Effect of chewing on postural stability during quiet standing in healthy young males

Effect of masticatory movements on head and trunk sways, and sitting and foot pressure distributions during sitting position

BACKGROUND

The head plays an important role in the postural control. Chewing co-activates jaw and neck muscles leading to coordinated jaw and head-neck movements. Therefore, to examine effect of masticatory movements on head and trunk sways, and sitting and foot pressure distributions during mastication is helpful in the attempt to understand the interrelationship between stomatognathic function and posture control system in the sitting position.

OBJECTIVES

The purpose of this study was to test the hypothesis in healthy subjects that masticatory movements affect head and trunk sways and sitting and foot pressure distributions during sitting position.

METHODS

A total of 30 healthy male subjects with an average age of 25.3  years (range, 22-32  years) were evaluated. The CONFORMat™ and MatScan™ system were used to analyse changes in sitting pressure distribution center of sitting pressure (COSP) and changes in foot pressure distribution center of foot pressure (COFP), respectively, and the three-dimensional motion analysis system was used to analyse changes in head and trunk postures while subjects remained sitting position with rest position, centric occlusion and chewing. The total trajectory length of COSP/COFP, COSP/COFP area, and head and trunk sway values were compared between the three conditions to evaluate whether masticatory movement affected the stability of head and trunk sways and sitting and foot pressure distributions.

RESULTS

Total trajectory length of COSP and COSP area during chewing were significantly shorter and smaller respectively than it was in rest position and centric occlusion (p  ⟨  .016). Head sway value during chewing was significantly larger than it was in rest position and centric occlusion (p  ⟨  .016).

CONCLUSION

Masticatory movements affect sitting pressure distribution and head movements during sitting position.

Effects of jaw clenching on dynamic reactive balance task performance after 1-week of jaw clenching training

Introduction

Good balance is essential for human daily life as it may help to improve the quality of life and reduce the risk of falls and associated injuries. The influence of jaw clenching on balance control has been shown under static and dynamic conditions. Nevertheless, it has not yet been investigated whether the effects are mainly associated with the dual-task situation or are caused by jaw clenching itself. Therefore, this study investigated the effects of jaw clenching on dynamic reactive balance task performance prior to and after 1 week of jaw clenching training. It was hypothesized that jaw clenching has stabilizing effects resulting in a better dynamic reactive balance performance, and these effects are not related to dual-task benefits.

Methods

A total of 48 physically active and healthy adults (20 women and 28 men) were distributed into three groups, one habitual control group (HAB) and two jaw clenching groups (JAW and INT) that had to clench their jaws during the balance tasks at T1 and T2. One of those two groups, the INT group, additionally practiced the jaw clenching task for 1 week, making it familiar and implicit at T2. The HAB group did not receive any instruction regarding jaw clenching condition. Dynamic reactive balance was assessed using an oscillating platform perturbed in one of four directions in a randomized order. Kinematic and electromyographic (EMG) data were collected using a 3D motion capture system and a wireless EMG system, respectively. Dynamic reactive balance was operationalized by the damping ratio. Furthermore, the range of motion of the center of mass (CoM) in perturbation direction (RoM_{CoM_AP} or RoM_{CoM_ML}), as well as the velocity of CoM (V_CoM) in 3D, were analyzed. The mean activity of the muscles relevant to the perturbation direction was calculated to investigate reflex activities.

Results

The results revealed that jaw clenching had no significant effects on dynamic reactive balance performance or CoM kinematics in any of these three groups, and the automation of jaw clenching in the INT group did not result in a significant change either. However, high learning effects, as revealed by the higher damping ratio values and lower V_CoM at T2, were detected for the dynamic reactive balance task even without any deliberate balance training in the intervention phase. In the case of backward perturbation of the platform, the soleus activity in a short latency response phase increased for the JAW group, whereas it decreased for HAB and INT after the intervention. In the case of forward acceleration of the platform, JAW and INT showed a higher tibialis anterior muscle activity level in the medium latency response phase compared to HAB at T1.

Discussion

Based on these findings, it can be suggested that jaw clenching may lead to some changes in reflex activities. However, the effects are limited to anterior-posterior perturbations of the platform. Nevertheless, high learning effects may have overall overweighed the effects related to jaw clenching. Further studies with balance tasks leading to less learning effects are needed to understand the altered adaptations to a dynamic reactive balance task related to simultaneous jaw clenching. Analysis of muscle coordination (e.g., muscle synergies), instead of individual muscles, as well as other experimental designs in which the information from other sources are reduced (e.g., closed eyes), may also help to reveal jaw clenching effects.

