Wireless optoelectronic recordings of mandibular and associated head-neck movements in man: a methodological study

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.

Jaw-neck motor strategy during jaw-opening with resistance load

BACKGROUND

The jaw and neck motor systems have a close functional integration but the effect of resistance load to the mandible during jaw opening on the jaw-neck integration is not known.

OBJECTIVES

To evaluate the effect of resistance load compared to no load on integrated jaw and neck motor function in individuals free from pain and dysfunction in the jaw and neck regions.

METHODS

Jaw and head movements during continuous jaw opening were recorded with an optoelectronic system (MacReflex^® ) in 26 pain-free individuals (14 women, 12 men, mean age 22 years). Jaw opening was performed with and without resistance load (1600 g) to the mandible. The relationship between jaw movement amplitude, head movement amplitude, head/jaw ratio (quotient of head and jaw movement amplitude) and resistance load were modelled using linear mixed-model analysis. A p-value <.05 was considered statistically significant.

RESULTS

The expected head/jaw ratio mean was increased by 0.05 (95% CI: 0.03, 0.08, p < .001) with resistance load as compared to no load. This corresponds to an increase in expected mean by 55.6%. With resistance load, expected mean head movement amplitude increased by 1.4 mm (95% CI: 0.2, 2.5, p = .018), and expected mean jaw movement amplitude decreased by 3.7 mm (95% CI: -7.0, -0.5, p = .025).

CONCLUSION

There is a compensation and adaptation of integrated jaw-neck motor function with an altered jaw-neck motor strategy during jaw opening with resistance load compared to no load. The head/jaw ratio demonstrates increased proportional involvement of the neck during increased load on the jaw system.

Cervical musculoskeletal disorders in patients with temporomandibular dysfunction: A systematic review and meta-analysis

OBJECTIVE

To verify which are the neck musculoskeletal disorders presented by individuals with temporomandibular disorders (TMD).

METHODS

It is a systematic review and meta-analysis that were included cohort, case-control and cross-section studies that analyzed the presence of cervical musculoskeletal disorders in individuals with TMD, with age between 18 and 55 years. The searches were carried out in the databases: Medline/PubMed, Cinahl, Web of Science, Cochrane, Lilacs and Scopus; and there was no linguistic or temporal restriction. The evidence quality was evaluated by GRADE system and methodological quality by Newcastle-Ottawa Quality Assessment Scale (NOS) and the risk of publication bias assessed by the funnel plot graph. The data was quantitatively analyzed by the meta-analysis using the mean differences (MD) as an effect measure.

RESULTS

There were included 21 manuscripts in the synthesis, of theses 16 were evaluated by meta-analysis with methodological quality ranging from poor to excellent by NOS scale. Individuals with TMD present lower endurance of extensor neck muscle compared to TMD-free (MD = -194.66s [95%CI: 212.44;-176.88]), with moderate to excellent quality. As, upper neck hymobility on the right (MD = -8.59° (95%CI: -10.43°;-6.75°) and left (MD = -7.99° (95%CI: -9.63°;-6.35°), and in all global neck movements. Also, individuals with TMD presented worse self-reported neck disability (MD = 7.91 (95%CI: 7.39; 8.43)) compared to free-TMD.

CONCLUSION

There is moderate and strong evidence that patients with TMD present lower endurance of extensor neck muscle, global and upper neck hypomobility, worse self-reported neck disability, however, their cranio-cervical posture is similar to individuals without TMD, based on a moderate to excellent methodological quality.

SYSTEMATIC REVIEW REGISTRATION NUMBER

PROSPERO CRD42018103918.

Jaw-neck motor function in the acute stage after whiplash trauma

BACKGROUND

Jaw-neck motor function is affected in the chronic stage following whiplash trauma. It is not known whether motor function is affected also in the early stage after neck trauma.

OBJECTIVES

To determine how jaw and head movement amplitudes and movement cycle times correlate with jaw and neck pain, and neck disability in the acute stage after whiplash trauma.

METHODS

Jaw and head movements during jaw opening-closing were recorded with an optoelectronic system in 23 cases (4 men, 19 women, 18-66 years) within 1 month after whiplash trauma and compared with 27 controls without neck trauma (15 men, 12 women, 20-66 years). Jaw and head movement amplitudes, head/jaw ratio (quotient of head and jaw movement amplitude) and movement cycle times were evaluated in relation to jaw and neck pain (Numeric Rating Scale) and neck disability (Neck Disability Index). Analyses were performed with Mann-Whitney U test and Spearman's correlation.

