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Dental film processing
-X-ray film is made of blue tinted plastic covered in an emulsion. The emulsion contains gelatin and silver halide crystals. Silver halide crystals are energized by radiation exposure. When film is exposed to x-rays, energy reacts with silver halide crystals and creates latent images depending on tissues the x-rays have passed through. The image is latent, because it does not appear until the film is developed. -Tooth fillings block out most of an x-ray beam. Conversely, interproximal spaces let most radiation through. When film is developed, crystals in those areas of film are full of stored energy and will precipitate on the film base as black metallic silver particles. The ability of different tissue densities to absorb radiation is called attenuation. Over time, latent images will disappear, so it is best to process x-ray films as soon as possible after exposure. Film should be stored in a refrigerator to slow attenuation if immediate processing is not possible. -When x-ray films are immersed in developer chemicals, the developing chemicals soak into the film gelatin and react with silver halide crystals. Energized crystals form metallic silver and bromide. In metallic form, silver appears black. Silver is deposited onto the film and causes darker areas. Crystals that are not energized wash away by the fixer, and that area of the film remains white. -The developer reacts with energized crystals to make black areas, and the fixer removes unenergized crystals and leaves those areas white. If the film comes out too dark, it is because it is overexposed (too much radiation) or underdeveloped. If the film is too light, it is underexposed, underdeveloped, or over fixed.
THE STAGES IN THE PRODUCTION OF THE RADIOGRAPH: Many dentists who utilize manual processing, intentionally over expose patients and under process the radiograph in an attempt to save time resulting in radiographs that are inferior in diagnostic quality because of incomplete developing.
When an X-ray film has been exposed, it must be processed in order to produce a permanent visible radiographic image that can be kept without deterioration for a number of years. Processing transforms the latent image into a visible image. The term for the several procedures that collectively produce the visible, permanent image is processing and consists of developing, rinsing, fixing, washing and drying procedures.
Latent image created
Converts latent image to black metallic silver.
Removes excess developer.
Wash [stop bath] 3)
Dissolves out unexposed silver halide crystals.
4)Fixing and Hardening
Removes products of processing.
For manual processing a floating thermometer, a timer and the time -temperature chart are essential.
1) the latent image formation:
The latent (invisible) image formation is the ionization of the exposed silver bromide crystals (by photon energy that emerges from the patient) occurring in the emulsion layer before processing occurs. The primary interaction with the bromide crystals is by Compton and photoelectric interactions, thereby knocking out electrons. Thus, a physical change occurs when the radiograph is exposed. When X-ray photons [or light photons] strike the silver bromide crystals in the emulsion, minute amounts of silver ions are formed on the surface of the crystal and bromine is liberated and is absorbed by the gelatin. Crystals are purposely constructed with electron traps (sensitivity specks) consisting of sulfur impurities but also because of the addition of silver iodide. Electrons are trapped by the sulfur in the sensitivity specks giving it a negative charge. When this situation is created a latent image is produced in the film emulsion.
AgBr + X-ray photons = Ag+ + Br-
Silver bromide Silver ions + Bromine ions
The latent image is formed by deposits of free (ionized) silver ions that cannot be seen or detected by any physical test devised as yet. It remains in the emulsion of the X-ray film until it is changed into a visible silver image by chemical processing procedures.
The free electrons move through the crystal until they are attracted to a sensitivity site where they become trapped and impart a negative charge to the site.
2) PROCESSING THE EXPOSED Film:
Exposed radiographs that contain a latent image should be processed as soon as possible as they are more sensitive to energy. Film packets are only to be opened in the darkroom or under safe-light conditions. [ in a daylight loader] The developer solution is the first solution into which the films are placed. The developer chemically reduces the energized ionized silver bromide crystals by donating electrons, removing the halides and precipitating metallic silver in the emulsion layer. The negative charge attracts positively charged free silver ions and is reduced to black metallic atoms. This precipitation corresponds to the black (radiolucent) areas on the radiograph. The concentration of the developer slowly weakens due to the number of films processed, [a chemical reaction] and with time by oxidation of the developer by exposure to air. Traditionally, the developer tank is placed on the left side of the other chemicals solutions.