Cervical Range of Motion Analysis Performed with an Accelerometer: A Study of Intersession Reliability for Dental Practice

During the clinical examination of subjects with temporomandibular disorders (TMDs), the dentist sometimes must evaluate the cervical spine, due to the anatomical and functional connections between the cervical portion of the spine and the stomatognathic apparatus. The accelerometer is a device that evaluates the Range of Motion (ROM) of the main movements of the head on the neck. To date, only a few studies have investigated the repeatability of the use of the accelerometer in the assessment of cervical ROM. Therefore, the present longitudinal observational study analyzed the repeatability of acquired cervical movements on a sample of volunteer subjects who underwent accelerometer testing. A sample of 32 subjects was tested twice within 14 days to assess cervical ROM using a standardized protocol based on a review of existing literature. The results show that the examination is reliable for all the positions of the jaw, except for the parameters regarding the asymmetries of rotation and bending. In conclusion, the accelerometer can be considered a reliable tool for evaluating the active cervical ROM. However, further studies will be necessary to make better evaluations.

Effect of static and dynamic jaw positions on postural stability among people with blindness

BACKGROUND

In comparison with the people with normal sight, the mean center of gravity (COG) velocity is significantly higher among blind people. A strong relationship has been shown between jaw and neck sensorimotor and postural control. The purpose of this study was to determine the effect of different static and dynamic jaw positions on postural stability among subjects with blindness.

METHODS

Postural stability was measured as COG velocity in 39 blind subjects under the following five conditions: resting jaw (natural jaw position with no instructions, control), open jaw (teeth of both jaws slightly apart), clenched jaw (teeth tightly closed across each other), chewing (a standard bolus of gum at the natural palace), and tongue position (positioned behind the upper incisors) while standing on firm and foam surfaces.

RESULTS

The mean COG velocity while standing on the firm surface during resting, open jaw position, clenched jaw position, chewing, and tongue positions were 0.54, 0.50, 0.44, 0.59, and 0.46 deg/s, respectively. The mean COG velocity while standing on the foam surface during resting, open jaw position, clenched jaw position, chewing, and tongue positions were 1.42, 1.23, 1.10, 1.14, and 1.06 deg/s, respectively. Compared to the firm surface, the COG velocity was significantly higher on the foam surface in all five conditions (p < .001). In the comparison between the conditions, there were no significant differences in either the firm or foam surface in all five conditions (p > .05).

CONCLUSION

People with blindness behave in the same way as sighted subjects on firm and foam surfaces. However, changes in static and dynamic jaw positions do not affect postural stability among them.

Chewing gum reduces visually induced motion sickness

Visually induced motion sickness (VIMS) is a common side-effect of exposure to virtual reality (VR). Its unpleasant symptoms may limit the acceptance of VR technologies for training or clinical purposes. Mechanical stimulation of the mastoid and diverting attention to pleasant stimuli-like odors or music have been found to ameliorate VIMS. Chewing gum combines both in an easy-to-administer fashion and should thus be an effective countermeasure against VIMS. Our study investigated whether gustatory-motor stimulation by chewing gum leads to a reduction of VIMS symptoms. 77 subjects were assigned to three experimental groups (control, peppermint gum, and ginger gum) and completed a 15-min virtual helicopter flight, using a VR head-mounted display. Before and after VR exposure, we assessed VIMS with the Simulator Sickness Questionnaire (SSQ), and during the virtual flight once every minute with the Fast Motion Sickness Scale (FMS). Chewing gum (peppermint gum: M = 2.44, SD = 2.67; ginger gum: M = 2.57, SD = 3.30) reduced the peak FMS scores by 2.05 (SE = 0.76) points as compared with the control group (M = 4.56, SD = 3.52), p < 0.01, d = 0.65. Additionally, taste ratings correlated slightly negatively with both the SSQ and the peak FMS scores, suggesting that pleasant taste of the chewing gum is associated with less VIMS. Thus, chewing gum may be useful as an affordable, accepted, and easy-to-access way to mitigate VIMS in numerous applications like education or training. Possible mechanisms behind the effect are discussed.

Masticatory coefficient and physical functioning in older frail patients admitted for a Comprehensive Gerontological Assessment

BACKGROUND

Physical functioning may be limited in older, frail patients with missing teeth without prosthetic correction. This cross-sectional study examined the relationship between physical performance and the geriatric masticatory coefficient (GMC) in patients who underwent both a comprehensive gerontological assessment (CGA) to improve poly-pathology management and an intra-oral exam.

METHODS

All patients were evaluated based on the following: (corrected) GMC, number of posterior occluding pairs (POPs), short physical performance battery (SPPB) or timed up and go (TUG) test, and mini-nutritional assessment (MNA).

