Effects of Different Gum Hardness on Masseter Muscle Activity During Gum Chewing: An NIRS Oximetry Study.

Gum chewing is used in orofacial therapy to improve oral functions, such as a patient's chewing ability, bite force, tongue pressure, and lip closure strength. However, its effects on masseter muscle oxygen dynamics and muscle activity may vary with the hardness and features of the gum base. Therefore, when considering gum chewing for therapeutic purposes, it is essential to select gum of an appropriate hardness. This study aimed to elucidate the impact of gum hardness differences on masseter muscle tissue oxygen dynamics and muscle activity. We conducted a 120-s gum chewing study using three types of gum with different hardness levels on 11 healthy adult males. Each patient's masseter muscle tissue oxygen dynamics, muscle activity, and heart rate were measured, and the extent of masseter fatigue was assessed using a visual analogue scale (VAS). Per our findings, as gum hardness increased, significant reductions in oxygen saturation (StO2) and significant increases in deoxyhaemoglobin (Deoxy-Hb) concentrations were observed in masseter muscle tissue oxygen dynamics. Likewise, muscle activity, heart rate, and muscle fatigue (according to VAS) also increased significantly as gum hardness increased. The findings of this study reveal that increasing gum base hardness not only affects masseter muscle tissue oxygen dynamics but also increases muscle activity, masseter fatigue, and heart rate. When selecting gum for orofacial therapy involving gum chewing exercises, it is crucial to choose the appropriate gum.

Effect of Gum Chewing Training on Masseter Muscle Oxygen Dynamics.

This study aimed to clarify the effect of 1 month of gum chewing (GCh) training on masseter muscle oxygen dynamics and determine its effectiveness in improving muscle endurance and fatigue. A total of 16 healthy adult subjects were included in this study. The subjects were randomly assigned to two groups: control and training groups (eight subjects each). GCh training using prototype gum of moderate hardness was performed for 10 min (5 min for each side) three times a day before each meal for 30 days. Clenching effects were evaluated before and after interventions. Masseter muscle oxygen dynamics were measured using spatially resolved near-infrared spectroscopy. Furthermore, masseter muscle fatigue was assessed using the Visual Analog Scale (VAS). After training, a significant increase was observed in total haemoglobin and oxygenated haemoglobin during clenching, and the 1/2 recovery time was significantly shortened. The changes in the VAS score showed a decreasing trend after training. In conclusion, 1 month of GCh training changed masseter oxygen dynamics during clenching and recovery and improved muscle aerobic capacity.

The Influence of the Type of Breathing on the Masticatory Muscle Patterns in Children.

Background and Objectives: The aim was to compare the activity of the masseter muscles in children with different types of breathing. Materials and Methods: A cross-sectional study was conducted including patients aged 6-12 years with mixed dentition, who came for oral care at the Master's Degree in Pediatric Dentistry program at the Complutense University of Madrid (UCM), according to inclusion and exclusion criteria. The sample was divided into three groups: nasal breathers without dental alterations (control group), oral breathers with dental malocclusion, and oral breathers with previous orthodontic treatment. An electromyography was performed, and statistic methods were conducted with a 95% confidence to contrast hypothesis. Results: A total of 122 children were analyzed and distributed into three groups. The electrical muscle activity of masseters was significantly different between the study groups (p < 0.001 for all comparisons). Pairwise comparisons revealed a significantly higher electrical muscle activity in the control group (nasal breathers) during chewing compared to both groups of oral breathers (p < 0.001 for both comparisons). Orthodontic treatment decreased electrical muscle activity during isometric contraction in oral breathers compared to nasal breathers (p < 0.001), but did not significantly affect electrical muscle activity during chewing. Higher decompensation values were obtained in oral breathers without previous orthodontic treatment compared the other study groups (p < 0.001 for both comparisons), although electrical muscle activity values were similar in both groups of oral breathers (p > 0.05 for both comparisons). Conclusions: Differences in electrical muscle activity between nasal and oral breathers can be confirmed. Oral breathers with and without orthodontic treatment showed lower electrical muscle activity of masseters during chewing than nasal breathers, while at isometric contraction, only oral breathers with previous orthodontic treatment showed lower electrical activity. Higher decompensation values were found in oral breathers without previous orthodontic treatment, in comparison to the control group and oral breathers with previous orthodontic treatment.