brings out sharp contrast. The reducer acts slowly Is a benzene product and made from dyes
Elon OR metol
Provides alkaline medium in which the reduce reacts. It softens and swells the gelatin emulsion r and attracts the exposed silver bromide crystals
b) Alkalizer [Accelerator]
Slows oxidation and therefore preserves the strength of the other chemicals If not present the strength of the other chemicals would rapidly weaken. This explains the darkening of the solution
Restrains the developing agent from the strength. The developing agent will deposit silver in the unexposed crystals in the emulsion causing a silver deposit (fogging) on the film if the restrainer is not added
Provides a means for the chemicals in the developer to react (Ionize). Water helps to soften gelatin
The reaction does not occur unless alkalizer is present. The alkali "opens the doors" and permits the developing agents to enter the pores of the emulsion. If the lid is left off the developing tank, the preservative will be rapidly become exhausted by oxidation. In addition to the above a fungicide is added to prevent growth of fungi and a buffer is added to maintain the pH within specific limit..
3. RINSING PROCESS / STOP BATH (WASHING):
When the film is removed from the developer the gelatin emulsion is soft and swollen and contains chemicals which are removed by placing the film in a water bath. By rinsing the film in the water the soluble chemicals are removed, the development reaction is stopped, and the alkalinity of the residual developer is reduced. The unexposed silver halide crystals are not water soluble and will not be washed away. The film should be rinsed for 10-15 seconds in a bath of fresh, running water. The temperature of the water must be as close as possible to the temperature of the developer and fixer to avoid reticulation - uneven expansion and contractions of the emulsion layer. If this step were omitted, the alkaline developer retained by the film would soon neutralize the acid of the fixer. The fixing and hardening action of the fixer would be impaired and as a result, brown stains will be produced on the radiograph within a few weeks. Because the emulsion layer (gelatin) is soft when wet, the film scratches easily. Safe-light conditions must be maintained when transferring the film from the developer to the wash tank and then to the fixing tank to avoid fogging. For automatic processing there are "squeegy" rollers that remove the chemicals and thus the film goes from the developer solution straight into the fixer.
The acidic fixing solution removes the unexposed and undeveloped silver bromide crystals from the film emulsion and re-hardens the emulsion that has softened during the development process. For manual processing, if the film is placed in the developer solution for X amount of time it should be placed in the fixer for 2X and in the final rinse for 3X amount of time. "X" is determined by the time-temperature chart. The ideal time to process radiographs in the developer is 680 F for 5 minutes. However, films may be removed from the fixing solution after five minutes for viewing only in cases of emergency - this procedure is known as wet reading \ viewing. The film must then be placed back in the fixer. If these unwanted silver bromide crystals are not removed, the resultant film will discolor after a few months. If the film is only partially fixed the film will turn brown in color with age. The gelatin protective coating is hardened by the potassium alum so the film will resist abrasion / scratching.
Removes unexposed crystals
[Removes all crystals]
a. Fixing Agent
Sodium Thiosulfate (hypo)
Prevents deterioration of solution.
Shrinks and hardens the gelatin
c. Hardening agent
Provides acid medium. Alum reacts better in acid medium. Stops developing process
The fixing agent removes all the silver halide crystals and therefore if a film is first placed into the fixer solution, the processed film will appear clear.
5. FINAL WASH:
The purpose of the final wash is to remove residual fixer chemicals i.e. acid, thiosulfate and silver salts from the film. Insufficient washing results in the film turning brown as all the chemicals have not been washed away. If the temperature difference between developer and / OR fixer and water exceeds 15 F, there is a possibility of unequal swelling and shrinkage of the emulsion layer, commonly referred to as reticulation. Also, prolonged washing tends to make the emulsion soft, and it then scratches more easily.
In most offices, films are dried merely by hanging them on a rack in the darkroom above a drip tray designed to catch the run-off excess water. Others use a fan to dry the film. The fan should not blow directly on the films. Cabinet dryers are available which are equipped with a fan and heating elements.
Wet films are subject to damage from scratching and abrasion if not handled properly. If there is dust in the air, dirt will become easily embedded within the emulsion. Do not remove wet radiographs from their hangers until they are completely dry.
In most darkrooms the developer will be in the left-hand tank as you face the tank, the water bath in the center and the fixing solution in the right-hand tank. The developer can be identified by its soapy feel, (alkali) the fixer by its vinegary odor when fresh and acid taste.