RESULTS

Compared with controls, cases showed smaller jaw movement amplitudes (P = .006) but no difference in head movement amplitudes, head/jaw ratios or movement cycle times. There were no significant correlations between movement amplitudes or cycle times and jaw and neck pain, and neck disability. Cases with high neck pain intensity had smaller jaw movement amplitudes compared to cases with low neck pain intensity (P = .024).

CONCLUSION

The results suggest that jaw-neck motor function may be affected in the acute stage after whiplash trauma and more so in cases with higher neck pain intensity.

Assessment of early orthodontic treatment on functional shifts by telemonitoring mandibular movements using a smart phone

Introduction

To assess effect of orthodontic treatment on anterior or lateral functional shift in mixed dentition stage by telemonitoring mandibular movements in four-dimensions using a novel objective method that can assist in orthodontics and other dental specialties without the need of expensive, bulky or complicated equipment.

Methods

A sample of 60 patients was divided into two groups. Group I included 30 patients with normal occlusion and TMJ functions. Group II included 30 patients that were diagnosed with an abnormal path of closure in antero-posterior or transverse directions due to disharmony between centric occlusion and centric relation. The latter group was orthodontically treated and mandibular movements were measured before, during, directly after orthodontic treatment, and one year after treatment using our proposed method. To evaluate validity and reliability of our method, it was compared with two methods, a commercially available mandibular scanner, and a low-cost graphical method that utilizes a sheet of wax and a stylus.

Results

It was found that the overall differences between opening and closing curves of our proposed method and the other two methods were small and negligible (p > 0.05).

Discussion

It was found that our proposed method is offering a reasonably accurate, simple and rapid way to telemonitor the mandible movements in four-dimensions using the rear/front camera of any smart-phone.

Instant reduction in postural sway during quiet standing by intraoral dental appliance in patients with Whiplash associated Disorders and non-trauma neck pain

OBJECTIVES

This study tested the hypothesis that modulation of jaw sensorimotor control by intraoral dental appliance can reduce postural sway during quiet standing and hence improve standing balance, in patients with whiplash associated disorders (WAD) and non-trauma neck pain.

DESIGN

Postural sway during quiet standing with feet together was examined in 54 WAD patients (40 females) and 10 non-trauma patients (8 females) using wireless 3D movement recording technique. Recordings were performed alternating without and with intraoral dental appliance, and with closed eyes and open eyes, respectively. In this protocol the participants served as their own controls. A reference group of 30 healthy subjects (17 females) was also recorded. Each recording lasted 120 s, followed by 3-5 min of rest. Speed, acceleration and perimeter of postural sway area were documented.

RESULTS

In the patients, but not in the healthy group, the intraoral dental appliance instantly and significantly reduced standing postural sway in recordings with closed and open eyes.

CONCLUSIONS

The prompt reduction in standing postural sway from intervention by intraoral dental appliance i.e. improved standing balance, suggests a potent effect on the postural control system by modulation of the jaw sensorimotor system, probably involving reflex transmission. The result opens for new insight into mechanisms behind postural control and the pathophysiology of balance disorders, and adds to the knowledge on plasticity of the nervous system. It may help developing new procedures for assessment and management of impaired balance in WAD and non-trauma neck pain patients.

Relative trajectory-driven virtual dynamic occlusal adjustment for dental restorations

The abnormal occlusal contact can disrupt the coordination and health of the oral jaw system. Therefore, the dynamic adjustment of the occlusal surface is of great significance for assessing the status of occlusal contact and clarifying jaw factors of stomatognathic system diseases. To solve this problem, a trajectory subtraction algorithm based on screw theory to improve the accuracy of the occlusal movement trajectory is proposed in our paper. Driving by the relative trajectory, a virtual dynamic occlusal adjustment system is developed to realize 3D occlusal movement simulating, automatic occluding relation detection, and automatic occlusal adjustment. Furthermore, we adapt an active occlusal adjustment method based on Laplacian deformation to increase the contact areas of the occlusal surface, which can aid dentists to realize the automatic adjustment of the non-interference regions. As a consequence, the proposed subtraction algorithm is feasible and the root-mean-square is 0.097 mm, and the adjusted occlusal surface is more consistent with the natural occlusal morphology. Graphical abstract ᅟ.

