Dental radiology د. باسم الاعسم

Darkroom

Construction Since x-ray films are more sensitive to light than most photographic films, it is important to have a good darkroom.

An entrance built in the form of a maze to keep out light is better than a door. If the darkroom has a door, it should have an inside lock so that no one can accidentally enter while films are being processed.

The walls of the darkroom and the maze should be painted black to absorb light. The ceiling may be painted white so that enough illumination will be reflected when the correct type of safelight is used.

The room should be supplied with both hot and cold water The room should be supplied with both hot and cold water. The water pipes should lead to a mixing valve so the temperature of the flow can be regulated.

Adequate ventilation must be provided Adequate ventilation must be provided. This can be done by forcibly changing the air with a ventilator fan.

Cleanliness Because of the extreme sensitivity of x-ray films, rigid cleanliness must be observed when processing films.

Clean all equipment and only use for its intended purpose Clean all equipment and only use for its intended purpose. The dental specialist must not spill chemicals. If chemicals are spilled, wipe up immediately and wash the area with clear water.

Spilled chemicals that are not wiped up will evaporate and leave a precipitated concentrate that contaminates films. Wash the thermometers and film holders thoroughly before transferring them to either the developing or fixing solutions.

Film hangers require particular attention after films have been removed from them. If a hanger is not washed properly, the fixing solution dries on it. Then, when new films are placed on the hanger and immersed in the developing solution, the dried fixing solution runs down onto the films and causes streaked or spotted radiographs. It also contaminates the developing solution.

Thermometer Since films must be processed at an exact and predetermined temperature, a thermometer is needed to register the temperature of the solutions.

Timer Because of the direct relationship between temperature and time in processing, the dental specialist must know the exact time and any given film is to be left in each solution. A good watch may be used for this purpose, but it is much better to use an interval timer. The interval timer is a small clock giving the time in minutes and fractions of minutes. When set for the exact time required for development, it sounds an alarm at the expiration of that time.

Film Holders:

The frame type is used for extraoral films

The clip

The hinge types are used for intraoral films

Illumination The darkroom has two sources of illumination: white light and safelight. A white light is a standard ceiling light. It provides regular illumination for mixing solutions and cleaning the darkroom. An unwrapped, unprocessed X-ray film must never be exposed to white light.

The standard for a safelight is that it must be possible to permit underdeveloped film to be exposed to the light for 1 minute without the least evidence of fogging.

Safelights are used to provide sufficient illumination in the darkroom so essential activities can be carried out safely without exposing the film. Safelights should use 15 watt frosted bulbs. They should be installed at a distance no closer than 4 feet from the work surface. Safelights that are closer than 4 feet may be directed away from the work surface or should use 7.5 watt frosted bulbs.

Safelight filters are selected to transmit light outside the normal spectral sensitivity range of the film that is used. Most films only have a reduced sensitivity to the light transmitted through the safelight filter; therefore, it is necessary to keep safelight illumination levels and film handling times to a practical, safe minimum. A safelight’s effect on film can vary with the type of film being used

. In general, red filters can be used for both blue and green sensitive film. Amber, yellow or orange filters can be used only for blue sensitive film. Green sensitive film as used in panoramic and cephalometric exams is fogged by amber/yellow/orange filters. Amber/yellow/orange filters are appropriate for direct exposure (non-screen, intra-oral) film only. “Little red light bulbs” from photographic darkrooms need to be evaluated on a case by case basis. If there is any doubt as to the compatibility of the film and safelight, a fog test should be done.

Safelight filters tend to crack over time Safelight filters tend to crack over time. To maintain good image quality, periodically check the safelight filters for scratches and cracks and replace them when any defects are found. If the safelight filter is scratched, cracked, or damaged, it may leak enough light to fog the film. If the safelight housing is regularly handled it should also be checked for holes and cracks.

Sink A sink is useful in the darkroom for mixing solutions, washing hands, and disposing of used chemicals. Remember that the fixing solution is not disposed of like other chemicals. It is retained for silver recovery.

Solutions There are two types of processing solutions.

The automatic processor

The manual processor

Before changing the processing solutions, check the manufacturers' instructions to be sure that you have the proper chemicals for the processor you are using. Also, follow manufacturers instruction when preparing them. Some will require several chemicals mixed with water while others may be used directly from the container.

The recommended temperature for the developing solution is 68º F (20º C). At this temperature, most films should be left in the developer exactly 4 1/2 minutes. Without adequate equipment, 68º F (20º C) cannot always be obtained. In that case, the time factor should be adjusted according to the chart in figure 3-5. Temperatures above 70º F (21ºC) and below 60ºF (15ºC) should be avoided if possible.

 After its removal from the rinse, x-ray film should be placed in the fixing solution and agitated for 15 seconds. This helps prevent streaking and staining of the finished radiograph and hastens the fixation process.

Dryness After finishing processing the film must be dry under stem of air to prevent any the drop of water stay on the surface of the film and effect the image clearness.

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