Human masticatory muscle activity and jaw position under experimental stress

Facial mimicry depends on the emotion we recognize in others' faces

Facial mimicry is known to play an important role in emotional communication. While major models of facial mimicry assume a relationship between facial mimicry and emotion recognition, the empirical evidence for such a relationship is mixed. In this study, the facial movements of the same participants were compared when they recognised the same uncertain faces as "happiness" or "anger." When faces expressed anger in the upper half (upper anger) and happiness in the lower half (lower happiness), participants responded that it was "happiness" in some trials and "anger" in others. The electromyography data showed that participants frowned more in trials in which they recognised anger in the upper anger and lower happiness faces than in trials in which they recognised happiness in the same faces (Experiment 1). By presenting the upper and lower half of expressions individually, we confirmed that upper anger and lower happiness were both salient in the expression intensity and that both the upper and lower half of the faces individually induced emotionally congruent facial movements (Experiment 2). Despite limitations, this study supported the relationship between facial mimicry and emotional recognition. These findings aid in further understanding social interaction at an unconscious and physical level.

Neuroticism Overestimated? Neuroticism Versus Hypertonia, Pain and Rehabilitation Outcomes in Post-Spinal Cord Injury Patients Rehabilitated Conventionally and with Robotic-Assisted Gait Training

BACKGROUND

The aim of the present study was to analyse the association between neuroticism (one of the Big Five personality traits) and the most common secondary sensorimotor complications occurring in patients after spinal cord injury (SCI), i.e., muscle spasticity (hypertonia) and pain, and to investigate the associations between neuroticism and the effects of conventional rehabilitation (dynamic parapodium) and those using robotic-assisted gait training (RAGT) in this group of patients. In addition, the association of neuroticism with self-efficacy, personal beliefs about pain control, and adopted coping strategies among SCI patients was analysed. These data can be used as a reference for designing effective forms of therapy and support dedicated to this group of patients.

METHODS AND PROCEDURES

Quantitative analysis included 110 patients after SCI. The participants were divided by simple randomisation into a rehabilitation group with RAGT and a rehabilitation group with dynamic parapodium therapy (DPT). The following survey instruments were used for data collection: Revised NEO Personality Inventory (NEO-PI-R); Ashworth Scale; the Spinal Cord Independence Measure III (SCIM III); the Walking Index for Spinal Cord Injury II (WISCI-II); the American Spinal Injury Association Impairment Scale (AIS); the Pain Coping Strategies Questionnaire-CSQ; and the Beliefs about Pain Control Questionnaire-BPCQ.

OUTCOMES AND RESULTS

analyses showed a positive association between neuroticism and spastic tension (rho = 0.39; p < 0.001).

CONCLUSIONS AND IMPLICATIONS

the study showed that a high level of neuroticism correlates with a higher level of spasticity, but no such correlation was observed for pain. Additionally, the study did not show a significant correlation between neuroticism and rehabilitation outcome depending on the rehabilitation modality (RAGT vs. DPT). The results underline the importance of carrying out a psychological diagnosis of patients to provide therapeutic support in the rehabilitation process.

Awake bruxism behaviors frequency in a group of healthy young adults with different psychological scores

OBJECTIVE

To assess the frequency of awake bruxism (AB) behaviors in a group of undergraduate dentistry students and correlate it with the status of anxiety and depression.

MATERIALS AND METHODS

The frequency of five oral behaviors (i.e., relaxed jaw muscle, teeth contact, mandible bracing, teeth clenching, teeth grinding) was evaluated using a smartphone-based ecological momentary assessment (EMA) approach. The anxiety and depression status was investigated with the four-item patient health questionnaire for anxiety and depression (PHQ-4). ANOVA with Tukey post-hoc test was used to assess the difference in frequency of AB behaviors among the four PHQ-4 groups.

RESULTS

Among the four groups, there was a statistically significant difference in the frequency of relaxed jaw muscle, teeth contact, mandible bracing, and teeth clenching, but not for teeth grinding.

CONCLUSION

Based on this cross-sectional study's findings, psyche seems to have a determinant impact on AB behaviors, which is significantly higher in individuals with anxiety and depression traits.

Nutrient insufficiencies and deficiencies involved in the pathogenesis of bruxism (Review)

Stress has been well-documented to have a significant role in the etiopathogenesis of bruxism. Activation of the hypothalamic-pituitary-adrenal axis (HPA) and subsequent release of corticosteroids lead to increased muscle activity. Neurological studies have demonstrated that chronic stress exposure induces neurodegeneration of important neuronal structures and destabilization of the mesocortical dopaminergic pathway. These disruptions impair the abilities to counteract the overactivity of the HPA axis and disinhibit involuntary muscle activity, while at the same time, there is activation of the amygdala. Recent evidence shows that overactivation of the amygdala under stressful stimuli causes rhythmic jaw muscle activity by over activating the mesencephalic and motor trigeminal nuclei. The present review aimed to discuss the negative effects of certain vitamin and mineral deficiencies, such as vitamin D, magnesium, and omega-3 fatty acids, on the central nervous system. It provides evidence on how such insufficiencies may increase stress sensitivity and neuromuscular excitability and thereby reduce the ability to effectively respond to the overactivation of the sympathetic nervous system, and also how stress can in turn lead to these insufficiencies. Finally, the positive effects of individualized supplementation are discussed in the context of diminishing anxiety and oxidative stress, neuroprotection and in the reversal of neurodegeneration, and also in alleviating/reducing neuromuscular symptoms.

Electromyography: Processing, Muscles' Electric Signal Analysis, and Use in Myofunctional Orthodontics

Electromyography, commonly known as EMG, utilizes superficial or needle electrodes to record and analyze the fundamental electrical characteristics of skeletal muscles, determining whether the muscles are contracting. The motor unit, which consists of a collection of group muscle fibers and the motor neurons that govern them, is the structural basis of EMG. Three types of electrode are used in EMG which are needle electrode, fine wire electrode, and surface electrode. A significant amount of literature indicates that the correction of muscle function affects the relationships between teeth within the same jaw and between the jaws on opposing sides. The mechanism of action in myofunctional appliance therapy is linked to neuromuscular and skeletal adaptations resulting from altered function in the orofacial region. Both myofunctional therapy and orthodontics aim to address abnormal muscular behavior, restore abnormal muscle activity, and maintain proper alignment in various areas, including the lips, lower jaw, and tongue. This knowledge is essential for functions such as swallowing, speaking, chewing, and respiration as well as for minimizing incorrect movements and positioning. This article aims to describe the application of surface EMG as a diagnosis tool for assessing muscle activities in various orthodontic disorders, such as class II malocclusion open bite, crossbite, maxillary constriction, cleft lip and palate (CLP), and temporomandibular dysfunction, in patients. The electrodes used in EMG can be utilized to detect bioelectric activity in the muscles of the jaws and abnormalities in jaw movement. Analyzing EMG data is vital for obtaining a comprehensive understanding of the masticatory muscle system.

Electromyographic Evaluations of Masticatory Muscle Activity between Patients with Skeletal Class I and III Relationships

OBJECTIVE

 The aim of this study was to compare the muscle activity of the masseter muscle (MM) and anterior temporal muscle (TA) of patients with skeletal Class I and III during maximum voluntary clenching (MVC) at the intercuspal position (ICP) and during chewing.

