Abstract
Background
This study aimed to compare three-dimensional displacements of the maxilla and mandible, and upper airway changes, following tooth-borne rapid palatal expansion (TB-RPE) (Hyrax) and tooth-bone-borne miniscrew-assisted rapid palatal expansion (TBB-MARPE). Additionally, the correlation between skeletal movements and upper airway changes was evaluated.
Methods
This was a secondary analysis of a previous randomized clinical trial (RCT), recruiting patients with transverse maxillary deficiency and allocating them to TB-RPE or TBB-MARPE. Low-dose cone-beam computed tomography images obtained at pre-expansion and after 3 months of consolidation post-expansion were analyzed for 32 patients (TB-RPE group: n = 13, mean age = 13.15 ± 3.85; TBB-MARPE: n = 19, mean age = 13.68 ± 4.20). Skeletal displacements and changes in airway volume and cross-sectional area of the nasal cavity, nasopharynx, and total upper airway were assessed. Intergroup comparison and correlation analysis were performed. The level of statistical significance was set at 0.05. For multiple comparison correction of skeletal movements and upper airway changes, the significance level was determined using false discovery rate (FDR) adjusted p-values < 0.05.
Results
TBB-MARPE resulted in significantly greater maxillary expansion than TB-RPE; however, no significant difference was observed in maxillary and mandibular displacement between groups. Both groups demonstrated a slight forward and downward displacement of the maxilla (FDR-adjusted p < 0.05), with no significant mandibular position changes (FDR-adjusted p > 0.05). Significant increases were observed in anterior and middle airway cross-sectional areas, nasal cavity volume, and total upper airway volume in both groups, with greater improvement in the TBB-MARPE group (FDR-adjusted p < 0.05). No significant changes were found in the posterior cross-sectional area or nasopharynx volume (FDR-adjusted p > 0.05). Maxillary expansion were positively correlated with the increase in nasal cavity volume and total upper airway volume (p < 0.05).
Conclusions
TBB-MARPE facilitated greater maxillary expansion and upper airway enlargement after consolidation; however, both approaches presented similar skeletal displacement patterns, characterized by slight forward and downward maxillary movement and insignificant mandibular position changes. Within the limitations of this study, orthopedic maxillary expansion positively enhances the nasal airway but has minimal influence on the nasopharynx.
Trial registration
The original trial was retrospectively registered at the WHO International Clinical Trial Registry Platform (Registration number: KCT0006871 / Registration date 27/12/2021).
Supplementary Information
The online version contains supplementary material available at https://doi.org/10.1186/s12903-026-09784-4.
Keywords: Orthopedic maxillary expansion, Rapid palatal expander, Miniscrew-assisted rapid palatal expander, Skeletal displacements, Upper airway
Background
In orthodontics, orthopedic maxillary expansion is considered an effective approach for correcting maxillary transverse deficiency [1–3]. While conventional rapid palatal expansion (RPE) effectively addresses maxillary constriction, it is often associated with undesirable dentoalveolar and periodontal effects, including buccal tipping of anchor teeth, alveolar dehiscence, and thinning of the buccal cortical plate [4, 5]. To mitigate these complications, miniscrew-assisted RPE (MARPE) appliances were developed by incorporating orthodontic miniscrews to provide skeletal anchorage and enhance orthopedic outcomes [4–6]. Depending on their configuration, MARPE can be either tooth–bone-borne or purely bone-borne expanders [7]. Compared with conventional RPE, MARPE has been reported to achieve greater skeletal expansion while minimizing dentoalveolar side effects, potentially improving treatment stability [4, 8]. Although transverse dentoskeletal effects of RPE and MARPE have been extensively investigated, direct comparisons of the treatment effects in the sagittal and vertical dimensions accompanying transverse correction between these two treatment modalities are rarely discussed in the literature [9].
Upper airway enlargement is considered a secondary effect of maxillary expansion [10]. Mechanistically, separation of the midpalatal suture induces lateral displacement of the nasal floor, which may reduce nasal airway resistance and improve airflow [11]. Nevertheless, interpretation of airway changes remains inconsistent across studies due to heterogeneity in appliance design, skeletal maturity, imaging timing, and assessment methods [12–16]. Furthermore, although MARPE may facilitate greater skeletal expansion and thereby potentially induce more pronounced airway changes, high-quality randomized comparisons between conventional tooth-borne RPE (TB-RPE) and tooth-bone-borne MARPE (TBB-MARPE), which share an identical tooth-borne framework with the primary distinction being the addition of skeletal anchorage via four miniscrews, remain scarce, particularly in adolescent and young adult populations [12, 13, 17, 18].
Therefore, the present study conducted a secondary analysis of cone-beam computed tomography (CBCT) data derived from a prior randomized clinical trial (RCT) to comprehensively evaluate three-dimensional skeletal displacements and upper airway changes in adolescents and young adults treated with TB-RPE and TBB-MARPE. Additionally, the relationship between skeletal movements and airway alterations following orthopedic maxillary expansion was investigated. By providing a comprehensive three-dimensional comparison of these treatment modalities, this study addresses an important knowledge gap regarding their skeletal and airway effects. The findings may help orthodontists optimize treatment selection for patients with maxillary transverse deficiency, particularly when improvement of upper airway dimensions is a potential therapeutic consideration.
