Introduction
Class II functional appliances are widely used to treat skeletal Class II malocclusion in growing patients, whereas molar distalization is often employed for dental Class II malocclusion. However, the impact of these treatment modalities on upper airway dimensions remains controversial. This study examines the effects of Herbst appliance treatments on the upper airway changes compared with the Pendex appliance in adolescent patients with Class II malocclusion.
Methods
Cone-beam computed tomography (CBCT) scans of 50 patients with Class II malocclusion were obtained from a private orthodontic office (Chalfont, Pa). Twenty-five patients were treated with Herbst appliances (12.16 ± 1.89 years; 13 males and 12 females) and 25 patients with Pendex appliances (11.72 ± 1.22 years; 12 males and 13 females). Measurements were taken for volume, length, and cross-sectional areas of the total, retropalatal, and retroglossal upper airway. CBCTs were taken at baseline (T1), after appliance removal (T2), and from final records after fixed edgewise appliance treatment (T3) (T1-T3: 41.11 ± 9.95 months for Herbst appliances and 44.81 ± 9.63 months for Pendex appliances). In addition to 3-dimensional CBCT analysis, 2-dimensional measurements were performed and compared with a Class II untreated control group comprising 25 age- and sex-matched patients from the American Association of Orthodontists Foundation Bolton-Brush Craniofacial Growth Legacy Collection. Differences across time points within groups were assessed using repeated-measures analysis of variance test, whereas between-group differences at individual time points and for changes from T1 to T3 were evaluated using independent-samples t tests adjusted for baseline (T1) outcome values and follow-up duration.
Results
From T1 to T3, both the Herbst and Pendex groups showed a significant increase in total upper airway volume and length. However, the magnitude of these changes did not differ significantly between the 2 groups. In the 2-dimensional analysis, no significant differences were observed among the Herbst, Pendex, and untreated control groups in airway area changes from T1 to T3.
Conclusions
Both the Herbst and Pendex appliances resulted in comparable increases in total upper airway volume and length in adolescent patients with Class II malocclusion, primarily attributable to normal growth.
Highlights
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After Herbst appliance treatment, a significant increase in the upper airway was observed.
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Pendex appliance treatment showed notable improvements over a similar follow-up period.
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No significant differences were found in the upper airway caliber changes between 2 groups.
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Herbst appliance treatment minimally affects the upper airway dimension compared with natural growth.
Skeletal Class II malocclusion with a retrognathic mandible is a common orthodontic condition, affecting approximately 20% of the global population with permanent dentition. Both removable and fixed functional appliances, such as the Twin-block, Herbst appliance, and mandibular anterior repositioning appliance (MARA), are widely used to treat adolescent patients with skeletal Class II malocclusion. These appliances facilitate anterior mandibular positioning and encourage adaptive changes in the bone and muscles. Among them, the Herbst appliance is currently the most commonly used device for mandibular advancement in growing patients with Class II malocclusion in the United States. However, the extent to which functional appliances induce condylar remodeling and promote mandibular growth remains a topic of debate. ,,,,,
Skeletal discrepancies between the maxilla and mandible in the sagittal dimension, particularly mandibular retrognathism, are linked to oropharyngeal airway constriction, and they may contribute to the development of obstructive sleep apnea syndrome. , Forward positioning of the mandible with functional appliances is associated with anterior tongue displacement and an improvement in the upper airway dimensions. ,,, Interestingly, oral devices used to treat obstructive sleep apnea share a similar design with the Herbst appliance, advancing the mandible to increase upper airway caliber. Previous studies evaluating removable functional appliances, such as activators, Twin-blocks, or bionators, have yielded controversial outcomes. Although some studies demonstrate significant improvements in upper airway dimensions in groups treated with removable functional appliances compared with controls, ,,, other studies report minimal or no significant changes. This variability may partially result from reliance on patient compliance, as removable appliances depend heavily on consistent use. In contrast, fixed functional appliances, such as the Herbst appliances and MARA, operate continuously and do not require patient cooperation. Studies investigating these fixed functional appliances have reported significant increases in oropharyngeal airway dimensions compared with groups without Class II malocclusion correction. , However, these studies have primarily assessed immediate or short-term effects. In addition, some research has reported negligible changes, underscoring the variability and inconsistent outcomes associated with Class II growth modification treatments on upper airway dimensions. , At present, robust evidence supporting the long-term positive effects of Herbst appliance therapy on the upper airway dimensions in adolescent patients with Class II malocclusion remains limited.
