Baseline masticatory muscles' performance may predict pain relief in temporomandibular disorders.

OBJECTIVES: To compare masticatory muscles' recruitment in patients with temporomandibular disorders and asymptomatic control subjects. To evaluate if the masticatory muscles' recruitment pattern may predict symptoms' improvement after temporomandibular disorders treatment. MATERIALS AND METHODS: Standardized surface electromyography of anterior temporalis and superficial masseters muscles were recorded and compared at baseline in 26 patients with arthrogenous temporomandibular disorders (study group) and 26 asymptomatic subjects (control group). The study group was treated pharmacologically and by means of five arthrocentesis sessions. Pre-, during-, and post-treatment pain and mandibular function were assessed and compared among timepoints. Clinical improvement in terms of pain and mandibular function was correlated with pre-treatment standardized surface electromyography values. RESULTS: Temporomandibular disorders patients showed improved maximum mouth opening and pain during and after treatment with arthrocentesis compared to baseline (T-test p < 0.01). Standardized surface electromyography values were significantly different in temporomandibular disorders subjects compared to controls (T-test p < 0.05). Improvement in pain at rest after treatment was inversely correlated with pre-treatment masseters standardized surface electromyography symmetry (R-coefficient 0.3936; p < 0.05). CONCLUSIONS: Temporomandibular disorders patients showed a different muscular recruitment pattern compared to controls. The lesser the pre-treatment masseters symmetry, the greater the improvement of pain at rest after treatment.

Pain Patterns of the Temporomandibular Joint Dysfunction and Implications of Stress-Related Behaviors: A Pilot Study / Patrones de Dolor de la Disfunción de la Articulación Temporomandibular e Implicaciones de los Comportamientos Relacionados con el Estrés: Un Estudio Piloto

SUMMARY: Temporomandibular joint dysfunction interferes with the quality of life and activities of daily living among patients. The symptoms of temporomandibular dysfunction, including pain and clicking and popping sounds, are worsened during stressful events, and patients report increased pain around the temporomandibular joint. Stress-related behaviors, such as teeth clenching and teeth grinding, are commonly reported as increasing during stress. The prevalence of temporomandibular dysfunction and stress-related behaviors is reported differently in the literature. Stress in higher education is common. The purpose of this pilot study was to investigate the prevalence of temporomandibular joint dysfunction and stress-related behaviors among staff members at a local University. The study also sought to explore pain patterns described by people experiencing temporomandibular joint dysfunction and the relationship between stress-related behaviors and pain symptoms experienced. Further, the impact of stress on symptoms experienced by people with temporomandibular dysfunction was investigated in this pilot study.

La disfunción de la articulación temporomandibular interfiere con la calidad de vida y las actividades de la vida diaria entre los pacientes. Los síntomas de la disfunción temporomandibular, incluidos el dolor y los chasquidos, empeoran durante los eventos estresantes, y los pacientes informan un aumento del dolor alrededor de la articulación temporomandibular. Los comportamientos relacionados con el estrés, como apretar y rechinar los dientes, suelen aumentar durante el estrés. La prevalencia de la disfunción temporomandibular y los comportamientos relacionados con el estrés se informa de manera diferente en la literatura. El estrés en la educación superior es común. El propósito de este estudio piloto fue investigar la prevalencia de la disfunción de la articulación temporomandibular y los comportamientos relacionados con el estrés entre los miembros del personal de una universidad local. El objetivo del estudio además fue explorar los patrones de dolor descritos por personas que experimentan disfunción de la articulación temporomandibular y la relación entre los comportamientos relacionados con el estrés y los síntomas de dolor experimentados. Además, en este estudio piloto se investigó el impacto del estrés en los síntomas que experimentan las personas con disfunción temporomandibular.

Bruxism an issue between the myths and fact / Bruxismo, un problema entre los mitos y los hechos

Abstract Is our goal in this paper to discuss the current concepts about bruxism, a topic that has been a matter of discussion on the dental field for many years. Recent International efforts have been made to challenge bruxism old definitions; this has derivate to a consensus and an actual new concept that defines bruxism as a behavior instead of a disorder. As a behavior, it is explained in this review how it can have negative health consequences, can be innocuous and how new research support that bruxism can even be a protective factor. Different etiological factors are reviewed in this paper as well the influence of external and internal mechanism related to medications, emotional stress, systemic factors, and potential pharmacological pathways. Moreover, it is briefly summarized the role of oral appliances on sleep bruxism. Finally, clinical considerations and recommendation for the dental professional regarding sings that should be notice during the exam are part of this overview.

