ORIGINAL ARTICLE
Analysis of mandibular asymmetry in
adolescent and adult patients with
unilateral posterior crossbite on
cone-beam computed tomography
Min Huang, Baoyi Chen, Huiyi Lin, Weiqi Guo, Guan Luo, Wenjun Chen, Weijun Zhang, and Chang Liu
Guangzhou, Guangdong, China
Introduction: This study aimed to evaluate mandibular asymmetry in unilateral posterior crossbite (UPXB) patients and compare the asymmetry between adolescents and adults with UPXB. Methods: This study included
and analyzed cone-beam computed tomography scans of 125 subjects. The subjects were divided into a UPXB
group and a control group according to the presence or absence of UPXB, and each group included adolescent
patients (aged 10-15 years) and adult patients (aged 20-40 years). Linear, angular, and volumetric
measurements were obtained to evaluate the asymmetries of the mandibles. Results: Both adolescent and
adult patients in the UPXB group presented asymmetries in condylar unit length, ramal height, body length,
and mediolateral ramal inclination (P \0.05). Adult patients with UPXB showed greater asymmetries than adolescents. Differences with condylar unit length, condylar unit width, ramal height, condylar unit volume, and hemimandibular volume were significantly greater in adult UPXB patients than adolescent UPXB patients (P \0.05).
Conclusions: The worsening of mandibular asymmetries in UPXB adults suggests that asymmetry in UPXB
patients may progress over time; therefore, early treatment should be considered for UPXB adolescent patients.
Further studies are still needed to evaluate the effectiveness of early treatment. (Am J Orthod Dentofacial Orthop
2024;165:27-37)
P
osterior crossbite (PXB) is a kind of malocclusion
related to the transverse discrepancy of the dental
arches, mainly manifesting as the buccal cusps of
the mandibular dentition occluding the buccal cusps of
the maxillary dentition.1 Only 1 side of the dental arch is
affected in patients with unilateral posterior crossbite
(UPXB), the most common type of PXB, and the
mandible usually shifts toward the crossbite side when
occluded. The prevalence of UPXB ranges from 1.00%
From the Department of Orthodontics, Affiliated Stomatology Hospital of
Guangzhou Medical University, Guangdong Engineering Research Center of
Oral Restoration and Reconstruction, Guangzhou Key Laboratory of Basic and
Applied Research of Oral Regenerative Medicine, Guangzhou, Guangdong,
China.
All authors have completed and submitted the ICMJE Form for Disclosure of
Potential Conflicts of Interest, and none were reported.
This work was supported by the National Key Research and Development Program of China (no. 2021YFE0108000) and the Guangzhou Science and Technology Plan Project (no. 2023A03J0327).
Address correspondence to: Chang Liu, Department of Orthodontics, Stomatology Hospital of Guangzhou Medical University, 59th Huangsha Rd, Guangzhou,
Guangdong, China 510000; e-mail, changliudentist@gzhmu.edu.cn.
Submitted, November 2022; revised and accepted, June 2023.
0889-5406/$36.00
Ó 2023 by the American Association of Orthodontists. All rights reserved.
https://doi.org/10.1016/j.ajodo.2023.06.023
to 11.65% in patients with deciduous dentition,2,3
from 8.40% to 9.13% in those with mixed dentition,4,5
and 12.37% in those with permanent dentition.5 A narrow maxilla resulting from genetic and/or environmental influences, nonnutritive sucking, mouth
breathing, low tongue position, and so on, is a possible
cause of UPXB.6
Early treatment for UPXB is recommended by most
clinicians because of the possible adverse effect of
malocclusion on maxillofacial structures and function.
The asymmetrical activity of the masticatory muscle7
and an asymmetrical temporomandibular joint (TMJ)
space8 in UPXB patients might have long-term effects
on the growth and development of the mandible. In
some previous studies, researchers have suggested a
close relationship between UPXB and mandibular
asymmetry.9-11 In contrast, mandibular asymmetry was
not associated with UPXB in other studies that were
mainly based on an adolescent population.7,12,13 Bj€
ork14
analyzed longitudinal profile radiographs of 45 Danish
boys and found that the growth of mandibular condyles
continued to age 22. Sherwood et al15 reported that the
age at which the increase in mandibular height ceased
27
Huang et al
28
was 24.58 years and 23.37 years for males and females,
respectively. Accordingly, the continuous growth of the
mandible in UPXB adolescents may worsen the deformation of the mandible. However, Evangelista et al16 found
3 different age groups (children, adolescents, and adults)
in patients with a skeletal Class I relationship with UPXB
had surprisingly similar slight mandibular asymmetries.
Hence, it is important to understand the effect of growth
on mandibular symmetry by grouping UPXB patients according to biological age and developmental stages.
Various methods have been proposed to evaluate
mandibular asymmetry. Lopatien_e and Trumpyt_e10 and
Kasimoglu et al17 used panoramic radiographs to assess
condylar and ramal height asymmetry in UPXB patients.
Although less invasive, a major limitation of panoramic
radiographs is the unequal magnification of the right
and left sides in the horizontal dimension if the
midsagittal plane (MSP) of the patient’s head is not
positioned in the rotational midline of the machine.18
Submentovertex radiographs were also used to evaluate
structural, positional, and dentoalveolar asymmetry of
the mandible in patients with PUXB.8,19 However,
2-dimensional measurement tools cannot compensate
for distortion, magnification, and superimposition.
