LESSON 3 - PRODUCTION OF DENTAL RADIOGRAPHS
|After completing this lesson, you should be able to: |
- Define selected terms related to radiographic film.
- List in sequence the steps for exposing, processing, and viewing dental radiographs.
- Describe the facilities, materials, and methods used in processing quality x-rays.
- List the reasons for nondiagnostic quality (faulty) radiographs.
- Identify procedures for mounting dental radiographs.
- Identify radiolucent landmarks on maxillary radiographs.
- Identify radiolucent landmarks on mandibular radiographs.
- Identify radiopaque landmarks on maxillary radiographs.
- Identify radiopaque landmarks on mandibular radiographs
Section I. INTRODUCTION
A diagnostic radiograph is vitally important for most procedures in dentistry. A high level of skill and training is required of the dental specialist. The production of suitable diagnostic radiographs requires knowledge of the anatomical characteristics of the oral cavity and the relationship between individual teeth. It also requires knowledge of types of dental film, appropriate exposure and processing techniques, and use of darkroom equipment.
3-2. GENERAL EXPOSURE FACTORS
Each type of dental film requires a specific exposure time and technique to obtain satisfactory radiographs. The exposure depends upon the type of emulsion, the density of the tissues to be radiographed, the target-film distance, and the characteristics of the exposing rays. X-ray units are designed to provide exacting control of voltage, amperage, and exposure time. Satisfactory results are best achieved by carefully following the film manufacturers' instructions.
3-3. DENTAL RADIOGRAPHIC FILM
Dental radiographic film is supplied in various sizes and degrees of sensitivity, each designed for a specific purpose. Film should be stored in a cool, dry place free from chemical contamination. High temperatures, moisture, and certain chemicals will cause deterioration of the film's emulsion. Dispensers made of radiopaque metal are commonly used to provide a limited stock of periapical films. Lead-lined boxes are available for storage and protection of film used in the dental clinic (see figure 3-1). An expiration date is stamped on each film package by the manufacturer. Film should not be overstocked, but maintained in quantities that will be used before the expiration date.
- Film Construction.
(1) An x-ray film has two parts, the cellulose acetate base and the emulsion covering it. The base is made of cellulose and is a transparent plastic that is clear or with a slightly bluish tint. The emulsion is a thin coating of a special gelatin with minute particles of a silver compound. When x-rays penetrate through soft tissue, such as the cheek or the gingiva, they also penetrate the emulsion easily, which causes the silver compound to stick to the cellulose base during processing. Therefore, the film is darker (this is known as radioluscence). When x-rays are directed to hard tissue (which is dense), such as bone, tooth enamel, and metal restorations, fewer x-rays reach the film. So, more of the silver compound is removed by processing. This results in lighter shades on the film (which is known as radiopaque).
Figure 3-1. Dental film dispenser.
(2) All dental x-ray films (intraoral films) have an embossed dot (a raised spot) to identify right and left. This raised dot is on the side of the film facing the x-ray tube. The purpose of the embossed dot is to assist in mounting radiographs in correct anatomical order.
- Types of Film.
(1) Intraoral film. Periapical, bite-wing, and occlusal are three types of intraoral film used to reveal different dental structures.
- Periapical film is used primarily for radiographic examination of teeth and adjacent tissues to include the periapical region. The standard periapical film (Type 2) used in the Army is 1 1/4 by 1 5/8 inches, which is large enough to include a view of about three teeth. A small size periapical film (Type O) is also a standard item of issue for use in radiography of children's teeth and measures 7/8 by 1 3/8 inches.
- Bite-wing film is used to obtain a radiograph of the coronal two-thirds of opposing maxillary and mandibular teeth and their adjacent tissues on a single film. The film packets are provided with tabs that extend from the center of the film. When a radiograph is being made, the patient is instructed to bite down on the tab. The tab holds the film firmly in position with the lower half lying lingual to the mandibular teeth and the upper half held lingual to the maxillary teeth. Type 3 is the standard type of bite-wing film used in the Army. It measures 1 1/16 by 2 1/8 inches. When the type 3 bite-wing film is unavailable or if the dentist requests it, the type 2 periapical film may be used to take bite-wing x-rays. However, these films would require the use of paper adapters. Type O periapical film may be used as a bite-wing film for children. These, also, would require the use of paper adapters.
- Occlusal film is a highly sensitive double-emulsion film supplied in packets similar to periapical film but in a size convenient for obtaining a view of the entire upper or lower arch or portions thereof. It measures 2 1/4 by 3 inches. Some packets contain two films. The first film is developed at normal time to give a detailed image of hard structures. The second film is developed in one half the normal time to reveal soft tissue images.
