Airway volume analysis: is there a correlation between two and three-dimensions?

Airway volume analysis: is there a correlation between two and three-dimensions? Summary Objectives No consensus exists on the assessment of airway in CBCT scans. Two-dimensional measures remain the standard in the cephalometric analysis. This research aimed to evaluate linear and area measurements in two-dimensional views from specific airway regions of interest and compare these to the correspondent volume in CBCT exams. Materials and Methods 250-selected CBCT scans were retrospectively analyzed. A trained and calibrated examiner performed the linear, area and volume measurements in specific sites for nasal cavity, nasopharynx and oropharynx compartments. Dolphin Software was used for the analysis. The correlations were performed using Pearson coefficient. Results The highest positive correlations were observed in the nasopharynx and oropharynx sagittal areas and the most constricted area in the oropharynx. Nasopharynx linear measures and nasopharynx coronal area did not present correlation with whole volume. Two-dimensional measurements in the soft palate (width and sagittal area) showed very low positive correlations. Although nasal cavity presented highest volume means, changes in oropharynx contributed more to variations in total volume, compared with the other two sections. Conclusion Airway sagittal areas, as well as the most constricted axial area in oropharynx remains a useful guide to correlate with airway volume in two-dimensional images. Introduction The obstruction of airway space can alter normal breathing, which can have a significant impact on the development and stability of craniofacial structures (1). Since airway space disorders can affect the patient condition and could influence orthodontic outcomes, the diagnosis, and treatment needs dentists’ attention and should be reported by the radiologist. Therefore, a diagnostic method that provides accurate data is a valuable tool in digital imaging science. Cephalometric analyses are usually the diagnostic instrument in Orthodontics (2–4). Although the conventional lateral cephalogram was reported to be inexpensive, and simple to perform, this two-dimensional imaging modality seems to have limitations (5, 6), especially to represent three-dimensional structures. The development of cone-beam computed tomography (CBCT) allowed a detailed multiplanar analysis of the dentomaxillofacial complex (7–9). Some studies suggested limitations of a 2D-airway analysis, such as Lenza et al. (10), which evaluated 34 patients and showed a weak correlation (r < 0.8) between most of the 2D and 3D measurements. Evaluating obstructive sleep apnea (OSA) patients, Alsufyani concludes that there is insufficient literature to the use of CBCT to assess treatment outcomes and high-quality evidence level studies are needed to determine if CBCT airway dimensional changes are suitable for assessment of treatment outcome (11). Nevertheless, when a CBCT is taken, the accuracy and reliability of craniofacial measurements were shown to be better, compared to 2D lateral cephalograms (7, 8, 12–16), even though sometimes clinically inconsiderable. According to SEDENTEXCT (17), CBCT scans should not be appointed as a routine method in orthodontic patients, but should still be used on particular indications. Regarding airway evaluation, there is still no consensus whether the airway volume calculated on CBCT images gives a better indication of the airway function compared to measurements performed on two-dimensional images (6, 11, 13, 17), Therefore, this research aims to evaluate linear and area measurements in two-dimensional views from specific airway regions of interest and compare these to the correspondent volume in CBCT exams, suggesting 2D surrogate measurements for the 3D volume analysis. Methods The Ethics Research Committee approved the project (number 25300). This investigation is a retrospective study, so all patients were scanned according to standard clinical indications. The sample size was estimated considering an intermediate correlation (0.4), α error of 0.05 and β of 0.2 (a power test of 80%), and a dropout of 10%, totaling 267 scans. The CBCT scans were randomly collected from the Oral Radiology Section database. The inclusion criteria were CBCT scans acquired with the same exposure protocols (i-CAT device [Imaging Sciences International, Hatfield, Pennsylvania], large field of view [FOV], 120 kVp, scan time 26.9 s, 0.2 mm voxel size). Seventeen scans were excluded because FOV did not cover whole upper airway, comprising a total of 250 (138 female, 112 male, mean age of 50.6) evaluated. CBCT image sequences were exported in DICOM format and opened on the same computer (Intel core i7 3GHz processor, LG Flatron E2250 display, 21 inches, 32 bits) using Dolphin software version 13.8 (Dolphin Imaging & Management Solutions; Chatsworth, California). The measurements were made by a trained and calibrated examiner (LSM) under the same viewing conditions in a room with reduced light. The calibration process was performed by two examiners (LSM and MBV), starting with a training and discussion about the standardization, airway tool sensitivity, and measurements. Next, 25 scans were randomly selected from the database, and each examiner completed all measurements twice, with an interval of two weeks. Intra- and inter-examiner intraclass correlation coefficient was calculated, and values >0.9 were achieved for all evaluated measurements. The reproducibility was guaranteed repeating these same scans during the study analysis. Before the measurements, the patient’s skull was oriented according to the anatomical planes. The contrast of the images was adjusted by the examiner to better fit soft tissue visualization. Subsequently, the ‘airway space’ tool was accessed and the borders of the nasal cavity, nasopharynx, and oropharynx were defined. The airway sensitivity was established according to the examiner visual choice, aiming that only airspace was included, and then the volume was calculated. For the sagittal area in nasopharynx and oropharynx, the values were collected in the midsagittal plane (based on anterior and posterior nasal spine) and for axial and coronal planes in particular points explained in Figure 1 and 2. The limits of the nasal cavity, nasopharynx, and oropharynx are described in Table 1. Figure 1. View largeDownload slide The standard head position (sagittal plane), and the airway compartment borders and corresponding area and volume measurements evaluated. 1 = NC coronal area; 2 = N coronal area; 3 = N linear measure and N axial area; 4 = O linear measure and O axial area. The areas located at the sagittal standard image correspond to the correspondent compartment coronal area. ANS, anterior nasal spine; PNS, posterior nasal spine. Figure 1. View largeDownload slide The standard head position (sagittal plane), and the airway compartment borders and corresponding area and volume measurements evaluated. 1 = NC coronal area; 2 = N coronal area; 3 = N linear measure and N axial area; 4 = O linear measure and O axial area. The areas located at the sagittal standard image correspond to the correspondent compartment coronal area. ANS, anterior nasal spine; PNS, posterior nasal spine. Figure 2. View largeDownload slide Illustration of minimum cross-sectional area (a) and measurements for oropharynx and soft palate in sagittal plane (b, c). Figure 2. View largeDownload slide Illustration of minimum cross-sectional area (a) and measurements for oropharynx and soft palate in sagittal plane (b, c). Table 1. Anatomical borders of the upper airway, as well as the multiplanar measurements evaluated in this study. ANS, anterior nasal spine; PNS, posterior nasal spine. Standard head position Coronal plane: right and left infraorbital foramen parallel to the ground Sagittal plane: palatal plane (ANS-PNS) parallel to the ground Axial plane: palatal plane (ANS-PNS) vertical line, perpendicular to the ground Nasal cavity Anterior limit: ANS line through up to nasal bone (in coronal plane reported as nasal cavity coronal area) Posterior limit: PNS line through up to skull basis Nasopharynx Anterior limit: ≅posterior limit of the nasal cavity (in coronal plane reported as