Hand-Jaw Coordination as Mice Handle Food Is Organized around Intrinsic Structure-Function Relationships.

Rodent jaws evolved structurally to support dual functionality, for either biting or chewing food. Rodent hands also function dually during food handling, for actively manipulating or statically holding food. How are these oral and manual functions coordinated? We combined electrophysiological recording of muscle activity and kilohertz kinematic tracking to analyze masseter and hand actions as mice of both sexes handled food. Masseter activity was organized into two modes synchronized to hand movement modes. In holding/chewing mode, mastication occurred as rhythmic (∼5 Hz) masseter activity while the hands held food below the mouth. In oromanual/ingestion mode, bites occurred as lower-amplitude aperiodic masseter events that were precisely timed to follow regrips (by ∼200 ms). Thus, jaw and hand movements are flexibly coordinated during food handling: uncoupled in holding/chewing mode and tightly coordinated in oromanual/ingestion mode as regrip-bite sequences. Key features of this coordination were captured in a simple model of hierarchically orchestrated mode-switching and intramode action sequencing. We serendipitously detected an additional masseter-related action, tooth sharpening, identified as bouts of higher-frequency (∼13 Hz) rhythmic masseter activity, which was accompanied by eye displacement, including rhythmic proptosis, attributable to masseter contractions. Collectively, the findings demonstrate how a natural, complex, and goal-oriented activity is organized as an assemblage of distinct modes and complex actions, adapted for the divisions of function arising from anatomical structure. These results reveal intricate, high-speed coordination of disparate effectors and show how natural forms of dexterity can serve as a model for understanding the behavioral neurobiology of multi-body-part coordination.

The reliability and validity of rapid transcranial magnetic stimulation mapping for muscles under active contraction.

Rapid mapping is a transcranial magnetic stimulation (TMS) mapping method which can significantly reduce data collection time compared to traditional approaches. However, its validity and reliability has only been established for upper-limb muscles during resting-state activity. Here, we determined the validity and reliability of rapid mapping for non-upper limb muscles that require active contraction during TMS: the masseter and quadriceps muscles. Eleven healthy participants attended two sessions, spaced two hours apart, each involving rapid and 'traditional' mapping of the masseter muscle and three quadriceps muscles (rectus femoris, vastus medialis, vastus lateralis). Map parameters included map volume, map area and centre of gravity (CoG) in the medial-lateral and anterior-posterior directions. Low to moderate measurement errors (%SEMeas = 10-32) were observed across muscles. Relative reliability varied from good-to-excellent (ICC = 0.63-0.99) for map volume, poor-to-excellent (ICC = 0.11-0.86) for map area, and fair-to-excellent for CoG (ICC = 0.25-0.8) across muscles. There was Bayesian evidence of equivalence (BF's > 3) in most map outcomes between rapid and traditional maps across all muscles, supporting the validity of the rapid mapping method. Overall, rapid TMS mapping produced similar estimates of map parameters to the traditional method, however the reliability results were mixed. As mapping of non-upper limb muscles is relatively challenging, rapid mapping is a promising substitute for traditional mapping, however further work is required to refine this method.

Influence of restricted mastication on swallowing function.

BACKGROUND: 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. OBJECTIVE: This study investigated the effect of restricted mastication, achieved by experimentally reducing the duration of mastication, on masticatory patterns and subsequent swallowing function. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.

Evaluation of the bioelectrical activity of the masticatory muscles in patients with narrowed maxillary transverse dimension compared to the occlusal norm.

