Effects of different stimulus locations on inhibitory responses in human jaw-closing muscles

Application of facial neuromuscular electrical stimulation (fNMES) in psychophysiological research: Practical recommendations based on a systematic review of the literature

Facial neuromuscular electrical stimulation (fNMES), which allows for the non-invasive and physiologically sound activation of facial muscles, has great potential for investigating fundamental questions in psychology and neuroscience, such as the role of proprioceptive facial feedback in emotion induction and emotion recognition, and may serve for clinical applications, such as alleviating symptoms of depression. However, despite illustrious origins in the 19th-century work of Duchenne de Boulogne, the practical application of fNMES remains largely unknown to today's researchers in psychology. In addition, published studies vary dramatically in the stimulation parameters used, such as stimulation frequency, amplitude, duration, and electrode size, and in the way they reported them. Because fNMES parameters impact the comfort and safety of volunteers, as well as its physiological (and psychological) effects, it is of paramount importance to establish recommendations of good practice and to ensure studies can be better compared and integrated. Here, we provide an introduction to fNMES, systematically review the existing literature focusing on the stimulation parameters used, and offer recommendations on how to safely and reliably deliver fNMES and on how to report the fNMES parameters to allow better cross-study comparison. In addition, we provide a free webpage, to easily visualise fNMES parameters and verify their safety based on current density. As an example of a potential application, we focus on the use of fNMES for the investigation of the facial feedback hypothesis.

Evaluation of the masticatory muscle function, physiological sleep variables, and salivary parameters after electromechanical therapeutic approaches in adult patients with Down syndrome: a randomized controlled clinical trial

Background

There are many comorbidities associated with Down syndrome (DS), including obstructive sleep apnea (OSA) and masticatory muscle alteration. Muscular hypotonia, in particular, of the masticatory and oropharyngeal muscles is one of the main characteristics of individuals with DS, resulting in impairments of speech, swallowing, and mastication in these individuals. In addition, total or partial obstruction of the airways during sleep can occur due to pharyngeal hypotonia, leading to snoring and to OSA. This progressive respiratory disorder is associated with a high risk of morbidity and mortality in individuals with DS. The aim of this research is to assess the therapeutic effects of surface neuromuscular electrical stimulation (NMES), the mastication apparatus (MA), and a mandibular advancement oral appliance (OA_m) with an embedded thermosensitive microchip on the functions of masticatory muscles (bilateral masseter and temporal muscles), physiological sleep variables, and salivary parameters in adult patients with DS.

Methods

The patients with DS will be randomly selected and divided into three groups (DS-NMES, DS-MA, and DS-OA_m) with a minimum of 10 patients in each group. A thermosensitive microchip will be embedded in the OA_m to record its compliance. The therapeutic effects on masticatory muscle function will be investigated through electromyography, a caliper, and a force-transducer device; the sleep variables, in turn, will be evaluated by means of polysomnography. The physicochemical and microbiological properties of the saliva will also be analyzed, including the salivary flow, viscosity, buffer capacity, cortisol levels (susceptibility to psychological and/or physical stress), and Pseudomonas aeruginosa levels (risk of aspiration pneumonia) in these patients. The methods determined for this study will be carried out prior to and after 2 months of the recommended therapies.

Discussion

The primary outcomes would be the improvement and/or reestablishment of the function of masticatory muscles and the physiological sleep variables in this target public since individuals with DS commonly present generalized muscular hypotonia and dysfunction of the oropharyngeal musculature. As a secondary outcome indicator, the impact of the applied therapies (NMES, MA, and OA_m) on the salivary microbiological and physicochemical properties in DS individuals will also be assessed. Furthermore, the compliance of OA_m usage will be measured through a thermosensitive microchip.

Trial registration

Registro Brasileiro de Ensaios Clínicos, RBR-3qp5np. Registered on 20 February 2018.

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3300-0) contains supplementary material, which is available to authorized users.

Assessment of periodontal mechano-nociceptive function in healthy Chinese individuals

OBJECTIVE

Few clinical techniques are available for the description of mechano-nociceptive function in human periodontal tissues. The objective of this study was to test a new technique for assessment of periodontal mechano-nociceptive function by direct application of controlled forces to the teeth and quantify site, side and gender differences in healthy individuals.

DESIGN

Twenty healthy young adults (ten males and ten females) participated. A handheld pressure algometer was used to assess pressure pain threshold (PPT) on the maxillary and mandibular central incisors, canines and first premolars on the left and the right side from two directions: lateral and vertical. Statistical analysis was performed using analyses of variance (ANOVA) with repeated measures to compare data.

RESULTS

There were significant gender differences of PPT for both lateral (P_lateral=0.007) and vertical (P_vertical=0.001) directions with lower thresholds in females (higher sensitivity) than in males. A significant site effect (P_lateral=0.002, P_vertical<0.001) was observed with less sensitivity at the first premolar compared to the anterior teeth. No significant right-to-left side differences (P=0.082) were found for the PPTs. There were significant PPT differences between maxillary and mandibular teeth (P_lateral=0.020, P_vertical=0.041,) and significant differences between lateral and vertical direction (P<0.001).

CONCLUSION

The novel application of PPTs directly to the teeth indicated an adequate and practical method with potential value for clinical assessment of painful conditions affecting the periodontal ligament.

