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The aim of this study was to understand the temporal and spatial distribution of canonical endochondral ossification (CEO) and non-canonical endochondral ossification (NCEO) of the normal growing rat condyle, and to evaluate their histomorphological changes following the simultaneous hypotrophy of the unilateral masticatory closing muscles with botulinum toxin (BTX). 46 rats at postnatal 4 weeks were used for the experiment and euthanized at postnatal 4, 8, and 16 weeks. The right masticatory muscles of rats in experimental group were injected with BTX, the left being injected with saline as a control. The samples were evaluated using 3D morphometric, histological, and immunohistochemical analysis with three-dimensional regional mapping of endochondral ossifications. The results showed that condylar endochondral ossification changed from CEO to NCEO at the main articulating surface during the experimental period and that the BTX-treated condyle presented a retroclined smaller condyle with an anteriorly-shifted narrower articulating surface. This articulating region showed a thinner layer of the endochondral cells, and a compact distribution of flattened cells. These were related to the load concentration, decreased cellular proliferation with thin cellular layers, reduced extracellular matrix, increased cellular differentiation toward the osteoblastic bone formation, and accelerated transition of the ossification types from CEO to NCEO. The results suggest that endochondral ossification under loading tended to show more NCEO, and that masticatory muscular hypofunction by BTX had deleterious effects on endochondral bone formation and changed the condylar growth vector, resulting in a retroclined, smaller, asymmetrical, and deformed condyle with thin cartilage. • spatial and temporal patterns of endochondral ossification in growing rat condyle. • normal transition from canonical to non-canonical endochondral ossification under loading over time. • accelerated endochondral transition due to BTX-induced masticatory muscular hypofunction. • retroclined condyle with anteriorly shifted narrower articulating surface following BTX treatment. [ABSTRACT FROM AUTHOR]

The prevalence of obesity is increasing significantly worldwide, raising great concern among health professionals. This observational study evaluated the electromyographic activity and thickness of the masseter and temporalis muscles, in addition to the maximum molar bite force, in obese and eutrophic subjects. Sixty subjects were divided into three groups: I (7–12 years), II (13–20 years), III (21–40 years) and sex: with 10 men and 10 women for each group. Electromyographic recordings of the masticatory muscles were obtained during mandibular tasks. The masticatory muscles thicknesses were obtained at rest and during dental clenching. The maximum molar bite forces were measured on the right and left sides. The difference in outcome measures between the groups and sex was analyzed using Mann-Whitney U test (p < 0.05) and analysis of covariance (ANCOVA). Electromyographic activity in the masseter and temporal muscles consistently displayed lower levels in obese subjects of both sexes across all three age groups during mandibular tasks. Additionally, greater thickness of the masticatory muscles was observed in obese subjects of both sexes across all three age groups. Obese women in Group II displayed higher values of molar bite force, both on the right and left sides, compared to eutrophic women. On the other hand, women in Group III exhibited higher values of molar bite force on the right side in comparison to eutrophic women. This study underscores the potential impact of obesity on the morphofunctional aspects of the stomatognathic system in subjects aged 7 to 40 years. • Obesity's impact on masticatory muscle function and bite force. • Obesity reveals altered masticatory muscle function and morphology. • Elevation of bite force in obesity reveals morphofunctional effects. [ABSTRACT FROM AUTHOR]

This cross-sectional study aimed to establish normative values for masticatory side switch (MSS) frequency in young Mexican adults and to assess the relationship between various indices and MSS frequency when masticating different chewing materials. We enrolled 101 dentate adults and performed four masticatory assays that involved masticating different chewing materials (i.e., two-colored chewing gum, sweet cracker, salty cracker, and bread). Participants were asked to eat and swallow these foods and to chew the gum for 40 cycles and the following indices were determined: MSS index (MSSI), unilateral chewing index, chewing cycle duration, and number of cycles before terminal swallowing. The participants then rated perceived flavor intensity, salivary flow, and muscle fatigue during each trial. The MSSI ranged from 0.03–0.06 (10th percentile) to 0.48–0.54 (90th percentile). A repeated-measures general linear model revealed a mean MSSI value of 0.28 (95 %CI, 0.25–0.30) adjusted by several factors. Male sex, soft food, and the last chewing period were associated with lower MSS frequency. Spearman's test showed a high correlation for the MSSI among the different foods. MSSI correlated negatively with the unilateral chewing index for each chewing material and with number of cycles for the sweet cracker. However, no significant correlation was detected between MSSI and sensory perception. In healthy dentate individuals, the mean MSS relative frequency is 25–30 % with an 80-central percentile of 5–50 % of the maximum possible side changes. Lower MSS frequencies were detected in men, when chewing soft food, and during the final chewing period. • The mean side switch relative frequency is 25–30 % while chewing nutritive foods. • The normal range of masticatory side switch relative frequency is 5–50 %. • Gender, food type, and chewing period are related to side switch frequency. • Masticatory side switch frequency is stable for each chewing material. • Side switch frequency is not obviously correlated with sensory perception. [ABSTRACT FROM AUTHOR]