Maxillary molar distalization, using the Pendulum, Pendex, distal jet, and modified Nance appliance, is considered an effective treatment option for patients with mild Class II malocclusion. Although treatment with functional appliances can achieve both skeletal and dental improvements in the maxillomandibular relationship, Class II malocclusion correction through maxillary molar distalization primarily results in dentoalveolar changes. Generally, molar distalization is associated with an increase in the mandibular plane angle, leading to mandibular clockwise rotation. Previous studies suggest that the vertical changes induced by molar distalization have a negligible impact on the upper airway and that this treatment is not associated with long-term airway dimensional changes in adolescent patients. ,
This study aims to evaluate the upper airway changes in adolescent patients with Class II malocclusion treated with the Herbst appliance vs those treated with molar distalization using the Pendex appliance. We hypothesize that treatment with the Herbst appliance will lead to a greater increase in oropharyngeal airway dimensions compared with the Pendex appliance.
Material and methods
The retrospective study was approved by the institutional review board at the University of Pennsylvania (Protocol No. 851012). This study analyzed cone-beam computed tomography (CBCT) images from 50 patients who consecutively received either Herbst or Pendex appliance treatment between October 2016 and January 2023 at a private orthodontic office in Chalfont, Pennsylvania. Patients with a history of previous orthodontic treatment, permanent tooth extractions, or craniofacial surgeries before undergoing Herbst or Pendex appliance treatment were excluded. The study sample was divided into 2 groups ( Table I ).
Table I
Demographics
| Herbst group (n = 25) | Pendex group (n = 25) | P value | |
|---|---|---|---|
| Sex | 13 M, 12 F | 12 M, 13 F | 0.777 |
| Age at T1 (y) | 12.16 ± 1.89 | 11.72 ± 1.22 | 0.332 |
| ANB (°) at T1 | 5.20 ± 1.89 | 3.47 ± 1.83 | 0.002 |
| SN-GoGn (°) at T1 | 30.15 ± 5.92 | 30.82 ± 4.18 | 0.634 |
| Age at T3 (y) | 15.59 ± 1.91 | 15.46 ± 1.19 | 0.768 |
| ANB (°) at T3 | 3.22 ± 2.10 | 2.50 ± 2.33 | 0.260 |
| SN-GoGn (°) at T3 | 29.52 ± 7.12 | 29.84 ± 4.40 | 0.851 |
| Treatment period (mo) | |||
| T1-T2 | 29.22 ± 9.80 | 14.77 ± 8.15 | <0.001 |
| T2-T3 | 11.89 ± 7.86 | 30.03 ± 13.43 | <0.001 |
| T1-T3 | 41.11 ± 9.95 | 44.81 ± 9.63 | 0.188 |
M , male; F , female.
Herbst group (growth modification group): 25 patients (aged 12.2 ± 1.9 years at T1; 13 males and 12 females) treated with Herbst appliances, followed by fixed orthodontic appliances. CBCT scans were acquired in the natural head position at preorthodontic treatment records (T1), 6 months after Herbst appliance removal (T2, aged 14.6 ± 2.1 years), and posttreatment final records after the removal of fixed edgewise appliances (T3, aged 15.6 ± 1.9 years). The time period from T1 to T2 was 29.2 ± 9.8 months, from T2 to T3 was 11.9 ± 7.9 months, and from T1 to T3 was 41.1 ± 10.0 months.
Pendex group (nongrowth modification control): 25 patients (aged 11.7 ± 1.2 years at T1; 12 males 13 females) treated with Pendex appliances, followed by fixed orthodontic appliances. CBCT scans were acquired in the natural head position at preorthodontic treatment records (T1), immediately after the removal of Pendex (T2, aged 13.0 ± 1.6 years), and posttreatment final records after the removal of fixed edgewise appliances (T3, aged 15.5 ± 1.2 years). The time period from T1 to T2 was 14.8 ± 8.2 months, from T2 to T3 was 30.0 ± 13.4 months, and from T1 to T3 was 44.8 ± 9.6 months.