Study of exteroceptive suppression of voluntary muscular activity in healthy volunteers and patients with paroxysmal neuropathic pain

The exteroceptive suppression of voluntary electromyographic activity of the masseter and temporal muscles was studied in healthy volunteers and patients with paroxysmal neuropathic pain (trigeminal neuralgia). The latent period of the exteroceptive suppression was prolonged and the duration of its late fragment was shortened in the patients in comparison with normal subjects. A short exteroceptive suppression period in patients with trigeminal neuralgia reflected deficient activity of inhibitory interneurons of the reflector loop and excessive activity of the antinociceptive system of the brain stem, while prolongation of the latent period reflected prolongation of inhibitory interneurons activation. A direct correlation between the degree of changes in the exteroceptive suppression parameters and pain intensity, evaluated by the patients by the visual analog scale, was detected.

Effect of contingent electrical stimulation on jaw muscle activity during sleep: a pilot study with a randomized controlled trial design

OBJECTIVE

To determine the effect of contingent electrical stimulation (CES) on jaw muscle activity during sleep in a double-blinded randomized controlled trial (RCT).

MATERIALS AND METHODS

Eleven patients with myofascial TMD (mean age 37 years) and with a clinical diagnosis of bruxism were included. EMG activity (Grindcare®) was recorded from the anterior temporalis muscle during sleep and analyzed online. Jaw muscle activity related to clenching or grinding triggered an electrical square-wave pulse train (450 ms) adjusted to a clear, but non-painful intensity. TMD patients were randomized into two groups: active treatment with CES or no CES (placebo). Number of EMG episodes/hour sleep was the primary outcome parameter. The following variables were assessed as secondary outcome parameters; number of painful muscles, maximum pain-free jaw opening, characteristic pain intensity, depression scores and Oral Health Impact Profile scores. Numerical Rating Scale scores for self-reported pain and muscle tension were registered for at least 4 nights per week during the experiment.

RESULTS

The number of EMG episodes/hour sleep was significantly reduced (52 ± 12%) in the CES group during the sessions with CES (ANOVA: p = 0.021) compared to baseline. There were no significant differences in the secondary outcome parameters (ANOVA: p > 0.513) or pain or muscle tension scores between groups (p = 0.645). The average duration of sleep hours during the nights with and without CES was not significantly different (p = 0.646).

CONCLUSIONS

These results demonstrate a significant inhibitory effect of CES on jaw muscle EMG activity during sleep in a RCT, but with no effects on self-reported pain.

Electrical stimulation device as possible treatment for nocturnal bruxism: preliminary results

Nocturnal bruxism (NB) is a temporomandibular disorder characterized by an excessive clenching and involuntary parafunctional grinding of the teeth during sleep. It can cause dental damage and irreversible temporomandibular joint dysfunction. We designed a device that generates electrical stimulation on inhibitory sensory afferents when an EMG signal is measured. This stimulation was applied to the right mental nerve to produce a decrease in the contraction intensity of the mandibular elevation muscles. To measure the intensity of contraction, electromyographic (EMG) signal of the left temporalis anterior (LTa) muscle was used. The results showed that, on average, the percentage decrease in the bruxist group was 30.53% and for the control group was 28.91%. These results indicate that the device implemented generates an important decrease in the muscle contractile activity. Therefore, the device could be useful as a possible treatment to decrease nocturnal bruxism.

Effects of neuromuscular electrical stimulation, laser therapy and LED therapy on the masticatory system and the impact on sleep variables in cerebral palsy patients: a randomized, five arms clinical trial

BACKGROUND

Few studies demonstrate effectiveness of therapies for oral rehabilitation of patients with cerebral palsy (CP), given the difficulties in chewing, swallowing and speech, besides the intellectual, sensory and social limitations. Due to upper airway obstruction, they are also vulnerable to sleep disorders. This study aims to assess the sleep variables, through polysomnography, and masticatory dynamics, using electromiography, before and after neuromuscular electrical stimulation, associated or not with low power laser (Gallium Arsenide- Aluminun, =780 nm) and LED (= 660 nm) irradiation in CP patients.

METHODS/DESIGN

50 patients with CP, both gender, aged between 19 and 60 years will be enrolled in this study. The inclusion criteria are: voluntary participation, patient with hemiparesis, quadriparesis or diparetic CP, with ability to understand and respond to verbal commands. The exclusion criteria are: patients undergoing/underwent orthodontic, functional maxillary orthopedic or botulinum toxin treatment. Polysomnographic and surface electromyographic exams on masseter, temporalis and suprahyoid will be carry out in all sample. Questionnaire assessing oral characteristics will be applied. The sample will be divided into 5 treatment groups: Group 1: neuromuscular electrical stimulation; Group 2: laser therapy; Group 3: LED therapy; Group 4: neuromuscular electrical stimulation and laser therapy and Group 5: neuromuscular electrical stimulation and LED therapy. All patients will be treated during 8 consecutive weeks. After treatment, polysomnographic and electromiographic exams will be collected again.

DISCUSSION

This paper describes a five arm clinical trial assessing the examination of sleep quality and masticatory function in patients with CP under non-invasive therapies.

TRIAL REGISTRATION

The protocol for this study is registered with the Brazilian Registry of Clinical Trials - ReBEC RBR-994XFS.