RESULTS

Of the 256 patients (mean age 83.76[SD 6.16], 148F), 75 (29.30%) were malnourished. The corrected GMC was lower in malnourished patients. When adjusted for age, gender, and MNA, the corrected GMC correlated with the TUG time (r=-0.198, p=0.005) and SPPB score (r=0.282, p=0.009). Correlations between GMC and POPs were determined for the SPPB (r=0.269, p=0.013; r=0.319, p=0.004, respectively) but not for the TUG (r=-0.108, p=0.128; r=-0.136, p=0.072).

CONCLUSION

The correlation between physical performance and decreased masticatory capacity was not fully explained by malnutrition in mildly to severely frail and multi-morbid patients; posture may also be impaired by missing teeth. The study of dental care effects on physical performance will provide further insights.

Can jaw position affect the fine motor activity of the hand during writing?

BACKGROUND

Jaw and neck systems have been shown to be functionally related and changes in either system can modulate gross motor functions, such as posture control. It remains to be seen if any change in jaw position can affect fine motor skills. The objective of this study was to determine the effect of resting, open and clenched jaw positions on various handwriting parameters while standing on firm and unstable surfaces.

METHODS

Handwriting samples were collected from 36 healthy male participants (age, 15-35 years) using a digitizer tablet (WACOM Intuos 4) with noninking pen in the resting, open and clenched jaw positions while standing on firm and unstable surfaces. The measured handwriting parameters included duration, vertical size, horizontal size, absolute size, average absolute velocity, and absolute jerk. Recordings and analyses were performed using NeuroScript MovAlyzeR software.

RESULTS

All handwriting parameters varied among the resting, open, and clenched jaw positions on both the firm and unstable surfaces. However, based on statistical analyses, there were no significant differences in the handwriting parameters among three jaw positions on both surfaces (p > .05).

CONCLUSION

This study revealed that all handwriting parameters varied among the resting, open, and clenched jaw positions on both the firm and unstable surfaces, showing that change in the jaw motor system may potentially affect the fine motor skills. However, on statistical analysis, there was no significant effect of 3 studied jaw positions on fine motor skills as seen on gross motor skills among healthy individuals.

Head Posture and Postural Balance in Community-Dwelling Older Adults Who Use Dentures

Background and objectives: Tooth loss and consequent denture use and impaired posture and postural balance are more prevalent in older adults than in the young ones. The aim of this cross-sectional study was to identify the association between denture use, head posture, postural balance, and neck muscle strength (NMS). Materials and methods: We included 107 participants (56 in the non-denture use group and 51 in the denture use group) and measured their NMS, forward head posture, and postural balance. Forward head posture was measured using the craniocervical angle (CRA). Postural balance was assessed using a timed up-and-go test (TUG) and postural sway. An independent t-test was used to analyze the differences between the groups; Pearson correlation analysis was used to analyze the correlation of period of denture use, head posture, and postural balance. Results: We found that the denture use group had lower NMS, smaller CRA, longer TUG, and longer postural sway length than the non-denture use group. Duration of denture use was significantly correlated with TUG. Conclusions: Our findings reveal that denture use does not help with NMS, forward head maintain NMS, head posture, and postural balance in older adults.

Influence of different jaw positions on dynamic balance using Y-balance test

BACKGROUND

Jaw sensory-motor system has been shown to affect static balance of the body. It would be interesting to know whether it can influence dynamic balance as well. The objective of this study is to examine the influence of different jaw positions on dynamic balance using the Y-balance test.

METHODS

Eighty healthy male participants aged 20-35 years were invited to participate in this study. Dynamic balance was measured by the Y-balance test in three directions (anterior, posteromedial, and posterolateral) for each leg separately in three jaw positions: resting jaw (control), open-jaw, and clenched jaw.

RESULTS

There were no significant differences in reach distances between the different jaw positions except in the posterolateral direction. In comparison with resting jaw position, reach distance was significantly higher in open-jaw position for the right leg and in clenched and open-jaw positions for the left leg in the posterolateral direction.

CONCLUSIONS

Although various studies have shown direct or indirect influence of jaw sensory-motor system on static postural control, results of this study point to limited relation with dynamic postural control among healthy subjects. However, it supports the potential of the jaw sensory-motor system to affect motor control during functional tasks in patients with postural instability or similar disorders.

Effect of voluntary teeth clenching and sitting posture on maximal static force of limb muscles

BACKGROUND

People clench their teeth to activate facial, neck and abdominal muscles when they need to generate heavy muscle force against large resistance like lifting heavy objects, in order to gain possible ergogenic advantage. These are termed as remote voluntary contractions. Aim of this study was to evaluate the effect of voluntary teeth clenching on maximal voluntary contraction of extensors and flexors of the knee, shoulder and elbow joints of the dominant side during slouch and unsupported upright sitting.