OBJECTIVE: The aim of the study was to determine how the electrical activity of the temporalis, masseter and sternocleidomastoid muscles differs in children with reduced transverse jaw dimension compared to children with normal occlusion. DESIGN: It was a experimental study. Thirty-seven patients were included in the study. 18 in the study group received orthodontic treatment with removable appliances and 19 subjects were classified as normal occlusion subjects in the control group. A panoramic X-ray and digital intraoral scan were taken, followed by an surface electromyography of three muscle pairs (temporalis muscles, masseter muscles, sternocleidomastoid muscles) in resting position, while clenching and clenching on cotton rollers. RESULTS: There was significantly greater activity in the experimental group than in the control group comparing muscles: temporalis muscles and masseter muscles in the resting position. Additionally, significantly greater activity of muscles in the control group was found during clenching. However, the asymmetry index of muscles indicates that there is significantly greater asymmetry of muscles activity in the experimental group. Compared to children with normal occlusion, children with a narrowed transverse dimension of the jaw have statistically significant differences in the bioelectrical activity of the temporalis, masseter and sternocleidomastoid muscles, as well as greater asymmetry in the bioelectrical voltage of the masseter muscles. CONCLUSIONS: Patients with reduced transverse dimension of the jaw are characterized by increased resting activity of the masticatory muscles and reduced functional activity of the masticatory muscles. These patients have increased asymmetry in the bioelectrical tension of the masticatory muscles.

Decoding Age-Linked Masseter Vestibular Evoked Myogenic Potential Changes in Healthy, Aging Individuals.

PURPOSE: The primary objective of this study was to assess how age influences masseter vestibular evoked myogenic potential (mVEMP) parameters by utilizing 500-Hz tone burst stimuli delivered through air conduction. METHOD: The study involved 110 participants ranging from 15 to 60 years of age, grouped into five categories, all of whom had no previous issues related to their vestibular system. The participants were exposed to 500-Hz tone burst stimuli at 125 dB SPL through ER-3A inserts. These stimuli were presented to one ear at a time, with alternating polarity. A Tukey's honestly significant difference test was conducted to compare rectified and unrectified amplitude, along with latencies (P11 and N21) and the asymmetric ratio across all age groups. Additionally, a multivariate analysis of variance was performed to assess the impact of sex on the study variables. RESULTS: All 110 participants (220 ears) in the study provided mVEMP responses, encompassing 100% of the subjects. The results revealed a significant reduction in both amplitude and latency extension for the P11 and N21 peaks. Interestingly, P11 latency was also prolonged in the youngest participants (Group 1), suggesting ongoing maturation of the system even beyond the age of 16 years. Moreover, a significant sex difference was observed in the P11 latencies. However, there were no substantial sex differences (p > .05) in N1 peak latency, peak-to-peak amplitude, rectified amplitude, and asymmetric ratio. CONCLUSIONS: Changes in structure occur due to degeneration, and the quantity of vestibular sensory hair cells gradually diminishes with age. The rate of decline is faster in semicircular canals compared to end organs, as observed by Merchant et al. (2000). Following a linear degeneration starting at the age of 40 years, a continuous reduction in sensory cells and primary neurons takes place until approximately 40% of vestibular sensory cells are lost by the age of 75 years and insufficient maturation can lead to prolonged peaks and reduced amplitudes compared with those that are considered normal. Therefore, it is crucial to consider the age of the participants when making diagnoses and incorporate relevant correction factors based on age-related reference data.

The effect of clear aligner treatment on masticatory muscles (masseter, temporalis) activity in adults: a systematic review and meta-analysis.