Inter- and intra-rater reliability of 3D kinematics during maximum mouth opening of asymptomatic subjects

Previous studies evaluated 3D human jaw movements using kinematic analysis systems during mouth opening, but information on the reliability of such measurements is still scarce. The purpose of this study was to analyze within- and between-session reliabilities, inter-rater reliability, standard error of measurement (SEM), minimum detectable change (MDC) and consistency of agreement across raters and sessions of 3D kinematic variables during maximum mouth opening (MMO). Thirty-six asymptomatic subjects from both genders were evaluated on two different days, five to seven days apart. Subjects performed three MMO movements while kinematic data were collected. Intraclass correlation coefficient (ICC), SEM and MDC were calculated for all variables, and Bland-Altman plots were constructed. Jaw radius and width were the most reproducible variables (ICC>0.81) and demonstrated minor error. Incisor displacement during MMO and angular movements in the sagittal plane presented good reliability (ICC from 0.61 to 0.8) and small errors and, consequently, could be used in future studies with the same methodology and population. The variables with smaller amplitudes (condylar translations during mouth opening and closing and mandibular movements on the frontal and transversal planes) were less reliable (ICC<0.61) and presented larger SEM and MDC. Although ICC, SEM and MDC showed less between-session reproducibility than within-session and inter-rater, the limits of agreement were larger in inter-rater comparisons. In future studies care must be taken with variables collected on different days and with mandibular movements in the frontal and transversal planes.

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.

Cervical flexion-rotation test and physiological range of motion - A comparative study of patients with myogenic temporomandibular disorder versus healthy subjects

BACKGROUND

Temporomandibular Disorders (TMD) refer to several common clinical disorders which involve the masticatory muscles, the temporomandibular joint (TMJ) and the adjacent structures. Although neck signs and symptoms are found with higher prevalence in TMD patients compared to the overall population, whether limitation of cervical mobility is an additional positive finding in this cohort is still an open question.

OBJECTIVE

To compare the physiological cervical range of motion (CROM) and the extent of rotation during cervical flexion (flexion-rotation test, FRT) in people with TMD (muscular origin) and healthy control subjects.

METHOD

The range of motion of the neck and FRT was measured in 20 women with myogenic TMD and 20 age matched healthy controls.

RESULTS

Women with myogenic TMD had significantly lower FRT scores compared to their matched healthy women. No difference was found between groups in CROM in any of the planes of movement. The FRT was positive (less than 32°) in 90% of the TMD participants versus 5% in the healthy control but the findings were not correlated with TMD severity.

CONCLUSION

The results point out a potential involvement of the upper cervical joints (c1-c2) in women with myogenic TMD.

Head Immobilization can Impair Jaw Function

Findings that jaw-opening/-closing relies on both mandibular and head movements suggest that jaw and neck muscles are jointly activated in jaw function. This study tested the hypothesis that rhythmic jaw activities involve an active repositioning of the head, and that head fixation can impair jaw function. Concomitant mandibular and head-neck movements were recorded during rhythmic jaw activities in 12 healthy adults, with and without fixation of the head. In four participants, the movement recording was combined with simultaneous registration of myoelectric activity in jaw and neck muscles. The results showed neck muscle activity during jaw opening with and without head fixation. Notably, head fixation led to reduced mandibular movements and shorter duration of jaw-opening/-closing cycles. The findings suggest recruitment of neck muscles in jaw activities, and that head fixation can impair jaw function. The results underline the jaw and neck neuromuscular relationship in jaw function.

Head Movements during Chewing: Relation to Size and Texture of Bolus

Coordinated mandibular and head-neck movements during jaw opening-closing activities suggest a close functional linkage between the jaw and the neck regions. The present study investigated whether size and texture of bolus can influence head-neck behavior during chewing. Using an optoelectronic 3-D recording technique, we analyzed concomitant mandibular and head-neck movements in 12 healthy adults chewing small (3 g) and large (9 g) boluses of chewing gum and Optosil®. The main finding was a head extension during chewing, the amount of which was related mainly to bolus size. Furthermore, each chewing cycle was accompanied not only by mandibular movements, but also by head extension-flexion movements. Larger head movement amplitudes were correlated with larger size and, to some extent, also with harder texture of the bolus. The results suggest that head-neck behavior during chewing is modulated in response to changes in jaw sensory-motor input.