Cone-beam computed tomography (CBCT) has been
widely used in dental research as a reliable and accurate
method for quantitative analysis of jaw deformity.20
Enlow and Hans21 proposed a theory of craniofacial
growth, which suggested that different regional areas
have different local developmental and functional and
structural conditions; therefore, regional signals activate
local osteogenic tissues to adapt as a part of overall growth.
It is reasonable to assume that functional changes in UPXB
patients might cause a continuous imbalanced signal that
perpetually alters the development and growth of the
mandible. Therefore, this study aimed to compare the
shape and morphology of mandibles between adolescent
and adult patients with or without UPXB. The following
null hypothesis was tested: there are no significant
differences in the shape and morphology of the mandible
between adolescent and adult patients with UPXB.
MATERIAL AND METHODS
This study is a cross-sectional study. CBCT scans of
125 subjects were included in this study and analyzed.
The subjects were divided into a UPXB group and a control group according to the presence or absence of UPXB,
and each group included adolescents (aged 10-5 years;
n 5 29 in the control group and n 5 38 in the UPXB
group) and adult (aged 20-40 years; n 5 29 in each
group) subjects. Adolescents with UPXB were then
subdivided according to different cervical vertebral
January 2024 Vol 165 Issue 1
maturation stages (CVMSs) proposed by Baccetti
et al.22 All subjects were selected from a large pool of patients who were sequentially admitted for orthodontic
treatment from 2015 to 2023 in our institution. This
study was approved by the Research and Ethics Committee of the Affiliated Stomatology Hospital of Guangzhou
Medical University (no. LCYJ2022005).
The inclusion criteria for the UPXB group were as follows: (1) UPXB involving at least 2 posterior teeth, (2) no
history of orthodontic treatment, (3) no prostheses, (4)
no absence of permanent teeth (except third molars)
and no early loss of primary teeth. The exclusion criteria
were as follows: (1) signs of a TMJ disorder, (2) history of
orthodontic or facial surgical procedures, (3) pathologic
conditions in the craniomaxillofacial complex, (4)
congenital craniofacial deformities, (5) signs of maxillofacial trauma, and (6) diagnosed with a systemic disease.
The inclusion and exclusion criteria of the control group
were the same as those for the UPXB group, except for
the absence of PUXB. The patient characteristics of the
control and UPXB groups are listed in Table I.
The CBCT scans were obtained using NewTom (QR
srl, Verona, Italy), and the imaging parameters were as
follows: 110 kV, 3.07 mA, a scan time of 18 seconds, a
voxel size of 0.3 mm and a focal spot of 0.3 mm. Images
were saved in digital imaging and communications in
medicine format. These data were reconstructed into
3-dimensional (3D) images using Mimics Research software (version 20.0; Materialise NV, Liege, Belgium). The
mandibles were separated from the whole image, and
the teeth above the alveolar bone in the mandibles
were removed. All landmark identifications and measurements were made by this software.
Landmarks and measurements were selected according to previous studies.23-25 Landmarks (Table II) were
designated on the surface of reconstructed 3D images
and were verified on the axial, coronal, and sagittal
views. The following planes were identified: (1) the
Frankfort horizontal plane (FH plane): the plane passing
through bilateral Or and left Po; (2) the MSP: the plane
passing through N, Ba, and perpendicular to the FH
plane; (3) the frontal plane: the plane passing through
N and perpendicular to the FH plane and the MSP; (4)
the Sig plane: the plane passing through the sigmoid
notch (Sig) and parallel to the FH plane; (5) the
Gomid-Jlat-Jmed plane: the plane passing through Gomid, Jlat, and Jmed; (6) the B-Me-G plane: the plane
passing through B, Me and G; (7) the Mid-mandibular
plane (MMP): the plane passing through the MGo and
Me and perpendicular to the mandibular plane.
All the measurements are shown in Figure. Linear measurements (Fig) were as follows: (1) mandibular deviation:
distance from Me to the MSP; (2) condylar unit length:
American Journal of Orthodontics and Dentofacial Orthopedics
Huang et al
29
Table I. Characteristics of the patients in the control group and UPXB group
Adolescents (aged 10-15 y)
Adults (aged 20-40 y)
UPXB
Characteristics
Number
Age (y)
Sex
Male
Female
Crossbite side
Right
Left
Mandibular deviation (mm)
Mean 6 SD
P value
Mandibular rotation ( )
Mean 6 SD
P value
Control
29
12.97 6 1.16
CVMS I1II
19
10.79 6 0.98
CVMS III
19
13.84 6 1.07
Control
29
24.97 6 4.69
UPXB
29
23.75 6 3.14
6
23
6
13
5
14
11
18
11
18
–
–
8
11
8
11
–
–
16
13
0.91 6 0.58
2.75 6 1.84
0.001***
3.39 6 2.32
0.001***
0.88 6 0.49
0.001***
4.73 6 2.40
1.24 6 0.99
2.30 6 1.63
0.019*
2.31 6 1.94
0.015*
0.92 6 0.72
0.001***
2.97 6 1.93
Note. Values are presented as mean 6 SD. An independent Student t test was used to analyze differences between the control and UPXB groups.
SD, standard deviation.
*P \0.05; ***P \0.001.