BACKGROUND: The use of clear aligners is becoming more common for aesthetic orthodontic treatment, but there are still concerns about how they affect mastication biomechanics in the short and long term. The clear aligners treatment (CAT) mechanism changes the position of the mandible and maxilla, especially impacting the masseter muscle. Surface electromyography (sEMG) proves to be a useful method to evaluate masticatory muscle activity (MMA). OBJECTIVES: To analyze the effect of clear aligners treatment on alterations in masticatory muscles (masseter, temporalis) using surface electromyography. SEARCH METHODS: Five databases (PubMed, Web of Science, SCOPUS, Cochrane Library, and Google Scholar) were searched up to March 2024. SELECTION CRITERIA: Studies in which MMA was evaluated after the installation of orthodontic clear aligners. DATA COLLECTION AND ANALYSIS: Screening, data extraction, and quality assessments were performed by four investigators independently. The data, which evaluated temporalis and masseter muscle characteristics during CAT using surface electromyography, was extracted, and the quality of the studies was evaluated. The risk of bias was assessed using the Newcastle-Ottawa Scale (NOS). RESULTS: Six studies (two prospective cohort studies, three observational longitudinal studies, and one observational longitudinal case-control study) with low and moderate risk of bias were included in the qualitative synthesis. Six of these were also included in the meta-analysis. Our study investigated the dynamics of masseter and temporalis muscle activity during CAT. The results show that during maximal voluntary clenching, the masseter muscle demonstrated a significant initial increase (P < .05) followed by a subsequent non-significant decrease. It also showed that submaximal voluntary clenching consistently exhibited a significant reduction in muscle activity throughout the study period (P < .01). Assessment of muscle activity at the mandibular resting position revealed a variety of responses, with some participants showing a significant increase while others exhibited non-significant changes (P < .05, P > .05, respectively). However, the meta-analysis showed a non-significant difference in measuring masseter and temporalis muscles activity during CAT. CONCLUSIONS: Based on existing evidence, it is reasonable to conclude that CAT affected MMA. During maximal voluntary clenching, masseter muscle activity initially increased but later decreased, while temporalis muscle activity showed mixed results. Submaximal voluntary clenching revealed a consistent decrease in muscle activity over time. Mandibular resting position assessments showed both increases and no significant changes in muscle activity. However, the existing literature is insufficient to draw concrete conclusions; therefore, well-conducted further research is needed to confirm this statement. REGISTRATION: This systematic review and meta-analysis were registered in the International Prospective Register of Systematic Reviews (PROSPERO CRD42024522231).

Signal to noise ratio of masticatory muscle activity of functional and non-functional oral tasks.

BACKGROUND: Electromyographic activity (EMG) of masticatory muscles during wakefulness is understudied. It is unclear if single channel ambulatory EMG devices are sensitive enough to detect masticatory muscle activity (MMA) during wakefulness. OBJECTIVES: To compare the MMA of various oral tasks recorded with a single channel EMG device ((Grindcare4-datalogger Prototype device) (GC4-ß)) and a conventional EMG (cEMG) device. METHODS: EMG activity of 30 standardised oral tasks was recorded unilaterally from the masseter and anterior temporalis muscle in 24 healthy volunteers using GC4-ß and a cEMG device. To compare the EMG data, signal-to-noise ratios (SNR) were calculated as a way to normalise EMG activity across tasks. Analysis of variance was used to compare the SNR between the devices, muscles and oral tasks. RESULTS: SNR measured from GC4-ß was overall significantly higher than the cEMG device (p =.001). The SNR for maximum voluntary contraction (MVC) was significantly higher than all other tasks (p <.001). SNR for temporalis with GC4-ß was significantly higher for MVC, hard food, soft food, gum chewing (dominant side), rhythmic clenching and upper lip biting compared to the cEMG device (p <.021). The SNR for masseter with GC4-ß was significantly higher for hard food and gum chewing (dominant side), rhythmic clenching, rhythmic biting of an object and yawning compared to the cEMG device (p <.022). CONCLUSIONS: This study provides novel insight into the EMG patterns of numerous oral tasks enhancing knowledge of physiological differences between the masticatory muscles. Further, single channel EMG devices can effectively measure the EMG activity of various oral tasks during wakefulness.

Impact of salivary flow inhibition on masticatory behaviours in healthy individuals.

