Functional adaptation of the infant craniofacial system to mechanical loadings arising from masticatory forces.

The morphology and biomechanics of infant crania undergo significant changes between the pre- and post-weaning phases due to increasing loading of the masticatory system. The aims of this study were to characterize the changes in muscle forces, bite forces and the pattern of mechanical strain and stress arising from the aforementioned forces across crania in the first 48 months of life using imaging and finite element methods. A total of 51 head computed tomography scans of normal individuals were collected and analysed from a larger database of 217 individuals. The estimated mean muscle forces of temporalis, masseter and medial pterygoid increase from 30.9 to 87.0 N, 25.6 to 69.6 N and 23.1 to 58.9 N, respectively (0-48 months). Maximum bite force increases from 90.5 to 184.2 N (3-48 months). There is a change in the pattern of strain and stress from the calvaria to the face during postnatal development. Overall, this study highlights the changes in the mechanics of the craniofacial system during normal development. It further raises questions as to how and what level of changes in the mechanical forces during the development can alter the morphology of the craniofacial system.

Moving beyond bruxism episode index: Discarding misuse of the number of sleep bruxism episodes as masticatory muscle pain biomarker.

The objective of the current study was to evaluate the clinical utility of bruxism episode index in predicting the level of masticatory muscle pain intensity. The study involved adults (n = 220) recruited from the Outpatient Clinic of Temporomandibular Disorders at the Department of Experimental Dentistry, Wroclaw Medical University, during the period 2017-2022. Participants underwent medical interview and dental examination, focusing on signs and symptoms of sleep bruxism. The intensity of masticatory muscle pain was gauged using the Numeric Rating Scale. Patients identified with probable sleep bruxism underwent further evaluation through video-polysomnography. Statistical analyses included the Shapiro-Wilk test, Spearman's rank correlation test, association rules, receiver operating characteristic curves, linear regression, multivariate regression and prediction accuracy analyses. The analysis of correlation and one-factor linear regression revealed no statistically significant relationships between bruxism episode index and Numeric Rating Scale (p > 0.05 for all analyses). Examination of receiver operating characteristic curves and prediction accuracy indicated a lack of predictive utility for bruxism episode index in relation to masticatory muscle pain intensity. Multivariate regression analysis demonstrated no discernible relationship between bruxism episode index and Numeric Rating Scale across all examined masticatory muscles. In conclusion, bruxism episode index and masticatory muscle pain intensity exhibit no correlation, and bruxism episode index lacks predictive value for masticatory muscle pain. Clinicians are advised to refrain from employing the frequency of masticatory muscle activity as a method for assessing the association between masticatory muscle pain and sleep bruxism.

Effects of the low Fowler's sleep position and methazolamide treatment on sleep bruxism: A randomized controlled trial.

Intracranial pressure is one of the determinants of sympathetic activities, and sleep bruxism is associated with increased sympathetic activities. This study aimed to investigate effects of the low Fowler's sleep position and methazolamide treatment on the occurrence of rhythmic masticatory muscle activities/sleep bruxism episodes in patients with sleep bruxism in a randomized controlled trial. Polysomnographic recordings were performed on the patients with sleep bruxism sleeping in the low Fowler's (15°-30°) or supine position (n = 11), and with methazolamide or placebo treatment (100 mg, 3-4 hr before bedtime, P.O., n = 9), and changes in sleep variables and heart rate variance during sleep in the low Fowler's position or with methazolamide treatment were determined. Sleep bruxism index, number of masseter muscle electromyographic bursts per hour of sleep, ratio of rhythmic masticatory muscle activities/sleep bruxism duration to the total sleep duration, index of total limb movements, index of limb movements with rhythmic masticatory muscle activities, and number of sleep bruxism clusters per hour of sleep in the low Fowler's position and after methazolamide intake were significantly smaller (p < 0.05-0.001) than those in the supine position and after placebo intake, respectively. The low-frequency heart rate variance powers during non-rapid eye movement sleep stage 2 (N2) in the low Fowler's position and with methazolamide treatment were significantly lower (p < 0.05) than those during sleep in the supine position and with placebo treatment, respectively. In conclusion, sleep in the low Fowler's position and methazolamide treatment were associated with significant decreases in the occurrence of rhythmic masticatory muscle activities/sleep bruxism episodes, which might be due to a reduction in intracranial pressure and sympathetic activities mainly during non-rapid eye movement sleep stage 2.