MATERIALS AND METHODS

 Twenty patients were divided into Steiner's skeletal Class I and III groups. MM and TA activity during each task was measured by using surface electromyography. Averaged MM and TA activity during both tasks, symmetry of each muscle activity, synergy between ipsilateral MMs and TAs, and muscle effort were compared.

STATISTICAL ANALYSIS

 Means and standard deviations of intergroup variables were compared by an independent sample t-test for parametric evaluations or by the Mann-Whitney U test for nonparametric evaluations. A probability value of p less than 0.05 was considered significant.

RESULTS

 Averaged MM activity and muscle synergy during MVC at the ICP in skeletal Class III patients were lower than that in skeletal Class I patients. Neither symmetry nor muscle effort during both tasks was different.

CONCLUSION

 Masticatory muscle performance of skeletal Class III patients was inferior to that of skeletal Class I patients.

Awake and Sleep Bruxism Prevalence and Their Associated Psychological Factors in First-Year University Students: A Pre-Mid-Post COVID-19 Pandemic Comparison

There is a broad consensus accepting that psychological variables such as stress, anxiety, or depression play an important role in bruxism. The COVID-19 pandemic has led to an increase in stress, anxiety, and depression levels. The purpose of this study was to evaluate the impact of the COVID-19 pandemic on possible awake and sleep bruxism prevalence and on the psychological factors associated with bruxism, comparing pre-pandemic, pandemic/lockdown, and post-pandemic samples of first-year students. A total of 274 dentistry students from the Complutense University of Madrid participated in the study: 92 from 2018/2019 (pre-pandemic), 90 from 2020/2021 (pandemic), and 92 students from 2021/2022 (post-pandemic) academic years. The participants filled out a thorough battery of validated questionnaires evaluating bruxism and different psychological characteristics, such as anxiety, depression, somatization, personality, and stress coping styles. While sleep bruxism prevalence was significantly higher for the pandemic group, awake bruxism was smaller in comparison to pre-pandemic and post-pandemic groups. The post-pandemic group also presented higher levels of neuroticism and agreeableness personality traits, and positive reappraisal than the pre-pandemic group, with the pandemic group somewhere in between. Additionally, both the pandemic and post-pandemic group showed higher levels of depression and acceptance/resignation coping styles than the pre-pandemic group. Thus, among the three groups of students, the post-pandemic group was the one that showed a larger effect of the pandemic situation in their psychological variables, presenting higher levels of anxiety (state and trait), depression, acceptation/resignation coping style, higher neuroticism (emotional instability trait), and lower agreeableness trait. Nonetheless, the increase of positive reappraisal in the post-pandemic group (an adaptive coping stress style) might be also a sign of recovery. The higher sleep bruxism for the pandemic group might be related to the pandemic situation and lockdown, passively suffered, possibly promoting feelings of impotency, increased levels of depression and acceptance/resignation (normally considered a passive/maladaptive coping style), while acute stressful situations derived from daily personal social interactions might have increased anxiety levels and induced higher levels of awake bruxism observed in both the pre-pandemic and post-pandemic groups. However, further research, including larger and more representative samples, is needed to confirm this possible relationship.

Wear Management of Colored Foils for the Assessment of Sleep Bruxism Patterns-A Prospective, Randomized Crossover Study

The assessment of bruxism relies on clinical examinations, questionnaires, and polysomnography. The additional use of colored foils (BruxChecker^®) could enable a more precise evaluation of bruxing patterns. To assess differences between use of the foils during stress periods or just on consecutive nights and to determine a reasonable duration of using the foils, 28 patients were classified according to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) and were randomly assigned to wearing the 12 foils for six consecutive nights (alternately in the upper and lower jaw; "consecutive") or six nights within one month following days of high stress ("stress") in a crossover design. The sizes of the attrition areas were measured with ImageJ. Stress was evaluated using the Perceived Stress Scale. The Stress Coping Questionnaire (SVF-120) was used for assessing habitual stress coping strategies. Areas of attrition increased significantly from day 1/2 to 5/6, both for the upper and lower jaw. Molars in the mandible had significantly larger attrition areas than in the maxilla. No significant differences were detected between "consecutive" and "stress" phases. The foils were suitable for differentiating teeth more or less affected by bruxism and were able to show that areas of attrition increased with days, indicating that some adaptation takes place and several days of wearing the foils are required to show the full picture. However, no differences between low/moderate- and high-stress phases were detected.

Temporomandibular Disorders, Bruxism, Perceived Stress, and Coping Strategies among Medical University Students in Times of Social Isolation during Outbreak of COVID-19 Pandemic

The COVID-19 pandemic caught universities along with their students off-guard, enforcing online education. Fear of the unknown, disinformation, and isolation resulted in an increased stress level in the entire population. Medical university students are particularly endangered with high stress levels and developing TMD. Temporomandibular disorders (TMD) are of multifactorial etiology, and manifest with jaw dysfunction, masticatory muscle tension or pain, as well as headache. Though bruxism can act as an exacerbating factor for TMD, stress can also play crucial role in the onset. The study aimed to measure occurrence of TMD and bruxism symptoms in the medical student population, asses the stress level, and evaluate adopted stress-coping strategies during the COVID-19 pandemic outbreak. A survey study was performed among 1018 students at Medical University of Lodz during April 2020. A self-designed questionnaire for screening TMD and bruxism symptoms, Perceived Stress Scale (PSS-10), and Brief-COPE questionnaires were applied. TMD and bruxism symptoms were observed in the majority of subjects during social isolation. The perceived stress levels were significantly higher in those experiencing TMD and bruxism symptoms. Mostly maladaptive, emotion-focused coping strategies were chosen by study subjects experiencing high levels of stress. Choosing Self-Blaming as a coping strategy is the strongest predictor of perceived stress.

Altered electromyographic responses to emotional and pain information in awake bruxers: case-control study

OBJECTIVES

This study aims to investigate how emotional information and pain-related information affect the activity of the masticatory muscles in participants with awake bruxism and controls.

MATERIAL AND METHODS

Different videos and texts, with positive, negative, and neutral valence or related to pain, were presented to a sample of university students, while their electromyographic (EMG) activity around the masseter muscle and their skin conductance were recorded. Two groups were selected, with 24 subjects each: one group of subjects with definitive awake bruxism (confirmed by posterior EMG activity) who also suffered from moderate jaw discomfort, and another group of subjects without bruxism.

RESULTS

The results demonstrated that the subjects with definitive awake bruxism displayed greater muscular activity when presented videos and texts with negative valence, especially when related to pain, than the non-bruxist group.

CONCLUSIONS

This study supports the idea that persons with bruxism who also suffer moderate levels of jaw discomfort present greater bruxism activity when watching pain-related stimuli, and to a lesser extent when watching negative stimuli.

CLINICAL RELEVANCE

The increased muscular activity induced by negative and pain-related information might contribute to pain exacerbation and perpetuation in persons with bruxism who suffer from discomfort.

The Correlation between Pain, Stress, and Oral Function in Oral and Maxillofacial Infection and Trauma Patients

Background:

The relationship between stress and acute pain has been documented in previous studies. Yet, very few studies have evaluated the relationship between stress and acute orofacial pain and its impact on jaw functional activities.