Materials and methods
Trial design
This study was conducted in accordance with the Consolidated Standards of Reporting Trials (CONSORT) guidelines. It represents a blinded secondary analysis of data derived from a previously conducted RCT with a 1:1 allocation ratio. The original trial was retrospectively registered at the WHO International Clinical Trial Registry Platform (Registration number: KCT0006871 / Registration date 27/12/2021).8 No modifications to the study protocol or trial procedures were implemented after trial initiation.
Participants, eligibility criteria, and setting
A total of fifty-one patients requiring maxillary expansion were recruited over a 12-month period as part of a previously conducted RCT (Fig. 1). Ethical approval was obtained from the Institutional Review Board of Yonsei University Dental Hospital (IRB No. 2-2024-0067) [8].
Fig. 1.
CONSORT flow diagram for the secondary analyses
Eligibility criteria included: (1) presence of maxillary transverse deficiency, diagnosed by posterior crossbite or buccal edge-to-edge occlusion; (2) age between 7 and 25 years; (3) healthy periodontal status with adequate oral hygiene; (4) no prior history of orthodontic treatment or orthognathic surgery; (5) absence of significant craniofacial anomalies, such as cleft lip or palate; and (6) provision of informed consent.
Exclusion criteria were: (1) age < 7 years or > 25 years; (2) absence of suitable anchor teeth for appliance placement; (3) presence of active periodontal disease; (4) history of previous orthodontic treatment; (5) craniofacial deformities; and (6) failure or refusal to provide informed consent.
Interventions
All clinical procedures were performed by a single orthodontist (J-H C) to ensure procedural consistency and minimize operator-dependent variability.
In the TB-RPE group, a Hyrax-type expander (Dentaurum, Germany) was utilized. The appliance was anchored to four bands placed on the maxillary first premolars and first molars (Fig. 2).
Fig. 2.
(A, B) Tooth-borne rapid palatal expansion (TB-RPE); and (C, D) tooth-bone-borne miniscrew-assisted rapid palatal expansion (TBB-MARPE) before and after expansion, respectively
In the TBB-MARPE group, the appliance consisted of a jackscrew body with four screw holes (Biomaterials Korea, Seoul, Korea) and four soldered arms connected to bands on the maxillary first premolars and first molars. Following appliance cementation, four self-drilling miniscrews (1.8 mm diameter; 9 mm length anteriorly and 7 mm length posteriorly) were inserted perpendicularly to the palatal surface under local infiltration anesthesia. The anterior miniscrews were positioned in the paramedian region, medial to the first premolars, along a line parallel to the midpalatal suture and between the central and lateral incisors. The posterior miniscrews were placed lateral to the midpalatal suture in the region corresponding to the first molars (Fig. 2).
Both TB-RPE and TBB-MARPE were activated once daily with one-quarter turn increments (0.20 mm per turn). Activation was continued for a total of 35 turns, corresponding to 7.0 mm of screw expansion. Following the active phase, the appliances were maintained for a 3-month consolidation period to allow stabilization and connective tissue remodeling of the midpalatal suture.
CBCT protocol and analysis
All participants underwent CBCT imaging in an upright position with standardized head orientation. The Frankfort horizontal (FH) plane was aligned parallel to the ground, and the midsagittal plane was adjusted to coincide with the vertical axis of the imaging device.
CBCT scans (Alphard 3030, Asahi Roentgen Ind. Co., Ltd., Kyoto, Japan) were obtained at two time points: before maxillary expansion (T0) and after a 3-month post-expansion consolidation period (T2). Image acquisition followed a previously validated low-dose protocol (exposure time: 17 s, 3.0 mA, 80 kV, field of view [FOV]: 200 × 200 mm², voxel size: 0.39 mm) [8].
The acquired datasets were exported in Digital Imaging and Communications in Medicine (DICOM) format and processed using Invivo5 software (Anatomage, San Jose, CA, USA) and OnDemand3D software (Cybermed Co., Seoul, Korea). Image reorientation was performed using standardized reference planes: the midsagittal plane (MSP), defined by Sella, Nasion, and anterior nasal spine; and the FH plane, defined by the right orbitale and the right porion landmarks (Fig. 3) [19].
Fig. 3.
(A) Horizontal, sagittal, and coronal reconstructions after head reorientation. (B) Superimposition of three-dimensional images acquired at T0 (white) and T2 (blue)
A three-dimensional (3D) coordinate system (x, y, z) was established with the origin set at the Nasion point (0,0,0). Positive directions were defined as leftward (x-axis), posterior (y-axis), and superior (z-axis), whereas negative values indicated rightward, anterior, and inferior displacements, respectively (Fig. 3).