Consup-F; (3) coronoid unit length: Corsup-F; (4) angular
unit length: F-Gomid; (5) body unit length: F-MF; (6) chin
unit length: MF-Pog; (7) condylar width: ConmedConlat; (8) ramal height: Consup-Gomid; and (9) body
length: Gomid-Me. Angular measurements (Fig) were as
follows: (1) mandibular rotation: the intersection angle
between the MSP and the MMP; (2) gonial angle: the
angle between the Me-Gomid and Consup-Gomid vectors
of both sides; (3) mediolateral ramal inclination: the inner
angle between the right and left Consup-Gomid and the
FH plane projected on the frontal plane; (4) anteroposterior ramal inclination: the inner angle between the right
and left Consup-Gomid and the FH plane projected on
the MSP plane; (5) condylar angle to the MSP: the inner
angle between the right and left Conmed-Conlat and
the MSP plane projected on the FH plane. Volumetric
measurements (Fig) were as follows: (1) hemimandibular
volume: the mandibular volume was divided into 2 hemimandibular volumes by the B-Me-G plane; (2) body unit
volume and hemiramal volume: the hemimandibular volume was divided into the body unit volume and the hemiramal volume by the Gomid-Jlat-Jmedplane; (3) condylar
unit volume: coronoid unit volume and ramal unit volume: the hemiramal volume was divided into the condylar
unit volume, the coronoid unit volume and the ramal unit
volume by the Sig plane.
Statistical analysis
PASS software (version 15.0; NCSS, LLC, Kaysville,
Utah) was used to estimate the minimum sample size
(power 5 0.8; a 5 0.05) on the basis of the pilot and
previous studies.9
The intraclass correlation coefficient (ICC) was used
to assess the intraoperator and interoperator error. To
determine the intraoperator error, thirty-five 3D images
were randomly selected, and the entire workflow,
including separation of the mandible and landmark
identifications, was repeated by the same operator
(M.H.) 2 weeks apart. To evaluate the interoperator error,
a second blinded experienced operator (B.C.) analyzed
35 randomly selected CBCT images and repeated the
workflow sequence.
The statistical analysis was performed with SPSS software (version 26.0; IBM, Armonk, NY). Descriptive statistics were calculated for all variables, including mean and
standard deviation. The difference between the measurements of the 2 sides was the right side minus the
left side in the control group and the noncrossbite
(non-XB) side minus the crossbite (XB) side in the
UPXB group. Positive difference values in the control
group indicated that the measurements on the right
side were larger than those on the left side, and in the
UPXB group, the measurements on the non-XB side
were larger than those on the XB side. The data were
then checked for normal distribution by the ShapiroWilk test. As all the data were normally distributed, parametric tests were used. The paired t test was performed
to compare the intragroup differences between the measurements. An independent Student t test was used to
compare the mandibular measurement differences between sides among groups. Because no significant
American Journal of Orthodontics and Dentofacial Orthopedics
January 2024 Vol 165 Issue 1
Huang et al
30
Table II. Description of landmarks
Landmark
Definition
Consup (condylion superius) The most superior point of the
condylar head
Conmed (condylion medialis) The most medial point of the
condylar head
Conlat (condylion lateralis) The most lateral point of the
condylar head
Corsup (coronoid superius) The most superior point of the
coronoid process
Sig (sigmoid notch)
The most inferior point of the sigmoid
notch
F (fossa of mandibular
The most inferior point on the fossa of
foramen)
the mandibular foramen
Jlat
The most lateral and deepest point of
the curvature formed at the
junction of the mandibular ramus
and body
Jmed
The most medial and deepest point of
the curvature formed at the
junction of the mandibular ramus
and body
Gopost (gonion posterius)
The most posterior point on the
mandibular angle
Gomid (gonion midpoint)
The midpoint between the Gopost and
Goinf on the mandibular angle
Goinf (gonion inferius)
The most inferior point on the
mandibular angle
MGo
The midpoint between the left and
right Gomid
MF (mental foramen)
The entrance of the mental foramen
Me (menton)
The most inferior midpoint on the
symphysis
Pog (pogonion)
The most anterior midpoint on the
symphysis
B (supramentale)
The midpoint of the greatest
concavity on the anterior border of
the symphysis
G (genial tubercle)
The midpoint on the genial tubercle
N (Nasion)
Most anterior and median point of the
frontonasal suture
Or (Orbitale)
The deepest point on the infraorbital
margin
Po (Porion)
The highest point on the roof of the
external auditory meatus
Ba (Basion)
The middle point on the anterior rim
of the occipital foramen
difference could be detected for any measurement differences between CVMS I 1 CVMS II and CVMS III subjects, all the measurements were pooled in subsequent
analysis. P values \0.05 were considered statistically
significant.
RESULTS
All 3D measurements showed high intraoperator and
interoperator agreements. The intraoperator ICC ranged
January 2024 Vol 165 Issue 1
from 0.982% (for body unit volume) to 0.998% (for body
unit length), and the interoperator ICC ranged from
0.816% (for body unit volume) to 0.977% (for coronoid
unit length). Table I shows that patients in the UPXB
group presented significantly greater mandibular deviation and rotation than subjects in the same age range in
the control group.
A significantly larger coronoid unit length and a
shorter body length were detected on the XB side than
on the non-XB side in both CVMS I 1 CVMS II and
CVMS III subjects. Although the condylar unit length
was larger on the non-XB side in CVMS I 1 CVMS II patients, the statistical significance for condylar unit
length was found only in CVMS III patients. None of
the measurement differences significantly differed between CVMS I 1 II and CVMS III subjects (Table III).
The adolescents in the control group had significantly greater ramal heights on the right side than on
the left (P \0.01; Table IV). In the adolescent UPXB patients, 4 linear variables (condylar unit length, coronoid
unit length, ramal height, body length), 2 angular variables (mediolateral ramal inclination, anteroposterior
ramal inclination), and one volumetric measurement
(condylar unit volume) were significantly different between the 2 sides (P \0.05). Among the 4 linear measurements with statistical significance, condylar unit
length, coronoid unit length, and body length were
considerably different between the 2 sides (P \0.01).