Objective:

The objective of the current study was to evaluate the correlation between acute orofacial pain, stress, and the limitation of the jaw and facial activities in oral and maxillofacial infection and oral and maxillofacial trauma patients.

Methods:

The current study recruited 50 (16 male, 34 female) patients from the Emergency Unit of the Ujung Berung Hospital, Bandung Indonesia. Twenty-five patients were those who had oral and maxillofacial trauma, and the rest were those who had an oral and maxillofacial infection. The patient’s stress level was evaluated by measuring their salivary alpha-amylase level, the pain level was measured by using the numeric rating scale (NRS), whilst the limitation of the jaw and facial activities was measured by using the Jaw and Facial Activities Limitation (JFAL) Questionnaire. All data were analysed using the Spearman correlation test.

Results:

Based on the analysis, it was revealed that there was no significant correlation (r = 0.176, p= 0.22) between stress and pain level. When associated with jaw and facial activities limitation, there was a significant positive correlation (r = 0.555, p < 0.01) found between pain level and jaw and facial activity limitation.

Conclusion:

The current study concluded that there was a significant positive correlation found between pain and jaw activity limitation on oral and maxillofacial infection and trauma patients.

Pain and Stress Detection Using Wearable Sensors and Devices-A Review

Pain is a subjective feeling; it is a sensation that every human being must have experienced all their life. Yet, its mechanism and the way to immune to it is still a question to be answered. This review presents the mechanism and correlation of pain and stress, their assessment and detection approach with medical devices and wearable sensors. Various physiological signals (i.e., heart activity, brain activity, muscle activity, electrodermal activity, respiratory, blood volume pulse, skin temperature) and behavioral signals are organized for wearables sensors detection. By reviewing the wearable sensors used in the healthcare domain, we hope to find a way for wearable healthcare-monitoring system to be applied on pain and stress detection. Since pain leads to multiple consequences or symptoms such as muscle tension and depression that are stress related, there is a chance to find a new approach for chronic pain detection using daily life sensors or devices. Then by integrating modern computing techniques, there is a chance to handle pain and stress management issue.

Temporomandibular Disorders: Fundamental Questions and Answers

This review aimed to present the current evidence-based answers to a questionnaire which was developed to evaluate the beliefs and knowledge of dental professionals concerning temporomandibular disorder (TMD). A literature review was conducted using the PubMed/Medical Literature Analysis and Retrieval System Online (MEDLINE), Cochrane, Google Scholar, and Scopus search engines from January 1980 to June 2020 corresponding to TMD diagnosis, causes, management, and consequences. A total of 50 articles were considered relevant and selected for full review. The etiology of TMD is multifactorial and complicated and involves several direct and indirect factors. Orthodontic treatment does not appear to either prevent or relieve TMD to a great degree. Nevertheless, condylar and occlusal stability reduces the risk of TMD development. As a result, an assessment of the function of masticatory system prior to beginning orthodontic therapy is fundamental. If signs and symptoms of TMD are significantly present, they should be managed before any orthodontic intervention. Moreover, psychological disorders are strongly associated with joint and facial pain. Thus, professionals who work with chronic TMD patients need to be aware of the psychological aspects of chronic pain and refer the patient for psychological evaluation when warranted. Future research elucidating a cause-effect relationship and neurobehavioral processes underlining chronic pain should be performed.

Manifestation of stress and anxiety in the stomatognathic system of undergraduate dentistry students

Objective

To assess the relationship between psychoemotional state and signs of oral cavity occlusal and nonocclusal parafunctions, together with masseter muscle tone, in undergraduate dentistry students.

Methods

The study population comprised first and fifth grade dentistry students who were investigated using psychological and health questionnaires, and stomatological examination with electromyography of the masseter muscles. Differences in variables between first and fifth grade students were analysed using Student’s t-test or χ²-test and Pearson’s correlation coefficient was used to analyse associations between variables.

Results

A total of 113 students (52 first-grade, mean age 20 years; and 61 fifth-grade, mean age 23.6 years) were included. Older age was associated with lower level of perceived stress and anxiety. Moreover, a significant positive relationship was observed between level of perceived stress and anxiety and tone of both masseter muscles.

Conclusions

Increased psychoemotional burden and increased rates of experienced anxiety were associated with growth of masseter muscle tone in this study population.

Effects of intra-oesophageal acid infusion and a stress task on masseter muscle activity and autonomic nervous activity in wakefulness

BACKGROUND

Gastroesophageal reflux disease may be an important risk factor for awake bruxism. Additionally, it has been known that a psychological stress task affects masseter muscle activity, and autonomic nervous system (ANS) activity modulation induces masseter muscle activity.

OBJECTIVES

This study aimed to investigate whether task-induced stress and experimental oesophageal acid infusion increase masseter muscle activity and alter ANS activity, compared to rest task and oesophageal saline infusion, respectively.

METHODS

Polygraphic monitoring, consisting of electromyography of the masseter muscle and electrocardiography, was performed in 12 healthy adult men during 30-min interventions with intra-oesophageal saline or acid infusion, while reading a book quietly, as rest, and while performing calculation, as a stress task.

RESULTS

At rest, masseter muscle activity and parasympathetic nervous system (PNS) activity during acid infusion were significantly higher (P = .019) and lower (P = .021) than during saline infusion, respectively. During saline infusion, both masseter muscle activity and sympathetic nervous system (SNS) activity or PNS activity while performing the calculation task were higher (P = .022 and .012, respectively) or lower (P = .007) than those during the reading task, respectively. In two-way repeated-measures ANOVA, intra-oesophageal infusion (saline or acid) significantly affected masseter muscle activity (P = .008) and PNS activity (P = .021). However, performing tasks (reading or calculation) significantly affected only PNS activity (P = .028).

CONCLUSION

Intra-oesophageal acid infusion significantly increased masseter muscle activity and decreased PNS activity. In contrast, stress task not only significantly decreased PNS activity, but only modestly increased masseter muscle activity and SNS activity.

Dental Treatment on Cephalea from Orofacial Origin

INTRODUCTION

Cephalea from orofacial origin is a diffuse, mild to moderate pain that appears as a bandage around the head. There are many different etiological causes of dental origin that contribute to the appearance of cephalea.

PURPOSE

The purpose of our research is dental treatment of patients with traumatic occlusion, bruxism and loss of occlusal support, which have a pathological condition - cephalea from orofacial origin.

MATERIAL AND METHODS

For the purposes of this paper, 15 patients with cephalea from orofacial origin were analysed, diagnosed and treated. The control group consisted of 15 patients without etiological factors. A butterfly deprogrammer and a stabilization splint were made depending on the indication.

RESULTS AND DISCUSSION

According to our patient study results, it appears to be a link between inadequately made prosthetic devices, bruxism and loss of occlusal support with cephalea. The therapy should help the patient urgently and continue to relieve the cephalea symptoms from orofacial origin. The results show an improvement in 86.7% of the examinees.

CONCLUSION

The butterfly deprogrammer and stabilization splint are new methods that can contribute along with other therapeutic modalities in improving the quality of life in a patient with cephalea from orofacial origin.

Assessment of the Pain, Stress and Emotional Factor Related to the Occurrence of Bruxism

Background/Aim: Bruxism is a parafunctional habit that has multiple etiology. Globally it is a widespread problem. The purpose of this study was to assess the presence of pain, stress and to understand the emotional factor and their relations to the occurrence of bruxism.

