Abstract
Backgroud
Maxillary transverse deficiency in adults presents a therapeutic challenge due to fused craniofacial sutures. This study aimed to assess the changes in craniofacial sutures induced by C-expander treatment in adults.
Methodology
This retrospective study included 35 patients diagnosed with maxillary transverse deficiency following successful treatment with C-expander. Cone- beam computed tomography(CBCT)scans were performed and analyzed both before and after the intervention. Changes in the widths of nine craniofacial sutures were measured and compared, including the frontonasal, frontomaxillary, frontozygomatic, nasomaxillary, internasal, pterygomaxillary, zygomaticomaxillary, temporozygomatic, and midpalatal sutures. Additionally, five linear measurements in the coronal plane were quantified and analyzed.
Results
C-expander induced significant increases in the widths of the midpalatal, frontomaxillary, nasomaxillary, internasal, frontozygomatic, superior zygomaticotemporal and pterygomaxillary sutures (P < 0.05), except the zygomaticomaxillary and inferior zygomaticotemporal sutures (P > 0.05). The most pronounced increase was observed in the midpalatal suture (3.76 ± 1.63 mm), followed by the frontomaxillary (1.25 ± 0.70 mm) and the inferior nasomaxillary sutures (0.64 ± 0.41 mm). All of the linear measurements have significant increases (P < 0.05). The largest change was at the maxillary base bone width (3.61 ± 1.34 mm), followed by the inter-zygomaticomaxillary suture width (3.16 ± 1.05 mm), the inter-zygomaticotemporal suture width (1.67 ± 0.49 mm), the inter-frontozygomatic suture width (0.43 ± 0.26 mm), and the inter-frontomaxillary suture width (0.30 ± 0.19 mm).
Conclusions
C-expander treatment achieves clinically significant midpalatal suture expansion in adults with maxillary transverse deficiency, and widens most craniofacial sutures. Suture displacement magnitude varies by suture site, the greater anterior suture expansion may drive a clinically clockwise rotation of the nasomaxillary complex.
Keywords: C-expander, Maxillary expansion, Craniofacial suture, Maxillary transverse deficiency, Midpalatal suture, Adult
Introduction
Maxillary transverse deficiency (MTD) is a prevalent craniofacial condition, with a prevalence of nearly 10% in adult orthodontic patients, which is characterized by a narrow maxillary arch, dental crowding, buccal tipping of posterior teeth and compromised arch coordination, affecting both adolescents and adults [1]. Rapid maxillary expansion (RME) appliance, a widely adopted treatment for MTD in adolescents, demonstrates high rate of success and longterm stability. However, with progressive interdigitation of the midpalatal suture during skeletal maturation, achieving effective separation becomes increasingly challenging in adults [2].
To overcome this limitation in adults, surgically assisted rapid palatal expansion (SARPE) was developed, which including Le Fort I osteotomy and separation of the midpalatal and other resistant sutures to facilitate expansion. While effective, SARPE carries significant risks, including postoperative pain, hemorrhage, periodontal defects, sinusitis, and in rare cases, serious complications such as skull base fractures [3]. The substantial morbidity and cost associated with SARPE have driven the search for less invasive alternatives. Recently, miniscrew-assisted rapid palatal expansion (MARPE) has been applied in adults to open the midpalatal suture with minimally invasive, as an effective alternative to SARPE [4, 5]. Compared to RME and SARPE, MARPE leads to a more parallel expansion of the midpalatal suture, with less dentoalveolar side effect. For all its virtues, MARPE still has some disadvantages, including its anchor teeth buccal tipping, root resorption, screw loosening, jackscrew malfunction, pain, and soft tissue inflammation [6, 7].
More recently, a tissue-bone-borne appliance, the C-expander, has been used to correct MTD in adults, and achieved an approximal parallel expansion of the midpalatal sutures [8]. C-expander comprises two acrylic resin plates with an expansion screw, anchored to the palatal slope using four miniscrews. Supported by skeletal anchorage, orthopedic force is evenly dispersed to maxilla through the resin plates, with less stress concentration around the miniscrews, thereby minimizing the risk of screw loosening, unwanted dental effects, and promoting a more efficient transfer of force to the maxillary skeleton [9].
As the maxilla articulates with the frontal, nasal, zygomatic, and sphenoid bones via sutural connections, biomechanical stresses may propagate through these craniofacial junctions. Therefore, in mature adults, the resistance to expansion is not solely due to the midpalatal suture. Instead, it is offered by a complex network of tightly interdigitated craniofacial sutures [9–11]. The clinical success of any non-surgical expansion device hinges on its ability to generate sufficient orthopedic force to overcome the resistance of this entire network, not just the midpalatal suture.
