Mouth opening: a new angle.

BACKGROUND The authors hypothesized that craniocervical extension occurs during normal mouth opening. METHODS Twenty volunteers were studied. Interdental distance was measured at four different degrees of craniocervical extension. RESULTS Interdental distance increased from 28 mm (95% confidence interval, 25-30) in slight flexion to 46 mm (95% confidence interval, 42-49) at full extension. Nearly maximal mouth opening was obtained with 26 degrees (95% confidence interval, 22-30) of craniocervical extension from neutral. CONCLUSION Craniocervical extension is an integral part of complete mouth opening in conscious subjects. Fixation of the craniocervical junction by disease, an internal or external fixation device, or technique may restrict mouth opening, with consequences for airway management.