Bisecting (bisection of the angle) technique Intraoral technique of exposing dental images.
Central ray X-ray at center of beam.
Interproximal Between two adjacent surfaces.
Intersecting Cutting across or through.
Long axis of the tooth Imaginary line dividing the tooth longitudinally (vertically) into two equal halves.
Occlusal technique Used to examine large areas of the upper or lower jaw.
Paralleling technique Intraoral technique of exposing periapical and bitewing images.
Perpendicular Intersecting at or forming a right angle.
Positioning instrument Device used to hold the image receptor in place during exposure.
It is possible for every dental assistant to be successful in producing quality dental images that are free from distortion, have the correct density and contrast, and can be used for the detection of dental disease. You can create such images by carefully following the steps in image receptor placement, exposure, and processing (Fig. 41-1).
Your patients will come in a variety of sizes, physical and mental abilities, types of dentitions, and personalities. Often, you will take x-rays on patients with special needs. For example, you will explain x-rays to a 6-year-old patient differently than you will to an adult. Your technique will vary depending on whether you are using digital sensors, phosphor storage plates (PSPs) or conventional dental film. In addition, you will have to modify your technique if your patient has a palate that is very high and narrow, or your patient may have a sensitive gag reflex. This chapter provides guidelines about various situations you are likely to encounter in your career.
Even the most skilled operators can make errors; the ability to recognize errors and to know the steps to take to prevent their recurrence is most important. This chapter explains common technique errors and how to prevent them. In addition, you will learn to recognize and use normal anatomical landmarks in mounting radiographs.
No dental examination can be complete without dental images, and, in almost all cases, the full-mouth survey is the preferred technique.
An intraoral full-mouth survey (FMX) contains both periapical and bitewing images. The bitewing image shows the upper and lower teeth in occlusion. Only the crowns and a small portion of the root are seen. This view is used for detecting interproximal decay, early periodontal disease, recurrent decay under restorations, and the fit of metallic fillings or crowns (Fig. 41-2). The periapical image shows the entire tooth from occlusal surface or incisal edge to about 2 to 3 mm beyond the apex to show the periapical bone. This view is used to diagnose pathologic conditions of the tooth, root, and bone, as well as tooth formation and eruption (Fig. 41-3). Periapicals are essential in endodontics and in oral surgical procedures.
For the average adult, a full-mouth series consists of 18 to 20 images—generally, 14 periapical views and 4 to 6 bitewing views. The number may vary, however, depending on the dentist’s preference and the number of teeth present. For example, for the patient without teeth, 14 periapical views are enough to cover the edentulous arches; bitewings are not necessary. For the patient with a full dentition, the number of periapical views varies depending on whether the paralleling or the bisecting technique is used.
The anterior area is the region in which the number of images varies. Variables include the size of the sensor, if you are using digital, and the technique used (Fig. 41-4, A). When using dental film and the bisecting technique, three anterior views are taken on each arch (maxillary and mandibular) with size #2 film. For the paralleling technique, three or four size #1 films would be used on each arch (Fig. 41-4, B).
Intraoral Imaging Techniques
Whether using conventional film, digital sensors, or PSPs, two basic techniques can be used to obtain periapical images: the paralleling technique and the bisecting (bisection of the angle) technique. The American Academy of Oral and Maxillofacial Radiology and the American Association of Dental Schools recommend use of the paralleling technique because it provides the most accurate image with the least amount of radiation exposure to the patient. In some situations, however, such as a small mouth, a shallow palate, or tori, the operator may need to use the bisecting technique. This chapter provides step-by-step procedures on how to produce diagnostic-quality images with both techniques (Fig. 41-5).
The paralleling technique is also known as the extension-cone paralleling (XCP), right-angle, or long-cone technique. To use the paralleling technique competently, you must understand the terminology, including parallel (Fig. 41-6), intersecting, perpendicular, right angle, long axis of the tooth (Fig. 41-7), and central ray, in addition to the five basic rules.
Five Basic Rules
2 Image receptor position. The image receptor must be positioned parallel to the long axis of the tooth. The image receptor, in the appropriate holder (positioning instrument), must be placed away from the teeth and toward the middle of the mouth (Fig. 41-8).
The patient who is having dental images taken should be seated after the room has been prepared and infection control procedures completed. See Procedure 41-1.
Exposure Sequence for Image Receptor Placement
You should plan an exposure sequence, or a definite order, for periapical image receptor placement when you are exposing images. When working with dental film without a planned exposure sequence, you are more likely to omit an area or to expose the same area twice. This does not occur as easily when using direct digital imaging because the image most recently exposed appears on the computer screen.
Anterior Exposure Sequence
• Patients are less likely to gag with anterior image receptor placement. Once the gag reflex is stimulated, the patient may gag on subsequent views that would normally be tolerated (see later discussion).
When using a size #1 film, a total of seven or eight anterior placements are used in the paralleling technique: four maxillary exposures and three mandibular exposures (Fig. 41-11). Some operators will choose to expose four maxillary and four mandibular anterior views. If size #2 film or small sensors are used instead, six anterior placements are needed: three maxillary and three mandibular exposures. The authors recommend the use of #1 film or the smallest sized sensor for the anteriors.