Cephalometric and three-dimensional assessment of superior posterior airway space after maxillomandibular advancement

Abstract

The purpose of this study was to quantify cephalometric and three-dimensional alterations of the posterior airway space of patients who underwent maxillomandibular advancement surgery. 20 patients treated by maxillomandibular advancement were selected. The minimal postoperative period was 6 months. The treated patients underwent cone-beam computed tomography at 3 distinct time intervals, preoperative (T1), immediate postoperative period up to 15 days after surgery (T2), and late postoperative period at least 6 months after surgery. The results showed that the maxillomandibular advancement promoted an increase in the posterior airway space in each patient in all the analyses performed, with a statistically significant difference between T2 and T1, and between T3 and T1, p < 0.05. There was a statistical difference between T2 and T3 in the analysis of area and volume, which means that the airway space became narrower after 6 months compared with the immediate postoperative period. The maxillomandibular advancement procedure allowed great linear area and volume increase in posterior airway space in the immediate and late postoperative periods, but there was partial loss of the increased space after 6 months. The linear analysis of airway space has limited results when compared with analysis of area and volume.

Orthognathic surgery has made treatment of dentoskeletal deformities increasingly more precise, particularly over the last 30 years. Its main objective is to re-establish the patient’s facial harmony and ideal occlusion. Advancements in orthodontic techniques have enabled the surgical repositioning of the maxilla, mandible, dentoalveolar and chin segments, alone or in combinations.

Several bone structures and soft tissues such as the soft palate, uvula, palatoglossal arch, the base of tongue and all the suprahyoid muscles, hyoid bone and epiglottis may be directly or indirectly moved using this technique. Anatomically, these structures are closely related to the superior posterior airway space and their movements lead to alterations in this region.

In addition to correcting Class II dentofacial deformities in patients with anteroposterior maxillary and mandibular deficiency, maxillomandibular advancement surgery significantly increases the airway space. Therefore, it may be indicated even for patients with Class I deformities, who present obstructive sleep apnea.

Another important parameter that involves the increase in the airway space in orthognathic surgery is anticlockwise rotation of the occlusal plane (OP). This movement causes advancement of the soft palate as well as projecting the chin anteriorly. The increase in airway space may be optimized when associated with the movement of maxillomandibular advancement, and it can sometimes avoid the need for advancement genioplasty.

Similarly, mandibular setback surgeries may cause airway narrowing since they posteriorly displace all the structures, such as the base of tongue, palatoglossal arch and soft palate. According to Kitagawara et al., in a study in which 17 patients underwent orthognathic surgery to treat Class III dentofacial deformities by means of mandibular setback surgery, a reduction in oxygen saturation was found immediately after the surgery, but during the late postoperative period, stabilization of oxygen desaturation was observed. The authors emphasized the need for preventing sleep disturbances when this type of surgical movement is performed.

Obstructive sleep apnea syndrome (OSAS) is a disorder that consists of partial (over 50% of respiratory volume) or total interruption of breathing during sleep for a period ranging from 10 s up to over a minute. The patient is considered syndromic when these episodes are repeated more than 10 times per hour on average, and associated with minimum oxygen saturation lower than 85% during this period. The cause of OSAS is associated with several factors such as airway narrowing, obesity, Class II facial pattern, turbinate hypertrophy, tonsils, adenoids and tongue.

Clinically, the syndromic patient may present characteristics such as excessive daytime sleepiness, snoring during sleep, fatigue even after a night’s sleep, xerostomia, daytime headache, lack of dreams, decreased libido, signs of depression, as well as respiratory and cardiovascular disorders.

Functional increase in airway space by means of maxillomandibular advancement justifies the procedure as the surgical treatment of choice for patients with OSAS. Better understanding of the dimensional alterations in airway space after maxillomandibular advancement, in addition to understanding the stability of dimensional gains associated with the movement, would be important when planning the treatment of these patients, which justifies the present study.

Cephalometry of the upper airways has been the object of several studies in different dental specialties such as orthodontics, surgery, bucco-maxillo-facial traumatology and radiology. Three-dimensional (3D) studies may provide additional information, especially with regard to posterior airway space. Cone-beam computed tomography (CBCT) has been used in dentistry since the 1990s and has attracted a great deal of interest. The combination of high image accuracy associated with the low-dose radiation exposure offered to the patient has been the main motivation for using this technology. In addition to these advantages, the tomography device is compact, occupying little space in the imaging or dental clinic and the examination is performed in a short period of time. The files captured also allow the reconstruction of multiplanar and 3D images, and there are resources for the reconstruction of conventional radiographic images with good resolution and reduced metal artefacts.

