Muscle Hyperactivity Research Articles

Occlusal Appliance Therapy for Temporomandibular Joint Disorders: Mechanisms, Efficacy, and Limitations

Disorders of the temporomandibular joint (TMJ) are chronic conditions that involve pain, muscle spasm, and dysfunction of the joint and surrounding structures. Occlusal appliances have come to be regarded as essential tools in the non-surgical treatment of these disorders as they help in the management of symptoms and protection of teeth and the structures of the TMJ. In various types of reviews of occlusal appliances, including stabilization splints, anterior and posterior bite planes, repositioning devices, and soft appliances, are discussed in detail with regard to their mechanism of action, indications, and limitations. Improvements in the material and the fabrication method, such as printing, have enhanced CAD/CAM systems accuracy and comfort, as well as the patients’ cooperation in the use of these appliances. Thus, combining occlusal appliances with other treatments, including physiotherapy and Botox, offers a systemic approach to TMJ treatment, dealing with both appliances mechanical help and muscular factors. reduction Although there are certain risks involved, like occlusal changes and discomfort, which need close observation and patient counselling, of occlusal pain, muscle hyperactivity, and joint loading. This review focuses on the need to choose the right appliance, make the right fabrication and to ensure that there is a follow up to check on the progress of the patient. Further developments and multi-disciplinary work will continue to improve the effectiveness and applicability of occlusal appliances in the treatment of TMJ disorders.

Neurophysiological Insights into the Pathophysiology of Stiff-Person Spectrum Disorders.

Stiff Person Spectrum Disorders (SPSD) are classically defined by the presence of muscle stiffness, spasms and hyperactivity of the central nervous system. There is a notable correlation between neurophysiological features and the clinical hallmark of SPSD, which has greatly encouraged the use of these techniques for diagnostic purposes. Besides, electrophysiological techniques allow for a functional evaluation of the 'hyperactivity of the CNS', thus offering the opportunity to clarify the mechanisms underlying this disorder. This review delves into the current knowledge on the electrophysiological aspects of SPSD, highlighting the pivotal role of various studies in unravelling its pathophysiology. Literature review for studies on SPSD that included a neurophysiological evaluation. We first examined the abnormal neurophysiological findings of SPSD across the central nervous system, from the spinal circuit to the motor cortex. Subsequently, we discussed their pathological implications and explored how these findings can be interpreted within the framework of an immune-mediated disorder. Two primary questions remain unanswered: the localization of the primary abnormality within the central nervous system and the connection between the autoimmune basis of SPSD and its neurophysiological aspects. Addressing these questions could provide invaluable insights into SPSD etiology and targeted therapeutic strategies.

Correlation between occlusal contacts and masticatory muscle activity: A comparative study of cotton and wax normalization methods showing improved repeatability and comfort.

This study aimed to correlate occlusal marks on posterior teeth and cusp tips, recorded using an analog qualitative method, with digital evaluations of masseter and temporal muscle activity through electromyography indexes, comparing two normalization techniques (cotton and wax) using the standardized Percentage Overlap Coefficient of the Anterior Temporal muscle and Percentage Overlap Coefficient of the Masseter muscle indexes. This is a comparative cross-sectional observational study. Occlusal contact and electromyography records of the anterior temporal and masseter muscles were detected in 30 individuals with an average age of 34.9 years. During the electromyography examination, two repetitions of normalization were performed, each with maximum voluntary clenches of 5 seconds on cotton and on wax. The average electromyography amplitude was calculated from three repetitions for each material. According to the average obtained for each pair of muscles, the muscle activity index was calculated and correlated to the number of contacts, which were converted into percentages. Normalization with cotton showed a positive correlation between occlusal contacts and muscle activity (rs = 0.465, p = 0.010). The mean muscle activity index for cotton was 79.4 ± 13.9 for the masseter and 83.3 ± 9.2 for the temporal muscle, with no significant difference between the two muscles (p = 0.195). Normalization with wax showed better intra-subject repeatability with less than 5 % variation (masseter: 4.9 %, temporal: 4.2 %). There was no significant difference in muscle contraction between the different normalization materials (p = 0.902). Both normalization methods demonstrated a variation of less than 10 %, with wax being considered more comfortable by the participants, indicating occlusal and muscular adaptation to the different methods. The results showed a positive correlation between posterior occlusal contacts and masticatory muscle activity, especially with cotton normalization, suggesting that occlusal contacts significantly influence muscle activity, potentially leading to muscle fatigue or hyperactivity.