(2) Extraoral film. Extraoral film is used for radiographs of the jaws, facial bones, the temporomandibular joints, and other relatively large areas. This film has no embossed dot to identify right and left.
- Intensifying screens are used with extraoral film to intensify the effects of the exposing rays and lessen the exposure time.
- A cassette is constructed of rigid metal, plastic, or cardboard. It often contains intensifying screens that magnify the x-ray beam, thus reducing exposure time. The film must be transferred to the cassette from its paper covering in the protection of the dark room.
(3) Panoramic film. Panoramic film, a type of extraoral film, is used in panoramic radiography. This film shows the entire dentition and surrounding bone structure.
3-4. BASIC PROCEDURES
Radiographs are never taken unless requested or authorized by a dentist. When a patient reports to the dental radiographic service, the desired radiographs are determined, appropriate information is recorded in the logbook (depending upon local policy), and certain basic procedures are performed.
- Exposing Procedure.
(1) Seat the patient and adjust the headrest to establish the proper position of his head.
(2)Drape the patient with the lead apron and attach the cervical collar. Position the film packet.
(3)Align the x-ray tube.
(4)Select the proper exposure factor.
(5)Make the exposure.
(6)Place the film in a film safe until ready to process.
- Processing Procedure. The processing procedure is performed in total darkness or with a special "safe" light.
(1) Prepare the darkroom.
(2) Stir the developing solution and note its temperature.
(3) Open the film packet and attach it to the film hanger.
(4) Set the timer in accordance with the graph as shown in figure 3-6 and place the film in the developing solution.
(5) Rinse the film in clear water.
(6) Set the timer again and place the film in the fixing solution.
NOTE: If a wet reading is desired, the film(s) may be removed from the fixing solution after it clears or after about two minutes. They are washed and taken to the dentist for viewing. After the wet reading, the film(s) must be returned to the fixing bath for complete fixation.
(7) Wash the film.
(8) Dry the film.
- Viewing Procedure.
(1) Mount in a suitable frame.
(2) Label the mount for proper identification.
Section II. RADIOGRAPHIC PROCESSING FACILITIES AND MATERIALS
Precise methods in the processing of x-ray films are as important in attaining good results, as is the use of precise exposure technique. Regardless of the method (automatic or manual) used by the dental specialist, if proper processing procedures are followed, quality radiographs will result.
- Construction. Since x-ray films are more sensitive to light than most photographic films, it is important to have a good darkroom. The room need not be large, but it must be constructed so that no light can enter through cracks or crevices. 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 water pipes should lead to a mixing valve so the temperature of the flow can be regulated. 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. 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. There are three types of film holders. The frame type is used for extraoral films and the clip and hinge types are used for intraoral films (see figure 3-2).
Figure 3-2. Film holders for processing intraoral and extraoral films.
- Illumination. A photographically safe light must be used to illuminate the darkroom. The standard for a safelight is that it must be possible to permit underdeveloped film to be exposed to the light at a distance of 4 feet for 1 minute without the least evidence of fogging.
- 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. One is used for the automatic processor and another for the manual processor. They are not designed to work interchangeably. 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.
3-7. AUTOMATIC PROCESSOR
The automatic processor (see figure 3-3) is used by most dental treatment facilities. Following exposure, the film is unwrapped in the darkroom and immediately loaded into the automatic processor. The unit consists of rollers and compartments filled with chemical solutions through which the film advances. At the end of the processing cycle, the film is released. The cycle duration varies from 4 to 6 minutes.
a. Preventive Maintenance. Preventive maintenance is the key for keeping this machine operational. The operator must adhere to the daily, weekly, and monthly maintenance schedule as prescribed by the manufacturer.
Figure 3-3. Automatic processor.
b. Operation. There are several automatic processors on the market today. Each machine has a slightly different design as well as maintenance and operational requirements. Therefore, you must consult the operator's manual; otherwise a very expensive piece of equipment may be damaged.
3-8. MANUAL PROCESSING
The manual processor uses the standard time-temperature method and small containers of the different processing solutions. The dental specialist should be familiar with the manual processor in case the automatic processor is not available. The manual processor will allow the dental specialist to continue providing support to the dentist without interrupting patient treatment.
NOTE: Manual processing is the primary method whereby film will be processed when field equipment is used.