BACKGROUND: It remains unclear how the salivary flow and the fat content of food affect bolus formation during mastication. OBJECTIVES: We aimed to clarify: (1) how hyposalivation affects jaw-closing and hyoid-elevating muscle activities in bolus formation, and (2) if the effect of hyposalivation on muscle activity depends on the fat content of food. METHODS: Eighteen healthy male volunteers were instructed to freely ingest four test foods: Plain, Fat without seasoning, Fat with seasoning, and Soft rice crackers. Masseter and suprahyoid electromyographic activities were recorded before and 30 min after the administration of atropine sulfate, a muscarinic receptor antagonist that induces hyposalivation. RESULTS: Hyposalivation extended the masticatory duration significantly in all the test foods except Fat with seasoning. Masticatory cycle time was significantly longer with vs without hyposalivation for the Soft (p = .011). Suprahyoid activity/cycle was significantly greater with vs without hyposalivation (p = .013). Masticatory cycle time was significantly longer at the late stage with vs without hyposalivation for the Soft (p < .001). Suprahyoid activity/cycle was significantly greater at the middle (p = .045) and late stages (p = .002) with vs without hyposalivation for the Soft and greater at the late stage with vs without hyposalivation for the Plain (p = .043). Changes in masticatory cycle time and suprahyoid activity/cycle for these foods had significantly positive relationship (p < .001). CONCLUSION: Hyposalivation-induced changes in masticatory behaviours resulted from the middle and late stage suprahyoid activity. Fat content and seasoning compensate for salivary flow inhibition.

Bichectomy Surgery and EMG Masticatory Muscles Function in Adult Women: A Longitudinal Study.

AIM: This longitudinal study aimed to evaluate the electromyographic activity of the masseter and temporal muscles in adult women who underwent buccal fat removal. MATERIALS AND METHODS: The sample consisted of 20 healthy adult women with no temporomandibular dysfunction and normal occlusion, who were assessed before, 30, and 60 days after the surgery. The electromyographic signal of the masseter and temporal muscles was captured through mandibular tasks including rest, protrusion, right and left laterality, and maximum voluntary contraction with and without parafilm. The results obtained were tabulated and the Shapiro-Wilk normality test was performed, which indicated a normal distribution. Statistical analysis was performed using the repeated measures test (p < 0.05). RESULTS: Significant differences were observed between time periods in maximum voluntary contraction for the left masseter muscle (p = 0.006) and in maximum voluntary contraction with parafilm for the right temporal (p = 0.03) and left temporal (p = 0.03) muscles. CONCLUSION: Bichectomy surgery did not modify the electromyographic activity of the masseter and temporal muscles during the rest task but may have influenced variations in the electromyographic signal during different mandibular tasks after 60 days of surgery, suggesting compensatory adaptations and functional recovery. CLINICAL SIGNIFICANCE: Understanding the impact of buccal fat removal surgery on the stomatognathic system function provides insights into postoperative functional recovery and potential compensatory adaptations, guiding clinical management and rehabilitation strategies for patients undergoing such procedures. How to cite this article: Cardoso AHDLS, Palinkas M, Bettiol NB, et al. Bichectomy Surgery and EMG Masticatory Muscles Function in Adult Women: A Longitudinal Study. J Contemp Dent Pract 2024;25(3):207-212.

Clinical and electromyographic signals analysis about the effect of space-adjustment splint on overerupted maxillary molars.