Material and Methods: For the purpose of this paper, 40 patients with partial edentuloissness and bruxism were treated prosthetically and with night dentures. They were assessed for the degree of the pain they feel and were given questionnaires for the level of stress they feel and for their psychological situation. The control group consisted of 40 patients who were not treated but were diagnosed with the same methods like the previous group.

Results: Patient feel pain from the consequences of bruxism, disregarding the statistical significance related to gender. Stress pays a major role as we live in a dynamic and demanding society. The more competitive and ambitious the person is the more there are possibilities for occurrence of bruxism. Emotions are a very complex matter that unconsciously can be connected to the presence of bruxism.

Conclusions: Besides prosthetic rehabilitation, sometimes a multidisciplinary approach is needed. Dentists should be aware of their role as psychiatrist and need to be educated of the principles of a patient’s analysis and of the cognitive behavioral therapy.

NMDAR and JNK Activation in the Spinal Trigeminal Nucleus Caudalis Contributes to Masseter Hyperalgesia Induced by Stress

It is commonly accepted that psychological stress is closely associated with the occurrence and development of chronic orofacial pain. However, the pathogenesis underlying this process has not been fully elucidated. In the present study, we explored the role of N-methyl-D-aspartate receptors (NMDARs) and Jun N-terminal kinase (JNK) mediated intercellular communication between neurons and astrocytes in the spinal trigeminal nucleus caudalis (Vc) in the induction of masseter hyperalgesia by psychological stress in rats. We found that subjecting rats to 14 days of restraint stress (8 h/d) caused a significant decrease in body weight gain, behavioral changes and marked masseter hyperalgesia in the rats. We also found that exposure to restraint stress for 14 days caused the expression of pJNK in astrocytes in the Vc to significantly increase, and intrathecally infusing a JNK inhibitor significantly prevented restraint stress-induced masseter hyperalgesia in the rats. In addition, after exposure to restraint stress for 14 days, the stressed group exhibited a noticeably increased expression level of pNR2B in neurons in the Vc. Then, we intrathecally injected MK-801 (an NMDAR inhibitor) and ifenprodil (a selective NR2B subunit antagonist) and observed that the two types of inhibitors not only alleviated masseter hyperalgesia but also significantly inhibited the phosphorylation of JNK in the Vc after restraint stress; this indicates that the effect of NMDAR antagonists may influence the activation of astrocytic JNK. Furthermore, inhibitors of neuronal nitric oxide synthase (nNOS) activation and guanylate cyclase (GC) inhibitor could not only inhibit the expression of pJNK in the Vc, but also effectively alleviate masseter hyperalgesia induced by restraint stress. Taken together, our results suggest that NMDAR activation could increase JNK phosphorylation in astrocytes after restraint stress, which may depend on the nNOS-GC pathway. The intercellular communication between neurons and astrocytes in the Vc may play a key role in the induction of masseter muscle hyperalgesia by psychological stress in rats.

Malocclusion Generates Anxiety-Like Behavior Through a Putative Lateral Habenula-Mesencephalic Trigeminal Nucleus Pathway

Malocclusion is an important risk factor for temporomandibular disorder (TMD), a series of disorders characterized by dysfunction in the orofacial region involving the temporomandibular joint (TMJ) and jaw muscles. We recently showed that experimental unilateral anterior crossbite (UAC) produced masseter hyperactivity through a circuit involving the periodontal proprioception, trigeminal mesencephalic nucleus (Vme), and trigeminal motor nucleus (Vmo). Anxiety is a common complication in patients with TMD. The lateral habenula (LHb) is involved in emotional modulation and has direct projections to the Vme. Therefore, the present research examined whether UAC facilitates excitatory input from the LHb to the Vme and, subsequently, anxiety-like behaviors in rats. The LHb activation was evaluated by the electrophysiological recording, assessment of vesicular glutamate transporter-2 (VGLUT2) mRNA expression, and measurement of anxiety-like behaviors. The effects of LHb activity on Vme were evaluated by electrophysiological recording from Vme neurons and local changes in VGLUT2 protein density. UAC produced anxiety in modeled rats and increased neuronal activity in the LHb. VGLUT2 mRNA expression was also increased in the LHb. Further, VGLUT2-positive boutons were observed in close apposite upon parvalbumin (PV)-labeled Vme neurons. VGLUT2 protein expression was also increased in the Vme. Significantly, injection of VGLUT2-targeted shRNA into the LHb reduced the expression of VGLUT2 protein in the Vme, attenuated UAC-associated anxiety-like behaviors, and attenuated electrophysiological changes in the Vme neurons. In conclusion, we show that UAC activates the LHb neurons as well as the periodontal proprioceptive pathway to provide excitatory input to the Vme and produce anxiety in rats. These findings provide a rationale for suppressing activity of the LHb to attenuate both the physical and psychological effects of TMD.

Bruxism Unconscious Oral Habit in Everyday Life

BACKGROUND

Bruxism is defined as an unconscious oral habit of rhythmical, unfunctional clenching, grinding and making chewy sounds with the teeth while making movements that are not part of the masticatory function and that lead to occlusal trauma.

AIM

The purpose of this article is to show the habit bruxism, in everyday life, reviewing literature data.

METHODS

Data was researched by using information on the internet on Researchgate, Pubmed, ScienceDirect, by analysing written articles and books and student books. From 200 articles that were analysed, 45 articles and two textbooks were involved in writing of this review article.

RESULTS

Results derived from the analyzed literature, classify the main consequences of bruxism, from fatigue, pain, wasting of the incisal edges and occlusal surfaces of the teeth to loss of teeth, dental implants, headaches, periodontal lesions and TMD (dysfunctions of the masticatory muscles and temporomandibular joint (TMJ)) in severe cases. All these problems negatively affect the quality of everyday life of the patient.

CONCLUSION

Bruxism as a parafunctional habit is present in everyday life needing a multidisciplinary approach for prevention of the teeth, bone and prosthetic restorations. The prevalence of bruxism is growing related to stress, drugs, changes in lifestyle, bad nutrition and sleep problems. The therapist should follow signs and symptoms to ensure the best treatment plan of the patient.

Muscle activity and masticatory efficiency with bilateral extension base removable partial dentures with different cusp angles

STATEMENT OF PROBLEM

Whether masticatory efficiency and electromyographic activity are influenced by type of artificial teeth and food is unclear.

PURPOSE

The purpose of this clinical study was to evaluate the influence of extension base removable partial dentures (RPDs) with different cusp angles: anatomic (33 degrees), semianatomic (20 degrees), and nonanatomic (0 degrees) teeth on masticatory efficiency and muscle activity during the mastication of test foods with different textures.

MATERIAL AND METHODS

Twelve participants with RPDs were selected to perform masticatory efficiency and electromyographic tests. Surface electromyograms (EMGs) were used to record the activities of the masseter and temporalis muscles during the mastication of different types of test foods. The maximal voltage and duration were measured on the integrated EMG signal in each muscle during food mastication, and the mean reading of both sides was then recorded. Analysis of variance and the Tukey post hoc test were used to perform statistical analyses (α=.05).