- Processing Tank. The processing tank most commonly used in dental clinics has three compartments (see figure 3-4). The compartment to the left contains the developing solution, water is in the center compartment, and the fixing solution is on the right. In addition to the three compartments, a source of hot and cold water, a drain, an overflow valve, and a cover are needed. The water is adjusted to the proper temperature and is allowed to circulate in the middle compartment and pass from the tank by the overflow valve. This action provides temperature controls to the developing and fixing solution.
- Processing Procedures. In order to produce a radiographic image, the processing procedure for the film is sequenced as follows: developing, rinsing, fixing, washing, and drying. The quality and diagnostic value of radiographs depend upon proper processing procedures.
Figure 3-4. Tank for processing dental film.
- Developing. All equipment should have a definite place in the darkroom to facilitate handling when the user is working by the safelight only. Steps used when developing film are as follows:
(1) Wash gloved hands, so that hands are clean and dry. This is to prevent the appearance of finger marks on the developed film.
(2) Remove the lightproof wrapper from the film.
NOTE: Dispose of contaminated wrappers in accordance with (IAW) local standing operating procedures.
(3) Place the film on the film holder. The film should be held lightly by its edges to avoid the appearance of smudges or fingerprints on the developed film. They may appear even when the hands are clean.
(4) Set the interval timer (clock) for the prescribed developing time. Timer should start when the film is placed in the developing solution (developer).
NOTE: 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.
Figure 3-5. Time-temperature ratio for processing film.
(5) Immerse the film in the developing solution (figure 3-6), moving the film holder up and down several times to break up air bubbles that may have formed on the surface of the film.
Figure 3-6. Developing x-ray film.
NOTE: If bubbles are allowed to remain, they prevent the developer from acting on the area of film contained in each bubble. Also, care should be taken to ensure that the film does not touch another film or touch the sides of the tank. Such contact affects the emulsion and prevents the developer from acting upon it properly.
(6) Remove the film at the expiration of the developing time. Hold the film rack in a tilted position for a few seconds to allow excess solution to drain into the developing section of the tank.
(7) Rinse the film in clear water.
- Rinsing. The film should remain in the rinse water at least 20 seconds to remove the developing solution. Be sure to tilt the film rack to allow excess water to drain back in. (You do not want to dilute the fixing solution.) After removing the film from the rinse water (figure 3-7) and draining, place it in the fixing solution (fixer).
Figure 3-7. Rinsing x-ray film.
- Fixing. During the first stage of fixation, unexposed silver crystals are removed from the film, thereby clearing the film and making the image translucent. The hanger should be moved up and down several times (figure 3-8) to make sure the fixer contacts all surfaces. An average safe time for the film to remain in a fresh fixing solution is 10 minutes. This provides time for the emulsion to harden properly after the film has cleared. The film may be examined briefly after 1 minute in the fixer, but it must be returned to the solution to complete the hardening process. For wet readings, a minimum of 2 minutes of fixation is required. After readings, the film must be returned to the fixing solution to complete the process.
Figure 3-8. Fixing x-ray film.
- Washing. Upon the completion of fixation, the film should be immersed in fresh, cool, circulating water for at least 20 minutes to ensure complete removal of the fixing solution (figure 3-9). If not washed properly, the radiograph will turn yellow and fade with time if any of the fixing chemical remains on its surface.
Figure 3-9. Washing x-ray film.
- Drying. Wet films must be handled carefully so that the emulsion is not touched or marred. After washing, the hanger should be hung carefully upon the drying rack. A pan under the rack serves to catch water dripping from films. Drying is done by leaving the film suspended in the air until it is completely dry. Drying may be speeded up by directing a current of air from a small electric fan over the film's surface or by using an x-ray film drier (see figure 3-10).
Figure 3-10. X-ray drier.
Section III. FAULTY RADIOGRAPHS
Errors in improperly exposing or processing dental films can produce undesirable dental radiographs of nondiagnostic quality. These are known as faulty radiographs. The dental x-ray specialist should be familiar with the common causes of faulty radiographs and how to prevent them.
3-10. UNDEREXPOSED IMAGE
An underexposed image (see figure 3-11), an image that is too light, may be caused by:
- Insufficient radiation exposure.
- Insufficient development time.
- Use of an overused developing solution.
- Use of a developing solution that is too cold.
Figure 3-11. Underexposed image.
3-11. OVEREXPOSED IMAGE
An overexposed image (see figure 3-12), an image that is too dark, may be caused by:
- Too much radiation exposure.
- Too much development time.
- Use of developing solution that is too warm.
Figure 3-12. Overexposed image.
