Radiology Lecture 5.docx

Lecture 5 Chapter 9 – Dental X-ray Film An increasing number of dental practices are transitioning from film to digital imaging, but traditional film continues to be used in many practices. Consequently, the dental radiographer must be familiar with both film and digital imaging in order to be pr...

Lecture 5 Chapter 9 – Dental X-ray Film An increasing number of dental practices are transitioning from film to digital imaging, but traditional film continues to be used in many practices. Consequently, the dental radiographer must be familiar with both film and digital imaging in order to be prepared to work in a variety of offices. In dental radiography, the x-ray beam passes through teeth and adjacent structures and reaches the x-ray film. Receptor refers to something that responds to a stimulus. Film composition The x-ray film used in dentistry has four basic components: (1) a film base, (2) an adhesive layer, (3) film emulsion, and (4) a protective layer The film base is a flexible piece of polyester plastic 0.2 mm (200 microns) in thickness that is constructed to withstand heat, moisture, and chemical exposure. (This is what you hold/can see.) The film base is transparent and exhibits a slight blue tint that is used to emphasize contrast and enhance image quality. The primary purpose of the film base is to provide a stable support for the delicate emulsion. The base also provides strength. The adhesive layer is a thin layer of adhesive added to the film base before the emulsion is applied and serves to attach the emulsion to the base. (Covers both side of the film; this is the glue.) The film emulsion is a coating attached to both sides of the film The emulsion is a homogeneous mixture of gelatin and silver halide crystals. The gelatin is used to suspend and evenly disperse millions of microscopic silver halide crystals over the film base. Silver bromide (AgBr) and silver iodide (AgI) are two types of silver halide crystals found in the film emulsion; the typical emulsion is 80% to 99% silver bromide and 1% to 10% silver iodide. Silver halide crystals absorb raditation. The protective layer is a thin, transparent coating placed over the emulsion. It serves to protect the emulsion surface from manipulation as well as mechanical and processing damage. Think of this as Saran wrap The silver halide crystals on the film that are positioned behind an amalgam restoration receive almost no radiation. Amalgam is dense and absorbs the x-ray energy. As a result, the silver halide crystals are not energized. The result of this is that the amalgam will appear radiopaque The stored energy within the silver halide crystals forms a pattern and creates an invisible image within the emulsion on the exposed film. This pattern of stored energy on the exposed film cannot be seen and is referred to as a latent image. Think of the latent image like a fingerprint. X-rays strike and ionize some of the silver halide crystals. The density (thickness) of the object determines how much radiation will reach the film emulsion. The latent image remains invisible within the emulsion until it undergoes chemical processing procedures. **Application: For the latent image to be embedded in the silver halide crystals, where must the film be placed in relation to the teeth? The film is placed to the lingual of the teeth. **Application: The areas of the film that are less energized will appear darker or lighter? Lighter Irregularities in the lattice structure of the exposed crystal, known as sensitivity specks, attract the silver atoms. These aggregates of neutral silver atoms are known as latent image centers Three types of x-ray film may be used in dental radiography: Intraoral film Extraoral film Duplicating film An intraoral film is a film that is placed inside the mouth during x-ray exposure. An intraoral x-ray film packet is made up of four separate items: x-ray film paper film wrapper lead foil sheet outer film wrapping The intraoral x-ray film is a double-emulsion film (emulsion on both sides). Double-emulsion film is used instead of single-emulsion film (emulsion on one side) because it requires less radiation exposure to produce an image. A two-film packet produces two identical images with the same amount of exposure necessary to produce a single image. The two-film packet is used when a duplicate record of a radiographic examination is needed (e.g., for insurance claims, patient referrals, etc.). Double emulsion is used on both single and double film packets. A small, raised bump known as the identification dot is located in one corner of the intraoral x-ray film. The raised bump is used to determine film orientation. The paper film wrapper within the film packet is a protective black