The Impact of Upper Jaw Expansion Treatment on Vertical Craniofacial Characteristics and Upper Airway Dimensions

Abstract

Aim: This study aimed to assess the impact of rapid palatal expansion (RPE) treatment on vertical craniodentofacial characteristics and upper airway dimensions in individuals with crossbites and skeletal discrepancies. Subjects and Methods: The study involved 38 participants, including 15 boys and 23 girls who received treatment with RPE. Lateral cephalograms were taken before and after the treatment and were analyzed both before and after the treatment using the AudaxCeph version 6.6.12.4731 and Facad software version 3.15.0.1167. For airway dimensions, McNamara analysis was used, and for craniofacial characteristics, cephalometric analysis was used. The study measured 14 parameters in the standard cephalometric analysis and 6 parameters in the airway analysis. Results: The findings indicated a significant decrease in the mandibular angle (MeGoAr, p < 0.001). The angle between the cranial base and the nasal line (SNNL, p = 0.96), intermaxillary angle (p = 0.58), Björk’s polygon (p = 0.67) and the angle between the cranial base and the mandibular angle (SNGoGn, p = 0.96) did not change significantly. A significant increase in the upper pharynx was found after treatment in both the RPE group (p = 0.033) and the RPE + Face Mask (FM) group (p = 0.016) The increase in the upper airway in the RPE group was borderline significant (p = 0.048). Conclusion: No significant differences were found between the experimental groups for changes in airway dimensions after treatment. RPE treatment did not led to an increase in vertical craniodentofacial characteristics. Both RPE and RPE + FM treatments induced an increase in upper pharynx dimensions.

1. Introduction

Maxillary transverse deficiency (MTD) is one of the most common skeletal anomalies in the craniofacial region and the most prevalent affecting the upper jaw [1,2]. This malocclusion occurs during growth and development, and if not treated in a timely manner, it may impact the patient’s permanent dentition. The prevalence in the general population ranges between 2.7% and 23.3% [3]. The etiology of MTD is multifactorial, with one of the most common etiological factors being myofunctional disorders associated with unfavorable oral habits [3]. The activity of the surrounding muscles influences intramembranous bone formation in the maxilla [2]. According to Moss’s functional matrix theory, nasal breathing enables proper craniofacial growth and development. Continuous airflow through the nasal cavities stimulates transverse maxillary growth and the lowering of the palatal vault [4].

Patients with a reduced transverse maxillary dimension often present with unilateral or bilateral crossbites [1].

A transversely deficient maxilla also affects facial esthetics. Features include accentuated nasolabial folds, a narrow alar base and increased dark buccal corridors visible during smiling, creating an unesthetic appearance [5]. The absence of a crossbite does not exclude the presence of a skeletal transverse malocclusion. As previously mentioned, dental compensation often masks the discrepancy in transverse dimensions [6]. Undiagnosed skeletal transverse discrepancies and treating only the crossbite can lead to improper occlusal function, unstable dental corrections and unsatisfactory dentofacial esthetics [7].

Diagnostic methods for transverse deficiencies include the analysis of study casts, posteroanterior cephalograms and CBCT scans. Maxillary expansion, or the widening of the upper jaw, is a therapeutic approach aimed at increasing the transverse dimension of the underdeveloped maxilla by opening the midpalatal suture [8]. The midpalatal suture connects the two palatal bones and remains present during skeletal development. It contains secondary cartilage that changes morphology throughout growth and is sensitive to mechanical loading [9]. The fusion of the maxillary sutures is typically completed around the ages of 14–15 in females and 15–16 in males [10].

The most commonly used method for maxillary expansion today is rapid palatal expansion (RPE). Advocates of this method argue that when high intermittent forces are applied to the posterior teeth, there is insufficient time for significant tooth movement, causing forces to be transmitted to the sutures instead. Consequently, RPE should result in minimal dental tipping and maximal skeletal expansion [11].

Although the primary goal of maxillary expansion is to increase its transverse dimension, the effects extend beyond the maxilla. Since the maxilla is connected to ten different bones of the skull and face, expansion-related changes can also be observed in the mandible, nasal cavity, pharyngeal structures and zygomatic bone [7,11]. A known side effect of maxillary expansion treatment is the extrusion of maxillary posterior teeth, leading to occlusal interferences that induce mandibular post-rotation and an increase in the mandibular plane angle. Some studies analyzing radiographs and study casts have suggested that maxillary expansion results in the forward and downward movement of the entire maxilla. Other studies found no statistically significant maxillary advancement but still reported mandibular post-rotation [12].

