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).

FIG. 41-1 Steps to quality dental images.

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.

Full-Mouth Survey

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.

FIG. 41-2 Bitewing radiograph. Note that only the crowns and the alveolar ridge are visible, but the roots are not.

FIG. 41-3 A, Anterior periapical. B, Posterior periapical. Note that the entire tooth and surrounding bone are visible on the radiograph.

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).

1 What is the difference between a bitewing and a periapical image?

2 What are the two techniques that can be used for exposing images?

FIG. 41-4 A, Full-mouth survey using digital sensor. B, Mounted full-mouth series with eight anterior films using the paralleling technique. (A, Courtesy DEXIS, LLC, Des Plaines, IL.)

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).

Paralleling Technique

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.

FIG. 41-6 A, Parallel lines are always separated by the same distance and do not intersect. B, Intersecting lines cross one another. C, Perpendicular lines intersect one another to form right angles. D, Right angle measures 90 degrees and is formed by two perpendicular lines. (From Iannucci J, Jansen Howerton L: Dental radiography: principles and techniques, ed 4, St Louis, 2012, Saunders.)

FIG. 41-7 A, Long axis of maxillary incisor divides the tooth into two equal halves. B, Long axis of mandibular premolar divides the tooth into two equal halves. (From Iannucci J, Jansen Howerton L: Dental radiography: principles and techniques, ed 4, St Louis, 2012, Saunders.)

Five Basic Rules

The following basic rules must be followed when the paralleling technique is used:

1 Image receptor placement. The image receptor must be placed in the mouth, so that it will cover the correct teeth to be examined.

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).

3 Vertical angulation. The central ray of the x-ray beam must be directed perpendicular (at a right angle) to the image receptor and the long axis of the tooth.

4 Horizontal angulation. The central ray of the x-ray beam must be directed through the contact areas between the teeth (Fig. 41-9).

5 Central ray. The x-ray beam must be centered on the image receptor to ensure that all areas are exposed. Failure to center the x-ray beam results in a partial image, or cone cut (Fig. 41-10).

FIG. 41-8 Position of the film sensor, teeth, position indicator device (PID), and central ray of the x-ray beam in the paralleling technique. The film sensor and the long axis of the tooth are parallel. The central ray (CR) is perpendicular to the tooth and the film sensor. An increased distance (16 inches) is required. (From Iannucci J, Jansen Howerton L: Dental radiography: principles and techniques, ed 4, St Louis, 2012, Saunders.)

FIG. 41-9 In this diagram, x-rays pass through the contact areas of the premolars because the central ray is directed through the contacts and perpendicular to the film. If the central ray (CR) is not directed through the contacts, overlap of the premolar contacts occurs. (From Iannucci J, Jansen Howerton L: Dental radiography: principles and techniques, ed 4, St Louis, 2012, Saunders.)

FIG. 41-10 This radiograph demonstrates a cone cut, that is, a clear unexposed area on the film. The position indicator device was positioned too far distally, so the anterior portion of the film received no exposure. (From Iannucci J, Jansen Howerton L: Dental radiography: principles and techniques, ed 4, St Louis, 2012, Saunders.)

Patient Preparation

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.

PROCEDURE 41-1

Preparing the Patient for Dental Imaging

Goal

✓ To follow the basic steps in preparing a patient for intraoral x-ray procedures.

Equipment and Supplies

✓ Lead apron with thyroid collar

✓ Plastic container for prosthetic devices

✓ Tissue to remove lipstick

Procedural Steps

1 Update the medical history. Explain the x-ray procedure to the patient. Ask whether the patient has any questions.

2 Ask the patient to remove all objects from the mouth, including dentures, retainers, chewing gum, and any pierced tongue or pierced lip objects. Place any objects into a plastic container.
Purpose: Objects in the mouth can cause artifacts on the radiograph.

3 Make sure the exposure settings on the x-ray machine are correct.

4 Adjust the chair so that the patient is positioned upright. The level of the chair must be adjusted to a comfortable working height for the operator.