For longitudinal assessment, T0 and T2 images were superimposed using a voxel-based registration method based on the anterior cranial base, incorporating both point-to-point and volumetric registration methods with normalized mutual information, as previously described by Bazina et al. [20]. This approach minimizes operator-dependent variability and enhances registration accuracy. Following superimposition, both datasets shared a unified coordinate system, allowing precise quantification of skeletal changes (Fig. 4).
Fig. 4.
Superimposition of three-dimensional images acquired at T0 (white) and T2 (blue) using a voxel-based registration method based on the anterior cranial base
Maxillary and mandibular displacements were quantified by calculating the positional differences of predefined skeletal landmarks along the x-, y-, and z-axes between T0 and T2. Definitions of landmarks and measurement parameters are provided in Table 1; Fig. 4. The extent of transverse maxillary expansion was assessed by changes in nasal cavity width, nasal floor width, and intermolar width (Fig. 5).
Table 1.
Definition of skeletal, dentoalveolar, and upper airway variables used in this study
| Defination | ||
|---|---|---|
| Skeletal landmarks and measurements | Landmarks | |
| Anterior nasal spine (ANS) | The point located at the tip of the anterior nasal spine. | |
| Posterior nasal spine (PNS) | The point located at the tip of the posterior nasal spine. | |
| A point | The most posterior and deepest point on the anterior contour of the maxillary alveolar process in the mid-sagittal plane. | |
| B point | The point located at the largest concavity of the anterior portion of the mental symphysis. | |
| Menton (Me) | The most inferior point of symphysis of mandible. | |
| Pogonion (Pog) | The intersection between the midsagittal plane and the most anterior point of the mandibular symphysis. | |
| Gonion (Go) | The most inferior point at jaw angle between mandibular plane and ramus. | |
| Condyle (Co) | The most medial point of the condylar head. | |
| Hyoid bone | The most anterosuperior point of the hyoid bone. | |
| Measurements | ||
| Nasal cavity width (mm) | Distance at the widest portion of the nasal aperture parallel to the hard palatemeasured at maxilary first molars. | |
| Nasal floor width (mm) | Distance at the widest portion of the nasal floor parallel to the hard palatemeasured at maxilary first molars. | |
| Dentoalveolar measurements | Intermolar width (mm) | Distance between furcation of the right and left maxilary first molars. |
| Molar inclincation (°) | Angle between the line passing through the palatal cusp tip and palatal root apex, and the vertical line perpendicular to the hard palate measured on upper first molars in the coronal section. | |
| Airway landmarks, reference planes, and measurements | Landmarks | |
| Choanae | The choanae are bounded medially by the vomer, inferiorly by the horizontal plate of the palatine bone, laterally by the medial pterygoid plate, and superiorly by the body of the sphenoid bone. | |
| C3 | The most inferior and anterior point on the third cervical vertebra. | |
| Reference planes | ||
| ANS perpendicular plan | Perpendicular to the FH plane and passing through ANS. | |
| Choanae plane | The plane along the choanae. | |
| C3 plane | Parallel to the FH plane and passing through the third cervical vertebra. | |
| Measurements | ||
| CSA1 | The cross-sectional area at ANS perpendicular plane. | |
| CSA2 | The cross-sectional area at Choanae. | |
| CSA3 | The cross-sectional area at the third cervical vertebra. | |
| Nasal cavity volume | The airway volume of the area enclosed by the frontal (ANS-perpendicular) plane, the sides (Choanae) plane, the maxillary sinus opening, and the very highest level (FH) plane. | |
| Nasophrynx vloume | The airway volume of the area enclosed between the C3 plane below and the choanae plane above. | |
| Total upper airway volume | The sum of nasal cavity volume and nasophrynx vloume. | |
Fig. 5.
(A) Skeletal landmarks; and (B) skeletal and dentoalveolar measurements
Upper airway analysis was performed using anatomical landmarks including the anterior nasal spine (ANS), choanae, and the third cervical vertebra (C3), in combination with standardized horizontal and vertical reference planes [21]. The airway was divided into two regions: the nasal cavity and nasopharynx (Table 1; Fig. 6). Segmentation of airway structures was conducted using a semi-automated sculpting process, whereby non-relevant hard and soft tissues were removed [21]. Threshold values were adjusted to optimize visualization and minimize imaging artifacts. A software-based tracing tool (“smart pen”) was used to delineate the airway boundaries, enabling accurate calculation of cross-sectional areas and volumes [21]. Accordingly, cross-sectional areas were measured at three levels: the ANS-perpendicular plane, the choanae plane, and the C3 plane. Volumetric measurements were obtained separately for the nasal cavity and nasopharynx, and the total upper airway volume was calculated as the sum of these compartments (Table 1; Fig. 6).
Fig. 6.
Minimum cross-sectional area measurements at the ANS-perpendicular plane (A), the choanae plane (B), and at the C3 plane (C). Volumetric measurements were obtained separately for the nasal cavity and nasopharynx, and the total upper airway volume was calculated as the sum of these compartments
Outcomes
The outcomes for this secondary analysis were the 3D displacement of the maxilla and mandible, and changes in airway volume and cross-sectional area within the nasal cavity, nasopharynx, and total upper airway following maxillary expansion with TB-RPE and TBB-MARPE.