BACKGROUND: Overerupted maxillary molars is common in adults, which can lead to insufficient intermaxillary vertical space ,great difficulty in prosthetic reconstruction ,and cause occlusal interference in movements.To reconstruct occlusal function, it is necessary to prepare enough space for prostheses. The aim of the present study was to evaluate the effect of space-adjustment occlusal splint on overerupted maxillary molars by clinical and electromyographic signals analysis. METHODS: Eighteen patients with overerupted maxillary molars were selected to wear space-adjustment occlusal splint suppressing overerupted maxillary molars for three months. Satisfaction was assessed by 5-point Likert; intermaxillary vertical space and the teeth transportation distance were measured in models; clinical periodontal status were evaluated by periodontal probing depth (PPT) and bleeding index (BI); electromyographic recordings of the masseter and anterior temporal muscles were monitored by Cranio-Mandibular K7 Evaluation System. RESULTS: All the patients were satisfied with the treatment effect (Likert scale ≧ 4). The intermaxillary space in edentulous areas after treatment showed statistically significant increasing when compared with those before treatment. PPT and BI showed no significant difference. No statistically significant differences were found in electromyographic activity of anterior temporal muscles, while a reduction of muscle activity in masseter in the contralateral side were detected in post-treatment evaluations compared with pre-treatment at mandibular rest position. CONCLUSIONS: Space-adjustment occlusal splint is an efficient treatment option on overerupted maxillary molars by intruding the maxillary molar to obtain adequate intermaxillary space for prostheses.

Effects of age and diet consistency on the expression of myosin heavy-chain isoforms on jaw-closing and jaw-opening muscles in a rat model.

BACKGROUND: Skeletal craniofacial morphology can be influenced by changes in masticatory muscle function, which may also change the functional profile of the muscles. OBJECTIVES: To investigate the effects of age and functional demands on the expression of Myosin Heavy-Chain (MyHC) isoforms in representative jaw-closing and jaw-opening muscles, namely the masseter and digastric muscles respectively. METHODS: Eighty-four male Wistar rats were divided into four age groups, namely an immature (n = 12; 4-week-old), early adult (n = 24; 16-week-old), adult (n = 24; 26-week-old) and mature adult (n = 24; 38-week-old) group. The three adult groups were divided into two subgroups each based on diet consistency; a control group fed a standard (hard) diet, and an experimental group fed a soft diet. Rats were sacrificed, and masseter and digastric muscles dissected. Real-time quantitative polymerase chain reaction was used to compare the mRNA transcripts of the MyHC isoforms-Myh7 (MyHC-I), Myh2 (MyHC-IIa), Myh4 (MyHC-IIb) and Myh1 (MyHC-IIx)-of deep masseter and digastric muscles. RESULTS: In the masseter muscle, hypofunction increases Myh1 (26, 38 weeks; p < .0001) but decreases Myh4 (26 weeks; p = .046) and Myh2 (26 weeks; p < .0001) expression in adult rats. In the digastric muscle, hypofunction increases Myh1 expression in the mature adult rats (38 weeks; p < .0001), while Myh2 expression decreases in adult rats (26 weeks; p = .021) as does Myh4 (26 weeks; p = .001). Myh7 expression is increased in the digastric muscle of mature adult rats subjected to hypofunction (38 weeks; p = <.0001), while it is very weakly expressed in the masseter. CONCLUSION: In jaw-opening and jaw-closing muscles, differences in myosin expression between hard- and soft-diet-fed rats become evident in adulthood, suggesting that long-term alteration of jaw function is associated with changes in the expression of MyHC isoforms and potential fibre remodelling. This may give insight into the role of function on masticatory muscles and the resultant craniofacial morphology.

Comparison of masticatory muscle activity between young adults and elderly participants using a novel standardized bite device.

OBJECTIVES: Standardized bite training is required to prevent oral hypofunction in elderly individuals. We aimed to compare masticatory muscle activity between 24 young adults and 16 pre-elderly individuals during a biting task using a novel standardized bite device (BD). METHODS: The BD was made of silicone rubber and included a high-force or low-force plate spring or no plate spring (dummy). The compressive stiffness of the material in each BD was measured using a texture analyzer. All participants performed a biting task 50-times at a rate of 1/s each using the three types of BDs on the right first molar. Electromyographic (EMG) activity was recorded bilaterally from the masseter and temporalis muscles. The variability of each biting training session was calculated as the coefficient of variance (CV) from the EMG activity during each biting task for each muscle. Masticatory muscle fatigue was assessed using a numerical rating scale (NRS). RESULTS: Compressive stiffness was significantly different between each BD (P < 0.001). The CV and NRS scores were not significantly different between the groups. The EMG activities during each bite task in all muscles were not significantly different for any measurement item between the age groups. The EMG activities of high- and low-force BDs in the right temporalis (ipsilateral) muscle were significantly higher than those of the dummy BD (P < 0.001). CONCLUSIONS: Compressive stiffness of the BD affected EMG activity only in the ipsilateral temporalis muscle, but not in the masseter or contralateral temporalis muscles, without any age effect.

