver ions in the exposed crystals of silver halide to
metallic grains.
 To produce a diagnostic image, this reduction must be limited to crystals
containing latent image sites.
 For this, reducing agents used as developer are catalyzed by neutral silver
atoms at the latent image sites.
 When an exposed film is developed, initially there is no visible effect, later
density increases, rapidly at first and then more slowly.
 Development of unexposed crystals results in chemical fog on the film.

10. Components
I. Developer
II. Activator
III. Preservative
IV. Restrainer

11. Developer
 Converts the exposed halide crystals into metallic silver.
 Developing agents: phenidone and hydroquinone.
 Phenidone: first electron donor that converts silver ions to metallic silver at the
latent image site. This electron transfer generates oxidized form of phenidone.
 Hydroquinone: provides electron to reduce the oxidized phenidone back to its
original active state so that it can continue to reduce silver halide grains to
metallic silver.

12. Activator
 Developers are active only at ph value around 10.
 This ph is achieved by addition of alkali compounds such as sodium or
potassium hydroxide.
 Theses activators also cause gelatin to swell so that developing agents
diffuse more rapidly into the emulsion to reach silver bromide crystals.

13. Preservative
 Sodium sulfite is used as a preservative which extends the useful life of the
solution.
 Preservative combines with developer to produce a compound that stains
image brown if not washed out.

14. Restrainer
 Bromide containing compounds are added to restrain development of
unexposed silver halide crystals.
 Restrainers act as antifog agent and increase contrast.

15. Developer Replenisher
 Developing solutions should be replenished with fresh solutions each
morning to prolong the life of the used developer.
 Recommended amount to be added daily: 8 ounces of fresh developer per
gallon of developing solution. This assumes development of 30 periapical
or 5 panoramic films per day.

16. Rinsing
 After development, film emulsion swells and becomes saturated with
developer.
 Film are rinsed in water for 30 sec with continuous, gentle agitation before
they are placed in fixer.
 Use: dilution of developer
slowing development process
removes alkali activator preventing neutralization of acid fixer

17. Fixing solution
Use:
o Removes undeveloped silver halide crystals from the emulsion.
o If not removed, results in dark and non diagnostic radiograph.
o Hardens and shrinks the film emulsion.
Should be replenished daily at the rate of 8 ounces per gallon.

18. Components
I. Clearing agent
II. Acidifier
III. Preservative
IV. Hardener

19. Clearing agent
 Aqueous solution of ammonium thiosulphate dissolves the unexposed
silver halide grains.
 Forms stable, water soluble complexes with silver ions, which diffuse from
the emulsion.
 Excessive fixation: gradual loss of film density because the grains of silver
slowly dissolve in the acetic acid of the fixing solution.

20. Acidifier
 Acetic acid buffer system (ph 4- 4.5) is used to keep the fixer ph constant.
 Acidic ph is used to promote good diffusion of thiosulphate into emulsion
and of silver thiosulphate complex out of the emulsion.
 Also inactivates any residual developing agents in the film emulsion,
blocking continued development of any unexposed crystals while the film
is in the fixing tank.

21. Preservative
 Ammonium sulfite is the preservative
 It prevents oxidation of thiosulphate clearing agent, which is unstable in
the acid environment of fixing solution.

22. Hardener
 Aluminium sulfate is used.
 It complexes with gelatin during fixing and prevents damage to the gelatin
during subsequent handling.
 It also reduce swelling of the emulsion during final wash.
 This lessens mechanical damage to the emulsion and shortens drying time.

23. Washing
 After fixing, processed film is washed in water to remove all thiosulfate
ions and silver thiosulfate complexes.
 washing efficiency decreases rapidly when the water temperature
decreases to less than 60ºF.
 Improper washing discolors and causes stains, which are most apparent in
radiopaque areas.

24. DARKROOM AND EQUIPMENT
Darkroom
Requirements:
• Lightproof: to prevent film fogging and loss of contrast.
• Light tight door or doorless maze: should have lock to prevent accidental
opening and ruining of opened films
• Well ventilated: for the comfort of people working in the area and to
exhaust moisture from drying films.
• Room temperature: for developing, fixing and washing solutions.

26. Safelighting
 Should have both white illumination and safe lighting.
 Safe lighting is low intensity illumination of relatively long wavelength(red)
that does not rapidly affect open film but permits one to see well enough
to work in the area.
 Should have 15 watt bulb or a clear 7.5 watt bulb and should be mounted
at least 4 feet above the surface where films are handled.
 Film handling under a safe light should be limited to about 5minutes
because film emulsion shows some sensitivity to light from a safelight with
prolonged exposure.

27. Penny test
 A radiographic film is sensitive to visible light and x-rays. Excessive
exposure to safe light or an improper safe light condition can lead to
exposure of the film resulting in film fog.
 Such film appears dark and have a muddy gray appearance.
 The safe lighting conditions in the dark room can be evaluated using a
coin test, called penny test.

