Figure 3.

Lateral neck radiograph during conventional direct laryngoscopy (informed and written patient consent were obtained). The angle of head extension is defined as 90°–â².â¹, angle between AH and horizontal plane; â², angle between occlusal surface of maxillary molarsand horizontal plane; â³, angle of laryngoscope blade levering motion; AH, axis of handle; CH, chord corresponding to the radian formed by the proximal third of the laryngoscope blade convex surface; E, distal end point of said radian; OS, axis of occlusal surface of maxillary molars or gums.