Our sample size of 25 patients per group is relatively modest, with 80% power to detect a large effect size (0.80) in 2-group analyses and a moderate effect size (0.58) in paired analyses at an α = 0.05.
After the initial orthodontic records, patients in the Herbst group received a stainless-steel crown Herbst appliance, along with an expander and a lower lingual holding arch. For all patients in this study, patients and parents were instructed to carry out 1 turn per day (0.25 mm per turn) for 30-35 days. After expansion, the telescopic arms were placed, and the Herbst appliance was activated until the patient achieved an anterior edge-to-edge bite, which was maintained for at least 1 year. For the Pendex group, the Pendex appliance was delivered with bands on the maxillary first molars and occlusal rests on the premolars or primary molars. The maxillary expansion was completed with 30-35 turns. After the distalization of the maxillary first molars was completed, a Nance holding arch was placed for retention. For both groups, the fixed edgewise appliance treatment were followed. Based on the treatment protocols, the T1-T2 periods differed between the 2 groups. However, the T1-T3 time periods were similar, so we focused on the differences at T1, T3, and the T3-T1 changes.
CBCT scans were obtained in natural head position. ,, Patients were instructed to keep their mouths closed, breathe through the nose, bring the teeth into light contact, and swallow once. From the T1 and T3 CBCTs, lateral cephalograms were generated as an orthogonal view (0% magnification) of the right side of the face to the midpoint of the maxillary left central incisor, as previously described. Digital tracing and cephalometric measurements of ANB and SN-GoGn were performed using the Dolphin Imaging & Management Solutions software (version 12.0; Dolphin Imaging & Management Solutions, Chatsworth, Calif). Then, the Digital Imaging and Comunications in Medicine files were imported into the Amira software (version 5.3.0; Thermo Fisher Scientific, Waltham, Mass). CBCT images were oriented in the frontal and lateral views. In the frontal view, the inferior orbital rims were positioned symmetrically and parallel to the floor, and the midsagittal plane was defined by the nasion, anterior nasal spine, and midpoint of the chin. In the lateral view, the Frankfort horizontal plane was oriented parallel to the floor. Additional orientation adjustments were performed to optimize bilateral alignment of the orbital rims and the posterior borders of the mandibular rami. Brightness and contrast were standardized by setting the display range to–750 to 500 in the Zoom and Data window. Each scan was segmented into the retropalatal (RP) and retroglossal (RG) regions using boundary definitions on the midsagittal slice, as previously described ( Fig 1 ). ,,, The boundaries of each region are outlined in Table II . In the axial view, each 0.3 mm slice was individually segmented to remove artifacts and ensure accurate tracing of airway boundaries. After segmentation, volume, length, and mean and minimum cross-sectional areas (CSA) were calculated for the total upper airway and in the RP and RG regions.
The upper airway measurements. PNS, posterior nasal spine.
Table II
Definitions of the anatomic boundaries of the upper airway
| Superior boundary | Inferior boundary | Anterior boundary | Posterior boundary | |
|---|---|---|---|---|
| Total airway | A plane parallel to FH passing through PNS and extended to the posterior wall of the pharynx | The level of the base of the epiglottis parallel to the FH plane | The posterior aspect of the soft palate and the posterior border of the tongue | The pharyngeal wall |
| RP airway | A plane parallel to FH passing through PNS and extended to the posterior wall of the pharynx | A plane parallel to FH passing through the level of the most inferior aspect of the soft palate | The posterior aspect of the soft palate | The pharyngeal wall |
| RG airway | A plane parallel to FH passing through the level of the most inferior aspect of the soft palate | The level of the base of the epiglottis parallel to the FH plane | The posterior border of the tongue | The pharyngeal wall |
PNS , posterior nasal spine; FH , Frankfort horizontal plane.
Twenty-five age- and sex-matched untreated patients with Class II malocclusion (aged 12.0 ± 0.7 years at T1; 13 males and 12 females) were selected from the American Association of Orthodontists Foundation Bolton-Brush Craniofacial Growth Legacy Collection. Two-dimensional (2D) lateral cephalometric radiographs were obtained at T1 and T3 timepoints, with image magnification standardized using fiducial landmarks. At T1, the control group had an ANB of 5.0° ± 1.96° and an SN-GoGn of 29.61° ± 4.46°, with no significant differences compared with the corresponding skeletal values in the Herbst group. The average duration between T1 and T3 was 41.4 ± 8.2 months. After orientation of the lateral cephalometric radiographs, the area, length, and mean and minimum anterioposterior (AP) distances were measured for the total upper airway, as well as for the RP and RG regions, using boundaries consistent with those applied in the corresponding 3-dimensional (3D) measurements ( Fig 1 ).
