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Original Article
7 (
); 175-180

Effects of Rapid Maxillary Expansion on Head Posture, Postural Stability, and Fall Risk

Department of Orthodontics, Faculty of Dentistry, Gaziosmanpasa University, Tokat, Turkey
Address for correspondence: Dr. Fatih Celebi, Department of Orthodontics, Faculty of Dentistry, University of Gaziosmanpasa, 60100 Tokat, Turkey. E-mail:
This is an open access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 3.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.
This article was originally published by Wolters Kluwer and was migrated to Scientific Scholar after the change of Publisher; therefore Scientific Scholar has no control over the quality or content of this article.

How to cite this article: Celebi F, Hologlu F, Akbulut S, Bicakci AA. Effects of rapid maxillary expansion on head posture, postural stability, and fall risk. APOS Trends Orthod 2017;7:175-80.



The aim of this study was to investigate the effects of rapid maxillary expansion (RME) on head posture, postural stability, and fall risk.

Materials and Methods

A sample of 51 adolescent patients was randomly divided into two groups. In the first group, which consisted of 28 patients (15 females and 13 males), RME was performed as a part of routine orthodontic treatment. The remaining 23 individuals (12 females and 11 males) served as the control group. Lateral cephalometric radiographs taken in natural head position, postural stability, and fall risk scores were obtained during the first visit. They were repeated on average 3.8 months and 3.5 months later for the study and control groups, respectively. The changes were analyzed using the Wilcoxon signed-rank test, paired samples t-test, Mann–Whitney U-test, and independent samples t-test.


As a result of RME, a statistically significant decrease was detected in the fall risk score (P < 0.05) in the study group, while the head position and postural stability remained unchanged. For the control group, no significant changes were observed in all measurements.


The result of the present study suggests that RME has a capacity of improving fall risk.


Biodex balance system
head posture
rapid maxillary expansion


Rapid maxillary expansion (RME) has been widely used to correct maxillary transverse deficiency. Because of the anatomical proximity between the nasal cavity, auditory apparatus, airway passage, and hard palate, publications investigating the effects of RME have not limited themselves to the maxilla. The roof of the oral cavity, which is also the floor of the nasal cavity, is expanded by opening of the midpalatal suture, which could lead to increase in nasal airway volume and decrease in nasal resistance originating from constricted nasal cavity. Thus, patients who suffer from mouth breathing benefit from RME.[1] It has also been argued that craniofacial development could be affected by the alteration of respiratory function.[2] It was claimed that the head was oriented into extension to facilitate oral respiration in patients who breath orally.[3] Later, Solow and Kreiborg advocated this hypothesis and presented a new concept that they named “soft tissue stretching,” which elucidates the relationship between the respiratory function and craniofacial morphogenesis.[4] Huggare and Laine-Alava have shown changes in head posture due to impaired nasal breathing.[5] Similarly, Vig et al. have presented head extension relative to the cervical column and the true vertical as a result of nasal obstruction.[6] On this basis, it can be concluded that repairing of impaired nasal breathing could have favorable effects on craniocervical angulation and head posture.

Especially in the recent years, there has been growing interest in the relationship between the stomatognathic system and postural balance. However, studies in dentistry are limited to the possible relationship between occlusion and body balance.[7] The effects of constricted maxilla on body balance have not been identified to date.

Because balance has been an interesting topic for researchers since the 1850s,[8] researchers have tried to find out the best method of assessing body balance. Assessment methods are generally classified as functional and physiological tests. In clinical practice, functional tests are commonly utilized by clinicians because their costs are lower and they require uncomplicated equipment. The functional reach test, single-leg stance test, Berg balance test, and Barthel index are some of the functional tests. These functional tests could be used for detecting the presence of balance impairment; however, they are unsuccessful in detecting the level of impairment. Furthermore, their sensitivities to small balance changes are not sufficient. For more detailed analysis, physiological tests such as sway magnetometry, multisensor polymer insoles, muscle electrodes, and dynamic force platforms are preferred by researchers. In 2001, Browne and O’Hare[9] performed a review to assess different balance assessment methods and concluded that “Force platforms appear to be the balance assessment instrumentation most suited to the clinical situation since they produce a real-time display and can detect small changes in a subject’s ability to maintain their balance, making them suitable for thorough evaluations of balance and for monitoring a patient’s progress.”

