Radiographs come after the clinical examination, never instead of it. They answer questions the examination has raised.
The panoramic view
A panoramic radiograph is usually indicated before treatment, to check the presence and position of unerupted teeth and root length and morphology. Know its limits:
- Lack of sharpness: ghost images, summation images, static distortion and processing errors.
- Horizontal distortion, which tends to be non-linear.
- Vertical distortion, believed to be twice as severe as horizontal distortion.
- Superimposition of the cervical spine.
- A limited focal trough: lingually placed roots outside it are magnified, and steeply inclined teeth look narrow or foreshortened. The anterior region may therefore be unrepresentative, and poor positioning in the machine makes this worse.
Intra-oral views (periapicals, upper occlusal) give more detail, especially in the maxillary anterior region (Witcher et al., 2010), and the parallax technique locates unerupted teeth.
The cephalometric radiograph
A cephalometric radiograph is taken in a cephalostat, which holds the head at a fixed distance from the X-ray tube and the film. Magnification is therefore constant for a given machine, so films of the same patient taken at different times, or of different patients, can be compared directly. The lateral view is the standard; a postero-anterior view is occasionally taken for facial asymmetry or to locate impacted teeth.
A cephalometric analysis gives numerical information on:
- the skeletal base relationship;
- the position of the dentition within the face;
- the soft-tissue profile.
It helps explain the aetiology of a malocclusion, supports diagnosis and planning, and gives a measurable baseline to follow treatment and growth by superimposing serial films.
When to take one
Not routinely. A lateral cephalogram is justified when treatment will involve:
- significant anterior or posterior movement of the incisors;
- correction of a skeletal discrepancy by growth modification or orthognathic surgery;
- monitoring, or possible early treatment, of a young patient with a marked skeletal discrepancy.
Main source: Cobourne MT, Fleming PS, DiBiase AT, Ahmad S. Clinical Cases in Orthodontics. Wiley-Blackwell, 2012, chapter 1.