INTRODUCTION

Clefts involving the lip and/or palate are the most common congenital malformations of the craniofacial region,1,2 and the patients affected by clefts usually have complaints of mouth breathing, snoring, and hypopnea during sleep.3,4 In addition, the adenoidal tissue is significantly larger in patients affected by unilateral cleft lip and palate (UCLP) than in a cleft-free control group.5 In addition to those respiratory difficulties, these patients present reduced sagittal maxillary and mandibular development and larger vertical dimensions,6 which might affect the pharyngeal airway volume.

The relationship between different skeletal patterns and airway volume was previously evaluated by several authors7–11 using three-dimensional (3D) techniques, and significant difference for pharyngeal airway volumes were reported among different sagittal patterns. However, few studies12–15 were performed to assess pharyngeal airway volume in patients affected by cleft, and pharyngeal airway volume in patients affected by bilateral cleft lip and palate (BCLP) was almost neglected.

To our knowledge, only two studies13,15 included 3D data of patients affected by BCLP for the assessment of pharyngeal airway volume; however, the groups were not standardized and homogeneously distributed in those studies. Cheung and Oberoi13 investigated pharyngeal airway in 16 UCLP and 3 BCLP patients, who had been previously treated by maxillary expansion. Yoshihara et al.15 included 10 patients with UCLP and 5 patients with BCLP in the juvenile group, and 10 patients with UCLP and 4 patients with BCLP in the adolescent group. None of these studies separately investigated the airway volume as UCLP and BCLP groups, probably due to including a small number of patients affected by BCLP.

The aim of the present study was to evaluate pharyngeal airway volumes of adolescent patients affected by BCLP and compare the findings with a well-matched control group without cleft using cone beam computed tomography (CBCT). In addition, some craniofacial, pharyngeal linear and area measurements were also performed in order to establish the relationships of those measurements and pharyngeal airway volumes.

MATERIALS AND METHODS

All patients and patients' parents had signed an informed consent form allowing use of their data for scientific purposes prior to dental and/or orthodontic treatment as a usual protocol in our university. This retrospective study was approved by the local ethical committee of Erciyes University.

Study sample calculation of the present study was based on a formula described by Pandis,16 a significance level of .05 and a power of 80% to detect a difference of 2 cm³ (±2 cm³) for the pharyngeal airway volume between BCLP and control groups. The power analysis showed that 16 patients were required in each group.

In order to obtain 16 patients that matched the specific criteria to comprise the BCLP group, one operator searched the archives of Erciyes University and then examined the initial data of 20 adolescent patients affected by complete BCLP. Inclusion criteria were as follows: (1) the same surgical procedure (lip and hard tissue closure) before 3 years of age; and (2) no previous orthodontic treatment, orthognathic surgery, history of trauma, syndromes, tonsillectomy, adenoidectomy, and upper airway obstruction. Four patients were excluded due to the inclusion criteria, and finally 16 patients (11 female and 5 male; mean [SD] age 14.1 [2.1] years) affected by BCLP were included in the study. As a control group, 16 adolescent patients (10 female and 6 male; mean [SD] age 13.4 [2.0] years) were randomly selected from the data of 30 age- and sex-matched patients who had no cleft, syndrome, previous orthodontic treatment, orthognathic surgery, history of trauma, tonsillectomy, adenoidectomy, and upper airway obstruction using a random number table. None of the patients in both groups had a body mass index higher than 28.

The CBCT images were obtained in a standard supine position (scanning time 14–18 seconds; collimation height 13 cm; exposure time 3.6 seconds; and voxel size 0.3 mm³) using the same device (NewTom 5G, QR, Verona, Italy). Patients were asked to bite with maximum intercuspation and not to move their heads or tongues during scanning. All images had a full field of view so that the cranial base and face were completely observed. The 3D images were transformed to Digital Imaging and Communications in Medicine (DICOM) format, and then Simplant Pro software, version 13.0 Mimics 15.01 (Materialise HQ, Leuven, Belgium) was used to create 3D images. Each 3D-rendered image was then reoriented using the Frankfort horizontal plane as its horizontal reference plane, which was constructed from right and left porion that are located in the most laterosuperior point of the external auditory meatus and the right orbital, the most inferior point of the lower margin of the bony orbit. The sagittal reference plane was constructed from the nasion and mid porion point and perpendicular to the horizontal reference plane. The frontal plane was constructed from the nasion and perpendicular to the horizontal and sagittal planes.