Histomorphometric Changes of the Masseter Muscle of Rats After a Single Injection of Botulinum Toxin Type A.

BACKGROUND: It has been reported that botulinum toxin type A (BoNT-A) produces structural changes in masticatory muscles. However, not all histomorphometric parameters affected by BoNT-A parameters have been assessed. This study investigated the histomorphometric changes in the masseter muscle of rats after a single injection of BoNT-A. METHODS: Forty-four adult animals were randomly divided into control group (n = 22) and BoNT-A group (n = 22). Controls received a single dose of 0.14 mL/kg of saline in masseter muscles, and the BoNT-A group received a 7 U/Kg of BoNT-A. The groups received the same volume of injected substances. Animals were sacrificed on 7th (n = 5), 14th (n = 5), 21st (n = 5), 28th (n = 4) and 90th (n = 3) days post-treatment. Histological masseter tissue slides were obtained from hematoxylin-eosin treatment and analyzed in optical microscopy regarding muscle cross-sectional area, amount of connective tissue and quantity and diameter of myocytes. For statistical analysis, generalized linear models were used to compare the data (ANOVA). In all test, the significance level of 5% was set. RESULTS: BoNT-A values of cross-sectional area of the masseter muscle were significantly lower than controls (p < 0.01) throughout the study. Regarding myocytes quantity, BoNT-A subgroups presented higher values than controls (p < 0.0001) since the 14th day until the end of the study; however, the diameter of myocytes was smaller in all BoNT-A subgroups (p < 0.0001) in all assessment points. The amount of connective tissue was higher in BoNT-A subgroups (p < 0.0001) throughout the study. CONCLUSION: A single injection of BoNT-A altered the structure of masseter muscle of rats, regarding its histomorphometric parameters. NO LEVEL ASSIGNED: 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 .

ß2-adrenergic receptor activation decreases the mechanical sensitivity of rat masticatory muscle afferent fibres.

BACKGROUND: Activation of ß2 adrenergic receptors reduces cutaneous mechanical pain thresholds in rats. While ß2 adrenergic receptor activation may contribute to mechanisms that underlie temporomandibular joint pain, its effect on masticatory muscle pain sensitivity is uncertain. OBJECTIVES: The current study sought to determine the extent to which ß adrenergic receptors are expressed by masticatory muscle afferent fibres, and to assess the effect of local activation of these receptors on the mechanical sensitivity of masticatory muscle afferent fibres in rats. METHODS: Trigeminal ganglion neurons that innervate the rat (n = 12) masseter muscle and lower lip were identified by tissue injection of fluorescent dyes and were then stained with antibodies against ß1 or ß2 adrenergic receptors. Extracellular recordings from 60 trigeminal ganglion neurons that innervate the masticatory muscle were undertaken in a second group of anaesthetised rats of both sexes (n = 37) to assess afferent mechanical activation thresholds. Thresholds were assessed before and after injection of the ß adrenergic receptor agonists into masticatory muscle. RESULTS: ß1 and ß2 adrenergic receptor expression was greater in labial skin than in masticatory muscle ganglion neurons (p < .05, one-way ANOVA, Holm-Sidak test). There was a higher expression of ß2 adrenergic receptors in masticatory muscle ganglion neurons in males than in females. The mixed ß agonist isoproterenol increased afferent mechanical activation threshold in male but not female rats (p < .05, Mann-Whitney test). In male rats, salbutamol, a ß2 selective agonist, also increased afferent mechanical activation threshold but hydralazine, a vasodilator, did not (p < .05, Mann-Whitney test). CONCLUSION: Activation of ß2 adrenergic receptors decreases the mechanical sensitivity of masticatory muscle afferent fibres in a sex-related manner.

Reciprocal first night effect on rhythmic and non-rhythmic oromotor episodes in moderate to severe primary sleep bruxism: A retrospective physiological study.