nasopharynx coronal area) Inferior limit: PNS line extended to the pharynx’s posterior wall, correspondent to nasopharynx linear measure (in axial plane reported as nasopharynx axial area) Oropharynx Superior limit: ≅inferior limit of the nasopharynx Inferior limit: horizontal line through the superior point of the epiglottis, correspondent to oropharynx linear measure (in axial plane reported as oropharynx axial area) Standard head position Coronal plane: right and left infraorbital foramen parallel to the ground Sagittal plane: palatal plane (ANS-PNS) parallel to the ground Axial plane: palatal plane (ANS-PNS) vertical line, perpendicular to the ground Nasal cavity Anterior limit: ANS line through up to nasal bone (in coronal plane reported as nasal cavity coronal area) Posterior limit: PNS line through up to skull basis Nasopharynx Anterior limit: ≅posterior limit of the nasal cavity (in coronal plane reported as nasopharynx coronal area) Inferior limit: PNS line extended to the pharynx’s posterior wall, correspondent to nasopharynx linear measure (in axial plane reported as nasopharynx axial area) Oropharynx Superior limit: ≅inferior limit of the nasopharynx Inferior limit: horizontal line through the superior point of the epiglottis, correspondent to oropharynx linear measure (in axial plane reported as oropharynx axial area) View Large Table 1. Anatomical borders of the upper airway, as well as the multiplanar measurements evaluated in this study. ANS, anterior nasal spine; PNS, posterior nasal spine. Standard head position Coronal plane: right and left infraorbital foramen parallel to the ground Sagittal plane: palatal plane (ANS-PNS) parallel to the ground Axial plane: palatal plane (ANS-PNS) vertical line, perpendicular to the ground Nasal cavity Anterior limit: ANS line through up to nasal bone (in coronal plane reported as nasal cavity coronal area) Posterior limit: PNS line through up to skull basis Nasopharynx Anterior limit: ≅posterior limit of the nasal cavity (in coronal plane reported as nasopharynx coronal area) Inferior limit: PNS line extended to the pharynx’s posterior wall, correspondent to nasopharynx linear measure (in axial plane reported as nasopharynx axial area) Oropharynx Superior limit: ≅inferior limit of the nasopharynx Inferior limit: horizontal line through the superior point of the epiglottis, correspondent to oropharynx linear measure (in axial plane reported as oropharynx axial area) Standard head position Coronal plane: right and left infraorbital foramen parallel to the ground Sagittal plane: palatal plane (ANS-PNS) parallel to the ground Axial plane: palatal plane (ANS-PNS) vertical line, perpendicular to the ground Nasal cavity Anterior limit: ANS line through up to nasal bone (in coronal plane reported as nasal cavity coronal area) Posterior limit: PNS line through up to skull basis Nasopharynx Anterior limit: ≅posterior limit of the nasal cavity (in coronal plane reported as nasopharynx coronal area) Inferior limit: PNS line extended to the pharynx’s posterior wall, correspondent to nasopharynx linear measure (in axial plane reported as nasopharynx axial area) Oropharynx Superior limit: ≅inferior limit of the nasopharynx Inferior limit: horizontal line through the superior point of the epiglottis, correspondent to oropharynx linear measure (in axial plane reported as oropharynx axial area) View Large SPSS software (version 17.0; SPSS, Chicago, Illinois) was used for data analysis. Differences between gender for linear, area, and volume measurements were checked using Student’s t-test (P < 0.05). The Pearson correlation coefficient (r) was used to evaluate linear relationship degree among linear, area, and volume values from CBCT scans. This coefficient ranges from −1 to +1 and values close to 0 (zero) means that there is no linear relationship, the value of +1 indicates a perfect linear relationship and the value −1 also indicates a perfect inverse linear relationship. Scores closer to +1 or −1 suggest a stronger association between the variables. The levels of statistical significance were P <0.05. Multiple linear regression was performed using the area measurements that have had greater correlation with the volumes. Results Table 2 shows the mean values for linear, area, and volume measurements from upper airway regarding gender. Nasal cavity (NC) and oropharynx (O) presented statistical differences between genders. Furthermore, excluding O minimum area, all sites analyzed in NC, O, and soft palate presented differences with male showing higher values. Otherwise, no gender differences were observed in nasopharynx (N) volume, areas, and linear measures. Table 2. Mean values, standard deviation, standard error, and P value for age, linear, area, and volume measurements from upper airway considering gender (n = 250). N, nasopharynx; NC, nasal cavity; O, oropharynx. Gender: 1 = male 2 = female. Means of volume presented in mm3, area in mm2, and linear in mm (millimeter). Variable Gender Mean Std. deviation Std. error mean P value Age 1 50.0568 13.99393 1.37222 0.542 2 51.2117 14.56863 1.2877 NC volume 1 15073.983 4196.1761 396.5014 0.007* 2 13714.433 3723.322 316.9502 N volume 1 8663.713 2617.7458 247.3537 0.161 2 8250.653 2030.6094 172.857 O volume 1 13832.202 6757.9936 638.5704 0.000* 2 10878.828 4253.3989 362.0734 NC coronal area 1 222.729 48.3774 4.5712 0.000* 2 197.88 43.4939 3.7024 N coronal area 1 332.813 100.0927 9.4579 0.053 2 308.866 93.4957 7.9879 N axial area 1 559.962 143.4633 13.556 0.201 2 537.049 137.9316 11.7415 N sagittal area 1 307.804 98.485 9.306 0.617 2 301.699 93.9335 7.9962 N linear measure 1 20.956 4.3952 0.4153 0.939 2 20.995 3.6062 0.3081 O axial area 1 307.537 161.0091 15.2139 0.000* 2 226.382 116.1836 9.8902 O sagittal area 1 565.166 183.3113 17.3213 0.000* 2 448.568 129.2783 11.0049 O minim area 1 150.056 107.6576 10.1727 0.316 2 138.073 73.0668 6.2199 O linear measure 1 13.99 5.1266 0.4844 0.000* 2 11.143 3.823 0.3254 Soft palate length 1 46.061 4.7931 0.4529 0.000* 2 41.613 4.988 0.4246 Soft palate width 1 9.869 1.9573 0.1849 0.000* 2 8.776 1.559 0.1327 Soft palate sagittal area 1 352.866 69.8563 6.6008 0.000* 2 273.739 55.8739 4.7563 Total volume 1 36659.026 8336.4822 798.4902 0.000* 2 32843.914 7019.708 597.5572 Variable Gender Mean Std. deviation Std. error mean P value Age 1 50.0568 13.99393 1.37222 0.542 2 51.2117 14.56863 1.2877 NC volume 1 15073.983 4196.1761 396.5014 0.007* 2 13714.433 3723.322 316.9502 N volume 1 8663.713 2617.7458 247.3537 0.161 2 8250.653 2030.6094 172.857 O volume 1 13832.202 6757.9936 638.5704 0.000* 2 10878.828 4253.3989 362.0734 NC coronal area 1 222.729 48.3774 4.5712 0.000* 2 197.88 43.4939 3.7024 N coronal area 1 332.813 100.0927 9.4579 0.053 2 308.866 93.4957 7.9879 N axial area 1 559.962 143.4633 13.556 0.201 2 537.049 137.9316 11.7415 N sagittal area 1 307.804 98.485 9.306 0.617 2 301.699 93.9335 7.9962 N linear measure 1 20.956 4.3952 0.4153 0.939 2 20.995 3.6062 0.3081 O axial area 1 307.537 161.0091 15.2139 0.000* 2 226.382 116.1836 9.8902 O sagittal area 1 565.166 183.3113 17.3213 0.000* 2 448.568 129.2783 11.0049 O minim area 1 150.056 107.6576 10.1727 0.316 2 138.073 73.0668 6.2199 O linear measure 1 13.99 5.1266 0.4844 0.000* 2 11.143 3.823 0.3254 Soft palate length 1 46.061 4.7931 0.4529 0.000* 2 41.613 4.988 0.4246 Soft palate width 1 9.869 1.9573 0.1849 0.000* 2 8.776 1.559 0.1327 Soft palate sagittal area 1 352.866 69.8563 6.6008 0.000* 2 273.739 55.8739 4.7563 Total volume 1 36659.026 8336.4822 798.4902 0.000* 2 32843.914 7019.708 597.5572 *Student’s t-test (P < 0.05). View Large Table 2. Mean values, standard deviation, standard error, and P value for age, linear, area, and volume measurements from upper airway considering gender (n = 250). N, nasopharynx; NC, nasal cavity; O, oropharynx. Gender: 1 = male 2 = female. Means of volume presented in mm3, area in mm2, and linear in mm (millimeter). Variable Gender Mean Std. deviation Std. error mean P value Age 1 50.0568 13.99393 1.37222 0.542 2 51.2117 14.56863 1.2877 NC volume 1 15073.983 4196.1761 396.5014 0.007* 2 13714.433 3723.322 316.9502 N volume 1 8663.713 2617.7458 247.3537 0.161 2 8250.653 2030.6094 172.857 O volume 1 13832.202 6757.9936 638.5704 0.000* 2 10878.828 4253.3989 362.0734 NC coronal area 1 