RESULTS

The masticatory efficiency of RPDs with nonanatomic teeth was significantly inferior to that of RPDs with anatomic and semianatomic teeth (P<.05). However, masticatory efficiency did not differ between anatomic and semianatomic teeth (P>.05). Also, muscle activity (according to EMG) with RPDs with NA teeth was significantly higher than that with anatomic and semianatomic teeth (P<.05).

CONCLUSIONS

RPDs with NA teeth were associated with higher EMG muscle activity and reduced masticatory efficiency than anatomic or semianatomic teeth.

Electromyographic ratio of masseter and anterior temporalis muscles in children with and without temporomandibular disorders

OBJECTIVE

This study investigated differences in surface electromyography (sEMG) activity of the masseter and anterior temporalis muscles in children with and without temporomandibular disorders (TMD).

PARTICIPANTS

Thirty-four children aged 8-12 years were recruited, comprising 17 children with TMD and 17 without TMD (control group [CG]). The children were quasi-matched for sex, age, weight, and height. sEMG data were obtained using Myosystem^® Br-1 equipment with 12 channels to evaluate the bilateral masseter, anterior temporalis, and suprahyoid muscles. For sEMG analysis, raw and normalized root mean square (RMS) values were obtained at rest and during maximum clenching. The sEMG ratios of the raw RMS data of the bilateral masseter in relation to the anterior temporalis muscles (sEMG-M/AT ratio) were also assessed. Mann-Whitney tests (p ≤ 0.05) were used to compare sEMG ratio between TMD group and CG.

RESULTS

Significant prevalences of pain during chewing (53% vs. 0%, X² = 5.87, p = 0.01), TMJ pain (58% vs. 0%, X² = 6.67, p = 0.01), neck pain (58% vs. 18%, X² = 3.77, p = 0.05) and pain in the temples (47% vs. 6%, X² = 5.44, p = 0.02) were identified in the TMD group compared to CG. Our results revealed lower sEMG-M/AT ratios during maximum clenching (p = 0.01) in children with TMD compared to those in the asymptomatic CG.

CONCLUSION

The results showed that children with TMD preferentially used their temporalis muscles during maximum voluntary clenching, probably as a consequence of nociceptive inputs in order to obtain pain relief.

Influence of time and different tooth widths on masticatory efficiency and muscular activity in bilateral free-end saddles

PURPOSE

To evaluate the influence of time on masticatory efficiency and muscular activity during mastication of different types of test foods in participants fitted with a lower bilateral free-end saddle removable partial denture (RPD) with wide or narrow teeth.

METHODS

Thirty-six participants consented to undergo evaluation of their masticatory efficiency and recording of their muscular activity, while they wore an RPD with a unified bilateral design, during mastication of different types of test foods. The width of the artificial teeth was changed as follows. Initially (A), the length was adjusted so that the distal end of the mandibular second molars occluded with the distal end of the maxillary second molar (buccolingual width of 7-8 mm). Next (B), the width was decreased to half the maxillary second molars (buccolingual width of only 5 mm). A statistical analysis was performed using SAS software. One-way analysis of variance (ANOVA) was performed followed by Duncan's multiple range tests.

RESULTS

At the 2-month follow-up visit, wider teeth demonstrated greater masticatory efficiency than narrower teeth. However, after 4 months, no significant differences were observed between the two tooth widths. No significant differences in muscular activity were observed.

CONCLUSION

A reduction of the occlusal table width in free-end saddle RPDs resulted in decreased masticatory efficiency 2 months after denture fabrication, but there was no significant difference in muscular activity between narrow and wide teeth. However, after 4 months, the masticatory efficiency of the participants with narrower teeth improved without any changes in muscular activity.

Masticatory efficiency and muscular activity in removable partial dental prostheses with different cusp angles

STATEMENT OF PROBLEM

The loss of posterior teeth has a negative effect on the masticatory efficiency and activity of mastication muscles. How these muscles are affected by partial removable dental prostheses (PRDPs) with different cusp angles is unknown.

PURPOSE

The purpose of this clinical study was to evaluate the influence of different cusp angles, with anatomic (33 degrees), semianatomic (20 degrees), and nonanatomic teeth (0 degree), on the masticatory efficiency and muscular activity of participants receiving mandibular bilateral distal PRDPs.

MATERIAL AND METHODS

Fifteen participants consented to the evaluation of masticatory efficiency and electromyographic (EMG) activity with a PRDP with a unified bilateral design. The cusp angles of the artificial teeth were randomly changed from anatomic (33 degrees), semianatomic (20 degrees), and nonanatomic teeth (0 degree). Masticatory efficiency was evaluated by recording 5 parameters, including number of strokes, and time of mastication while the EMG activities of the masseter and temporalis muscles, measured using surface electromyography. The data were analyzed with 1-way ANOVA and the Tukey multiple post hoc test with statistical software (α=.05).

RESULTS

With regard to masticatory efficiency, PRDPs with anatomic and semianatomic teeth exhibited higher masticatory efficiency than those with nonanatomic teeth, whereas no significant differences were found between PRDPs with anatomic and semianatomic teeth. With respect to EMG activity, the least EMG activity was observed in PRDPs with anatomic teeth, whereas the highest activity was observed with nonanatomic teeth. No significant differences were found between the effect of PRDPs with anatomic and semianatomic teeth on masseter activity.

CONCLUSIONS

Changing the cusp angle from 33 to 20 degrees in PRDPs did not influence the masticatory efficiency or the EMG activity of the masseters. However, it did lead to increased EMG activities of the temporalis muscle. PRDPs with nonanatomic teeth were associated with a significant decrease in masticatory efficiency accompanied by a significant increase in EMG activity.

Metabolic Changes in Masseter Muscle of Rats Submitted to Acute Stress Associated with Exodontia

Clinical evidence has shown that stress may be associated with alterations in masticatory muscle functions. Morphological changes in masticatory muscles induced by occlusal alterations and associated with emotional stress are still lacking in the literature. The objective of this study was to evaluate the influence of acute stress on metabolic activity and oxidative stress of masseter muscles of rats subjected to occlusal modification through morphological and histochemical analyses. In this study, adult Wistar rats were divided into 4 groups: a group with extraction and acute stress (E+A); group with extraction and without stress (E+C); group without extraction and with acute stress (NO+A); and control group without both extraction and stress (NO+C). Masseter muscles were analyzed by Succinate Dehydrogenase (SDH), Nicotinamide Adenine Dinucleotide Diaphorase (NADH) and Reactive Oxygen Species (ROS) techniques. Statistical analyses and two-way ANOVA were applied, followed by Tukey-Kramer tests. In the SDH test, the E+C, E+A and NO+A groups showed a decrease in high desidrogenase activities fibers (P < 0.05), compared to the NO+C group. In the NADH test, there was no difference among the different groups. In the ROS test, in contrast, E+A, E+C and NO+A groups showed a decrease in ROS expression, compared to NO+C groups (P < 0.05). Modified dental occlusion and acute stress - which are important and prevalent problems that affect the general population - are important etiologic factors in metabolic plasticity and ROS levels of masseter muscles.

