3.1 Lateral cephalometric analysis for prediction planning

The cephalometric analysis of the lateral facial skull is the next necessary step in the surgical planning of dentofacial malformations in order to measure the existing individual skeletal structures and to determine the location and extent of skeletal deviations from the norm. Once clinical correction planning has taken place (see Chapter 2), it serves the surgeon as a basis for the surgical simulation to determine precise displacement distances of the jaws and teeth.

3.1.1 Basis

The basis of the preoperative cephalometric analysis is the Bergen technique of Hasund.¹ This was originally developed from a purely orthodontic point of view. It has been modified for surgical purposes:

• The occlusal plane (OP) is adapted to the surgical planning requirements: the Occl line connects the incisor tips of the maxillary anterior teeth with the buccal cusps of the maxillary first molars. This radiographically defined incisor tip, called “is” = incision superius according to Hasund,¹ is also used as an imaginary point in the subsequent model surgery. “is” indicates the maxillary center between the two maxillary incisor tips (Fig 3-1) and differs from the orthodontic definition of the dentoalveolar maxillary center, which is defined by the approximal contact of both maxillary central incisors, which lies approximately 2 mm below the incisor tips.

• The definition of Occl results in a modified Wits-value measurement, which is performed on the Occl line and not on a differently defined occlusal plane.

• In cases with facial asymmetries and double contours of the dental arches and the mandibular margin, averaging of the double contours can be performed. However, depending on the initial situation, it is also possible to partially or completely follow the more normative contours individually depending on the transverse deficit or elongation.

• The maxillary anterior inclination angle according to Hasund,¹ measured between the cranially extended connecting line through the points Is and Isa to the nasal line (NL), is not relevant for surgical concerns and is measured with the sella-nasion line (SN) due to the surgical displacement possibilities of the maxilla (Fig 3-1). In the mandible, the measurement of the angle of inclination between the caudally extended line through points ii and iia to the mandibular line (ML) is performed as described by Hasund.¹

• The determination of the anterior and posterior facial heights appears reasonable under the aspect of a simultaneous rotation of the maxilla and mandible in the context of maxillomandibular intervention possibilities. The proportion of the distances (62% to 65%) to each other characterizes a neutral growth pattern. CCWR increases the posterior facial height, increases the distance ratio, and leads to a vertical skull structure. CWR increases the anterior facial height, reduces the facial height ratio, and results in a horizontal skull buildup (Fig 3-2).

• In order to obtain a cephalometric basis for surgical planning in the anterior vertical plane of the facial skull, measured values for the anterior height of the maxilla and mandible are integrated. For this purpose, the vertical line from the horizontal reference lines NL and ML to the incisor tips of the maxillary (is) and mandibular incisors (ii) is cut (Fig 3-2). These measurements have proved particularly useful in the correction of short and long faces.

• The standard or guideline values given in this modified cephalometric analysis with their deviations result from comparative values obtained from an extensive patient collective of the last 20 years and are also based on the harmony box of Hasund¹ and the explanations of Nötzel et al² and Jacobson and Jacobson.³ These standard or guideline values are, of course, only indicative and can be modified individually as required (Table 3-1).

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