Film radiography – Each polyester dental film base is covered by an emulsion of silver halide crystals suspended in a gelatin with a special adhesive holding them to the base. These crystals are sensitive to X-rays and change when struck by radiation. In areas where all the radiation strikes the film, the emulsion is greatly affected.
In areas where no radiation reaches the film, the emulsion is not affected at all. Remember, the amount of radiation that strikes the film depends upon the type of tissue the radiation passes through. The created image remains invisible until the film is acted on by chemicals during the developing process. It is called a latent image.
PROCESSING OF Film radiography
Three methods are used to process Film radiography:
Instant or chairside, automatic (machine) processing, and manual processing.
(1) Instant or Chairside Developing of Film radiography
The instant or chairside developing method uses a special chemical formula and apparatus to bring out the latent image. It enables the dentist to perform a wet read—an interpretation of the film made before it is fully fixed or dried (in about one minute). Processing then is completed in the operatory (chairside). The instant method is used in general dentistry offices for emergencies because it saves time. In most cases, endodontic (root canal treatment) procedures require a “quick read” film during treatment to determine if:
• The canal has been thoroughly cleaned.
• The filling material has completely filled the canal and not exited through the apical foramen.
• Other problems exist that could easily be solved before treatment is completed.
Along with special chemicals, this method requires a special light-tight box (a portable darkroom) which can be placed on a table in the operatory. To process film using this method, merely insert your hands with the film in the light-tight openings of the box. Elasticized rubber at the opening of the box will close tightly around your arms as they enter the box.
The special tinted glass window in the lid won’t allow in any room light, but it will permit you to see how to open the film packet and to view the developing process. There are separate containers holding developer solution, water, and fixer solution. The special window will enable you to watch the chemicals act on the latent image. Wash the film well in the water tank next to the developer, and place it in the fixing solution until it becomes transparent.
This is also known as clearing time. Wash the film again and then give it to the dentist for a wet read. After a wet read, the film must always be returned to the fixer before being washed and dried.
However, the instant chairside processing method does have disadvantages. Because special (stronger) chemicals are used and the temperature of the solutions is greater, usually 85° Fahrenheit (F) (29.2° Celsius (C)), the visual quality of the film deteriorates over time. It also can not be used as part of the permanent record or for comparison with other films in the future because it will have poor density, contrast, or fogging.
(2) Automatic Processing of Film radiography
There are many types of automatic film processors. Some take both intraoral and extraoral films; others will only develop intraoral size films. Some work by moving the films through the processing solutions on rollers; others utilize a wire wheel or rack that looks like a Ferris wheel.
Most have the following features in common:
• Temperature control for solutions.
• A processing cycle which takes the film through the developer, then the fixer, and then is washed and dried.
• A fan area at the end of the processing cycle which produces a dry film.
• Special solutions (not the same chemicals used in instant or manual processes).
A darkroom is needed only for opening the film and placing it in the machine. Advantages of this system are the following:
1. The processing time is reduced to five to seven minutes.
2. The film is dry at the end of the processing.
3. There is less time spent in film processing for the dental assistant.
Disadvantages of the system are the following.
1. Rollers in older machines absorb chemicals from the films and pass them on to succeeding films; leaving marks, streaks, and overdeveloped areas.
2. Films tend to stick and “get lost” in the machine.
3, One patient’s films can get mixed up with another when the films are developed one right after another.
4. The maintenance and cleaning of some machines are difficult and time-consuming.
(3) Manual Processing of Film radiography
The manual processing method requires a darkroom, a special tank, film-holding racks, a thermometer, and developing and fixing solutions. This method is also known as the time! temperature method of developing.
For best results, follow these rules in the darkroom:
• Keep surfaces dry and clean and free from splashes of solution, dust, and water.
• Keep the room light-tight; no regular light must be able to seep in.
• Lock the door so no one can come in during the developing stage. If the film is exposed to light, it will turn black and no pictures will be seen.
• Use the correct time and temperature. Develop films in solutions that are between 68° and 70°F (20° and 21.5°C). If the solutions are warmer, the films will develop faster. If they are cold, the films will take longer to develop. Developing time is also affected by the age of the solutions. Newly mixed ones will work faster than those that are old and have been used a lot.
USE AND CARE OF DEVELOPER AND FIXER
The developing and fixing solutions used in dental work are made up of chemicals mixed with distilled water. The developer and fixer are not compatible. If one contaminates the other, the effectiveness of the contaminated one is reduced and it won’t work properly on the emulsion, which in turn affect quality of the film. With time and usage, the solutions deteriorate and get weaker. When a film is developed at the usual time and temperature, the first sign of a weakened developer is light films. When the film takes two or more minutes to clear, this is a sign of weakened fixel Covering the tanks when they are not being used can reduce evaporation of solutions. If the levels of solutions get low, more of each can be added or new solutions can be mixed.
• Hydroquinone—Gives film contrast
• Elon—Gives film detail
• Sodium Sulfate—Acts as a preservative
• Sodium Carbonate—Makes solution non- acidic
• Potassium Bromide—Makes chemicals act
• Distilled Water—Absolutely needed in automatic processors.