222.729 48.3774 4.5712 0.000* 2 197.88 43.4939 3.7024 N coronal area 1 332.813 100.0927 9.4579 0.053 2 308.866 93.4957 7.9879 N axial area 1 559.962 143.4633 13.556 0.201 2 537.049 137.9316 11.7415 N sagittal area 1 307.804 98.485 9.306 0.617 2 301.699 93.9335 7.9962 N linear measure 1 20.956 4.3952 0.4153 0.939 2 20.995 3.6062 0.3081 O axial area 1 307.537 161.0091 15.2139 0.000* 2 226.382 116.1836 9.8902 O sagittal area 1 565.166 183.3113 17.3213 0.000* 2 448.568 129.2783 11.0049 O minim area 1 150.056 107.6576 10.1727 0.316 2 138.073 73.0668 6.2199 O linear measure 1 13.99 5.1266 0.4844 0.000* 2 11.143 3.823 0.3254 Soft palate length 1 46.061 4.7931 0.4529 0.000* 2 41.613 4.988 0.4246 Soft palate width 1 9.869 1.9573 0.1849 0.000* 2 8.776 1.559 0.1327 Soft palate sagittal area 1 352.866 69.8563 6.6008 0.000* 2 273.739 55.8739 4.7563 Total volume 1 36659.026 8336.4822 798.4902 0.000* 2 32843.914 7019.708 597.5572 Variable Gender Mean Std. deviation Std. error mean P value Age 1 50.0568 13.99393 1.37222 0.542 2 51.2117 14.56863 1.2877 NC volume 1 15073.983 4196.1761 396.5014 0.007* 2 13714.433 3723.322 316.9502 N volume 1 8663.713 2617.7458 247.3537 0.161 2 8250.653 2030.6094 172.857 O volume 1 13832.202 6757.9936 638.5704 0.000* 2 10878.828 4253.3989 362.0734 NC coronal area 1 222.729 48.3774 4.5712 0.000* 2 197.88 43.4939 3.7024 N coronal area 1 332.813 100.0927 9.4579 0.053 2 308.866 93.4957 7.9879 N axial area 1 559.962 143.4633 13.556 0.201 2 537.049 137.9316 11.7415 N sagittal area 1 307.804 98.485 9.306 0.617 2 301.699 93.9335 7.9962 N linear measure 1 20.956 4.3952 0.4153 0.939 2 20.995 3.6062 0.3081 O axial area 1 307.537 161.0091 15.2139 0.000* 2 226.382 116.1836 9.8902 O sagittal area 1 565.166 183.3113 17.3213 0.000* 2 448.568 129.2783 11.0049 O minim area 1 150.056 107.6576 10.1727 0.316 2 138.073 73.0668 6.2199 O linear measure 1 13.99 5.1266 0.4844 0.000* 2 11.143 3.823 0.3254 Soft palate length 1 46.061 4.7931 0.4529 0.000* 2 41.613 4.988 0.4246 Soft palate width 1 9.869 1.9573 0.1849 0.000* 2 8.776 1.559 0.1327 Soft palate sagittal area 1 352.866 69.8563 6.6008 0.000* 2 273.739 55.8739 4.7563 Total volume 1 36659.026 8336.4822 798.4902 0.000* 2 32843.914 7019.708 597.5572 *Student’s t-test (P < 0.05). View Large Table 3 indicates the correlation between linear and area findings with corresponding volume measurements through different multiplanar reconstructions and three-dimensional images. In general, the measurements studied presented positive correlation. The highest positive correlations could be observed in both oropharynx and nasopharynx sagittal areas and their respective volume (range from 0.734 to 0.893), as well in the most constricted area in the oropharynx (0.899 and 0.811 for male and female, respectively). 2D measures in soft palate did not exhibit correlation with volume; however, they presented some correlation with age. On this issue, nasopharynx coronal and sagittal area presented positive correlations with age, as well as NC and N volume. Oropharynx sagittal area, for male, presented negative correlation with age. Table 3. Pearson correlation coefficient for the measurements analyzed on multiplanar and 3-dimensional reconstructions (n = 250). N, nasopharynx; NC, nasal cavity; O, oropharynx. Gender 1 = male and 2 = female. Gender Age Nasal cavity volume Nasopharynx volume Oropharynx volume Total volume NC coronal area 1 −0.080 0.457** 0.229* 2 0.057 0.499** 0.330** N coronal area 1 0.212* 0.642** 0.408** 0.562** 2 0.176* 0.654** 0.544** 0.544** N axial area 1 0.096 0.662** 0.580** 2 −0.062 0.452** 0.430** N sagittal area 1 0.227* 0.796** 0.329** 2 0.200* 0.734** 0.227** N linear measure 1 0.035 0.451** 0.446** 0.368** 2 0.023 0.329** 0.237** 0.260** O axial area 1 0.064 0.740** 0.562** 2 0.133 0.551** 0.446** O sagittal area 1 −0.250* 0.877** 0.567** 2 −0.072 0.893** 0.611** O minimum area 1 −0.155 0.411** 0.899** 0.664** 2 −0.045 0.176* 0.811** 0.606** O linear measure 1 −0.084 0.609** 0.433** 2 0.145 0.453** 0.337** Soft palate length 1 0.389** −0.017 0.125 2 0.470** −0.190* 0.042 Soft palate width 1 0.183 −0.082 −0.067 2 0.222* −0.113 −0.074 Soft palate sagittal area 1 0.329** −0.035 0.027 2 0.349** −0.065 0.094 NC Volume 1 0.252** 0.635** 2 0.257** 0.734** N Volume 1 0.237* 0.631** 2 0.251** 0.582** O Volume 1 −0.058 0.766** 2 −0.049 0.730** Gender Age Nasal cavity volume Nasopharynx volume Oropharynx volume Total volume NC coronal area 1 −0.080 0.457** 0.229* 2 0.057 0.499** 0.330** N coronal area 1 0.212* 0.642** 0.408** 0.562** 2 0.176* 0.654** 0.544** 0.544** N axial area 1 0.096 0.662** 0.580** 2 −0.062 0.452** 0.430** N sagittal area 1 0.227* 0.796** 0.329** 2 0.200* 0.734** 0.227** N linear measure 1 0.035 0.451** 0.446** 0.368** 2 0.023 0.329** 0.237** 0.260** O axial area 1 0.064 0.740** 0.562** 2 0.133 0.551** 0.446** O sagittal area 1 −0.250* 0.877** 0.567** 2 −0.072 0.893** 0.611** O minimum area 1 −0.155 0.411** 0.899** 0.664** 2 −0.045 0.176* 0.811** 0.606** O linear measure 1 −0.084 0.609** 0.433** 2 0.145 0.453** 0.337** Soft palate length 1 0.389** −0.017 0.125 2 0.470** −0.190* 0.042 Soft palate width 1 0.183 −0.082 −0.067 2 0.222* −0.113 −0.074 Soft palate sagittal area 1 0.329** −0.035 0.027 2 0.349** −0.065 0.094 NC Volume 1 0.252** 0.635** 2 0.257** 0.734** N Volume 1 0.237* 0.631** 2 0.251** 0.582** O Volume 1 −0.058 0.766** 2 −0.049 0.730** *Asterisks indicate correlation as tested under Pearson correlation coefficient (P < 0.05). **Asterisks indicate correlation as tested under Pearson correlation coefficient (P < 0.001). View Large Table 3. Pearson correlation coefficient for the measurements analyzed on multiplanar and 3-dimensional reconstructions (n = 250). N, nasopharynx; NC, nasal cavity; O, oropharynx. Gender 1 = male and 2 = female. Gender Age Nasal cavity volume Nasopharynx volume Oropharynx volume Total volume NC coronal area 1 −0.080 0.457** 0.229* 2 0.057 0.499** 0.330** N coronal area 1 0.212* 0.642** 0.408** 0.562** 2 0.176* 0.654** 0.544** 0.544** N axial area 1 0.096 0.662** 0.580** 2 −0.062 0.452** 0.430** N sagittal area 1 0.227* 0.796** 0.329** 2 0.200* 0.734** 0.227** N linear measure 1 0.035 0.451** 0.446** 0.368** 2 0.023 0.329** 0.237** 0.260** O axial area 1 0.064 0.740** 0.562** 2 0.133 0.551** 0.446** O sagittal area 1 −0.250* 0.877** 0.567** 2 −0.072 0.893** 0.611** O minimum area 1 −0.155 0.411** 0.899** 0.664** 2 −0.045 0.176* 0.811** 0.606** O linear measure 1 −0.084 0.609** 0.433** 2 0.145 0.453** 0.337** Soft palate length 1 0.389** −0.017 0.125 2 0.470** −0.190* 0.042 Soft palate width 1 0.183 −0.082 −0.067 2 0.222* −0.113 −0.074 Soft palate sagittal area 1 0.329** −0.035 0.027 2 0.349** −0.065 0.094 NC Volume 1 0.252** 0.635** 2 0.257** 0.734** N Volume 1 0.237* 0.631** 2 0.251** 0.582** O Volume 1 −0.058 0.766** 2 −0.049 0.730** Gender Age Nasal cavity volume Nasopharynx volume Oropharynx volume Total volume NC coronal area 1 −0.080 0.457** 0.229* 2 0.057 0.499** 0.330** N coronal area 1 0.212* 0.642** 0.408** 0.562** 2 0.176* 0.654** 0.544** 0.544** N axial area 1 0.096 0.662** 0.580** 2 −0.062 0.452** 0.430** N sagittal area 1 0.227* 0.796** 0.329** 2 0.200* 0.734** 0.227** N linear measure 1 0.035 0.451** 0.446** 0.368** 2 0.023 0.329** 0.237** 0.260** O axial area 1 0.064 0.740** 0.562** 2 0.133 0.551** 0.446** O sagittal area 1 −0.250* 0.877** 0.567** 2 −0.072 0.893** 0.611** O minimum area 1 −0.155 0.411** 0.899** 0.664** 2 −0.045 0.176* 0.811** 0.606** O linear measure 1 −0.084 0.609** 0.433** 2 0.145 0.453** 0.337** Soft palate length 1 0.389** −0.017 0.125 2 0.470** −0.190* 0.042 Soft palate width 1 0.183 −0.082 −0.067 2 0.222* −0.113 −0.074 Soft palate sagittal area 1 0.329** −0.035 0.027 2 0.349** −0.065 0.094 NC Volume 1 0.252** 0.635** 2 0.257** 0.734** N Volume 1 0.237* 0.631** 2 0.251** 0.582** O Volume 1 −0.058 0.766** 2 −0.049 0.730** *Asterisks indicate correlation as tested under Pearson correlation coefficient (P < 0.05). **Asterisks indicate correlation as tested under Pearson correlation coefficient (P < 0.001). View Large The linear regression model showed that, regardless of gender and age, an increment of one mm2 in the nasopharynx sagittal area indicates 18.41 mm3 increased in the nasopharynx volume (R2 = 57.84%). In the same way, 1 mm2 increased in the oropharynx