The condylar unit length, ramal height, body length,
and condylar unit volume were remarkably larger on
the non-XB side than on the XB side (Table V).
Significantly greater chin unit length and condylar
width were found on the right side of adults in the control group (P \0.05; Table VI). In adult UPXB patients, 4
linear variables (condylar unit length, condylar width,
ramal height, body length), one angular variable (mediolateral ramal inclination), and 3 volumetric measurements (condylar unit volume, hemiramal volume, and
hemimandibular volume) were significantly different between the 2 sides (P \0.05). Among these statistically
significant measurements, 7 variables were significantly
larger on the non-XB side than on the XB side, except for
mediolateral ramal inclination (P \0.01) (Table VII).
There were no significant differences in measurements between the adolescents and adults in the control
group (Table VIII). Significantly larger measurement differences were detected in the adult UPXB subjects than
in the adolescent UPXB subjects in terms of condylar
unit length difference, condylar width difference, ramal
height difference, condylar unit volume difference, and
hemimandibular volume difference (P \0.05). The adult
UPXB subjects showed a remarkably smaller coronoid
unit length difference than the adolescent UPXB
American Journal of Orthodontics and Dentofacial Orthopedics
Huang et al
31
Fig. Measurements used in this study: A, Linear and angular measurements: a, condylar unit length; b,
body unit length; c, coronoid unit length; d, angular unit length; e, chin unit length; f, anteroposterior
ramal inclination; g, gonial angle; B, Linear and angular measurements: h, condylar width; i, ramal
height; j, body length; k, mediolateral ramal inclination; C, Linear and angular measurements: l, mandibular deviation; m, condylar angle to MSP; n, mandibular rotation; D, Volumetric measurements used in
this study: 1, condylar unit volume; 2, coronoid unit volume; 3, ramal unit volume; 4, body unit volume;
11213, hemiramal volume; 1121314, hemimandibular volume.
patients (P \0.01). Significantly greater coronoid unit
and body length differences were detected in adolescent
UPXB subjects than in adolescents without UPXB. When
the adults with or without UPXB were compared, the
UPXB adults presented markedly larger condylar unit
length difference, ramal height difference, body length
difference, condylar unit volume difference, hemiramal
volume difference, and hemimandibular volume difference (P \0.05) (Table VIII).
DISCUSSION
It is well-known that unilateral posterior crossbite in
children can result in possible asymmetrical growth of
the skeletal structures; thus, early treatment for UPXB
is recommended in clinical practice. However, whether
UPXB will lead to increasingly severe mandibular skeletal
asymmetry over time remains unclear. Previous studies
on the relationship between the UPXB and skeletal
asymmetry showed controversial results, and one important confounding factor could have been the heterogeneous age of samples.7 In this study, the UPXB subjects
were categorized according to biological age and CVMS
to investigate whether the mandibular skeletal asymmetries in UPXB patients progress during growth.
Baccetti et al22 reported that the timing of the pubertal growth peak occurs between CVMS II and CVMS III. A
American Journal of Orthodontics and Dentofacial Orthopedics
January 2024 Vol 165 Issue 1
32
January 2024 Vol 165 Issue 1
Table III. Comparison of the measurements in adolescent UPXB patients with different CVMSs
CVMS I 1 CVMS II (n 5 19)
XB side
Non-XB side
Difference
P value
XB side
Non-XB side
Difference
P valueƚ
P valuey
39.58 6 3.99
53.10 6 3.27
35.7 6 3.53
17.01 6 2.28
28.47 6 2.03
17.29 6 1.95
50.34 6 4.86
78.33 6 4.71
40.46 6 3.55
53.65 6 3.66
35.02 6 3.51
17.18 6 2.98
28.31 6 2.46
17.35 6 2.31
51.17 6 6.12
79.21 6 4.77
0.89 6 2.13
0.55 6 1.68
0.68 6 1.27
0.16 6 1.71
0.16 6 1.12
0.05 6 1.39
0.83 6 2.66
0.88 6 1.62
0.086
0.172
0.031*
0.679
0.542
0.870
0.190
0.030*
42.43 6 3.77
54.43 6 2.17
39.55 6 3.59
19.25 6 2.48
28.69 6 1.86
17.22 6 2.29
54.53 6 4.55
81.47 6 4.03
43.74 6 4.17
54.78 6 2.71
38.79 6 3.00
19.18 6 2.52
29.42 6 1.29
17.47 6 1.89
55.68 6 3.40
82.67 6 4.41
1.31 6 2.22
0.35 6 2.06
0.75 6 1.42
0.07 6 1.25
0.73 6 1.36
0.25 6 1.20
1.14 6 3.01
1.20 6 2.30
0.019*
0.468
0.033*
0.814
0.072
0.375
0.114
0.036*
0.553
0.749
0.864
0.634
0.062
0.642
0.735
0.622
124.34 6 4.67
81.15 6 4.23
80.90 6 3.94
72.58 6 6.52
125.11 6 4.84
79.99 6 3.92
80.19 6 4.88
72.18 6 7.74
0.76 6 1.95
1.16 6 3.29
0.71 6 2.21
0.40 6 5.81
0.106
0.143
0.179
0.768
122.32 6 4.58
83.54 6 3.72
82.49 6 4.34
70.63 6 9.32
122.96 6 4.51
82.69 6 4.22
81.56 6 4.12
71.93 6 8.29
0.64 6 2.86
0.85 6 2.40
0.93 6 2.44
1.30 6 6.43
0.350
0.140
0.110
0.389
0.874
0.746
0.772
0.398
1.33 6 0.27
0.18 6 0.06
5.48 6 1.40
16.47 6 2.59
6.62 6 1.71
23.17 6 3.68
1.42 6 0.40
0.17 6 0.06
5.55 6 1.64
16.39 6 2.71
6.77 6 1.96
23.24 6 4.10
0.09 6 0.23
0.01 6 0.05
0.08 6 0.52
0.08 6 0.62
0.15 6 0.64
0.07 6 1.01
0.110
0.640
0.530
0.596
0.335
0.758
1.40 6 0.40
0.29 6 0.11
6.33 6 1.39
18.32 6 1.98
7.65 6 1.79
25.97 6 3.41
1.50 6 0.35
0.28 6 0.10
6.34 6 1.49
18.46 6 2.17
7.78 6 1.83
26.22 6 3.65
0.10 6 0.28
0.01 6 0.06
0.02 6 0.52
0.14 6 0.58
0.13 6 0.57
0.25 6 0.87
0.138
0.388
0.881
0.299
0.336
0.223
0.922
0.707
0.732
0.269
0.940
0.562
Note. Values are presented as mean 6 standard deviation. The difference is defined as the non-XB side XB side.
