The applicability of the occipital reference base in cephalometrics.

An occipital reference system, located outside the anterior half of the skull, has been designed which reveals sagittal as well as vertical relationships among facial components. The anatomic structures chosen had consistent behavior during growth, were located close to the midsagittal plane, and could be identified in a lateral cephalograph. Among the basal structures of the neurocranium, the occipital bone around the foramen magnum is the first to ossify. This appears to be indispensably necessary as the head is supported by the trunk precisely in the area of this individual bone. The ventrocaudal contour of the basal part of the occipital bone, anterior to the foramen magnum, and the internal occipital (sagittal) ridge, posterior to the foramen magnum, form the reference base. The intersection of the ventrocaudal contour and the anterior outlines of the occipital condyles serve as the key reference point (occipital point O') for constructing the occipital coordinate system whose horizontal axis is oriented to the earth's surface. This orientation is accomplished by a special photographic registration of the natural head position. The coordinate system has its center at the O' point and its abscissa thus adjusted to the horizontal. The use of a template permits the transfer of the occipital reference cross from the first to subsequent radiographs in the same relation to the occipital reference line as first registered. By the aid of a digitizer or a transparent graph paper with millimeter and centimeter squares on which the coordinate cross is marked, all measurements can be made on the radiograph directly as the reference points O' and O'' are marked on the radiograph itself, thus defining the position of the horizontal coordinate. In the past 50 years, a considerable amount has been learned about the function-form relationship in skeletal morphogenesis. It has been recognized that a faulty or poor postural behavior must be regarded as a major contributory factor to the maldevelopment in skeletal morphology and is taken into consideration in this reference system.