BACKGROUND: Sleep on the first night in a sleep laboratory is characterized by a lower sleep quality and frequency of rhythmic masticatory muscle activity (RMMA) than that on the second night in moderate to severe sleep bruxism (SB) patients. OBJECTIVE: The aims of this study was to clarify the physiological factors contributing to the first night effect on oromotor activity during sleep and investigate whether physiological factors involved in the first night effect differed between rhythmic and non-rhythmic oromotor activities. METHODS: Polysomnographic data collected on two consecutive nights from 15 moderate to severe SB subjects (F 7: M 8; age: 23.2 ± 1.3 [mean ± SD] years) were retrospectively analysed. Sleep variables, RMMA and non-specific masticatory muscle activity (NSMA) were scored in relation to episode types (i.e. phasic or tonic and cluster or isolated), sleep architecture and transient arousals. The relationships between nightly differences in oromotor and sleep variables were assessed. The distribution of oromotor events, arousals, cortical electroencephalographic power, RR intervals and heart rate variability were examined in relation to sleep cycle changes. These variables were compared between the first and second nights and between RMMA and NSMA. RESULTS: Sleep variables showed a lower sleep quality on Night 1 than on Night 2. In comparisons with Night 1, the RMMA index increased by 18.8% (p < .001, the Wilcoxon signed-rank test) on Night 2, while the NSMA index decreased by 17.9% (p = .041). Changes in the RMMA index did not correlate with those in sleep variables, while changes in the NSMA index correlated with those in arousal-related variables (p < .001, Spearman's rank correlation). An increase in the RMMA index on Night 2 was found for the cluster type and stage N1 related to sleep cyclic fluctuations in cortical and cardiac activities. In contrast, the decrease in the NSMA index was associated with increases in the isolated type and the occurrence of stage N2 and wakefulness regardless of the sleep cycle. CONCLUSION: Discrepancies in first night effect on the occurrence of RMMA and NSMA represent unique sleep-related processes in the genesis of oromotor phenotypes in SB subjects.

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).

Unilateral nasal obstruction mediates reversible morphological and phenotypic changes in masticatory muscles of growing rats.

OBJECTIVE: Mouth breathing as a result of nasal obstruction affects craniofacial growth and development. This study aimed to investigate the effects of unilateral nasal obstruction and its recovery, along with the role of nitric oxide (NO) in masticatory muscle physiology. MATERIALS AND METHODS: Forty-eight 4-week-old male rats were divided into control and experimental groups. The five experimental groups were subjected to left-sided nasal obstruction by suturing the external nostril, and the sutures were removed after 1, 3, 5, 7, or 9 weeks to allow for varying recovery periods. We assessed morphological changes in masseter, temporalis, and digastric muscle, by examining cross-sectional area (CSA) and myosin heavy chain (MHC) isoform composition of muscle fibers. Reverse transcription-quantitative real-time polymerase chain reaction to measure messenger RNA (mRNA) levels for tumor necrosis factor-α (TNF-α), glucose transporter 4 (GLUT4), and neuronal nitric oxide synthase (nNOS) were conducted. RESULTS: The SpO2, CSA, and fibers showing MHC-2b isoforms were significantly lower, while RT-PCR showed higher mRNA levels in TNF-α and nNOS, and a decrease in GLUT4 mRNA in the jaw-closing muscles in the long-term nasal obstruction groups than that in the control group. LIMITATIONS: The study findings should be interpreted cautiously because of the functional differences between rodents and humans in terms of respiratory mechanisms. CONCLUSIONS: Unilateral nasal obstruction affects the morphology and contractile characteristics of the rat masticatory muscles during development, with possible involvement of NO in muscle hypofunction. These changes may revert to baseline levels if the nasal obstruction is eliminated before puberty in rats.

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.

[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.

Gαi2 regulates the adult myogenesis of masticatory muscle satellite cells.

Although similar to trunk and limb skeletal muscles, masticatory muscles are believed as unique in both developmental origins and myogenesis. Gαi2 has been demonstrated to promote muscle hypertrophy and muscle satellite cell differentiation in limb muscles. However, the effect of Gαi2 on masticatory muscles is still unexplored. This study aimed to identify the role of Gαi2 in the proliferation and differentiation of masticatory muscle satellite cells, further exploring the metabolic mechanism of masticatory muscles. The proliferation rate, myotube size, fusion index of masticatory muscle satellite cells and Pax7, Myf5, MyoD, Tcf21 and Musculin expressions were significantly decreased by Gαi2 knockdown, while in cells infected with AdV4-Gαi2, the proliferation rate, myotube size, fusion index and Tbx1 expression were significantly increased. Masticatory muscle satellite cells also displayed phenotype transformation as Gαi2 changed. In addition, Gαi2 altered myosin heavy chain (MyHC) isoforms of myotubes with less MyHC-2A expression in siGαi2 group and more MyHC-slow expression in AdV4-Gαi2 group. In conclusion, Gαi2 could positively affect the adult myogenesis of masticatory muscle satellite cells and maintain the superiority of MyHC-slow. Masticatory muscle satellite cells may have their unique Gαi2-regulated myogenic transcriptional networks, although they may share some common characteristics with trunk and limb muscles.