Markerless three-dimensional tracking of masticatory movement

Conventional methods for measuring mandibular movement are expensive and require headgear and a marker attached to the mandibular incisors. These make assessment of normal chewing difficult. The aim of the present study was to test the validity of a markerless three-dimensional system for tracking masticatory movement by comparing it with a conventional method using an incisal marker. The study investigated 100 chewing cycles in 10 participants. The jaw tracking system consisted of a camera capable of recording depth and red, green, and blue data simultaneously, a laptop computer, and data analysis software. Depth data for each participant's face, tracked in real time, produced a computed 3D mask. The most prominent point of the soft tissue under the lip was defined as the chin point. A dental clasp cemented to the labial surface of the mandibular incisors was defined as the incisal point. The movement of these two measuring points was simultaneously recorded during mastication of chewing gum for 20s. To conduct the same analysis on each cycle from the two measuring points, all cycles were normalized by dividing by the corresponding vertical displacement because of their size variation. The findings showed excellent intramethod correlation for normalized horizontal displacement at every level (>0.9; except for 2 out of 19 levels; 0.896 and 0.898), and a lack of proportional bias. These findings suggest a correlation between the chewing cycles from two measuring points, the incisor and the chin, further suggesting the feasibility of a markerless system for tracking masticatory movement.

Jaw-opening accuracy is not affected by masseter muscle vibration in healthy men

There is a functional integration between the jaw and neck regions with head extension-flexion movements during jaw-opening/closing tasks. We recently reported that trigeminal nociceptive input by injection of hypertonic saline into the masseter muscle altered this integrated jaw-neck function during jaw-opening/closing tasks. Thus, in jaw-opening to a predefined position, the head-neck component increased during pain. Previous studies have indicated that muscle spindle stimulation by vibration of the masseter muscle may influence jaw movement amplitudes, but the possible effect on the integrated jaw-neck function is unknown. The aim of this study was to investigate the effect of masseter muscle vibration on jaw-head movements during a continuous jaw-opening/closing task to a target position. Sixteen healthy men performed two trials without vibration (Control) and two trials with bilateral masseter muscle vibration (Vibration). Movements of the mandible and the head were registered with a wireless three-dimensional optoelectronic recording system. Differences in jaw-opening and head movement amplitudes between Control and Vibration, as well as achievement of the predefined jaw-opening target position, were analysed with Wilcoxon's matched pairs test. No significant group effects from vibration were found for jaw or head movement amplitudes, or in the achievement of the target jaw-opening position. A covariation between the jaw and head movement amplitudes was observed. The results imply a high stability for the jaw motor system in a target jaw-opening task and that this task was achieved with the head-neck and jaw working as an integrated system.

4D Clinical Imaging for Dynamic CAD

A basic 4D imaging system to capture the jaw motion has been developed that produces high resolution 3D surface data. Fluorescent microspheres are brushed onto the areas of the upper and the lower arches to be imaged, producing a high-contrast random optical pattern. A hand-held imaging device operated at about 10 cm from the mouth captures time-based perspective images of the fluorescent areas. Each set of images, containing both upper and the lower arch data, is converted to a 3d point mesh using photogrammetry, thereby providing an instantaneous relative jaw position. Eight 3d positions per second are captured. Using one of the 3d frames as a reference, incremental transforms are derived to express the free body motion of the mandible. Conventional 3d models of the dentition are directly registered to the reference frame, allowing them to be animated using the derived transforms.

A specialized motion capture system for real-time analysis of mandibular movements using infrared cameras

BACKGROUND

In the last years, several methods and devices have been proposed to record the human mandibular movements, since they provide quantitative parameters that support the diagnosis and treatment of temporomandibular disorders. The techniques currently employed suffer from a number of drawbacks including high price, unnatural to use, lack of support for real-time analysis and mandibular movements recording as a pure rotation. In this paper, we propose a specialized optical motion capture system, which causes a minimum obstruction and can support 3D mandibular movement analysis in real-time.

METHODS

We used three infrared cameras together with nine reflective markers that were placed at key points of the face. Some classical techniques are suggested to conduct the camera calibration and three-dimensional reconstruction and we propose some specialized algorithms to automatically recognize our set of markers and track them along a motion capture session.