As a consequence, vertical facial dimensions increase. While this effect is desirable in patients with deep bites and Class III tendencies, it may negatively impact facial esthetics in patients with open bites, Class II malocclusion, convex profiles, and vertical growth patterns. Studies suggest that the use of bonded hyrax expanders with interocclusal acrylic coverage may help control vertical facial dimensions during RPE. Covering the occlusal surfaces of maxillary posterior teeth with acrylic prevents extrusion and buccal tipping, thereby reducing mandibular post-rotation, bite opening, and facial height increase [12]. A study by Garib et al. found that vertical dimension changes in conventional banded hyrax expansion treatment were not significant in the long term, suggesting that a patient’s vertical growth pattern should not be a contraindication for maxillary expansion [12,13]. Maxillary expansion may also impact the upper airway. Since the nasal cavity structure is largely formed by the maxilla, maxillary expansion increases the distance between the septum and the lateral walls of the nasal cavity while lowering the palate. This leads to an overall enlargement of the nasal cavity’s dimensions, potentially improving nasal airflow and reducing nasal breathing difficulties, but the quality of evidence in this study ranges from low to critically low [3]. Also, different studies showed contradictory results. A study by Kilinç et al. showed a significant increase in upper airway dimensions; in contrast, a study by Baccetti et al. showed no significant difference [14,15]. One study showed that airway stenosis was common in mouth breathing children, which may result in insufficient improvement in breathing despite the increase in upper airway dimensions [16]. Based on this systematic review, it can be concluded that RME causes a significant increase in nasal cavity volume, but its effect on nasopharyngeal and oropharyngeal volume is not statistically significant in the majority of studies. This increase in volume may not be considered as an equivalent for the enhancement of airway function unless proven so. In order to establish its significance in the improvement of breathing, it is necessary to conduct more well-designed RCTs with samples actually comprising mouth breathers [17].

This study aimed to evaluate the effect of maxillary expansion treatment on vertical craniofacial characteristics and upper airway dimensions, measured using lateral cephalograms. Specific objectives included assessing the impact of maxillary expansion treatment on vertical craniofacial features before and after treatment, comparing the effects of banded and acrylic appliances, both individually and in combination with a face mask, and also evaluating the influence of maxillary expansion treatment, with or without a face mask, on upper airway dimensions. The hypotheses proposed were as follows: Maxillary expansion treatment would increase vertical craniofacial characteristics. Banded appliances would have a greater effect than acrylic appliances. Maxillary expansion treatment would not significantly impact airway dimensions.

2. Materials and Methods

2.1. Participants

This retrospective study included patients who were treated with a rapid palatal expander (RPE) device, either alone or in combination with a face mask, between 2021 and 2023 at the orthodontic clinic of the Department of Dental Medicine at the Clinical Hospital Center Rijeka. All parents or guardians of the patients were informed that the medical documentation could be used for scientific research purposes and signed an informed consent form.

The study included 38 participants, 15 boys and 23 girls. The median age of the participants before the start of treatment was 10.3 years (IQR 8.9–11.9 years), and at the end of treatment, it was 11.2 years (IQR 9.7–12.9 years). Out of the total 38, 22 participants were treated with an acrylic RPE device and 16 with a banded device. A total of 20 participants were treated with the RPE device in combination with a facemask. According to previous studies, the sample size for the analysis of changes in vertical dimensions is a minimum of 20 participants [18].

The inclusion criteria for the study were participants of both sexes in the growth period with a transverse maxillary deficiency, the presence of a unilateral or bilateral crossbite, no prior orthodontic treatment and adequate pre- and post-treatment lateral cephalograms. The presence of a transverse maxillary deficiency was detected on dental scans. Dental scans were measured on MeshLab (MeshLab_64 bit version 1.3.4 BETA, Pisa, Italy). Measurements taken were the anterior arch width of the upper and lower jaws, the posterior arch width of the upper and lower jaws and the sum of mesiodistal width of four mandibular incisors (LSI). All measurements were taken in millimeters. The sum of four maxillary incisors (USI) was calculated via Tonn’s formula (LSI × 4)/3 + 0.5. Ideal anterior and posterior arch widths for both the upper and lower jaws were calculated with the Harth index.