Statistical analysis
All measurements were carried out by 1 examiner (W.K.) in a blinded fashion. To verify the consistency and reliability of the measuring protocol, the CBCT images of 10 patients were randomly selected and remeasured by the same examiner at least 1 month after initial measurements. The intraclass correlation coefficient (ICC) of the measurements was calculated using SPSS software (version 26.0; IBM, Chicago, Ill). Using guidelines provided by Landis and Koch, ICC values can be interpreted as poor (ICC <0.00), slight (0.00-0.20), fair (0.21-0.40), moderate (0.41-0.60), substantial (0.61-0.80), and almost perfect (0.81-1.00) reliability.
Participant characteristics were summarized as means and standard deviations for continuous traits or frequencies and percentages for categorical traits. Mean percentage change from the baseline (T1) to postintervention time points (T2 and T3) was calculated to describe within-group change magnitudes. Baseline between-group differences in continuous variables were assessed using independent-samples t tests or Mann-Whitney U tests (3D metrics; Herbst vs Pendex only) and Welch 1-way analysis of variance (ANOVA) (2D metrics; Herbst, Pendex, and untreated control). Categorical variables (eg, sex) were compared using chi-square tests. Parametric assumptions were examined by visual inspection of histograms and the Shapiro-Wilk test for normality and by tests of homogeneity of variance (eg, Levene-type tests).
To evaluate longitudinal change in 3D measures within the Herbst and Pendex groups, repeated-measures ANOVA or the Friedman test (repeated-measures ANOVA on ranks) was applied. When omnibus tests were significant, pairwise comparisons between time points were conducted. For repeated-measures ANOVA models, differences between estimated marginal means at each time-point pair were obtained from linear mixed-effects modeling. For nonparametric analysis, Friedman tests were followed by Wilcoxon signed-rank tests. Additional linear regression models (analysis of covariance) were fitted to evaluate differences in 2D variables among the Herbst, Pendex, and untreated control groups at T3, as well as changes from T1 to T3. These models were adjusted for the baseline (T1) outcome values and the duration of follow-up (ie, the interval between T1 and T3 in months) to account for initial differences and variations in treatment duration. For 2D metrics, pairwise differences in adjusted means (Herbst vs Pendex, Herbst vs control, and Pendex vs control) were derived from model contrasts after a significant omnibus group test.
To control the family-wise error rate at 5% for multiple between-group comparisons of airway measurements, the Hochberg step-up procedure was applied. Statistical significance was determined based on the Hochberg-adjusted α thresholds. , Effect sizes were reported to describe the magnitude of group differences, using Cohen d for parametric contrasts (small: |0.2|, medium: |0.5|, and large: |0.8|) or Cliff delta (δ) for nonparametric contrasts (small: |0.15|, medium: |0.33|, and large: |0.47|). All statistical analyses were conducted using Stata/SE (version 16.1; StataCorp, College Station, Tex).
Results
The ICC of the 10 samples ranged 0.99-1.00, indicating almost perfect reliability of the measuring protocol when applied to the same image >1 month apart.
The sample in this study showed no statistically significant differences in sex, age, or vertical skeletal pattern (SN-GoGn) at T1 ( Table I ). However, ANB differed significantly between the 2 groups at T1, with the Herbst group exhibiting a mean ANB angle of 5.20° ± 1.89° compared with 3.47° ± 1.83° in the Pendex group ( P = 0.002). At T3, both the vertical (SN-GoGn) and sagittal skeletal patterns (ANB) were comparable between the 2 groups. The total treatment duration from T1 to T3 showed no statistically significant difference between the Herbst and Pendex appliance groups.