The Use of Botulinum Toxin Type A and the Occurrence of Anaphylaxis: A Descriptive Analysis of Data from the European Spontaneous Reporting System.

Botulinum toxin type A (BTA) is a protein produced by Clostridium botulinum bacteria. It is the most widely used among botulinum toxin types, and it is recommended for the treatment of many clinical conditions, including muscle hyperactivity syndromes and for esthetic indications too. BTA is generally considered safe, and the most reported adverse events (AEs) include eyelids ptosis, immunogenicity, neuromuscular disorders and hypersensitivity reactions. In addition, serious idiosyncratic AEs, such as anaphylactic shock, have been highlighted. Taking into account that BTA skin toxicity has been already investigated recently by our research group and that, in many cases, the BTA-induced skin toxicity represents a symptom of an hypersensitivity reaction, the aim of the present study was to better characterize cases of anaphylaxis occurring after intramuscular administration of BTA by analyzing Individual Case Safety Reports (ICSRs) sent to the EudraVigilance database. A total of 86 ICSRs, covering 449 Preferred Terms, reporting BTA as suspected drug and "anaphylactic reaction," "anaphylactic shock," "anaphylactoid reaction" or "anaphylactoid shock" as ADR were suitable for our analysis. The majority of patients who experienced BTA-induced anaphylaxis were female (89.5%) and mostly belonged to the age group 18-64years. The most common outcome was "recovered/resolved," while the seriousness criteria was mostly reported as "caused/prolonged hospitalization." Our results showed that anaphylactic reactions may occur after esthetic use of BTA; thus, a close monitoring before, during and after BTA intramuscular injection is highly recommended in order to prevent the occurrence of this event and ensure an appropriate management of the patients receiving this drug. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266.

Effects of Nitric Oxide on Bladder Detrusor Overactivity through the NRF2 and HIF-1α Pathways: A Rat Model Induced by Metabolic Syndrome and Ovarian Hormone Deficiency.

Metabolic syndrome (MetS) includes cardiovascular risk factors like obesity, dyslipidemia, hypertension, and glucose intolerance, which increase the risk of overactive bladder (OAB), characterized by urgency, frequency, urge incontinence, and nocturia. Both MetS and ovarian hormone deficiency (OHD) are linked to bladder overactivity. Nitric oxide (NO) is known to reduce inflammation and promote healing but its effect on bladder overactivity in MetS and OHD is unclear. This study aimed to investigate NO's impact on detrusor muscle hyperactivity in rats with MetS and OHD. Female Sprague-Dawley rats were divided into seven groups based on diet and treatments involving L-arginine (NO precursor) and L-NAME (NOS inhibitor). After 12 months on a high-fat, high-sugar diet with or without OVX, a cystometrogram and tracing analysis of voiding behavior were used to identify the symptoms of detrusor hyperactivity. The MetS with or without OHD group had a worse bladder contractile response while L-arginine ameliorated bladder contractile function. In summary, MetS with or without OHD decreased NO production, reduced angiogenesis, and enhanced oxidative stress to cause bladder overactivity, mediated through the NF-kB signaling pathway, whereas L-arginine ameliorated the symptoms of detrusor overactivity and lessened oxidative damage via the NRF2/HIF-1α signaling pathway in MetS with or without OHD-induced OAB.

Proposal of a New Therapeutic Classification in Gingival Smiles Focused on Treatment with Semi-Permanent Infiltrations.

A gummy smile, defined as excessive gingival exposure while smiling, is an esthetic and functional condition affecting an individual's quality of life. Despite its prevalence and impact, the classification and treatment of the gummy smile remain challenging in clinical practice. The problem lies in (1) the fact that the etiology of this pathology is multifactorial, and these factors sometimes go unnoticed, (2) the lack of consensus on the classification criteria, which, together, create (3) challenges in designing an optimal treatment plan for each patient. This article reviews the etiologic factors of this condition as the main basis for understanding the existing classifications of the gummy smile. It highlights the importance of muscle dynamics in the genesis and treatment of this clinical condition. We present a new, treatment-oriented classification that integrates the muscle hyperactivity present within the classification criteria and explore the implication of this interaction in the design of effective treatments. The ultimate goal of this present work is to improve the clinical understanding of the gingival smile and offer more personalized treatment strategies, through a more complete classification.