sagittal area means 30.05 mm3 in the volume of the oropharynx (R2 = 78.83%). For the most constricted area, an increase of 1 mm2 represents 64.43 mm3 extra in the whole volume (R2 = 50.54%; Table 4). Table 4. Linear regression model analyzing the greater correlated variables for each airway compartment (P < 0.05). Variable Estimated coefficient Std. error R2 Total volume  Intercept 20944.95 1919.48 0.5054  Gender* −4080.35 748.19  Age 135.42 26.15  Minimum area 64.43 4.65 Oropharynx volume  Intercept −3072.63 528.15 0.7883  Oropharynx sagittal area 30.5 1.00 Nasopharynx volume  Intercept 2832.02 317.31 0.5784  Nasopharynx sagittal area 18.41 0.99 Variable Estimated coefficient Std. error R2 Total volume  Intercept 20944.95 1919.48 0.5054  Gender* −4080.35 748.19  Age 135.42 26.15  Minimum area 64.43 4.65 Oropharynx volume  Intercept −3072.63 528.15 0.7883  Oropharynx sagittal area 30.5 1.00 Nasopharynx volume  Intercept 2832.02 317.31 0.5784  Nasopharynx sagittal area 18.41 0.99 *Female used as the basis for analysis. View Large Table 4. Linear regression model analyzing the greater correlated variables for each airway compartment (P < 0.05). Variable Estimated coefficient Std. error R2 Total volume  Intercept 20944.95 1919.48 0.5054  Gender* −4080.35 748.19  Age 135.42 26.15  Minimum area 64.43 4.65 Oropharynx volume  Intercept −3072.63 528.15 0.7883  Oropharynx sagittal area 30.5 1.00 Nasopharynx volume  Intercept 2832.02 317.31 0.5784  Nasopharynx sagittal area 18.41 0.99 Variable Estimated coefficient Std. error R2 Total volume  Intercept 20944.95 1919.48 0.5054  Gender* −4080.35 748.19  Age 135.42 26.15  Minimum area 64.43 4.65 Oropharynx volume  Intercept −3072.63 528.15 0.7883  Oropharynx sagittal area 30.5 1.00 Nasopharynx volume  Intercept 2832.02 317.31 0.5784  Nasopharynx sagittal area 18.41 0.99 *Female used as the basis for analysis. View Large Discussion This research evaluated multiplanar CBCT scans and its performance in the analysis of the airway region. Several studies proposed to assess the airway space using CBCT scans (18–22). CBCT acquisition protocols and software segmentation may interfere on the volume measurements (15). Weissheimer and colleagues (23) compared the precision and accuracy of six imaging software for measuring upper airway volumes in CBCT and concluded that all programs were reliable but had errors in the volume segmentations of the oropharynx. Some advantages of Dolphin Software were highlighted by the authors: user friendly, quick upper airway segmentation, good segmentation sensitivity, segmentation can be checked in 2D slices, and minimal cross-sectional area analysis. On the other hand, de Water et al. (24) suggest that the airway analysis tool of Dolphin 3D is not accurate or reliable enough to be used for airway evaluation in osteotomy evaluation. In fact, as commented by the previous authors (23), Dolphin 3D software uses a threshold sensitivity value tool to determine the airway space, which is examiner-dependent, and should be further evaluated. This limitation was overcome in the present study by trained and calibrated examiner. A study investigating linear and area measurements performed on CBCT images compared to lateral cephalograms showed a positive correlation to the respective areas in the axial plane (21). The results of this study corroborate the previous findings and also exhibited positive correlation values for volumes in the nasopharynx (19) and oropharynx sagittal areas. Moreover, the most constricted area in the oropharynx, that means the narrowest air passage, proved to be an important measurement when correlating with airway volume. Cephalometric radiographs have been widely used for airway assessment, providing sufficient information for patient’s initial diagnosis (25, 26). Considering the similarity between two-dimensional sagittal view and a lateral radiograph, the present study corroborates this information, and possibly the sagittal area remains as the most applicable measure correlated with the airway volume. On the other hand, linear measurements showed moderate correlation with the volume. The length, width, and area of soft palate were also analyzed, since it could play a role in the final airway volume calculation. Shigeta et al.(27) evaluating OSA and control subjects concluded that OSA patients had a longer soft palate in proportion to their oropharyngeal airway. This study did not show correlation between the soft palate dimensions in sagittal view and the airway volume, suggesting that soft tissue boundaries are not suitable to predict changes in airway volumes. On the other hand, it was observed correlation with age, suggesting that an increase of age means an expansion in borders of soft palate. As expected by the growth, age influenced nasopharynx coronal and sagittal areas, as well as the nasal cavity and nasopharynx volumes (28). The breathing is a dynamic process while the CBCT is a static exam. Consequently, some attentions regarding airway-imaging evaluation have to be addressed (29). Some authors claim that changing body position may influence the results (29–32) and consequently the data understanding, especially for OSA diagnosis. During the CBCT acquisitions of the present study, the patients were positioned sited, resulting in an upright representation of the airway space. Camacho et al. (31), evaluating OSA patients, found that the airway space reduction ranged from 32.3 to 75.9% when patients were in a supine position compared with an upright position and this may be an important issue for OSA patients’ evaluation. However, even this study did not have clinical information about the patients and the results maintain an important application for general CBCT exams assessment since the proposal was to evaluate the improvement with this analysis for the airway. In this view, the sagittal and the most constricted area in oropharynx seems to remain the most important measurement to understand the oropharynx collapses. CBCT scans have been introduced for orthodontic patients, but excluding selected clinical conditions, up to now there is no substantial evidence indicating CBCT scans to general orthodontic patients (16, 17, 33). The results of this study corroborate the literature findings and support the use of 2D images (in this study the midsagittal CBCT slice) instead of taking CBCT scans for airway assessment. Sagittal areas measured on 2D images remain as a useful guide about the corresponding airway volume, which could also be achieved with a two-dimensional image. If the CBCT scan is available, the most constricted area showed substantial correlation with the airway volume. However, more studies evaluating different groups of breathing or apnea patients should be performed to analyze the CBCT efficacy for diagnosis thinking and therapeutic processes. Conclusion Nasopharynx and oropharynx sagittal areas, as well as the most constricted axial area in oropharynx are the most 2D-correlated measurements to the volume when evaluating upper airway measurements. Conflict of Interest None to declare. References 1. McNamara , J.A . ( 1981 ) Influence of respiratory pattern on craniofacial growth . The Angle Orthodontist , 51 , 269 – 300 . Google Scholar PubMed 2. Broadbent B.H . ( 1931 ) A new X-ray technique and its application to Orthodontia . The Angle Orthodontist , 51 , 93 – 114 . 3. Armalaite , J. and Lopatiene , K . ( 2016 ) Lateral teleradiography of the head as a diagnostic tool used to predict obstructive sleep apnea . 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( 2006 ) Assessment of lateral cephalometric diagnosis of adenoid hypertrophy and posterior upper airway obstruction: a systematic review . American Journal of Orthodontics and Dentofacial Orthopedics , 130 , 700 – 708 . Google Scholar CrossRef Search ADS PubMed 27. Shigeta , Y. , Ogawa , T. , Tomoko , I. , Clark , G.T. and Enciso , R . ( 2010 ) Soft palate length and upper airway relationship in OSA and non-OSA subjects . Sleep and Breathing , 14 , 353 – 358 . Google Scholar CrossRef Search ADS PubMed 28. Mayer , P. , Pépin , J.L. , Bettega , G. , Veale , D. , Ferretti , G. , Deschaux , C. and Lévy , P . ( 1996 ) Relationship between body mass index, age and upper airway measurements in snorers and sleep apnoea patients . The European Respiratory Journal , 9 , 1801 – 1809 . Google Scholar CrossRef Search ADS PubMed 29. Zhang , J. , Chen , G. , Li , W. , Xu , T. and Gao X . ( 2015 ) Upper airway changes after orthodontic extraction treatment in adults: a preliminary study using cone beam computed tomography . PLoS ONE , 10 , e0143233 . Google Scholar CrossRef Search ADS PubMed 30. Ogawa , T. , Enciso , R. , Shintaku , W.H. and Clark , G.T . ( 2007 ) Evaluation of cross-section airway configuration of obstructive sleep apnea . Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontics , 103 , 102 – 108 . Google Scholar CrossRef Search ADS PubMed 31. Camacho , M. , Capasso , R. and Schendel , S . ( 2014 ) Airway changes in obstructive sleep apnoea patients associated with a supine versus an upright position examined using cone beam computed tomography . The Journal of Laryngology and Otology , 128 , 824 – 830 . Google Scholar CrossRef Search ADS PubMed 32. Battagel , J.M. , Johal , A. , Smith , A.M. and Kotecha , B . ( 2002 ) Postural variation in oropharyngeal dimensions in subjects with sleep disordered breathing: a cephalometric study . European Journal of Orthodontics , 24 , 263 – 276 . Google Scholar CrossRef Search ADS PubMed 33. Horner , K. , O’Malley , L. , Taylor , K. and Glenny , A.M . ( 2015 ) Guidelines for clinical use of CBCT: a review . Dento Maxillo Facial Radiology , 44 , 20140225 . Google Scholar CrossRef Search ADS PubMed © The Author(s) 2017. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: journals.permissions@oup.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The European Journal of Orthodontics Oxford University Press

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Abstract

Summary Objectives No consensus exists on the assessment of airway in CBCT scans. Two-dimensional measures remain the standard in the cephalometric analysis. This research aimed to evaluate linear and area measurements in two-dimensional views from specific airway regions of interest and compare these to the correspondent volume in CBCT exams. Materials and Methods 250-selected CBCT scans were retrospectively analyzed. A trained and calibrated examiner performed the linear, area and volume measurements in specific sites for nasal cavity, nasopharynx and oropharynx compartments. Dolphin Software was used for the analysis. The correlations were performed using Pearson coefficient. Results The highest positive correlations were observed in the nasopharynx and oropharynx sagittal areas and the most constricted area in the oropharynx. Nasopharynx linear measures and nasopharynx coronal area did not present correlation with whole volume. Two-dimensional measurements in the soft palate (width and sagittal area) showed very low positive correlations. Although nasal cavity presented highest volume means, changes in oropharynx contributed more to variations in total volume, compared with the other two sections. Conclusion Airway sagittal areas, as well as the most constricted axial area in oropharynx remains a useful guide to correlate with airway volume in two-dimensional images. Introduction The obstruction of airway space can alter normal breathing, which can have a significant impact on the development and stability of craniofacial structures (1). Since airway space disorders can affect the patient condition and could influence orthodontic outcomes, the diagnosis, and treatment needs dentists’ attention and should be reported by the radiologist. Therefore, a diagnostic method that provides accurate data is a valuable tool in digital imaging science. Cephalometric analyses are usually the diagnostic instrument in Orthodontics (2–4). Although the conventional lateral cephalogram was reported to be inexpensive, and simple to perform, this two-dimensional imaging modality seems to have limitations (5, 6), especially to represent three-dimensional structures. The development of cone-beam computed tomography (CBCT) allowed a detailed multiplanar analysis of the dentomaxillofacial complex (7–9). Some studies suggested limitations of a 2D-airway analysis, such as Lenza et al. (10), which evaluated 34 patients and showed a weak correlation (r < 0.8) between most of the 2D and 3D measurements. Evaluating obstructive sleep apnea (OSA) patients, Alsufyani concludes that there is insufficient literature to the use of CBCT to assess treatment outcomes and high-quality evidence level studies are needed to determine if CBCT airway dimensional changes are suitable for assessment of treatment outcome (11). Nevertheless, when a CBCT is taken, the accuracy and reliability of craniofacial measurements were shown to be better, compared to 2D lateral cephalograms (7, 8, 12–16), even though sometimes clinically inconsiderable. According to SEDENTEXCT (17), CBCT scans should not be appointed as a routine method in orthodontic patients, but should still be used on particular indications. Regarding airway evaluation, there is still no consensus whether the airway volume calculated on CBCT images gives a better indication of the airway function compared to measurements performed on two-dimensional images (6, 11, 13, 17), Therefore, this research aims to evaluate linear and area measurements in two-dimensional views from specific airway regions of interest and compare these to the correspondent volume in CBCT exams, suggesting 2D surrogate measurements for the 3D volume analysis. Methods The Ethics Research Committee approved the project (number 25300). This investigation is a retrospective study, so all patients were scanned according to standard clinical indications. The sample size was estimated considering an intermediate correlation (0.4), α error of 0.05 and β of 0.2 (a power test of 80%), and a dropout of 10%, totaling 267 scans. The CBCT scans were randomly collected from the Oral Radiology Section database. The inclusion criteria were CBCT scans acquired with the same exposure protocols (i-CAT device [Imaging Sciences International, Hatfield, Pennsylvania], large field of view [FOV], 120 kVp, scan time 26.9 s, 0.2 mm voxel size). Seventeen scans were excluded because FOV did not cover whole upper airway, comprising a total of 250 (138 female, 112 male, mean age of 50.6) evaluated. CBCT image sequences were exported in DICOM format and opened on the same computer (Intel core i7 3GHz processor, LG Flatron E2250 display, 21 inches, 32 bits) using Dolphin software version 13.8 (Dolphin Imaging & Management Solutions; Chatsworth, California). The measurements were made by a trained and calibrated examiner (LSM) under the same viewing conditions in a room with reduced light. The calibration process was performed by two examiners (LSM and MBV), starting with a training and discussion about the standardization, airway tool sensitivity, and measurements. Next, 25 scans were randomly selected from the database, and each examiner completed all measurements twice, with an interval of two weeks. Intra- and inter-examiner intraclass correlation coefficient was calculated, and values >0.9 were achieved for all evaluated measurements. The reproducibility was guaranteed repeating these same scans during the study analysis. Before the measurements, the patient’s skull was oriented according to the anatomical planes. The contrast of the images was adjusted by the examiner to better fit soft tissue visualization. Subsequently, the ‘airway space’ tool was accessed and the borders of the nasal cavity, nasopharynx, and oropharynx were defined. The airway sensitivity was established according to the examiner visual choice, aiming that only airspace was included, and then the volume was calculated. For the sagittal area in nasopharynx and oropharynx, the values were collected in the midsagittal plane (based on anterior and posterior nasal spine) and for axial and coronal planes in particular points explained in Figure 1 and 2. The limits of the nasal cavity, nasopharynx, and oropharynx are described in Table 1. Figure 1. View largeDownload slide The standard head position (sagittal plane), and the airway compartment borders and corresponding area and volume measurements evaluated. 