Search Results (246)

Background/Objective: Postural stability and motor coordination require precise regulation of agonist and antagonist muscle activities. Jaw clenching modulates neuromuscular control during static and reactive postural tasks. However, its effects on dynamic voluntary movement remain unclear. This pilot study aimed to investigate the effects of jaw clenching on muscle activity and kinematics during repetitive single-leg sit-to-stand task performance. Methods: Eleven healthy adults (age: 21.2 ± 0.4 years; 6 males and 5 females; height: 167.9 ± 9.6 cm; body weight: 59.7 ± 8.1 kg) performed repetitive single-leg sit-to-stand tasks for 30 s under jaw-clenching and control conditions. Electromyography (EMG) signals from eight muscles and kinematic data from 16 inertial measurement unit sensors were analyzed, focusing on the seat-off phase. Results: Jaw clenching resulted in a significantly lower success rate than the control condition (success rate: 0.96 ± 0.13 vs. 0.78 ± 0.29, p = 0.047). Under the jaw clenching condition, failed trials exhibited higher medial gastrocnemius and masseter EMG activity (p < 0.001), lower erector spinae longus EMG activity (p < 0.001), and altered kinematics, including increased trunk yaw and roll angles (p < 0.001). Jaw clenching increased the coactivation of the gastrocnemius and tibialis anterior muscles (p < 0.001), disrupting the reciprocal muscle patterns critical for task performance. Conclusions: These findings suggest that jaw clenching may reduce task performance by altering neuromuscular coordination during dynamic postural tasks. Full article

Background/Objective: This study aimed to evaluate the strain values (SVs) of masseter muscle activity in dentofacial deformities (DDs) using ultrasound elastography. Methods: The DD group consisted of 60 patients with dentofacial deformities with skeletal class II or III malocclusion, and the control group consisted of 26 volunteers with normal occlusion. The SVs and the cross-sectional area of the masseter muscle were measured using an ultrasonic elastography. These were measured at three functional positions: resting, mouth opening, and clenching. The SVs were statistically compared with the DD and control groups. Changes in the cross-sectional area and factors (patient status, skeletal morphology, and oral function) related to the SVs in the study group were statistically analyzed. Results: The SVs were significantly higher during clenching than in resting and mouth opening in both groups, although there was no correlation between the DD group and the control group. The cross-sectional area was larger during clenching, resting, and mouth opening. The resting SVs decreased as the masseter muscle cross-sectional area increased. The SVs of clenching increased with higher resting SVs and decreased with greater maximum mouth opening. Conclusions: The SVs measured by ultrasound elastography changed depending on functional mandibular movement and have the potential to evaluate the masseter muscle activity of dentofacial deformities. Full article

Bruxism, defined as a repetitive jaw-muscle activity characterized by clenching or grinding of teeth and/or by bracing or thrusting of the mandible, is a prevalent behavior affecting up to 22% of adults worldwide. While traditionally viewed as a disorder, current understanding recognizes bruxism as a behavior that may have both positive and negative consequences. Objective assessment methods for evaluating the effectiveness of interventions in symptomatic patients remain limited. This article presents the first longitudinal study using myotonometry to quantify changes in masseter muscle following botulinum toxin type A (BoNT-A) treatment in patients with symptoms of bruxism. In total, 57 patients were recruited and their masseter muscle tone, stiffness, elasticity, relaxation time, and creep parameters were measured. Measurements were performed at baseline, 3 weeks, and 3 months post-injection during both rest and maximum voluntary contraction. BoNT-A treatment produced significant improvements in all biomechanical parameters, with the greatest effects observed in patients with the highest baseline muscle values. The objective biomechanical changes correlated with the duration of BoNT-A’s therapeutic effects. These findings establish myotonometry as a valuable tool for objective assessment of masticatory muscle function and demonstrate that BoNT-A produces measurable, long-lasting biomechanical changes in masseter muscle parameters, supporting its possible clinical application in this challenging condition. Full article