Finite element model (FEM) studies of C-expander have provided valuable insights into its biomechanical action, also revealing that the forces are dissipated not only through the maxilla but also across pterygoid, zygomatic, frontal and nasal bones, which are connected with maxilla via sutures [9, 10]. Notably, significant stress concentrations have been identified along the midpalatal, pterygomaxillary, and zygomaxillary sutures, suggesting their potential for remodeling [10].
While FEM analyses are powerful for predicting stress patterns, they cannot directly quantify the actual biological response—specifically, the morphological changes in suture width that constitute true skeletal expansion. Clinical trials using CBCT have shown that RME in adolescent induces dramatics changes of craniofacial sutures [12, 13]. However, few study focus on the effect of maxillary expansion appliance on craniofacial sutures in adults. The work of Cho et al. was the only relevant study identified; it demonstrated that MARPE can increase the width of nine circummaxillary sutures in adults, including the frontonasal, frontomaxillary, frontozygomatic, nasomaxillary, zygomaticomaxillary, intermaxillary, midpalatal, zygomaticotemporal, and pterygopalatine sutures [14]. Due to the unique expansion mechanism, C-expander produces different dental and skeletal outcomes compared with RME and MARPE [15, 16]. A critical gap remains in the literature, as no clinical study has quantitatively evaluated the three-dimensional morphological changes in the craniofacial sutures following expansion with the C-expander in adult patients.
Therefore, this study aimed to test the null hypothesis that the craniofacial sutures would exhibit no significant bony displacement following treatment with the C-expander in adults. The findings of this study will provide essential clinical evidence regarding the orthopedic effects of C-expander, clarifying its mechanism of action and its potential as a truly non-surgical alternative for correcting MTD in adults.
Materials and methods
This retrospective study was approved by the Medical Ethics Committee of Xiangya Central South University in accordance with the Declaration of Helsinki (No. 202308113). The sample size for this study was determined according to a power analysis performed by Cho et al. in a comparable cohort, which indicated that 23 subjects would be required to achieve a power of 0.85 with a two-tailed alpha of 0.05 [14]. A total of 35 adult patients with maxillary transverse deficiency were subsequently recruited from the Department of Orthodontics at Xiangya Hospital.
In accordance with the Declaration of Helsinki, all patients provided written informed consent. The inclusion criteria were as follows: (1) age > 18 years; (2) diagnosis of maxillary transverse deficiency; (3) availability of CBCT images taken before and three months after the maxillary expansion; and (4) expansion width of jackscrew > 5 mm. The exclusion criteria included patients with syndromic conditions, cleft lip and palate, craniofacial malformations, or a history of prior orthopedic or orthognathic treatment.
Patients underwent maxillary expansion using the C-expander appliance at the start of treatment. The C-expander consists of two resin plates and an expansion screw (028-LXKGQAI, Xihubiom, China). Four miniscrews (1.4 mm × 8 mm, Ormco, USA) were placed into the palatal slope to anchor the appliance (Fig. 1). The expansion screw was activated one-quarter turn every two days until the desired expansion level was achieved. The expansion screw was adjusted to open by 6 to 9 mm.
Fig. 1.
C-expander treatment before (A, B) and after (C) the expansion
CBCT records were obtained at the beginning of treatment (T0) and three months after expansion (T1). Scans were performed using a KaVo apparatus (KaVo Dental, Germany) at 120 kV and 5 mA pulse mode, with a 17 × 23 cm2 field of view, 0.20 mm voxel size, and a scan time of 26.9 s. Images were saved in Digital Imaging and Communication in Medicine (DICOM) format. For analysis, the DICOM files were imported into Invivo 6 software (version 6.0, Anatomage, San Jose, CA, USA) and reoriented in three planes: the axial view aligned with the Frankfort plane, the sagittal view passing through the nasion and ANS points, and the coronal view passing through the bilateral porion points (Fig. 2A). As shown in (Fig. 2B, C), and Table 1, nine craniofacial sutures were measured, comprising six bilateral sutures and three single sutures. The resulting linear dimensions were recorded to the nearest 0.01 mm to maximize internal consistency.
Fig. 2.
A Reorientation of head position. B and (C), the craniofacial sutures that measured in this study: 1, frontonasal suture; 2, frontomaxillary suture; 3, internasal suture; 4, nasomaxillary suture; 5, frontozygomatic suture; 6, zygomaticomaxillary suture; 7, zygomaticotemporal suture; 8, midpalatal suture; 9, pterygomaxillary suture
Table 1.