Successful maxillary expansion was defined as radiographic evidence of midpalatal suture separation observed on periapical radiographs within 4 weeks after initiation of appliance activation. Cases in which suture separation was not achieved were classified as expansion failures.
Randomization, allocation concelment, and implementation
Random sequence generation was performed using a computer-generated permuted block design with a block size of four, implemented in IBM SPSS 24.0 statistical software (IBM Co., Armonk, NY, USA), to ensure balanced group allocation.
Allocation concealment was achieved using sequentially numbered, opaque, sealed envelopes prepared prior to the trial.
Blinding
Blinding of participants, the treating clinician, and the outcome assessor was not feasible due to awareness of the expander type before treatment.
Error study
To evaluate measurement reliability, all variables were assessed twice by a single examiner at a 2-week interval. The examiner was independent of the clinical procedures and not involved in the treatment allocation process.
Intra-examiner reliability was quantified using the intraclass correlation coefficient (ICC), indicating high reliability (ICC > 0.90) (IBM SPSS 24.0 statistical software, IBM Co., Armonk, NY, USA). To further quantify the measurement errors, the Dahlberg error was calculated, [22] demonstrating that the errors for linear and angular measurements were up to 0.262 mm and 0.380°, respectively. The errors for area and volumetric measurements were up to 3.093 mm² and 59.432 mm³, respectively, while the maximum error for skeletal displacement measurements was 0.311 mm (Supplementary Table).
Statistical analysis
All statistical analyses were conducted using IBM SPSS 24.0 statistical software (IBM Co., Armonk, NY, USA). Data distribution was assessed using the Shapiro–Wilk test.
Baseline demographic characteristics were compared between groups using the Pearson chi-square test and the Mann–Whitney U test. Within-group comparisons (T0 versus T2) were performed using the paired t-test and the Wilcoxon signed-rank test. Between-group comparisons of treatment-induced changes were analyzed using the independent t-test and the Mann–Whitney U test. The level of statistical significance was set at 0.05, with corresponding 95% confidence intervals. To control for multiple comparisons, the Benjamini–Hochberg false discovery rate (FDR) procedure was applied within predefined families of related outcomes, including maxillary, mandibular, and hyoid bone displacements in each spatial dimension (anteroposterior, transverse, and vertical) and upper airway changes [23]. Statistical significance was determined using FDR-adjusted p-values, with an adjusted significance level of P < 0.05 for both within-group and between-group analyses.
Results
Participant flow, baseline characteristics, and primary outcomes of the original trial have been reported previously [8].
For the present secondary analysis, 8 patients (7 from the TB-RPE group and 1 from the TBB-MARPE group) were excluded due to failure of midpalatal suture separation (n = 3) and inadequate CBCT records for skeletal and airway analyses (n = 5) (Fig. 1).
Consequently, a total of 32 patients were included in the final analysis, comprising 13 patients in the TB-RPE group (aged 8–20 years) and 19 patients in the TBB-MARPE group (aged 8–20 years) (Fig. 1). This sample provided at least 80% statistical power to detect intergroup differences in maxillary transverse expansion and total upper airway volume changes, with a significance level of 0.05 and effect sizes of 0.92 and 1.98, respectively, using an independent t-test.
The demographic characteristics of the sample population are summarized in Table 2. No significant differences were observed between groups in terms of age, age group, or sex distribution (p > 0.05). At baseline (T0), there were no statistically significant intergroup differences in the Yonsei Transverse Index (YTI) 24]. or airway measurements (p > 0.05, Table 2).
Table 2.
Demographic characteristics of the study sample at T0
| Variables | TB-RPE (n = 13) |
TBB-MARPE (n = 19) |
P | |
|---|---|---|---|---|
| Age (years) | 13.15 3.85 |
13.68 4.20 |
0.902 | |
| Age group (years) | 8- < 11 | 3 | 6 | 0.599 |
| 11–20 | 10 | 13 | ||
| Gender | Male | 4 | 8 | 0.515 |
| Female | 9 | 11 | ||
| YTI (mm) | -3.01 2.53 |
-4.05 2.06 |
0.099 | |
| CSA1 (mm2) | 180.44 10.53 |
185.10 13.08 |
0.238 | |
| CSA2 (mm2) | 340.15 29.04 |
348.75 24.93 |
0.495 | |
| CSA3 (mm2) | 233.74 33.68 |
230.30 35.13 |
0.705 | |
| Nasal cavity volume (mm3) | 6854.76 566.86 |
6990.28 578.63 |
0.516 | |
| Nasopharynx volume (mm3) | 17276.8569 697.15 |
17110.54 669.98 |
0.507 | |
| Total upper airway volume (mm3) | 24131.62 1041.48 |
24100.82 758.45 |
0.923 | |
Data are shown as mean ± standard deviation
Intergroup comparisons were tested by Pearson chi-square test (age group and gender), and Mann-Whitney U test (others)
Changes in maxillary expansion and molar inclinations are presented in Table 3. Both groups demonstrated significant skeletal and dental expansion following treatment (p < 0.05). The TBB-MARPE group presented greater transverse skeletal expansion compared to TB-RPE (p < 0.05). Specifically, mean increases in the TBB-MARPE group were approximately 2.20 mm at the nasal cavity, 3.13 mm at the nasal floor width, and 5.30 mm at the intermolar width. Whereas, corresponding increases in the TB-RPE group were 1.39 mm, 1.77 mm, and 4.91 mm, respectively. No significant intergroup difference was observed in changes in molar inclination. However, within-group analysis revealed a significant increase of in maxillary first molar inclination following the consolidation period in the TB-RPE group (mean, 2.280; p < 0.05).