Correlation of stress and muscle activity of patients with different degrees of temporomandibular disorder

[Purpose] Temporomandibular disorder is one of the many different adverse health conditions that can be triggered by stress. Therefore, a biopsychosocial model has been proposed to characterize the multifactorial nature of temporomandibular disorder. The aim of the present study was investigate the correlation of salivary cortisol levels with the activities of the masseter and anterior temporal muscles of patients with different degrees of temporomandibular disorder. [Subjects and Methods] Forty-nine women between 18 and 40 years of age with a diagnosis of myogenous temporomandibular disorder based on the Research Diagnostic Criteria for temporomandibular disorders were evaluated using the Fonseca Index to determine the degree of the disorder. Salivary cortisol levels were determined and surface electromyography was used to evaluate electrical activity in the masticatory muscles. [Results] Positive correlations were found among the degree of temporomandibular disorder, electromyographic activity and salivary cortisol: as women with more severe temporomandibular disorder had greater electrical activity in the muscles analyzed, especially the anterior temporal muscle, and higher levels of cortisol. [Conclusion] Muscle activity was greater among individuals with severe temporomandibular disorder and positive correlations were found among electromyographic activity, salivary cortisol and the degree of temporomandibular disorder severity.

Correlation of Anxiety Levels between Temporomandibular Disorder Patients and Normal Subjects

Background. Temporomandibular disorders (TMDs) are among the common musculoskeletal conditions affecting the individual. Anxiety plays an important role in the pathogenesis of TMD. Modern lifestyle and work environment bring to focus the role of anxiety in everyday life which is changing the demographics of diseases like TMD. This study compared the anxiety scores between TMD patients and normal subjects. Material and Methods. 505 individuals were included in the study who were divided into group 1 with 255 individuals presenting with signs and symptoms of TMD and group 2 with 250 normal individuals as controls. Hospital anxiety depression scale was used to calculate the anxiety scores. Fischer’s t test was used to compare the anxiety scores between the two groups. Results. 80% of individuals in group 2 and 44% in group 1 individuals had normal anxiety scores. 45% of the individuals in group 1 and 19% in group 2 had borderline anxiety scores. 11% of group 1 individuals and <1% of group 2 individuals demonstrated high anxiety scores. These results were statistically significant. Conclusion. Individuals with TMD exhibited higher levels of anxiety scores whereas significant number of control subjects exhibited normal anxiety scores.

Lamotrigine reverses masseter overactivity caused by stress maybe via Glu suppression

Experimental and non-experimental stress significantly increase masseter muscle tone, which has been linked to the symptoms and pathogenesis of several stomatognathic system diseases. Until now, the mechanism underlying this phenomenon has remained unclear. The current study was performed to determine the mechanism of the stress-induced increase in masseter muscle tone and to investigate the effect of lamotrigine on this change. Animals challenged by repeated restraint stress received either saline as a vehicle or lamotrigine in doses of 20, 30 or 40 mg/kg body weight, whereas control animals received saline without stress treatment. Masseter muscle tone was assessed using electromyography. The activity of glutamate-related metabolic enzymes (glutaminase and glutamine synthetase) in the trigeminal motor nucleus was also investigated. Our results showed an interesting phenomenon: masseter muscle activity increased concurrently with the upregulation of the glutamate concentration after stress treatment. The activities of glutaminase and glutamine synthetase in the trigeminal motor nucleus were also upregulated and downregulated, respectively, when the rats were challenged by prolonged stress. The animals treated with lamotrigine at moderate and high doses had significantly decreased masseter muscle tone compared with stressed animals treated with vehicle. These results suggested that increased glutaminase activity and decreased glutamine synthetase activity increased glutamate production and decreased glutamate decomposition, causing an increase in glutamate levels in the trigeminal motor nucleus and eventually increasing masseter muscle tone. The administration of lamotrigine at doses of 30 or 40 mg/kg body weight effectively mitigated the adverse effects of stress on masseter muscle tone via inhibition of glutamate release.

Is there an association between anxiety/depression and temporomandibular disorders in college students?

Objective

Considering the high incidence of Temporomandibular Disorders (TMD) in the population aged 15-30 years and the fact that students are exposed to stressful psychosocial factors, the purposes of this study were: to verify clinical symptoms and jaw functionality in college students with TMD according to the anxiety/depression (A/D) level and to evaluate the correlation between A/D and functionality, maximum mouth opening (MMO) and pain and muscle activity.

Material and Methods

Nineteen students with TMD diagnosed according to the Research Diagnostic Criteria for Temporomandibular Disorders underwent two assessments during an academic semester. The evaluations were based on questionnaires (MFIQ - Mandibular Function Impairment Questionnaire; HADS - Hospital Anxiety and Depression Scale), clinical measurements (MMO without pain, MMO and assisted MMO; palpation of joint and masticatory muscles), and electromyography. The HADS scores obtained in the two assessments were used to classify all data as either "high" or "low" A/D. Data normality, differences and correlations were tested with the Shapiro-Wilk test, Student's t-test (or the Wilcoxon test), and Spearman test, respectively. The alpha level was set at 0.05.

Results

None of the clinical variables were significantly different when comparing low and high A/D data. In low A/D there was a significant correlation between HADS score and: MFIQ (P=0.005, r=0.61), and MMO without pain (P=0.01, r=-0.55).

Conclusions

Variation in A/D level did not change clinical symptoms or jaw functionality in college students with TMD. Apparently, there is a correlation between TMJ functionality and A/D level, which should be further investigated, taking into account the source of the TMD and including subjects with greater functional limitation.

Influence of temporomandibular disorder on temporal and masseter muscles and occlusal contacts in adolescents: an electromyographic study

Background

The aim of the present study was to analyse the influence of temporomandibular disorder (TMD) on electromyographic activity in the masseter and temporal muscles of adolescents and investigate a possible association with the number of occlusal contacts.

Methods

The Helkimo Index was administered for the diagnosis of TMD and classification of the adolescents into three groups: without TMD; with mild TMD; and with moderate/severe TMD. Carbon paper was used for the determination of occlusal contact points. A standardised electromyographic evaluation was performed on the masticatory muscles at rest, during habitual chewing and during maximum voluntary clenching. The readings were normalised to maximum voluntary clenching. Statistical analysis involved the chi-squared test and Fisher’s exact test. The Kruskal-Wallis test and one-way analysis of variance with Dunn’s post hoc test were used to compare differences between groups. Pearson’s correlation coefficients (r) were calculated for the determination of correlations between the number of occlusal contacts and RMS values.

Results

Electromyography revealed significant differences in the right and left masseter and temporal muscles at rest and during chewing among the three groups. These differences were not observed during maximum voluntary clenching. No statistically significant differences were found between the groups with and without TMD regarding the number of occlusal contacts.

Conclusion

Electromyographic activity in the masseter and temporal muscles was greater among adolescents with moderate to severe TMD.