Clinical and prognostic role of sarcopenia based on masticatory muscle index on MR images in patients with extranodal natural killer/T cell lymphoma, nasal type.

Sarcopenia is known to be associated with an increased risk of adverse outcomes in a variety of malignancies, but its impact in extranodal natural killer/T cell lymphoma, nasal type (ENKTL-NT) is unknown. The aim of this study was to explore the prognostic relevance of sarcopenia defined by MRI-based masticatory muscle index in ENKTL-NT patients. A total of 112 patients with newly diagnosed ENKTL-NT who underwent cranial magnetic resonance imaging (MRI) were enrolled. The masticatory skeletal muscle index (M-SMI) was measured based on T2-weighted MR images and sarcopenia was defined by M-SMI<5.5 cm2/ m2. The median M-SMI was 5.47 (4.91-5.96) cm2/m2; 58 were identified with sarcopenia in this cohort. On multivariate analyses, sarcopenia was the only independently risk factor predicting overall survival (HR, 4.590; 95% CI, 1.657-12.715; p = 0.003), progression-free survival (HR, 3.048; 95% CI, 1.515-6.130; p = 0.002), and treatment response (HR, 0.112; 95% CI, 0.042-0.301; p < 0.001). In addition, we found that integrating sarcopenia into prognostic indices could improve the discriminative power of the corresponding original model. Stratification analysis showed that sarcopenia was able to further identify survival differences in patients that could not be distinguished by prognostic models. In summary, our study suggests that sarcopenia defined by MRI-based M-SMI represents a new and routinely applicable prognostic indicator of clinical outcome or predictor of treatment response in ENKTL-NT patients, and may aid in risk stratification and treatment decisions.

A case-control study on the effect of rhythmic masticatory muscle activity (RMMA) clusters on sleep fragmentation and severity of orofacial muscle pain in sleep bruxism.

Rhythmic masticatory muscle activity (RMMA) is a periodic muscle activity that characterises sleep bruxism (SB) events. These can occur as a single event, in pairs, or in clusters. Since RMMA episodes often occur in clusters and the relevance of this occurrence is unknown, we conducted a study to investigate the effect of RMMA clusters on sleep fragmentation and the severity of orofacial muscle pain. This study involved a secondary analysis using data from 184 adult subjects with orofacial muscle pain who underwent definitive polysomnography (PSG) for sleep bruxism diagnosis. Self-reported orofacial muscle pain (OFMP) was assessed using the numeric rating scale, and additional evaluation of side-to-side equivalence (symmetry) was described using a binary system. Among the 184 participants, 60.8% (n = 112) did not exhibit clusters and among the 72 participants with clusters, 36.1% (n = 26) and 63.9% (n = 46) were in the high and low RMMA frequency groups, respectively. The high SB group had significantly three times more phasic RMMA events than the noncluster group. A total of 89.67% (n = 165) of subjects reported orofacial muscle pain. While there was no difference in the severity of OFMP among groups, a significant decrease in symmetry between the severity of temporal muscle pain on the left and right sides was noted in the cluster group compared with the noncluster group. Clustering of RMMA events is associated with sleep fragmentation. The asymmetry of temporal muscle pain is related to the presence of RMMA clusters in sleep bruxism.

Effect of occlusal equilibration on masticatory muscle activity in females with sleep bruxism: a double-blind randomised controlled trial.

Masticatory muscle activity during sleep has been considered independent of variations in the structural characteristics of the dental occlusion. However, scientific evidence contradicting an occlusal causal role is missing. The purpose of this study was to test the null hypothesis that sleep bruxism (SB) is independent of the presence of occlusal interferences. A total of 17 healthy female subjects (mean [SD] age 24.9 [4.1] years) presenting with SB, and randomly divided into two groups, were evaluated after receiving either elimination of occlusal interferences (Test group) or elimination of sharp margins without change in occlusal contacts (Control group). Audio-video polysomnography (PSG) recordings were undertaken before and after treatment (mean [SD] duration 14.4 [3.8] months). Two subjects in each group (< 2 rhythmic masticatory muscle activity [RMMA]/h) were excluded for statistical analysis. During the total sleep time (TST), the Test group exhibited a higher reduction in frequency of episodes per hour than the Control group (p < 0.05). The reduction in duration of episodes was also higher in the Test group during the TST. The Test group presented an increase in sleep stage N3 (p < 0.05) at the final PSG when compared with the initial PSG, and a higher percentage of N3 (p < 0.05) at the final PSG when compared to the Control group. Elimination of occlusal interferences resulted in a significant reduction of masseter and temporal muscle activity during sleep in females presenting with SB. Based on these results, the null hypothesis is rejected. The hypothesis of occlusal interferences as a risk factor for SB is still patent.