RESULTS

To test the system, we developed a prototype software and performed a clinical experiment in a group of 22 subjects. They were instructed to execute several movements for the functional evaluation of the mandible while the system was employed to record them. The acquired parameters and the reconstructed trajectories were used to confirm the typical function of temporomandibular joint in some subjects and to highlight its abnormal behavior in others.

CONCLUSIONS

The proposed system is an alternative to the existing optical, mechanical, electromagnetic and ultrasonic-based methods, and intends to address some drawbacks of currently available solutions. Its main goal is to assist specialists in diagnostic and treatment of temporomandibular disorders, since simple visual inspection may not be sufficient for a precise assessment of temporomandibular joint and associated muscles.

Experimental masseter muscle pain alters jaw-neck motor strategy

BACKGROUND

A functional integration between the jaw and neck regions has been demonstrated during normal jaw function. The effect of masseter muscle pain on this integrated motor behaviour in man is unknown. The aim of this study was to investigate the effect of induced masseter muscle pain on jaw-neck movements during a continuous jaw opening-closing task.

METHODS

Sixteen healthy men performed continuous jaw opening-closing movements to a target position, defined as 75% of the maximum jaw opening. Each subject performed two trials without pain (controls) and two trials with masseter muscle pain, induced with hypertonic saline as a single injection. Simultaneous movements of the mandible and the head were registered with a wireless optoelectronic three-dimensional recording system. Differences in movement amplitudes between trials were analysed with Friedman's test and corrected Wilcoxon matched pairs test.

RESULTS

The head movement amplitudes were significantly larger during masseter muscle pain trials compared with control. Jaw movement amplitudes did not differ significantly between any of the trials after corrected Wilcoxon tests. The ratio between head and jaw movement amplitudes was significantly larger during the first pain trial compared with control.

CONCLUSIONS

Experimental masseter muscle pain in humans affected integrated jaw-neck movements by increasing the neck component during continuous jaw opening-closing tasks. The findings indicate that pain can alter the strategy for jaw-neck motor control, which further underlines the functional integration between the jaw and neck regions. This altered strategy may have consequences for development of musculoskeletal pain in the jaw and neck regions.

Sequential analysis of head movement during mandibular open-close movements in TMD patients with disc displacement with reduction

This study examined relationships between starting points of head and mandibular movements in 11 female control subjects and 10 TMD patients showing disc displacement with reduction during consecutive open-close movements, using a six-degree-of-freedom measuring device. During the first mandibular opening cycle, in the TMD group, head movement was significantly preceded in relation to mandibular movement when compared with the control group, and major differences in onset were seen between maximum and minimal values at the beginning of mandibular movements. After the second cycle, significant differences in starting points were not evident. In TMD patients showing disc displacement with reduction, in the first cycle, at the commencement of opening movements, it is proposed that the head precedes the mandible in order to compensate for irregular condylar movements, and the degree of the condylar movement irregularity might affect the onset relation between the head and the mandible.

Measurement of jaw motion: the proposal of a simple and accurate method

The analysis of jaw movements has long been used as a measure for clinical diagnosis and assessment. A number of strategies are available for monitoring the trajectory; however most of these strategies make use of expensive tools, which are often not available to many clinics in the world. In this context, this research proposes the development of a new tool capable of quantifying the movements of opening/closing, protrusion and laterotrusion of the mandible. These movements are important for the clinical evaluation of both the temporomandibular function and muscles involved in mastication. The proposed system, unlike current commercial systems, employs a low-cost video camera and a computer program, which is used for reconstructing the trajectory of a reflective marker that is fixed on the jaw. In order to illustrate the application of the devised tool a clinical trial was carried out, investigating jaw movements of 10 subjects. The results obtained in this study were compatible with those found in the literature with the advantage of using a low-cost, simple, non-invasive and flexible solution customized for the practical needs of clinics. The average error of the system was less than 1.0%.

Deflections of an implant-supported cantilever beam subjected to vertically directed loads. In vitro measurements in three dimensions using an optoelectronic method. II Analysis of methodological errors

AIM

The aim of this study was to evaluate the accuracy, i.e. trueness (validity) and precision (repeatability) for load-dependent deflections in three dimensions of an implant-supported cantilever beam obtained with an optoelectronic motion analysis system compared with a well-known reference method.