Definition of the line measurements
| Measurements (mm) | definition |
|---|---|
| Coronal view | |
| Frontonasal suture width | The width was measured between the superior and inferior boards at the middle site of the frontonasal suture. |
| Frontomaxillary suture width | The width was measured between the superior and inferior boards at the middle site of the frontomaxillary suture. |
| zygomaticomaxillary suture | The width was measured between proximal and distal boards at the inferior and superior zygomaticomaxillary suture. |
| Zygomaticotemporal suture | The width was measured between proximal and distal boards at the inferior and superior zygomaticotemporal suture. |
| Axial view | |
| Internasal suture width | The width was measured between the proximal and distal boards of the internasal suture at the inferior and superior sites. |
| Nasomaxillary suture width | The width was measured between the proximal and distal boards of the nasomaxillary suture at the inferior and superior sites. |
| Midpalatal suture width | The width was measured between the mesial edges of the midpalatal suture at the posterior nasal spine. |
| zygomaticomaxillary suture | The width was measured between proximal and distal boards at the inferior and superior zygomaticomaxillary suture. |
| Zygomaticotemporal suture | The width was measured between proximal and distal boards at the inferior and superior zygomaticotemporal suture. |
| Sagittal view | |
| Frontozygomatic suture | The width was measured between the superior and inferior boards at the middle site of frontozygomatic suture. |
| Pterygomaxillary suture | The width was measured between the proximal and distal edges of pterygomaxillary suture. |
| zygomaticomaxillary suture | The width was measured between proximal and distal boards at the inferior and superior zygomaticomaxillary suture. |
| Zygomaticotemporal suture | The width was measured between proximal and distal boards at the inferior and superior zygomaticotemporal suture. |
| Inter-suture width | |
| Inter- frontozygomatic suture width (FZW) | The distance between the mesial border of left and right frontozygomatic sutures. |
| Inter- frontomaxillary suture width (FMW) | The distance between the most distal borders of left and right frontomaxillary sutures. |
| Inter-zygomaticomaxillary suture width (ZMW) | The distance between the most inferior borders of left and right zygomaticomaxillary sutures. |
| Inter-Zygomaticotemporal suture width (ZTW) | The distance between the most superior borders of left and right zygomaticotemporal suture. |
| Maxillary base bone width (MBBW) | The distance between the most concave points of the cortical plates on both sides of the maxilla. |
Linear measurements were taken in accordance with the literature, as detailed in Figs. 2 and 3; Table 1 [12–14].
Fig. 3.
Linear measurements taken before (A) and after (B) treatment. FZW, Inter- frontozygomatic suture width; FMW, Inter- frontomaxillary suture width; ZMW, Inter-zygomaticomaxillary suture width; ZTW, Inter-Zygomaticotemporal suture width; MBBW, Maxillary base bone width
The frontonasal and frontomaxillary sutures were assessed in the coronal views (Fig. 4). The nasomaxillary, internasal, and midpalatal sutures were evaluated in the axial views (Figs. 5 and 6). The frontozygomatic and pterygomaxillary sutures were measured in the sagittal views (Fig. 7). The zygomaticomaxillary and zygomaticotemporal sutures were examined in the coronal, axial, and sagittal views at both the superior and inferior regions of the sutures (Figs. 8 and 9).
Fig. 4.
The frontonasal suture before (A) and after (B) treatment. The frontomaxillary suture before (C) and after (D) treatment
Fig. 5.
The superior border of internasal and nasomaxillary sutures before (A) and after (B) treatment. The inferior border of internasal and nasomaxillary sutures before (C) and after (D) treatment
Fig. 6.
The midpalatal suture before （A） and after （B） treatment
Fig. 7.
The frontozygomatic suture before (A) and after (B) treatment. The pterygomaxillary suture before (C) and after (D) treatment
Fig. 8.
The superior zygomaticomaxillary suture before (A) and after (B) treatment at coronal, sagittal, and axial views, respectively; The inferior zygomaticomaxillary suture before (C) and after (D) treatment at coronal, sagittal, and axial views, respectively. 6U, the superior zygomaticomaxillary suture; 6 L, the inferior zygomaticomaxillary suture
Fig. 9.
The superior zygomaticotemporal suture before (A) and after (B) treatment at coronal, sagittal, and axial views, respectively; The inferior zygomaticotemporal suture before (C) and after (D) treatment at coronal, sagittal, and axial views, respectively. 7U, superior zygomaticotemporal suture; 7 L, inferior zygomaticotemporal suture
By adjusting the cursor to the same reference point for T0 and T1, the location of each suture was identified based on its position within the three-dimensional volume model, following methodologies outlined in previous research [12]. To evaluate random error in the methodology, 10 CBCT records were randomly selected and measured by the same examiner three times at two-week intervals. To assess inter-observer reliability, CBCT records were re-measured by a second examiner. The intraclass correlation coefficient (ICC) was calculated to determine the reliability of the measurements.
Statistical analysis
Data analysis was conducted using SPSS 22.0 software. The Shapiro‒Wilk test and Levene’s test were applied to assess data normality and homogeneity of variance, respectively. A paired t-test and Wilcoxon rank-sum test were used to evaluate differences in measurements between T0 and T1 for normally and non-normally distributed data, respectively. Cohen’s d test was used to assess the effect size between the values at T0 and T1. A confidence level of 95% (P < 0.05) was considered statistically significant.
