Digastric Research Articles

Nrf2 Deficiency Exacerbates the Decline in Swallowing and Respiratory Muscle Mass and Function in Mice with Aspiration Pneumonia

Aspiration pneumonia exacerbates swallowing and respiratory muscle atrophy. It induces respiratory muscle atrophy through three steps: proinflammatory cytokine production, caspase-3 and calpain, and then ubiquitin–proteasome activations. In addition, autophagy induces swallowing muscle atrophy. Nrf2 is the central detoxifying and antioxidant gene whose function in aspiration pneumonia is unclear. We explored the role of Nrf2 in aspiration pneumonia by examining swallowing and respiratory muscle mass and function using wild-type and Nrf2-knockout mice. Pepsin and lipopolysaccharide aspiration challenges caused aspiration pneumonia. The swallowing (digastric muscles) and respiratory (diaphragm) muscles were isolated. Quantitative RT-PCR and Western blotting were used to assess their proteolysis cascade. Pathological and videofluoroscopic examinations evaluated atrophy and swallowing function, respectively. Nrf2-knockouts showed exacerbated aspiration pneumonia compared with wild-types. Nrf2-knockouts exhibited more persistent and intense proinflammatory cytokine elevation than wild-types. In both mice, the challenge activated calpains and caspase-3 in the diaphragm but not in the digastric muscles. The digastric muscles showed extended autophagy activation in Nrf2-knockouts compared to wild-types. The diaphragms exhibited autophagy activation only in Nrf2-knockouts. Nrf2-knockouts showed worsened muscle atrophies and swallowing function compared with wild-types. Thus, activation of Nrf2 may alleviate inflammation, muscle atrophy, and function in aspiration pneumonia, a major health problem for the aging population, and may become a therapeutic target.

The importance of muscle activation on the interpretation of muscle mechanical performance.

The work loop technique was developed to assess muscle performance during cyclical length changes with phasic activation, simulating the in vivo conditions of many muscles, particularly during locomotion. To estimate muscle function in vivo, the standard approach involves subjecting a muscle to length trajectories and activation timings derived from in vivo measurements, whilst simultaneously measuring force. However, the stimulation paradigm typically used, supramaximal, 'square-wave' stimulation, does not accurately reflect the graded intensity of activation observed in vivo. While the importance of the timing and duration of stimulation within the cycle on estimates of muscle performance has long been established, the importance of graded muscle activation has not been investigated. In this study, we investigated how the activation pattern affects muscle performance by comparing square-wave, supramaximal activation with a graded in vivo activation pattern. First, we used in vivo electromyography-derived activation patterns and fibre strains from the rabbit digastric muscle during mastication and replayed them in situ. Second, we used Hill-type musculoskeletal model-derived activation patterns and fibre strains in a trotting mouse, replayed ex vivo in the soleus (SOL) and extensor digitorum longus (EDL) muscles. In the rabbit digastric muscle, square-wave activation led to an 8-fold higher estimate of net power, compared with the in vivo graded activation pattern. Similarly, in the mouse SOL and EDL, supramaximal, square-wave activation resulted in significantly greater positive and negative muscle work. These findings highlight that realistic interpretations of in vivo muscle function rely upon more accurate representations of muscle activation intensity.

Variation and Arrangement of the Digastric Muscle in a Chinese Population.

The digastric, a prominent anatomic feature of the head and neck, exhibits clear ethnographic differences in the incidence of variation in its anterior belly (AB) and the relationship of its intermediate tendon (IT) to the stylohyoid (SH). There is a limited amount of information available regarding the digastric in the Chinese population, with most descriptions being individual cases. The present study aims to investigate the variability of AB, elucidate the relationship between IT and SH, and further address the arrangement of individual digastric muscles according to the type of AB and posterior belly (PB) of the digastric, as well as IT, in a Chinese population. Anatomic dissections of the head and neck were carried out bilaterally after student-performed neck dissections during a topographic anatomy course. The types of AB, PB, and IT were recorded to characterize and classify each digastric muscle. The incidence of AB variation was 21.05%. IT type Ⅰ and IT type Ⅱ accounted for 31.25% and 68.75%, respectively. The gross anatomy of the digastric was dominated by the arrangement of AB type I, IT type Ⅱ, and PB type I (63.16%). In addition, 2 rare AB variations were identified. To the best of our knowledge, this is the first report describing individual digastric arrangements and anatomically defining the normal digastric arrangement in the Chinese population. Careful consideration of the variant and anomaly of the digastric is critical for both surgeons and radiologists to provide accurate diagnostic and therapeutic procedures.