The masticatory function is intricately linked to several factors like natural teeth count, occlusion, masticatory muscles, and tongue coordination. This study's goal was to formulate a comprehensive masticatory function model, considering sarcopenia's conceptual structure, and subsequently validate its measurement efficacy. The study encompassed 753 participants (59.1 % women; mean age: 73.0 ± 5.1 years) from an urban community. The model amalgamated masseter muscle mass, occlusal force, and mixing ability. Based on the Asian Working Group for Sarcopenia 2019 classification, participants were categorized into a multiple masticatory dysfunction (MMD) or severe MMD (S-MMD) group. Logistic regression analysis gauged the model's validity, using serum albumin levels and self-reported chewing difficulties as dependent variables. Of the total, 61 (8.1 %) participants exhibited MMD, while 24 (3.2 %) had S-MMD. S-MMD was correlated with low serum albumin levels (odds ratio: 3.62; 95 % confidence interval: 1.07–12.29) and heightened self-reported chewing difficulties (odds ratio: 2.82; 95 % confidence interval: 1.09–7.28). Our multiple masticatory function model offers a straightforward approach for assessing MMD. Furthermore, the study establishes a link between S-MMD, nutritional vulnerability, and self-reported chewing challenges, thus affirming the model's credibility. • Declines in masticatory function have been linked to frailty and sarcopenia. • We designed a multiple masticatory function model comprising multiple factors. • The model evaluated multiple masticatory dysfunction in 753 community patients. • Multiple masticatory dysfunction was correlated with nutritional risks in older adults. [ABSTRACT FROM AUTHOR]

• Cannabidiol and cannabinol alone and in combination reversed masseter muscle sensitization in a behavioral model of temporomandibular disorders. • Both cannabinoids decreased the mechanical sensitivity of masseter muscle afferent fibers. • Though not as effective as delta-9-tetrahydrocannabinol, these compounds do not cause psychotropic effects. This study investigated whether local intramuscular injection of non-psychoactive cannabinoids, cannabidiol (CBD), cannabinol (CBN), cannabichromene (CBC) and their combinations can decrease nerve growth factor (NGF)-induced masticatory muscle sensitization in female rats. In awake rats, changes in mechanical sensitivity induced by intramuscular injection of NGF and cannabinoids were measured by applying an electronic von Frey hair over the masseter muscle to measure the withdrawal response. The effect of CBD (5 mg/ml) and CBN (1 mg/ml) or their combinations CBD/CBN (1:1 mg/ml or 5:1 mg/ml) were assessed. To confirm a peripheral action, electrophysiological experiments were undertaken in anesthetized rats to examine whether intramuscular injections of CBD (5 mg/ml) and CBN (1 mg/ml) altered the mechanical threshold of masticatory muscle mechanoreceptors. In behavioral experiments, CBD (5 mg/ml) or CBN (1 mg/ml) decreased NGF-induced mechanical sensitization. Combinations of CBD/CBN induced a longer-lasting reduction of mechanical sensitization than either compound alone. No significant change in mechanical withdrawal threshold was observed in the contralateral masseter muscles and no impairment of motor function was found with the inverted screen test after any of the treatments. Consistent with behavioral results, CBD (5 mg/ml), CBN (1 mg/ml) and the combination of CBD/CBN (1:1 mg/ml) increased the mechanical threshold of masseter muscle mechanoreceptors. However, combining CBD/CBN (5:1 mg/ml) at a higher ratio reduced the duration of this effect. This may indicate an inhibitory effect of higher concentrations of CBD on CBN. These results suggest that peripheral application of these non-psychoactive cannabinoids may provide analgesic relief for chronic muscle pain disorders such as temporomandibular disorders and fibromyalgia without central side effects. [ABSTRACT FROM AUTHOR]