Results
The average age of the patients was 22.45 years (range: 18–31 years, 5 males, 30 females). The expansion screw was adjusted to open by 6 to 9 mm. According to the ICC analysis, both intra- and inter-examiner reliability showed excellent agreement (ICC values > 0.80), indicating strong reliability. No significant differences were observed in the width variations of bilateral sutures between the left and right sides (Table 2). As a result, the mean widths of the left and right sutures were used to analyze the differences between T0 and T1.
Table 2.
Comparison of the changes in bilateral suture width between right and left (mean ± SD) (mm)
| Measurements | T1-T0 (R) | T1-T0 (L) | P | Cohen’s d |
|---|---|---|---|---|
| Coronal plane | ||||
| Frontomaxillary suture width | 1.27 ± 1.14 | 1.23 ± 0.69 | 0.744 | 0.02 |
| Superior zygomaticomaxillary suture width | 0.05 ± 0.14 | 0.08 ± 0.17 | 0.663 | 0.19 |
| Inferior zygomaticomaxillary suture width | -0.02 ± 0.12 | -0.03 ± 0.14 | 0.415 | 0.08 |
| Superior zygomaticotemporal suture width | 0.05 ± 0.24 | 0.06 ± 0.16 | 0.589 | 0.05 |
| Inferior zygomaticotemporal suture width | 0.07 ± 0.10 | 0.11 ± 0.22 | 0.380 | 0.23 |
| Axial plane | ||||
| Superior nasomaxillary suture width | 0.33 ± 0.32 | 0.36 ± 0.31 | 0.713 | 0.10 |
| Inferior nasomaxillary suture width | 0.65 ± 0.55 | 0.63 ± 0.32 | 0.931 | 0.04 |
| Superior zygomaticomaxillary suture width | 0.08 ± 0.19 | 0.12 ± 0.19 | 0.465 | 0.21 |
| Inferior zygomaticomaxillary suture width | -0.01 ± 0.07 | 0.08 ± 0.17 | 0.146 | 0.54 |
| Superior zygomaticotemporal suture width | 0.02 ± 0.23 | 0.08 ± 0.17 | 0.175 | 0.30 |
| Inferior zygomaticotemporal suture width | 0.00 ± 0.00 | 0.02 ± 0.04 | 0.363 | 0.71 |
| Sagittal plane | ||||
| Frontozygomatic suture width | 0.37 ± 0.40 | 0.33 ± 0.45 | 0.421 | 0.09 |
| Pterygomaxillary suture width | 0.37 ± 0.31 | 0.40 ± 0.47 | 0.405 | 0.08 |
| Superior zygomaticomaxillary suture width | -0.02 ± 0.17 | 0.03 ± 0.05 | 0.323 | 0.08 |
| Inferior zygomaticomaxillary suture width | 0.03 ± 0.09 | 0.03 ± 0.08 | 0.901 | 0.00 |
| Superior zygomaticotemporal suture width | 0.20 ± 0.19 | 0.23 ± 0.13 | 0.804 | 0.18 |
| Inferior zygomaticotemporal suture width | 0.11 ± 0.17 | 0.15 ± 0.23 | 0.425 | 0.20 |
Suture width
Descriptive statistics for measurements at T0 and T1, including coronal, sagittal, and axial views, as well as the observed variations, are summarized in Tables 3, 4 and 5. Significant increases in the midpalatal suture width were observed in all patients at T1 (PNS, 3.76 ± 1.63 mm). Additionally, significant increases were noted in the frontonasal, frontomaxillary, frontozygomatic, internasal, nasomaxillary, zygomaticotemporal and pterygomaxillary sutures. Among the sutures, aside from the midpalatal suture, the frontomaxillary suture exhibited the greatest changes (1.25 ± 0.70 mm), followed by the inferior nasomaxillary (0.64 ± 0.41 mm), pterygomaxillary (0.38 ± 0.37 mm), frontonasal (0.37 ± 0.29 mm), frontozygomatic (0.35 ± 0.34 mm), superior nasomaxillary (0.34 ± 0.31 mm), superior zygomaticotemporal (0.32 ± 0.14 mm), inferior internasal (0.25 ± 0.15 mm), and superior internasal sutures (0.23 ± 0.21 mm). In contrast, the zygomaticomaxillary and inferior zygomaticotemporal sutures showed no significant changes in coronal, sagittal, or axial views (P > 0.05).
Table 3.