Do We Know the Long-Term Effects of the Most Popular Traditional Swallow Maneuvers on the Submental Muscles?

Various trainings focus on the submental muscles (SMs) for dysphagia rehabilitation because of their importance for swallowing safety and efficiency. According to the current literature, swallow-specific tasks may be optimal exercises for dysphagia. The effortful swallow (ES) and the Masako maneuver (MM) are the most commonly used swallow-specific tasks in the clinical settings for dysphagia for years, but long-term effects for these trainings is insufficient. This study aims to investigate and compare the effects of ES and MM on SM activity, strength and thickness. Thirty-seven healthy adults were randomised to ES, MM and control groups, and ES and MM groups completed 6 weeks of swallowing training. Participants in both training groups performed a total of 120 swallows in each session, while control group did not participate in any swallowing training. Surface electromyography was used to evaluate SM activity, digital dynamometer for SM strength and ultrasonography for SM thickness. Both trainings did not change SM activity (p > 0.05), but increased SM strength (p < 0.05). MM increased the thickness of all SM (p < 0.05), and ES increased the thickness of mylohyoid (right, left) and digastric muscle (right) (p < 0.05), and there was no change in all evaluation parameters in the control group (p > 0.05). Also, trainings were not superior to each other in any parameter (p > 0.05). The results of this study provided new evidence to the literature to show that ES and MM trainings are effective for improving SM strength and thickness. Considering that SM is important in terms of swallowing safety and effectiveness, it is thought that both trainings may be promising by increasing the strength and mass of SM, especially in individuals with reduced SM strength and mass.

Evaluation of masticatory muscles in patients with different sagittal direction skeletal anomalies by ultrasonography and ultrasonographic elastography.

The aim of this study was to evaluated the masseter, anterior digastric and geniohyoid muscles of individuals with similar growth and developmental periods but different sagittal skeletal malocclusions using ultrasonography and ultrasonographic elastography and to make interclass assessments. In this study, ultrasonography and ultrasonographic elastography records of 30 Class I individuals (17 females, 13 males), 30 Class II individuals (14 females, 16 males), and 27 Class III individuals (12 females, 15 males) in the normodivergent and growth development periodwere used. The masseter, anterior digastric, and geniohyoid muscles of individualswere examinedusing ultrasonography and ultrasonographic elastography, andcomparisons were madebetween the classes. Statistical analysis was accomplished by Mann Whitney U, One-way ANOVA, Kruskal Wallis H tests. Interclass differences were foundin ultrasonography and elastography measurements of the masseter muscle. However, no differences were observed in ultrasonography measurements of the auxiliary masticatory muscles, whereas differences were seen only in the geniohyoid muscle in elastography measurements among the classes (p<0.05). Individuals with different sagittal skeletal malocclusions during growth and development exhibited similar muscle sizes and elasticities, approximately close to each other.

Incidental Finding of Double Posterior Belly of Digastric Muscle in Head and Neck Cancer Patient.

The digastric muscles have important roles in swallowing, chewing, speech, and landmark identification during neck dissection. The posterior belly of the digastric muscle (PBDM) is often useful for defining boundaries in surgical neck dissection as it contributes to the carotid, submandibular, and submental triangles. The cadaveric prevalence rate of anatomic variations in the digastrics has been reported to be 31.4% of the population with most occurring in relation to the anterior belly of the digastric muscle (ABDM). Few reports describe variations in the PBDM. While anatomic variants of the digastric muscles do not present with clinical manifestations, they can be mistaken as neck masses and contribute to intraoperative complications. We present a case report of a 73-year-old male with a past medical history significant for Parkinson's Disease, who was incidentally found to have a duplicate PBDM intraoperatively while receiving surgical management of a left buccal squamous cell cancer. Nine months prior to surgery, the patient began experiencing trismus and some mild dysphagia that were eventually worked up to reveal left buccal squamous cell carcinoma (SCC). Prior to this, the patient did not have clinical symptoms demonstrating dysfunction that could be related to or indicative of this anatomical abnormality preceding symptoms related to left buccal SCC growth. The procedure included a wide local excision, left modified radical neck dissection and left submental artery island flap with suprahyoid neck dissection. The superior duplicate PBDM was found to be overlying the stylohyoid muscle. It is important for surgeons operating in the head and neck to be aware of the possibility of this rare variation, and to be conscientious when it is identified so that it does not prohibit or limit a thorough dissection of the neck structures where oncologic clearance is paramount.