The Biodex Balance System is a versatile device that can be used to evaluate the ability to maintain dynamic unilateral or bilateral postural stability on either a stable or unstable platform. The postural stability test intends to measure the ability to maintain the center of balance. The test evaluates the angular excursion of the subject’s center of gravity. For a more detailed analysis, deviations in the sagittal and frontal directions are quantified separately as anterior/posterior and medial/lateral stability indexes. Higher scores represent deviation from the center, which is indicative of poor balance. Lower scores are more favorable than higher ones.

The fall risk test (FRT) aims to identify potential fall candidates. Subjects’ scores are compared with the normative data depending on age and then an interpretation is done. In this mode, a patient’s dynamic postural stability is measured using a movable platform. Higher scores suggest that there may be problematic conditions involving lower extremity strength, proprioception, and vestibular and visual deficiencies.[10] Reliability of Biodex measurements was reported in the literature.[11]

Although there are many studies evaluating the effects of RME on various systems such as craniofacial structure, nocturnal enuresis, conductive hearing loss, voice, and the respiratory system,[12-15] there is no information about the possible relationship between RME and total body balance and fall risk in the literature. The aims of the present study were to investigate the alteration of head posture in patients who experienced the RME procedure and to evaluate the effects of RME on postural stability and fall risk scores.

Materials and Methods

This study was approved by the Clinical Research Ethics Committee of the Gaziosmanpaşa University (Approval No. 14-KAEK-061). Informed consent signed by parents was obtained.

Fifty-four patients who were referred to Gaziosmanpaşa University, Faculty of Dentistry for orthodontic treatment were included in the study. The selection criteria included unilateral or bilateral crossbite, narrow buccal corridors, patient–parent compliance, no previous orthodontic treatment, and good oral health.

Individuals were randomly allocated to the two groups, study and control, through the use of http// The study group consisted of 28 patients (15 females and 13 males), while the control group consisted of 26 patients (14 females and 12 males). During the test period, three individuals from the control group (2 females and 1 male) refused to be included in the study. Ultimately, the control group performed with 23 individuals (12 females and 11 males). The mean ages of the study and control groups at the first visit were 13.52 years and 14.21 years, respectively.

A tooth- and tissue-borne RME appliance was used on the patients in the study group, and the expansion screw was activated until the occlusal aspects of the lingual cusps of the maxillary posterior teeth made contact with the occlusal aspects of the labial cusps of the mandibular posterior teeth. The average expansion at the screw level was 9–12 mm. After the RME appliance had been left in place for 1 month without any activation, a Hawley appliance was used for retention. Individuals in the control group were not subjected to any type of treatment during the investigation period.

Orthodontic records including anamnesis, dental casts, photographs, and panoramic and lateral cephalometric radiographs were obtained before treatment (T1). Lateral cephalometric radiographs were taken in the natural head position (NHP) as defined by Siersbaek-Nielsen and Solow.[16] Before taking the radiograph, exercises for relaxing the head and neck muscles were performed. In order not to influence the NHP, ear rods and the forehead clamp of the cephalometer were not used.

Postural stability and FRTs were measured with the aid of the Biodex Balance System [Figures 1 and 2]. The Biodex Balance System (Biodex Medical Systems, Shirley, NY, USA) is a device which measures static and dynamic balance ability using the objective method. It consists of a platform which provides up to 20° of surface tilt in a 360° range of motion and a digital screen which guides patients for the purpose of evaluating postural stability and fall risk scores. Computer software which enables the device to provide objective measurements of postural stability and fall risk is connected to the platform.[17] Static and dynamic measurements used in this study consist of four categories: overall stability index (OA), anterior-posterior stability index, medial-lateral stability index, and FRT.

Figure 1: Biodex balance system device used in the present study
Figure 2: Biodex balance system device used in the present study

All measurements were repeated on average 3.8 months and 3.5 months later (T2) for the study and control groups, respectively. The measurements were compared between the study and control groups.

