The maxilla-related parameters are used to evaluate the position and orientation of the maxilla. Each of these parameters has its limitations. The variation in the SN and FH planes affects the values of SNA and Pt A to N perpendicular and maxillary depth, respectively. However, the SN plane variation is small compared to the FH plane. The error in landmark plotting of ANS point may cause variation in maxillary length.

The Point A landmark is often challenging to identify precisely in cephalograms. Jacobson et al. proposed a method of constructing point A, which resembles true point ‘A’ where there is difficulty in locating this point. They suggested that a point plotted 3.0 mm labial to a point between the upper third and lower two-thirds of the long axis of the root of the maxillary central incisor as an alternative.

Measuring the position and size of the mandible is an important aspect of cephalometric analysis. The two commonly used reference planes are the SN and FH planes. The variation in these reference structures will result in variation in the mandibular parameters.

Geometrically, the mandible is away from these cranial reference planes compared to the maxilla, so the variation in the mandibular parameters will be greater. Suppose the parameters defining the same anatomical entity give contradictory values. In that case, they must be checked for the variation of reference structures and corrected accordingly or given due consideration during interpretation.

The sagittal maxillomandibular relation is of utmost concern in orthodontics. Various parameters defining the intermaxillary relationship have been introduced over time. Sometimes, most of the reference structures used for these measurements are at fault; since then, various reference planes, both anatomical and constructed planes and analyses, have been introduced over time by different authors. These analyses have advantages and limitations, which must be understood thoroughly to use these parameters in a clinical situation ( Fig. 29.1 ).

Cephalometric parameters showing maxillomandibular relation.

(A) 1. AXD angle, 2. Yen angle, 3. MM bisector, 4. AF-BF distance; (B) 5. AXB angle, 6. APP-BPP distance, 7. Beta angle; (C) 8. Pi-angle, 9. Pi-linear, 10. W angle, 11. FH to AB plane angle (FABA); (D) I + II + III = APDI.

The most used anteroposterior indicator is the ANB angle. The variation in certain landmarks and lines affects the ANB angle. These are:

• 1.

  Position of nasion either anteroposterior or superoinferior

• 2.

  Inclination of SN plane

• 3.

  Inclination of jaws

• 4.

  Degree of facial prognathism

To overcome the shortcomings of the ANB angle, various new measurements have been introduced. A few of the commonly used alternatives for ANB angle are AO-BO discrepancy in mm (WITS appraisal), maxillomandibular plane angle bisector (MM bisector) and perpendicular projection of points A and B to the palatal plane (APP-BPP) and Frankfurt horizontal plane (AF-BF mm). The common pattern between these parameters is that they use point A and Point B perpendicular projection on the reference planes and measure the distances between them. Only the reference planes used are different between these measurements.

Foley et al. and Palleck et al. showed that the MM bisector is more reliable than functional or bisected occlusal plane measurements, especially for longitudinal measurements. Similarly, Oktay et al. compared ANB, WITS, AF-BF and anteroposterior dysplasia indicator (APDI) measurements and reported that these sagittal parameters could be used interchangeably for sagittal jaw discrepancy assessment.

Santo suggested that one should be careful while using ANB and WITS to assess the sagittal relationship of the jaws, especially in cases with high occlusal plane angle. Ishikawa et al. studied seven sagittal parameters to compare the prediction accuracy of post-pubertal jaw relationships and to evaluate inter-changeability among the seven parameters. They showed that the ANB angle and the angle of convexity showed better prediction accuracy for post-pubertal jaw relationships. Also, they recommended the conjunctive use of the ANB angle, the WITS appraisal and the APDI for the assessment of anteroposterior jaw relationships ( Table 29.3 ).

Face heights significantly contribute to the perception of facial attractiveness. Vertical proportions of the face are also significant determining factors for diagnosis and planning appropriate orthodontic treatment. The typical angular parameters are angle FMA, SN-GoGn, Y-axis and facial axis, and linear parameters are upper anterior face height (UAFH), lower anterior face height (LAFH), total anterior face height (TAFH) and total posterior face height (TPFH), Jarabak’s ratio. As we have discussed earlier, the reference plane variation may lead to the misinterpretation of the cephalometric parameter. Most of the angular parameters are based on the FH, SN and Ba-Na reference planes. The variation of the FH and SN planes was discussed earlier. Similarly, the Ba-Na plane used for the facial axis also shows variation since the Basion is not readily traceable ( Table 29.4 ).

Paranhos et al. showed that the Y-axis is inadequate to determine the vertical facial skeletal pattern of the patients with significant sagittal discrepancy due to the forward and backward position of the Gn point. Ahmed et al. evaluated the vertical parameter for assessing borderline cases. They found SN-GoGn and FMA to be the most reliable indicators, and facial height ratio (LAFH-TAFH) was the least reliable indicator for the assessment of vertical growth patterns. Paranhos et al. showed that the Sn-GoGn is the best parameter to define the facial type.