Resumen Es nuestro objetivo en este artículo discutir los conceptos actuales sobre el bruxismo, un tema que ha sido motivo de discusión en el campo odontológico durante muchos años. Se han hecho esfuerzos internacionales recientes para desafiar las viejas definiciones de bruxismo; esto ha derivado en un consenso y en la actualidad un nuevo concepto que define al bruxismo como un comportamiento en lugar de un trastorno. Como conducta, se explica en esta revisión cómo puede tener consecuencias negativas para la salud, puede ser inocuo y cómo nuevas investigaciones avalan que el bruxismo puede incluso ser un factor protector. En este artículo se exponen diferentes factores etiológicos, así como la influencia de mecanismos externos e internos relacionados como: medicamentos, estrés emocional, factores sistémicos y posibles vías farmacológicas. Además, se resume brevemente el papel de los aparatos orales en el bruxismo del sueño. Finalmente, se presentan consideraciones clínicas y la recomendación para el profesional en odontología con respecto a los signos que deben ser observados durante el examen clínico son parte de esta revisión.

Prevalence of temporomandibular disorders and its association with malocclusion in children: A transversal study.

This study investigated the prevalence of temporomandibular disorders (TMDs) in a sample of children and adolescents and evaluated the correlation with occlusal variables. TMD signs and symptoms were recorded in 411 subjects (age range 7-15 years), divided into two groups: 214 subjects treated in Chieti (Italy) CG group and 197 in Murcia (Spain) MG group. Once the Angle dental class was identified, it was recorded if there were signs and symptoms of temporomandibular disorders (TMDs) and occlusal interferences. The percentages of signs and symptoms were compared to determine the differences among the groups for TMDs, bruxism, joint sounds, deviation during the opening, reduced opening/lateral/protrusive movements, malocclusions, and myofascial pain. There is no statistically significant difference between the two groups (χ2 = 1.057, p > 0.05). Subjects with Angle Class I (37.37%), deep bite (43.43%), and increased overjet (41.41%) showed a higher prevalence of TMD symptoms.

Functional Magnetic Resonance Connectivity in Patients With Temporomadibular Joint Disorders.

Myofascial pain in the masticatory region, generally referred to as headache, is a common temporomandibular disorder (TMD) characterized by the hypersensitive regions of the contracted skeletal muscle fibers. A correct clinical treatment of myofascial pain has the potential to modify the functional activation of cerebral networks associated with pain and unconscious teeth clenching, specifically the pain network (PN) and default mode network (DMN). In this study, research is presented as a case series of five patients with myofascial pain: three were diagnosed with intra- and extra-articular disorders, and two were diagnosed with only extra-articular disorders. All five patients received gnathological therapy consisting of passive splints and biofeedback exercises for tongue-palatal vault coordination. Before and after treatment, patients underwent pain assessments (through measures of visual analog scales and muscular palpation tests), nuclear magnetic resonance of the temporomandibular joint, and functional nuclear magnetic resonance of the brain. In each patient, temporomandibular joint nuclear magnetic resonance results were similar before and after the gnathological treatment. However, the treatment resulted in a considerable reduction in pain for all patients, according to the visual analog scales and the palpation test. Furthermore, functional nuclear magnetic resonance of the brain clearly showed a homogeneous modification in cerebral networks associated with pain (i.e., PN and DMN), in all patients. In conclusion, gnathological therapy consisting of passive aligners and biofeedback exercises improved myofascial pain in all five patients. Most importantly, this study showed that all five patients had a homogeneous functional modification of pain and default mode networks. Using passive splints in combination with jaw exercises may be an effective treatment option for patients with TMD. This research could be a starting point for future investigations and for clinicians who want to approach similar situations.

Development of a Wearable Mouth Guard Device for Monitoring Teeth Clenching during Exercise.