3-12. BLURRED IMAGE
A blurred image (see figure 3-13) is easily recognized by the appearance of more than one image of the object, or objects, on the film. It may be caused by movement of the patient, film, or tube during exposure.
Figure 3-13. Blurred image.
3-13. PARTIAL IMAGE
A partial image (see figure 3-14) may be caused by failure to immerse the film completely in the developing solution, contact of the film with another film during developing, or improper alignment of the central ray.
Figure 3-14. Partial image.
3-14. DISTORTED IMAGE
A distorted image (figure 3-15) may be caused by improper angulation of the central ray due to bending of the film packet.
Figure 3-15. Distorted image.
3-15. FOGGED FILM
Fogged film ( figure 3-16) may be caused by:
- Exposure of film to light during storage.
- Leaving film unprotected (that is, outside the lead-lined box or in the x-ray room during operation of the x-ray machine).
- Use of film that has been exposed to heat or chemical fumes.
- Use of improperly mixed or contaminated developer.
- Defective safelight.
Figure 3-16. Fogged film.
3-16. STAINED OR STREAKED FILM
Stained or streaked film ( figure 3-17) may be caused by dirty solutions, dirty film holders or hangers, incomplete washing, or solutions left on the workbench.
Figure 3-17. Stained or streaked film.
3-17. BLEACHED IMAGE
A bleached image (see figure 3-18) is caused by leaving the film in a freshly-mixed fixing solution too long or at a temperature that is too warm.
Figure 3-18. Bleached image.
3-18. LEAD-FOIL IMAGE
A lead-foil image (see figure 3-19) occurs when the embossing pattern from the lead foil backing appears on the radiograph. The embossing pattern consists of raised diamonds across both ends of the film. This happens when the film is put in backwards.
Figure 3-19. Lead-foil image.
3-19. NO IMAGE
No image may result if no current was passing through the tube at the time of exposure or if the film was placed in the fixing solution before it was placed in the developing solution.
A reticulated film appears as a network of wrinkles or corrugations on the emulsion of the x-ray film. When reticulation occurs, the finished film has a netlike or puckered appearance resulting from swelling of the film's gelatin. Swelling is caused by sudden changes in temperature during processing, as in the transfer from a cool fixing bath to warm wash water or from a warm rinse water to a cool fixing bath.
Section IV. MOUNTING AND FILING/DISPOSING OF RADIOGRAPHS
Cardboard or plastic mounts for 16-film, full-mouth radiographs and bite-wing mounts are available as standard items of dental supply. Sections of these, or small paper envelopes, are used for protecting and identifying individual periapical or bite-wing radiographs. The film mounts are designed so that the film may be arranged in the same order as the teeth in the mouth. Thus, mounting not only protects and labels the radiographs, but also facilitates viewing and studying of the film, particularly in full-mouth examinations. See figure 3-20.
Figure 3-20. Full-mouth radiographic mount.
In mounting radiographs, care must be taken to avoid marks from damp or perspiring fingers. Hands and fingers should be clean and dry. The film should be handled only on the edge. Under adequate illumination, the radio- graphs are removed one at a time from the hanger and placed carefully into the appropriate opening in the film mount. Radiographs are mounted so that the raised part of the embossed dot faces the dental specialist. In this way the radiographs are viewed from the facial aspect in correct anatomical order.
- Maxillary and mandibular radiographs may be identified by the anatomy of the teeth and surrounding structures. (See paragraphs 3-24 through 3-28 for anatomic landmarks.) Radiographs are mounted with apices of maxillary teeth directed upward and apices of mandibular teeth directed downward.
- The mesial aspect of a radiograph may also be determined by the anatomic features of tissues included on the film. If the mesial is to the right (when viewed from the facial side), it is a film taken on the patient's right side. If the mesial is to the left (when viewed from the facial side), it is a film taken of the patient's left side.
3-23. FILING AND DISPOSING
Dental radiograph holders or containers should be identified with the patient's name, address and other pertinent information, such as date and teeth, or area, included in the films.
- The Dental Health Record. Dental radiographs needed for future treatment or follow-up observation of a patient are kept in the dental health record.
- Disposition of Radiographs. Some radiographs may be kept for extended periods if the dentist deems necessary. These radiographs may serve as history with regard to future treatment of the patient.
Section V. ANATOMIC RADIOGRAPHIC LANDMARKS
A number of anatomic landmarks are visible in dental radiographs. Knowledge of the location and normal appearances of these landmarks is important in identification and orientation of radiographs. This knowledge is valuable to the dentist in determining whether the area is normal or abnormal. The landmarks that appear as dark areas on the film are radiolucent. The areas that appear as light areas on the film are radiopaque. Anatomic characteristics and the relationship between individual teeth are anatomic landmarks with which all dental specialists should be familiar.