1 = NC coronal area; 2 = N coronal area; 3 = N linear measure and N axial area; 4 = O linear measure and O axial area. The areas located at the sagittal standard image correspond to the correspondent compartment coronal area. ANS, anterior nasal spine; PNS, posterior nasal spine. Figure 1. View largeDownload slide The standard head position (sagittal plane), and the airway compartment borders and corresponding area and volume measurements evaluated. 1 = NC coronal area; 2 = N coronal area; 3 = N linear measure and N axial area; 4 = O linear measure and O axial area. The areas located at the sagittal standard image correspond to the correspondent compartment coronal area. ANS, anterior nasal spine; PNS, posterior nasal spine. Figure 2. View largeDownload slide Illustration of minimum cross-sectional area (a) and measurements for oropharynx and soft palate in sagittal plane (b, c). Figure 2. View largeDownload slide Illustration of minimum cross-sectional area (a) and measurements for oropharynx and soft palate in sagittal plane (b, c). Table 1. Anatomical borders of the upper airway, as well as the multiplanar measurements evaluated in this study. ANS, anterior nasal spine; PNS, posterior nasal spine. Standard head position Coronal plane: right and left infraorbital foramen parallel to the ground Sagittal plane: palatal plane (ANS-PNS) parallel to the ground Axial plane: palatal plane (ANS-PNS) vertical line, perpendicular to the ground Nasal cavity Anterior limit: ANS line through up to nasal bone (in coronal plane reported as nasal cavity coronal area) Posterior limit: PNS line through up to skull basis Nasopharynx Anterior limit: ≅posterior limit of the nasal cavity (in coronal plane reported as nasopharynx coronal area) Inferior limit: PNS line extended to the pharynx’s posterior wall, correspondent to nasopharynx linear measure (in axial plane reported as nasopharynx axial area) Oropharynx Superior limit: ≅inferior limit of the nasopharynx Inferior limit: horizontal line through the superior point of the epiglottis, correspondent to oropharynx linear measure (in axial plane reported as oropharynx axial area) Standard head position Coronal plane: right and left infraorbital foramen parallel to the ground Sagittal plane: palatal plane (ANS-PNS) parallel to the ground Axial plane: palatal plane (ANS-PNS) vertical line, perpendicular to the ground Nasal cavity Anterior limit: ANS line through up to nasal bone (in coronal plane reported as nasal cavity coronal area) Posterior limit: PNS line through up to skull basis Nasopharynx Anterior limit: ≅posterior limit of the nasal cavity (in coronal plane reported as nasopharynx coronal area) Inferior limit: PNS line extended to the pharynx’s posterior wall, correspondent to nasopharynx linear measure (in axial plane reported as nasopharynx axial area) Oropharynx Superior limit: ≅inferior limit of the nasopharynx Inferior limit: horizontal line through the superior point of the epiglottis, correspondent to oropharynx linear measure (in axial plane reported as oropharynx axial area) View Large Table 1. Anatomical borders of the upper airway, as well as the multiplanar measurements evaluated in this study. ANS, anterior nasal spine; PNS, posterior nasal spine. Standard head position Coronal plane: right and left infraorbital foramen parallel to the ground Sagittal plane: palatal plane (ANS-PNS) parallel to the ground Axial plane: palatal plane (ANS-PNS) vertical line, perpendicular to the ground Nasal cavity Anterior limit: ANS line through up to nasal bone (in coronal plane reported as nasal cavity coronal area) Posterior limit: PNS line through up to skull basis Nasopharynx Anterior limit: ≅posterior limit of the nasal cavity (in coronal plane reported as nasopharynx coronal area) Inferior limit: PNS line extended to the pharynx’s posterior wall, correspondent to nasopharynx linear measure (in axial plane reported as nasopharynx axial area) Oropharynx Superior limit: ≅inferior limit of the nasopharynx Inferior limit: horizontal line through the superior point of the epiglottis, correspondent to oropharynx linear measure (in axial plane reported as oropharynx axial area) Standard head position Coronal plane: right and left infraorbital foramen parallel to the ground Sagittal plane: palatal plane (ANS-PNS) parallel to the ground Axial plane: palatal plane (ANS-PNS) vertical line, perpendicular to the ground Nasal cavity Anterior limit: ANS line through up to nasal bone (in coronal plane reported as nasal cavity coronal area) Posterior limit: PNS line through up to skull basis Nasopharynx Anterior limit: ≅posterior limit of the nasal cavity (in coronal plane reported as nasopharynx coronal area) Inferior limit: PNS line extended to the pharynx’s posterior wall, correspondent to nasopharynx linear measure (in axial plane reported as nasopharynx axial area) Oropharynx Superior limit: ≅inferior limit of the nasopharynx Inferior limit: horizontal line through the superior point of the epiglottis, correspondent to oropharynx linear measure (in axial plane reported as oropharynx axial area) View Large SPSS software (version 17.0; SPSS, Chicago, Illinois) was used for data analysis. Differences between gender for linear, area, and volume measurements were checked using Student’s t-test (P < 0.05). The Pearson correlation coefficient (r) was used to evaluate linear relationship degree among linear, area, and volume values from CBCT scans. This coefficient ranges from −1 to +1 and values close to 0 (zero) means that there is no linear relationship, the value of +1 indicates a perfect linear relationship and the value −1 also indicates a perfect inverse linear relationship. Scores closer to +1 or −1 suggest a stronger association between the variables. The levels of statistical significance were P <0.05. Multiple linear regression was performed using the area measurements that have had greater correlation with the volumes. Results Table 2 shows the mean values for linear, area, and volume measurements from upper airway regarding gender. Nasal cavity (NC) and oropharynx (O) presented statistical differences between genders. Furthermore, excluding O minimum area, all sites analyzed in NC, O, and soft palate presented differences with male showing higher values. Otherwise, no gender differences were observed in nasopharynx (N) volume, areas, and linear measures. Table 2. Mean values, standard deviation, standard error, and P value for age, linear, area, and volume measurements from upper airway considering gender (n = 250). N, nasopharynx; NC, nasal cavity; O, oropharynx. Gender: 1 = male 2 = female. Means of volume presented in mm3, area in mm2, and linear in mm (millimeter). Variable Gender Mean Std. deviation Std. error mean P value Age 1 50.0568 13.99393 1.37222 0.542 2 51.2117 14.56863 1.2877 NC volume 1 15073.983 4196.1761 396.5014 0.007* 2 13714.433 3723.322 316.9502 N volume 1 8663.713 2617.7458 247.3537 0.161 2 8250.653 2030.6094 172.857 O volume 1 13832.202 6757.9936 638.5704 0.000* 2 10878.828 4253.3989 362.0734 NC coronal area 1 222.729 48.3774 4.5712 0.000* 2 197.88 43.4939 3.7024 N coronal area 1 332.813 100.0927 9.4579 0.053 2 308.866 93.4957 7.9879 N axial area 1 559.962 143.4633 13.556 0.201 2 537.049 137.9316 11.7415 N sagittal area 1 307.804 98.485 9.306 0.617 2 301.699 93.9335 7.9962 N linear measure 1 20.956 4.3952 0.4153 0.939 2 20.995 3.6062 0.3081 O axial area 1 307.537 161.0091 15.2139 0.000* 2 226.382 116.1836 9.8902 O sagittal area 1 565.166 183.3113 17.3213 0.000* 2 448.568 129.2783 11.0049 O minim area 1 150.056 107.6576 10.1727 0.316 2 138.073 73.0668 6.2199 O linear measure 1 13.99 5.1266 0.4844 0.000* 2 11.143 3.823 0.3254 Soft palate length 1 46.061 4.7931 0.4529 0.000* 2 41.613 4.988 0.4246 Soft palate width 1 9.869 1.9573 0.1849 0.000* 2 8.776 1.559 0.1327 Soft palate sagittal area 1 352.866 69.8563 6.6008 0.000* 2 273.739 55.8739 4.7563 Total volume 1 36659.026 8336.4822 798.4902 0.000* 2 32843.914 7019.708 597.5572 Variable Gender Mean Std. deviation Std. error mean P value Age 1 50.0568 13.99393 1.37222 0.542 2 51.2117 14.56863 1.2877 NC volume 1 15073.983 4196.1761 396.5014 0.007* 2 13714.433 3723.322 316.9502 N volume 1 8663.713 2617.7458 247.3537 0.161 2 8250.653 2030.6094 172.857 O volume 1 13832.202 6757.9936 638.5704 0.000* 2 10878.828 4253.3989 362.0734 NC coronal area 1 222.729 48.3774 4.5712 0.000* 2 197.88 43.4939 3.7024 N coronal area 1 332.813 100.0927 9.4579 0.053 