Teeth clenching during exercise is important for sports performance and health. Recently, several mouth guard (MG)-type wearable devices for exercise were studied because they do not disrupt the exercise. In this study, we developed a wearable MG device with force sensors on both sides of the maxillary first molars to monitor teeth clenching. The force sensor output increased linearly up to 70 N. In four simple occlusion tests, the trends exhibited by the outputs of the MG sensor were consistent with those of an electromyogram (EMG), and the MG device featured sufficient temporal resolution to measure the timing of teeth clenching. When the jaw moved, the MG sensor outputs depended on the sensor position. The MG sensor output from the teeth-grinding test agreed with the video-motion analysis results. It was comparatively difficult to use the EMG because it contained a significant noise level. Finally, the usefulness of the MG sensor was confirmed through an exercise tolerance test. This study indicated that the developed wearable MG device is useful for monitoring clenching timing and duration, and the degree of clenching during exercise, which can contribute to explaining the relationship between teeth clenching and sports performance.

Seasonality of bruxism: evidence from Google Trends.

OBJECTIVE: Seasonality of bruxism and its symptoms has not been tested and reflects a major niche in our understanding and the epidemiology of bruxism. Our aim is to use the Google Trends data to examine whether there was a seasonal pattern in the Google search volumes of bruxism and its symptoms on a population basis. METHODS: In the observational, ecological research, we interrogated Google Trends for the following query terms: [bruxism] and [teeth grinding + teeth clenching] to obtain the internet search query volume. These queries were searched within the USA, the UK, Canada, and Australia from January 2004 to December 2017. RESULTS: The cosinor analysis showed statistically significant seasonal patterns in [bruxism] in the USA (amplitude {A} = 1.91, p = 0.003), Canada (A = 1.91, p < 0.001), and Australia (A = 2.25, p < 0.001), and a trend towards a seasonal variation in the UK (A = 1.11, p = 0.032), with a peak in the winter months and trough in the summer months. Similarly, a statistically significant seasonal variation was found in [teeth grinding + teeth clenching] in the USA (A = 5.54, p < 0.001), the UK (A = 4.36, p < 0.001), and Australia (A = 3.11, p < 0.001), and a trend towards a seasonal variation in Canada (A = 1.53, p = 0.034). The peaks in winter and troughs in summer were reversed by 6 months in countries of northern hemisphere compared to Australia. Time series plots emphasized the consistency of seasonal trend that was ascertained in the cosinor analysis, by repeating in nearly all years. CONCLUSION: The preliminary evidence showed a seasonal variation in bruxism and its symptoms, with a peak in the winter months. This novel finding in bruxism epidemiology requires to be verified with clinical studies, and further researches are necessary to elucidate the potential mechanism behind seasonal variation in bruxism.

Reflex arc of the teeth clenching-induced pressor response in rats.

Although "teeth clenching" induces pressor response, the reflex tracts of the response are unknown. In this study, dantrolene administration inhibited teeth clenching generated by electrical stimulation of the masseter muscles and completely abolished the pressor response. In addition, trigeminal ganglion block or hexamethonium administration completely abolished the pressor response. Local anesthesia of molar regions significantly reduced the pressor response to 27 ± 10%. Gadolinium (mechanoreceptor blocker of group III muscle afferents) entrapment in masticatory muscles also significantly reduced the pressor response to 62 ± 7%. Although atropine methyl nitrate administration did not change the pressor response, a significant dose-dependent augmentation of heart rate was observed. These results indicate that both periodontal membrane and mechanoreceptors in masticatory muscles are the receptors for the pressor response, and that the afferent and efferent pathways of the pressor response pass through the trigeminal afferent nerves and sympathetic nerves, respectively.

Effect of upright and slouch sitting postures and voluntary teeth clenching on hand grip strength in young male adults.

BACKGROUND: Estimation of handgrip strength (HGS) is routinely used by clinicians and epidemiologists for objective assessment of functional status of hand and upper extremity. It is also used as an indirect indicator of overall physical strength and health status in variety of clinical situations and chronic general medical conditions. OBJECTIVE: The present study was conducted to examine the effects of upright and slouch sitting postures and voluntary teeth clenching on hand grip strength in healthy young male subjects. METHODS: One hundred healthy young males (aged 18-30 years) participated in this study. The HGS was measured using a commercially available dynamometer for the dominant hand. The HGS was measured during four test conditions; (a) slouch sitting without teeth contact, (b) slouch sitting with teeth clenching, (c) upright sitting without teeth contact, and (d) upright sitting with teeth clenching. RESULTS: The HGS values were significantly higher during slouch than upright sitting posture, both during similar and opposite teeth related conditions (p< 0.001). Teeth clenching had no effect on the in HGS values during slouch or upright sitting posture (P> 0.05). CONCLUSIONS: As compared to upright sitting, higher HGS values can be obtained during slouch sitting in young healthy males. Teeth clenching does not affect the HGS values during slouch or upright sitting posture.