sheet that covers the film and shields the film from light. The lead foil sheet is a single piece of lead foil within the film packet that is located behind the film wrapped in protective paper. The thin lead foil sheet is positioned behind the film to shield the film from backscattered (secondary) radiation that results in film fog. The manufacturer-placed embossed pattern on the lead foil sheet is visible on a processed radiograph if the film packet is inadvertently positioned in the mouth backward and then exposed. This error may result in a retake if the resultant image is too light and nondiagnostic. The outer package wrapping is a soft-vinyl or paper wrapper that hermetically seals the film packet, protective paper, and lead foil sheet. The outer wrapper of the film packet has two sides: (1) the tube side and (2) the label side. The tube side is solid white and has a raised bump in one corner that corresponds to the identification dot on the x-ray film. When placed in the mouth, the white side (tube side) of the film packet must face the teeth and the tubehead. The label side has a flap, the information about the film, and is color-coded to identify films outside of the plastic packaging container; color codes are used by the manufacturer to distinguish one-film and two-film packets and film speeds. When placed in the mouth, the color-coded side (label side) of the packet must face the tongue. An easy way to remember this is “white in sight”—the white side of the film should be facing the operator when placed in the mouth. Three types of intraoral films are available: periapical bite-wing occlusal. As the term suggests, periapical shows the tip of the tooth root and surrounding structures as well as the crown. The apex (tip) of the teeth can be seen in both the periapical and occlusal projections. Three sizes (0, 1, and 2) of the periapical film are available. The size 0 periapical film is the smallest intraoral film available and is used for very small children. The size 1 periapical film is used primarily to examine the anterior teeth in adults. The size 2 periapical film, also known as the standard film, is used to examine the anterior and posterior teeth in adults. Application: What size film would you use to take posterior periapical radiographs on your adult patient? 2 The bite-wing film is used to examine the crowns of both maxillary and mandibular teeth on one film. The bite-wing film is particularly useful in examining interproximal, or adjacent, tooth surfaces. In addition to seeing the interproximal areas, the bite-wing film shows the crestal bone level and existing restorations. Three sizes (0, 2, and 3) of the bite-wing film are available. With the exception of the size 3 film, the size and shape of the bite-wing film are identical to the size and shape of the periapical film. The size 0 bite-wing film is used to examine the posterior teeth in small children. The size 2 bite-wing film is used to examine the posterior teeth in older children and adults. This is the most frequently used bite-wing film. The size 3 film is longer and narrower than the standard size 2 film and is used only for bite-wing images. This bite-wing film shows all the posterior teeth on one side of the arch in one radiograph. Size 3 film is almost never used. Application: Your dentist asks you to take radiographs on your patient in order to check the interproximal surfaces on the posterior maxillary and mandibular teeth for decay. Which type of film would be the best to take the radiograph? Bite-wing film. Application: What size film should be used to take a bitewing on a 3 year old child? 0 What size film would you use to take a bite-wing on your adult patient? 2 The occlusal film is used for examination of large areas of the maxilla or the mandible. The occlusal film is the largest intraoral film and is almost four times as large as a standard size 2 periapical film. The size 4 occlusal film is used to show large areas of the maxilla or the mandible. The occlusal film projection should be used on pediatric patients if the maxillary or mandibular teeth need to be seen. WHAT SIZE FILM IS USED FOR THE OCCLUSAL PROJECTION? 