y
Paired t test between the XB side and the non-XB side; zIndependent Student t test between the measurement differences of different CVMSs; *P \0.05.
Huang et al
American Journal of Orthodontics and Dentofacial Orthopedics
Measurements
Linear measurements (mm)
Condylar unit length
Body unit length
Coronoid unit length
Angular unit length
Chin unit length
Condylar width
Ramal height
Body length
Angular measurements ( )
Gonial angle
Mediolateral ramal inclination
Anteroposterior ramal inclination
Condylar angle to MSP
Volumetric measurements (103 mm3)
Condylar unit volume
Coronoid unit volume
Ramal unit volume
Body unit volume
Hemiramal volume
Hemimandibular volume
CVMS III (n 5 19)
y
Huang et al
33
Table IV. Comparison of the measurements between the left and right sides (paired t test) in the adolescents in the
control group
Aged 10-15 y
Measurements
Linear measurements (mm)
Condylar unit length
Body unit length
Coronoid unit length
Angular unit length
Chin unit length
Condylar width
Ramal height
Body length
Angular measurements ( )
Gonial angle
Mediolateral ramal inclination
Anteroposterior ramal inclination
Condylar angle to MSP
Volumetric measurements (103 mm3)
Condylar unit volume
Coronoid unit volume
Ramal unit volume
Body unit volume
Hemiramal volume
Hemimandibular volume
95% Confidence interval
P value
0.32 6 1.34
0.00 6 1.48
0.31 6 1.38
0.36 6 1.29
0.31 6 1.13
0.03 6 0.98
0.65 6 0.94
0.14 6 1.33
0.19 to 0.83
0.56 to 0.57
0.21 to 0.84
0.13 to 0.85
0.12 to 0.74
0.35 to 0.40
0.29 to 1.01
0.37 to 0.64
0.214
0.989
0.232
0.144
0.146
0.891
0.001**
0.588
120.36 6 4.70
83.03 6 3.27
83.89 6 4.15
71.91 6 7.11
0.04 6 2.26
0.73 6 2.25
0.10 6 1.82
1.75 6 5.91
0.82 to 0.90
1.59 to 0.12
0.79 to 0.59
4.00 to 0.49
0.920
0.090
0.766
0.121
1.47 6 0.28
0.26 6 0.10
6.31 6 1.32
19.44 6 2.73
8.17 6 1.58
27.93 6 4.04
0.02 6 0.12
0.01 6 0.05
0.01 6 0.36
0.11 6 0.53
0.04 6 0.43
0.08 6 0.70
0.02 to 0.06
0.00 to 0.04
0.13 to 0.15
0.32 to 0.09
0.12 to 0.20
0.35 to 0.18
0.367
0.202
0.900
0.259
0.625
0.524
Left side
Right side
42.11 6 3.67
54.47 6 4.33
38.65 6 3.40
19.24 6 2.68
28.29 6 1.58
17.36 6 2.27
53.74 6 4.76
82.29 6 4.61
42.42 6 3.34
54.47 6 4.11
38.96 6 3.30
19.6 6 2.74
28.6 6 1.40
17.39 6 2.28
54.39 6 4.84
82.42 6 4.35
120.32 6 5.24
83.76 6 3.46
83.99 6 3.88
73.67 6 6.22
1.45 6 0.26
0.25 6 0.09
6.3 6 1.35
19.56 6 2.80
8.13 6 1.60
28.01 6 4.18
Difference
Note. Values are presented as mean 6 standard deviation. The difference is defined as the right left side.
