Relation of the SNA angle to the NSAr angle in excellent occlusion and in malocclusion.

The correlation between the NSAr and the SNA angles was studied in two separate samples. The first sample consisted of twenty young adults with excellent Class I (Angle) occlusion and proportionate facial skeleton, and the second sample consisted of sixty-one children with Class II, Division 1 (Angle) malocclusion. In the excellent-occlusion group, the correlation between the angles was remarkably higher (-0.94) than it was in the malocclusion group (-0.57). In both groups, in only a small number of cases were the extents of the angles close to the intersection of the calculated mean values. In orthodontic diagnosis, treating the values of the NSAr and the SNA angles separately can be extremely misleading, just as the use of the sella-nasion plane as a sole reference plane can lead to diagnostic errors. Thus, the SNA angle should be used with special caution, and a differing reference plane such as, for example, the Frankfort plane, should be preferred.