Spastic Equinovarus Foot Deformity.

Acute brain injuries are caused by a variety of etiologies, each potentially disrupting neurological function. The neurologic impairments are on a spectrum of severity often creating functional barriers to completing activities of daily living. Initial treatment starts immediately upon diagnosis and requires a multimodal approach working to prevent systemic changes. Therapy, bracing treatment, injections, and pharmacologic treatments are the mainstay of early intervention. Worsening upper motor neurological impairment associated with involuntary muscle hyperactivity can lead to a spastic equinovarus foot deformity. Spastic equinovarus foot deformities secondary to anoxic brain injuries or traumatic brain injury pose a challenging situation for orthopaedic surgeons because of associated cognitive impairment, spastic tone, and extensive soft-tissue contractures prohibiting bracing treatment. Tendon releases and transfers in combination with functional bracing treatment are initially attempted, and selective fusions are performed for severe cases. Surgical indications are primarily focused on obtaining a balanced, braceable, functional lower extremity with a plantigrade foot.

Anatomical considerations of medial eye wrinkles: Guidelines for botulinum neurotoxin injections.

Crow's feet lines in the lateral canthal region are a common concern among aging patients, initially appearing as dynamic wrinkles during facial expressions and becoming more pronounced with age. Botulinum neurotoxin temporarily paralyzes muscles by inhibiting acetylcholine release, smoothing wrinkles and enhancing skin's youthful appearance. Effective treatment requires tailored approaches considering individual anatomy and muscle activity. Recent cadaveric studies identified the tear trough muscle, emphasizing its role in infraorbital support and aging. Clinically, patients often present medial eye wrinkles after BoNT treatment for crow's feet, prompting exploration of underlying mechanisms and management strategies. Three cases demonstrated that medial BoNT injections in the orbicularis oculi muscle significantly improve medial eye wrinkles and tear trough appearance. The study underscores the importance of understanding muscle hyperactivity and anatomical variations for precise treatment. Enhanced injection techniques targeting specific areas can achieve better outcomes and minimize complications, particularly in culturally sensitive regions where facial expressions are valued. This research highlights the necessity for comprehensive anatomical knowledge and patient-specific treatment strategies to address medial eye wrinkles effectively.

Is Muscle Pain in Temporomandibular Disorder a Hyperactivity Problem? A Clinical, Thermographic, and Electromyographic Analysis.

This study aimed to report clinical data on muscle pain in temporomandibular disorders using thermography, algometry, and surface electromyography (EMG). This was done to support or rule out the hypothesis that painful muscles are always related to muscular hyperactivity. This cross-sectional, analytical study included 50 participants who underwent clinical examination and evaluation of anterior temporal muscles and bilateral masseters using thermography, algometry, and EMG. The muscles with greater pain symptoms had hyporadiation and a lower temperature compared with both contralateral muscles and muscles in the asymptomatic group. There was no muscle hyperactivity at rest on EMG analysis; however, there was a greater capacity for muscle recruitment of these symptomatic muscles after a joint decompression test with cotton rolls, suggesting hypoactivity of the affected muscles in the symptomatic patient group. Muscle pain may be related to hypoactivity of the musculature when there is neurological inhibition of the recruitment of muscle fibers, and treatment must consider these neurophysiological alterations. Level IV.