Correlation of masticatory muscle activity and occlusal function with craniofacial morphology: a prospective cohort study.

OBJECTIVES: Masticatory function, including masticatory muscle activity and occlusal function, can be affected by craniofacial morphology. This study aimed to investigate the relationship between craniofacial morphology and masticatory function in participants who had completed orthodontic treatment at least two years before and had stable occlusion. MATERIALS AND METHODS: Fourty-two healthy participants were prospectively enrolled and divided into three vertical cephalometric groups according to the mandibular plane angle. Masticatory muscle activity (MMA) in the masseter and anterior temporalis muscles was assessed using surface electromyography. The occlusal contact area (OCA) and occlusal force (OF), defined as occlusal function in this study, were evaluated using occlusal pressure mapping system. Masticatory muscle efficiency (MME) was calculated by dividing MMA by OF. The craniofacial morphology was analyzed using a lateral cephalogram. The masticatory function was compared using one-way analysis of variance. Pearson correlations were used to assess relationships between craniofacial morphology and masticatory function. RESULTS: The hypodivergent group had the lowest MMAand the highest MME in the masseter (167.32 ± 74.92 µV and 0.14 ± 0.06 µV/N, respectively) and anterior temporalis muscles (0.18 ± 0.08 µV/N, p < 0.05). MMA in the masseter showed a positive relationship with mandibular plane angle (r = 0.358), whereas OCA (r = -0.422) and OF (r = -0.383) demonstrated a negative relationship (p < 0.05). The anterior temporalis muscle activity negatively correlated with ramus height (r = -0.364, p < 0.05). CONCLUSIONS: Vertical craniofacial morphology was related to masticatory function. Hypodivergent individuals may have low MMA and high occlusal function, resulting in good masticatory muscle efficiency. CLINICAL RELEVANCE: Hypodivergent individuals require careful consideration in orthodontic diagnosis and prosthetic treatment planning.

Wearables for personalized monitoring of masticatory muscle activity - opportunities, challenges, and the future.

Wearable devices are worn on or remain in close proximity of the human body. The use of wearable devices specific to the orofacial region is steadily increasing. Orofacial applications of wearable devices include supplementing diagnosis, tracking treatment progress, monitoring patient compliance, and understanding oral parafunctional behaviours. In this short communication, the role of wearable devices in advancing personalized dental medicine are highlighted with a specific focus on masticatory muscle activity monitoring in naturalistic settings. Additionally, challenges, opportunities, as well as future research areas for successful use of wearable devices for precise, personalized care of muscle disorders are discussed.

The influence of age on the frequency of rhythmic masticatory muscle activity during sleep in general population differs from that in clinical research samples.

BACKGROUND: During sleep, limb and jaw muscle motor activity can be quantified by electromyography (EMG). The frequency of periodic limb activity during sleep increases with age in both the general and clinical research populations. The literature is controversial regarding stability, over age, of the frequency of rhythmic masticatory muscle activity (RMMA), which is one biomarker of sleep bruxism (SB). OBJECTIVES: The purpose of this retrospective sleep laboratory study was to assess if any change in RMMA frequency occurs over age in the general population (GP) and two clinical research (CR) samples. METHODS: RMMA signals from polysomnography (PSG) recordings of 465 individuals, irrespective of SB awareness, were analysed. The sample comprised 164 individuals from the GP of Sao Paulo, and 301 individuals from Montreal and Osaka CR samples. Data were divided into two subgroups, younger (15-39) and older (40-80) participants. RMMA was classified as low frequency (<2 events/h) or high (≥2 events/h). Pearson correlation (R) and B (slope) analyses were performed with power estimations. RESULTS: In the GP sample, no significant change over age was noted in the RMMA index/year. In the CR samples, a significant reduction was observed in the RMMA index/year (-0.05) with age (R2  = .042; p < .001; 3.5 to 1.5 RMMA/h from 20 to 60 years old). CONCLUSIONS: In the GP, the RMMA index remained stable over age. In the CR samples, a significant, reduction was observed. Prospective studies with multiple home sleep recordings, in both general and clinical research populations, are needed before extrapolating from the present findings.