• Occlusal interference induces oxidative stress in the masseter muscle. • UCP3 regulates redox status in occlusal abnormally related masseter muscle. • Oxidative stress links occlusal interference to masticatory dysfunction. To determine whether occlusal alteration contributes to masticatory muscle damage by inducing oxidative stress. Thirty Sprague-Dawley rats were randomly divided into six groups, including occlusal interference groups (3 days, 7 days, 14 days, 21 days, and removal for 3 days) and a sham group. A rat experimental model of occlusal interference was generated by a 0.6-mm unilateral bite-raise. The rats were euthanised for evaluation of histologic changes in the masseter muscles using haematoxylin-eosin staining. To further investigate the role of oxidative stress and uncoupling protein (UCP3) in the development of occlusal dysfunction-induced masseter damage, levels of UCP3 protein were measured by western blot analysis. Compared with the sham group, the connective tissue of the masseter muscle was extended partially and inflammatory cells appeared following the induction of malocclusion. With respect to the oxidative stress markers, there were increases in malondialdehyde (MDA) content but decreases in superoxide dismutase (SOD) and glutathione peroxidase (GPX) activities; furthermore, the expression of UCP3 was upregulated. After eliminating the occlusal interference for 3 days, the degree of inflammation was substantially alleviated, the MDA content decreased, and SOD and GPX activities increased. The expression of UCP3 decreased. Occlusal interference induces oxidative stress in the masseter muscle, regulated by UCP3. Overall, these findings have significant implications for the understanding of how occlusal dysfunction causes muscle fatigue and pain. [ABSTRACT FROM AUTHOR]

• Trigeminal, cervical, and upper limb systems have been functionally linked. • Modification in masticatory muscles contraction has been shown to affect whole body. • Distal muscle strength and performance has been shown to improve during clenched jaw. • Modification of jaw position can affect neck muscle endurance. • Any effort to maintain clenched jaw position should be noted during rehabilitations. To investigate the effect of resting jaw and maximum voluntary clenching on neck flexor and extensor muscle endurance. Neck flexor and extensor endurance was measured in a college health clinic in 85 male college students in two test positions: resting jaw (control) and maximum voluntary clenching. Mean neck flexor muscle endurance values during resting jaw and maximum voluntary clenching were 70.06 SD 28.24, and 60.03 SD 16.5, seconds respectively. Mean neck extensor muscle endurance values during resting jaw and maximum voluntary clenching were 105.54 SD 29.9, and 98.32 SD 24.54, respectively. Both values were significantly lower while maximum voluntary clenching as compared to resting jaw position (p < 0.05). Modification of jaw position can affect neck muscle endurance. Results of this study further supports sensory-motor relation between jaw and neck region. [ABSTRACT FROM AUTHOR]

• Unilateral simultaneous hypotrophy of masticatory muscles after BTX. • Compensatory supraerupted molars and occlusal plane cant on hypotrophic side. • Maxillomandibular asymmetry with decreased size and lateral tilting. • Adjusted dentoalveolar bone density and disorganized periodontal ligaments. The purpose of this study was to investigate changes in the dentoalveolus and occlusal plane associated with the hypotrophy of unilateral masticatory muscles following botulinum toxin (BTX) treatment in the juvenile period of rats. We hypothesized that the loss of functional loading of masticatory muscles and occlusal force invites compensatory dentoalveolar supraeruption, accelerating occlusal cant and skeletal asymmetry. In order to confirm this hypothesis, six-week-old male rats (N = 5) were treated with BTX simultaneously at the unilateral masseter, temporalis, and medial pterygoid muscles, with a booster injection after six weeks for the experimental group. The control group (N = 6) had saline injections on both sides at the same sites and on the same schedule. After 12 weeks, masseter and medial pterygoid muscles on the BTX side showed hypotrophic change. The mandibular structure was asymmetrical, with decreased size and lateral tilting. The maxillary and mandibular molars were supraerupted from the Frankfort plane or mandibular inferior border with lateral tilt. They accompanied downward occlusal plane cant resulting from the supraerupted maxillary and mandibular molars on the BTX side. The dentoalveolar structural changes included diminished alveolar bone density, narrow periodontal ligament space, and disorganized distribution of periodontal collagen fiber. Unilateral hypotrophy of masticatory muscles affected the growth, symmetry, and structure of the skeletal jaws and dentoalveolus. Our hypothesis about the dentoalveolar compensation, that muscular hypotrophy was closely integrated with dentoalveolar supraeruption and an inclined occlusal plane, was confirmed. [ABSTRACT FROM AUTHOR]