METHODS

One hundred healthy young male adults (mean age 23.3 years) participated in this study. Maximal voluntary contraction was measured using a hand-held dynamometer.

RESULTS

Jaw clenching caused different ergogenic effect during slouch versus unsupported sitting postures. The data revealed that during unsupported upright sitting, the effect of jaw clenching consistently results in larger maximal voluntary contraction of both extensor and flexor muscles of all the three studied joints. However, during slouch sitting, only the maximal voluntary contraction of extensors of elbow and flexors of knee were larger with clenched teeth position.

CONCLUSIONS

Jaw clenching can affect the maximal voluntary contraction of limb muscles which is sitting posture dependent. Jaw clenching can consistently facilitate certain muscles of the upper and lower limbs to generate greater force production during upright sitting.

Temporal more than spatial regulation of sway is important for posture in response to an ultra-compliant surface

BACKGROUND AND AIM

Many people use balance training as a rehabilitation or habilitation modality. Although the time course of changes to temporal and spatial aspects of postural sway over the initial weeks of such training is as yet unclear. Particularly, we sought to explore the effects of training on sway during a dynamic task of stance on an ultra-compliant surface. Such a task provides different mechanical, and thus sensorimotor, constraints compared to stance on a solid surface.

METHODS

Center of pressure (COP) was measured on an ultra-compliant surface atop a force plate at the start of each of 18 days of a 6-week balance training program. Range and standard deviation quantified amount of sway while velocity and Lyapunov exponent (LyE) quantify speed and rhythmicity of sway, respectively.

RESULTS

Trend analysis indicated quadratic changes in COP range and standard deviation, with initial reductions followed by returns to initial values by the end of training. Linear reduction of movement velocity and LyE continued through the duration of the program. Reduced LyE indicates regular (self-similar) structure of the COP path.

CONCLUSIONS

These results provide insight to the developing postural strategy necessary for maintaining upright stance within the dynamics created by interactions with an ultra-compliant surface. Participants showed sensitivity to surface properties, moving both more slowly and with a more regular movement pattern; suggesting that they were able to develop a more feed-forward approach to the maintenance of balance by exploiting task constraints.

Effect of posture on swallowing

BACKGROUND

Swallowing is a systematic process. Any structural, physiological or neurological disturbance in this process may cause dysphagia. Although there are studies that report head/neck movements during mastication, there are fewer studies that show the effect of different head/neck postures on difficulty while swallowing.

OBJECTIVES

To observe the effect of different body postures on the self-perceived difficulty while swallowing in normal healthy subjects.

METHODS

Participants were asked to swallow 25 ml of water in one go while sitting upright, sitting with head/neck flexed, head/neck extended and lying supine. Following this, they had to rate their self-perceived difficulty while swallowing on a scale of 0-10, 0 being most easy and 10 being most difficult.

RESULTS

186 subjects with mean age 32.7 SD 9.04 participated in this study. It was found to be least difficult to swallow when subjects were asked to swallow in upright sitting position. Statistically significant differences were found between sitting upright, sitting with head/neck flexed, head/neck extended and lying supine.

CONCLUSION

Postural modification may help in rehabilitation of patients with dysphagia by affecting bolus flow to improve speed and safety of swallowing by closure of airways to prevent aspiration.

Influence of the mandibular position on the active cervical range of motion of healthy subjects analyzed using an accelerometer

OBJECTIVE

The aim of this study is to analyze the influence of the mandibular positions (habitual rest position, habitual maximum intercuspation, habitual maximum intercuspation with clenching, and mandibular position with cotton rolls) on the active cervical range of motion (ROM) (flexion-extension, lateroflexions, rotations) using an accelerometer in a sample of healthy subjects.

METHODS

A total of 21 (14 M, 7 F) healthy volunteers aged from 18 to 27 years (mean age 23.88 ± 2.34 years; mean weight 67.86 ± 11.38 kg; mean height 172.52 ± 9.00 cm) underwent a cervical range of movement examination using a 9-axis accelerometer. A one-way ANOVA analysis was performed in order to statistically evaluate the effective influence of the mandibular position on the recorded parameters.

RESULTS

The analysis showed no statistically significant differences (all p-values > 0.1) with variations smaller than three degrees among the different mandibular positions.

DISCUSSION

The mandibular position seems to have no influence on the active cervical ROM in healthy subjects. Further studies are needed to assess the usefulness of the accelerometer in the cervical analysis of temporomandibular disorder subjects.