The other face of facioscapulohumeral muscular dystrophy: Exploring orofacial weakness using muscle ultrasound.

One of the most distinct clinical features of facioscapulohumeral muscular dystrophy (FSHD) is facial weakness. It leads to diminished facial expression and functional impairments. Despite its clinical relevance, little else is known about orofacial muscle involvement. We therefore evaluated orofacial muscle involvement in a sizeable cohort of FSHD participants with muscle ultrasound. Muscle ultrasound images of the following orofacial muscles were scored visually and quantitatively: depressor anguli oris (DAO), orbicularis oris (OO), buccinator, temporalis, masseter, digastric, zygomaticus major and minor bilaterally, and the geniohyoid. Reliability analyses of both visual and quantitative evaluations were performed. Ultrasound results were correlated with other measures: the FSHD clinical score, facial weakness score, and facial function scale. We included 107 FSHD participants (male 54%; age 52 ± 14 years), of whom 92% showed signs of facial weakness. The reliability of visual ultrasound analysis varied widely (κ 0.0-1.0). Quantitative ultrasound reliability was high (intraclass correlation analysis ≥ 0.96). The DAO, buccinator, OO, temporalis, and zygomaticus minor muscles were affected most often (15%-39%). The digastric, geniohyoid, zygomaticus major, and masseter muscles were least often affected (<5%). The ultrasound compound score correlated weakly to moderately with other outcome measures used (ρ = 0.3-0.7). This study adds to the understanding of orofacial weakness in FSHD, confirming the involvement of the muscles of facial expression in FSHD using ultrasound. We showed that orofacial muscle ultrasound is feasible and reliable when quantitatively assessed. Future studies should evaluate orofacial muscle ultrasound longitudinally, alongside clinical and patient-reported facial weakness outcome measures, to assess their potential as outcome measures.

The functional role of the rabbit digastric muscle during mastication.

Muscle spindle abundance is highly variable in vertebrates, but the functional determinants of this variation are unclear. Recent work has shown that human leg muscles with the lowest abundance of muscle spindles primarily function to lengthen and absorb energy, while muscles with a greater spindle abundance perform active-stretch-shorten cycles with no net work, suggesting that muscle spindle abundance may be underpinned by muscle function. Compared with other mammalian muscles, the digastric muscle contains the lowest abundance of muscle spindles and, therefore, might be expected to generate substantial negative work. However, it is widely hypothesised that as a jaw-opener (anatomically) the digastric muscle would primarily function to depress the jaw, and consequently do positive work. Through a combination of X-ray reconstruction of moving morphology (XROMM), electromyography and fluoromicrometry, we characterised the 3D kinematics of the jaw and digastric muscle during feeding in rabbits. Subsequently, the work loop technique was used to simulate in vivo muscle behaviour in situ, enabling muscle force to be quantified in relation to muscle strain and hence determine the muscle's function during mastication. When functioning on either the working or balancing side, the digastric muscle generates a large amount of positive work during jaw opening, and a large amount of negative work during jaw closing, on average producing a relatively small amount of net negative work. Our data therefore further support the hypothesis that muscle spindle abundance is linked to muscle function; specifically, muscles that absorb a relatively large amount of negative work have a low spindle abundance.