Mandibular asymmetry often requires orthognathic surgery, and postsurgical relapse remains a concern. The masseter muscle may influence stability, but most studies have emphasized volumetric rather than qualitative changes. This prospective study evaluated 24 patients with mandibular asymmetry using ultrasonography preoperatively and at 1, 3, and 6 months after surgery. The parameters measured were thickness, stiffness ratio, echo intensity, and blood flow. The results showed significant postoperative adaptations. Masseter echo intensity increased markedly at 1 month (p < 0.001), peaked at 3 months (p = 0.042), and decreased toward baseline at 6 months (p < 0.001). Blood flow increased significantly from T1 to T2 (p < 0.001). Bite force dropped transiently at 1 month (p < 0.001) but recovered by 6 months (p < 0.001). At baseline, BMI correlated with echo intensity (r = 0.724, p < 0.001) and grip strength correlated with bite force (r = 0.705, p < 0.001). The stiffness ratio difference (contraction–rest) correlated with bite force (right: r = 0.629; left: r = 0.690). Relapse occurred in 25% of patients and correlated only with preoperative deviation and not ultrasound indices. Conclusions: Ultrasonography revealed meaningful qualitative muscle changes during recovery, though these were not strong predictors of relapse. Ultrasound remains a reliable, noninvasive tool for monitoring postoperative adaptation. Full article

Background: The high perimandibular approach (HPA) is a feasible surgical technique for open reduction and internal fixation (OR-IF) of mandibular condylar fractures, offering reduced complication rates. In this study, we retrospectively evaluated the treatment outcomes and complications associated with HPA use. Patients and Methods: Patients who underwent OR-IF for mandibular condylar fractures using the HPA at three hospitals in Shimane between June 2019 and March 2024 were included. Data collected included the mechanism of injury, AO classification of the fracture site, fracture type and mode, surgical duration, mouth-opening range at 6 months post-operatively, and peri- and post-operative complications. Results: A total of 42 patients (46 condylar fractures; 18 males and 24 females; mean age, 63.0 years) were included. The fracture pattern included dislocations in 18 cases (42.8%). The mean surgical duration was 75.0 min. Post-operative trismus occurred in 16 patients (38.1%) at 6 months. Longer surgical duration and dislocated fractures were significantly associated with post-operative trismus (p < 0.05). Conclusions: The HPA is safe and effective for managing mandibular condylar fractures. However, post-operative trismus may be influenced by longer surgical duration and fracture types, warranting further investigation and potential post-surgical management. Full article

Introduction: Botulinum toxin-A (BTX-A) injections are regularly used to treat temporomandibular disorders (TMD). However, consensus regarding the long-term efficacy of BTX-A for TMD-related myalgia remains lacking. This pragmatic, practice-based clinical study aimed to evaluate the Patient-Reported Outcome Measures of pain, health status, quality of life, and function after BTX-A injections in patients with TMD-related myalgia. Methods: This prospective cohort study included 35 patients with TMD-related myalgia who received BTX-A injections in the masseter and temporalis muscles. The Visual Analogue Scale for pain, the EQ-5D-3L for health status, the Oral Health Impact Profile-14 for oral health-related quality of life, the Mandibular Function Impairment Questionnaire for function and the maximum interincisal opening were assessed before treatment and at one, three and six months follow-up. Results: Patients reported a statistically significant and clinically relevant reduction in pain (p < 0.001), improvement of health status (p ≤ 0.003), and oral health-related quality of life (p < 0.001) at one-month follow-up, which remained present at three and six months post-treatment. Self-reported mandibular function and active and passive mouth opening showed no significant change over all time points. Conclusions: In this pragmatic cohort, BTX-A injections in the masseter and temporalis muscles seem to improve pain and oral health-related quality of life in patients with TMD-related myalgia within one month and show effects lasting up to six months, while mandibular function did not improve. Full article

