Automatic Processing Techniques Bisecting
Angle Technique Bite-Wing Image Cassette Charge-Coupled Device (CCD) Diagnostic Quality Image Digital Image Digitized Film
Duplicating Horizontal Angulation Latent Image Manual Processing Occlusal Technique Panoramic Radiography Paralleling Technique Periapical Views Phosphor Storage Plates (PSP) Point of Entry Positioning Instrument Radiograph Scanning Sensor-Holding Devices Teledentistry Vertical Angulation In the modern dental office, digital radiography is rapidly replacing traditional film-based techniques. When discussing digital radiography, the term digital image is used instead of radiograph, film, or x-rays. A radiograph is an image on a conventional dental film. It is important for the dental assistant to be
competent with all forms of dental radiography. You must also be familiar with dental x-ray equipment, dental-x-ray film, and film- or sensor-holding devices (Figure 16-1). There are three types of intraoral views. Each type of view provides specific
information (Table 16-1). The three types of intraoral views are: TABLE 16-1 Types of Dental Images < ?comst?> < ?comen?>< ?comst1?> < ?comen1?>Oral Radiography
Learning Objectives
Key Terms
Intraoral Views
Types of Intraoral Views
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Occlusal radiograph from Miles DA, Van Dis ML, Williamson GF, et al: Radiographic imaging for the dental team, ed 4, Philadelphia, 2009, Saunders.
Film-Based Radiography
Placing a film in the patient’s mouth and then exposing it to a beam of x-rays captures the image on the film to make dental radiographs. The latent image (invisible) on the film becomes visible only after the film is processed in a darkroom (a light-tight room) or in an automatic film-processing machine. Once the film is processed and dried, it becomes a radiograph; it is placed into a film mount and is ready to be viewed and interpreted by the dentist.
Intraoral Dental X-Ray Film
The Film Packet
A film packet consists of an outer wrap, a lead foil, black paper, and one or two films (Figure 16-2).
The front of the packet is white. This side is always placed toward the position indicator device (PID). The back, which is colored and has the tab used for opening the packet before processing, is always placed away from the PID. A small circle on the back indicates where the embossed dot, or raised bump, is on the film. This dot will aid later in mounting and determining the right side from the left.
Within the packet, the film is protected on either side by a sheet of black paper; a thin sheet of lead foil absorbs most of the x-rays that pass through the film (thus protecting the patient).
Double Film Packets
Double film packets contain two pieces of film between the black paper lining. This makes it possible to produce a duplicate set of the radiographs without exposing the patient to additional radiation or having to go through the film duplicating process.
Double film packets are useful when the insurance company requests radiographs or when a patient is referred to a specialist.
X-Ray Film
Intraoral dental film consists of a semiflexible plastic film base coated on both sides with an emulsion containing x-ray–sensitive crystals of silver bromide, silver halide, and silver iodine embedded in gelatin. The size of the crystals determines the film speed. (Film speed is discussed in Chapter 15.) These are numbered from 0 to 4, with 0 being the smallest (Figure 16-3 and Table 16-2).
TABLE 16-2
Commonly Used Film Sizes
| Size | Uses |
| 0 | Usually for children younger than 3 years |
| 1 | Anterior film for adult full-mouth surveys |
| 2 | Adult BWXs and adult posterior periapicals |
| 3 | Less common, but used for adult BWX |
| 4 | Occlusal radiographs |
BWX, Bite-wing survey.
Care of Dental Films
Film Storage
All dental films should be stored according to the manufacturer’s instructions. This includes storing them so that they are protected from light, heat, moisture, chemicals, and scatter radiation. The box of radiographic film is marked with an expiration date.
Film Care During Exposure
Films to be exposed are dispensed before the radiographic procedure begins. They are placed on a clean towel just outside the room where the films are to be exposed.
Never leave films, whether exposed or unexposed, in the room where additional films are being exposed. This could result in the new films being exposed to scatter radiation, which results in film fog and reduces their diagnostic value.
Infection Control in Dental Radiography
Dental radiographic procedures present special infection control challenges (Box 16-1). The operator contacts the patient’s saliva while placing and removing the film packets or sensors, and touches many things while exposing and processing film. Protective measures and barriers used while producing radiographs are illustrated in Figure 16-4. Dental film is now available with plastic barriers over the packet. The film is exposed as usual, and then the plastic barrier cover is removed before entering the darkroom for processing. The infection control protocol is more efficient and effective when the dental assistant plans for the procedure before the patient is seated (Box 16-2 and see Procedure 16-1).