2 308.866 93.4957 7.9879 N axial area 1 559.962 143.4633 13.556 0.201 2 537.049 137.9316 11.7415 N sagittal area 1 307.804 98.485 9.306 0.617 2 301.699 93.9335 7.9962 N linear measure 1 20.956 4.3952 0.4153 0.939 2 20.995 3.6062 0.3081 O axial area 1 307.537 161.0091 15.2139 0.000* 2 226.382 116.1836 9.8902 O sagittal area 1 565.166 183.3113 17.3213 0.000* 2 448.568 129.2783 11.0049 O minim area 1 150.056 107.6576 10.1727 0.316 2 138.073 73.0668 6.2199 O linear measure 1 13.99 5.1266 0.4844 0.000* 2 11.143 3.823 0.3254 Soft palate length 1 46.061 4.7931 0.4529 0.000* 2 41.613 4.988 0.4246 Soft palate width 1 9.869 1.9573 0.1849 0.000* 2 8.776 1.559 0.1327 Soft palate sagittal area 1 352.866 69.8563 6.6008 0.000* 2 273.739 55.8739 4.7563 Total volume 1 36659.026 8336.4822 798.4902 0.000* 2 32843.914 7019.708 597.5572 *Student’s t-test (P < 0.05). View Large Table 2. Mean values, standard deviation, standard error, and P value for age, linear, area, and volume measurements from upper airway considering gender (n = 250). N, nasopharynx; NC, nasal cavity; O, oropharynx. Gender: 1 = male 2 = female. Means of volume presented in mm3, area in mm2, and linear in mm (millimeter). Variable Gender Mean Std. deviation Std. error mean P value Age 1 50.0568 13.99393 1.37222 0.542 2 51.2117 14.56863 1.2877 NC volume 1 15073.983 4196.1761 396.5014 0.007* 2 13714.433 3723.322 316.9502 N volume 1 8663.713 2617.7458 247.3537 0.161 2 8250.653 2030.6094 172.857 O volume 1 13832.202 6757.9936 638.5704 0.000* 2 10878.828 4253.3989 362.0734 NC coronal area 1 222.729 48.3774 4.5712 0.000* 2 197.88 43.4939 3.7024 N coronal area 1 332.813 100.0927 9.4579 0.053 2 308.866 93.4957 7.9879 N axial area 1 559.962 143.4633 13.556 0.201 2 537.049 137.9316 11.7415 N sagittal area 1 307.804 98.485 9.306 0.617 2 301.699 93.9335 7.9962 N linear measure 1 20.956 4.3952 0.4153 0.939 2 20.995 3.6062 0.3081 O axial area 1 307.537 161.0091 15.2139 0.000* 2 226.382 116.1836 9.8902 O sagittal area 1 565.166 183.3113 17.3213 0.000* 2 448.568 129.2783 11.0049 O minim area 1 150.056 107.6576 10.1727 0.316 2 138.073 73.0668 6.2199 O linear measure 1 13.99 5.1266 0.4844 0.000* 2 11.143 3.823 0.3254 Soft palate length 1 46.061 4.7931 0.4529 0.000* 2 41.613 4.988 0.4246 Soft palate width 1 9.869 1.9573 0.1849 0.000* 2 8.776 1.559 0.1327 Soft palate sagittal area 1 352.866 69.8563 6.6008 0.000* 2 273.739 55.8739 4.7563 Total volume 1 36659.026 8336.4822 798.4902 0.000* 2 32843.914 7019.708 597.5572 Variable Gender Mean Std. deviation Std. error mean P value Age 1 50.0568 13.99393 1.37222 0.542 2 51.2117 14.56863 1.2877 NC volume 1 15073.983 4196.1761 396.5014 0.007* 2 13714.433 3723.322 316.9502 N volume 1 8663.713 2617.7458 247.3537 0.161 2 8250.653 2030.6094 172.857 O volume 1 13832.202 6757.9936 638.5704 0.000* 2 10878.828 4253.3989 362.0734 NC coronal area 1 222.729 48.3774 4.5712 0.000* 2 197.88 43.4939 3.7024 N coronal area 1 332.813 100.0927 9.4579 0.053 2 308.866 93.4957 7.9879 N axial area 1 559.962 143.4633 13.556 0.201 2 537.049 137.9316 11.7415 N sagittal area 1 307.804 98.485 9.306 0.617 2 301.699 93.9335 7.9962 N linear measure 1 20.956 4.3952 0.4153 0.939 2 20.995 3.6062 0.3081 O axial area 1 307.537 161.0091 15.2139 0.000* 2 226.382 116.1836 9.8902 O sagittal area 1 565.166 183.3113 17.3213 0.000* 2 448.568 129.2783 11.0049 O minim area 1 150.056 107.6576 10.1727 0.316 2 138.073 73.0668 6.2199 O linear measure 1 13.99 5.1266 0.4844 0.000* 2 11.143 3.823 0.3254 Soft palate length 1 46.061 4.7931 0.4529 0.000* 2 41.613 4.988 0.4246 Soft palate width 1 9.869 1.9573 0.1849 0.000* 2 8.776 1.559 0.1327 Soft palate sagittal area 1 352.866 69.8563 6.6008 0.000* 2 273.739 55.8739 4.7563 Total volume 1 36659.026 8336.4822 798.4902 0.000* 2 32843.914 7019.708 597.5572 *Student’s t-test (P < 0.05). View Large Table 3 indicates the correlation between linear and area findings with corresponding volume measurements through different multiplanar reconstructions and three-dimensional images. In general, the measurements studied presented positive correlation. The highest positive correlations could be observed in both oropharynx and nasopharynx sagittal areas and their respective volume (range from 0.734 to 0.893), as well in the most constricted area in the oropharynx (0.899 and 0.811 for male and female, respectively). 2D measures in soft palate did not exhibit correlation with volume; however, they presented some correlation with age. On this issue, nasopharynx coronal and sagittal area presented positive correlations with age, as well as NC and N volume. Oropharynx sagittal area, for male, presented negative correlation with age. Table 3. Pearson correlation coefficient for the measurements analyzed on multiplanar and 3-dimensional reconstructions (n = 250). N, nasopharynx; NC, nasal cavity; O, oropharynx. Gender 1 = male and 2 = female. Gender Age Nasal cavity volume Nasopharynx volume Oropharynx volume Total volume NC coronal area 1 −0.080 0.457** 0.229* 2 0.057 0.499** 0.330** N coronal area 1 0.212* 0.642** 0.408** 0.562** 2 0.176* 0.654** 0.544** 0.544** N axial area 1 0.096 0.662** 0.580** 2 −0.062 0.452** 0.430** N sagittal area 1 0.227* 0.796** 0.329** 2 0.200* 0.734** 0.227** N linear measure 1 0.035 0.451** 0.446** 0.368** 2 0.023 0.329** 0.237** 0.260** O axial area 1 0.064 0.740** 0.562** 2 0.133 0.551** 0.446** O sagittal area 1 −0.250* 0.877** 0.567** 2 −0.072 0.893** 0.611** O minimum area 1 −0.155 0.411** 0.899** 0.664** 2 −0.045 0.176* 0.811** 0.606** O linear measure 1 −0.084 0.609** 0.433** 2 0.145 0.453** 0.337** Soft palate length 1 0.389** −0.017 0.125 2 0.470** −0.190* 0.042 Soft palate width 1 0.183 −0.082 −0.067 2 0.222* −0.113 −0.074 Soft palate sagittal area 1 0.329** −0.035 0.027 2 0.349** −0.065 0.094 NC Volume 1 0.252** 0.635** 2 0.257** 0.734** N Volume 1 0.237* 0.631** 2 0.251** 0.582** O Volume 1 −0.058 0.766** 2 −0.049 0.730** Gender Age Nasal cavity volume Nasopharynx volume Oropharynx volume Total volume NC coronal area 1 −0.080 0.457** 0.229* 2 0.057 0.499** 0.330** N coronal area 1 0.212* 0.642** 0.408** 0.562** 2 0.176* 0.654** 0.544** 0.544** N axial area 1 0.096 0.662** 0.580** 2 −0.062 0.452** 0.430** N sagittal area 1 0.227* 0.796** 0.329** 2 0.200* 0.734** 0.227** N linear measure 1 0.035 0.451** 0.446** 0.368** 2 0.023 0.329** 0.237** 0.260** O axial area 1 0.064 0.740** 0.562** 2 0.133 0.551** 0.446** O sagittal area 1 −0.250* 0.877** 0.567** 2 −0.072 0.893** 0.611** O minimum area 1 −0.155 0.411** 0.899** 0.664** 2 −0.045 0.176* 0.811** 0.606** O linear measure 1 −0.084 0.609** 0.433** 2 0.145 0.453** 0.337** Soft palate length 1 0.389** −0.017 0.125 2 0.470** −0.190* 0.042 Soft palate width 1 0.183 −0.082 −0.067 2 0.222* −0.113 −0.074 Soft palate sagittal area 1 0.329** −0.035 0.027 2 0.349** −0.065 0.094 NC Volume 1 0.252** 0.635** 2 0.257** 0.734** N Volume 1 0.237* 0.631** 2 0.251** 0.582** O Volume 1 −0.058 0.766** 2 −0.049 0.730** *Asterisks indicate correlation as tested under Pearson correlation coefficient (P < 0.05). **Asterisks indicate correlation as tested under Pearson correlation coefficient (P < 0.001). View Large Table 3. Pearson correlation coefficient for the measurements analyzed on multiplanar and 3-dimensional reconstructions (n = 250). N, nasopharynx; NC, nasal cavity; O, oropharynx. Gender 1 = male and 2 = female. Gender Age Nasal cavity volume Nasopharynx volume Oropharynx volume Total volume NC coronal area 1 −0.080 0.457** 0.229* 2 0.057 0.499** 0.330** N coronal area 1 0.212* 0.642** 0.408** 0.562** 2 0.176* 0.654** 0.544** 0.544** N axial area 1 0.096 0.662** 0.580** 2 −0.062 0.452** 0.430** N sagittal area 1 0.227* 0.796** 0.329** 2 0.200* 0.734** 0.227** N linear measure 1 0.035 0.451** 0.446** 0.368** 2 0.023 0.329** 0.237** 0.260** O axial area 1 0.064 0.740** 0.562** 2 0.133 0.551** 0.446** O sagittal area 1 −0.250* 0.877** 0.567** 2 −0.072 0.893** 0.611** O minimum area 1 −0.155 0.411** 0.899** 0.664** 2 −0.045 0.176* 0.811** 0.606** O linear measure 1 −0.084 0.609** 0.433** 2 0.145 0.453** 0.337** Soft palate length 1 0.389** −0.017 0.125 2 0.470** −0.190* 0.042 Soft palate width 1 0.183 −0.082 −0.067 2 0.222* −0.113 −0.074 Soft palate sagittal area 1 0.329** −0.035 0.027 2 0.349** −0.065 0.094 NC Volume 1 0.252** 0.635** 2 0.257** 0.734** N Volume 1 