The exclusion criteria included the presence of hypodontia, congenital anomalies, craniofacial deformities, systemic diseases affecting craniofacial growth and previous orthodontic treatment.

2.2. Craniofacial Characteristics Analysis

Lateral cephalograms for each participant were taken and analyzed before and after treatment. The median duration of treatment was 9.0 months (IQR 0.9–1.1 years). A standard cephalometric analysis was performed for all 38 participants before and after treatment with the rapid palatal expander, with or without a face mask. Lateral cephalograms for each participant were analyzed by a single researcher on a personal computer using the AudaxCeph software version 6.6.12.4731 (Audax, Ljubljana, Slovenia) for cephalometric analysis. Prior to the measurement, calibration was performed for each lateral cephalogram, and landmarks visible in Figure 1 and Figure 2 were marked on each lateral cephalogram.

2.3. Upper Airway Dimensions Analysis

For 24 participants within the main sample, an airway analysis (McNamara) was also performed. Two experimental groups were formed: one treated only with the RPE device (N = 11, 73% male, median age 11.3 years and [IQR 10.3–11.8 years]) and the other treated with the RPE device in combination with a face mask (N = 13, 31% male, median age 10.9 years and [IQR 9.7–11.9 years]). The decision to add a facemask was based on Wits ≤ −2 mm findings and the presence of a reverse overbite or edge-to-edge incisor relationship. The sample size was estimated based on previous research. A minimum of 11 participants was required for a power of 0.80 and an alpha of 0.05 to detect a 2.4 mm difference in airway dimensions [14]. The median treatment duration was 11.0 months (IQR 9.0–12.0 months) in the RPE group and 11.0 months (IQR 9.5–12.5 months) in the RPE + face mask group. The Facad software version 3.15.0.1167 (Ilexis AB, Linköping, Sweden) was used for airway dimension analysis (airway analysis McNamara).

In the cephalometric analysis, 14 parameters were measured for all 38 subjects, as demonstrated in Figure 1 and described in

Table 1. Display of measured parameters in the cephalometric analysis used.

Measured Parameter	Description
SNA	Position of the maxilla relative to the cranial base
SNB	Position of the mandible relative to the cranial base
ANB	Sagittal intermaxillary relationship
Wits	Linear measurement of the skeletal class
ANPG	Profile of the facial bone structures
SN:NL	Angle between the cranial base and the nasal line
IntermaxAngle	Intermaxillary angle
SArGo	Gonial angle
MeGoAr	Mandibular angle
Bjork	Björk’s polygon
NSGn	Y-axis angle
Sn:gogn	Angle between the cranial base and the mandibular plane
U1Mx	Angle of inclination of the upper incisors to the skeletal base of the maxilla
L1Md	Angle of inclination of the lower incisors to the skeletal base of the mandible

.

In the airway analysis (McNamara) on lateral cephalograms, the cephalometric points and lines are marked, as described in

Table 2. Cephalometric points, lines and measured parameters in the airway analysis (McNamara).

Point, Lines and Measured Parameters	Description
S (Sella turcica)	Central point of the sella turcica
Ba (Basion)	Point on the lower part of the occipital bone
PNS (Posterior Nasal Spine)	Spina nasalis posterior
H (Hormion)	Point on the posterior border of the foramen magnum
AD2 (Adenoid upper point)	Upper point of the adenoids
D1 (Adenoid lower point)	Lower point of the adenoids
SPs (Upper soft palate dorsum)	Upper part of the soft palate dorsum
PPW-s (Posterior pharynx wall, superior point)	Upper point of the posterior wall of the pharynx
APW-mand (Anterior pharynx wall at mandible)	Anterior wall of the pharynx at the level of the mandible.
PPW-i (Posterior pharynx wall, inferior point)	Lower point of the posterior wall of the pharynx
SBa line	Line defined by the points S and Ba
SBa line|PNS	Line perpendicular to the SBa line passing through the PNS point
BaPNS line	Line defined by the points Ba and PNS
Upper airway	Distance between the points AD2 and PNS
Upper adenoid	Distance between the points H and AD2
Lower airway	Distance between the points AD1 and PNS
Lower adenoid	Distance between the points Ba and AD1
Upper pharynx	Minimal distance between the point SPs and the closest point on the posterior pharyngeal wall (PPW-s)
Lower pharynx	Minimal distance between the point APW-mand and the closest point on the posterior pharyngeal wall (PPW-i)

and shown in Figure 2.