An area of less density, say the pulp, will allow greater penetration of X-rays; therefore more X rays will reach that part of the film. Thus more silver bromide crystals will be energized and more silver will precipitate to give a black or radiolucent outline to the pulp chamber. Areas that have received smaller amounts of radiation will have correspondingly less silver precipitated and will appear gray. Individually if a crystal is energized the whole crystal turns black. The silver bromide behind a gold crown, will precipitate no or very little silver as there was minimal energy reaching that area, and will appear white, or radiopaque on the radiograph. Gold and amalgam have high z values.
The X-ray film is a delicate product, sensitive to many things, e.g. light photons, X-rays and gamma rays, pressure, to various gases and fumes, to heat and moisture and even aging causes a gradual change in it; known as fogging.
A dark room is a room from which normal light is excluded.
It is made completely dark to allow the processing of lite sensitive photographic materials.
It should be centrally sited and served by hatches (pass boxes) from the adjacent imaging room.
It should be a way from damp and hot areas.
The entrance of the dark room is light tight.
The door should have lock in the knob that will keep people from entering the room while film is being processed.
Ventilation and heating:
Satisfactory working conditions for staff.
Good film handling and storing.
.Relative humidity: 40-60%
Min of 10 air changes per hour.
Room temp 18-20 C.
Durable and easy to maintain eg: plastic tiles
Non-porous non slip flooring material.
Light in color.
Easy to wipe over and keep clean.
Minimum floor area of 10 m2
Ceiling height 2.5-3m
Coating the walls with barium.
Or increase the thickness
Lining the doors with LEAD ply-sheet
Shielding any gaps around the door
Dark room entrance:
(Efficient but expensive, composed of 2 black cylinders, the outer is fixed and the inner is the revolving door with only one opening).
(Simplest and cheapest type, weather stripping around the door frame, can cause accidental exposure of the film to white light).
(has 2 doors, one leading in and other out with a short hallway in-between, one door cannot be opened unless the other is closed, can cause trapping).
(Has no doors, people can enter at any moment and takes up too much building space).
Dark room illumination:
1-Ordinary white light
Inspection and maintenance of cassettes and screens
Cleaning of works surfaces and floors
Servicing of equipment
It should be moderate in intensity
Close to the ceiling to avoid shadow.
it is a lamp which produces light in area of spectrum which will not affect the photographic materials like film and photographic paper.
Amber-blue lite sensitive film (400-450nm).
Red- green light sensitive film orthochromatic) 500-550nm)
Total darkness for panchromatic films (1200nm)
It should be at least two feet from the film tray.
There are two safe lights in the dark room
One is on the wet bench
Other one is on the dry bench
It can be direct or indirect
It is not 100% safe! (Why)
No filter completely absorbs all undesirable wavelengths.
All films are sensitive to all wavelength.
Filters from both its upper& lower surfaces
Filters form the upper surface
Filters form the undersurface
Directs light toward both the floor& the ceiling
Directs light toward the ceiling
Directs light toward the floor
For both the purposes
For general illumination of the dark room
For film loading and unloading areas
Dark room equipment:
a) Processing tanks.
e) Automatic processor.
They are made of stainless steel to avoid erosion.
It is an instrument used for holding g films during processing
Available in variant sizes
Made up of stainless steel.
Three types of hangers:
a) Clip type
b) Channel type.
c) Spring type.
A radiographic film cassette is a rectangle or square plastic or metallic container used to hold x ray film (exposed or unexposed) and intensifying screens in close and uniform contact with one another.
USES OF CASSETTES
1. Hold intensifying screen and protect them from damage.
2. Exclude all light from entering the cassette and fogging the film.
3. Maintain a close and uniform contact between the screen and film.
4. Exclude dust and dirt from the sensitive films.
5. Act as a medium from exposure up to further processing of film.
* Hatches are designed to transfer film cassettes to and from the dark room without radiation light entering
* It consist of metallic structures with a lead lining to provide x ray shielding
. * They are typically wall mounted and include automatic interlocks that close one door when other is opened.
* It is also used for the temporary storage of loaded cassettes.
* Film racks are used to keep the film boxes.
* It is very important that film boxes are always kept vertically. Not horizontally
*When we keep horizontally pressure on the film boxes may produce artifacts
Methods of processing
Most offices have an automatic processor and tanks for quick processing. At some times in your career, you may be called upon to develop x-rays manually.
The chemicals and the theory are the same as with an automatic processor.
