A radiograph of the head taken in a Cephalometer (Cephalostat) that is a head-holding device introduced in 1931 by B. H. Broadbent in the USA and by H. Hofrath in Germany. The original design included two ear rods for insertion into the external auditory canals, an infraorbital pointer and a forehead clamp, to achieve parallelism of the Frankfort plane with the floor. The cephalometer is used to obtain standardized and comparable craniofacial images on radiographic film.
Lateral Cephalometric Radiograph
A radiograph of the head taken with the x-ray beam perpendicular to the patient’s sagittal plane. The beam most commonly enters on the patient’s right side, with the film cassette adjacent to the patient’s left side (so that the patient’s head is oriented to the right on the radiograph), but the reverse convention also is used.
Natural head position is a standardized orientation of the head that is reproducible for each individual and is used as a means of standardization during analysis of dentofacial morphology both for photos and radiographs. The concept of natural head position was introduced by C. F. A. Moorrees and M. R Kean in 1958 and now is a common method of head orientation for cephalometric radiography.
To accomplish natural head position, the patient is asked to look into a mirror placed in front of him/her at eye level (as if he/she were looking at the horizon), with the interpupillary line parallel to the floor. Advocates of this method maintain that registration of the head in its natural position while obtaining a cephalogram has the advantage that an extracranial line (the true vertical or a line perpendicular to that) can be used as a reference line for cephalometric analysis, thus bypassing the difficulties imposed by the biologic variation of intracranial reference lines. True vertical is an external reference line, commonly provided by the image of a free-hanging metal chain on the cephalostat registering on the film or digital cassette during exposure. The true vertical line offers the advantage of no variation (since it is generated by gravity) and is used with radiographs obtained in natural head position.
Posteroanterior (P-A) cephalometric radiograph
A radiograph of the head taken with the x-ray beam perpendicular to the patient’s coronal plane with the x-ray source behind the head and the film cassette in front of the patient’s face. P-A cephalograms are usually taken for evaluation and treatment planning of patients with facial asymmetry.