For the assessment of the upper airway dimensions in the airway analysis (McNamara), the following parameters were measured for 24 subjects: upper airway, upper adenoid, lower airway, lower adenoid, upper pharynx and lower pharynx (Table 2).

2.4. Statistical Analysis

All data were processed using the SPSS software version 24 (IBM Corp., Armonk, New York, NY, USA). Descriptive statistics were used to calculate the mean and the standard deviation. To test the significance of differences in cephalometric characteristics before and after RPE treatment, a paired t-test was used. For upper airway dimensions, a paired t-test was used for normally distributed data and the Wilcoxon test for non-normally distributed data. The change in airway dimensions between the RPE-only group and the RPE plus face mask group was assessed with a paired t-test. Pearson’s correlation coefficient was used to evaluate the relationship between the measured parameters. The significance level was set at p < 0.05. Measurement reliability was assessed using the intraclass correlation coefficient (ICC), and normality was tested with the Shapiro–Wilk test.

3. Results

The Shapiro–Wilk test for normality indicated a normal distribution for all measured variables (p > 0.05) in the standard cephalometric analysis and airway analysis except for the upper airway and upper pharynx, which were not normally distributed (p < 0.05).

The intraclass correlation coefficient (ICC) showed high reliability for most variables (ICC > 0.9) in both analyses except for the ANB and upper pharynx, which had good reliability (ICC 0.828–0.865). This assessment was based on repeated measurements of lateral cephalograms taken before and after treatment for ten randomly selected participants two weeks after the initial measurements.

3.1. Vertical Craniofacial Characteristics

The average values of the measured variables in the standard cephalometric analysis, before and after treatment, are shown in

Table 3. Descriptive statistics of the measured variables before (1) and after (2) treatment (N = 38).

		Arithmetic Mean	Standard Deviation
Par 1	SNA1	79.66	3.96
	SNA2	80.23	3.84
Par 2	SNB1	78.64	3.64
	SNB2	78.48	3.69
Par 3	ANB1	1.02	3.42
	ANB2	1.74	2.69
Par 4	Wits1	−3.86	4.33
	Wits2	−2.50	3.45
Par 5	ANPG1	1.00	8.12
	ANPG2	2.14	6.68
Par 6	SN:NL1	8.34	2.71
	SN:NL2	8.45	2.66
Par 7	IntermaxAngle1	26.22	5.54
	IntermaxAngle2	25.97	4.73
Par 8	SArGo1	143.87	6.96
	SArGo2	145.11	6.89
Par 9	MeGoAr1	128.29	5.60
	MeGoAr2	126.53	6.13
Par 10	Bjork1	394.56	5.29
	Bjork2	394.41	4.66
Par 11	NSGn1	66.26	3.50
	NSGn2	66.76	3.33
Par 12	Sn:gogn1	32.29	5.21
	Sn:gogn2	32.27	4.64
Par 13	U1Mx1	109.86	6.69
	U1Mx2	111.04	7.26
Par 14	L1Md1	88.97	6.15
	L1Md2	88.49	6.09

.

Pearson’s correlation coefficient showed significant correlations (p < 0.05) between all variables before and after treatment.

The results of the dependent t-test are shown in

Table 4. Results of the dependent t-test for the measured variables.

		Differences in Dependent Samples		t	ss	p Value
		Aritmetic Mean	Standard Deviation
Par 1	SNA1–SNA2	−0.57	1.74	−2.01	37	0.05
Par 2	SNB1–SNB2	0.16	1.26	0.79	37	0.43
Par 3	ANB1–ANB2	−0.73	1.66	−2.71	37	0.01
Par 4	wits1–wits2	−1.36	2.32	−3.61	37	0.00
Par 5	ANPG1–ANPG2	−1.13	3.25	−2.16	37	0.04
Par 6	SN: NL1–SN: NL2	−0.11	1.72	−0.38	37	0.71
Par 7	IntermaxAngle1–IntermaxAngle2	0.26	2.86	0.56	37	0.58
Par 8	SArGo1–SArGo2	−1.24	3.10	−2.46	37	0.02
Par 9	MeGoAr1–MeGoAr2	1.76	2.73	3.98	37	0.00
Par 10	Bjork1–Bjork2	0.15	2.20	0.43	37	0.67
Par 11	NSGn1–NSGn2	−0.50	1.25	−2.46	37	0.02
Par 12	sn:gogn1–sn:gogn2	0.02	2.27	0.05	37	0.96
Par 13	U1Mx1–U1Mx2	−1.18	5.00	−1.45	37	0.16
Par 14	L1Md1–L1Md2	0.47	4.27	0.68	37	0.50

