Method: Were selected 30 tomographic images of 15 individuals (initial age of 15.7 years ± 1.7). The CBCT images were taken before (T1) and after (T2) eigth months of treatment with Herbst appliance, and using Dolphin 3D software. Patients meet the following inclusion criteria (1.-Class II Division 1 malocclusion, mandibular retrusion associated. 2.- permanent dentition with the exception of third molars. 3 .- No severe crowding. 4 .- Absence of cross problems. 5 .- Overjet greater than 5 mm and less than 7 mm. 6 .- Period pubertal after growth spurt, analyzed with hand-wrist radiographs). We measured the maximum area in transverse sections in the N and O. These areas were measured by two investigators (S and K). Statistical analysis was performed in two steps, first, to confirm the reliability of data (measurement error), where we applied the coefficient of intraclass correlation (ICC). Second step, we analyzed the effect of the Herbst appliance for which we applied the Student t test at the significance level of 5%.
Result: The ICC showed good reliability for both observers, S (ICC ≥ 0.993) and K (ICC ≥ 0.992). It was found statistically significant difference in largest cross section of N (p = 0.009).
Conclusion: The Herbst appliance increases in the largest cross section the nasopharynx, and the changes induced by this appliance cam be evaluate and measured with the CBCT.