BRUXISM AS A CAUSE OF NEUROPHYSIOLOGICAL ALTERATIONS IN THE TRIGEMINAL COMPLEX

All components of the dentoalveolar structures demonstrate close interconnections, especially in the intricate relationship between the nervous and muscular aspects of the temporomandibular joint (TMJ). The muscular system relies hierarchically on the regulatory mechanisms of the nervous system. Consequently, any disruption in the interaction between these components can lead to pathology affecting the overall function of the TMJ. One of the most prevalent myogenic disorders is bruxism, impacting 6-20% of the global population. However, pronounced signs of this condition are observed in only 3-5% of individuals. Bruxism is a multifactorial disorder, and its exact etiology remains unclear. Currently, a primary factor in bruxism is considered to be a disturbance in the body's adaptive capacity to cope with stress. Psychological stress induces hyperactivity in the masticatory muscles, leading to intense clenching of the dentition. This, in turn, results in an overload of the supporting tooth tissues, pathological abrasion of the dentition, dysfunction of the temporomandibular joint (TMJ), and the emergence of general clinical symptoms such as headaches, orofacial issues, and neurological symptoms. The pathophysiological foundation of bruxism lies in the excessive strain on the masticatory muscles, causing ischemia and inflammation in the muscle fibers. The inflammatory process in these fibers triggers a persistent excitation of afferent nerve fibers of type C, giving rise to a dull, aching pain. As bruxism is a chronic condition, there is a physiological restructuring of nerve fibers. This involves the initial peripheral and subsequent central sensitization of C-type nerve fibers, resulting in an inappropriate response of the body to physiological stimuli. For instance, the nervous system begins to interpret minor stimuli as painful (hyperalgesia). Currently, no treatment methods completely eliminate bruxism. Modern treatment approaches involve the use of intraoral dental appliances, pharmacotherapy (with muscle relaxants such as botulinum toxin type A and drugs from the benzodiazepine group), and psychotherapy courses aims to teach patients sleep hygiene, self-control, and the elimination of detrimental habits, including clenching the dentition as a response to psychological stress.

The role of Function Generating Bite (FGB) devices on changes of chewing patterns and muscle activity in deep bite malocclusion

Background: A malocclusion known as a deep bite occurs when the mandibular incisors are covered by the maxillary incisors by more than the normal value of 30-40% or 2-4 mm. Deep bite is a type of malocclusion that is often found in children and adults, with a prevalence of 23.83% in the Asian population. Patients with a deep bite have a restricted masticatory pattern and have excess function of the mastication muscles. Active muscle training should be recommended to improve jaw bone morphology. Objective: This review aims to explain the role of the Function Generating Bite (FGB) device on changes in masticatory patterns and muscle activity in deep bite malocclusion. Methods: The search for literature reviews was conducted using the ScienceDirect, PubMed, and Google Scholar databases. The selected literature was published between 2010 - 2023 in English and Indonesian. Discussion: Treatment of deep bite in each patient varies depending on the etiology of the malocclusion. One of the functional therapies that can be used to correct malocclusion is FGB. The FGB device has an anchorage system on the muscles, which can regulate and exert pressure intermittently, so as to correct dental malocclusion and functional imbalance. Conclusion: Treatment with FGB has been shown to significantly improve the lateral component of the masticatory pattern and reduce muscle hyperactivity in deep bite patients during mastication.

Beyond neuromuscular activity: botulinum toxin type A exerts direct central action on spinal control of movement

Overt muscle activity and impaired spinal locomotor control hampering coordinated movement is a hallmark of spasticity and movement disorders like dystonia. While botulinum toxin A (BoNT-A) standard therapy alleviates mentioned symptoms presumably due to its peripheral neuromuscular actions alone, the aim of present study was to examine for the first time the toxin's trans-synaptic activity within central circuits that govern the skilled movement. The rat hindlimb motor pools were targeted by BoNT-A intrasciatic bilateral injection (2 U per nerve), while its trans-synaptic action on premotor inputs was blocked by intrathecal BoNT-A–neutralising antitoxin (5 i.u.). Effects of BoNT-A on coordinated and high intensity motor tasks (rotarod, beamwalk swimming), and localised muscle weakness (digit abduction, gait ability) were followed until their substantial recovery by day 56 post BoNT-A. Later, (day 62–77) the BoNT-A effects were examined in unilateral calf muscle spasm evoked by tetanus toxin (TeNT, 1.5 ng). In comparison to peripheral effect alone, combined peripheral and central trans-synaptic BoNT-A action induced a more prominent and longer impairment of different motor tasks, as well as the localised muscle weakness. After near-complete recovery of motor functions, the BoNT-A maintained the ability to reduce the experimental calf spasm evoked by tetanus toxin (TeNT 1.5 ng, day 62) without altering the monosynaptic reflex excitability. These results indicate that, in addition to muscle terminals, BoNT-A-mediated control of hyperactive muscle activity in movement disorders and spasticity may involve the spinal premotor inputs and central circuits participating in the skilled locomotor performance.