Table 3.
Maxillary expansion and molar inclination changes after orthopedic maxillary expansion by using TB-RPE and TBB-MARPE
| Measurements | TB-RPE | TBB-MARPE | Sig.†† | ||||||
|---|---|---|---|---|---|---|---|---|---|
| T0 | T2 |
 T2-T0 |
p † | T0 | T2 |
 T2-T0 |
p † | ||
| Nasal cavity width (mm) | 32.92 4.09 |
34.24 3.73 |
1.31 0.94 |
0.000* | 33.29 2.29 |
35.49 2.21 |
2.20 0.93 |
0.000* | 0.014* |
| Nasal floor width (mm) | 66.53 3.89 |
68.30 3.86 |
1.77 1.33 |
0.000* | 63.85 3.45 |
66.99 3.06 |
3.13 1.59 |
0.000* | 0.014* |
| Intermolar width (mm) | 44.26 3.43 |
49.17 3.25 |
4.91 1.87 |
0.000* | 44.96 3.05 |
50.26 3.01 |
5.30 1.73 |
0.000* | 0.557 |
| Molar inclination (R) (0) | 8.99 5.18 |
9.92 6.62 |
0.93 4.85 |
0.502 | 9.63 5.62 |
11.27 5.88 |
1.64 4.44 |
0.125 | 0.678 |
| Molar inclination (L) (0) | 10.79 6.74 |
13.08 7.03 |
2.28 3.34 |
0.030* | 11.35 6.64 |
12.93 7.51 |
1.58 4.25 |
0.123 | 0.604 |
Data are shown as mean ± standard deviation
T0, before maxillary expansion
T2, after a 3-month post-expansion consolidation period
* Statistically significant at p < 0.05
† Intragroup difference (T0 versus T2) was tested by pair t-test, †† Intergroup differences in the amount of maxillary expansion and molar inclination changes were evaluated by independence t-test
Skeletal displacements associated with maxillary expansion are shown in Table 4. No statistically significant intergroup differences were identified in the displacement of any skeletal landmarks. In the TB-RPE group, ANS and A point demonstrated anterior and displacements of approximately 0.43 mm and 0.51 mm, along with inferior displacements of 0.70 mm and 0.96 mm, respectively (p < 0.05). Similarly, in the TBB-MARPE group, ANS and A point moved forward by approximately 0.76 mm and 0.49 mm, and downward by 0.81 mm and 0.87 mm (p < 0.05). However, no significant position changes were noted for mandibular landmarks or the hyoid bone in either group.
Table 4.
Skeletal displacements after TB-RPE and TBB-MARPE (mm)
| Landmarks | Coordinate | TB-RPE | p † | TBB-MARPE | p † | Sig. †† |
|---|---|---|---|---|---|---|
| PNS |
 Fx |
0.11 0.38 |
0.329 | 0.03 0.48 |
0.815 | 0.599 |
 Fy |
-0.34 0.76 |
0.135 | -0.59 0.35 |
0.080 | 0.216 | |
 Fz |
-0.41 0.50 |
0.013* | -0.81 0.73 |
0.000** | 0.074 | |
| ANS |
 Fx |
0.10 0.62 |
0.574 | -0.30 0.66 |
0.064 | 0.094 |
 Fy |
-0.43 0.52 |
0.011* | -0.76 0.88 |
0.001* | 0.189 | |
 Fz |
-0.70 1.09 |
0.039* | -0.81 0.60 |
0.000** | 0.731 | |
| A point |
 Fx |
0.15 0.52 |
0.333 | -0.18 0.64 |
0.230 | 0.122 |
 Fy |
-0.51 0.48 |
0.002* | -0.49 0.55 |
0.001* | 0.911 | |
 Fz |
-0.96 1.49 |
0.039* | -0.87 0.93 |
0.001* | 0.844 | |
| B point |
 Fx |
0.16 0.62 |
0.367 | 0.00 0.86 |
0.979 | 0.555 |
 Fy |
0.17 1.44 |
0.680 | 0.70 1.65 |
0.079 | 0.339 | |
 Fz |
-0.88 2.33 |
0.200 | -0.45 1.95 |
0.218 | 0.590 | |
| Pog |
 Fx |
0.49 1.04 |
0.115 | -0.26 1.00 |
0.276 | 0.053 |
 Fy |
-0.11 1.29 |
0.768 | 0.69 1.64 |
0.082 | 0.133 | |
 Fz |
-0.50 1.60 |
0.283 | -0.51 1.23 |
0.084 | 0.976 | |
| Me |
 Fx |
0.38 1.04 |
0.206 | -0.04 1.13 |
0.904 | 0.292 |
 Fy |
-0.19 1.61 |
0.674 | 0.72 1.70 |
0.082 | 0.136 | |
 Fz |
-0.65 1.39 |
0.116 | -0.15 1.04 |
0.530 | 0.282 | |
| Co (L) |
 Fx |
0.24 0.95 |
0.384 | 0.22 0.49 |
0.067 | 0.946 |