Box 16-1
Surfaces Likely To Be Contaminated During X-Ray Procedures
Box 16-2
CDC Guidelines for Dental Radiology
1 Wear gloves when exposing radiographs and handling contaminated film packets. Use other PPE (e.g., protective eyewear, mask, gown) as appropriate if spattering of blood or other body fluids is likely. (IA, IC)
2 Use heat-tolerant or disposable intraoral devices whenever possible (e.g., film-holding and positioning devices). Clean and heat-sterilize heat-tolerant devices between patients. (IB)
3 Transport and handle exposed film in an aseptic manner to prevent contamination of the developing equipment. (II)
4 The following apply for digital radiography sensors:
a Use FDA-cleared barriers. (IB)
b Clean and heat-sterilize, or high-level disinfect, between patients; barrier protect semicritical items. If an item cannot tolerate these procedures, then at a minimum, between patients protect with an FDA-cleared barrier, and clean and disinfect with an EPA-registered hospital disinfectant with intermediate-level (i.e., tuberculocidal claim) activity. Consult the manufacturer for methods of disinfection and sterilization of digital radiography sensors and for protection of associated computer hardware. (IB)
CDC, Centers for Disease Control and Prevention; EPA, Environmental Protection Agency; FDA, U.S. Food and Drug Administration; PPE, personal protective equipment.
Modified from Guidelines for infection control in dental health care settings—2003, Atlanta, Georgia, 2003, Department of Health & Human Services, Centers for Disease Control and Prevention.
Intraoral Radiography Techniques
Regardless of whether you are using conventional film-based techniques or digital techniques, two basic techniques are used to obtain periapical views: the paralleling technique and the bisecting angle technique. The paralleling technique is preferred because it provides a more accurate image of the teeth and surrounding structures. The bisecting angle technique is discussed in this chapter as a supplemental method (Figure 16-5).
The Paralleling Technique
Basic Principles
Two basic principles define the paralleling technique: (1) The film is placed parallel to the long axis of the teeth being radiographed, and (2) the x-ray beam is directed at right angles (perpendicular) to the film or sensor and the long axis of the tooth.
Film/Sensor-Holding Instruments
To place and keep the film packet or sensor in its proper position in relation to the tooth, the paralleling technique requires the use of film- or sensor-holding instruments. A variety of film/sensor-holding instruments are available (Figure 16-6).
A commonly used type of film/sensor-holding instrument is the Rinn XCP (extension cone paralleling) instrument (Figure 16-7). In addition to film/sensor positioning, these instruments include a localizing ring, also known as an aiming ring, which facilitates aligning the PID with the film/sensor in both horizontal and vertical planes. This increases accuracy and reduces the need for unnecessary retakes. The procedures that follow at the end of this chapter include the use of XCP film/sensor-holding instruments; however, the basic principles of placement and paralleling are similar regardless of the film/sensor-holding instrument that is used (see Procedure 16-2).
Using the Paralleling Technique
Important factors to be considered in exposing periapical views include the dental chair position, film/sensor position and placement, point of entry of the x-ray beam, vertical and horizontal angulation, and the use of a film/sensor-holding instrument.
The dental chair is positioned so the patient’s head is straight. For most exposures, this means that the patient is seated in an upright position. This position is adjusted so that the occlusal plane of the jaw being radiographed is parallel to the floor when the film/sensor is in position.
The film/sensor is placed in a vertical position for anterior projections and in a horizontal position for posterior periapical projections. The film/sensor is held in position by the patient closing on a bite-block or other film/sensor-holding device.
When conventional film is used, the film is placed so that the raised dot is toward the occlusal surface and is facing the PID. This technique places the front of the film packet toward the PID, prevents the dots from becoming superimposed over the apex of a tooth, and later aids in mounting the processed film. The film position must be parallel to the entire tooth, not just parallel to the crown. This is an important concept to understand. Although the crowns of the teeth appear to tilt one way, the entire structure actually tilts another. For example, the apices of most of the maxillary teeth tilt inward toward the palate. The mandibular premolars are more nearly vertical, and the mandibular molars tilt inward slightly (Figure 16-8).
To achieve parallelism between the long axes of the teeth and the film/sensor, the film/sensor must be placed slightly away from the teeth toward the midline of the oral cavity. In addition, film/sensors that are placed too close to the teeth may not record enough tissue in the area of the root apices. The film/sensor must be positioned away from the teeth, with the patient biting near the anterior edge of the bite-block.