Standardised surface electromyography allows effective submental muscles assessment.

The aims of this pilot study were to evaluate: (i) the reproducibility and variability of an electromyographical protocol developed for the assessment of submental muscles (SM) (ii) to apply the new protocol to maximal teeth clenching, a simple and largely studied static task in order to quantify the relative contribution of submental muscles. In 20 healthy subjects, aged 19-35years, surface electromyography of SM, masseter (MM) and anterior temporalis (TA) muscles was performed during maximal voluntary clenching (MVC) with and without cotton rolls and the pushing of the tongue against the palate. Clenching on cotton rolls and pushing the tongue against the palate were used to standardise respectively MM and TA, and SM muscular potentials. The exercises were repeated in two appointments (T1-T2); submental muscles standardisation was also repeated twice (A-B) in each session to assess repeatability. Symmetry and activity were calculated for each couple of muscles. A two-way analysis of variance was computed for SM: no Factor 1 (T1 vs T2) or Factor 2 (A vs B) or F1×F2 significant effects were found. SM recruitment was 31% of the maximal activity, with symmetry values larger than 80%. In conclusion, standardised electromyography allows a reliable assessment of Submental muscles activity.

Effect of mouthguards on impact to the craniomandibular complex.

BACKGROUND: The aim of this study was to investigate the effect of wearing a mouthguard and teeth-clenching on impact to the head and temporomandibular joint (TMJ) during a blow to the jaw. MATERIAL AND METHODS: A custom-made mouthguard was fabricated for five participants. A 4.1-N impact load was applied to the chin with a pendulum. Two acceleration sensors were attached to the forehead and left TMJ. The amplitudes and durations of the accelerations were obtained under five conditions: mouth-open without mouthguard; light teeth-clenching without mouthguard; maximum voluntary clenching (MVC) without mouthguard; mouth-open with mouthguard and MVC with mouthguard. RESULTS: Wearing a mouthguard led to significant decreases in the amplitude (mouth-open with mouthguard vs mouth-open without mouthguard, P = 0.035 at forehead, P = 0.022 at TMJ) and duration (mouth-open with mouthguard vs mouth-open without mouthguard, P = 0.043 at forehead, not significant at TMJ). Similarly, teeth-clenching caused significant decreases in the amplitude (mouth-open without mouthguard vs MVC without mouthguard, P = 0.024 at forehead, P = 0.025 at TMJ) and duration (mouth-open without mouthguard vs MVC without mouthguard, P = 0.033 at forehead, not significant at TMJ). Furthermore, wearing a mouthguard in itself provided an impact reduction effect similar to the combination of teeth-clenching and wearing a mouthguard. CONCLUSIONS: Wearing a mouthguard and/or teeth-clenching reduced the impact to the head and TMJ during a blow to the jaw. However, it should be noted that the findings are the results from a small impact load to the jaw.

The Effect of Teeth Clenching on Dynamic Balance at Jump-Landing: A Pilot Study.

The aim of this study was to analyze the effect of teeth clenching on dynamic balance at jump landing. Twenty-five healthy subjects performed jump-landing tasks with or without teeth clenching. The first 3 trials were performed with no instruction; subsequently, subjects were ordered to clench at the time of landing in the following 3 trials. We collected the data of masseter muscle activity by electromyogram, the maximum vertical ground reaction force (vGRFmax) and center of pressure (CoP) parameters by force plate during jump-landing. According to the clenching status of control jump-landing, all participants were categorized into a spontaneous clenching group and no clenching group, and the CoP data were compared. The masseter muscle activity was correlated with vGRFmax during anterior jump-landing, while it was not correlated with CoP. In comparisons between the spontaneous clenching and the no clenching group during anterior jump-landing, the spontaneous clenching group showed harder landing and the CoP area became larger than the no clenching group. There were no significant differences between pre- and postintervention in both spontaneous clenching and no clenching groups. The effect of teeth clenching on dynamic balance during jump-landing was limited.