The borderlines of the pharyngeal airway were modified from the study9 and consisted of the posterior border, the posterior wall of the pharynx; inferior border, a plane tangent to the most caudal medial projection of the third cervical vertebra perpendicular to the sagittal plane; and anterior border, a vertical plane through the point (the intersection of vertical plane from sella to nasion-basion plane) to the sagittal plane at the lowest border of the vomer. The modification of the anterior border was needed due to the different positions of PNS in these patients. The plane perpendicular to the sagittal plane through the most caudal superior of the first cervical vertebra divided the pharyngeal airway into two segments, the nasopharyngeal airway and oropharyngeal airway compartments (Figures 1 and 2). The 3D volumetric measurements described above were blindly calculated with the same software by an experienced operator in random. Posterior airway space (PAS) (the most constricted space behind the base of the tongue and limited by the soft tissue), the area of the most constricted region at the base of the tongue (minAx), and craniofacial measurements on posteroanterior (bizygomatic width) and cephalometric (SNA, SNB, ANB, SN-GoGn, Co-a, CoGn) radiographs obtained from CBCT were performed by the same operator (Figures 3 through 5).

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RESULTS

The ICC values were above 0.977 for all variables confirming the reliability of measurements. Additionally, the results of paired t-test confirmed that all measurements were free of systemic error (P > .05).

Table 1 shows the demographic values of the patients in the BCLP and control groups. The results of Pearson chi-square and Student's t-tests showed that both groups were matched on gender distribution and chronologic age, respectively (P > .05).

Table 1. Descriptive Statistics of the Groups

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Table 2 shows the comparison of nasopharyngeal, oropharyngeal, and total airway volumes between genders in the BCLP and control groups. The genders in both groups were not normally distributed, and thus the Mann-Whitney U-test was performed to compare genders. Results showed that no significant difference was present between genders (P > .05). Therefore, the subjects were pooled for further statistical comparisons.

Table 2. Descriptive Statistics and Comparisons of Airway Volumes Between Genders^a

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Table 3 shows the comparison of craniofacial and pharyngeal airway (linear, area, and volumetric) measurements between the BCLP and control groups. Statistically significant differences were found for SNB (P < .05), SN-GoGn (P < .05), Co-A (P < .05), PAS (P < .01), minAx (P < .01), and oropharyngeal airway volume (P < .05). However, no statistically significant differences were found for SNA, ANB, Co-Gn, bizygomatic width, nasopharyngeal, and total airway volumes (P > .05).

Table 3. Descriptive Statistics and Comparisons of Craniofacial and Airway Volume Measurements Among Groups

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The multiple linear regression analyses were performed to establish the relationships of the statistically significant difference of oropharyngeal airway volume as a dependent variable and the other variables as predictors. After performing the analysis, chronologic age, SNA, and bizygomatic width measurements were excluded, and a new regression model was created using the SNB, ANB, SN-GoGn, Co-A, Co-Gn, PAS, and minAx as predictor variables (R²  =  .704). The coefficient correlation and P values between oropharyngeal airway volume and all predictor values are shown in Table 4. The most predictive variables were found as PAS (r  =  .655 and P  =  .000) and minAx (r  =  .787 and P  =  .000).

Table 4. Correlations Between Oropharyngeal Airway Volume and the Linear and Area Measurements

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DISCUSSION

Numerous oropharyngeal problems were encountered in patients affected by cleft.12 Due to the nasal deficiencies observed in those patients, nasal resistance increases, and this causes to breath orally, which affects the craniofacial growth.17 Craniofacial morphology of the patients affected by UCLP and BCLP has been investigated.6,18–23 Although several studies7–11,24,25 were performed to investigate the pharyngeal airway volume in patients with different skeletal patterns, limited numbers of studies12–15 were published examining the pharyngeal airway volumes in patients affected by cleft. Aras et al.12 used computed tomography (CT) to assess the pharyngeal airway, stating that the cephalometric techniques seemed to be insufficient and that the CT method providing 3D images appeared to be more appropriate. To the best of our knowledge, there was no study published to evaluate pharyngeal airway volume in patients affected by BCLP using CBCT. Only two studies13,15 included a small number of patients affected by BCLP in their studies; however, they did not separately investigate the pharyngeal airway in BCLP patients.