End-stage temporomandibular joint (TMJ) disorders often necessitate total joint replacement, and the selection of biomaterial directly impacts long-term outcomes. Ti6Al4V and CoCrMo are commonly used alloys, yet their biomechanical performance in patient-specific prostheses remains insufficiently compared. This study aimed to evaluate the mechanical response of custom TMJ prostheses fabricated from these alloys using finite element analysis (FEA). A three-dimensional mandibular model was created from computed tomography data, and a patient-specific prosthesis was designed in SolidWorks (Dassault Systèmes, SolidWorks Corp., Waltham, MA, USA) and analyzed in ANSYS Workbench 2022 R1 (Ansys Inc., Canonsburg, PA, USA). Physiological loading was simulated by applying forces at the insertion sites of the temporalis, masseter, and medial pterygoid muscles. In the Ti6Al4V model, maximum von Mises stresses reached 192.18 MPa on the mandibular component and 92.004 MPa on the fossa prosthesis, whereas the CoCrMo model demonstrated higher stresses of 204.31 MPa and 94.182 MPa, respectively. Both alloys exhibited similar stress distributions, but Ti6Al4V generated lower stress magnitudes, indicating more favorable load transfer and a reduced risk of mechanical overload on articulating components. These findings underscore the significance of alloy selection in optimizing TMJ prostheses and demonstrate the value of FEA as a tool for guiding future patient-specific designs. Full article

This study investigated bite force changes after botulinum toxin type A (BoNT-A) injection into different masticatory muscles. Thirty-five male participants were divided into three groups: masseter only (M), masseter and temporalis (MT), and masseter, temporalis, and medial pterygoid (MTP). Bite force was measured before and up to 6 months after injection with the Dental Prescale II system. Baseline values showed no significant group differences. Group M exhibited significant reduction at 1 and 2 weeks, with recovery within 1 month. Group MT showed a similar transient decrease, also recovering after 1 month. In contrast, Group MTP demonstrated a more pronounced and prolonged reduction, persisting up to 4 months before recovery. These results indicate that the extent and duration of BoNT-A effects depend on the number of muscles injected. Multi-muscle injections, including the medial pterygoid, provide more durable suppression. However, further research involving patient populations is needed to clarify whether multi-muscle injection strategies provide therapeutic benefits in clinical conditions such as temporomandibular disorders or oromandibular dystonia. Full article

Background: Sleep bruxism (SB) is increasingly recognized not merely as a movement disorder but as a multifactorial condition in which physiological, behavioral, and contextual factors converge. Objective: To comprehensively characterize SB in young adults, integrating polysomnography (PSG) and surface electromyography (sEMG) to describe sleep architecture, periodic limb movements (PLMs), and masticatory muscle activity; compare these parameters with matched controls; and explore clinical correlations relevant to dental practice and individualized management. Methods: Forty university adults (20 PSG-confirmed SB; 20 controls) underwent PSG assessment of total sleep time, sleep stages, arousals, apnea, oximetry, and PLMs. EMG activity of the masseter and temporalis muscles was recorded in 37 participants (18 SB, 19 controls). Statistical analyses included t-tests, Mann–Whitney U tests, and multivariate logistic regression to identify independent predictors of SB. Results: SB participants exhibited higher bruxism event counts (p ≤ 0.001; PS = 0.94), increased PLMs (p ≤ 0.01; PS = 0.75), shorter REM sleep duration (p = 0.04; d = 0.69), and higher bruxism-related arousal indices (p ≤ 0.001; PS = 83.4). Left masseter activity differed significantly (p = 0.03; d = 0.50), while other muscle measures showed no significant differences. Logistic regression identified age (OR = 0.59, p = 0.02), PLMs (OR = 0.96, p = 0.03), and REM sleep duration (OR = 0.98, p = 0.05) as independent predictors, explaining 58% of the variance. Conclusions: These findings provide a comprehensive profile of SB in young adults. Integrating PSG, sEMG, and oral assessments supports early diagnosis, personalized management, and interdisciplinary collaboration to prevent complications. Full article