In the Herbst group, from T1 to T2, significant increases were observed in total volume (27.7%, 12,273 ± 4625 mm 3 to 15,668 ± 4659 mm 3), total length (13.1%, 51.98 ± 5.19 mm to 58.79 ± 5.54 mm), RP volume (32.7%, 6987 ± 2772 mm 3 to 9272 ± 3530 mm 3), RP length (14.7%, 26.81 ± 4.21 mm to 30.76 ± 4.76 mm), RP mean CSA (15.8%, 258.20 ± 91.45 mm 2 to 299.00 ± 93.15 mm 2), and RG length (11.3%, 25.18 ± 6.02 mm to 28.03 ± 4.85 mm) ( Table III ). From T2 to T3, values were maintained or slightly increased across all measurements, with no statistically significant changes observed in the upper airway dimensions. In addition, these changes from T1 to T2 were perpetuated to T3 and led to the same pattern of differences. From T1 to T3 in the Herbst group, significant increases were noted in total volume (31.6%, 12,273 ± 4625 mm 3 to 16,155 ± 5979 mm 3), total length (15.5%, 51.98 ± 5.19 mm to 60.01 ± 6.33 mm), RP volume (38.5%, 6987 ± 2772 mm 3 to 9677 ± 4480 mm 3), RP length (16.2%, 26.81 ± 4.21 mm to 31.15 ± 5.65 mm), RP mean CSA (18.6%, 258.20 ± 91.45 mm 2 to 306.20 ± 120.80 mm 2), and RG length (14.6%, 25.18 ± 6.02 mm to 28.86 ± 5.93 mm) ( Fig 2 ).
Table III
Three-dimensional Herbst group treatment outcomes
| T1 (n = 25) | T2 (n = 25) | T3 (n = 25) | P value | Significant pairwise comparisons | ||||
|---|---|---|---|---|---|---|---|---|
| Mean | SD | Mean | SD | Mean | SD | |||
| Total volume (mm 3) | 12,273 | 4625 | 15,668 | 4659 | 16,155 | 5979 | <0.001 | T2-T1 , T3-T1 |
| Total length (mm) | 51.98 | 5.19 | 58.79 | 5.54 | 60.01 | 6.33 | <0.001 | T2-T1 , T3-T1 |
| Total mean CSA (mm 2) | 235.90 | 87.70 | 266.10 | 74.44 | 269.20 | 97.40 | 0.070 | – |
| Total minimum CSA (mm 2) | 159.30 | 76.24 | 153.30 | 59.32 | 166.40 | 78.27 | 0.716 | – |
| RP volume (mm 3) | 6987 | 2772 | 9272 | 3530 | 9677 | 4480 | <0.001 | T2-T1 , T3-T1 |
| RP length (mm) | 26.81 | 4.21 | 30.76 | 4.76 | 31.15 | 5.65 | <0.001 | T2-T1 , T3-T1 |
| RP mean CSA (mm 2) | 258.20 | 91.45 | 299.00 | 93.15 | 306.20 | 120.80 | 0.011 | T2-T1 , T3-T1 |
| RP minimum CSA (mm 2) | 180.30 | 85.40 | 183.60 | 78.12 | 196.40 | 97.76 | 0.530 | – |
| RG volume (mm 3) | 5286 | 2407 | 6396 | 2255 | 6478 | 2716 | 0.023 | T2-T1 |
| RG length (mm) | 25.18 | 6.02 | 28.03 | 4.85 | 28.86 | 5.93 | <0.001 | T2-T1 , T3-T1 |
| RG mean CSA (mm 2) | 213.20 | 88.64 | 227.30 | 65.54 | 226.20 | 78.40 | 0.604 | – |
| RG minimum CSA (mm 2) | 168.20 | 77.00 | 171.30 | 55.90 | 178.10 | 71.41 | 0.537 | – |
SD , standard deviation.
The average upper airway dimensional changes before and after Herbst appliance treatment.