Cephalometric analysis

Dolphin Imaging 11.5 Software (Dolphin Imaging and Management Solutions, Chatsworth, California, USA) was used to obtain cephalometric measurements. To evaluate the postural differences between the T1 and T2, cephalometric measurements, including OPT/NSL°, CVT/NSL°, OPT/CVT°, NSL/VER°, OPT/HOR°, and CVT/HOR°, were used [Figure 3].

Figure 3: Cephalometric measurements traced on the lateral cephalometric radiographs in natural head position

OPT: The line tangent to the odontoid process (CV2tp) through the most inferior and posterior point on the corpus of the second cervical vertebra (CV2ip).

CVT: The line tangent to the odontoid process (CV2tp) through the most inferior and posterior point on the fourth cervical vertebra (CV4ip).

  • NSL: The nasion-sella line

  • VER: The true vertical line

  • HOR: The true horizontal line

  • OPT/NSL°: The angle formed between the line OPT and NSL

  • CVT/NSL°: The angle formed between the line CVT and NSL

  • OPT/CVT°: The angle formed between the line OPT and CVT

  • NSL/VER°: The angle formed between the line NSL and true vertical

  • OPT/HOR°: The angle formed between the line CVT and true horizontal

  • CVT/HOR°: The angle formed between the line CVT and true horizontal.

Statistical analysis

Statistical analysis was performed using the Statistical Package for the Social Sciences (SPSS for Windows, version 22.0, SPSS Inc., Chicago, IL, USA). Means and standard deviations were presented. Normality of data was tested using the Kolmogorov–Smirnov test. According to the Kolmogorov–Smirnov test results, both parametric and nonparametric tests were required for statistical analysis. The Mann–Whitney U-test and the independent samples t-test were performed to detect any differences between the groups with regard to pretreatment Biodex scores and cephalometric measurements. In the comparison of pretreatment and posttreatment changes, the Wilcoxon signed-rank test and paired samples t-test were used. For evaluation of the differences in the amount of Biodex score and cephalometric measurement changes, the Mann–Whitney U-test and independent samples t-test were performed. Statistical significance was set at a level of P < 0.05.

For examining the method error, 13 radiographies which were selected randomly were retraced at least 3 weeks later by the same examiner. The intraclass correlation coefficient was used and the results confirmed the reliability of the measurements.


Demographic data regarding the test and control groups are shown in Table 1.

Table 1: Gender and age of the groups
  Female Male Total
n Mean age±SD n Mean age±SD n Mean age±SD
Study group 15 13.74±2.04 13 13.28±1.52 28 13.52±1.80
Control group 12 14.27±1.99 11 14.13±2.11 23 14.21±1.97
P   0.523   0.309   0.236

P<0.05. SD – Standard deviation

Tables 2 and 3 present a comparison of the Biodex scores and cephalometric measurements between the groups at time T1.

Table 2: Comparison of the pretreatment (T1) Biodex scores between the groups
  Mean±SD P
Study group Control group
OA 0.69±0.30 0.63±0.26 0.341
APSI 0.46±0.20 0.45±0.15 0.962
MLSI 0.40±0.23 0.34±0.21 0.189
FRT 1.05±0.42 1.14±0.57 0.585

P<0.05. OA – Overall stability index; APSI – Anterior-posterior stability index; MLSI – Medial-lateral stability index; FRT – Fall risk test; SD – Standard deviation

Table 3: Comparison of the pretreatment (T1) cephalometric measurements between the groups
  Mean±SD P
Study group Control group
OPT/NSL (°) 97.27±8.01 101.88±9.59 0.090
CVT/NSL (°) 101.88±8.11 106.72±8.71 0.066
OPT/CVT (°) 5.29±2.98 5.06±3.10 0.807
NSL/VER (°) 95.55±4.08 100.50±6.51 0.003
OPT/HOR (°) 88.73±8.20 88.76±8.64 0.991
CVT/HOR (°) 83.47±8.09 83.91±7.29 0.855

P<0.05. SD – Standard deviation

In the evaluation of the Biodex scores and cephalometric variables, no differences between the groups at the start of treatment were found, except for NSL/VER°.