Background: The deep head of the masseter muscle (DHMM) is an underrecognized anatomical structure, frequently absent from standard anatomical references and often overlooked in maxillofacial surgical planning. Its morphological variability, spatial complexity, and relationship with neurovascular structures carry significant implications for imaging interpretation, diagnosis, and surgical outcomes. Objective: The objective of this paper is to synthesize current anatomical, embryological, and radiological knowledge on the DHMM, and to introduce a refined morphological classification with direct clinical and surgical relevance. Methods: A comprehensive literature review was performed, incorporating cadaveric dissections, radiological imaging (MRI, DTI, HRUS, CT), and clinical case reports. Emphasis was placed on anatomical variability, radiological detectability, and surgical accessibility. Based on these findings, a three-type classification with clinically relevant subtypes was formulated and correlated with imaging features and procedural risk. Results: The DHMM can be categorized into three principal types: Type I—classical form with fascial separation; Type II—fused with the medial pterygoid; Type III—segmented into two muscular bellies. Each type may present a subtype b, characterized by neurovascular penetration, which significantly increases surgical risk and alters procedural strategy. MRI and high-resolution ultrasonography were identified as the most reliable modalities for in vivo differentiation, with HRUS providing additional value for dynamic and volumetric assessment. Conclusions: Recognition of DHMM morphology, including high-risk neurovascular subtypes, is essential for accurate diagnosis, surgical planning, and prevention of complications. The proposed classification offers a reproducible framework for imaging standardization, surgical risk stratification, and integration into anatomical atlases and clinical guidelines. Full article

Background/Objectives: Bruxism is a prevalent parafunctional activity that induces masticatory muscle hypertrophy and physiological mandibular bone alterations. While botulinum toxin type A (BTX-A) injections effectively reduce muscle hyperactivity, objective radiological assessment of their skeletal effects remains limited. This study aimed to quantitatively evaluate the impact of BTX-A on mandibular trabecular bone structure by assessing potential reductions in fractal dimension (FD) in bruxism patients compared to controls. Methods: This retrospective matched-pair study included 42 bruxism patients (39 females, 3 males) receiving 50 U of BTX-A in masseter muscles and 32 age-matched non-bruxism controls (30 females, 2 males). Pre- and 6-month post-treatment panoramic radiographs were analyzed. FD values were calculated from bilateral condylar neck, ramus, and angulus regions. Results: Statistically significant reductions in FD values were observed in the angulus regions post-treatment (Right: 1.3856 to 1.2995; Left: 1.3718 to 1.2529, p < 0.001). Postoperative FD values in the BTX-A group showed no significant differences when compared to the control group (p > 0.05). Conclusions: BTX-A administration leads to measurable, region-specific reductions in mandibular trabecular bone fractal dimension, particularly in the angulus. The postoperative similarity to the control group suggests a potential normalization of bone structure following treatment. These findings highlight the clinical utility of fractal analysis for monitoring osseous adaptations in neuromuscular interventions. Full article

Background: Temporomandibular disorders are a generic term referred to clinical conditions involving the jaw muscles and temporomandibular joint with multifactorial pattern and genetic background. The aim of this observational study was to investigate the correlation between craniomandibular disorders and the presence of occlusal alterations. A clinical evaluation of the occlusal and articular status of the patients was carried out, integrating the latter with the electromyographic recording the activity of the masseter and temporalis muscles. Methods: A clinical observational study on 20 adults assessed temporomandibular disorders using DC/TMD criteria, anamnesis, clinical exams, occlusal and electromyographic analyses. Occlusion was evaluated morphologically and functionally. Electromyography tested static/dynamic muscle activity. Data were statistically analyzed using t-tests and Pearson correlation (p < 0.05). Results: Electromyographic analysis revealed significant differences between subjects with and without visual correction, suggesting that visual input influences masticatory muscle activity. Correlations emerged between occlusal asymmetries and neuromuscular parameters. These findings highlight clinical implications for mandibular function, muscle symmetry, and the potential for therapeutic rebalancing through targeted interventions. Conclusions: The study demonstrates a significant correlation between visual–motor integration and masticatory muscle efficiency. It emphasizes lateralized neuromuscular activation’s influence on occlusal contact distribution. Moreover, it identifies mandibular torsion–endfeel inverse correlation as a potential diagnostic marker for craniomandibular dysfunctions via surface electromyography. Full article