. Statistically significant differences were found in ANB (p = 0.01), Wits (p < 0.001), ANPg (p = 0.04), SArGo (p = 0.02), NSGn (p = 0.02) and MeGoAr (p < 0.001). After treatment with the RPE appliance, ANB, Wits, ANPg, SArGo and NSGn increased, while MeGoAr decreased. The SNNL angle (p = 0.96), intermaxillary angle (p = 0.58), Björk’s polygon (p = 0.67) and SNGoGn angle (p = 0.96) did not change significantly. Superimposition of a typical lateral cephalograms before and after treatment depicting main craniodentofacial features is shown in supplement Figure S1.

No statistically significant differences were found in cephalometric values after treatment between the group treated with the ringed RPE appliance and the group treated with the acrylic RPE appliance and also between the group treated with RPE combined with a facemask and the group treated with RPE alone.

3.2. Upper Airway Dimensions

In the airway analysis (McNamara), Pearson’s correlation showed significant correlations (p < 0.05) for all measured variables before and after treatment.

The average airway dimensions before (T0) and after (T1) treatment, along with statistical test results, for the hyrax and hyrax + face mask groups are shown in

Table 5. Results of the airway (McNamara) analysis of lateral cephalograms before and after treatment.

HYRAX
Start			End
	M ± SD (mm)	Median (IQR) (mm)		M ± SD (mm)	Median (IQR) (mm)	p Value
Upper airway	14.1 ± 3.0	13.4 (12.4–16.1)	Upper airway	14.9 ± 2.6	14.5 (12.2–16.6)	0.048 *
Upper adenoid	21.8 ± 2.7	23.3 (19.6–23.5)	Upper adenoid	21.5 ± 2.6	22.1 (19.5–23.9)	0.530 *
Lower airway	18.3 ± 4.3	18.0 (14.7–20.7)	Lower airway	17.5 ± 3.2	18.0 (14.5–20.5)	0.386 **
Lower adenoid	22.5 ± 4.2	22.7 (18.3–26.1)	Lower adenoid	23.0 ± 3.3	23.3 (19.4–24.7)	0.589 *
Upper pharynx	9.8 ± 2.9	9.2 (7.8–11.3)	Upper pharynx	10.7 ± 3.0	9.8 (8.6–14.0)	0.033 **
Lower pharynx	10.5 ± 2.1	10.5 (9.1–12.6)	Lower pharynx	11.0 ± 2.6	12.1 (9.3–12.9)	0.395 *
HYRAX + FACE MASK
Start			End
Upper airway	12.1 ± 1.5	11.7 (11.3–13.7)	Upper airway	13.4 ± 1.7	13.4 (12.7–14.7)	0.103 *
Upper adenoid	23.8 ± 1.9	23.7 (22.4–25.1)	Upper adenoid	23.6 ± 1.3	23.7 (23.1–24.4)	0.740 *
Lower airway	15.3 ± 2.6	13.9 (13.5–17.4)	Lower airway	17.3 ± 3.2	17.3 (14.3–19.7)	0.173 **
Lower adenoid	25.9 ± 3.1	26.6 (22.6–28.7)	Lower adenoid	24.4 ± 3.6	24.0 (22.0–27.0)	0.154 *
Upper pharynx	7.9 ± 1.4	7.8 (6.7–8.7)	Upper pharynx	9.3 ± 1.6	9.1 (8.1–10.5)	0.016 **
Lower pharynx	10.9 ± 3.1	9.1 (8.6–13.9)	Lower pharynx	12.0 ± 3.1	10.8 (9.8–1.4)	0.234 *

Note: * indicates the dependent t-test, ** indicates the Wilcoxon test, M represents the mean, SD represents the standard deviation.

.

In the hyrax group, there was a significant difference in the upper pharynx (p = 0.033) and borderline significant difference in the upper airway (p = 0.048). In the hyrax + face mask group, a significant difference in the upper pharynx was found (p = 0.016).

