Volumetric upper airway assessment in patients with transverse maxillary deficiency after surgically assisted rapid maxillary expansion


Transverse maxillary deficiency is commonly found in patients with sleep apnea and is also related to abnormal breathing patterns. Maxillary expansion procedures promote widening of the nasal floor and reduce the resistance to airflow, and have a positive influence on nasopharynx function. In order to evaluate volume changes in the upper airway, 15 adult patients with transverse maxillary deficiency underwent surgically assisted rapid maxillary expansion (RME) until a slight overcorrection of the crossbite was obtained. Cone beam computed tomography (CBCT) volumetric images were obtained at three predefined time points. The mean age of the patients was 30.2 (±7.4) years; nine were females and six were males. The area, volume, and the smallest transverse section area of the airway were assessed using Dolphin Imaging 3D software. Statistical comparisons were made of the changes between time periods. No statistically significant differences were found for volume or area. However a significant difference was found between the preoperative and immediate postoperative smallest transverse section area ( P < 0.05). Maxillary expansion, as an isolated procedure, does not result in a statistically significant improvement in the airway dimensions and results in an inferior relocation of the smallest transverse section area.

Transverse maxillary deficiency is a pathological condition that may be associated with other types of dentoskeletal alterations, with esthetic and functional implications, including respiratory problems. The incidence is around 3–18% in orthodontic patients.

Patients with this condition have a narrow nasal cavity, which increases the resistance to nasal airway flow. Recently, the relationship between transverse maxillary deficiency and obstructive sleep apnea (OSA) has received attention in the literature. It is a common finding in sleep apnea patients, as well as being related to abnormal breathing patterns.

OSA syndrome is a condition that occurs secondary to the collapse of the upper airway. It results in mechanical obstruction of the airflow during sleep, producing hypoxia and/or tachycardia and bradycardia episodes, and increasing peripheral vasoconstriction and the risk for cardiovascular and cerebrovascular events. The obstruction can occur at the level of the nasal cavities, soft palate, tonsils, and retro-lingual area of the oral pharynx. Retrusion of the jaws is frequently associated with sleep apnea syndrome due to malpositioning of the soft tissue structures and a reduction in the volume of the upper airway.

Maxillary expansion procedures, both orthodontic (patients with growth potential) and surgically assisted (adult patients), promote widening of the nasal floor and reduce resistance to airflow, with a positive influence on the function of the nasopharynx and correction of respiratory dysfunction. To define the modality of treatment, age, skeletal maturation, severity of the deformity, and functional implications have to be considered. Well planned and performed treatment can be executed, even in adult patients, without excessive inclination or extrusion of teeth, dental or periodontal damage, or pain. The surgical treatment of adult patients can be performed through a segmented Le Fort I osteotomy or by surgically assisted expansion. The first option can correct the maxillary position in three dimensions. Surgically assisted expansion will correct the transverse dimension and is followed by orthodontic treatment and/or orthognathic surgery. It is a simpler technique than the Le Fort I osteotomy procedure, and is considered an efficient and stable method.

Several studies have shown an improvement in nasal obstruction after maxillary expansion. It improves the distance between the nasal walls and the septum, promoting widening of the nasal cavity, mainly in its anterior portion. The vertical dimension of the nasal cavity is also improved due to inferior rotation of the palate and the associated correction to the nasal septum. Although the nasal cavity alterations are variable and depend on age and the procedure, some authors have recorded improvements in nasal patency, with a decrease in respiratory problems.

Postoperative stability is very similar for surgical maxillary expansion and orthodontic expansion, if the indication is correct. Changes after maxillary expansion can be evaluated by frontal and lateral cephalometry, tomography, and photography. Is also possible to evaluate the nasal airway resistance (NAR) and the nasopharyngeal space by rhinomanometry, acoustic rhinomanometry, and nasofibroscopy.

There is a need for more studies to clarify the correlation between maxillary expansion and upper airway changes. The aim of this study was to perform a three-dimensional (3D) evaluation of the upper airway in patients submitted to surgically assisted maxillary expansion. A prospective evaluation was done of the upper airway volume of 15 patients presenting with transverse maxillary deficiency treated with surgically assisted rapid maxillary expansion (RME).