Effects and biological limitations of +Gz acceleration on the autonomic functions-related circulation in rats.

The effects of gravitational loading (G load) on humans have been studied ever since the early 20th century. After the dangers of G load in the vertical head-to-leg direction (+Gz load) became evident, many animal experiments were performed between 1920 and 1945 in an effort to identify the origins of high G-force-induced loss of consciousness (G-LOC), which led to development of the anti-G suit. The establishment of norms and training for G-LOC prevention resulted in a gradual decline in reports of animal experiments on G load, a decline that steepened with the establishment of anti-G techniques in humans, such as special breathing methods and skeletal muscle contraction, called an anti-G straining maneuver, which are voluntary physiological functions. Because the issue involves humans during flight, the effects on humans themselves are clearly of great importance, but ethical considerations largely preclude any research on the human body that probes to any depth the endogenous physiological states and functions. The decline in reports on animal experiments may therefore signify a general decline in research into the changes seen in the various involuntary, autonomic functions. The declining number of related reports on investigations of physiological autonomic systems other than the circulatory system seems to bear this out. In this review, we therefore describe our findings on the effects of G load on the autonomic nervous system, cardiac function, cerebral blood flow, tissue oxygen level, and other physiological autonomic functions as measured in animal experiments, including denervation or pharmacological blocking, in an effort to present the limits and the mechanisms of G-load response extending physiologically. We demonstrate previously unrecognized risks due to G load, and also describe fundamental research aimed at countering these effects and development of a scientific training measure devised for actively enhancing +Gz tolerance in involuntary, autonomic system functions. The research described here is rough and incomplete, but it is offered as a beginning, in the hope that researchers may find it of reference and carry the effort toward completion. The advances described here include (1) a finding that cerebral arterial perfusion pressure decreases to nearly zero under +5.0 Gz loads, (2) indications that G load may cause myocardial microinjuries, (3) detection of differences between cerebral regions in tissue-oxygen level under +3.0 Gz load, (4) discovery that hypotension is deeper under decreasing +Gz loads than increasing +Gz loads with use of an anti-G system, due in part to suppression of baroreceptor reflex, and (5) revelations and efforts investigating new measures to reduce cerebral hypotension, namely the "teeth-clenching pressor response" and preconditioning with slight but repeated G loads.

Altered neural activation pattern during teeth clenching in temporomandibular disorders.

OBJECTIVE: The aim was to explore the neural activations during teeth clenching in TMDs patients pre- and post-treatment. SUBJECTS AND METHODS: Thirty TMDs patients and 20 controls underwent clinical evaluations and functional magnetic resonance imaging with a teeth clenching task. Eleven patients received repeat evaluation and imaging after wearing a stabilization splint for 3 months. RESULTS: During teeth clench, the TMDs patients showed decreased positive activity in the left precentral gyrus, right and left inferior temporal gyrus, and left cerebellum and increased negative activations in the right medial prefrontal cortex (P < 0.05 after AlphaSim correction). The 11 TMDs patients after treatment showed a return to normal neural activity in these areas. No brain areas in TMDs patients showed differences in activation after treatment compared with the controls, except for an increase in activation in the right cerebellum in the 11 TMDs patients (P < 0.05 after AlphaSim correction). CONCLUSION: Decreased activations in cerebral areas associated with motor and cognitive functions in TMDs patients during teeth clenching were observed. Normalized activations of these areas happened in patients after routine treatment. These findings may facilitate the understanding of TMDs pathogenesis and the therapeutic mechanisms of the stabilization splint.

Sleep-Related Breathing Disorders and Bruxism.