 Fy |
0.25 0.85 |
0.320 | 0.09 0.88 |
0.645 | 0.631 | |
 Fz |
0.43 1.28 |
0.247 | -0.30 1.27 |
0.316 | 0.123 | |
| Co (R) |
 Fx |
0.04 0.33 |
0.680 | 0.23 0.78 |
0.211 | 0.344 |
 Fy |
0.38 0.72 |
0.084 | 0.43 1.04 |
0.090 | 0.857 | |
 Fz |
-0.03 1.26 |
0.931 | 0.39 1.26 |
0.200 | 0.365 | |
| Go (L) |
 Fx |
0.51 0.88 |
0.061 | 0.38 0.91 |
0.085 | 0.692 |
 Fy |
-0.21 1.28 |
0.571 | 0.53 1.38 |
0.111 | 0.133 | |
 Fz |
-0.71 1.43 |
0.100 | -0.21 1.26 |
0.467 | 0.327 | |
| Go (R) |
 Fx |
0.42 0.92 |
0.122 | -0.18 0.56 |
0.179 | 0.402 |
 Fy |
0.26 1.13 |
0.422 | 0.60 1.44 |
0.087 | 0.465 | |
 Fz |
-0.55 1.22 |
0.128 | -0.63 1.50 |
0.086 | 0.882 | |
| Hyoid |
 Fx |
0.41 1.23 |
0.248 | -0.04 1.59 |
0.910 | 0.368 |
 Fy |
-0.84 5.46 |
0.590 | 1.18 3.44 |
0.151 | 0.251 | |
 Fz |
-1.79 3.21 |
0.067 | 0.16 3.00 |
0.815 | 0.095 |
Data are shown as mean
standard deviation
* Statistically significant at FDR-adjusted p < 0.05
† Intragroup difference was tesetd by pair t-test, †† Intergroup difference was evaluated by independence t-test
Upper airway changes following expansion are presented in Table 5. Significant increases were observed in the anterior and middle cross-sectional areas, nasal cavity volume, and total upper airway volume in both groups (p < 0.05), with greater increases in the TBB-MARPE group (p < 0.05). In contrast, no statistically significant changes were detected in the posterior cross-sectional area or nasopharynx volume.
Table 5.
Upper airway changes after orthopedic maxillary expansion by using TB-RPE and TBB-MARPE
 Airway Measurements |
C-RPE | p † | TBB-MARPE | p † | Sig.†† |
|---|---|---|---|---|---|
| CSA1 (mm2) | 30.79 7.54 |
0.000* | 80.32 7.42 |
0.000* | 0.000* |
| CSA2 (mm2) | 78.40 6.52 |
0.000* | 120.69 8.39 |
0.000* | 0.000* |
| CSA3 (mm2) | 1.51 2.85 |
0.080 | 1.14 2.39 |
0.052 | 0.704 |
| Nasal cavity volume (mm3) | 515.47 184.06 |
0.000* | 1179.96 201.52 |
0.000* | 0.000* |
| Nasopharynx volume (mm3) | 70.62 130.53 |
0.075 | 142.43 303.96 |
0.056 | 0.369 |
| Total upper airway volume (mm3) | 586.10 311.58 |
0.000* | 1322.39 407.14 |
0.000* | 0.000* |
Data are shown as mean ± standard deviation
* Statistically significant at FDR-adjusted p < 0.05.
† Intragroup difference was tested by pair t-test, †† Intergroup difference was evaluated by independence t-test.
Correlation analysis demonstrated a significant positive association between increases in nasal cavity width and nasal floor width and changes in nasal cavity volume and total upper airway volume (p < 0.05, Tables 6 and 7).
Table 6.
Pearson’s correlation analysis between the upper airway changes and skeletal displacements after TB-RPE
| CSA1 | CSA2 | Nasal cavity volume | Total upper airway volume | ||
|---|---|---|---|---|---|
| Nasal cavity width | -0.204 | -0.045 | 0.649* | 0.661* | |
| Nasal floor width | 0.100 | -0.020 | 0.648* | 0.695* | |
| Intermolar width | 0.315 | 0.041 | 0.376 | 0.351 | |
| Molar inclination (L) | 0.479 | 0.268 | -0.334 | -0.272 | |
| PNS |
Fz
|
-0.075 | 0.139 | -0.300 | -0.276 |
| ANS |
Fy
|
-0.121 | -0.119 | -0.077 | -0.058 |
Fz
|
-0.120 | -0.063 | -0.304 | -0.317 | |
| A point |
Fy
|
0.305 | 0.031 | -0.364 | -0.320 |
Fz
|
0.108 | 0.429 | -0.323 | -0.353 | |
* Statistically significant at p < 0.05
Table 7.
Pearson’s correlation analysis between the upper airway changes and skeletal displacements after TBB-MARPE
| CSA1 | CSA2 | Nasal cavity volume | Total upper airway volume | ||
|---|---|---|---|---|---|
| Nasal cavity width | -0.187 | 0.194 | 0.409 | 0.571* | |
| Nasal floor width | -0.231 | -0.002 | 0.648* | 0.740* | |
| Intermolar width | -0.303 | -0.331 | 0.425 | 0.545* | |
| PNS |
Fz
|
0.000 | -0.243 | 0.062 | -0.205 |
| ANS |
Fy
|
-0.298 | -0.152 | 0.135 | -0.058 |
Fz
|
-0.297 | -0.164 | -0.184 | -0.026 | |
| A point |
Fy
|
0.325 | 0.306 | -0.025 | -0.261 |
Fz
|
-0.104 | -0.055 | -0.164 | -0.205 | |
* Statistically significant at p < 0.05
Discussion
This study is a secondary analysis of a previously conducted RCT involving adolescent and young adult patients with transverse maxillary deficiency, who were randomly treated with either TB-RPE or TBB-MARPE [8]. Low-dose CBCT imaging was employed to minimize radiation exposure during the critical growth period. To the best of our knowledge, this is the first comparative study to comprehensively evaluate 3D displacements of the maxilla and mandible, and upper airway changes, in growing patients treated with TB-RPE versus TBB-MARPE. In addition, the relationship between skeletal movements and upper airway alterations following orthopedic maxillary expansion was investigated.
The findings indicated that, although TBB-MARPE facilitated greater maxillary expansion and enlargement of the upper airway after the consolidation period, both treatment modalities produced similar extent of forward and downward maxillary displacement and maintained a stable mandibular position. Orthopedic maxillary expansion significantly improved nasal cavity volume but had minimal effect on nasopharyngeal airway dimensions, regardless of the expander type used in this study.
Several factors influence the effectiveness of orthopedic maxillary expansion and the associated airway changes, including appliance design and patient demographic characteristics [25, 26]. In this study, both expanders were anchored to four bands on the maxillary first premolars and first molars, with the main distinction being the presence or absence of bone anchorage via miniscrews. Comparison of demographic variables, including age and gender, showed no significant differences between groups. Baseline evaluations revealed no intergroup differences in maxillomandibular transverse discrepancy, assessed by the Yonsei Transverse Index (YTI) measured at the estimated center of resistance of the posterior segment using CBCT imaging, [24] or in any airway parameters, confirming comparability between groups before treatment (Table 2).
The efficacy of RPE and MARPE in achieving transverse maxillary expansion has been reported previously [8, 17, 27]. In agreement with prior studies, both TB-RPE and TBB-MARPE in this study produced effective expansion with a triangular pattern, with the base at the dental arch level. This pattern is attributed to the force vector being applied below the estimated center of resistance of the maxilla, which is supported by multiple bony structures, including the calvarial bones, irrespective of the presence of miniscrews [1–4, 8]. In the current study, TBB-MARPE achieved greater skeletal transverse expansion, with mean increases from intermolar width (TB-RPE, 4.91 mm; TBB-MARPE, 5.30 mm) to nasal cavity width (TB-RPE, 1.77 mm; TBB-MARPE, 3.13 mm), and nasal floor width (TB-RPE, 1.39 mm; TBB-MARPE, 2.20 mm). However, no significant intergroup differences were observed in the extent of first molar inclination changes (Table 3). Since the main difference in the expander designs used in this study was the presence of bone anchorage via miniscrews, these findings highlight the important role of bone anchorage in enhancing skeletal expansion; however, it does not guarantee translation of the anchored teeth to the buccal side during orthopedic expansion [8].
In addition to transverse effects, this study investigated sagittal and vertical displacements of the maxilla and mandible. Although intergroup differences in transverse expansion were observed, no significant differences were found in any skeletal landmark displacements between TB-RPE and TBB-MARPE, which may be explained by the small magnitude of maxillary movement and insignificant mandibular displacement after the 3-month consolidation period (Table 4). Both groups exhibited slight forward and downward maxillary movement, as indicated by ANS and A point displacements. This aligns with previous reports suggesting that orthopedic expansion not only separates the midpalatal suture but also exerts forces on the circummaxillary system, resulting in modest skeletal movements [28, 29]. On the other hand, prior studies have reported immediate clockwise rotation of the mandible after maxillary expansion, attributed to buccal tipping of anchored teeth and the resultant extrusion of their palatal cusps [9, 30]. In contrast, this study investigated skeletal effects after a 3-month consolidation period, during which partial dental decompensation may have occurred. This may contribute to derotation or stabilization of the mandible over this period. Consequently, no significant alterations in either sagittal or vertical dimensions of the mandible were observed in either group, confirming findings from previous long-termstudies (Table 4) [31–33].
Previous studies have suggested that both RPE and MARPE may improve nasal function by increasing nasal cavity dimensions following maxillary expansion [34]. For example, Mehta et al. investigated the long-term effects of TB-RPE and bone-borne MARPE (BB-MARPE) using CBCT and reported that both modalities increased nasal cavity width and alar base width in the short term; however, sustained long-term improvement was observed only in the BB-MARPE group [14]. Similarly, other RCT investigations assessing nasal airflow changes in patients treated with TB-RPE and TBB-MARPE with two anterior miniscrews demonstrated comparable success rates for midpalatal suture opening between groups, while indicating that TBB-MARPE may produce more pronounced improvements in nasal patency [17]. Variability in skeletal outcomes following MARPE has been widely reported and is likely attributed to differences in appliance design, including the number and positioning of miniscrews and the placement of the expander [35, 36].
In the present study, both expanders shared an identical tooth-borne framework, with the primary distinction being the addition of skeletal anchorage via two anterior and two posterior miniscrews in the TBB-MARPE group (Fig. 2). Despite potential variations in MARPE configurations in the literature, the current findings are consistent with previous evidence demonstrating significant increases in airway dimensions at the nasal cavity level following maxillary expansion [14, 17]. Specifically, both groups exhibited significant increases in cross-sectional area at the ANS-perpendicular plane and the choanae plane, as well as in nasal cavity volume and total upper airway volume after the consolidation period, with greater changes observed in the TBB-MARPE group (Table 5). Furthermore, a statistically significant positive correlation was identified between the amount of maxillary expansion and the corresponding increase in nasal cavity volume in both groups (Tables 6 and 7). Consistent with the greater extent of maxillary transverse expansion observed in the TBB-MARPE group (Table 3), these findings underscore the contribution of skeletal anchorage to enhancing not only maxillary expansion but also its subsequent impact on nasal airway dimensions.
This study has some limitations. Firstly, the evaluation of airway changes was limited to static morphological measurements derived from CBCT imaging, without assessment of dynamic airway function or respiratory performance due to the availability of the prior RCT data. Second, the follow-up period was restricted to the short-term consolidation phase; therefore, the long-term stability of the observed skeletal and airway changes could not be determined. Third, although no significant between-group differences in age or sex distribution were observed and efforts were made to minimize potential confounding, the influence of age- and sex-related biological differences on the 3D displacement of the maxilla and mandible and on airway changes following MARPE and RPE remains unclear. Further studies with larger sample sizes should be performed to evaluate the long-term effects of MARPE and RPE, especially in patients with breathing disorders, and to determine whether treatment responses to these two treatment modalities differ according to chronological age and sex.
Conclusions
Both TB-RPE and TBB-MARPE effectively facilitated maxillary expansion and upper airway enlargement after the consolidation period, with greater changes in the TBB-MARPE group.
Following maxillary transverse expansion, similar maxillary displacements were observed in both groups, with approximately 0.5 mm of forward movement and 1.0 mm of downward movement at A point, whereas mandibular positional changes were not significant.
Orthopedic maxillary expansion by both treatment modalities positively improves upper airway volume at the nasal cavity level but does not significantly affect the nasopharyngeal airway.
Supplementary Information
Supplementary Material 1: Supplementary Table. Intraclass correlation coefficient analysis and Dahlberg error of each variables between two assessments taken at 2-week intervals.
Acknowledgements
Not Applicable.
Authors’ contributions
Dr. Hai-Van Giap and Dr. Moayad Alomaym have equally contributed as first authors. Hai-Van Giap and Moayad Alomaym participated in data collection, processing, analyzing, writing, and editing the original draft. Joo-Hee Chun performed clinical operations and data curation. Chooryung J. Chung, Sung-Hwan Choi, and Amani Alkhamees contributed to manuscript editing. Kee-Joon Lee made the major clinical decisions while participating in writing, reviewing, and editing the manuscript. All authors reviewed the manuscript.
Funding
This case report was supported by the research grant from the National IT Industry Promotion Agency (NIPA) in Korea (S0901-25-1003).
Data availability
The datasets used and/or analyzed during the current study are available from the corresponding author upon request.
Declarations
Ethics approval and consent to participate
The study protocol conformed to the Declaration of Helsinki and was approved by the Institutional Review Board of Yonsei University Dental Hospital (IRB No. 2-2024-0067). The original trial was retrospectively registered at the WHO International Clinical Trial Registry Platform (Registration number: KCT0006871 / Registration date 27/12/2021). No modifications to the study protocol or trial procedures were implemented after trial initiation. Written informed consent was obtained from all participants prior their inclusion in the study, in which consent to participate was obtained from the parents or legal guardians of any participant under the age of 16.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Hai-Van Giap and Moayad Alomaym have equally contributed as first authors.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Supplementary Material 1: Supplementary Table. Intraclass correlation coefficient analysis and Dahlberg error of each variables between two assessments taken at 2-week intervals.
Data Availability Statement
The datasets used and/or analyzed during the current study are available from the corresponding author upon request.