7: Periapical radiography

Periapical radiography

Periapical radiography describes intraoral techniques designed to show individual teeth and the tissues around the apices. Each film usually shows two to four teeth and provides detailed information about the teeth and the surrounding alveolar bone.

Ideal positioning requirements

The ideal requirements for the position of the image receptor and the X-ray beam, relative to a tooth, are shown in Fig. 7.1. They include:

Radiographic techniques

The anatomy of the oral cavity does not always allow all these ideal positioning requirements to be satisfied. In an attempt to overcome the problems, two techniques for periapical radiography have been developed:

Paralleling technique

Theory

This positioning has the potential to satisfy four of the five ideal requirements mentioned earlier. However, the anatomy of the palate and the shape of the arches mean that the tooth and the image receptor cannot be both parallel and in contact. As shown in Fig. 7.2, the image receptor has to be positioned some distance from the tooth.

To prevent the magnification of the image that this separation would cause, a parallel, non-diverging, X-ray beam is required (see Fig. 7.3). As explained in Chapter 3, this is achieved usually by having a long focal spot to skin distance (fsd), ideally of 200 mm.

Film packet/sensor holders

A variety of holders has been developed for this technique. The choice of holder is a matter of personal preference and dependent on the type of image receptor – film packet or digital sensor (solid-state or phosphor plate) – being used. The different holders vary in cost and design, as shown in Fig. 7.4 but essentially consist of three basic components:

The different components of the various holders usually need to be assembled together before the holder can be used clinically. The holder design used depends upon whether the tooth under investigation is:

These variables mean that assembling the holder can be confusing, but it must be done correctly. To facilitate this assembly some manufacturers now colour-code the various components. Once assembled correctly the entire image receptor should be visible when viewed through the beam-aiming device, as shown in Fig. 7.5. A selection of different holders is shown in Fig. 7.6.

Typically, the same anterior holder can be used for right and left maxillary and mandibular incisors and canines utilizing a small image receptor (22 × 35 mm) with its long axis vertical. Four images in the maxilla and three images in the mandible are usually required to cover the right and left incisors and canines, as shown in Fig. 7.7.

Typically different holders are required for the right and left premolar and molar maxillary and mandibular posterior teeth. The different designs allow the holders to hook around the cheek and corner of the mouth. A large image receptor (31 × 41 mm) is ideally utilized with its long axis horizontal. Two images are usually required to cover the premolar and molar teeth in each quadrant, as shown is Fig. 7.8.

Positioning techniques

The radiographic techniques for the permanent dentition can be summarized as follows:

1. The patient is positioned with the head supported and with the occlusal plane horizontal.

2. The holder and image receptor are placed in the mouth as follows:

3. The holder is rotated so that the teeth under investigation are touching the bite block.

4. A cottonwool roll is placed on the reverse side of the bite block. This often helps to keep the tooth and image receptor parallel and may make the holder less uncomfortable.

5. The patient is requested to bite gently together, to stabilize the holder in position.

6. The locator ring is moved down the indicator rod until it is just in contact with the patient’s face. This ensures the correct focal spot to film distance (fsd).

7. The spacer cone is aligned with the locator ring. This automatically sets the vertical and horizontal angles and centres the X-ray beam on the image receptor.

8. The exposure is made.

Positioning clinically using film packets and digital phosphor plates is shown in Figs 7.97.16 for the following different areas of the mouth:

Note:

Jan 12, 2015 | Posted by in Oral and Maxillofacial Radiology | Comments Off on 7: Periapical radiography
Premium Wordpress Themes by UFO Themes