Comparison of the measurements at T0, T1, and the changes in the craniofacial sutures at coronal plane (mean ± SD) (mm)
| Measurements | T0 | T1 | T1-T0 | P | Cohen’s d | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Frontonasal suture width | 0.32 ± 0.14 | 0.69 ± 0.39 | 0.37 ± 0.29 | 0.032 | 1.26 | ||||||
| Frontomaxillary suture width R | 0.23 ± 0.17 | 1.50 ± 1.16 | 1.27 ± 1.14 | 0.004 | 1.53 | ||||||
| Frontomaxillary suture width L | 0.24 ± 0.17 | 1.46 ± 0.64 | 1.23 ± 0.69 | 0.000 | 2.63 | ||||||
| Superior zygomaticomaxillary suture width R | 0.18 ± 0.08 | 0.23 ± 0.16 | 0.05 ± 0.14 | 0.415 | 0.40 | ||||||
| Superior zygomaticomaxillary suture width L | 0.17 ± 0.05 | 0.25 ± 0.16 | 0.08 ± 0.17 | 0.289 | 0.67 | ||||||
| Inferior zygomaticomaxillary suture width R | 0.40 ± 0.21 | 0.38 ± 0.15 | -0.02 ± 0.12 | 0.780 | 0.11 | ||||||
| Inferior zygomaticomaxillary suture width L | 0.45 ± 0.32 | 0.42 ± 0.27 | -0.03 ± 0.14 | 0.576 | 0.10 | ||||||
| Superior zygomaticotemporal suture width R | 0.32 ± 0.19 | 0.37 ± 0.08 | 0.05 ± 0.24 | 0.313 | 0.34 | ||||||
| Superior zygomaticotemporal suture width L | 0.27 ± 0.10 | 0.33 ± 0.18 | 0.06 ± 0.16 | 0.431 | 0.41 | ||||||
| Inferior zygomaticotemporal suture width R | 0.39 ± 0.20 | 0.46 ± 0.22 | 0.07 ± 0.10 | 0.465 | 0.33 | ||||||
| Inferior zygomaticotemporal suture width L | 0.37 ± 0.21 | 0.48 ± 0.26 | 0.11 ± 0.22 | 0.146 | 0.47 | ||||||
Table 4.
Comparison of the measurements at T0, T1, and the changes in the craniofacial suture at axial plane (mean ± SD) (mm)
| Measurements | T0 | T1 | T1-T0 | P | Cohen’s d |
|---|---|---|---|---|---|
| Superior internasal suture width | 0.16 ± 0.08 | 0.39 ± 0.27 | 0.23 ± 0.21 | 0.006 | 1.16 |
| Inferior internasal suture width | 0.16 ± 0.06 | 0.41 ± 0.19 | 0.25 ± 0.15 | 0.001 | 1.77 |
| Superior nasomaxillary suture width R | 0.28 ± 0.12 | 0.61 ± 0.30 | 0.33 ± 0.32 | 0.007 | 1.44 |
| Superior nasomaxillary suture width L | 0.26 ± 0.10 | 0.63 ± 0.31 | 0.36 ± 0.31 | 0.003 | 1.56 |
| Inferior nasomaxillary suture width R | 0.47 ± 0.24 | 1.12 ± 0.63 | 0.65 ± 0.55 | 0.003 | 1.36 |
| Inferior nasomaxillary suture width L | 0.45 ± 0.28 | 1.08 ± 0.40 | 0.63 ± 0.32 | 0.001 | 1.82 |
| Midpalatal suture width | 0.00 ± 0.00 | 3.76 ± 1.63 | 3.76 ± 1.63 | 0.000 | 3.26 |
| Superior zygomaticomaxillary suture width R | 0.10 ± 0.18 | 0.18 ± 0.13 | 0.08 ± 0.19 | 0.256 | 0.51 |
| Superior zygomaticomaxillary suture width L | 0.13 ± 0.10 | 0.25 ± 0.16 | 0.12 ± 0.19 | 0.107 | 0.90 |
| Inferior zygomaticomaxillary suture width R | 0.28 ± 0.20 | 0.27 ± 0.19 | -0.01 ± 0.07 | 0.363 | 0.05 |
| Inferior zygomaticomaxillary suture width L | 0.30 ± 0.18 | 0.38 ± 0.27 | 0.08 ± 0.17 | 0.289 | 0.35 |
| Superior zygomaticotemporal suture width R | 0.47 ± 0.22 | 0.48 ± 0.25 | 0.02 ± 0.23 | 0.866 | 0.08 |
| Superior zygomaticotemporal suture width L | 0.37 ± 0.16 | 0.45 ± 0.28 | 0.08 ± 0.17 | 0.287 | 0.35 |
| Inferior zygomaticotemporal suture width R | 0.00 ± 0.00 | 0.00 ± 0.00 | 0.00 ± 0.00 | 1.00 | 0.00 |
| Inferior zygomaticotemporal suture width L | 0.02 ± 0.04 | 0.00 ± 0.00 | 0.02 ± 0.04 | 0.363 | 0.71 |
Table 5.
