Introduction

Oblique lateral radiographs are extraoral views of the jaws that can be taken using a dental X-ray set (see Fig. 12.1). Before the development of panoramic equipment they were the routine extraoral radiographs used both in hospitals and in general practice. In recent years, their popularity has waned, but the limitations of panoramic radiographs (see Ch. 15) have ensured that oblique lateral radiographs still have an important role.

Terminology

Lateral radiographs of the head and jaws are divided into:

The differentiating adjectives true and oblique are used to indicate the relationship of the image receptor, patient and X-ray beam, as shown in Fig. 12.2.

Main indications

The main clinical indications for oblique lateral radiographs include:

Equipment required

This includes (see Fig. 12.3):

Specially constructed angle boards, as shown in Fig. 12.3B, can be used to facilitate positioning, but are not considered necessary by the authors.

Basic technique principles

As stated, a wide range of different oblique lateral projections of the jaws are possible. However, all the variations rely on the same basic principles regarding the position of:

Cassette position

The cassette is held by the patient against the side of the face overlying the area of the jaws under investigation. The exact position of the cassette is determined by the area of interest.

Patient’s head position

The patient is normally seated upright in the dental chair and is then instructed to:

1. Rotate the head to the side of interest. This is done to bring the contralateral ramus forwards, avoiding its superimposition and to increase the space available between the neck and shoulder in which to position the X-ray set.

2. Raise the chin. This is done to increase the triangular space between the back of the ramus and the cervical spine (the so-called radiographic keyhole, see Fig. 12.4) through which the X-ray beam will pass.

X-ray tubehead position

The X-ray tubehead is positioned on the opposite side of the patient’s head to the cassette. There are two basic positions, depending on the area of the jaws under investigation:

• Behind the ramus aiming through the radiographic keyhole. The X-ray tubehead is positioned along the line of the occlusal plane, just below the ear, behind the ramus aiming through the radiographic keyhole at the particular maxillary and mandibular teeth under investigation. The view from this position is illustrated in Fig. 12.4A. As shown, the X-ray beam will not pass directly between the contact areas of the posterior teeth. This may result in some overlapping of the crowns.

• Beneath the lower border of the mandible. The X-ray tubehead is positioned beneath the lower border of the contralateral body of the mandible, directly opposite the particular mandibular teeth under investigation, aiming slightly upwards. The view from this position is illustrated in Fig. 12.4B. As shown, the X-ray beam will now pass between the contact areas of the teeth. However, there will still be some distortion of the image in the vertical plane owing to the upward angulation of the X-ray beam. In addition, the shadow of the body of the mandible will be superimposed over the maxillary teeth.

Once these principles are understood, the technique becomes straightforward and can be modified readily for different anatomical regions and clinical situations.

Positioning examples for various oblique lateral radiographs

Examples of the required positioning for different oblique laterals and the resultant radiographs are shown in Figs 12.5–12.8. Illustrations show the positioning for both adults and children.

Bimolar technique

As mentioned earlier, bimolar is the term used for the radiographic projection showing oblique lateral views of the right and left sides of the jaws on the different halves of the same radiograph as shown in Fig. 12.9.

The technique can be summarized as follows: