Damage to teeth has long been associated with endotracheal intubation. But, no rules designed to predict dental injuries have been formulated. In this prospective study, we undertook to identify relationships between anatomic airway measurements used customarily in bedside practice, and blade-tooth distance during laryngoscopy, to assess the usefulness of these anatomic measurements as predictors of dental injury.

Four hundred and eighty-three patients scheduled for elective surgery requiring general anesthesia with endotracheal tube placement were included. During a preoperative visit, a number of measurements and assessments of features that might predict difficult intubation were performed. When optimum visibility of the glottis was obtained during laryngoscopy, the distance between the flange of the blade and the upper incisor was measured. We determined which of the individual airway characteristics correlated with the blade-tooth distance and best predicted the potential of dental injury.

The blade-tooth distance was found to correlate with the individual scales of the Mallampati classification (Spearman's correlation coefficient, r = - 0.356, P < 0.01), mandibular protrusion (r = - 0.390, P < 0.01), head and neck movement (r = - 0.276, P < 0.01), interincisor gap (r = - 0.648, P < 0.01), and the condition of the upper teeth (r = - 0.313, P < 0.01). The frequency of direct blade-tooth contact significantly increased as the scales of these five anatomic measurements increased (P < 0.01).

This study shows for the first time that some airway measurements are correlated with blade-tooth distance, and that they can be considered as useful predictors of dental injury during laryngoscopy.