Comparison of the measurements at T0, T1, and the changes in the craniofacial suture at sagittal plane (mean ± SD) (mm)
| Measurements | T0 | T1 | T1-T0 | P | Cohen’s d |
|---|---|---|---|---|---|
| Frontozygomatic suture width R | 0.83 ± 0.29 | 1.20 ± 0.46 | 0.37 ± 0.40 | 0.036 | 0.96 |
| Frontozygomatic suture width L | 0.88 ± 0.40 | 1.21 ± 0.47 | 0.33 ± 0.45 | 0.023 | 0.76 |
| Pterygomaxillary suture width R | 0.41 ± 0.16 | 0.78 ± 0.36 | 0.37 ± 0.31 | 0.031 | 1.33 |
| Pterygomaxillary suture width L | 0.43 ± 0.26 | 0.83 ± 0.55 | 0.40 ± 0.47 | 0.006 | 0.93 |
| Superior zygomaticomaxillary suture width R | 0.30 ± 0.13 | 0.28 ± 0.12 | -0.02 ± 0.17 | 0.822 | 0.16 |
| Superior zygomaticomaxillary suture width L | 0.32 ± 0.12 | 0.35 ± 0.10 | 0.03 ± 0.05 | 0.375 | 0.27 |
| Inferior zygomaticomaxillary suture width R | 0.25 ± 0.21 | 0.28 ± 0.19 | 0.03 ± 0.09 | 0.378 | 0.15 |
| Inferior zygomaticomaxillary suture width L | 0.25 ± 0.14 | 0.28 ± 0.16 | 0.03 ± 0.08 | 0.363 | 0.20 |
| Superior zygomaticotemporal suture width R | 0.67 ± 0.26 | 0.87 ± 0.32 | 0.20 ± 0.19 | 0.022 | 0.69 |
| Superior zygomaticotemporal suture width L | 0.72 ± 0.23 | 0.95 ± 0.24 | 0.23 ± 0.13 | 0.017 | 0.98 |
| Inferior zygomaticotemporal suture width R | 0.40 ± 0.15 | 0.51 ± 0.23 | 0.11 ± 0.17 | 0.165 | 0.57 |
| Inferior zygomaticotemporal suture width L | 0.47 ± 0.22 | 0.62 ± 0.20 | 0.15 ± 0.23 | 0.133 | 0.71 |
Inter-sutures width
As shown in Table 6, all linear measurements increased significantly at T1 compared with the initial values. The Maxillary base bone width exhibited the greatest change (3.61 ± 1.34 mm), followed by the inter-zygomaticomaxillary suture width (3.16 ± 1.05 mm), the inter-zygomaticotemporal suture width (1.67 ± 0.49 mm), the inter-frontozygomatic suture width (0.43 ± 0.26 mm), and the inter-frontomaxillary suture width (0.30 ± 0.19 mm).
Table 6.
Comparison of the linear measurements at T0, T1 (mean ± SD)(mm)
| Measurements | T0 | T1 | T1-T0 | P | Cohen’s d |
|---|---|---|---|---|---|
| Inter- frontomaxillary suture width | 15.90 ± 0.97 | 16.20 ± 1.01 | 0.30 ± 0.19 | 0.000 | 0.30 |
| Inter- frontozygomatic suture width | 90.95 ± 3.03 | 91.38 ± 3.07 | 0.43 ± 0.26 | 0.000 | 0.14 |
| Inter-zygomaticotemporal suture width | 113.49 ± 6.11 | 115.17 ± 6.21 | 1.67 ± 0.49 | 0.000 | 0.27 |
| Inter-zygomaticomaxillary suture width | 89.51 ± 2.77 | 92.68 ± 2.69 | 3.16 ± 1.05 | 0.000 | 1.16 |
| Maxillary base bone width | 61.60 ± 2.03 | 65.25 ± 2.22 | 3.61 ± 1.34 | 0.000 | 1.70 |
Discussion
The null hypothesis was rejected, C-expander treatment induced significant increases in the widths of all craniofacial sutures, except the zygomaticomaxillary and inferior zygomaticotemporal sutures. Furthermore, this research fills an important gap in the literature by providing the first clinical evidence detailing the three-dimensional orthopedic effects of the tissue-bone-borne (C-expander) on the craniofacial suture system in adults. The findings offer clinical insight into the non-surgical correction of MTD, demonstrating that this approach can achieve true skeletal expansion.
Post-expansion analysis revealed that the zygomaticomaxillary and inferior zygomaticotemporal sutures exhibited no measurable dimensional changes. This is contrary to Cho’s findings, who demonstrated that MARPE in adult patients induced statistically significant disarticulation across all circummaxillary sutures, including the two sutures [14]. This discrepancy may be attributed to fundamental differences in the biomechanical profiles of the two appliances. Unlike MARPE’s force distribution pattern, C-expander delivers orthopedic forces uniformly across the palatal slopes via its skeletal anchorage system. This design promotes a conical expansion vector on coronal plane, characterized by progressive apical narrowing, which likely redistributes stress away from the zygomaticomaxillary suture [17].
