Cephalometric measurement of the head
The proportions of the face and head can be measured cephalometrically. Cephalometry is the science of measuring the skull. Cephalometric points and reference lines are used in profile analysis during orthodontic examination. This facilitates analysis of the maxillofacial relationship and determination of the position of the teeth in the jaws and the relationship of the dental arches.
Starting from a reference point or line, the position of other parts of the skull, in this case the teeth, dental arches, mandible, and lips, can be described on the basis of average measurements and values. A selection of cephalometric points and reference lines used in dental technology are described below and illustrated in Figs 1-9 and 1-10.
- The Camper plane (CP; tragus-subnasale plane; nasoauricular plane) runs from the superior margin of the external opening of the ear (tragus point; tragion) to the subnasal point (subnasale) (see Fig 1-9a). The occlusal plane runs roughly parallel to this, about 2 cm below and passing through the closed lips. CP lies at an angle of 15 to 20 degrees to the auriculo-infraorbital plane (AIP). The Camper facial angle represents the angular relationship between CP and a line starting from glabella and passing through sub-nasale. The angle is usually between 80 and 90 degrees. Steep vertical lines (eg, the line from glabella to subnasale) pass through prosthion as well as nasion
- Frankfort horizontal plane (FH) is a cephalometric plane established in 1884. It can easily be constructed on the bony skull by drawing a line through the cephalometric points of tragion (uppermost point on the superior edge of the auditory canal) and the orbital point (orbitale; lowest point of the infraorbital margin) (see Fig 1-9b). With the head positioned normally (in natural head position) and the eyes looking straight ahead, it lies horizontally
- Glabella vertical is a vertical line drawn from the glabella to the AIP; it was formerly used for profile analysis but has now been superseded by the nasion vertical.
- Nasion vertical (nasal vertical) also runs vertical to the AIP It starts from the root of the nose (nasion) and touches the upper lip (see Fig 1-9b). It can be used to assess the profile.
- The auriculo-infraorbital plane (AIP) is a plane of orientation that runs through the highest points of the superior margins of the two external bony openings of the ears (ear points, poria; soft tissue porion) and the lowest point at the inferior margin of the orbit (orbitale) (see Fig 1-9b). The AIP is not identical to the FH, differing from it by about 2 degrees.
- Orbital vertical is a vertical line perpendicular to the AIP, starting from the soft tissue orbital point, running via the apices of the incisors, and meeting the bony tip of the chin (gnathion) (see Fig 1-9a). This relationship can be seen on the skull within the normal range of variation.