Table 1. Craniocervical Position, Mean Craniocervical Angle, and Mean IDD

The interdental distances (IDDs) are all significantly different from one another (*P* = 0.0004, *P* < 0.0001, *P* = 0.0028 for flexion *vs.* neutral, neutral *vs.* extension allowed, extension allowed *vs.* full extension, respectively). The craniocervical angles (CCAs) in the four positions were all significantly different from one another (*P* < 0.0001). Comparisons were made using the paired *t* test.

CI = confidence interval.