3-25. RADIOLUCENT LANDMARKS ON MAXILLARY RADIOGRAPHS
- Maxillary Sinus. The maxillary sinus (see figure 3-21) is a very prominent radiolucent structure. It sometimes appears as overlapping lobes or a single radiolucent area with a radiopaque border. The maxillary sinus is partially seen in all periapical radiographs of the bicuspid-molar area. It occupies a large part of the body of the maxilla, varying greatly in dimension, but normally extending into the alveolar process adjacent to the apices of the posterior teeth.
- Incisive Foramen. The incisive foramen (see figure 3-22) is seen as a dark area located between and extending above the central incisors. In radiographs exposed from the region of the cuspid or lateral incisor, the incisive foramen may appear as a radiolucency at the apex of one of the incisors.
Figure 3-21. Maxillary Sinus.
Figure 3-22. Incisive foramen.
- Median Palatal Suture. The median suture of the palate (see figure 3-23) may appear as a radiolucent line extending posteriorly from the alveolar border in the sagittal plane of the maxilla, on an anterior periapical film, or occlusal film.
- Nasal Fossae. In a radiograph of the maxillary central incisors, the images of the paired fossae appear as somewhat elliptical radiolucent areas of various sizes separated by a radiopaque band representing the nasal septum (see figure 3-24).
Figure 3-23. Median palatal suture.
Figure 3-24. Nasal fossae.
3-26. RADIOPAQUE LANDMARKS ON MAXILLARY RADIOGRAPHS
- Maxillary Tuberosity. The maxillary tuberosity (see figure 3-25) is the convex distal inferior border of the maxilla, curving upward from the alveolar process and distal of the third molar. An extension of the maxillary sinus is occasionally seen within the maxillary tuberosity.
- Coronoid Process of the Mandible. The coronoid process of the mandible (see figure 3-26) sometimes appears on maxillary molar films as a triangular opaque area located in the region of or distal to the maxillary tuberosity.
Figure 3-25. Maxillary tuberosity.
Figure 3-26. Coronoid process of the mandible.
- Zygomatic Process (Malar Bone). The zygomatic arch (see figure 3-27) commonly appears as a well-defined radiopaque area that may be superimposed over the molar roots. Additional radiographs are sometimes made at adjusted angulation to provide a better view of the molar root area.
Figure 3-27. Zygomatic process (malar bone).
- Nasal Septum. The nasal septum is usually seen as a white ridge extending above and between the central incisors.
3-27. RADIOLUCENT LANDMARKS ON MANDIBULAR RADIOGRAPHS
- Mandibular Foramen. The mandibular foramen is seen on extraoral mandibular films as a dark area near the middle of the mandibular ramus.
- Mandibular Canal. The mandibular canal (see figure 3-28) appears as a dark band with radiopaque borders running downward and forward from the mandibular foramen in the ramus to the region of the bicuspid teeth in the body of the mandible. It may be seen below the roots of the posterior teeth.
Figure 3-28. Mandibular canal.
- Mental Foramen. The mental foramen (see figure 3-29) is seen as a dark area below and between the bicuspids. Since it is not contiguous with either bicuspid, its relationship to these teeth appears different on radiographs made at different angulations.
3-28. RADIOPAQUE LANDMARKS ON MANDIBULAR RADIOGRAPHS
- Border of the Mandible. The border of the mandible is seen as a heavy white line (see figure 3-30). A similar line does not appear on maxillary radiographs.
- External Oblique Ridge. The external oblique ridge is a white line of variable density extending into the molar region as a continuation of the anterior border of the ramus of the mandible (see figure 3-31).
Figure 3-30. Border of the mandible.
Figure 3-31. External oblique ridge.
- Genial Tubercles. Genial tubercles are seen as round white areas, having dark centers, located below and between the central incisors (see figure 3-32).
Figure 3-32. Genial tubercles.
- Mental Process (Mental VRidge). The mental ridge may appear as a dense white ridge of varying density extending from the anterior midline to the bicuspid region, usually located below the anterior teeth, but occasionally superimposed over the apices.
- Mylohyoid Ridge (Internal Oblique Ridge). The mylohyoid ridge appears as a white line of varying width and indensity, extending from close to the lower border of the symphysis of the mandible, upward and distally, to end beyond the third molar. It reaches its greatest prominence in the molar region. It is generally not a prominent feature.