There are many software programs that help preoperative planning for orthognathic surgery, such as the Dentofacial Planner Plus ® and Dolphin Imaging ® programs. According to Magro-Filho et al., these programs have been widely accepted for surgical prediction in patients with dentofacial deformities, particularly for informing the patients and making them aware of the surgical treatment before they undergo surgery, although, according to the authors, the use of predictive images of the patients has some limitations when compared with the result achieved for each patient. Dolpin Imaging ® is the most popular program among professionals, particularly because of the virtual planning resources that it offers. Its 3D planning is useful for evaluating airway space. Using the resources for identifying the image in grey scale it is possible to visualize, precisely and accurately, the morphology of patient’s nasopharyngeal or oropharyngeal airway space, which makes this program an important tool in orthognathic surgery for the study of this anatomical region.

The aim of this study was to make a comparative assessment of the cephalometric and 3D alterations of the superior posterior airway space of patients with Class II dentofacial deformity submitted to maxillomandibular advancement surgery.

Materials and methods

The present study was submitted to and approved by the Ethics Committee on Research Involving Human Beings of the Araçatuba Dental School-UNESP, Protocol No. FOA-02077/10.

For this study, 264 medical records from a private clinic were assessed. Of these, patients with Class II facial occlusal and profile pattern with maxillary and mandibular deficiency, who had undergone ortho-surgical treatment by maxillomandibular advancement, either associated with advancement genioplasty or anticlockwise rotation of the occlusal plane, or not, at least 6 months previously, and operated on by a single bucco-maxillo-facial surgeon were selected. Patients were excluded if they: did not meet the inclusion criteria; had maxillary transverse discrepancy; had any complication during orthodontic-surgical treatment; and had incomplete records.

Of the patients assessed, 36 underwent maxillomandibular advancement surgery, and of these, only 20 met the inclusion criteria for the study. In this sample, 9 patients were women and 11 were men, aged between 19 and 57 years. The patients selected for this study did not have OSAS. The patients were assessed at the following three distinct time intervals: preoperative period (T1) up to 1 month before surgery; immediate postoperative period (T2) up to 15 days after surgery; and late postoperative period (T3) at least 6 months after surgery. Only one examiner participated in the study.

The evaluations were performed by CT using Cone Beam I-Cat ® tomography (Imaging Science, Hatfield, PA, USA) at the proposed time intervals. The CT images were assessed by Dolphin Image 11.0 Premium ® software (Dolphin Imaging & Management Solutions, Chatsworth, CA, USA) and the following evaluations were made: cephalometric assessment, divided into linear and area assessment; and volumetric assessment. The cephalometric assessment was performed using the profile radiographs of the face reconstructed from the CT by using the same software.

First, the real movement presented by each patient after maxillomandibular advancement treatment was quantified. Quantification was performed using the cephalometric tracing of all the radiographs according to the method of Arnett and Gunson. Afterwards, based on the nasion and sella craniometric points, the ‘super-impose’ tool ( Fig. 1 ) was used to superimpose the immediate postoperative and the preoperative radiographs, the late preoperative and the preoperative radiographs of each patient, and perform the cephalometric tracings.

Fig. 1
Superimposition of pre- and postoperative cephalometric tracings to quantify the real movements after maxillomandibular advancement.

The craniometric point of reference used was the maxillary central incisor (MCI) point for maxillary advancement. For mandibular advancement, the craniometric point of reference used was the pogonion (Pog). This allowed comparison between the increase in airway space and the maxillomandibular advancement achieved by this surgical technique. Afterwards, the airway space was quantified according to the two previously mentioned analyses with the respective statistical analyses using the Sigmastat 3.0 ® software (Aspire Software International, Ashburn, VA, USA).

Cephalometric assessment

Cephalometric assessment was divided into linear assessment and area assessment of the airway space.

Linear assessment

For the linear assessment the parameters adopted were the linear measurements of the airway space proposed by the cephalometric analysis of Arnett and Gunson. The superior posterior airway space was measured at four points. For the first point, a line was drawn perpendicular to the true vertical line that passed through point A. From there, the distance between the crossing points of the same line with the anterior and posterior wall of the superior posterior airway space was measured. This measurement was then called superior posterior airway space (SPAS) at point A (SPAS at A).

The second point was measured in a similar way, but the line perpendicular to the true vertical line passed through the MCI point. At this point, the distance between the crossing points of this line with the anterior and posterior wall of the superior posterior airways was measured. This measurement was called SPAS at MCI. Similarly, B and Pogonion (Pog) points were measured and the measurements of SPAS at B and SPAS at Pog were quantified.