4 Full Mouth Series 20 projections 8 Anterior projections 5 Maxillary projections 3 Mandibular projections 8 Posterior projections 2 Maxillary premolar projections (left and right) 2 Maxillary molar projections (left and right) 2 Mandibular premolar projections (left and right) 2 Mandibular molar projections (left and right) 4 Bitewings 2 premolar projections (left and right) 2 molar projections (left and right) Film Speed A fast film requires less radiation exposure because the film responds more quickly; a fast film responds more quickly because the silver halide crystals in the emulsion are larger. The larger the crystals, the faster the film speed. Thickness of emulsion also affects film speed. Thicker emulsion results in a faster speed film requiring less radiation. An alphabetical classification system is used to identify film speed. X-ray films are given speed ratings ranging from A speed (the slowest) to F speed (the fastest). Only D-speed, E-speed, E/F-speed, and F-speed film are used for intraoral radiography. The American Dental Association (ADA) and the American Academy of Oral and Maxillofacial Radiology (AAOMR) currently recommend the use of F-speed film. The F-speed film requires 60% (40% less) of the exposure time of the D-speed film and has comparable image contrast and resolution. A-speed film is the slowest. F-speed film is the fastest. Extraoral Film An extraoral film is placed outside the mouth during x-ray exposure. Extraoral images are used to examine large areas of the skull or jaws. Common extraoral images include panoramic and cephalometric. A panoramic image shows a panoramic (wide) view of the maxilla and the mandible and surrounding structures on a single image. The cephalometric radiograph is a side facial profile projection that includes the skeletal structure, tissues, jaw, and teeth. Unlike intraoral films, extraoral films are designed for use outside the mouth and therefore are not enclosed in moisture-proof packets. Two types of film may be used in extraoral radiography: (1) screen film and (2) non-screen film. The majority of extraoral films are screen films. A screen film is a film that requires the use of a screen for exposure (see later discussion). A screen film is placed between two special intensifying screens in a cassette. When the cassette is exposed to x-rays, the screens convert the x-ray energy into light, which, in turn, exposes the screen film. The screen film is sensitive to fluorescent light rather than to direct exposure to x- radiation, which decreases patient exposure to radiation. Some screen films are sensitive to blue light (X-Omat DBF film), whereas others are sensitive to green light (T-Mat film). Blue-sensitive film must be paired with screens that produce blue light. Green-sensitive film must be paired with screens that produce green light. Properly matched film-screen combinations are imperative to obtain high- quality images and to minimize exposure of the patient. A non-screen extraoral film requires more exposure time than does a screen film and is not recommended for use in dental radiography. In extraoral radiography, screen films are used in combination with two special equipment items: intensifying screens and cassettes. An intensifying screen is a device that transfers x-ray energy into visible light; the visible light, in turn, exposes the screen film. These screens intensify the effect of x-rays on the film. With the use of intensifying screens, less radiation is required to expose a screen film, and the patient is exposed to less radiation. An intensifying screen is a smooth plastic sheet coated with minute fluorescent crystals known as phosphors. When exposed to x-rays, the phosphors fluoresce and emit visible light in the blue or green spectrum; the emitted light then exposes the film Conventional calcium tungstate screens have phosphors that emit blue light. The newer rare earth screens have phosphors that are not commonly found in the earth (thus “rare earth”) and emit green light. Rare earth intensifying screens are more efficient at converting x-rays into light than are calcium tungstate intensifying screens. As a result, rare earth screens require less x-ray exposure than do calcium tungstate screens and are considered faster. The use of rare earth screens means less exposure of the patient to x-radiation. A cassette is a special device that is used to hold the extraoral film and the intensifying screens. Contact between the screen and the film is critical; lack of contact between screen and film results in loss of image sharpness. Application: Screen films are sensitive to VISIBLE LIGHT. Duplicating Film Duplicating film is a type of photographic film used to make an identical copy of an intraoral or extraoral radiograph. Unlike intraoral and extraoral films, the duplicating film is used only in a darkroom setting and is not exposed to x-rays Films are adversely affected by heat, humidity, and radiation. To prevent film fog, unexposed, unprocessed films must be kept in a cool, dry place. The optimum temperature for film storage ranges from 50° F to 70° F, and the optimum relative humidity level ranges from 30% to 50%. Films must be stored in areas that are adequately shielded from sources of radiation and should not be stored in areas where patients are exposed to x-radiation.