In the Pendex group, no significant changes were observed in any airway dimensions from T1 to T2 ( Table IV ). From T2 to T3 in the Pendex group, significant increases were observed in total volume (31.3%, 13,831 ± 6086 mm 3 to 18,154 ± 7422 mm 3), total length (6.2%, 55.07 ± 5.18 mm to 58.48 ± 5.75 mm), total mean CSA (43.2%, 251.60 ± 110.00 mm 2 to 307.80 ± 110.40 mm 2), RP volume (35.9%, 7908 ± 3167 mm 3 to 10745 ± 4499 mm 3), RP mean CSA (24.8%, 284.20 ± 111.00 mm 2 to 354.60 ± 119.90 mm 2), and RP minimal CSA (34.12%, 191.40 ± 112.80 mm 2 to 256.70 ± 103.30 mm 2) ( Table IV ). From T1 to T3 in the Pendex group, significant increases were observed in total volume (31.9%, 13,763 ± 7335 mm 3 to 18,154 ± 7422 mm 3), total length (7.5%, 54.40 ± 5.43 mm to 58.48 ± 5.75 mm), total mean CSA (23.29%, 249.70 ± 116.60 mm to 307.80 ± 110.40 mm), RP volume (39.9%, 7679 ± 3402 mm 3 to 10745 ± 4499 mm 3), RP length (8.79%, 27.86 ± 3.60 mm to 30.31 ± 5.30 mm), and RP mean CSA (27.1%, 279.00 ± 120.60 mm 2 to 354.60 ± 119.90 mm 2) ( Table IV and Fig 3 ).
Table IV
Three-dimensional Pendex group treatment outcomes
| T1 (n = 25) | T2 (n = 25) | T3 (n = 25) | P value | Significant pairwise comparisons | ||||
|---|---|---|---|---|---|---|---|---|
| Mean | SD | Mean | SD | Mean | SD | |||
| Total volume (mm 3) | 13,763 | 7335 | 13,831 | 6086 | 18,154 | 7422 | 0.023 | T3-T1 , T3-T2 |
| Total length (mm) | 54.40 | 5.43 | 55.07 | 5.18 | 58.48 | 5.75 | 0.031 | T3-T1 , T3-T2 |
| Total mean CSA (mm 2) | 249.70 | 116.60 | 251.60 | 110.00 | 307.80 | 110.40 | 0.023 | T3-T1 , T3-T2 |
| Total minimum CSA (mm 2) | 166.90 | 105.60 | 148.00 | 89.64 | 211.90 | 100.50 | 0.051 | – |
| RP volume (mm 3) | 7679 | 3402 | 7908 | 3167 | 10,745 | 4499 | 0.004 , | T3-T1 , T3-T2 |
| RP length (mm) | 27.86 | 3.60 | 28.01 | 3.61 | 30.31 | 5.30 | 0.009 | T3-T1 , T3-T2 |
| RP mean CSA (mm 2) | 279.00 | 120.60 | 284.20 | 111.00 | 354.60 | 119.90 | 0.002 | T3-T1 , T3-T2 |
| RP minimum CSA (mm 2) | 205.80 | 113.30 | 191.40 | 112.80 | 256.70 | 103.30 | 0.002 , | T3-T2 |
| RG volume (mm 3) | 6083 | 4235 | 5922 | 3235 | 7408 | 3257 | 0.039 | T3-T1 |
| RG length (mm) | 26.53 | 5.40 | 27.06 | 5.24 | 28.16 | 3.49 | 0.304 | – |
| RG mean CSA (mm 2) | 218.90 | 121.80 | 219.00 | 116.40 | 262.00 | 110.90 | 0.333 | – |
| RG minimum CSA (mm 2) | 173.00 | 106.50 | 160.30 | 99.52 | 220.30 | 108.10 | 0.141 | – |
SD , standard deviation.
The average upper airway dimensional changes before and after Pendex appliance treatment.
At T1, no statistically significant differences were observed between the Herbst and Pendex groups ( Table V ), although a moderate effect size was noted for total airway length (Cohen d =–0.45). At T3, after adjusting for the baseline (T1) values and differences in follow-up duration, most measurements similarly showed no significant differences between the groups ( Table VI ), but moderate effect sizes were evident in some dimensions (Cohen d near |0.5|), including a nominally larger RP minimal CSA in the Pendex group (adjusted mean: 253.62 mm 2; 95% confidence interval [CI]: 216.16, 291.08) compared with the Herbst group (adjusted mean: 199.41 mm 2; 95% CI: 161.94, 236.87; P = 0.048). This difference, however, did not remain statistically significant after the Hochberg adjustment. When analyzing changes from T1 to T3, after adjusting for the baseline (T1) values and differences in follow-up duration, no statistically significant differences in the upper airway measurements were identified between the groups ( Table VII ), although a moderate effect size was observed for total minimal CSA (Cohen d =–0.56; P = 0.061).