**P \0.01.
Table V. Comparison of the measurements between the XB and non-CB sides (paired t test) in the adolescents in the
UPXB group
Aged 10-15 y
Measurements
Linear measurements (mm)
Condylar unit length
Body unit length
Coronoid unit length
Angular unit length
Chin unit length
Condylar width
Ramal height
Body length
Angular measurements ( )
Gonial angle
Mediolateral ramal inclination
Anteroposterior ramal inclination
Condylar angle to MSP
Volumetric measurements (103 mm3)
Condylar unit volume
Coronoid unit volume
Ramal unit volume
Body unit volume
Hemiramal volume
Hemimandibular volume
XB side
Non-XB side
Difference
95% Confidence interval
P value
41.00 6 4.09
53.77 6 2.82
37.62 6 4.01
18.13 6 2.61
28.58 6 1.92
17.26 6 2.10
52.43 6 5.11
79.90 6 4.61
42.10 6 4.16
54.22 6 3.23
36.91 6 3.74
18.18 6 2.90
28.86 6 2.04
17.41 6 2.08
53.42 6 5.39
80.94 6 4.86
1.10 6 2.15
0.45 6 1.86
0.72 6 1.33
0.05 6 1.48
0.28 6 1.47
0.15 6 1.29
0.99 6 2.80
1.04 6 1.97
0.39-1.81
0.16 to 1.06
1.15 to 0.28
0.44 to 0.54
0.20 to 0.76
0.27 to 0.58
0.07-1.91
0.39-1.69
0.003**
0.145
0.002**
0.842
0.242
0.469
0.036*
0.003**
123.33 6 4.67
82.34 6 4.11
81.69 6 4.17
71.61 6 8.00
124.03 6 4.74
81.34 6 4.24
80.87 6 4.51
72.06 6 7.91
0.70 6 2.42
1.00 6 2.84
0.82 6 2.30
0.45 6 6.10
0.0961 to 1.494
1.9392 to 0.0703
1.5759 to 0.0635
1.5555 to 2.4566
0.083
0.036*
0.034*
0.652
1.37 6 0.34
0.24 6 0.10
5.90 6 1.44
17.39 6 2.46
7.14 6 1.80
24.57 6 3.77
1.46 6 0.37
0.23 6 0.10
5.95 6 1.59
17.43 6 2.46
7.27 6 1.94
24.73 6 4.11
0.10 6 0.25
0.01 6 0.05
0.05 6 0.52
0.03 6 0.60
0.14 6 0.60
0.16 6 0.94
0.01-0.18
0.03 to 0.01
0.12 to 0.22
0.17 to 0.23
0.06 to 0.33
0.15 to 0.47
0.026*
0.327
0.574
0.742
0.165
0.292
Note. Values are presented as mean 6 standard deviation. The difference is defined as the non-XB side XB side.
*P \0.05; **P \0.01.
American Journal of Orthodontics and Dentofacial Orthopedics
January 2024 Vol 165 Issue 1
Huang et al
34
Table VI. Comparison of the measurements between the left and right sides (paired t test) in the adults in the control
group
Aged 20-40 y
Measurements
Linear measurements (mm)
Condylar unit length
Body unit length
Coronoid unit length
Angular unit length
Chin unit length
Condylar width
Ramal height
Body length
Angular measurements ( )
Gonial angle
Mediolateral ramal inclination
Anteroposterior ramal inclination
Condylar angle to MSP
Volumetric measurements (103 mm3)
Condylar unit volume
Coronoid unit volume
Ramal unit volume
Body unit volume
Hemiramal volume
Hemimandibular volume
Left side
Right side
Difference
95% Confidence interval
P value
43.22 6 2.67
55.74 6 2.90
40.65 6 3.58
22.05 6 3.13
28.61 6 1.72
20.16 6 2.24
57.36 6 4.69
84.76 6 3.42
43.79 6 3.08
55.52 6 2.73
41.12 6 3.51
22.01 6 3.00
28.95 6 1.80
20.66 6 2.10
57.86 6 4.43
84.82 6 4.02
0.57 6 1.54
0.21 6 1.26
0.47 6 1.44
0.04 6 1.27
0.34 6 0.81
0.50 6 0.96
0.51 6 1.53
0.06 6 1.40
0.02 to 1.16
0.07 to 1.02
0.69 to 0.26
0.52 to 0.44
0.03-0.65
0.13-0.86
0.08 to 1.09
0.47 to 0.59
0.056
0.365
0.088
0.868
0.032*
0.009**
0.086
0.813
117.20 6 5.23
81.82 6 4.30
85.24 6 3.36
74.18 6 6.78
117.63 6 5.68
80.76 6 5.84
85.04 6 3.16
73.94 6 7.03
0.43 6 2.39
1.06 6 3.20
0.20 6 2.08
0.24 6 4.30
0.48 to 1.34
2.28 to 0.16
0.99 to 0.59
1.87 to 1.40
0.337
0.086
0.616
0.766
1.81 6 0.52
0.30 6 0.16
7.22 6 1.51
21.09 6 3.34
9.48 6 1.98
30.90 6 5.16
1.85 6 0.48
0.31 6 0.14
7.21 6 1.53
21.11 6 3.33
9.53 6 1.90
30.97 6 5.09
0.05 6 0.19
0.01 6 0.07
0.01 6 0.56
0.01 6 0.76
0.05 6 0.61
0.07 6 1.03
0.03 to 0.12
0.01 to 0.04
0.22 to 0.20
0.28 to 0.30
0.18 to 0.29
0.32 to 0.46
0.214
0.367
0.913
0.920
0.651
0.720
Note. Values are presented as mean 6 standard deviation. The difference is defined as the right left side.
*P \0.05; **P \0.01.
rapid increase in mandibular length and the greatest
bone apposition at the condyle are closely associated
with the individual pubertal growth peak.26 Our finding
that pubertal growth peak onset could worsen asymmetry in the condylar region in adolescent UPXB patients
was in agreement with the above mentioned studies.
Condylar cartilage was more vulnerable to imbalances
in UPXB adolescents during accelerated growth, which
could have led to condylar asymmetry. We noticed that
many parameters measured in adolescent UPXB patients
with different CVMSs showed no significant difference
between the XB and non-XB sides. A limited sample
size (n 5 19) might be a reasonable explanation. Further
analysis with a larger sample size is needed. The differences between the sides of subjects in different CVMSs
were not significant, so the data were combined for subsequent statistical analysis.
