Afferent sensory mechanisms involved in jaw gape-related muscle activation in unilateral biting

Changes in jaw and neck muscle coactivation and coordination in patients with chronic painful TMD disk displacement with reduction during chewing

The treatment of a complex temporomandibular disorder (TMD), such as disk displacement with reduction (DDR) associated with arthralgia and myalgia, may depends on understanding the impairments in muscle function. The aim of this study was to investigate the behavior of the anterior temporalis, masseter and sternocleidomastoid muscles in the time and frequency domains during chewing in patients with chronic painful TMD-DDR using electromyographic (EMG) analysis. Thirty-three patients who met the diagnostic criteria for TMD and 32 volunteers without TMD (control group) underwent clinical examination, chewing pattern classification and EMG analysis. For the EMG analyses, the side of habitual unilateral chewing, as determined by the chewing pattern classification, was selected for recording; in cases of bilateral chewing, the recording side was randomly selected. The EMG-EMG coherence function and EMG-EMG transfer function (gain and phase) values were obtained at the first chewing frequency peak, and the working-side masseter signal was used as a reference in the analyses of the other muscles. Compared to the control group, the TMD group showed a longer chewing stroke duration (P = 0.01) as well as changes in the coactivation and coordination strategies of the jaw muscles, evidenced by greater relative energy expenditure (P< 0.01) and impaired differential recruitment (P< 0.05) and coherence (P< 0.01). Delays in peak and temporal asynchrony occurred in the jaw and neck muscles (P< 0.05). Patients with chronic painful TMD-DDR during chewing presented changes in the jaw and neck muscles, with more compromised function of the former, which are specific to chewing.

MRI characteristics of the asymptomatic temporomandibular joint in patients with unilateral temporomandibular joint disorder

OBJECTIVE

To determine the association between unilateral temporomandibular joint disorder (TMD) and the presence of imaging abnormalities in the contralateral, asymptomatic joint.

METHODS

MRI studies of 219 subjects with symptoms of unilateral TMD were examined for signs of disc displacement, osteoarthritis, disc deformation, and effusion in both temporomandibular joints (TMJ). The Chi-Square test and stepwise logistic regression analysis were performed.

RESULTS

Disc displacement, osteoarthritis, disc deformation, and effusion were more common on the symptomatic side. However, in the category of disc displacement with a reduction in open mouth position (DDWR), the difference was not significant between the symptomatic and the asymptomatic TMJs. Stepwise logistic regression showed that the presence of any imaging abnormality other than DDWR was related to osteoarthritis and disc deformity on the symptomatic side. On the other hand, the presence of any MRI abnormality (including DDWR) on the asymptomatic side was related only to the presence of osteoarthritis on the symptomatic side.

CONCLUSIONS

Unilateral symptomatic TMD is related to the presence of imaging abnormalities on the contralateral, asymptomatic side, suggesting that the development and progression of joint changes in symptomatic and contralateral asymptomatic TMJs are interrelated.

Somatosensory perception sensitivity in voluntary postural sway movements: Age, gender and sway effect magnitudes

OBJECTIVES

1) to develop a reliable device for assessing somatosensory perception sensitivity in voluntary postural sway movement, specifically a sway discrimination apparatus (SwayDA) for testing voluntary lateral sway discrimination sensitivity (VLSDS); 2) to explore the relationship between mobility performance and VLSDS in older adults, and 3) to determine the effects of age, gender and sway magnitude on VLSDS.

METHODS

First, eighteen healthy young adults (8 males, 10 females, age ranging from 22 to 70) were recruited for a test-retest reliability study. During the SwayDA test, the participants were asked to discriminate between four possible medial-lateral sway extents when moving away from neutral standing. For Objective 2, twenty-five older participants (9 males, 16 females, mean age 70.1) undertook both the SwayDA and the mobility tests. The mobility testing battery consisted of single task and cognitive dual task timed-up and-go tests, and the 5 times sit-to-stand test. Pearson's correlation was calculated between SwayDA scores and mobility performance. For Objective 3, 20 community-dwelling adults over 65 years old (10 males, 10 females, mean age 71.3) and 20 young volunteers (10 males, 10 females, mean age 23.6) were recruited to study the effects of age, gender and sway magnitude on VLSDS. To obtain a bias-free measure of VLSDS, the probability of correct response was considered as the true-positive judgment, while the probability of incorrect response was considered as false-positive judgment, and these were cumulated across the response values. A receiver operating characteristic (ROC) curve was then generated and the Area Under the ROC Curve (AUC) was used to measure VLSDS.