Highlights • The anterior digastric jaw-opening muscle (AD) is crucial for vital oral functions. • Tooth loss and dental implant treatment can induce adaptive changes in the rat AD: • Increased variability of AD myofibre cross-sectional area. • Altered myosin heavy chain (MyHC) isoform myofibre-type composition. • Such changes may contribute to motor adaptation after dental treatment in humans. Abstract Objective: to determine if tooth loss and dental implant placement in rats induce changes in the morphological and histochemical features of the Anterior Digastric muscle. Design: Adult male Sprague-Dawley rats had their right maxillary molar teeth extracted. 'Extraction-1' and 'Extraction-2 groups were sacrificed, respectively, 4 or 8 weeks later, and an Implant group had an implant placement 2 weeks after the molar extraction, and rats were sacrificed 3 weeks later (n = 4/group). Naive rats (n = 3) had no treatment. Morphometric and immunohistochemical techniques quantified Anterior Digastric muscle myofibres' cross-sectional area (CSA) and myosin heavy chain (MyHC) isoform proportions. Significant ANOVAs were followed by post-hoc tests; p < 0.05 and 0.1 were considered to reflect levels of statistical significance. Results: In naïve rats, the peripheral regions of the Anterior Digastric muscle was dominated by MyHC-IIx/b isoform and there were no MyHC-I isoforms; the central regions dominated by MyHC-IIx/b and MyHC-IIa isoforms. Compared with naive rats, tooth extraction produced, 8 (but not 4) weeks later, a decreased proportion of fast-contracting fatigue-resistant MyHC-IIa isoform (p = 0.08), and increased proportion of fast and intermediate fatigue-resistance MyHC-IIa/x/b isoform (p = 0.03). Dental implant placement following tooth extraction attenuated the extraction effects but produced a decreased proportion of fast-contracting fatiguable MyHC-llx/b isoform (p = 0.03) in the peripheral region, and increased inter-animal variability in myofibre-CSAs. Conclusions: Given the crucial role that the Anterior Digastric muscle plays in many vital oral functions (e.g., chewing, swallowing), these changes may contribute to the changes in oral sensorimotor functions that occur in humans following such treatments. [ABSTRACT FROM AUTHOR]

Highlights • Masseter EMG activities decreased with increased interocclusal distances (IOD). • Mandibular plane angle was associated with IOD-EMG relationships at 0% MVOBF. • Diversity in masticatory muscle activities may depend on craniofacial morphology. Abstract Objective: The aim was to investigate relationships amongst interocclusal distances, masticatory muscle electromyographic (EMG) activity during isometric contraction of masticatory muscles, and craniofacial morphology. Design: Twenty-eight women and 12 men (25.3 ± 3.8 years old) participated. After measuring maximal voluntary occlusal bite force (MVOBF) between the right-first premolars, the participants were asked to bite at submaximal levels of 0 (= holding the bite force transducer), 15, 22.5, and 30% MVOBF with the use of visual feedback. The thickness of a bite force transducer was set at 10, 12, 13, 14, 16, 17, 18, 19, 20, 22, and 24 mm (= interocclusal distance: IOD). Nine soft tissue craniofacial factors were assessed through digital photograph: face height, middle face height, lower face height, face width, inter-pupil distance and mandibular plane angle, lower face height / face height ratio, inter-pupil distance / facial width ratio and face width / face height ratio. Results: In the masseter muscle, EMG activity decreased with increased IODs. The participants with higher mandibular plane angle had more negative slope coefficients of IOD-EMG graphs at 0% MVOBF especially in male temporalis and female masseter and temporalis muscles, suggesting that a greater mandibular plane angle is associated with lower EMG activity at longer IOD. Conclusions: Overall the findings support the notion that craniofacial morphology is associated with differences in neuromuscular activity of the masticatory muscles, and suggest that the neuromuscular effects of oral appliances may be dependent on patients' craniofacial morphology and the thickness of the device. (247/250 words) [ABSTRACT FROM AUTHOR]