28. Procedure:
I. Open the packet of an exposed film and place the film in the area where
the films are usually unwrapped and clipped on the film hanger.
II. Place a coin on the film and leave it in this position for about 5minutes.
III. Develop the film as usual. If the image of the coin is visible on the
resultant film, the room is not light safe.

30. Manual Processing Tanks
 The tank must have hot and cold running water and a means of
maintaining the temperature between 60ºF and 75ºF.
 Size: 20cm*25cm (8inches*10inches) that can serve as a water jacket for
two removable inserts that fit inside.
 Insert tanks hold 3.8 L of developer or fixer and are placed within the
outer, larger master tank.
 Outer tank holds the water for maintaining the temperature of developer
and fixer in the insert tanks and for washing films.

31.  Developer is placed on the left side and fixer is on the right.
 All three tanks should be made of stainless steel, which does not react
with the processing solutions and is easy to clean.
 Should have a cover to reduce oxidation of processing solutions, protect
developing film from accidental exposure to light, and minimize
evaporation of the processing solutions.

33. Thermometer
 Temperature of the solutions should be closely controlled.
 A thermometer can be left in water circulating through the master tank to
monitor the temperatureand ensure that the water temperature regulator
is working properly.
 Thermometers are clipped onto the side of the tank.
 Thermometers may contain alcohol or other metal, but should not contain
mercury because they could break and contaminate the processor or
solutions.

34. Timer
 X-ray film must be exposed to the processing chemicals for specific
intervals.
 An interval timer is indispensable for controlling development and fixation
times

35. Drying Racks
 Two or three drying racks can be mounted on a convenient wall for film hangers.
 Drip trays are placed underneath the racks to catch water that may run off the wet
films.
 An electric fan can be used to circulate the air and speed the drying of films, but it
should not be pointed at the films.

36. Manual processing procedures
1. Replenish solutions
2. Stir solutions
3. Mount film on the hangers
4. Set timer
5. Develop
6. Rinse
7. Fix
8. Wash
9. Dry

37. Temperature (ºF) Development time (minutes)
68 5
70 4½
72 4
76 3
80 2½

38. Rapid processing chemicals
 Rapid processing solutions typically develop films in 15seconds and fix
them in 15 seconds at room temperature.
 They have same general formulation but concentration of hydroquinone is
higher and ph is more alkaline.
 These are advantageous in endodontics and in emergency situations,
when short processing time is essential.

39. Visual method
 It is always recommended to use the time temperature controlled method
of processing films. However, when the facility of temperature controlled
processing is not available, the visual method can be used.
 Here, no predetermined time for the placement of the film in the
developer solution is used. The exposed film is placed in the developer
solution and taken out at regular intervals and examined under the safe
light for the most calcified/radiopaque structures (enamel cap,
restorations, artificial crowns) to be evident.

40.  At this point, films are taken out of the developer solution, rinsed in water
and placed in the fixer solution.
 Disadvantage: inter examiner errors,
films of poor density and contrast
films can be very light or dark making it unfit for
diagnostic evaluation.

41. Salvaging dark radiographs
• Most common method of reducing,or lightening, dark films is described by E. Howard
farmer in 1884.
Potassium ferrocyanide + silver silver ferrocyanide +potassium ferrocyanide
• Silver ferrocyanide is then made soluble by its reaction with thiosulphate, and thus can be
removed from the film.
• However, this reducer is considered dangerous because it contains ferrocyaniode.
• Other reducers: potassium permanganate and potassium dichromate.
• Wakefield in 1970, described a single solution reducer with a very long life.

42. The reducing solution
(Modification of Wakefield solution)
 Chemicals used are mixed in order they are listed, in a glass or ceramic
container
a. Copper sulphate crystals(5 ml)
b. Sodium chloride (5 ml)
c. Concentrated hydrochloric acid (5 ml)
d. Water (200 ml)

43. Lightening a film
 To lighten a overexposed or overdeveloped film,
it should first be soaked in water to soften emulsion.
Rinse in the reducing solution
• The film will turn a whitish color as silver chloride is produced on the
surface of the film.
• Reduction process should take between 4-10 seconds.
• Film is rapidly rinsed in cold water fixed washed dried

44. Alternate technique of lightening dark
radiographs
 The dark radiograoh if dry
Place in the fixer tank for few minutes.
place on an even surface
use sharp Bard Parker blade to scrape away emulsion one side of the film
in a even regular strokes.
Rinse under running tap water
Dried

45. Automatic processing

46.  Automatic film processing refers to the processing of radiographs using
machines specifically designed for that purpose.
Advantages:
• Need for dark room is eliminated.
• Human errors is eliminated
• Is a time saving procedure
Disadvantage
• Costly
• Need for regular maintenance and cleaning of the rollers.

47. Working mechanism
 Automatic processor are made up of roller mechanism, which is driven by
by chains, belts or gears which carry the film through the developer, fixing
and water tanks.
 Roller:
• Used to carry the film at a constant preset rate through the processing
solutions.
• Help in drying the film as they squeeze the processing solutions out of the
film.

48. References
 Clinical manual for oral medicine and radiology: Ravikiran
ongole
 Oral radiology: White and Pharoah