Research indicated that maxillary expansion appliance leaded to triangular separation patterns of the nasomaxillary complex (NMC), due to the circummaxillary sutures’ resistance [8, 16]. In this study, we found that the superior nasomaxillary sutures experienced significantly less changes than the inferior nasomaxillary sutures (0.35 and 0.64, respectively), which provided indirect evidence of a pyramidal cleavage pattern within the NMC. Moreover, the maxillary base bone width increased more than the inter-frontomaxillary suture width by 3.61 mm and 0.30 mm, respectively. This finding further revealed asymmetric outward rotation of the NMC, with a more pronounced effect in the inferior region compared to the superior region.
Yoon demonstrated that maxillary expansion can improve respiratory function in adults with obstructive sleep apnea [18]. In this study, significant increases in the nasomaxillary and internasal sutures are observed, which provides an anatomical basis for respiratory improvements. However, this alteration may impact the aesthetic appearance of the nose. Liu’s findings highlighted a positive relationship between alar width and nasal cavity width, suggesting that maxillary expansion may indirectly influence nasal aesthetics via soft tissue adaptation [19]. Moreover, Alan observed a significant increase in alar nasal width following maxillary expansion [20]. Whether a pretreatment nasal analysis should be taken to assess nose morphology need to discuss in further study. Notably, the nasomaxillary suture exhibited greater changes than internasal suture, which contradicts Ghoneima’s finding (nasomaxillary suture: 0.4 mm, internasal suture: 0.6 mm) [12]. This discrepancy may be partly attributed to differences in patient age. Studies indicate that ossification of the internasal suture typically begins in the 20s and completes by the 30s, whereas the nasomaxillary suture remains incompletely interdigitated in the 60–70s [21]. Therefore, the internasal suture in adults exhibit greater rigidity and resistance to orthopedic expansion force compared to the nasomaxillary suture, underscoring the importance of age-related suture maturation in clinical outcomes.
The frontomaxillary, frontonasal, and frontozygomatic sutures lie along nearly horizontal anatomical planes, reflecting their orientation at the junctions of the frontal bone with the maxilla, nasal, and zygomatic bone, respectively. The frontomaxillary suture exhibited the greatest changes, followed by the frontonasal, and frontozygomatic sutures. The observed hierarchy of sutural expansion is consistent with Priyadarshini’s stress mapping (frontomaxillary suture, 19.6 kg/mm2, frontonasal suture, 9.41 kg/mm2 and frontozygomatic suture, 8.21 kg/mm2), confirming tension magnitude-dependent suture response [22]. However, our results are contrary to the findings of Xu on C-expander, which showed approximate changes between the frontomaxillary and frontonasal sutures, and reduction width changes of the frontozygomatic sutures [23]. The miniscrews’ position in this study was more posterior, which may account for the discrepancy. Choi also suggested that posterior placement of miniscrews can maximize posterior palatal expansion and enhance lateral nasal displacement [24]. The significant increase in the frontomaxillary suture width may be attributed to the direct transmission of stress through the frontal process of the maxilla to the frontal bone [22]. In addition, the varying rates and extents of ossification in facial sutures likely play an important role in determining these differences. For instance, cadaveric studies have shown that the frontomaxillary suture does not begin to close until the 70s [21]. The differing width changes among these three horizontal sutures also provide an anatomical explanation for the downward movement and lateral rotation of the maxilla, as shown in the previous studies using finite element analysis and clinical trials [8–10, 16].
The zygomaticomaxillary and pterygomaxillary sutures, which articulate directly with the maxilla, serve as primary resistance points during the maxillary expansion [25]. The zygomaticomaxillary sutures showed no significant changes at either the superior or inferior sites. This is conflict with the results reported by Allam, who showed a significant decrease in width after treatment [26]. This discrepancy may be attributed to differences in radiographic detection timing. In their study, CBCT was performed only three weeks after MARPE, which may have been insufficient time to observe subsequent bone resorption and sutural reorganization. According to Leonardi’s founding, sutures which articulate directly to the maxilla are more affected by the RME therapy [12]. Interestingly, this study reveals distinct behaviors of the two sutures, as the pterygomaxillary sutures exhibited significant increases. This difference can be explained by the distinct stress patterns acting on these sutures. A finite element analysis revealed that the zygomaticomaxillary sutures experience both compressive and tensile stress simultaneously, while the pterygomaxillary sutures are subjected solely to tensile stress [27]. The observed increases in pterygomaxillary suture width also confirm the forward movement of the maxilla, which facilitates the disarticulation of the pterygopalatine suture, as proved by previous studies [28].