• Sodium Thiosulfate—Dissolves undeveloped silver salts
• Alum—Shrinks and hardens the emulsion
• Sodium Sulfate—Acts as a preservative
• Acetic Acid—Increases the action of the preservative
• Distilled Water.
The developer reduces the exposed silver halide crystals to metallic silver but does not affect unexposed crystals. The fixer washes away the unexposed crystals and hardens the image onto the film base.
EFFECT OF CHEMICAL Film radiography
The effectiveness of the chemicals to bring out the latent image depends on several factors:
1. Age. How long ago the chemicals were mixed.
2. Usage. How many films have been developed with the solutions (per day, per week).
3. Contamination. How well the films were rinsed before they were placed in that solution and how much splashing of other chemicals into that solution occurred.
4. Temperature. Whether the solutions were kept at the proper temperature or not, affects the processing time and quality.
RADIOGRAPHIC ERRORS in Film radiography
There are three major areas in which incorrect procedures cause errors:
1. Projection. How the X-ray source is positioned in relation to the film.
2. Exposure. How films are positioned in relation to the teeth and the collimator.
3. Processing. How the film is developed.
Some of the Common Errors in Film radiography
(i) Apical Area Missing. There are two reasons why the apical area is missing. Either the film is not parallel to the long axis of the tooth or the film is too far below the incisal or occiusal edge.
ii Overlapping. Overlapping is caused by an incorrect horizontal angle of the Pm.
iii Foreshortening. Foreshortening is caused by too steep of a vertical angle of the PID.
(iv) Elongation. Elongation is caused by a vertical angle that is not steep enough.
(v) Cone Cutting. Cone cutting occurs when the film is not centered in the path of the primary beam.
(vi) Dark Lines on the Film. Bending or creasing the film, which breaks the emulsion, causes dark lines on the film.
(vii) Film Too Light (Thin Image). Light film images are caused by under- development, a low mA setting, and too short of an exposure time.
(viii) Film Too Dark (Dense). Dark film is caused by overdeveloping, too high mA or kVp settings, and too long of an exposure time.
(ix) Partial Image. If only a partial image develops on the film, the film was placed incorrectly iii relation to the teeth or structures being examined.
(x) Fogged Film. Out-of-date film, a light leak in the darkroom, the film’s exposure to secondary or scattered radiation, contaminated developer, or the film being placed in the water before developer can cause a fogged film
(xi) Haze. A herringbone pattern at one end of the film or overall haze indicates that the film is placed backwards in the mouth. To correct, make sure the plain side of the film faces the CR.
(xii) Dot Interfere with Apical Area. A dot interfering with the apical area can be caused by two errors. Either the dot is not placed in the film holder or the dot is not at the incisal or occlusal surface. Both errors can be corrected by checking the dot placement during the assembly of the XCP instrument.
(xiii) Double Exposure. A double exposure occurs when the same film is exposed in two different areas.
(xiv) Blurred Image. The patient, film, or tube head moving during exposure causes a blurred image.
(xv) Superimposed Objects. Superimposed objects can interfere with the area being radiographed. They are caused by poor patient position and failure to remove objects such as earrings and necklaces.
(xvi) Spots or Streaks. Spots or streaks are errors indicated by white spots caused by solutions and water spills splashed on the film during darkroom procedures; dark spots caused by developer splashed on the film before it is processed; and white spots caused by air bubbles on the film. Streaks are caused by dried solutions left on film rack clips and by dirty developer, fixer, or water. These errors can be corrected by keeping spills cleaned up and counters dry, agitating dry films when placed in fixer, and keeping film racks and solutions clean and tanks scrubbed.
(xvii) Static Electricity. Static electricity causes dark root-like lines in the radiographic image. Static electricity is caused by friction. The light from static electricity can affect films, This happens mostly in panoramic films. Do not hurry when loading films between the intensifying screens or removing them from the cassette to develop them.
(xviii) Scratches on Film. Careless handling of film causes scratches on film. To correct this problem, hold the film by the edges.
(xix) Reticulation. Reticulation (a condition in which the emulsion peels from the film base) is caused by two factors. Either the film is taken from too hot a solution to too cold a solution causing the emulsion to crack, or the film is left in the water for a long period of time causing the emulsion to soften. To correct these problems, watch the solution temperatures and make sure no films are left in the darkroom tanks overnight.
(xx) Saliva Stain. A saliva stain is caused by failure to wipe the film packet before opening it to process.
(xxi) Cutoff image. A cutoff image at the top or bottom of the film, is either caused by low-level solutions (indicated by a wavy line) or films that were overlapped on the rack (indicated by a straight line).
(xxii) Brown Haze. Brown haze is caused by dried fixer on film.
MOUNTING OF Film radiography
A dental assistant must prepare the radiograph for the doctor’s interpretation and diagnosis by placing the films in a special cardboard or plastic holder. The mounted radiograph will present a view of the patient’s mouth with underlying conditions and structures visible.
There are four purposes for mounting of radiographs:
1. Enables the doctor to view the radiographic images in proper anatomic sequence.
2. Eliminates confusion of conditions found on the left or right side of the mouth and confirms charted conditions.
3. Makes reading and interpreting easier.
4. Prevents loss or scratching of films in the dental charts.