The point of entry is the position on the patient’s face at which the central x-ray beam is aimed. The goal is to completely cover the film/sensor with the beam of radiation.
Vertical angulation is the movement of the tubehead in an up-and-down direction, similar to shaking your head “yes” (Figure 16-9). In the paralleling technique, the vertical angulation must be perpendicular to the film/sensor and to the long axes of the teeth, or images will be elongated or foreshortened (Figures 16-10 and 16-11).
Horizontal angulation is the movement of the tubehead in a side-to-side direction, similar to shaking your head “no” (Figure 16-12). In the paralleling technique, the horizontal angulation of the x-ray beam must be directed through the contacts of the teeth and be as perpendicular (perpendicular means at a right angle with the film/sensor) to the horizontal plane of the film/sensor as possible. Failure to do this will cause overlapping of proximal contacts (Figure 16-13).
The Bisecting Angle Technique
The bisecting angle technique can be used in some special circumstances, for example, in difficult or unusual anatomy, such as in patients with a very shallow palate or a very short lingual frenum, or when palatal or mandibular tori (bone growths) are present. In addition, small children and some endodontic views may require use of this technique. Using proper technique, diagnostic images can be obtained with this method.
Basic Principles
The bisecting angle technique is based on the geometric principle of bisecting a triangle (bisecting means dividing into two equal parts) (Figure 16-14).
The angle formed by the long axis of the teeth and the film/sensor is bisected, and the x-ray beam is directed at a right angle (perpendicular) to the bisecting line.
In this technique, the film/sensor is placed close to the crowns of the teeth to be radiographed and extends at an angle into the palate or floor of the mouth. Film/sensor holders for the bisecting angle technique, including some with alignment indicators, are available commercially.
Patient Positioning
The patient’s midsagittal plane should be perpendicular to the floor. This means that the patient’s head is upright for maxillary film and is tipped back slightly for the mandibular arch.
A No. 2 film/sensor is used in both the anterior (in a vertical position) and posterior (in a horizontal position) regions. Only three films are needed in the maxillary anterior region because all four maxillary incisors can be imaged on the No. 2 film/sensor.
Beam Alignment
The x-ray beam is directed to pass between the contacts of the teeth being radiographed in the horizontal dimension, just as it does in the paralleling technique. The vertical angle, however, must be directed at 90 degrees to the imaginary bisecting line. Too much vertical angulation will produce images that are too short (foreshortened), and too little vertical angulation will result in images that are too long (elongated). The beam must be centered to prevent cone cutting. A short or a long PID can be used (Table 16-3).
The Full-Mouth Radiographic Survey
A full-mouth radiographic survey (FMX) consists of a specified number of periapical and bite-wing views. A complete full-mouth survey may have as few as 10 or as many as 18 periapical views, plus whatever bite-wing views are indicated. The number and size of the film/sensor to be used depend on:
The procedure described here includes positioning and steps for each exposure in one half of the maxillary arch and one half of the mandibular arch with use of the paralleling technique and XCP film/sensor-holding instruments (Box 16-3).
Box 16-3
Guidelines for Film Placement
When the opposite side of each arch is radiographed, the same procedures are followed. The completed radiographic survey is shown in Figure 16-15 (see Procedure 16-3).
Producing Bite-Wing Views
Bite-wing views are always parallel films regardless of the technique used for the periapical radiographs (see Procedure 16-4).
The film/sensor is positioned (by a bite tab or by a holding device) parallel to the crowns of both upper and lower teeth, and the central ray (CR) is directed perpendicular to the film/sensor.
The premolar bite-wing image should include the distal half of the crowns of the cuspids, both premolars, and often the first molars on both the maxillary and mandibular arches. The molar film should be centered over the second molars.
Correct horizontal angulation is crucial to the diagnostic value of a bite-wing view. Even a slight amount of overlapping of the proximal (contact) surfaces on the image may lead to a misdiagnosis.
The Occlusal Technique
The occlusal technique is used to examine large areas of the upper or lower jaw (Box 16-4). The occlusal technique is so named because the patient bites or “occludes” the entire film. This technique requires the use of conventional dental film. In adults, No. 4 intraoral film is used, but No. 2 film is used in children. The occlusal technique is used when large areas of the maxilla or mandible must be radiographed (see Procedure 16-5).
Box 16-4
Uses for Occlusal Radiographs