CBCT was found to be a simple and effective method for the evaluation of pharyngeal airway.26 The reliability of CBCT method to assess the pharyngeal airway volume and craniofacial measurements was confirmed by several authors.8,9,14,26–28 In agreement with this finding, the ICC values were above 0.977 for all variables, thus confirming the reliability of those measurements performed on CBCT.

Hermann et al.23 reported that the patients affected by BCLP had retruded mandible and maxilla, bimaxillary retrognathia, vertical growth pattern, and reduced PAS. Previous studies6,18–22 have also reported the maxillary retrusion and the vertical growth pattern in these patients. In agreement with the literature, BCLP patients examined in the present study showed maxillary and mandibular retrusion, decreased maxillary and mandibular lengths and increased vertical growth pattern compared to control group. The differences for SNB (degrees) (P < .05), Co-A (mm) (P < .05), SN-GoGn (degrees) (P < .05), PAS (mm) (P < .01), and minAx (mm²) (P < .01) were found to be statistically significant, while the other variables were not (P > .05). In addition, BCLP group showed decreased nasopharyngeal (357.8 mm³) (P > .05), oropharyngeal (4272.8 mm³) (P < .05), and total (4631.2 mm³) (P > .05) airway volumes compared to the control group. Total airway volume difference was not significant (P  =  .072), probably due to the presence of high standard deviations for this variable in both groups (Table 3). It is difficult to compare our findings with the previous studies since no study homogeneously examined the pharyngeal airway volume in patients affected by BCLP. Yoshihara et al.15 who included 10 adolescent patients affected by UCLP and 4 adolescent patients affected by BCLP in their study, reported statistically significant decrease in pharyngeal airway volumes compared to the control group. The other study,13 including 16 UCLP and 3 BCLP patients who had all previously been treated by maxillary expansion prior to the CBCT taken, reported increased pharyngeal airway volumes compared to the control group. However, this finding probably seems to be affected by maxillary expansion.13,29 Vertical growth pattern and maxillary growth deficiency observed in these patients might be possible reasons for the decreased airway volume.

Since statistically significant differences were observed for oropharyngeal airway volume (P  =  .032) regarding 3D measurements, multiple linear regression analysis was performed to create a model using the SNB, ANB, SN-GoGn, Co-A, Co-Gn, PAS, and minAx as predictor variables (R²  =  .704). The most predictive variables were found as PAS (mm) (r  =  .655 and P  =  .000) and minAx (mm²) (r  =  .787 and P  =  .000). In addition, statistically significantly negative correlations were found for the measurements of ANB (r  =  −0.450 and P  =  .005) and SN-GoGn (r  =  −0.347 and P  =  .026). These findings were in agreement with previous studies.8,30,31

Patient positioning and changes in airway during the scanning are the factors that might affect the findings.32 The patients included in both groups were scanned in a standard condition and thus standardization was performed for both groups. On the other hand, the time required for scanning is a long period, and thus it is difficult to ask adolescent patients not to breathe. Although the study sample was determined using a formula16 prior to the study, small sample size might be noted as a limitation factor. Future studies including more patients are needed to discuss the present findings. In addition, it might be better to see future studies performed on cleft patients in sitting upright positions rather than in supine positions to compare the findings. Despite those limitations, the present study presented valuable information about the adolescent patients affected by BCLP, and an orthodontist should define the best treatment choice for these patients considering the decreased pharyngeal airway dimension, area, and volume.

CONCLUSIONS

• The null hypothesis was rejected. Oropharyngeal (P < .05) and total (P > .05) airway volumes were found to be less in the BCLP group, and thus the treatment choice in these patients should have positive effects on pharyngeal airway.

• The most predictive variables for oropharyngeal airway volume were found to be PAS (r  =  .655 and P  =  .000) and minAx (r  =  .787 and P  =  .000).