Highlights • A single intra-articular injection of CFA was efficient to induce a persistent inflammatory process in the ipsilateral TMJ. • The articular inflammation reduced area and diameter of fibers of masticatory muscles. • Induced inflammation in TMJ caused morphological and molecular changes in the contralateral joint. Abstract Objective To investigate morphological and biochemical changes in an experimental model of temporomandibular joint (TMJ) arthritis, as well as examine contralateral joint involvement and morphometric aspects of masticatory muscles in affected animals. Design Forty Wistar rats were allocated into three groups, as follows: a healthy control group (HG); and a group with arthritis induced in the left TMJ (IG); and a contralateral group with noninflamed right TMJ (CG). Arthritis was induced by intra-articular injection of 50 μL of Complete Freund's Adjuvant (CFA). Morphological analysis was performed using histological sections of TMJs stained with hematoxylin-eosin, picrosirius and toluidine blue. In addition, histomorphometric analyses of the articular cartilage, articular disc and masticatory muscles, were performed. Biochemical analysis of TMJ tissues included dosage of sulfated glycosaminoglycans (GAGs), zymography of the Matrix Metalloproteinases (MMPs) 2 and 9 and ELISA for the cytokines IL-6, TNF-α and IL-1β. The data were analyzed by paired and unpaired t-tests, with a p < 0.05. Results IG animals presented morphological and biochemical changes in their TMJ, including synovial membrane hyperplasia; chronic inflammatory infiltrate; collagen fiber disorganization in the disc; reduced proteoglycans in the cartilage; greater disc thickness; lower cartilage thickness; lower feed intake; higher activity of MMP-9 and MMP-2, and higher concentration of IL-6, TNF-α, and IL-1β, as compared to HG. CG animals showed posterior disc thickening; reduced proteoglycans in the cartilage; lower collagen fiber organization of the disc; active MMP-9, and higher concentration of IL-6 and TNF-α compared to HG animals. Articular inflammation reduced the area and diameter of fibers of the temporal (right), medial pterygoid (left), and lateral pterygoid (right and left) muscles as compared to HG animals. Conclusion TMJ arthritis reduced the area and diameter of masticatory muscle fibers and caused morphological and molecular changes in the contralateral joint. [ABSTRACT FROM AUTHOR]

Objective Mammalian mastication serves to improve intra-oral food reduction. Insufficient food reduction creates potential swallowing problems, whereas over-reduction may accelerate tooth wear and increase feeding time. Either extreme has consequences. The study’s objectives were: (1) to study the relationship between food reduction, number of chews in a sequence, and chewing rate, (2) to study how controlling the number of chews and chewing rate variability affects food reduction, and (3) to assess how dentoskeletal morphological and electromyographical (EMG) characteristics impact food reduction. Design Twenty-three healthy, fully-dentate adults chewed a standardized test food under three conditions: (1) no control, (2) number of chews controlled, and (3) number of chews and chewing rate controlled. EMG activity was sampled from masseter and temporalis muscles bilaterally. Demographic, occlusal contact area in maximum intercuspation, and cephalometric data were obtained. Results In uncontrolled conditions, food reduction and bout duration varied more than expected across subjects. Subjects with poor reduction under controlled conditions were those with poor reduction under uncontrolled conditions. Only occlusal contact area correlated with chewing performance under uncontrolled conditions. Chewing cycle duration, EMG burst duration, and EMG peak onset latency increased when the number of chews was restricted. EMG amplitude, a surrogate for bite force, increased in tasks controlling the number of chews and chewing rate. Chewing rate variability was difficult to diminish below individual-specific levels. Conclusions Results: provided evidence that bite force, chewing rate, chewing performance and chewing bout duration reflected individual preferences. Future work will determine whether similar findings occur among other mammals. [ABSTRACT FROM AUTHOR]

Objective This study assessed the reliability and validity of masticatory function assessment using a new test food, Optozeta. Design Thirty-five adults participated in the cross-sectional clinical part of the study; ten of them performed a retest. They performed two free-style masticatory tests consisting of five trials of 20 cycles each chewing three pieces of Optosil or Optozeta placed in a latex bag. Optozeta was created by mixing 50% Optosil with 50% of Zetalabor. Masticatory performance, masticatory laterality and chewing rate were assessed. Reliability and construct validity were assessed using the intraclass correlation coefficient (ICC) and Spearman correlations, respectively. Results Higher ICC values were observed for each aspect of masticatory function as assessed using Optozeta compared with Optosil. All the participants showed a lower median particle size value using Optozeta than Optosil. For each masticatory parameter, a high correlation was observed between using Optosil or Optozeta. Conclusions Optozeta seems to have good construct validity and appears to be more reliable than Optosil as a test food to assess masticatory function. [ABSTRACT FROM AUTHOR]