Parameters of an Optimal Physiological State of the Masticatory System: The Results of a Survey of Practitioners Using Computerized Measurement Devices

While bioelectronic instruments have been available for nearly 30 years to assist dentists in day-to-day evaluations of patients' masticatory systems, little guidance has been published to support physiological norms or ideals. An electronic questionnaire was developed and administered to an international group of dentists familiar with the use of bioelectronic instrumentation. Respondents were asked to provide feedback on the norms or ideal parameters of jaw movement, masticatory muscle function with electromyography, and joint sounds through electrosonography that they use in guiding evaluation and treatment of patients with temporomandibular disorders, neuromuscular occlusion, and orthodontics. Surveys were collated to determine areas of consensus. Out of 150 surveys, 55 responses were received from dentists representing nine different countries. Sixty percent of the respondents reported treating more than 150 cases in the past five years using bioelectronic testing. While experience ranged from 2-30 years with different types of devices, average experience was longer with mandibular/jaw tracking (mean 15.3 years) and electromyography (mean 14.1 years) than with electrosonography (mean 7.0 years). Parameters proposed as norms or ideals for electromyographic rest and clench values, and mandibular tracking (velocity, freeway space, and trajectory to closure) were very consistent. Although a smaller number of respondents reported utilization of electrosonography, their criteria for data significance and tissue-type genesis of joint sounds were consistent. While the intra-patient variability may limit the diagnostic use of bioelectronic instruments, the current study demonstrates that through decades of experience, dentists have independently arrived at very consistent definitions of an ideal physiology that can be used to guide treatment.

Alexithymia, anger and psychological distress in patients with myofascial pain: a case-control study

Aims: The aim of this study was to investigate psychological distress, anger and alexithymia in a group of patients affected by myofascial pain (MP) in the facial region.

Methods: 45 MP patients [mean (SD) age: 38.9 (11.6)] and 45 female healthy controls [mean (SD) age: 37.8 (13.7)] were assessed medically and psychologically. The medically evaluation consisted of muscle palpation of the pericranial and cervical muscles. The psychological evaluation included the assessment of depression (Beck Depression Inventory—short form), anxiety [State-Trait Anxiety Inventory Form Y (STAI-Y)], emotional distress [Distress Thermometer (DT)], anger [State-Trait Anger Expression Inventory—2 (STAXI-2)], and alexithymia [Toronto Alexithymia Scale (TAS)].

Results: the MP patients showed significantly higher scores in the depression, anxiety and emotional distress inventories. With regard to anger, only the Anger Expression-In scale showed a significant difference between the groups, with higher scores for the MP patients. In addition, the MP patients showed significantly higher alexithymic scores, in particular in the Difficulty in identifying feelings (F1) subscale of the TAS-20. Alexithymia was positively correlated with the Anger Expression-In scale. Both anger and alexithymia showed significant positive correlations with anxiety scores, but only anger was positively correlated with depression.

Conclusion: A higher prevalence of depressive and anxiety symptoms associated with a higher prevalence of alexithymia and expression-in modality to cope with anger was found in the MP patients. Because the presence of such psychological aspects could contribute to generate or exacerbate the suffering of these patients, our results highlight the need to include accurate investigation of psychological aspects in MP patients in normal clinical practice in order to allow clinicians to carry out more efficacious management and treatment strategies.

Effect of experimental stress in 2 different pain conditions affecting the facial muscles

Chronic facial muscle pain is a common feature in both fibromyalgia (FM) and myofascial (MF) pain conditions. In this controlled study, a possible difference in the mode of deregulation of the physiological response to a stressing stimulus was explored by applying an acute mental stress to FM and MF patients and to controls. The effects of the stress test were observed on pain, sympathetic variables, and both tonic and reflex electromyographic activities of masseteric and temporal muscles. The statistical analyses were performed through a generalized linear model including mixed effects. Painful reaction to the stressor was stronger (P < .001) and longer (P = .011) in FM than in MF independently of a higher pain level at baseline. The stress-induced autonomic changes only seen in FM patients did not reach significance. The electromyographic responses to the stress test were strongest for controls and weakest for FM. The stress test had no effect on reflex activity (area under the curve [AUC]) or latency, although AUC was high in FM and latencies were low in both pain groups. It is suggested that FM is characterized by a lower ability to adapt to acute stress than MF.

PERSPECTIVE

This study showed that an acute psychosocial stress triggered several changes in 2 pain conditions including an increase in pain of larger amplitude in FM than in MF pain. Similar stress-induced changes should be explored as possible mechanisms for differentiation between dysfunctional pain conditions.

Psychological stress alters microstructure of the mandibular condyle in rats

Psychological stress plays an important role in the occurrence and development of temporomandibular joint disorder (TMD). The correlation between psychological factors and TMD has been clinically shown, but the influence of psychological stress on the temporomandibular joint (TMJ) structure still lacks direct evidence. Here, we used communication box to establish the rat model of psychological stress. The stress level of animals was estimated by the elevated plus maze (EPM) test and hormonal assays. The histomorphology and three-dimensional microstructure of the rat condyles were observed by hematoxylin-eosin (HE) staining and Micro-CT, respectively. Compared with control rats, the anxious state of the stressed rats was evidenced by higher plasma adrenocorticotropic hormone (ACTH) and corticosterone (CORT), as well as lower ratios of open arm entries and time and lower time spent in open arms after 1, 2, 3, 4 and 5 week(s) post-exposure to psychological stimuli. HE staining and histomorphometric data analysis showed decreased thicknesses of the central and posterior condylar cartilages in stressed rats at weeks 3, 4 and 5, with the most obvious changes in the posterior part characterized by debonding and thinned fibrous layer, thickened proliferative layer, thinned mature layer and hypertrophic layer. Moreover, Micro-CT scanning revealed local lesion of the subchondral bone in the posterior condylar cartilages of stressed rats at week 5. Our findings indicate that pathologic changes of the histomorphology and three-dimensional microstructure occur in the condyles of stressed rats, hinting us a potential link between psychological factors and the pathogenesis or progression of TMD.

The influence of psychological stress on the rat temporomandibular joint with the application of countermeasures

OBJECTIVE

This study aimed to provide an experimental theoretical basis for the treatment of temporomandibular disorders by observing the effects of psychological stress and countermeasures on the rat temporomandibular joint (TMJ).

METHODS

Rats were exposed to psychological stress via a communication box and the lateral pterygoid muscle and TMJ were observed with transmission electron microscopy and scanning electron microscopy. Furthermore, the expression of interleukin-1 and tumor necrosis factor-α was assessed in control animals and psychological stress (PS) and stress with diazepam (PS+DI) groups.

RESULTS

Transmission electron microscopy of the lateral pterygoid muscle fibers in the PS showed vacuolar changes in the mitochondria, loss of cristae, and reduced matrix density to variable degrees after 1, 3, and 5 wk of stress. After 5 wk stress+recovery, the cristae and matrix were normal in the PS and PS+DI groups. Scanning electron microscopy of PS rats showed some synovial membranes were detached from the surface of the articular disc after 1 wk. After 3 wk, collagen fibers appeared to have wider waves and worn strips changing in size on the articular disc; after 5 wk, the distribution of collagen fibers was distorted. In PS+recovery and PS+DI rats, no obvious changes were observed on the surface of the articular disc after 1 to 5 wk stress. In PS rats, interleukin-1 and tumor necrosis factor-α expression increased significantly but was at control levels in the PS+DI and PS+recovery groups.

CONCLUSION

Counteracting psychological stress can antagonize its effects on the TMJ and provide a reference for the treatment of stress-related temporomandibular disorders.