The impact of measurement technique and sampling on estimates of skeletal muscle fibre architecture.

Skeletal muscle fibre architecture provides important insights into performance of vertebrate locomotor and feeding behaviours. Chemical digestion and in situ sectioning of muscle bellies along their lengths to expose fibres, fibre orientation and intramuscular tendon, are two classical methods for estimating architectural variables such as fibre length (Lf) and physiological cross-sectional area (PCSA). It has recently been proposed that Lf estimates are systematically shorter and hence less accurate using in situ sectioning. Here we addressed this hypothesis by comparing Lf estimates between the two methods for the superficial masseter and temporalis muscles in a sample of strepsirrhine and platyrrhine primates. Means or single-specimen Lf estimates using chemical digestion were greater in 17/32 comparisons (53.13%), indicating the probability of achieving longer fibres using chemical digestion is no greater than chance in these taxonomic samples. We further explored the impact of sampling on scaling of Lf and PCSA in platyrrhines applying a bootstrapping approach. We found that sampling-both numbers of individuals within species and representation of species across the clade significantly influence scaling results of Lf and PCSA in platyrrhines. We show that intraspecific and clade sampling strategies can account for differences between previously published platyrrhine scaling studies. We suggest that differences in these two methodological approaches to assessing muscle architecture are relatively less consequential when estimating Lf and PCSA for comparative studies, whereas achieving more reliable estimates within species through larger samples and representation of the full clade space are important considerations in comparative studies of fibre architecture and scaling.

Persisting effects of jaw clenching on dynamic steady-state balance.

The effects of jaw clenching on balance has been shown under static steady-state conditions but the effects on dynamic steady-state balance have not yet been investigated. On this basis, the research questions were: 1) if jaw clenching improves dynamic steady-state balance; 2) if the effects persist when the jaw clenching task loses its novelty and the increased attention associated with it; 3) if the improved dynamic steady-state balance performance is associated with decreased muscle activity. A total of 48 physically active healthy adults were assigned to three groups differing in intervention (Jaw clenching and balance training (JBT), only balance training (OBT) or the no-training control group (CON)) and attending two measurement points separated by two weeks. A stabilometer was used to assess the dynamic steady-state balance performance in a jaw clenching and non-clenching condition. Dynamic steady-state balance performance was measured by the time at equilibrium (TAE). The activities of tibialis anterior (TA), gastrocnemius medialis (GM), rectus femoris (RF), biceps femoris (BF) and masseter (MA) muscles were recorded by a wireless EMG system. Integrated EMG (iEMG) was calculated to quantify the muscle activities. All groups had better dynamic steady-state balance performance in the jaw clenching condition than non-clenching at T1, and the positive effects persisted at T2 even though the jaw clenching task lost its novelty and attention associated with it after balance training with simultaneous jaw clenching. Independent of the intervention, all groups had better dynamic steady-state balance performances at T2. Moreover, reductions in muscle activities were observed at T2 parallel to the dynamic steady-state balance performance improvement. Previous studies showed that jaw clenching alters balance during upright standing, predictable perturbations when standing on the ground and unpredictable perturbations when standing on an oscillating platform. This study complemented the previous findings by showing positive effects of jaw clenching on dynamic steady-state balance performance.

[Evaluation of the efficiency of the method of biological feedback in complex therapy of patients with hypertonus of the chewing muscles]. / Metod biologicheskoi obratnoi svyazi v kompleksnoi terapii patsientov s gipertonusom zhevatel'nykh myshts.