Research progress in effect of chewing-side preference on temporomandibular joint and its relationship with temporo-mandibular disorders. / åä¾§å’€åš¼å¯¹é¢žä¸‹é¢Œå ³èŠ‚ç»“æž„çš„å½±å“åŠå ¶ä¸Žé¢žä¸‹é¢Œå ³èŠ‚ç´Šä¹±çš„å ³ç³».

Chewing-side preference is one of the risk factors for temporomandibular disorders (TMD), and people with chewing-side preference is more prone to have short and displaced condyles, increased articular eminence inclination and glenoid fossa depth. The proportion of TMD patients with chewing-side preference is often higher than that of the normal subjects. Clinical studies have shown a strong correlation between chewing-side preference and TMD symptoms and signs; and animal studies have shown that chewing-side preference can affect the growth, development, damage and repair of the mandible. After long-term unilateral mastication, changes in the stress within the joint cause the imbalance of temporomandibular joint (TMJ) structural reconstruction, the transformation and even destruction of the fiber structure of masticatory muscle, resulting in uncoordinated movement of bilateral muscles. The joint neurogenic diseases caused by the increase of neuropeptide substance P and calcitonin-gene-related-peptide (CGRP) released locally by TMJ may be the mechanism of TMD. This article reviews the research progress of the influence of chewing-side preference on the structure of TMJ, the relationship between chewing-side preference and TMD, and the related mechanisms.

Comparison of percutaneous balloon compression and microvascular decompression in the treatment of trigeminal neuralgia.

Objective: To compare the effect of percutaneous balloon compression (PBC) and microvascular decompression (MVD) in the treatment of trigeminal neuralgia (TN). Methods: Data of 98 patients with TN, admitted to Chenzhou First People's Hospital from May 2020 to May 2022, were retrospectively collected. Patients were divided into two groups based on the surgical method. A total of 53 patients treated with PBC comprised the PBC-group and 45 patients treated with MVD comprised the MVD-group. The immediate pain relief, long-term efficacy, surgical complications, and masticatory muscle strength of the two groups were compared and analyzed. Results: There was no significant difference in the immediate pain relief and long-term e efficacy, between the two groups (P>0.05). Complication rate in the PBC-group was significantly lower than that in the MVD-group (3.77% vs 17.78%, P<0.05). Medical records within 14 days after the operation showed that the incidence of facial numbness and masticatory muscle weakness in the PBC-group were 37.74% and 28.30% respectively, significantly higher than those in MVD-group (4.44% and 2.22%) (P<0.05). These symptoms gradually improved three months after the surgery, and were almost completely resolved after six months. Conclusions: Compared with MVD, PBC has the same effect in the treatment of TN. PBC is a minimally invasive, safe, and effective method with a low complication rate. Although masticatory muscle strength is slightly impacted by PBC, it gradually recovers within six months after the operation.

A High Masticatory Muscle Tone Predicts the Risk of Malnutrition and Frailty in Inpatient Older Adults: A Cross-Sectional Study.

INTRODUCTION: The prevalence of malnutrition among inpatient older adults is as high as 20∼50%. Masticatory performance is known to affect the nutritional status of individuals. However, an objective measurement to reflect the real status of masticatory muscle performance is lacking at the bedside. METHODS: This pilot study analyzed the masticatory performance using surface electromyography (sEMG) of masticatory muscles that measures both muscle strength and muscle tone at the bedside. The nutritional status was measured using the Mini Nutritional Assessment tool. The handgrip strength was measured using a hand dynamometer. The statistical data were analyzed using SPSS 25 software. RESULTS: The data revealed that female inpatient older adults more frequently had substandard handgrip strength (p = 0.028), an at-risk and poor nutritional status (p = 0.005), and a higher masseter muscle tone (p = 0.024). Inpatient older adults with an at-risk and poor nutritional status had an older age (p = 0.016), lower handgrip strength (p = 0.001), and higher average masseter muscle tone (p = 0.01). A high masseter muscle tone predicted the risk of having an at-risk and poor nutritional status. The at-risk or poor nutritional status predicted having a substandard handgrip strength by 5-fold. CONCLUSIONS: A high masticatory muscle tone predicts malnutrition and frailty. Medical professionals should combat masticatory dysfunction-induced malnutrition by detecting masticatory muscle performance using sEMG and referring patients to dental professionals. Additionally, encouraging inpatient older adults to perform oral motor exercise is recommended.