Abstract
Aim: To evaluate the degree of the reliability of the S–N reference line by using highly stable reference lines (vertical and horizontal cranial axes). Materials and Methods: The sample of the study comprised of lateral cephalometric radiographs of patients 13–18 years, 12 males and 12 females for each of the three skeletal relationships. The ANB angles were 0–2, more than 2 and less than zero respectively. The method was conducted by localization of the anterior superior of anterior wall of sella turcica point (As), which is stable at age 5–6 years, drawing the Vertical Cranial Axis (VCA) which pass through the point As and tangent to the upper part of the anterior wall of the sella turcica (at least for 3 mm); then, drawing the Horizontal Cranial Axis (HCA), which is perpendicular to the VCA at the As point. The deflection and the sagittal dimension of the S–N line were measured to evaluate the variation in the location of the points S and N, which are the determinant of the S–N line. Results: Point N had significantly local variation between gender and among the three skeletal relationships, but that point S had insignificant local variation between gender and among the three skeletal relationships. Conclusion: The S–N line is not stable due to unstability of the location of point N.
