During which step of automatic film processing are the unexposed silver halide crystals removed from the film base?

Dental X-Ray Film Processing

• Processing is a series of steps that changes the latent image on the exposed film into a radiograph
  by producing a visible image on the film. 
• Proper processing is just as important as exposure technique in producing diagnostic-quality radiographs.
• Radiographs that are nondiagnostic because of poor processing techniques must be retaken, exposing the patient to unnecessary radiation.
• In many practices intraoral films are processed in an automatic processor; however, it is still necessary to know how to process the film manually.

The Five Steps in Processing Dental Radiographs

• Development 
• Rinsing 
• Fixation 
• Washing 
• Drying 

Developing

• Developing is the first step in processing films. 
• A chemical solution called the developer is used. 
• The purpose of the developer is to chemically reduce the exposed silver halide crystals to black metallic silver.
• The developer solution also softens the film emulsion during this process. 

Rinsing

• Rinsing of the films is necessary to remove the developer from the film so that the development process stops. 
• Usually, agitating the film rack for 20 seconds is sufficient. 
• This must be done under safelight conditions. 

Fixing

• The acidic fixing solution removes the unexposed silver halide crystals from the film emulsion. 
• The fixer also hardens the film emulsion during this process. 
• For permanent fixation, the film is kept in the fixer for a minimum of 10 minutes. 
• However, films may be removed from the fixing solution after 3 minutes for viewing. 
• Films that are not properly fixed will fade and turn brown in a short time. 
• Leaving films in the fixer for a long time (e.g., over a weekend) can remove the image from the film.

Washing

• After fixation, a water bath is used to wash the film.
• The washing step requires about 20 minutes to thoroughly remove all excess chemicals from the emulsion. 

Drying

• The final step in film processing is the drying of the films. 
• Films may be air-dried at room temperature in a dust-free area or placed in a heated drying cabinet. 
• Films must be completely dried before they can be handled for mounting and viewing. 

Film-Processing Solutions

• Film-processing solutions are available in the following forms: 
  • Powder 
  • Ready-to-use liquid 
  • Liquid concentrate 

Concentrated solutions of film developer and fixer. (Courtesy of Eastman Kodak, Rochester, N.Y.)

The Darkroom

• The term “light-tight” is often used to describe the darkroom.
• To be light-tight, no light leaks can be present. 
• When you are in the darkroom with the light turned off, no white light should be visible.
• X-ray film is extremely sensitive to visible white light.
• Any leakage of white light can cause film fog. A fogged film appears dull gray, lacks contrast, and is nondiagnostic. 

Types of Darkroom Lighting

• Room lighting: An overhead white light provides adequate lighting for tasks such as cleaning, restocking of materials, and mixing of chemicals. 
• Safelighting: A safelight is a low-intensity light in the red-orange spectrum. Safelighting provides enough illumination in the darkroom to process films safely without exposure of or damage to the film. 
• There must be a safe distance between the light and the working area, and the person developing the film must work quickly to keep the exposure to the safelight as short as possible.
• Unwrapped films that are left too close to the safelight or exposed to the safelight for more than 2 to 3 minutes appear fogged. 
• A safelight must be placed a minimum of 4 feet away from the film and working area.

A distance of at least 4 feet must separate the safelight from the working area. (From Iannucci J, Jansen Howerton L: Dental radiography: principles and techniques, ed 3, St Louis, 2006, Saunders.)

The Processing Tank

• Manual processing is a method that is used to develop, rinse, fix, and wash dental x-ray films. 
• The essential piece of equipment required for manual processing is a processing tank. 
• The processing tank is divided into compartments to hold the developer solution, water bath, and fixer solution. 
• A processing tank has two insert tanks and one master tank. 

Processing tanks showing developing and fixing tanks inserts in bath of running water. (From Iannucci J, Jansen Howerton L: Dental radiography: principles and techniques, ed 3, St Louis, 2006, Saunders.)

Things to remember:

Why is it necessary to know how to process the film manually in practices that have automatic processors? (Two reasons: [1] to be able to identify and correct errors in processing and [2] to have the ability to develop a film more quickly, as with endodontics. A film can be developed manually in about 2 minutes.)

Which step consumes the most time? (Drying.)

In manual processing for endodontic procedures, the film is typically placed in the developer just long enough for an image to appear. This usually takes less than a minute. However, initial and final films should never be developed in this way.

When rinsing, unexposed crystals still remain on the film. Therefore, rinsing needs to be done under a safelight, since white light will expose those crystals and distort the image.

A working film for endodontic procedures can be placed in the fixer for roughly 1 minute and will last long enough for the dentist to get the information he or she needs.

Washing – This step no longer needs to be done in safelight. Why? (Because the unexposed crystals have been removed, there is nothing to react with the white light.)

Automatic processors use warm air to dry films more quickly.

Ready-to-use liquid is by far the most commonly used solution. 

Powder and concentrate require mixing that most practices choose not to take the time to do.

Distilled water must be added to the concentrate before use.What would films look like if the developer solution was not diluted? (The films would appear overdeveloped.)

What might cause a fogged film besides light leaks in the darkroom? (The film may have been left in the x-ray room after the initial exposure and exposed to background radiation. Keep exposed films outside the radiography operatory.)

At what distance from the working area should the safelight be placed? (Four feet.)

Some safelights are made only for intraoral films, some for only extraoral films, and still others for both intraoral and extraoral films. 

Why does the safelight need to be placed at this distance? (To decrease the intensity of the light reaching the undeveloped film. Safelight will still expose a film if left long enough or held close enough.)

What’s the purpose of the cover on the processing tank? (To keep solutions from evaporating when not in use.)

How often should solutions be changed? (Every 3 to 4 weeks.)

Which film processing step removes the unexposed silver halide crystals from the film?

What stage of development process wherein remaining unexposed silver halide in the emulsion are removed?

What solution removes unexposed silver halide from the surface of the film?

During which step of the processing procedure are the exposed silver halide crystals reduced to metallic silver?