Comparisons of the changes in Biodex scores and cephalometric variables with treatment

Changes in Biodex scores and cephalometric variables between T1 and T2 are presented in Tables 4 and 5. Statistically significant differences were detected in FRT, CVT/NSL°, and CVT/HOR° for the study group (P < 0.05).

Table 4: Evaluation of the changes with treatment in postural stability and fall risk scores
  Study group (mean±SD) P Control group (mean±SD) P
T1 T2 T1 T2
OA 0.69±0.30 0.66±0.28 0.635 0.63±0.26 0.64±0.38 0.458
APSI 0.46±0.20 0.44±0.19 0.808 0.45±0.15 0.44±0.34 0.278
MLSI 0.40±0.23 0.38±0.22 0.414 0.34±0.21 0.34±0.15 0.794
FRT 1.05±0.42 0.78±0.30 <0.001 1.14±0.57 1.08±0.55 0.709

P<0.05. OA – Overall stability index; APSI – Anterior-posterior stability index; MLSI – Medial-lateral stability index; FRT – Fall risk test; SD – Standard deviation

Table 5: Evaluation of the changes with treatment in cephalometric measurements
  Study group (mean±SD) P Control group (mean±SD) P
T1 T2 T1 T2
OPT/NSL (°) 97.27±8.01 98.86±9.50 0.261 101.88±9.59 103.97±8.92 0.105
CVT/NSL (°) 101.88±8.11 104.11±10 0.029 106.72±8.71 109.09±8.86 0.063
OPT/CVT (°) 5.29±2.98 5.55±3.11 0.576 5.06±3.10 5.20±3.50 0.770
NSL/VER (°) 95.55±4.08 95.40±6.93 0.905 100.50±6.51 101.99±5.07 0.156
OPT/HOR (°) 88.73±8.20 86.74±8.83 0.078 88.76±8.64 88.19±8.04 0.468
CVT/HOR (°) 83.47±8.09 81.47±8.84 0.039 83.91±7.29 83.12±7.95 0.265

P<0.05. SD – Standard deviation

When the differences between the study and control groups were evaluated, only FRT was found statistically significant between the two groups (P < 0.05) [Tables 6 and 7].

Table 6: Evaluation of the differences in the amount of Biodex score changes between the study and control groups
  Mean±SD P
Study group Control group
OA −0.03±0.03 0.01±0.37 0.849
APSI −0.02±0.21 −0.01±0.32 0.293
MLSI −0.02±0.26 −0.01±0.17 0.382
FRT −0.28±0.36 −0.05±0.55 0.042

P<0.05. OA – Overall stability index; APSI – Anterior-posterior stability index; MLSI: Medial-lateral stability index; FRT – Fall risk test; SD – Standard deviation

Table 7: Evaluation of the differences in the amount of cephalometric measurement changes between the study and control groups
  Mean±SD P
Study group Control group
OPT/NSL (°) 1.58±7.32 2.09±5.02 0.916
CVT/NSL (°) 2.23±5.13 2.37±4.88 0.931
OPT/CVT (°) 0.25±2.37 0.13±1.87 0.862
NSL/VER (°) −0.15±6.76 1.49±4.13 0.371
OPT/HOR (°) −1.98±5.74 −0.56±3.13 0.353
CVT/HOR (°) −2.00±4.88 −0.79±2.85 0.360

P<0.05. SD – Standard deviation


Balance, which is managed by a complex system consisting of central processing, sensory input, and neuromuscular responses, is defined as the ability to maintain the center of gravity over the base of support, usually while in an upright position.[18]

Various systems have hitherto been employed to assess balance and postural control. The Biodex is a balance assessment system which is widely accepted in the evaluation of postural stability and fall risk. In the literature, there are a lot of studies using the Biodex balance system in different areas, such as orthopedics, exercise evaluations, sport studies, and neurological diseases.[19-21] Although it is not the only device which evaluates postural stability and fall risk, the reliability of Biodex measurements was demonstrated many times.[17,22,23]

In this study, the effects of RME on postural stability, fall risk, and head position were investigated. In a comparison of the Biodex scores and cephalometric variables at T1, although NSL/VER° was found to be different (P < 0.05), the remaining 5 cephalometric and 4 Biodex measurements showed that the groups were largely equal [Tables 2 and 3].