For all the patients the above-mentioned measurements were quantified at the three proposed time intervals (T1, T2 and T3), which allowed evaluation of the anteroposterior linear increase in airway space of the regions assessed at T2 in comparison with T1 and the stability of this movement at T3 in comparison with T1 and T2.

For analysis of the results, the data were organized in a table and a column chart was prepared to compare the three studied time intervals of each patient. Afterwards statistical analysis of the results was performed using the paired Student’s t test for the samples that showed normal distribution and the Wilcoxon test for the samples that did not pass the normality test.

SPAS area assessment

To assess the SPAS area, the Image J ® software (National Institute of Health Image, Public Domain) was used. For this purpose, the cephalometric images reconstructed from CT were captured and saved as JPG images using the same standard with pixel sizes of 2002 × 1252 and 9.6 megabytes. The entire superior posterior airway, which extended from the retropalatal region up to the base of the epiglottis, was delimited by using the ‘polygon selection’ tool ( Fig. 2 ).

Fig. 2
Demarcation of SPAS in the Image J ® program to quantify the area of the superior posterior airway space.

With the aid of the measuring tool, located on the analysis icon, the airway area measured in pixels was calculated. Therefore, it was possible to observe the proportion of the airway space increase in the cephalometry, measured in percentage, in the immediate postoperative period in comparison with the preoperative period. In the late postoperative period, the stability of this gain was observed in two dimensions. Using the ‘define scale’ tool, also on the analysis icon, the area values of the image in pixels was transformed into square millimetres using the image of a millimetre ruler found on each cephalogram. This tool allowed the data of maxillomandibular advancement and the increase in the SPAS area to be crossed.

For analysis of the results, column charts were prepared to compare the dynamics of the alterations in area of the airway space at the three studied time intervals. The paired Student’s t test was used for statistical analysis when the sample showed normal distribution and the Wilcoxon test was used for samples that did not pass the normality test. The tests were used to compare the preoperative, immediate postoperative and late postoperative periods of the sample.

Volumetric assessment

For volumetric assessment the 3D >> tool of the Dolphin Image 11.0 Premium ® software, located on the tool bar to the left of the initial page of the program was used. Next the ‘sinus/airway’ tool was used to analyse the airway space of each patient.

Using the ‘add seed points’ tool, the points to delimit the superior posterior airway region of each patient were marked on the axial, coronal and sagittal cuts to include the entire extension of SPAS in the analysis ( Fig. 3 ). The anatomical limits used in the analysis were: upper portion, the retropalatal region, delimited by a line that passed through the uppermost portion of the hard palate and touched the posterior airway space; lower portion, in the hypopharynx region, with a line crossing the superior posterior airway space at the height of the base of the epiglottis, parallel to the upper limit; posteriorly, by the posterior pharyngeal wall; and anteriorly, by the anterior wall of the pharynx, soft palate, tongue and epiglottis.

Fig. 3
Marking of the superior posterior airway area in the CBCT in axial cut by including seed points at sensitivity of 25%.

The detection sensitivity of the airway space was standardized at 25% and the ‘update volume’ tool was used to measure the volume of the delimitated airway space. Then the volume of the airway space at each time interval assessed was calculated, enabling the volumetric gain obtained in the immediate postoperative period to be compared with that of the preoperative period, and with the stability of this gain in the late postoperative period ( Fig. 4 ).

Fig. 4
Figure showing volumetric quantification of posterior airway space, evidencing the 3D image of airway space in pink. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of the article.)

By quantification of the real movements of the base of the bones, it was possible to compare the proportional relationship between the maxillomandibular advancement and the volumetric gain of the airways, in addition to evaluating the stability of these movements in soft tissues of the airway space.

For analysis of the results, tables were prepared showing the values of each volumetric measurement at all time intervals assessed, and a column chart with showing values of each patient at each time interval assessed. Statistical analysis was performed using the paired Student’s t test to compare the volumetric assessments of the pre- and postoperative periods.

Results

Of the patients assessed, the mean maxillary advancement achieved at T2 in comparison with T1 was 4.1 mm with standard deviation of 2.0. When comparing T3 with T1, the mean maxillary advancement was 3.6 mm with standard deviation of 2.0 ( Table 1 ).

Table 1
Mean and standard deviation (SD) for maxillary advancement, measured from MCI and for mandibular advancement, measured from craniometric point of the Pog.
Immediate post-op Late post-op
Mean SD Mean SD
MCI 4.1 2.04 3.6 2
Pog 12.5 5.7 11.8 5.5

After applying the Wilcoxon test, there was no statistically significant difference between the values in the immediate postoperative period and the late postoperative period for the incisor tip with p -value 0.164. These data showed the stability of real movement of the base of the maxillary bone, which is an important parameter of comparison to assess the airway space.