RESULTS

There was no significant difference in AUC scores between Day 1 and Day 8 (p > 0.05). ICC(3,1) reliability indices were 0.750 for sway to the left and 0.879 for sway to the right. Pearson's correlation revealed a significant correlation between the SwayDA sores and timed-up-and-go (TUG), cognitive dual task TUG, 5 times sit-to-stand test (r = -0.456, -0.522, and - 0.416 respectively, all p < 0.05). Factorial ANOVA showed age and gender main effects (F = 8.144, p < 0.01, and F = 8.806, p < 0.01, respectively), suggesting older adults and females had worse VLSDS. In addition, a significant difference was found between the young and older participants in the inner range of VLSDS (t = -2.875, p < 0.017), indicating that the decline of somatosensory perception of postural sway in older people may be magnitude-specific, and greatest for small deviations from upright stance.

CONCLUSIONS

The SwayDA has good to excellent test-retest reliability. The finding that VLSDS score was significantly correlated with mobility performance in older adults highlights the importance of somatosensory perception in postural control. More importantly, the significantly worse VLSDS in older people observed in the inner lateral movement range may represent a unique characteristic of neuromuscular degeneration associated with aging, which should be monitored and addressed in rehabilitation programs.

Mechanobehavioral Scores in Women with and without TMJ Disc Displacement

Cartilage fatigue may be a factor in the precocious development of degenerative changes in the temporomandibular joint (TMJ). This cross-sectional study estimated potential for cartilage fatigue via TMJ energy densities (ED) and jaw muscle duty factors (DF), which were combined to calculate mechanobehavioral scores (MBS) in women with (+) and without (-) bilateral TMJ disc displacement (DD). All subjects gave informed consent to participate and were examined using Diagnostic Criteria (DC) for Temporomandibular Disorders (TMD) and magnetic resonance (MR) and computed tomography (CT) images. Forty-seven subjects were categorized into +DD ( n = 29) and -DD ( n = 18) groups. Dynamic stereometry (MR images combined with jaw-tracking data) characterized individual-specific data of TMJ stress-field mechanics to determine ED (ED = W/ Q mJ/mm3, where W = work done, Q = volume of cartilage) during 10 symmetrical jaw-closing cycles with a 20-N mandibular right canine load. Subjects were trained to record masseter and temporalis electromyography over 3 days and 3 nights. Root mean square electromyography/bite-force calibrations determined subject-specific masseter and temporalis muscle activities per 20-N bite-force (T20 N, µV), which defined thresholds. Muscle DF (DF = % duration of muscle activity/total recording time) were determined for a range of thresholds, and MBS (ED2 × DF) were calculated. Intergroup differences in ED, DF, and MBS were assessed via analyses of variance with Bonferroni and Tukey honest significant difference post hoc tests. Average ED for contralateral TMJs was significantly larger ( P = 0.012) by 1.4-fold in +DD compared to -DD subjects. Average DF were significantly larger (all P < 0.01) for +DD compared to -DD subjects by 1.7-, 2.5-, and 1.9-fold for day, night, and overall, respectively. Daytime MBS were significantly larger (all P < 0.04) by up to 8.5-fold in +DD compared to -DD subjects. Significantly larger ED, DF, and MBS were shown in women with compared to women without bilateral TMJ DD.

Assessing proprioception: A critical review of methods

To control movement, the brain has to integrate proprioceptive information from a variety of mechanoreceptors. The role of proprioception in daily activities, exercise, and sports has been extensively investigated, using different techniques, yet the proprioceptive mechanisms underlying human movement control are still unclear. In the current work we have reviewed understanding of proprioception and the three testing methods: threshold to detection of passive motion, joint position reproduction, and active movement extent discrimination, all of which have been used for assessing proprioception. The origin of the methods, the different testing apparatus, and the procedures and protocols used in each approach are compared and discussed. Recommendations are made for choosing an appropriate technique when assessing proprioceptive mechanisms in different contexts.