Comparison of rhythmic jaw muscle activities induced by electrical stimulations of the corticobulbar tract during rapid eye movement sleep with those during wakefulness and non-rapid eye movement sleep in freely moving Guinea pigs

ObjectiveRhythmic jaw muscle activities (RJMAs) occur during rapid eye movement (REM) sleep in humans and animals even though motoneurons are inhibited. The present study compared the characteristics of jaw muscle activities induced by electrical microstimulations of the corticobulbar tract (CT) during REM sleep with those during wakefulness and non-REM sleep. MethodsEleven guinea pigs were surgically prepared for polygraphic recordings with the implantation of a stimulating electrode. Long- and short-train repetitive electrical microstimulations were applied to the CT under freely moving conditions. The response rate, latency, burst amplitude, and cycle length in the digastric muscle were calculated and cortical and cardiac activities were quantified. ResultsLong-train microstimulations induced RJMAs in the digastric muscle followed by masseter muscle activity during wakefulness and non-REM sleep and only induced rhythmic digastric muscle activity during REM sleep. The response rate of RJMAs and the burst amplitude of digastric muscles were significantly lower during REM sleep than during wakefulness and non-REM sleep. However, response latency did not significantly differ between REM sleep and wakefulness. Transient cortical and cardiac changes were associated with RJMAs induced during non-REM sleep, but not during REM sleep. Short-train microstimulations induced a short-latency digastric response, the amplitude of which was significantly lower during REM sleep than during non-REM sleep and wakefulness. ConclusionsThese results suggest that the masticatory CPG was activated by electrical CT stimulations independently of the motoneuron inhibitory system during REM sleep.

Effect of passive jaw opening on the electromyographic activity of the temporalis, masseter, digastric, and infrahyoid muscles in healthy adults

ABSTRACT Objective To investigate the surface electromyography (EMG) activity of the temporalis, masseter, digastric, and infrahyoid muscles during passive jaw opening in healthy adults. Methods The EMG activity of the masseter, temporalis, digastric anterior belly, and infrahyoid muscles on the right side was recorded during the four jaw-opening tasks: active opening to 20 mm (AO20); active opening to 40 mm (AO40); passive opening to 40 mm with a rubber mouth prop on the right posterior teeth (POR40); and passive opening to 40 mm with a mouth prop on the left posterior teeth (POL40). Results The EMG amplitude of the digastric anterior belly and infrahyoid muscles in either POL40 or POR40 was significantly less than that in AO20 or AO40, respectively. Conclusion Passive jaw opening reduces the EMG activity of the digastric and infrahyoid muscles significantly and could help reduce the load on these muscles during prolonged mouth-opening conditions.

Supra Digastric Muscles Approach for Styloid Process Resection

Abstract Objective Eagle syndrome, categorized into classical styloid syndrome and stylocarotid syndrome, presents challenges in determining the optimal surgical approach for styloid process (SP) resection. While intraoral resection suffices for many cases, especially classical styloid syndrome cases, stylocarotid syndrome sometimes demands a transcervical resection due to its intricate spatial dynamics. We describe a step-by-step procedure for modified transcervical resection using a supra digastric muscle approach (SDMA) for SP, emphasizing anatomical precision. Methods and Results The approach is described in the case of a 60-year-old woman with acute cerebral infarction from left internal carotid artery dissection. Employing carotid artery stenting, we identified SP elongation as the underlying cause requiring transcervical resection to avoid stent damage. The operative procedure involves meticulous dissection via a linear skin incision, exposing key anatomical structures such as the sternocleidomastoid muscles, digastric muscles (DMs), and the transverse process of the atlas. Surgical corridor via supra DM space is an invaluable technique, offering the shortest distance to the SP without compromising nearby nerves. The SP, covered by muscles and ligaments, is carefully stripped off, enabling its amputation near the temporal skull base. The entire procedure is performed under a microscope to preserve surrounding nerves. Conclusion The SDMA is a simple and safe technique, offering enhanced anatomical precision and minimizing the risk of nerve damage.

Physiological analyses of swallowing changes due to chronic obstructive pulmonary disease in anesthetized male rats.