MATERIALS AND METHODS

A cantilever beam with a length of 22 mm (roughly corresponding to the width of two premolars) was screw-connected to an implant-abutment unit stiffly anchored in a steel plate. The positional changes of beam-end were measured when the beam-end step by step was subjected to four loads, 15.5-40.1 N. This measurement procedure was repeated to comprise six consecutive measurements. The trueness of the method was estimated by comparing the data obtained for vertical deflections with those from a reference method where a hydraulic test system was used to measure the load-deflection ratios of the same beam when subjected to the four mentioned vertical loads.

RESULTS

All applied transducer-mediated loads had accuracies (truenesses and repeatabilities below 0.05%). Also, the trueness and precision of the reference method, regarding both movements (deflections) of tested objects and magnitude of applied loads, were tested and found to be high, not exceeding 0.5%. The optoelectronic method however underestimated the smallest vertical deflections for the cantilever beam when compared with the data obtained from the reference method. The underestimation was 26.4%, 15.5% and 8.6% for loads 15.5, 26.6 and 32.6 N, respectively, while there was a slight overestimation of 1.2% for 40.1 N. The precision for the optoelectronic method was found to be for z-axis 1.8 μm, y-axis 3.8 μm and x-axis 1.9 μm.

CONCLUSION

It can be concluded that the trueness (validity) for the optoelectronic method is very high for deflections above 143 μm. The precision (repeatability) of the optoelectronic method was found to be very high.

Seat-to-head transfer function of seated men--determination with single and three axis excitations at different magnitudes

Most research has investigated the seat-to-head transmissibility during single-axis excitations. Associations between head accelerations and discomfort or effects on vision were reported. Possible differences between the seat-to-head transmissibility determined during different vibration magnitudes with a variable number of excitation axes have not been systematically examined. An experimental study was performed with 8 male subjects sitting on a rigid seat with hands on a support. They were exposed to random whole-body vibration (E1=0.45 ms(-2), E2=0.90 ms(-2), and E3=1.80 ms(-2)) to single- and three-axis vibration. All translational and rotational seat-to-head transmissibilities were calculated. The effects of the factors vibration magnitude and number of axes on the peak modulus and frequency of the seat-to-head transmissibilities were tested. In general the head motions follow constant pattern. These pattern of head motions comprise a combination of rotational and translational shares of transmissions, i.e. the curves show a dependence on the factors 'vibration magnitude' and 'number of vibration axes'. Mechanical properties of the soft tissue, relative motions of body parts, and muscle reactions were supposed to cause the nonlinearities of the head. Future research should consider effects of multi-axis vibration, if conclusions shall be drawn for the evaluation of possible health effects and model validations.

A computational method for recording and analysis of mandibular movements

This study proposed the development of a new clinical tool capable of quantifying the movements of opening-closing, protrusion and laterotrusion of the mandible. These movements are important for the clinical evaluation of the temporomandibular function and muscles involved in mastication. Unlike current commercial systems, the proposed system employs a low-cost video camera and a computer program that is used for reconstructing the trajectory of a reflective marker that is fixed on the mandible. In order to illustrate the clinical application of this tool, a clinical experiment consisting on the evaluation of the mandibular movements of 12 subjects was conducted. The results of this study were compatible with those found in the literature with the advantage of using a low cost, simple, non-invasive, and flexible tool customized for the needs of the practical clinic.

Jaw–neck dysfunction in whiplash-associated disorders

This paper reports data from recent studies on integrative jaw-neck motor control in healthy subjects and disturbed jaw-neck behaviour in whiplash-associated disorders (WAD). The results show that neck function is an integral part of natural jaw behaviour, and that neck injury can impair jaw function and therefore disturb eating behaviour. We also show preliminary results from implementation of a new approach for rehabilitation of jaw-neck dysfunction and pain in WAD.