The aim the study. Evaluate the effectiveness of biofeedback therapy in the complex rehabilitation of masticatory muscle hypertonicity in patients with a high level of anxiety. MATERIAL AND METHODS: The study included 40 patients aged 20 to 32 years with complaints of fatigue and discomfort in the area of chewing muscles, teeth compression during the day, nocturnal bruxism, crowding of teeth. Two groups were formed: the study group, whose patients underwent splint therapy in combination with biofeedback therapy trainings; in the control group, patients received treatment with splint therapy without the use of biofeedback therapy. Electromyography of the masticatory muscles at rest and during compression were used to diagnose hypertonicity of the masticatory muscles. To assess the psycho-emotional state, a medical and social questionnaire was conducted using questionnaires: «Health Questionnaire¼, Beck Depression Inventory, Spielberger-Khanin Anxiety Scale, SF-16 Quality of Life Scale. RESULTS: A decrease in the level of depression, anxiety was revealed with the stabilization of emotional sensitivity in relation to other people, emotional involvement in everyday life, and an increase in the quality of life. When comparing electromyographic data at rest and during clenching of teeth in patients of the study group the indicators were lower than in the control group. CONCLUSIONS: The effectiveness of biofeedback therapy at the stages of orthodontic treatment using splint therapy was established in the form of a decrease in the activity of masticatory muscles in patients of the study group. In the control group, the index of masticatory muscle activity decreased to a lesser extent. Biofeedback methods have shown a high level of effectiveness in reducing the symptoms of anxiety and depression, improving the quality of life.

Cranial muscle architecture in wild boar: Does captivity drive ontogenetic trajectories?

The jaw system in mammals is complex and different muscle morphotypes have been documented. Pigs are an interesting group of animals as they are omnivorous and have a bunodont crushing dentition. Moreover, they have interacted with humans for over 10,000 years and grow nearly two orders of magnitude in size. Despite being a model system for studies on cranial form and function, data on the growth of the jaw adductor muscles are scant. Moreover, whether captivity impacts the growth and architecture of the jaw adductors remains unknown. Based on dissection data of the jaw adductors of 45 animals ranging from less than 1 kg to almost 100 kg, we show that muscle masses, muscle fiber lengths, and cross-sectional areas scale as predicted for geometrically similar systems or with slight negative allometry. Only the fiber length of the lateral pterygoid muscle grew with slight positive allometry. Animals raised in captivity in stalls or in an enclosure were overall very similar to wild animals. However, some muscles were larger in captive animals. Interestingly, variation in bite force in captive animals was well predicted by the variation in the size of the superficial masseter muscle relative to the overall jaw adductor mass.

Deep learning and predictive modelling for generating normalised muscle function parameters from signal images of mandibular electromyography.

Challenges arise in accessing archived signal outputs due to proprietary software limitations. There is a notable lack of exploration in open-source mandibular EMG signal conversion for continuous access and analysis, hindering tasks such as pattern recognition and predictive modelling for temporomandibular joint complex function. To Develop a workflow to extract normalised signal parameters from images of mandibular muscle EMG and identify optimal clustering methods for quantifying signal intensity and activity durations. A workflow utilising OpenCV, variational encoders and Neurokit2 generated and augmented 866 unique EMG signals from jaw movement exercises. k-means, GMM and DBSCAN were employed for normalisation and cluster-centric signal processing. The workflow was validated with data collected from 66 participants, measuring temporalis, masseter and digastric muscles. DBSCAN (0.35 to 0.54) and GMM (0.09 to 0.24) exhibited lower silhouette scores for mouth opening, anterior protrusion and lateral excursions, while K-means performed best (0.10 to 0.11) for temporalis and masseter muscles during chewing activities. The current study successfully developed a deep learning workflow capable of extracting normalised signal data from EMG images and generating quantifiable parameters for muscle activity duration and general functional intensity.