Chronic obstructive pulmonary disease (COPD) was previously known as chronic bronchitis and emphysema. It has various main symptoms, such as dyspnea, chronic cough, and sputum, and is often accompanied by dysphagia. Although many published clinical reports have described COPD-related dysphagia, the physiological mechanisms underlying swallowing changes due to COPD remain unclear. Therefore, we analyzed how COPD affects the swallowing reflex using COPD model rats. We performed an electrophysiological study of respiration and swallowing using COPD model induced by intratracheal administration of porcine pancreatic elastase and lipopolysaccharide in Sprague-Dawley male rats. To identify the respiration and swallowing responses, electromyographic activity was recorded from the diaphragm, digastric (Dig), and thyrohyoid (TH) muscles. We confirmed COPD using micro-computed tomography analysis and hematoxylin and eosin staining of the lungs. The duty cycle was defined as the ratio of the inspiration duration to the total respiratory duration. In COPD model rats, the duty cycle was significantly higher than that in control rats. The frequency of the swallowing reflex evoked by electrical stimulation of the superior laryngeal nerve during the inspiration phase was higher in COPD model rats than in control rats. Furthermore, long-term COPD altered Dig and TH muscle activity without pathological muscle change. Our results suggest that COPD increases the frequency of swallowing initiation during the inspiration phase. Furthermore, long-term COPD affects swallowing-related muscle activity without pathological muscle changes. These physiological changes may increase the risk of developing dysphagia. Further studies are necessary to clarify the mechanisms contributing to the functional changes in respiration and swallowing in COPD.

Functional involvement of the sternohyoid muscle during breathing and swallowing in rats.

The sternohyoid muscle depresses the hyoid bone, but it is unclear whether the muscle contributes to respiratory and swallowing mechanisms. This study aimed to clarify whether the sternohyoid muscle participates in the respiration and swallowing reflex and how the activity is modulated in two conditions: with airway stenosis and with a fixed sternohyoid muscle length. Electromyographic activity in the sternohyoid, digastric, thyrohyoid, and diaphragm muscles was recorded in anesthetized rats. The sternohyoid muscle activity was observed in the inspiratory phase and during swallowing, and was well coordinated with digastric and thyrohyoid muscle activity. With airway stenosis, the respiratory activity per respiratory cycle was facilitated in all assessed muscles but the facilitation of activity per second occurred only in the digastric, thyrohyoid, and sternohyoid muscles. With airway stenosis, the swallowing activity was facilitated only in the digastric muscle but not in the thyrohyoid and sternohyoid muscles. Swallowing activity was not observed in the sternohyoid muscle in the condition with the sternohyoid muscle length fixed, although increased inspiratory activity remained. The current results suggest that 1) the sternohyoid muscle is slightly activated in the inspiratory phase, 2) the effect of airway stenosis on respiratory function may differ between the upper airway muscles and diaphragm, and 3) swallowing activity in the sternohyoid muscle is not dominantly controlled by the swallowing central pattern generator but instead occurs as a myotatic reflex.NEW & NOTEWORTHY We found that the sternohyoid muscle was activated in the inspiratory phase. However, increased airway resistance had different effects on the extrathoracic muscles than on the diaphragm. The swallowing activity of the sternohyoid disappeared when the muscle length was fixed. These findings suggest that the sternohyoid muscle may be activated not by the swallowing central pattern generator but as a myotatic reflex.

African wild dog (Lycaon pictus) masticatory apparatus and oral cavity morphology.

African wild dogs (Lycaon pictus) are unique among canids in their specialized hunting strategies and social organization. Unlike other, more omnivorous canids, L. pictus is a hypercarnivore that consumes almost exclusively meat, particularly prey larger than its body size, which it hunts through cooperative, exhaustive predation tactics. Its bite force is also among the highest reported for carnivorans. Here, we dissected an adult male L. pictus specimen and conducted diffusion iodine contrast-enhanced computed tomography (diceCT) scans to evaluate and describe its masticatory and oral cavity musculature. Muscles of mastication in L. pictus are separated by deep layers of thick intermuscular fascia and deep insertions. The superficial surface of m. masseter is entirely covered by an extremely thick masseteric fascia. Deep to m. masseter pars reflexa and superficialis are additional bellies, m. masseter pars profunda and zygomaticomandibularis. Musculus temporalis in L. pictus, divides into suprazygomatic, superficial, and deep bellies separated by a deep layer of thick intermuscular fascia, and it inserts along the entire rostral margin of the mandibular ramus. Musculus digastricus appears to comprise a single, large fusiform belly which appears to receive its innervation exclusively from CN V3 (nervus mandibularis, division of nervus trigeminus). Musculus pterygoideus medialis and lateralis are each composed of a single, deep belly. However, despite its great bite force, the jaw adductor muscle mass in L. pictus is not increased for its body size over other canid taxa. This finding suggests there are other architectural adaptations to hypercarnivory beyond increased muscle volume (e.g., pennation angle, greater strength, optimization of lever arms for mechanical advantage).