Oxidative damage and HSP70 expression in masseter muscle induced by psychological stress in rats

Psychological stressors are generally associated with masseter muscle dysfunction and disorders in emotional response. In addition, oxidative states and HSP70 expression, which are involved in the physical and pathological changes of the masseter muscle, could be altered in the stressed tissues and organs. However, the link between psychological stress and the redox homeostasis or the expression of HSP70 in masseter muscles in rats has not been examined. Therefore, we used a communication box paradigm to induce psychological stress in rats. The successful establishment of the animal model was evidenced by an increase in plasma corticosterone and adrenocorticotropic hormone (ACTH). Meanwhile, the stressed rats showed a decrease in the number of entries on open arms, percentage of time spent in open arms, and distance moved in the elevated plus-maze test. The stressed rats also displayed a decrease in the time spent in the center zone, active velocity, and the distance moved in the open-field test. These results demonstrate affective-like behavioral changes in the stressed rats. Moreover, compared with the control rats, a decrease in SOD, GSH-Px and catalase activities and an increase in MDA content were observed in the masseter muscles in stressed rats after 3 weeks and 5 weeks, and the HSP70 expression was elevated in muscles in the rats exposed to stress for 5 weeks. These results indicate that psychological stress induces oxidative damage and up-regulates the expression of HSP70 in masseter muscles in rats, which are associated with behavior resembling anxiety.

Psychological stress induces temporary masticatory muscle mechanical sensitivity in rats

To explore the relationship between psychological stress and masticatory muscle pain, we created a communication stress animal model to determine whether psychological stress could induce increased mechanical sensitivity in masticatory muscles and to study the changes of mechanical nociceptive thresholds after stress removal. Forty-eight male Sprague-Dawley rats were divided into a control group (CON), a foot-shocked group (FS, including 3 subgroups recorded as FS-1, FS-2, and FS-3), a psychological stress group (PS), and a drug treatment group (DT). PS and DT rats were confined in a communication box for one hour a day to observe the psychological responses of neighboring FS rats.Measurements of the mechanical nociceptive thresholds of the bilateral temporal and masseter muscles showed a stimulus-response relationship between psychological stress and muscle mechanical sensitivity. The DT rats, who received a diazepam injection, showed almost the same mechanical sensitivity of the masticatory muscles to that of the control in response to psychological stress. Fourteen days after the psychological stressor was removed, the mechanical nociceptive thresholds returned to normal. These findings suggest that psychological stress is directly related to masticatory muscle pain. Removal of the stressor could be a useful method for relieving mechanical sensitivity increase induced by psychological stress.

Psychological stress alters ultrastructure and energy metabolism of masticatory muscle in rats

To investigate the effects of psychological stress on the masticatory muscles of rats, a communication box was applied to induce the psychological stress (PS) in rats. The successful establishment of psychological stimulation was confirmed by elevated serum levels of adrenocorticotropic hormone (ACTH) and changed behaviors in the elevated plusmaze apparatus. The energy metabolism of the bilateral masseter muscles was tested via chemocolorimetric analysis, whereas muscle ultrastructure was assessed by electron microscopy. In comparison to the control group, the PS group showed evidence of swollen mitochondria with cristae loss and reduced matrix density in the masticatory muscles after three weeks of stimulation; after five weeks of stimulation, severe vacuolar changes to the mitochondria were observed. Increased vascular permeability of the masticatory muscle capillaries was found in the five-week PS rats. In addition, there was decreased activity of Na⁺-K⁺ATPase and Ca²⁺-ATPase and a simultaneous increase in the activity of lactate dehydrogenase and lactic acid in the masticatory muscles of PS rats. Together, these results indicate that psychological stress induces alterations in the ultrastructure and energy metabolism of masticatory muscles in rats.

Effect of awareness through movement on the head posture of bruxist children

The aim of this study was to evaluate the effectiveness of physiotherapy to improve the head posture and reduce the signs of bruxism in a group of bruxist children. A single-blind randomized clinical trial was performed. All the subjects were 3- to 6-year old, had complete primary dentition, dental and skeletal class I occlusion and were classified as bruxist according to the minimal criteria of the ICSD for bruxism. For each child, a clinical, photographic and radiographic evaluation of the head and cervical posture were realized with standardized techniques. The children were randomized in an experimental (n = 13) and a control (n = 13) group. A physiotherapeutic intervention was applied to the children of the experimental group once a week, until 10 sessions were completed. Afterwards, the cephalogram and the clinical and photographic evaluation of the head posture were measured again. The data were analysed with the t-test and Mann-Whitney test. The subjects of the experimental group showed statistically significant improvement in the natural head posture. The physiotherapeutic intervention showed to be efficient to improve the head posture at the moment of measurement in the studied children. The relationship between bruxism and head posture, if exists, seems to be worthwhile to examine.

Influence of changing occlusal support on jaw-closing muscle electromyographic activity in healthy men and women

OBJECTIVES

To test whether changes in occlusal support differentially modulate masseter and anterior temporalis muscle electromyographic (EMG) activity during controlled maximal voluntary clenching.

MATERIAL AND METHODS

Forty-seven healthy subjects (32 M and 15 F, 22.9+/-1.3 years) were recruited. Cotton-rolls were used to modify the occlusal contact relations and were positioned on the right, left, or both sides, and either in the molar or premolar regions, i.e. six different occlusal combinations. Surface EMG activity was recorded bilaterally from the masseter and anterior temporalis area and normalized with respect to maximal voluntary clenching in the intercuspal position. Analysis of variance and the paired t-test were used to test the data.

RESULTS

Normalized EMG activity was influenced by changes in cotton-roll modified occlusal support, and there were differences between muscles (p<0.001). In general, EMG activity decreased in both muscles when occlusal support was moved from the molar to the premolar region. When occlusal support was moved from bilateral to unilateral contacts, EMG activity in the balancing-side anterior temporalis muscle and in bilateral masseter muscles decreased. Unilateral clenching on the molars, but not on the premolars, was associated with lower EMG activity in the balancing-side masseter and always associated with lower EMG activity in the balancing-side anterior temporalis compared to the working side (p<0.05).

CONCLUSIONS

Masseter and anterior temporalis muscles respond differently to changes in occlusal support, which may have implications for stability of the mandible during intense clenching.

Influence of chewing rate on salivary stress hormone levels

PURPOSE

The purpose of this study was to clarify the effect of different chewing rates on salivary cortisol levels as a stress indicator.

METHODS

The subject group consisted of 16 healthy males. They were required to rest for 30 min, and then given arithmetic calculations to perform for 30 min as stress loading. Immediately after, the first set of saliva specimens (S1) was collected over a period of 1 min to measure cortisol levels. Next, they were asked to chew a tasteless gum base for 10 min, and the second set of saliva specimens (S2) was collected in the same manner. They were then required to rest for 10 min, after which the third set of saliva specimens (S3) was collected. Chewing rates were set to slow, habitual, and fast in time with a metronome. Salivary cortisol levels were analyzed by radioimmunoassay. Changes in salivary cortisol levels comparing S1 with S2, and S1 with S3 were determined.

RESULTS

Changes in salivary cortisol levels between S1 and S2 showed a reduction of 4.7%, 14.6%, and 16.2% with slow, habitual, and fast chewing, respectively. A significant difference was observed between slow and fast chewing. Changes in salivary cortisol levels between S1 and S3 showed a reduction of 14.4%, 22.2%, and 25.8% with slow, habitual, and fast chewing, respectively. A significant difference was observed between slow and fast chewing.

CONCLUSION

This study showed that differences in chewing rate affected salivary cortisol levels as a stress indicator, and suggested that the effect on stress release with fast chewing is greater than that with slow chewing.