Objective Mastication consists of rhythmic jaw openings and closings. Recent studies suggest that muscle mechanical properties determine the rhythmic rate; however, speed-accuracy tradeoffs may also play a role. This study evaluated how variation in chewing rate affected chewing performance, how masticatory muscle activity varied with chewing rate, and whether morphology and demographics contributed to performance. Design Chewing performance and muscle activity were sampled in 23 healthy, fully-dentate adults, who chewed a standardized test food to a metronome set at 0.5, 0.75, 1, 2 and 3 times their ‘natural’ chewing rates. Subjects produced ten chews per trial, and five trials for each of the five rates. Surface electromyographic (EMG) activity was sampled from masseter and temporalis muscles bilaterally. Demographic, occlusal, and cephalometric data were also obtained. Results Chewing performance, defined by median particle size, was inversely related to chewing rate; however, performance was not remarkably improved at rates slower than the natural chewing rate. Above the natural chewing rate, variability in EMG bursts diminished, suggesting a reduction in muscle activity modulation at fast rates. Occlusal contacts and most morphological features appeared to play a limited or no role in performance. Conclusions Results support the hypothesis that the ‘natural’ chewing rate is selected to be as fast as possible while providing sufficient time to allow EMG modulation for improved performance. The interplay between EMG modulation and individual variation in skeletal morphology is likely critical for optimal chewing performance. [ABSTRACT FROM AUTHOR]

Objectives To introduce an index (Masticatory Stability Index, MSI) to analyze the stability of chewing cycles in standardized conditions and test it in a group of patients with subclinical mild temporomandibular disorder (TMD). Design 23 subjects with mild subacute TMD and 21 healthy subjects were involved; they all responded to a questionnaire about signs and symptoms of TMD (ProTMDmulti) and underwent a myofunctional orofacial evaluation with scores, using the protocol of orofacial myofunctional evaluation with scores (OMES). Their mandibular kinematics was assessed with a 3D motion capture system during deliberate unilateral gum chewing. The MSI was computed synthesizing the information contained in nine kinematics parameters into a single global figure. Patients’ and controls’ MSI were compared considering the preferred and non-preferred chewing side using a 2-way ANOVA (factors: group, side). Results Together with a lower total score of myofunctional orofacial status, the TMD group showed a reduced stability based on MSI (p < 0.05). Conclusions The MSI is an efficient method to measure the stability of the masticatory cycles. These preliminary results encourage validating the index on a larger sample. The variability in the motor behavior of chewing can impair the objectivity of its evaluations in several types of patients, including those with TMD. The MSI could be useful to complement clinical assessments, providing data for planning the rehabilitation of masticatory function in these patients. [ABSTRACT FROM AUTHOR]

Food properties influence the parameters of the masticatory process, such as jaw movement, muscle activity and chewing rate. Firm foods will require more muscle activity than softer foods. However, the influence of food hardness on chewing rate is ambiguous as both slower and higher chewing rates have been reported for harder foods. Rheological characteristics of the food, such as plasticity and elasticity, may help to explain differences in chewing rate. The aim of our study was to determine the influence of food properties on chewing rate and muscular work in five phases of a chewing sequence. Eighty-four participants chewed on five foods, which strongly differed in consistency. Chewing gum was used as a reference food. The phase in the chewing sequence had a large significant effect on cycle duration for the five foods. A significant decrease in cycle duration at the beginning of chewing was followed by an increase in later phases, leading to U-shaped curves. Food type had a small effect on the average cycle duration. However, large significant differences in cycle duration were observed between the foods at the beginning of a chewing sequence. In that phase, the firm foods were chewed much slower than the soft foods. Muscular work was significantly influenced by both chewing phase and food type. [ABSTRACT FROM AUTHOR]