Skin Toxicities Associated with Botulin Toxin Injection for Aesthetic Procedures: Data from the European Spontaneous Reporting System.

Botulinum toxin is a protein deriving from the bacteria Clostridium botulinum and it is widely used for the treatment of a variety of muscle hyperactivity syndromes and for cosmetic indications. Having a long-lasting effect, Botulinum toxin type A (BTA) is one of the most botulin toxin products used. Even if BTA has shown benefits in reducing the vertical lines between the eyebrows, Adverse Drug Reactions (ADRs) have been experienced as well, of which the most common ones are headache and drooping eyelids. In addition, since other local and systemic risks have been identified, a non-interventional post-authorization safety study (PASS) has been started. The aim of the present study was to report cases of skin toxicity associated with this drug, considering Individual Case Safety Reports (ICSRs) existing on the Eudravigilance website. Among 1464 ICSRs sent to the EV database, 718 ICSRs, including 5154 PTs, reported BTA as a suspected drug associated with cutaneous toxicity. The majority of patients experiencing BTA-induced skin toxicity were female (92.1%) belonging mostly to the age group of 18-64 years. The most serious criteria, when reported, were "Other Medically Important Condition" and "Caused/prolonged hospitalization", although the outcome was mainly reported as "Unknown". The most reported PTs, related to skin disorders, were: "Erythema", "Rash", "Pruritus", "Urticaria", "Swelling face", "Brow ptosis", "Eyelid ptosis", "Injection site pain", and "Angioedema". Considering that in most ICSRs, ADRs related to skin disorders were symptoms of hypersensitivity reactions which in some conditions could be life-threatening, further studies are required to better define the safety profile of BTA used for aesthetic procedures.

Adverse effect of botulinum toxin-A injections on mandibular bone: A systematic review and meta-analysis.

Botulinum toxin-A (BTX) is a potent neurotoxin that is emerging in the scope of dental practice for its ability to temporarily paralyse musculature and reduce hyperfunction. This may be desirable in diseases/disorders associated with hyperactive muscles such as the muscles of mastication, most implicated in painful temporomandibular disorders (TMDs). The use of BTX extends beyond its indications with off-label use in TMD's and other conditions, while potential adverse effects remain understudied. BTX is well-established hindlimb paralysis model in animals leading to significant bone loss with underlying mechanisms remaining unclear. The objective of this study is to systematically review the literature for articles investigating changes in mandibular bone following BTX injections and meta-analyse available data on reported bone outcomes. Comprehensive search of Medline, Embase and Web of Science retrieved 934 articles. Following the screening process, 36 articles in animals and humans were included for quantitative synthesis. Articles in human individuals (6) and three different animal species (14) presented mandibular bone outcomes that were included in the meta-analysis. The masseter and temporalis muscles were frequently injected across all species. In humans, we observe a decrease of about 6% in cortical thickness of mandibular regions following BTX injection with no evident changes in either volume or density of bone structures. In animals, bone loss in the condylar region is significantly high in both cortical and trabecular compartments. Our analysis supports the concept of BTX-induced bone-loss model in animal mandibles. Further, bone loss might be confined to the cortical compartments in humans. Most studies did not address the reality of repeated injections and excessive dosing, which occur due to the reversible action of BTX. More rigorous trials are needed to draw a full picture of potential long-term adverse effects on bone.

Fractal analysis of the effects on mandibular bone of botulinum toxin therapy of the masseter muscle in patients with bruxism

We examined changes in the mandibular angle, ramus, and condylar neck of patients with bruxism after botulinum toxin-A (BTX-A) injection into the masseter muscle as calculated with fractal analysis (FA) on panoramic radiographs (PRs). We examined the PRs of 3 groups of 22 patients each (n=66) obtained upon presentation and 6 months later. One group included healthy controls without bruxism, one group included patients with untreated bruxism, and one group included patients with bruxism who had undergone BTX-A injection into the masseter muscle. We performed FA of the bilateral angle, ramus, and condylar neck of the PRs to calculate fractal dimension (FD). The FD values of the angle on the second PRs of the untreated bruxism group were significantly higher than those of the other groups (P = .026), specifically when compared to the BTX-A injection group (P = .017). The FD values in the angle and ramus of the bruxism group were significantly higher on the second PRs (P ≤..005)) Conversely, the FD values in the angle of the BTX-A injection group were significantly lower on the second PR (P = .039). Masseter muscle hyperactivity due to bruxism increases bone density in masseter muscle attachment regions. BTX-A injection restricts muscle activity, thereby chnging bone structure and decreasing FD.

