Determination of the distance between the laryngoscope blade and the upper incisors during direct laryngoscopy: comparisons of a curved, an angulated straight, and two straight blades.

We compared visibility and dental complications from a variety of blades during tracheal intubation. Ninety-eight patients who received tracheal intubation were enrolled. They were divided into two groups: Study 1 (n = 50) and Study 2 (n = 48). Four laryngoscopic evaluations were planned for each patient using Miller and Wisconsin straight blades with different heel heights, a Macintosh curved blade, and a Belscope angulated straight blade (Study 1: Miller No. 3, Wisconsin No. 3, Macintosh No. 4, and Belscope medium; and Study 2: Miller No. 2, Wisconsin No. 2, Macintosh No. 3, and Belscope medium, respectively). All laryngoscopies were performed by the same anesthesiologist. The distance between the blade and the upper central incisors was measured when the optimum visibility of the glottis was obtained. The visibility was determined according to the Cormack and Lehane grading. Analysis of the distance between the blade and upper incisors was performed using the results of the 44 patients (166 distances) in Study 1 and the 48 patients (181 distances) in Study 2 who had a visibility of two or better. The Belscope blade provided a significantly greater visual field than the other types of blade. Two patients sustained a fracture of the central incisor and subluxation of the central incisor, respectively, during laryngoscopy in which a Wisconsin blade was used. The average incidence of dental injury was 1/191. The Belscope blade may contribute to a reduced likelihood of upper dental injuries during laryngoscopy.