The most important factors when developing film are the temperature of the chemicals. The higher the solution temperature, the less the time needed. The ideal time and temp for manually processing films is 41/2 to 5 minutes at 68 F .
Keep a non- mercury thermometer and a timer, accurate in minutes and seconds, in the dark room to check your solutions.
Manual processing cycle:
. The exposed film packet is unwrapped and
The film clipped on to a hanger.
. The film is immersed in DEVELOPER and
agitated several times in the solution to remove air
bubbles and left for about 5 minutes at 20°C.
Rinsing: a continuous , gentle rinsing for 30 seconds in water is necessary after developing to dilute the developer and slowing the development process and to remove alkali activator
The film is immersed in FIXER for about
The film is washed in running water for
about 10-20 minutes to remove any residual fixer.
The film is allowed to dry in a dust-free
IN THE TIME TEMPERATURE METHOD: before processing check the level of the developer and fixer solutions. if the solution level is low. Add fresh solution. Never add water to raise the level of the solution. as it dilute the strength of the chemicals. Stirring the processing solution with a string rod or paddle. Stirring the solution mixes the chemicals and regularizes the temperature of the solution. check the temp of the developer solution. the optimum temperature of the developer is between 650 to 750 F . IF THE TEMPERATURE IS OUTSIDE THIS RANGE CIRCULATING WATER TAP MUST BE REGULARIZES TO ADJUST THE TAP AND suffient time must be allowed to reach the correct temperature.
In modified time temperature method: in this method depending upon the temperature of solutions, the developing time is divided on daily basis. A table or a chart can be prepared by specifying developing time for a range of daytime temperature. Advantages: temperature need not be maintained at particular level and at the same time consistent image quality can be gained. Disadvantages: for every brand of developer separate time temperature chart should be prepared.
In visual method: in this method the exposed x-ray film is immersed in developing solution for about 10 second and then removed and observed in the safe lite. if adequate image have been obtained then it is put for rinsing, otherwise re-inserted in the developing solution till adequate image is obtained. Disadvantages: this method is highly objective in nature and does not give consistent quality.
Keep chemicals and water in the darkroom with the developer in the first tank, water bath in the center, and fixer in the third tank.
. Stir solutions so temperature is even throughout before submerging x-rays.
Use different instruments to stir the developer and fixer so the two aren't contaminated.
Make sure solution levels are adequate to cover films as they are dipped, and add appropriate chemicals if necessary.
. Use a timer--don't rely on your memory
Chemicals must be completely changed according to manufacturer's directions. There are many factors such as number of x-rays developed, exposure of chemicals to air, and amount of water dilution that determine when it is necessary to change out solutions.
The daily checker film is a good indicator of when to change solutions.
Chemicals must be checked daily and replenished as needed. Every day, six ounces of developer should be removed and replaced with six ounces of fresh developer. Stir the solution to mix well. The fixer should be replenished daily by removing three ounces and replacing it with three ounces of fresh solution.
During automatic processing, the film is transported through the processing sequence mechanically. It moves through the developing, fixing and washing stages at a controlled speed. With proper care, most mechanical processors can be efficient, reliable and consistent.
The chemicals used in automatic processing are specially designed to be used with mechanical transport systems. They operate at higher temperatures and do not require
film rinsing between developing and fixing.
Transport the X-ray cassette containing the exposed X-ray film to the darkroom. Turn off all lights except the red safe light. Place the cassette on the workbench. Open the latch on the cassette and remove the X-ray film. Place the film on the feed tray of the automatic processor so its short axis is parallel to and flush with the side of the tray. Slide the film toward the first set of rollers until you feel the transport system grasp the film. Listen for a chime or buzz that tells you the film is sufficiently advanced into the processor to safely turn on the lights, open the door or to put in another film.
Open the film bin and retrieve a replacement sheet of X-ray film. Close the bin. Place the film in the cassette and feel to make sure the film is seated inside the cassette. Close the cassette and latch securely.
Verify the security of your film before turning on any lights or opening the door to the darkroom that could potentially expose and damage light-sensitive X-ray film. In addition to listening for an audible signal that your processing film is safely inside the processor, where it cannot be exposed to outside light, sweep your hand across the feed tray and feel to ensure the film has been fed into the processor by the transport system. Tap the film bin door with your foot to make sure it is closed. This security measure is referred to as the "sweep-and-kick" maneuver.
