Effects of fixed appliances in correcting Angle Class II on the depth of the posterior airway space: FMA vs. Herbst appliance--a retrospective cephalometric study.

OBJECTIVE

The objective of this retrospective study based on the metric evaluation of lateral cephalograms was to investigate the extent to which treatment with two different fixed appliances for the correction of Angle Class II influenced the morphology of the extrathoracic airway space (the posterior airway space, PAS).

PATIENTS AND

METHODS

A total of 43 patients with Angle Class II malocclusion were classified into two groups according to the appliance used for treatment: the functional mandibular advancer (FMA; n = 18) or the Herbst appliance (n = 25). Lateral cephalograms were taken of each patient at the start of functional jaw orthopedic treatment (time point T1) and at its completion (time point T2). Specific distances and angles were measured and analyzed in a cephalometric analysis.

RESULTS

We observed major differences among the 43 patients in the depth of the posterior airway space during treatment with fixed appliances for Angle Class II correction. Regression analysis revealed that changes in sagittal and vertical positions had different effects on the depth of specific PAS sections: increases in anterior facial height are associated proportionately with increases in PAS width, particularly in the upper region. On the other hand, increases in posterior facial height and in the mandible's forward displacement correlated inversely to the decreases in depth, particularly in the central and lower PAS regions. The two treatment appliances (FMA, Herbst appliance) had the same effects on extrathoracic airway depth.

CONCLUSIONS

Analyses of lateral cephalograms indicate that Angle Class II treatment with fixed appliances does not prevent sleep apnea in patients at risk. Nevertheless, this study does not permit absolutely reliable conclusions about the dimensions of the pharyngeal airway space. As the lateral cephalogram provides good images of structures in the midsagittal plane but is incapable of imaging the transverse dimension, there is an automatic lack of information concerning the precise width and volume of the extrathoracic airway space.