Incisal orientation and biting efficiency

Broad-edged 'spatulate' upper and lower incisors are distinctive of catarrhines and platyrrhines who use them in various ways to peel fruits, remove bark, and strip leaves from branches. The incisors of modern humans not only control the bite size of foods during ingestion, but often grip items in a number of non-food related tasks. Such uses have long been implicated for Neandertals as well. Despite the evolutionary importance of incision and the fact that the incisors feature prominently in clinical dentistry (via orthodontic practices designed both to correct incisal misalignments and adjust their orientation), little is known about what affects their functional efficiency. Few mechanical analyses of incisal action have been published and none that seem to take note of the mechanisms of both fracture and friction at the tooth-food interface. Here, we modeled the incisal tip as a wedge, finding that the efficiency of biting foods that fracture elastically is strongly dependent on both the apex angle of the incisor and the coefficient of friction. Based on apex angle measurements from a small sample of human central incisors, the overall efficiency of upper central incisors is predicted to be greatest when the angle between the apex bisector and the direction of applied force is zero. However, this is complicated greatly by friction, particularly for the lower incisors. The analysis probably applies not only to the use of incisors by humans, but also to some extent to frugivorous primates. This model should clarify the mechanics behind incision and can provide a basic foundation upon which more advanced models can be built on in the future.

Deranged jaw-neck motor control in whiplash-associated disorders

Recent findings of simultaneous and well coordinated head-neck movements during single as well as rhythmic jaw opening-closing tasks has led to the conclusion that 'functional jaw movements' are the result of activation of jaw as well as neck muscles, leading to simultaneous movements in the temporomandibular, atlanto-occipital and cervical spine joints. It can therefore be assumed that disease or injury to any of these joint systems would disturb natural jaw function. To test this hypothesis, amplitudes, temporal coordination, and spatiotemporal consistency of concomitant mandibular and head-neck movements during single maximal jaw opening-closing tasks were analysed in 25 individuals suffering from whiplash-associated disorders (WAD) using optoelectronic movement recording technique. In addition, the relative durations for which the head position was equal to, leading ahead of, or lagging behind the mandibular position during the entire jaw opening-closing cycle were determined. Compared with healthy individuals, the WAD group showed smaller amplitudes, and changed temporal coordination between mandibular and head-neck movements. No divergence from healthy individuals was found for the spatiotemporal consistency or for the analysis during the entire jaw opening-closing cycle. These findings in the WAD group of a 'faulty', but yet consistent, jaw-neck behavior may reflect a basic importance of linked control of the jaw and neck sensory-motor systems. In conclusion, the present results suggest that neck injury is associated with deranged control of mandibular and head-neck movements during jaw opening-closing tasks, and therefore might compromise natural jaw function.

Comorbidity of internal derangement of the temporomandibular joint and silent dysfunction of the cervical spine

The aim of this evaluation was to examine correlations between internal derangement of the temporomandibular joint (TMJ) and cervical spine disorder (CSD). A prospective controlled clinical study was carried out. Thirty patients with signs and symptoms of internal derangement but without any subjective neck problems and 30 age- and gender-matched control subjects without signs and symptoms of internal derangement were examined. The investigation of the temporomandibular system was carried out using a 'Craniomandibular Index'. Afterwards an examiner-blinded manual medical investigation of the craniocervical system was performed. This included muscle palpation of the cervical spine and shoulder girdle as well as passive movement tests of the cervical spine, to detect restrictions in the range of movement as well as segmental intervertebral dysfunction. The internal derangement of the TMJ was significantly associated with 'silent' CSD (t-test, P < 0.05). Patients with raised muscle tenderness of the temporomandibular system exhibited significantly more often pain on pressure of the neck muscles than patients without muscle tenderness of the temporomandibular system (t-test, P < 0.05). As a result of the present study, for patients with internal derangement of the TMJ an additional examination of the craniocervical system should be recommended.

Disturbed jaw behavior in whiplash-associated disorders during rhythmic jaw movements

As shown previously, "functional jaw movements" are the result of coordinated activation of jaw as well as neck muscles, leading to simultaneous movements in the temporomandibular, atlanto-occipital, and cervical spine joints. In this study, the effect of neck trauma on natural jaw function was evaluated in 12 individuals suffering from whiplash-associated disorders (WAD). Spatiotemporal characteristics of mandibular and concomitant head movements were evaluated for three different modes of rhythmic jaw activities: self-paced continuous maximal jaw-opening/-closing movements, paced continuous maximal jaw-opening/-closing movements at 50 cycles/minute, and unilateral chewing. Compared with healthy subjects, the WAD group showed smaller magnitude and altered coordination pattern (a change in temporal relations) of mandibular and head movements. In conclusion, these results show that neck trauma can derange integrated jaw and neck behavior, and underline the functional coupling between the jaw and head-neck motor systems.

