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

Introduction

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//www.random.org. 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.

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Figure 1

Biodex balance system device used in the present study

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Figure 2

Biodex balance system device used in the present study

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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].

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Figure 3

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

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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.

Results

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

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

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°.

Discussion

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.

Conclusions

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.