The main finding of our study was that RME was capable of decreasing fall risk scores in patients who suffered from constricted transverse maxillary dimension. As shown many times before, RME is capable of increasing nasal airway dimensions depending on the patient’s age, skeletal maturation, type of the appliance, and screw activating frequency. Widening of the nasal cavity resulted in a decrease in nasal resistance and consequently an improvement in nasal respiration.[24] This improvement could lead to more efficient performance in all body functions as well as body balance, which resulted in a reduction in the fall risk score.

Balance is regulated through output data to the central nervous system from the eyes, as well as sensory systems of the body such as muscles, joints, skin, and the inner ear. In the literature, there are a great number of publications which show the effects of RME on the auditory apparatus.[25-27] Although the issue investigated in these studies was usually the effects of RME on the Eustachian tube and conductive hearing loss, the ear hosts not only the auditory apparatus but also the balance structures such as the vestibular system. Furthermore, there is a close anatomical relationship between the balance and auditory structures. Therefore, the effects of RME may not be limited to the Eustachian tube and auditory apparatus; because of the anatomical proximity, RME could also affect the balance structure in the inner ear.

cephalometric measurements between the groups

In the present study, changes in head position were also investigated on lateral cephalometric radiographs which were taken in NHP. Although a slight increase was observed in the OPT/NSL and CVT/NSL angles, which represent craniocervical angulation, due to RME (T1–T2), a similar increase was observed in the untreated control group. We can therefore conclude that RME has no effect on craniocervical angulation of the head in the short term [Table 7].

Differences in OPT/CVT° which is utilized to determine cervical lordosis were found to be statistically insignificant in both groups. NSL/VER°, which describes head elevation to the true vertical, also showed no statistically significant changes between T1 and T2 in both groups.

OPT/HOR° and CVT/HOR°, which can be defined as cervicohorizontal angles, were not changed after RME therapy [Table 7]. In the literature, there are studies showing the relationship between decreased cervicohorizontal angles and constricted nasopharyngeal dimensions-obstructive sleep apnea/hypopnea.[28-30] One could expect to find an increase in these angles due to an increase in nasal dimensions after RME. In these studies, the relationship between the nasopharyngeal dimensions and cervicohorizontal angles was generally attributed to changes in pharyngeal airway size. For example, cervicohorizontal angles were found to be increased in patients who underwent mandibular advancement surgery.[30]

In the literature, there are also studies evaluating the relationship between changes in the nasal airway and head posture. In 2011, Yagci et al. performed a study to evaluate the possible relationship between RME and NHP. They used an inclinometer incorporated into eyeglass frames to measure the differences in NHP. The results showed that RME has no effect on NHP.[31] McGuinness and McDonald studied the short- and long-term effects of RME on NHP using lateral cephalograms. Although the short-term results indicated that RME has no effect, in the long term, RME is capable of modifying NHP.[32] In addition, Tecco et al. have evaluated the long-term effects of RME in mouth-breathing girls and have shown that RME has the ability to influence head posture.[33]

As shown by McGuinness and McDonald, morphological adaptation of head posture to improved nasal breathing may take a relatively long time.[32] We have evaluated relatively short-term effects of RME on head posture; therefore, changes might be found to be insignificant. When considering the study of Yagci et al. and the short-term results presented by McGuinness and McDonald, our results were consistent with the literature.[31,32]

It is possible that if we had designed the study as a long-term structure, we could have detected significant differences in cephalometric measurements. This is because, in many variables, McGuinness and McDonald have detected statistically significant differences in the long-term results, although statistically insignificant in the short term. This means that physiological adaptation to RME takes much more time.

In addition to that, total sample size in this study was only 51 individuals (28 in study group and 23 in control group). We believe that the future studies with larger sample size can present the more definitive conclusions to the literature. Therefore, results in the present study must be interpreted with caution.


The findings of the present study suggest that RME is capable of decreasing fall risk scores when compared with the control group. However, no significant differences between the study and control groups in terms of postural stability scores and cephalometric variables were observed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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