Obstructive sleep apnea (OSA) syndrome is a sleep-related breathing disorder, due mainly to peripheral causes, characterized by repeated episodes of obstruction of the upper airways, associated with snoring and arousals. The sleep process fragmentation and oxygen desaturation events lead to the major health problems with numerous pathophysiological consequences. Micro-arousals occurring during sleep are considered to be the main causal factor for night jaw-closing muscles activation called bruxism. Bruxism is characterized by clenching and grinding of the teeth or by bracing or thrusting of the mandible. The causes of bruxism are multifactorial and are mostly of central origin. Among central factors there are secretion disorders of central nervous system neurotransmitters and basal ganglia disorders. Recently, sleep bruxism has started to be regarded as a physiological phenomenon occurring in some parts of the population. In this article we present an evaluation of the relationship between OSA and sleep bruxism. It has been reported that the frequency of apneic episodes and that of teeth clenching positively correlates in OSA. However, clinical findings suggest that further studies are needed to clarify sleep bruxism pathophysiology and to develop new approaches to tailor therapy for individual patients with concomitant sleep bruxism and OSA.

Augmentation of eccentric strength of knee extensors with teeth clenching / 体力科学

Previous research has demonstrated that the concentric muscle strength of knee extension exerted at slow to medium angular velocities is increased by teeth clenching. This study evaluated the isokinetic eccentric strength of knee extensors at 4 angular velocities (60, 120, 180 and 240 degrees per second) with and without teeth clenching on the Cybex 6000 Extremity Testing and Rehabilitation System. Twelve healthy adult male (26.8±1.8 years) volunteered for the study. Peak torque per body weight and average power per body weight were analyzed. The results demonstrated that peak torque per body weight accompanied by teeth clenching was significantly increased at 60, 120, 180 and 240 deg/s by 9.5%, 8.2%, 8.2% and 9.8%, respectively (p<0.01) . Similarly average power per body weight during teeth clenching was significantly higher at 60, 120, 180 and 240 deg/s by 9.1%, 9.5%, 9.4% and 7.7%, respectively (p<0.05) . These findings suggest that teeth clenching is a factor that leads to augmented eccentric strength of knee extensors. Its effect appears to be independent of angular velocity.

Effect of teeth clenching on muscle strength during repeated isokinetic knee extensions / 体力科学

The purpose of this study was to investigate the effect of teeth clenching on isokinetic knee extension force during repeated voluntary contractions. We assessed isokinetic muscle strength in association with teeth clenching during 100 consecutive knee extensions at 60 degrees per second (deg/s) using a Cybex 6000 isokinetic dynamometer. In this study, 8 healthy male volunteers (28.4 ± 3.89 years) were asked to perform isokinetic contractions in an extended cycle of five contractions without teeth clenching followed by five contractions with the teeth clenching. The peak torque per body weight was statistically analyzed. In our results, the peak torque per body weight with teeth clenching were significantly greater than those without teeth clenching in the first 70 cycles; however, no significant differences were shown at 71-100 cycles. There was a significant negative correlation between the number of knee extensions and the difference in peak torque per body weight derived from with and without teeth clenching (r=-0.475, p<0.0001) . Our findings reveal that the effect of teeth clenching on the isokinetic muscle strength of knee extension is dependent on muscular fatigue, and that the improving effect of teeth clenching on isokinetic muscle strength declines with increasing muscular fatigue.

Effect of teeth clenching on force-velocity relationships in isokinetic knee extension / 体力科学

To investigate the effect of teeth clenching on isokinetic knee extension at various velocities, isokinetic muscle strength during knee extension was measured in association with teeth clenching at 30, 60, 150, 300 and 450 degrees per second (deg/s) using the Cybex 6000 isokinetic dynamometer. The volunteer subjects were 9 healthy males (26.2±0.97 years) . The peak torque per body weight and average power per body weight were statistically analyzed. Our results demonstrated that the peak torque per body weight with teeth clenching at 30, 60 and 150 deg/s significantly increased by 7.0%, 7.4% and 4.9%, respectively (p<0.05), but no significant differences were found at 300 and 450 deg/s. While the average power per body weight with teeth clenching at 30, 60 and 150 deg/s significantly increased by 6.5%, 6.1% and 6.9%, respectively (p<0.05), no sig-nificant differences were found at 300 and 450 deg/s. A significant negative correlation was shown between the isokinetic angular velocity and the difference in peak torque per body weight derived from with and without teeth clenching (r=-0.699; p<0.05) . These findings suggested that the effect of teeth clenching on isokinetic muscle strength of knee extension was dependent on the angular velocity, and at lower angular velocities teeth clenching had the effect of increasing the isokinetic muscle strength during knee extension.