In conclusion, a significant increase in upper pharyngeal dimensions was observed after treatment in both groups: RPE only (p = 0.033) and RPE with facemask (p = 0.016). The increase in the upper airway in the RPE-only group was borderline significant (p = 0.048). No significant differences were found between the groups in airway dimension changes. Superimposition of a typical lateral cephalograms before and after treatment depicting main upper airway features is shown in supplement Figure S2.

4. Discussion

This study aimed to assess the impact of maxillary expansion treatment on vertical craniofacial characteristics and airway dimensions in patients with crossbites and transverse discrepancies. Results showed a significant increase in ANB, Wits, facial bone profile (ANPg), gonial angle (SArGo) and Y-axis angle (NSGn) after treatment. The mandibular angle (MeGoAr) significantly decreased. Other cephalometric values showed no significant changes. The increase in the gonial angle and the Y-axis angle suggests post-rotation of the mandible. Numerous previous studies have proven post-rotation of the mandible after maxillary expansion treatment, which could be explained by the extrusion of the maxillary posterior teeth [19,20]. In contrast, this study showed no statistically significant change in the SNA value, which would indicate a shift in the maxilla. However, the increase in the SNA value (p = 0.052) suggests a trend toward significance. After maxillary expansion treatment, there was a statistically significant increase in the values of ANB, ANPg and Wits, similar to the results by Rutili et al. [21]. These changes could be the result of forward movement of the maxilla combined with post-rotation of the mandible. Additionally, this study showed a statistically significant decrease in the mandibular angle. A previous study showed that the value of the mandibular angle decreases with the increase in the age of the participants [22].

In the study by Pinto et al., treatment with an acrylic RPE appliance did not show statistically significant changes in the vertical dimension, suggesting that this appliance is a better choice than a banded one for patients with a vertical growth pattern [12]. Similarly, our study did not show significant changes in many variables typically used to describe vertical skeletal relations. A study demonstrated that the SNNL angle remains relatively stable during growth and does not change significantly. That finding is consistent with the results observed in our treatment [23,24,25]. One study compared vertical variations in patients after the treatment with hyrax-type and McNamara-type rapid palatal expanders. Both appliances did not show any significant difference in vertical dimension changes. When comparing between these two appliances, although not significant, McNamara-type RPE did maintain a vertical dimension better than hyrax-type RPE [26].

The airway analysis showed a significant increase in upper pharyngeal dimensions after treatment in both groups, with a borderline significant increase in upper airway dimensions in the group treated solely with the RPE appliance. Baccetti et al. also applied the airway (McNamara) analysis in their study to assess the impact of face mask treatment on the airways in Class III patients. Their results showed no significant changes in the dimensions of the nasopharyngeal and oropharyngeal airways compared to the control group [15]. In contrast, Kilinç et al. observed a significant increase in the nasopharyngeal (upper and lower airways) and oropharyngeal (lower pharynx) airways on latero-lateral cephalograms [14]. One study showed a significant increase in retropalatal volume after the RME treatment, while changes in the total volume and retroglossal volume were not significant. This increase in volume may not be considered as an equivalent for the enhancement of airway function unless proven so. In order to establish its significance in the improvement of breathing, a functional examination needs to be performed, and it is necessary to conduct more well-designed RCTs with samples actually comprising mouth breathers [17,27]. In a systematic review of the literature, Bucci et al. concluded that although the impact of maxillary expansion on the airways shows promising results, studies confirming this have low methodological quality. Therefore, further research is needed to establish clinical significance [3].

Limits of this study: Compared to other studies using two-dimensional radiographs, a limiting factor in this research is the inability to compare the results in the treated group with a control group of participants. Additionally, a limiting factor was the small sample size, which was minimal according to the articles previously referenced.

A confounding factor was the fact that class II and class III patients were not divided into different groups when analyzing the vertical dimension.

A source of bias was the lack of randomization in the groups.

The evaluation of the upper airway changes using the lateral cephalograms cannot provide information about the airway volume; it is limited to the two-dimensional evaluation; also, it is not certain at which stage of breathing the x-rays are taken.

5. Conclusions

In conclusion, RPE appears safe with minimal vertical side effects and may provide airway benefits, though appliance choice (acrylic vs. banded) does not seem to influence vertical changes. No significant difference was found between the banded and acrylic appliances in terms of vertical craniofacial changes. Additionally, treatment using the RPE appliance alone or in combination with a face mask resulted in an increase in upper pharyngeal dimensions, though the clinical significance of this finding warrants further evaluation.