RESUMO
PURPOSE: Radiographic analysis is often used as a screening tool to assess for risk of sleep-related breathing disorders. This study aimed to address 2 questions: (1) Does head posture significantly affect the minimum cross-sectional area (MCA)? and (2) Is the NBC3 (nasion-basion-C3) angle a reliable measurement to control for alteration of head position in cone-beam computed tomography (CBCT) scans? METHODS: Study design: prospective cohort study. SETTING: Private practices affiliated with a research institution. PARTICIPANTS: convenience sample of adult volunteers. VARIABLES: CBCT scans were taken in 2 conditions: baseline (natural head position, NHP) and 1 of 5 experimental conditions (head tilted up, head tilted down, sitting vs standing, use of chin-rest, and swallow variation). For the primary aim of our study, the primary predictor variable was head posture and the main outcome variable was percentage change in MCA. For the secondary aim, the primary predictor variable was head posture and the main outcome variable was degree change in NBC3 angle. RESULTS: Ninety subjects were included (age 40.7 ± 13.7 years, 70% female). Mean NBC3 at baseline was 112.4 ± 8.3°. Head tilted down significantly decreased (-41.4 ± 18.5 mm2, P = .03∗) and head tilted up significantly increased MCA (+147.4 ± 43.3 mm2, P = .0018∗). Head tilted down significantly reduced the NBC3 angle measurement (-10.5 ± 6.8°, P = .006) and head tilted up significantly increased the NBC3 angle measurement (+14.4 ± 5.8°, P = .0004). A quadratic regression model was fitted with moderately strong correlation (R2 = 0.54) showing an exponential effect of small changes in the NBC3 angle on MCA, P < .0001. The model predicts that increasing NBC3 by +5 and + 10° resulted in MCA changes of +25% and +88%, whereas a decrease in NBC3 by -5 and -10° results in MCA changes of -21% and -23%, respectively. CONCLUSION: Alterations in head posture significantly affect the MCA of the upper airway on CBCT. The NBC3 angle can be used to reliably assess changes in cranio-cervical extension and validate comparisons of MCA between CBCT scans for the same patient. A standardized protocol for CBCT acquisition is proposed.