Effect of home-based tongue-strengthening exercise using a portable tool on oropharyngeal muscles in older adults with sarcopenic dysphagia: A randomised controlled study.

Tongue-strengthening exercises may be used at home to strengthen swallowing-related oropharyngeal muscles in community-dwelling older adults with sarcopenic dysphagia; however, evidence of their effectiveness remains unclear. This study aimed to investigate the effects of a home-based tongue-strengthening exercise (hTSE) using portable tool on swallowing-related oropharyngeal muscles in community-dwelling older adults with sarcopenic dysphagia. Forth community-dwelling older adults with sarcopenic dysphagia were enrolled in the study. The participants were randomly assigned to the experimental and control groups. 1-Repetition Maximum (1-RM) of tongue muscle was measured in the experimental group using the Iowa Oral Performance Instrument, and hTSE was performed using a portable tool with an intensity corresponding to approximately 70%-80% of the range based on the 1-RM value (90 times/day, 5 days/week, for 8 weeks). The control group did not perform any tongue exercises. The primary outcome measures were tongue strength and thickness. The secondary outcome measure was suprahyoid muscle strength (digastric and mylohyoid muscles). The experimental group showed significantly greater increases in suprahyoid muscle (mylohyoid and digastric) thickness (p = .01 and .011, d = 1.0 and .55), as well as tongue strength and thickness (p < .001 and .029, d = 2.2 and .6) than the control group. This study confirmed that hTSE using a portable tool is effective in increasing swallowing-related oropharyngeal muscle activity in older adults with sarcopenic dysphagia. Therefore, hTSE is recommended as an inexpensive, safe, and easy-to-use therapy for sarcopenic dysphagia in older adults.

Reliability of ultrasound real‐time tissue elastography in evaluating swallowing‐related muscle elasticity and effects of swallowing exercises

AbstractIntroductionEvaluating swallowing function, essential for eating, is necessary to detect functional decline, enabling the provision of effective interventions. There is a growing demand for a simple method for evaluating swallowing dynamics. Conventional methods of evaluating swallowing function, such as the fibreoptic endoscopic evaluation of swallowing or videofluoroscopic swallowing study, are highly invasive and require specific equipment only available at certain hospitals, making it difficult for older adults to receive convenient evaluations. Therefore, we used ultrasound real‐time tissue elastography (RTE), a low‐invasive method, to evaluate tissue elasticity as the strain ratio (SR). This study primarily aimed to verify whether RTE can evaluate the elasticity of swallowing‐related muscles (SRMs) and determine intra‐ and inter‐rater reliabilities. The secondary aim was to investigate the effect of swallowing exercises, such as head‐lifting exercises, on SRM elasticity.MethodsIntraclass correlation coefficients for SR were calculated using ultrasound B‐mode images to determine the reliability of SRM elasticity. SRs before and after the Shaker swallowing exercise were compared using the Wilcoxon signed‐rank test.ResultsHigh ICCs for intra‐ and inter‐rater reliabilities were obtained for all targeted SRMs. SR after the Shaker exercise indicated a significant decrease in the geniohyoid muscle and both sides of the digastric muscles, whereas both sides of the masseter exhibited no changes.ConclusionRTE can be used as a novel simple and non‐invasive method for assessing and capturing differences in SRs of SRMs after light exercise. Further research may develop a relationship with swallowing function in patients with dysphagia or older individuals.

Comparison between botulinum toxin type A injection on masseter muscle only and additional injection on anterior belly of digastric muscle in sleep bruxism patients: A clinical trial.

