Cephalometric radiography is a standardized and reproducible form of skull radiography used extensively in orthodontics to assess the relationships of the teeth to the jaws and the jaws to the rest of the facial skeleton. Standardization was essential for the development of cephalometry – the measurement and comparison of specific points, distances and lines within the facial skeleton, which is now an integral part of orthodontic assessment. The greatest value is probably obtained from these radiographs if they are traced or digitized and this is essential when they are being used for the monitoring of treatment progress.
When considering these indications, it should be remembered that all radiographs must be clinically justified – a legislative requirement in most countries. In the UK, indications and selection criteria for cephalometric radiographs are clearly identified in the British Orthodontic Society’s 2008 booklet Orthodontic Radiographs – Guidelines for the Use of Radiographs in Clinical Orthodontics (3rd Edition) and in the Faculty of General Dental Practice (UK)’s 2013 booklet Selection Criteria for Dental Radiography (3rd Edition). These guidelines are designed to assist in the justification process so as to avoid the use of unnecessary radiographs.
Several different types of equipment are available for cephalometric radiography, either as separate units, or as additional attachments to panoramic units. In some equipment the patients are seated, while in others they remain standing. Traditional equipment was designed to use indirect-action radiographic film in an extraoral cassette as the image receptor. The advent of digital imaging, using phosphor plates and solid-state sensors, has seen the development of new dedicated digital equipment. The basic components of these different types of equipment are described below.
This either consists of an additional attachment to a panoramic unit as shown in Fig. 14.1, or as a completely separate dedicated unit as shown in Fig. 14.2. The basic components include:
– Be in a fixed position relative to the cephalostat and film so that successive radiographs are reproducible and comparable. To minimize the effect of magnification the focus-to-film distance should be greater than 1 m and ideally in the range 1.5–1.8 m (see Fig. 14.2).
– Include a light beam diaphragm to facilitate the collimation. The beam should be collimated to an approximately triangular shape to restrict the area of the patient irradiated to the required cranial base and facial skeleton, so avoiding the skull vault and cervical spine and thyroid gland (see Fig. 14.2).
• Aluminium wedge filter designed to attenuate the X-ray beam selectively in the region of the facial soft tissues to enable the soft tissue profile to be seen on the final radiograph. This is either attached to the tubehead, covering the anterior part of the beam (the preferred position) or it is included as part of the cephalostat and positioned between the patient and the anterior part of the cassette.