Patients and methods

This study included 15 patients with the diagnosis of transverse maxillary deficiency. Surgically assisted RME by the technique described by Kraut, with separation of the pterygoid plates, was performed in all patients. No individuals presenting with clefts or craniofacial syndromes were included in the study. All subjects received a Hyrax-type palatal expander banded to the maxillary first premolars and first molars. Activation started after 7 days. The patients were monitored 3 times weekly for appropriate activation of the appliance. The activation consisted of one quarter turn (0.25 mm) performed 3 times a day (every 8 h), resulting in 0.75 mm every 24 h, until the required expansion with a slight overcorrection of the crossbite was obtained (mean 14.4 days); the appliance was the stabilized and maintained for an additional 4 months.

Cone beam computed tomography (CBCT) volumetric images (I-Cat; Fábrica KaVo do Brasil Ind. Com. Ltda, Joinville, SC, Brazil) were obtained in the immediate preoperative period (T1), immediately after the end of maxillary expansion (T2), and at 6 months after expansion (T3) ( Figs. 1–3 ).

Fig. 1
Example of the volumetric assessment of the patient’s airway using Dolphin Imaging software in the preoperative period (T1).

Fig. 2
Example of the volumetric assessment of the patient’s airway using Dolphin Imaging software immediately after the end of expansion (T2).

Fig. 3
Example of the volumetric assessment of the patient’s airway using Dolphin Imaging software at 6 months after the end of maxillary expansion (T3).

Computed tomography (CT) images were obtained with the patients seated and in natural head position. All patients were instructed not to breathe or swallow during image capture to avoid motion artefacts. The imaging field-of-view included the region from the hard palate to the third cervical vertebra. Images were taken parallel to the intervertebral space C2–C3. All were recorded on DVD for later analysis using computer software. 3D reconstructions were obtained using Dolphin Imaging 3D software (Dolphin Imaging and Management Solutions, Chatsworth, CA, USA).

Airway volume was assessed using a specific tool of the software. The region of interest was defined with its upper limit corresponding to a plane defined from the posterior limit of the hard palate and parallel to the Frankfort horizontal plane, and the inferior limit corresponding to a plane built from the most anterior and inferior point of the second cervical vertebra and also parallel to the Frankfort plane.

The volumetric analysis of the determined 3D area was done by the software using a grey-scale. The darkest zone on the image indicates the airway and the volume is given in cubic millimetres. Thus, it was possible to assess the total volume of the airway and the diameter of the region of the smallest transverse section or zone.

The airway was then measured: (1) the area (mm 2 ), using the predefined superior and inferior limits and a two-dimensional tool of the software, (2) the volume (mm 3 ), and (3) the smallest transverse section area (mm 2 ). The measurements were submitted to descriptive statistical analysis, and statistical comparisons of changes were made between periods using GraphPad statistical software package (GraphPad Software Inc., La Jolla, CA, USA).


The sample comprised adults of both genders; nine were female and six were male, and their mean age was 30.2 ± 7.4 years. The average period of activation of the appliance was 14.4 ± 1.8 days. The average expansion in the inter-molar region immediately at the end of the activation was 6.93 ± 3.43 mm.

Data were considered parametric and the Tukey test showed no significant statistical differences between the volumes and areas evaluated in the previously defined periods ( Table 1 ). Variations in the area, volume, and smallest transverse section area in relation to the different time periods are shown in Figs. 4–6 , respectively.

Table 1
Area and volume measurements obtained preoperatively and after maxillary expansion. Results are given as the mean ± standard deviation value, with the 95% confidence interval in parenthesis.
Immediately preoperative After maxillary expansion After 6 months
Area (mm 2 ) 601.6 ± 93.9 (549.6–653.6) 646.1 ± 165.3 (554.5–737.6) 646.9 ± 98.45 (592.4–701.4)
Volume (mm 3 ) 13,060 ± 3697 (11,012–15,107) 15,212 ± 5721 (12,044–18,380) 13,949 ± 4319 (11,557–16,341)
Smallest transverse section area (mm 2 ) 138.8 ± 58.2 (106.5–171.0) 181.7 ± 92.8 (130.3–233.1) 173.5 ± 88.0 (124.7–222.2)
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Jan 19, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Volumetric upper airway assessment in patients with transverse maxillary deficiency after surgically assisted rapid maxillary expansion
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