Exit the darkroom. Depending on the manufacturer and type of processor, the developed and dried film will emerge from the processor 90 to 180 seconds from the time it was initially fed into the transport system.
ADVANTAGES • Time saving. • Constant film quality is achieved, due to fixed processing cycles. • Need for dark room is eliminated. • Less floor space is required. • Chemicals can be replenished automatically by machine. • Large number of films can be processed continuously.
DISADVANTAGES • Equipment is relatively expensive. • Strict maintenance and regular change is required, dirty rollers produce marked films. • Films may get lost in the tank.
Fast and easy to use -- D-speed film allows chair-side fixing and developing in just 50 seconds. Compatible with all film holders and may be used for anterior or posterior. For use with #2 adult films. 10+ year archive life.
Step 1- Roll & squeeze monobath solution onto film Step 2- Unroll monobath end, slide thumb and index finger over entire length for 50 sec. Step 3- Squeeze monobath solution back into original end, open film end, & thoroughly rinse.
Digital radiography refers to a method of capturing a radiographic image using a sensor, breaking it into an electronic pieces, and presenting and storing the image using a computer. Instead of having an analog radiographic image on a film, in digital imaging the sensor is used to receive the analog information and through analog-to-digital converter (ADC) to convert it to a digital image that is an array of picture elements called pixels, with discrete gray values for each one. Special software is used to store and manipulate the digital image in the computer. The image is displayed within seconds or minutes on the computer screen in front of the clinician and the patient/client.
Radiation Exposure and Biologic Effects of Digital Radiation to Clients and Operators
Digital radiography requires less x-radiation than conventional radiography. Due to their larger sensitivity sensors provide an equivalent clinical image with about 70% less exposure to radiation than D-speed conventional film, and with the latest advances in F-speed film conventional technology, digital imaging still provides an equivalent image with about 20% less radiation. With less radiation exposure, the absorbed dose to the patient/client is significantly lower.
Disadvantages of Digital Radiography
Initial cost for purchase and set up of the equipment as well as the cost for personnel’s training how to properly use the equipment is a disadvantage of the digital imaging systems. Sensors are the weak part of the system due to their relative rigidity and thickness ( approximately 5 millimeters) that could produce uncomfort or pharyngeal reflex in patients/clients. The viewable surface area is smaller than the
total size of the sensor and sometimes sensors are not universal and interchangeable between different
systems. Digital sensors can’t withstand heat sterilization, therefore they require complete coverage with disposable plastic sleeves . Digital radiographs have legal issues because of their potential for fraudulent use.
The essential components of digital imaging include:
I. X-radiation source: most digital systems use conventional dental units as x-radiation source due to its compatibility. II. Intraoral Sensor: is a small detector that is placed intraorally and used to capture the radiographic image and send to the computer for future processing. Sensors are similar in dimensions like conventional films and may be either wired with 8 to 35 feet fiber optic cable for transmission of generated image to the computer or wireless. Intraoral sensor is composed of a silicon chip and a layer that surrounds it. A layer above the sensor chip is the scintillator (material that emits light when particles traverse it), which converts x-ray energy into light and directs it towards the top layer of the chip that is more sensitive to light than x-rays. Top layer of the chip then releases electrons that form the image and send them onto the well in the lower portion of the chip. The energy in each well is then read and digitized with an A/D (analog to digital) converter during the read-out process.
III. Computer: is used to digitize process and store information's received from the sensor in 0.5 to 120 seconds and then present the image on the computer monitor. As previously mentioned, this speed is very useful in endodontic and implant surgical procedures. The image may be stored permanently on the computer's hard drive, printed on a hard copy or transmitted electronically to insurance companies or referring dental specialists.
5. Radiology for the dental professional
6. Processing the radiograph (Neil serman)
1to receive the analog information and through analog-to-digital converter (ADC) to convert it to a digital image that is an array of picture elements called pixels, with discrete gray values for each one. Special software is used to store and manipulate the digital image in the computer. The image is displayed within seconds or minutes on the computer screen in front of the clinician and the patient/client.
Digital radiography requires less x-radiation than conventional radiography. Due to their larger sensitivity sensors provide an equivalent clinical image with about 70% less exposure to radiation than D-speed conventional film, and with the latest advances in F-speed film conventional