5 Adjust the headrest to support and position the patient’s head. The patient’s head must be positioned so that the upper arch is parallel to the floor and the midsagittal (midline) plane is perpendicular to the floor.

6 Place and secure the lead apron with the thyroid collar on the patient.

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

When exposing periapical views with the paralleling technique, always start with the anterior teeth (canines and incisors) for the following reasons:

• The size of the anterior image receptor (#1) is small and is easier for patients to tolerate.

• Patients more easily adapt to the anterior image receptor holder.

• 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.

FIG. 41-11 Anterior periapical film placement shows structures visible on the radiograph. A, Maxillary canine exposure. B, Maxillary incisor exposure. C, Mandibular canine exposure. D, Mandibular incisor exposure. (From Iannucci J, Jansen Howerton L: Dental radiography: principles and techniques, ed 4, St Louis, 2012, Saunders.)

The recommended anterior exposure sequence for the Rinn XCP instruments (Dentsply Rinn, Elgin, Illinois) is as follows:

1 Assemble the anterior XCP instrument. See Procedure 41-2.

2 Begin with the maxillary right canine (tooth #6).

3 Expose all maxillary anterior teeth from right to left.

4 End with the maxillary left canine (tooth #11).

5 Move to the mandibular arch.

6 Begin with the mandibular left canine (tooth #22).

7 Expose all mandibular anterior teeth from left to right.

8 Finish with the mandibular right canine (tooth #27).

PROCEDURE 41-2

Assembling the XCP (Extension-Cone Paralleling) Instruments

Goal

✓ To assemble the Rinn XCP instruments (Dentsply Rinn, Elgin, Illinois) for all areas of the mouth in preparation for radiographic surveys.

Equipment and Supplies

✓ Sterilized Rinn XCP instruments (film or brand-specific sensor holders)

Extension-cone paralleling (XCP) instruments for film. (Courtesy Dentsply Rinn, Elgin, IL.)

Extension-cone paralleling (XCP) instruments for digital sensors. (Courtesy Dentsply Rinn, Elgin, IL.)

Note: Depending on the manufacturer, digital sensors vary in size and thickness. Some brands are available in two or three sizes, and some are available in only one size. Sensor holders are available for each brand of digital system. Phosphor plates can be used with film-type holders.

Procedural Steps

Anterior Assembly

1 Lay out the blue parts for the anterior XCP instrument.
Purpose: Blue is the universal color for anterior film sensor-holding instruments.

2 Assemble the anterior XCP instrument by inserting the two prongs of the blue anterior indicator arm into the openings in the blue anterior bite-block.

3 Insert the anterior indicator arm into the opening on the blue anterior aiming ring.

4 For films, flex the plastic backing of the blue bite-block to open the film slot for easy insertion of the anterior film packet. For sensors, slide the sensor into position.

5 The blue anterior XCP instrument is correctly assembled when the film sensor is seen centered in the middle of the aiming ring.

Posterior Assembly

1 Lay out the yellow parts for the posterior XCP instrument.
Purpose: Yellow is the universal color for posterior film sensor-holding instruments.

2 Assemble the yellow posterior XCP instrument by inserting the two prongs of the yellow posterior indicator arm into the openings in the yellow posterior bite-block, as shown.

3 Insert the yellow posterior indicator arm into the opening on the yellow posterior aiming ring, as shown.

4 For film, flex the plastic backing of the yellow bite-block to open the film slot for easy insertion of the posterior film packet. For sensors, slide the sensor into position on the holder.

5 The posterior XCP instrument is correctly assembled when the film sensor is seen centered in the middle of the aiming ring.

No wasted movement or shifting of the position indicator device (PID) occurs when you work from right to left in the maxillary arch, and then from left to right in the mandibular arch. You may find an exposure sequence that works better for you. The most important thing is to always use the same sequence. This allows you to keep track of the last exposure if you are interrupted (Procedure 41-3).

PROCEDURE 41-3