0.237* 0.631** 2 0.251** 0.582** O Volume 1 −0.058 0.766** 2 −0.049 0.730** Gender Age Nasal cavity volume Nasopharynx volume Oropharynx volume Total volume NC coronal area 1 −0.080 0.457** 0.229* 2 0.057 0.499** 0.330** N coronal area 1 0.212* 0.642** 0.408** 0.562** 2 0.176* 0.654** 0.544** 0.544** N axial area 1 0.096 0.662** 0.580** 2 −0.062 0.452** 0.430** N sagittal area 1 0.227* 0.796** 0.329** 2 0.200* 0.734** 0.227** N linear measure 1 0.035 0.451** 0.446** 0.368** 2 0.023 0.329** 0.237** 0.260** O axial area 1 0.064 0.740** 0.562** 2 0.133 0.551** 0.446** O sagittal area 1 −0.250* 0.877** 0.567** 2 −0.072 0.893** 0.611** O minimum area 1 −0.155 0.411** 0.899** 0.664** 2 −0.045 0.176* 0.811** 0.606** O linear measure 1 −0.084 0.609** 0.433** 2 0.145 0.453** 0.337** Soft palate length 1 0.389** −0.017 0.125 2 0.470** −0.190* 0.042 Soft palate width 1 0.183 −0.082 −0.067 2 0.222* −0.113 −0.074 Soft palate sagittal area 1 0.329** −0.035 0.027 2 0.349** −0.065 0.094 NC Volume 1 0.252** 0.635** 2 0.257** 0.734** N Volume 1 0.237* 0.631** 2 0.251** 0.582** O Volume 1 −0.058 0.766** 2 −0.049 0.730** *Asterisks indicate correlation as tested under Pearson correlation coefficient (P < 0.05). **Asterisks indicate correlation as tested under Pearson correlation coefficient (P < 0.001). View Large The linear regression model showed that, regardless of gender and age, an increment of one mm2 in the nasopharynx sagittal area indicates 18.41 mm3 increased in the nasopharynx volume (R2 = 57.84%). In the same way, 1 mm2 increased in the oropharynx sagittal area means 30.05 mm3 in the volume of the oropharynx (R2 = 78.83%). For the most constricted area, an increase of 1 mm2 represents 64.43 mm3 extra in the whole volume (R2 = 50.54%; Table 4). Table 4. Linear regression model analyzing the greater correlated variables for each airway compartment (P < 0.05). Variable Estimated coefficient Std. error R2 Total volume  Intercept 20944.95 1919.48 0.5054  Gender* −4080.35 748.19  Age 135.42 26.15  Minimum area 64.43 4.65 Oropharynx volume  Intercept −3072.63 528.15 0.7883  Oropharynx sagittal area 30.5 1.00 Nasopharynx volume  Intercept 2832.02 317.31 0.5784  Nasopharynx sagittal area 18.41 0.99 Variable Estimated coefficient Std. error R2 Total volume  Intercept 20944.95 1919.48 0.5054  Gender* −4080.35 748.19  Age 135.42 26.15  Minimum area 64.43 4.65 Oropharynx volume  Intercept −3072.63 528.15 0.7883  Oropharynx sagittal area 30.5 1.00 Nasopharynx volume  Intercept 2832.02 317.31 0.5784  Nasopharynx sagittal area 18.41 0.99 *Female used as the basis for analysis. View Large Table 4. Linear regression model analyzing the greater correlated variables for each airway compartment (P < 0.05). Variable Estimated coefficient Std. error R2 Total volume  Intercept 20944.95 1919.48 0.5054  Gender* −4080.35 748.19  Age 135.42 26.15  Minimum area 64.43 4.65 Oropharynx volume  Intercept −3072.63 528.15 0.7883  Oropharynx sagittal area 30.5 1.00 Nasopharynx volume  Intercept 2832.02 317.31 0.5784  Nasopharynx sagittal area 18.41 0.99 Variable Estimated coefficient Std. error R2 Total volume  Intercept 20944.95 1919.48 0.5054  Gender* −4080.35 748.19  Age 135.42 26.15  Minimum area 64.43 4.65 Oropharynx volume  Intercept −3072.63 528.15 0.7883  Oropharynx sagittal area 30.5 1.00 Nasopharynx volume  Intercept 2832.02 317.31 0.5784  Nasopharynx sagittal area 18.41 0.99 *Female used as the basis for analysis. View Large Discussion This research evaluated multiplanar CBCT scans and its performance in the analysis of the airway region. Several studies proposed to assess the airway space using CBCT scans (18–22). CBCT acquisition protocols and software segmentation may interfere on the volume measurements (15). Weissheimer and colleagues (23) compared the precision and accuracy of six imaging software for measuring upper airway volumes in CBCT and concluded that all programs were reliable but had errors in the volume segmentations of the oropharynx. Some advantages of Dolphin Software were highlighted by the authors: user friendly, quick upper airway segmentation, good segmentation sensitivity, segmentation can be checked in 2D slices, and minimal cross-sectional area analysis. On the other hand, de Water et al. (24) suggest that the airway analysis tool of Dolphin 3D is not accurate or reliable enough to be used for airway evaluation in osteotomy evaluation. In fact, as commented by the previous authors (23), Dolphin 3D software uses a threshold sensitivity value tool to determine the airway space, which is examiner-dependent, and should be further evaluated. This limitation was overcome in the present study by trained and calibrated examiner. A study investigating linear and area measurements performed on CBCT images compared to lateral cephalograms showed a positive correlation to the respective areas in the axial plane (21). The results of this study corroborate the previous findings and also exhibited positive correlation values for volumes in the nasopharynx (19) and oropharynx sagittal areas. Moreover, the most constricted area in the oropharynx, that means the narrowest air passage, proved to be an important measurement when correlating with airway volume. Cephalometric radiographs have been widely used for airway assessment, providing sufficient information for patient’s initial diagnosis (25, 26). Considering the similarity between two-dimensional sagittal view and a lateral radiograph, the present study corroborates this information, and possibly the sagittal area remains as the most applicable measure correlated with the airway volume. On the other hand, linear measurements showed moderate correlation with the volume. The length, width, and area of soft palate were also analyzed, since it could play a role in the final airway volume calculation. Shigeta et al.(27) evaluating OSA and control subjects concluded that OSA patients had a longer soft palate in proportion to their oropharyngeal airway. This study did not show correlation between the soft palate dimensions in sagittal view and the airway volume, suggesting that soft tissue boundaries are not suitable to predict changes in airway volumes. On the other hand, it was observed correlation with age, suggesting that an increase of age means an expansion in borders of soft palate. As expected by the growth, age influenced nasopharynx coronal and sagittal areas, as well as the nasal cavity and nasopharynx volumes (28). The breathing is a dynamic process while the CBCT is a static exam. Consequently, some attentions regarding airway-imaging evaluation have to be addressed (29). Some authors claim that changing body position may influence the results (29–32) and consequently the data understanding, especially for OSA diagnosis. During the CBCT acquisitions of the present study, the patients were positioned sited, resulting in an upright representation of the airway space. Camacho et al. (31), evaluating OSA patients, found that the airway space reduction ranged from 32.3 to 75.9% when patients were in a supine position compared with an upright position and this may be an important issue for OSA patients’ evaluation. However, even this study did not have clinical information about the patients and the results maintain an important application for general CBCT exams assessment since the proposal was to evaluate the improvement with this analysis for the airway. In this view, the sagittal and the most constricted area in oropharynx seems to remain the most important measurement to understand the oropharynx collapses. CBCT scans have been introduced for orthodontic patients, but excluding selected clinical conditions, up to now there is no substantial evidence indicating CBCT scans to general orthodontic patients (16, 17, 33). The results of this study corroborate the literature findings and support the use of 2D images (in this study the midsagittal CBCT slice) instead of taking CBCT scans for airway assessment. Sagittal areas measured on 2D images remain as a useful guide about the corresponding airway volume, which could also be achieved with a two-dimensional image. 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The European Journal of OrthodonticsOxford University Press

Published: Sep 23, 2017

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