For mandibular movement, a mean advancement of 12.5 mm was found in the immediate postoperative period with standard deviation of 5.7, and mean of 11.8 mm in the late postoperative period with standard deviation of 5.5, which shows good stability for mandibular movement.

After applying the Wilcoxon statistical test, a statistically significant difference was found for mandibular advancement in the immediate postoperative period in comparison with the late postoperative period, with p -value of 0.006.

15 patients assessed underwent anticlockwise rotation of the occlusal plane, 2 underwent clockwise rotation and 3 patients showed no alteration in the measurement. The results were divided according to the method of evaluation used, as follows.

Cephalometric assessment

For the cephalometric assessment, 60 CT images were used to reconstruct 60 cephalometric radiographs, which corresponded to the images with reference to the three time intervals assessed for each of the 20 patients studied.

In the qualitative analysis of the images obtained, it was found that most patients presented a substantial gain in superior posterior airway space in the immediate postoperative period. Partial loss of the immediate gain was found in the late postoperative evaluation, representing an apparent accommodation of the soft tissues in this anatomical region ( Fig. 5 ). The linear and the area results quantified from the reconstructed cephalometric radiographs are given below.

Fig. 5
Qualitative assessment of the posterior airway space from cephalometric images reconstructed from CBCT of one of the patients assessed: (a) cephalometry at T1; (b) cephalometry at T2; and (c) cephalometry at T3.

Linear assessment

In the linear assessment, the movement of the base of the bones led to an increase in airway space. The measurement of SPAS at A, during the preoperative period, showed a dimensional mean of 12.8 mm with standard deviation of 3.4. This value in the immediate postoperative period increased to 14.6 mm on average, with standard deviation of 3.3. At T3 a mean loss of 0.8 mm in gain was found at T2, but there was no statistically significant difference between time intervals T2 and T3 after applying Wilcoxon statistical test with a p -value of 0.092. These data suggest good anteroposterior stability for movement in this region.

The measurement of SPAS at MCI showed mean value of 7.5 mm with standard deviation of 3.4. The value at T2 increased to 12.0 mm on average, with standard deviation of 3.3. This region was the one that showed a better response to linear increase when compared with the other regions, accumulating a mean increase of 4.5 mm at T2 with average loss of 1.6 mm at T3. After statistical assessment using the paired Student’s t test, there was no difference between the values at T2 and T3 with a p -value of 0.056.

For the measurement of SPAS at B, the patients assessed showed a mean value of 7.9 mm at T1 with standard deviation of 3.2. In the immediate postoperative period, this value increased to 3.7 mm on average, with standard deviation of 2.6. Whereas at T3, a gain of 2.3 mm was obtained in comparison with T1, showing a relapse of 1.3 mm on average.

Statistical assessment using the paired Student’s t test, in comparison with T2 and T3, showed no statistical difference with p -value of 0.059.

The assessment of the measurement of SPAS at Pog showed a mean of 8.6 mm in the preoperative period with standard deviation of 4.3. At T2, this value was 10.9 mm on average, with standard deviation of 4.7. At T3 there was a reduction of 0.7 mm in comparison with T2. The Wilcoxon test showed no statistical difference between these two time intervals with a p -value of 0.216, showing good stability in linear gain of the airway in this region.

With regard to linear assessment, a relationship was found between the gain in superior posterior airway space of each studied point and maxillomandibular advancement. When maxillary advancement is directly associated with gain in SPAS at A and MCI, and similarly, when mandibular advancement is associated with the gain in SPAS at B and Pog, more results may be observed.

Each millimetre of advancement in the maxilla in a combined movement of maxillary and mandibular advancement led to a mean increase of 0.5 mm in SPAS at A at T2 and 0.3 mm at T3 and a mean increase of 1 mm in SPAS at MCI at T2 and 0.8 mm at T3. Therefore, each millimetre of advancement in the mandible in the same type of movement led to a mean increase of 0.3 mm in SPAS at B at T2 and 0.2 mm at T3 and a mean increase of 0.2 mm in SPAS at Pog at T2 and 0.2 mm at T3.

All the mean values and standard deviation for SPAS at A, SPAS at MCI, SPAS at B and SPAS at Pog points were organized and are shown in Table 2 .

Jan 26, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Cephalometric and three-dimensional assessment of superior posterior airway space after maxillomandibular advancement
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