Active range of motion of the head and cervical spine: a three-dimensional investigation in healthy young adults

PURPOSE

To define reference values for head-cervical range of motion (ROM) in healthy young adults, to assess the effect of sex, and to quantify the separate contribution of other body districts.

METHODS

Thirty women and 30 men performed maximal head and cervical spine flexion-extension, lateral bending, and axial rotation. Movements were detected using a digital optoelectronic instrument. Maximum head-cervical spine and thoracic motions were separated.

RESULTS

Flexion and extension were performed mainly in the sagittal plane. The movement was larger in women (136 degrees) than in men (130 degrees). During flexion, both sexes moved the head-neck and the thorax in the same direction. During extension, men moved only the head-cervical spine, while women moved the two analyzed districts in the opposite directions. Lateral bending was nearly symmetric, associated with head-cervical rotation and extension, and larger in women (91 degrees) than in men (77 degrees). Adjunctive thoracic motion was limited in the sagittal and frontal planes, but larger in the horizontal plane (opposite motions of about 20 degrees). Head-neck rotation was symmetric, and associated with concomitant movements in both the sagittal and frontal planes. It was larger in women (162 degrees) than in men (155 degrees), and performed with limited adjunctive thoracic motions.

CONCLUSIONS

The present values can be used as a first group of normative data for head-cervical ROM in young men and women.

Temporal coordination between mandibular and head-neck movements during jaw opening-closing tasks in man

Previous finding of concomitant mandibular and head movements during jaw function suggest a functional relation between the human jaw and neck regions. This study examined the temporal coordination between mandibular and head-neck movements during maximal jaw opening-closing tasks, at fast and slow speed. Twenty-four healthy individuals, median age 25 years, participated in the study. They were seated with firm back support but without head-neck support. Mandibular and head movements were simultaneously monitored by a wireless optoelectronic system for three-dimensional movement recording. The timing of head movement in relation to mandibular movement was estimated at defined time-points (start, peak, end and maximum velocity of movement), and during the entire course of the jaw-opening and jaw-closing phases. The results showed that the head in general started to move simultaneously with or before the mandible, reached the peak position simultaneously with, before or after the mandible, and reached the end position after the mandible. A higher degree of temporal coordination was found for fast speed at the start and the peak positions. The head most often attained maximum velocity after the mandible, and mostly lagged behind the mandible during the entire jaw-opening and -closing phases. These findings support the notion of a functional linkage between the human temporomandibular and craniocervical regions. They suggest that "functional jaw movements" comprise concomitant mandibular and head-neck movements which involve the temporomandibular, the atlanto-occipital and the cervical spine joints, and are caused by jointly activated jaw and neck muscles. It is proposed that these jaw and neck muscle actions, particularly at fast speed, are elicited and synchronized by preprogrammed neural command(s) common to both the jaw and the neck motor systems. From the present results and previous observations of concurrent jaw and head movement during fetal yawning, we suggest that these motor programmes are innate.

Co-ordinated mandibular and head-neck movements during rhythmic jaw activities in man

Recent observations in man of concomitant mandibular and head movements during single maximal jaw-opening/-closing tasks suggest a close functional relationship between the mandibular and the head-neck motor systems. This study was aimed at further testing of the hypothesis of a functional integration between the human jaw and neck regions. Spatiotemporal characteristics of mandibular and associated head movements were evaluated for 3 different modes of rhythmic jaw activities: self-paced continuous maximal jaw-opening/-closing movements, paced continuous maximal jaw-opening/-closing movements at 50 cycles/minute, and unilateral chewing. Mandibular and head-neck movements were simultaneously recorded in 12 healthy young adults, by means of a wireless opto-electronic system for 3-D movement recordings, with retro-reflective markers attached to the lower (mandible) and upper (head) incisors. The results showed that rhythmic mandibular movements were paralleled by head movements. An initial change in head position (head extension) was seen at the start of the first jaw-movement cycle, and this adjusted head position was retained during the following cycles. In addition to this prevailing head extension, the maximal jaw-opening/-closing cycles were paralleled by head extension-flexion movements, and in general the start of these head movements preceded the start of the mandibular movements. The results support the idea of a functional relationship between the temporomandibular and the cranio-cervical neuromuscular systems. We therefore suggest a new concept for human jaw function, in which "functional jaw movements" are the result of activation of jaw as well as neck muscles, leading to simultaneous movements in the temporomandibular, atlanto-occipital, and cervical spine joints.