Moreover, we noticed a more pronounced width increase at the anterior (frontomaixllary and nasomaxillary sutures) compared to the posterior (zygomaticomaxillary and pterygomaxillary sutures). This anterior-predominant expansion pattern suggests a tendency for the maxillary complex to undergo clockwise rotation, as previous study showed [8]. Clinically, this rotational effect may have important implications. In patients with a hyperdivergent facial type or vertical growth pattern, such rotation may potentially increase lower facial height and worsen the profile. Therefore, clinicians should carefully evaluate the vertical skeletal pattern before treatment and consider employing orthopedic control or compensatory mechanics to manage this side effect when necessary.
In addition to the frontozygomatic and zygomaticomaxillary sutures, the zygomaticotemporal suture also acts as the primary areas of resistance [13]. Previous studies have measured the width changes of the zygomaticotemporal suture on different axial views of the CT scans, reporting conflicted results [12, 13]. In this study, we measured the zygomaticotemporal suture at the superior and inferior sites on coronal, sagittal, and axial views, respectively. Significant increases were only detected at the superior site on sagittal view. This asymmetric expansion pattern confirms a clockwise rotation of the zygomaticomaxillary complex (ZMC) and supports the hypothesis that the rotational center of the ZMC in the sagittal plane is located near the proximal portion of the zygomatic process of the temporal bone [14]. Additionally, a significant increase in the inter-zygomaticotemporal suture width was observed. According to the mechanical bending theory, structural features of the zygomatic arch, such as elongated, thin, and cylindrical shape, make it more susceptible to deformation under a given load in the cantilever bending mode [29]. Following maxillary expansion, the zygomatic arch appeared to undergo bending deformation. Based on these findings, we speculate that the rotational center of the ZMC in the axial plane is positioned near the distal portion of the zygomatic process of the temporal bone. Cantarella described a distinct center of rotation for the ZMC in cornal plane, which located slightly above the superior aspect of the frontozygomatic suture [30]. In this study, the outward rotation of ZMC was confirmed by the greater increase in inter-zygomaticomaxillary suture width compared to the inter-frontozygomatic suture width. Since the inter-frontozygomatic suture width also increased in our study, the center of rotation we identified was situated slightly higher than that reported by Cantarella. This founding is consistent with Alan’s report [20].
In this study, we confirmed the changes in the craniofacial sutures in adults after maxillary expansion. However, there are still some limitations. First, the activation protocol based on a subjective assessment of the ‘desired level,’ rather than a standardized endpoint. Consequently, the total amount of expansion achieved varied between patients, which limited our ability to directly correlate the expansion with the specific sutural changes. Second, correlations between changes in the midpalatal suture and other craniofacial sutures were not analyzed, due to methodological constraints imposed by the limited sample size. Third, data were collected from a single center. Though this ensured consistency in treatment protocol and radiographic technique, it may limit the generalizability of our findings to broader populations. Moreover, the study sample consisted of 5 males and 30 females, and the uneven gender distribution potentially limits the generalizability of our findings. Future prospective, multicenter studies with larger sample sizes, refine protocol standards and a specific focus on comparing outcomes across genders are warranted to validate these results. At last, our measurements were conducted on two-dimensional CBCT slices. While this provides valuable width data, a full evaluation of three-dimensional volumetric changes within the sutures requires further research. Future studies employing advanced 3D segmentation techniques would be invaluable to overcome this limitation [31].
Conclusions
C-expander treatment is an effective method for widening the midpalatal and craniofacial sutures in adults.
The amount of widening varied among different sutures. Midpalatal suture showed the greatest increases, followed by the frontomaxillary and inferior nasomaxillary sutures.
Sutures adjacent to the maxillary were more prone to being affected by C-expander, except for the zygomaticomaxillary suture.
The nasomaxillary complex underwent a characteristic pyramidal pattern of expansion at sagittal view.
This differential expansion between anterior and posterior sutures may induce a clockwise rotation of the nasomaxillary complex.
Acknowledgements
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Clinical trial number
Not applicable.
Authors’ contributions
Xiaohuan Zhong contributed to conceptualization, methodology, supervision, and revision; Huixin Wang contributed to investigation, resources, statistical analysis, figure preparation and original draft preparation.
Funding
No funding was received.
Data availability
No datasets were generated or analysed during the current study.
Declarations
Ethics approval and consent to participate
The study was approved by the Medical Ethics Committee of Xiangya Central South University in accordance with the Declaration of Helsinki (No. 202308113). All research procedures adhered strictly to the Declaration of Helsinki. Informed consent for the release of anonymized data was secured from all participating patients in this retrospective study, which did not contain any personally identifiable information.
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.
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Associated Data
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Data Availability Statement
No datasets were generated or analysed during the current study.