The differences in several measurements were statistically significant between the right and left sides in the
control group, although the differences were tiny (within
1 mm). It is well-known that perfect symmetry is rare,
and even faces considered aesthetically pleasing may
have some degree of asymmetry.27 The slight rightside predominance observed in the control group was
consistent with previous studies.28,29 Muscle and functional asymmetry may be a possible explanation. It was
January 2024 Vol 165 Issue 1
reported that humans and higher primates had a rightside preference for chewing.30 The asymmetry of mastication may have progressed to craniofacial asymmetry.
Our findings, consistent with previous studies,9,31
showed that UPXB was tightly associated with mandibular skeletal asymmetry. Significant asymmetry was
found in the condylar process, mandibular ramus, coronoid process, and mandibular body in patients in the
UPXB group. Enlow and Hans21 suggested that osteogenic, fibrogenic, and chondrogenic tissues in respective
local growth fields conduct remodeling activities of the
mandible. The signals from the composite of all related
soft tissue parts and their growth and functioning orchestrated the local remodeling patterns. The asymmetrical
activity of the masticatory muscle7 and an asymmetrical
TMJ space8 were found in UPXB patients, which might
have led to a morphologic alteration of the corresponding
skeletal unit in the mandible. We also observed the most
prominent asymmetry at the condylar process and ramus.
This finding could be explained by some previous studies.
Pinto et al8 and Almaqrami et al32 found that the TMJ
space was asymmetric in UPXB patients and that the
condyle on the non-XB side was relatively more anterior
and inferior than that on the crossbite side. Such positional asymmetry may stimulate the condyle on the
non-XB side to grow posteriorly and superiorly, which
American Journal of Orthodontics and Dentofacial Orthopedics
Huang et al
35
Table VII. Comparison of the measurements between the XB and non-CB sides (paired t test) in the adults in the UPXB
group
Aged 20-40 y
Measurements
Linear measurements (mm)
Condylar unit length
Body unit length
Coronoid unit length
Angular unit length
Chin unit length
Condylar width
Ramal height
Body length
Angular measurements ( )
Gonial angle
Mediolateral ramal inclination
Anteroposterior ramal inclination
Condylar angle to MSP
Volumetric measurements (103 mm3)
Condylar unit volume
Coronoid unit volume
Ramal unit volume
Body unit volume
Hemiramal volume
Hemimandibular volume
XB side
Non-XB side
Difference
95% Confidence interval
P value
43.62 6 3.98
57.08 6 4.56
40.88 6 5.09
20.40 6 2.49
29.96 6 2.20
18.62 6 2.74
57.36 6 5.71
84.84 6 5.85
46.95 6 2.77
57.37 6 5.08
41.39 6 4.66
20.55 6 2.93
29.93 6 1.73
19.86 6 2.56
60.25 6 4.25
86.19 6 6.26
3.33 6 2.80
0.29 6 1.99
0.51 6 2.35
0.15 6 1.36
0.03 6 1.53
1.24 6 3.07
2.89 6 3.07
1.35 6 2.24
2.26-4.39
0.46 to 1.05
0.39 to 1.40
0.37 to 0.67
0.61 to 0.55
0.55-1.93
1.72-4.06
0.50-2.21
0.001***
0.435
0.254
0.550
0.918
0.001**
0.001***
0.003**
121.10 6 5.02
84.38 6 3.07
80.32 6 6.43
72.73 6 8.40
121.01 6 5.27
82.91 6 4.11
79.56 6 5.65
73.58 6 9.14
0.09 6 2.32
1.45 6 3.56
0.76 6 2.60
0.85 6 8.29
0.97 to 0.80
2.81 to 1.10
1.75 to 0.23
2.31 to 4.00
1.61 6 0.65
0.32 6 0.17
7.24 6 1.76
20.11 6 4.25
8.83 6 2.32
28.67 6 6.25
1.94 6 0.58
0.30 6 0.17
7.49 6 1.66
20.51 6 3.95
9.39 6 2.19
29.66 6 5.96
0.33 6 0.42
0.02 6 0.07
0.25 6 0.73
0.40 6 1.11
0.55 6 1.02
1.00 6 1.69
0.17-0.49
0.04 to 0.01
0.02 to 0.53
0.00 to 0.83
0.17-0.94
0.35-1.64
0.839
0.036*
0.125
0.586
0.001***
0.147
0.070
0.072
0.007**
0.004**
Note. Values are presented as mean 6 standard deviation. The difference is defined as the non-XB side XB side.
*P \0.05; **P \0.01; ***P \0.001.
is similar to adaptive mechanisms proposed for some
functional forward mandibular positioning appliances.33
The sustained input of imbalanced signals activated
asymmetrical remodeling of the mandible to adapt to
asymmetrical regional circumstances in UPXB subjects;
thus, correcting UPXB before the peak of pubertal growth
is clinically significant.