Table V
Three-dimensional comparison of Herbst and Pendex groups at T1
| Herbst group (n = 25) | Pendex group (n = 25) | Effect size | P value | |||
|---|---|---|---|---|---|---|
| Mean | SD | Mean | SD | |||
| Total volume (mm 3) | 12,273 | 4625 | 13,763 | 7335 | – 0.04 | 0.808 |
| Total length (mm) | 51.98 | 5.19 | 54.40 | 5.43 | – 0.45 | 0.115 |
| Total mean CSA (mm 2) | 235.90 | 87.70 | 249.70 | 116.60 | – 0.01 | 0.946 |
| Total minimum CSA (mm 2) | 159.30 | 76.24 | 166.90 | 105.60 | – 0.08 | 0.773 |
| RP volume (mm 3) | 6987 | 2772 | 7679 | 3402 | – 0.09 | 0.580 |
| RP length (mm) | 26.81 | 4.21 | 27.86 | 3.60 | – 0.27 | 0.345 |
| RP mean CSA (mm 2) | 258.20 | 91.45 | 279.00 | 120.60 | – 0.19 | 0.494 |
| RP minimum CSA (mm 2) | 180.30 | 85.40 | 205.80 | 113.30 | – 0.25 | 0.374 |
| RG volume (mm 3) | 5286 | 2407 | 6083 | 4235 | – 0.05 | 0.749 |
| RG length (mm) | 25.18 | 6.02 | 26.53 | 5.40 | – 0.24 | 0.406 |
| RG mean CSA (mm 2) | 213.20 | 88.64 | 218.90 | 121.80 | 0.04 | 0.823 |
| RG minimum CSA (mm 2) | 168.20 | 77.00 | 173.00 | 106.50 | – 0.05 | 0.857 |
Note. No P values were statistically significant at the Hochberg-adjusted α-level. Effect size: Cohen d for t-test (small: 0.2, medium: 0.5, and large: 0.8) and Cliff delta for the Mann-Whitney U test (small: 0.15, medium: 0.33, and large: 0.47). Effect size calculated as Herbst– Pendex.
SD , standard deviation.
Table VI
Three-dimensional comparison of Herbst and Pendex groups at T3, adjusted for baseline (T1) values of the modeled variable and follow-up duration between T1 and T3
| Herbst group (n = 25) | Pendex group (n = 25) | Effect size | P value | |||
|---|---|---|---|---|---|---|
| Mean | 95% CI | Mean | 95% CI | |||
| Total volume (mm 3) | 16451.36 | 13,873.91, 19,028.81 | 17,857.96 | 15,280.51, 20,435.42 | – 0.22 | 0.449 |
| Total length (mm) | 60.32 | 57.82, 62.82 | 58.16 | 55.66, 60.66 | 0.36 | 0.241 |
| Total mean CSA (mm 2) | 270.82 | 232.18, 309.46 | 306.15 | 267.51, 344.80 | – 0.37 | 0.205 |
| Total minimum CSA (mm 2) | 165.70 | 131.38, 200.03 | 212.56 | 178.24, 246.89 | – 0.56 | 0.061 |
| RP volume (mm 3) | 9973.53 | 8322.87, 11,624.19 | 10,449.26 | 8798.60, 12,099.92 | – 0.12 | 0.069 |
| RP length (mm) | 31.63 | 29.73, 33.53 | 29.83 | 27.93, 31.73 | 0.39 | 0.189 |
| RP mean CSA (mm 2) | 310.48 | 266.24, 354.72 | 350.34 | 306.10, 394.57 | –0.37 | 0.212 |
| RP minimum CSA (mm 2) | 199.41 | 161.94, 236.87 | 253.62 | 216.16, 291.08 | –0.59 | 0.048 |
| RG volume (mm 3) | 6508.14 | 5373.79, 7642.48 | 7378.4 | 6244.06, 8512.75 | –0.31 | 0.029 |
| RG length (mm) | 29.07 | 27.32, 30.83 | 27.95 | 26.20, 29.70 | 0.26 | 0.376 |
| RG mean CSA (mm 2) | 225.25 | 188.88, 261.62 | 262.92 | 226.55, 299.29 | –0.42 | 0.151 |
| RG minimum CSA (mm 2) | 176.45 | 141.38, 211.53 | 221.98 | 186.90, 257.05 | –0.53 | 0.074 |
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