Chapter 6 Drawing the Extrafacial PLV Vertical Line

Various methods are used to diagnose dental anomalies including head teleradiography. Intracranial parameters are used: angular, linear, and index parameters. N-Se is used as the reference line which is used in many tests. However, intracranial parameters are unstable, and it is difficult to use them as a guide to identifying certain anomalies. In addition, it is difficult to compare cranial and facial parameters. Therefore, Arnett (Arnett G.W., 1993) suggested using the extrafacial reference point and the soft tissue sn point, relative to which a vertical line is drawn, and relative to this line, deviations from the norm in case of dentofacial anomalies are determined. In our opinion, the selected point is unstable, and it changes its position in the presence of anomalies such as upper prog-nathism, upper retrognathism. That is why in 1990 we suggested using an extrafacial parameter where Po-N is taken as a reference line, and from point N a perpendicular is drawn down and an extrafacial PLV line is drawn, in relation to which certain deviations from the norm are determined.

A Po-N line is drawn to build a vertical reference line. A perpendicular is drawn from point N to this line - PL line (Fig. 6.1).

Fig. 6.1. Po-N reference line. Building a perpendicular from point N - the line PL

The Po-Or line is drawn and the point (PL1) is drawn at the intersection with the PL line (Fig. 6.2).

Fig. 6.2. Setting the PL1 point at the intersection of the Po-Or line and PL

A perpendicular is then drawn from point PL1 to the line Po-Or (Fig. 6.3)

Fig. 6.3. Drawing the vertical extrafacial PLV line

In relation to PLV, the direction of the occlusal line is assessed by the angle OcP-PLV and the angle LP, and measurements are taken from points A, B, and Pg and anthro-pometric points on the incisors, canines, and molars to the vertical line PLV (Fig. 6.4).