In our study, adult UPXB patients showed greater
asymmetry than adolescent UPXB patients regarding
linear and volumetric measurements. These findings
were consistent with those found in some previous
studies. Kilic et al31 found a significant difference of
1.22 mm in the ramal heights between the 2 sides of
adolescent UPXB patients. The difference was smaller
than that reported in another study on adult patients.34
In addition, Veli et al35 found no statistically significant
difference in volumetric measurements between the 2
sides in adolescent UPXB patients. However, adult
UPXB patients seemed to present great asymmetry in
volumetric measurements. Leonardi et al9 found a significant difference (1.53 cm3) in the hemimandibular
volumes between the 2 sides of PUXB adult patients,
similar to these findings. These results implied that the
linear asymmetry of the mandible, which can be detected
in the early stage of UPXB, was more sensitive than volumetric measurement in the diagnosis of mandibular
asymmetry. However, our findings were not consistent
with those found in the study by Evangelista et al,16
who did not find any significant difference in
mandibular asymmetry between adult and adolescent
UPXB patients. This contradiction may be attributed to
differences in the inclusion criteria between our studies.
Subjects aged 10-15 years were defined as adolescents in
our study, and the age range for adolescents in
Evangelista et al16 were aged 12-18 years. This
discrepancy in age range may contribute to some extent
to the disagreement in the results. Moreover, only
patients with a skeletal Class I relationship were included
Evangelista et al,16 whereas we used samples with
different skeletal Classes in our study. The longer period
and larger magnitude of mandibular growth in subjects
with a skeletal Class III relationship might have led to a
higher occurrence of mandibular asymmetry.36 The
difference in angular measurements between the sides
did not show any significant intergroup differences
between the control and UPXB groups or between
UPXB patients of different ages. Miresmaeili et al11 did
not find asymmetry for mediolateral ramal inclination
and condylar angle to MSP between the sides in adult
UPXB patients. In addition, our findings implied that
the growth direction of the mandible was stable during
asymmetric growth in UPXB patients.
American Journal of Orthodontics and Dentofacial Orthopedics
January 2024 Vol 165 Issue 1
Huang et al
36
Table VIII. Comparison of the differences between the
measurements of each side in each group (independent Student t test)
Measurements
Linear measurement
differences (mm)
Condylar unit length
Body unit length
Coronoid unit length
Angular unit length
Chin unit length
Condylar width
Ramal height
Body length
Angular measurement
differences ( )
Gonial angle
Mediolateral ramal
inclination
Anteroposterior ramal
inclination
Condylar angle to MSP
Volumetric measurement
differences (103 mm3)
Condylar unit volume
Coronoid unit volume
Ramal unit volume
Body unit volume
Hemiramus volume
Hemimandibular
volume
C1 C2 X1 X2 C1 X1 C2 X2
0.505 \0.001*** 0.073 \0.001***
0.546
0.741
0.293
0.251
0.667
0.009** 0.003** 0.945
0.239
0.767
0.371
0.580
0.917
0.400
0.873
0.924
0.068
0.006** 0.659
0.059
0.665
0.010* 0.495
0.001**
0.838
0.542
0.029*
0.011*
0.525
0.658
0.184
0.567
0.262
0.675
0.403
0.657
0.854
0.924
0.171
0.363
0.269
0.822
0.143
0.534
0.543
0.952
0.872
0.461
0.929
0.512
0.010*
0.475
0.178
0.127
0.057
0.021*
0.141
0.051
0.730
0.303
0.458
0.240
0.002**
0.096
0.124
0.140
0.028*
0.015*
C1, adolescents in the control group (aged 10-15 y); C2, adults in
the control group (aged 20-40 y); X1, adolescents in the UPXB group
(aged 10-15 y); X2, adults in the UPXB group (aged 20-40 y).
*P \0.05; **P \0.01; ***P \0.001.
This study also found that the coronoid unit length in
adolescents with UPXB was asymmetrical and that the
XB side was larger than the non-XB side. This finding
was in accordance with that of Cardinal et al.13 Greater
electromyographic activity of the anterior temporalis
(AT) on the crossbite side may be one possible explanation. Kecik et al37 found that UPXB patients showed
higher AT activity during resting and maximum clenching on the XB side than on the non-XB side. As the temporalis muscle inserts directly onto the coronoid process
of the mandible, higher electromyographic activity of AT
on the crossbite side might act as a signal activating
bone deposition of the coronoid process. However, no
significant difference in coronoid unit length between
sides was found in the UPXB adult group, consistent
with Leonardi et al.9 Adaptive change might occur in
the temporalis over time.
A weakness of this study was that it was a crosssectional study. From an ethical point of view, it is
impossible to postpone the treatment of patients for a
January 2024 Vol 165 Issue 1
longitudinal study. Another limitation was differences
between sexes, which may have affected mandibular
growth and was not evaluated. Further studies with larger
samples are needed to uncover the association between
growth and mandibular asymmetries in UPXB patients.
CONCLUSIONS
The null hypothesis was rejected because of the
following:
1.
2.
Both adolescent and adult UPXB patients presented
remarkable mandibular asymmetry. The asymmetry
was most evident in the condylar region, and most
measurements were greater on the non-XB side
than on the XB side.
Adult patients with UPXB showed significantly
greater asymmetries than adolescents. Mandibular
asymmetry in patients with UPXB may progress
over time; therefore, early treatment should be
considered for UPXB adolescent patients. Further
studies are still needed to evaluate the effectiveness
of early treatment.
AUTHOR CREDIT STATEMENT
Min Huang contributed to conceptualization, methodology, validation, and original draft preparation; Baoyi
Chen contributed to investigation and data curation;
Huiyi Lin contributed to methodology and software;
Weiqi Guo contributed to software and validation;
Guan Luo contributed to investigation; Wenjun Chen
contributed to validation; Weijun Zhang contributed to
validation; and Chang Liu contributed to manuscript review and editing, supervision, and funding acquisition.
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American Journal of Orthodontics and Dentofacial Orthopedics
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