This study aims to evaluate the effects on bite force and muscle thickness of the botulinum toxin (BoNT) injection for patients with sleep bruxism (SB) by comparing injections into the masseter muscle only and both the masseter and the anterior belly of the digastric muscle (ABDM) in a clinical trial. Twelve SB patients received BoNT-A injections using US-guided techniques into the masseter muscle only (Group A), while the remaining 12 SB patients received injections into both the masseter and ABDM (Group B). Bite force and muscle thickness were measured before injection, as well as 1 and 2 months after injection. The bite force and masseter muscle thickness decreased in both Group A and Group B before injection, and at 1 and 2 months after injection. However, there was no significant difference (p > .05, repeated measures analysis of variance) between the two groups, and there was also no significant difference in ABDM thickness (p > .05, repeated measures analysis of variance). This study is the first to assess the short-term effects of BoNT injected into ABDM for SB control. Results show no influence on SB reduction, suggesting the need for further research on BoNT's effectiveness in controlling intense ABDM contractions during sleep and assessing suprahyoid muscle potential impact on rhythmic masticatory muscle activity occurrence.

Navigating the void: outcomes and adaptations during parotid surgery in the absence of posterior belly of digastric muscle.

It is well known that the digastric posterior belly is one of the essential landmarks for facial nerve identification during parotid surgery. While there were multiple reports about variations of the digastric anterior belly, only a few anatomical variations of the posterior belly of the digastric muscle have been described.In this article, we describe an anatomical variation of the posterior belly of digastric muscle found during superficial parotidectomy of a patient with pleomorphic adenoma. This anatomical variation also led to an anatomical variation in the position of the facial nerve.To our knowledge, this is the first report of an absent posterior belly of digastric muscle found during live parotid surgery. The knowledge of current anatomical variation may help to avoid facial nerve injury during parotid surgery and preserve the function of muscles of facial expression.

Sihler's staining of the anterior belly of digastric muscle for botulinum toxin injection.

The anterior belly of the digastric muscle (ABDM) is the target of botulinum toxin injection; however, anatomical considerations related to the injection point are absent. This study used Sihler's staining to analyze the intramuscular nerve distribution of ABDM to identify the most effective botulinum toxin injection points. We used 12 specimens from 6 embalmed cadavers in this study. The specimens were manually dissected to preserve the mylohyoid nerve and subjected to Sihler's staining. From the gnathion to and hyoid bone, the ABDM was divided into three equal parts, distinguishing the anterior, middle, and posterior thirds. Only a branch of the mylohyoid nerve entered the ABDM, and its entry point was located in the middle-third region in all cases. The nerve endings were concentrated in the middle third (100%), followed by the anterior third (58.3%) and were not observed in the posterior third. The landmarks used in this study (gnathion and hyoid bone) are easily palpable on the skin surface, allowing clinicians to target the most effective injection site (middle third of ABDM). These results provide scientific and anatomic evidence for injection points, and will aid in the management of ABDM injection procedures in clinical practice.

Influence of restricted mastication on swallowing function.

Oral food processing is an important part of daily food intake. A major part of this process is mastication, which prepares a bolus of food for swallowing by mechanically crushing and grinding ingested food between the teeth using rhythmic movements. Masticatory dysfunction is common in the elderly and in some neurological disorders and can have serious negative health consequences. This study investigated the effect of restricted mastication, achieved by experimentally reducing the duration of mastication, on masticatory patterns and subsequent swallowing function. Thirty healthy men (25 ± 3 years old) were instructed to chew gum jelly with a free mastication duration (G100), a half and a quarter duration of G100. Masseter and digastric electromyographic (EMG) activity was recorded to assess mastication and swallowing activity, respectively. In addition, the acceleration of the thyroid cartilage ridge was measured with an accelerometer. The root mean square (RMS) of muscle EMG activity in the masseter and digastric muscles, the number of masseter EMG bursts, time to peak and total duration of each masseter EMG burst, swallowing duration and laryngeal elevation latency were analysed. Restricting masticatory duration reduced the number of mastication cycles (p < .001), prolonged the time to peak (p < .001) and total duration of masseter EMG bursts (p < .001) and resulted in an overall increased RMS score of masseter muscle activity (p = .017). Furthermore, restricted masticatory duration led to a decrease in both swallowing duration (p = .001) and laryngeal elevation latency (p = .012), with a significant increase in the RMS score of digastric muscle activity (p < .001). Under the experimental conditions of restricted mastication, several adaptation features were observed, including changes in masticatory cycle characteristics and swallowing duration. Thus, although the overall masticatory efficiency was reduced, these adaptations allowed healthy individuals to still swallow safely.