A total of 304 patients with bruxism (206 women, 98 men; mean age: 52.5 years) received 25 units of botulinum toxin injected into the bilateral masseter muscles; the changes in various clinical symptoms and their contributing factors were analyzed 2 months after treatment. The mean masseter muscle electromyographic amplitude (189 μV) and maximal bite force (618.4 N) significantly decreased after botulinum toxin therapy compared to that at baseline (55.4 μV, 527.3 N, respectively; p < 0.001). Maximal mouth opening (44 mm), sleep quality (visual analog scale: 5.3), shoulder and neck stiffness (6.7), and headache (5.4) significantly improved after the injection (47.3 mm, 6.6, 4.7, and 2.6, respectively; p < 0.001). Multivariate analysis revealed that the mean masseter electromyographic amplitude reduction rate was significantly affected by age, sex, and baseline amplitude (all p < 0.001); the maximal bite force reduction rate was influenced by age (p < 0.001), sex (p = 0.007), and baseline bite force (p = 0.008). Age, sex, and muscle activity may affect the therapeutic effects. A more effective outcome for bruxism can be achieved using a tailored approach involving dose adjustment, thereby preventing the side effects attributed to excessive dosage. Full article

Background: Cannabidiol (CBD) has demonstrated potential as a therapeutic agent for muscle tension, pain, and sleep bruxism, yet its broader impact on comorbid conditions such as sleep disturbance and migraine disability remains underexplored. This study aimed to assess the effects of topical CBD on sleep quality and migraine-related disability in patients with bruxism-associated muscular pain. Methods: In a randomized, double-blind clinical trial, 60 participants with bruxism were allocated equally into three groups: control (placebo gel), 5% CBD gel, and 10% CBD gel. Participants applied the gel intraorally to the masseter muscles nightly for 30 days. Sleep quality and migraine-related disability were assessed using the Pittsburgh Sleep Quality Index (PSQI) and the Migraine Disability Assessment Scale (MIDAS), respectively. Surface electromyography (sEMG) and the Bruxoff^® device were used for objective evaluation of muscle tension and bruxism intensity. Results: Both CBD treatment groups demonstrated statistically significant improvements in PSQI and MIDAS scores compared to the control group (p < 0.001). No significant differences were observed between the 5% and 10% CBD groups, suggesting comparable efficacy. The sEMG findings corroborated a reduction in muscle tension. Improvements in sleep and migraine outcomes were positively correlated with reductions in muscle activity and pain. Conclusions: Topical CBD gel significantly improved sleep quality and reduced migraine-related disability in patients with bruxism-associated muscular pain, supporting its role as a multifaceted therapeutic option in the management of TMD and related comorbidities. Further research is needed to confirm long-term benefits and determine optimal dosing strategies. Full article

Background: The occlusal angle (OA), influenced by pillow height, may affect muscle tension in the head and neck. However, its optimal range for minimizing muscle activation has not been clearly defined. Objective: This study aimed to investigate the effects of OA on the resting muscle activity of masticatory and cervical muscles and to identify an optimal OA range using cluster analysis and linear mixed-effects modeling. Methods: The resting muscle activities of the masseter (MAS), temporalis (TEM), sternocleidomastoid (SCM), and posterior vertebral muscles (PVM) were measured at OA conditions modulated by pillow heights of 0, 5, and 10 cm at 0, 1, and 5 min in the supine position. Intraclass correlation coefficients (ICCs) assessed measurement reliability. Statistical analyses included ANOVA, ROC curve analysis, k-means clustering, and linear mixed-effects models. Results: MAS and TEM resting muscle activity ratio (RMR) significantly increased with larger OA values (p < 0.001), while SCM showed decreased activation (p = 0.001). An OA range of 105°–111° was identified as the center of a low-activity cluster, and an upper cut-off of 138° was associated with potential muscular overload. ICC values for MAS and SCM ranged from 0.82 to 0.89, indicating excellent test–retest reliability. Conclusions: OA modulated by pillow height is a modifiable factor that influences muscle activity. An OA of 105°–111° may serve as a practical comfort zone, especially for individuals at risk of TMDs. Full article