Muscle Ultrasound in Clinical Neurology: Diagnostic Uses and Guidance of Botulinum Toxin Injection

Muscle ultrasound (MUS) is increasingly used by neurologists, neuropediatricians, neurosurgeons, specialized radiologists and anaesthesiologists for the imaging-supported diagnosis of neuromuscular disorders. Especially, MUS is highly sensitive in detecting fasciculations in motor neuron diseases, and in revealing intensive care unit acquired weakness. Hereditary and inflammatory myopathies are associated with distinct patters of echo-intensity changes of affected muscles. Moreover, MUS can be used for guiding needle biopsy of muscle lesions, and for targeting intramuscular botulinum neurotoxin (BoNT) injection in neurological disorders with muscle hyperactivity. MUS-guidance of BoNT injection is especially recommendable in complex cervical dystonia, in task-related hand dystonia (writer’s cramp, musician dystonia), and in children and adolescents with cerebral palsy. Modern ultrasound technologies such as sono-elastography, tissue Doppler, and high-definition microvasculature imaging allow for novel diagnostic and therapeutic uses. Recently, an international expert group reported consensus guidelines for neuromuscular ultrasound training. The present review provides a concise overview of well-established diagnostic and therapeutic applications of MUS in clinical neurology, with specific focus at MUS for targeting intramuscular BoNT injections.

Botulinum toxin A and neuropathic pain: An update

Botulinum toxin type A is a widely used neurotoxin for the treatment of muscle hyperactivity such as dystonia and spasticity. Several clinical trials have also reported an efficacy of subcutaneous or intradermal administrations of botulinum toxin A on various neuropathic pain conditions including idiopathic trigeminal neuralgia and found that specific sensory phenotypes were predictors of the response. This narrative review summarizes the potential mechanisms of action, efficacy and safety of botulinum toxin A in neuropathic pain as well as its place in the therapeutic algorithm of neuropathic pain.

Neuromodulator Injection for Gummy Smile.

Neuromodulators have become a treatment of choice for the management of excess gingival show, or "gummy smile." There have been many proposed algorithms for the optimal placement and dosage of neuromodulator to inject in these locations. The authors aim to clarify these points and provide surgeons with a reliable way to manage the gummy smile that results from hyperactive muscles of the midface.

Axial Postural Abnormalities in Parkinsonism: Gaps in Predictors, Pathophysiology, and Management.

Axial Postural Abnormalities in Parkinsonism: Gaps in Predictors, Pathophysiology, and Management.

Electromyographic analysis of the stomatognathic system of children with Molar-incisor hypomineralization.

Molar-incisor hypomineralization (MIH) is a qualitative defect of dental enamel that affects one or more permanent first molars, with or without involvement of the incisor teeth. This condition leads to challenges to dental care and treatment planning. Based on the hypothesis that children who have MIH possibly present alterations in postural and masticatory activities and considering the absence of studies investigating these parameters, the present study evaluated the functionality of the stomatognathic system considering the mentioned aspects. The comparison of individuals with (MIHG; n = 32) and without MIH (CG; n = 32) was evaluated by electromyographic activity of the masseter and temporal muscles (right and left), as well as evaluation of the masticatory cycles during habitual mastication. MIHG showed muscle hyperactivity in postural and dynamic conditions compared to the CG; higher electromyographic values for MIHG when compared to CG in the following postural conditions: at rest for the right temporal (p = 0.00) and left temporal muscles (p = 0.03); in the protrusion to the right temporal muscle (p = 0.02); in the right laterality for the right masseter (p = 0.00) and left temporal muscles (p = 0.01); in the left laterality for the right masseter (p = 0.03) and left temporal (p = 0.04) muscles. In dynamic conditions with consistent food, significance was observed for the left temporal (p = 0.01); and with soft food for the right (p = 0.01) and left temporal muscles (p = 0.04). Children with MIH seem to have impaired functionality of the stomatognathic system. Children with MIH have alterations in the stomatognathic system.