The aims of this study were to develop a novel rodent model of masticatory muscle ischaemia via unilateral ligation of the external carotid artery (ECA), and to undertake a preliminary investigation to characterize its downstream effects on mechanosensitivity and cellular features of the masseter and temporalis muscles. The right ECA of 18 male Sprague-Dawley rats was ligated under general anaesthesia. Mechanical detection thresholds (MDTs) at the masseter and temporalis bilaterally were measured immediately before ECA ligation and after euthanasia at 10-, 20-, and 35-days (n = 6 rats/timepoint). Tissue samples from both muscles and sides were harvested for histological analyses and for assessing changes in the expression of markers of hypoxia and muscle degeneration (Hif-1α , VegfA, and Fbxo32) via real time PCR. Data were analyzed using mixed effect models and non-parametric tests. Statistical significance was set at p < 0.05. MDTs were higher in the right than left hemiface (p = 0.009) after 20 days. Histological changes indicative of muscle degeneration and fibrosis were observed in the right muscles. Hif-1α, VegfA, and Fbxo32 were more highly expressed in the masseter than temporalis muscles (all p < 0.05). Hif-1α and, VegfA did not change significantly with time in all muscles (all p > 0.05). Fbxo32 expression gradually increased in the right masseter (p = 0.024) and left temporalis (p = 0.05). ECA ligation in rats induced hyposensitivity in the homolateral hemiface after 20 days accompanied by tissue degenerative changes. Our findings support the use of this model to study pathophysiologic mechanisms of masticatory muscle ischaemia in larger investigations. • A novel rodent model of masticatory muscle ischaemia is described. • External carotid artery ligation in Sprague-Dawley rats is achievable in a short time. • The intervention produces evidence of masticatory muscle ischaemia. • Animals tolerate the surgical procedure well. • The model will inform studies evaluating orofacial pain mechanisms. [ABSTRACT FROM AUTHOR]

This scoping review aimed to identify the signs and symptoms of temporomandibular joint (TMJ) involvement in individuals with ankylosing spondylitis (AS). Systematic literature searches were performed on PubMed, Embase, and Web of Science databases (up to April 2022). Studies with signs and symptoms of temporomandibular joint disorder (TMD) in adults with AS were included. TMJ outcomes were extracted and analyzed qualitatively. From 527 potentially eligible studies, 22 were included. A total of 4309 individuals with AS were evaluated, aged between 18 and 80 years, being males approximately 65% of the sample. Signs and symptoms of pain, tenderness to palpation on TMJ and masticatory muscles, joint noises (i.e., clicking or crepitus), limited mouth opening, disc displacement, and radiographic changes were often observed. The available evidence shows that different signs and symptoms of TMD co-occur with AS disease, with a higher prevalence of TMD observed in individuals with AS than in individuals without AS. Indeed, it seems that individuals suffering from AS disease have an increased risk of developing TMD. • Individuals with AS have a higher prevalence of signs and symptoms of TMD compared to individuals without the disease. • Inflammation of the TMJ articular disc appears to predispose all signs and symptoms of TMD found in AS individuals. • Identifying TMJ pathology in individuals with AS should be useful in the early management of the signs and symptoms. [ABSTRACT FROM AUTHOR]

Objective: The aim of the present study was to compare the electromyographic activity of masticatory muscles of adult patients with different degrees of oral motor impairment (cerebral palsy) with the electromyographic activity of healthy individuals in a control group. Electromyographic activity was compared when the masticatory muscles were at rest and in motion. Design: Thirty adult patients with cerebral palsy and 30 subjects without neuromotor disorders were enrolled in the present study. Oral motor function impairment was classified for each subject according to the Orofacial Motor Function Assessment Scale. Surface electromyography was bilaterally recorded in the masseter and anterior temporalis muscles at rest, during maximal voluntary clench and mouth opening. Comparisons between the groups were statistically assessed using Mann-Whitney test. Results: At rest and mouth opening, electromyographic values were higher among patients with cerebral palsy than control group. During maximal voluntary clench, the opposite occurred. The degree of oral motor impairment affected mouth opening. Conclusion: There are significant differences in masticatory muscle activity between adult patients with CP and healthy individuals, and the degree of oral motor impairment is important. Significance: To improve the masticatory function of these patients, muscle therapy should approach rest, mouth opening and clenching differently. [ABSTRACT FROM AUTHOR]

The present study aimed to compare sympathetic hemodynamic effects in masticatory and limb muscles in response to different stressors. Twelve healthy participants were subjected to a randomized series of stressors, including cold pressor test (CPT), mental arithmetic test, apnea, isometric handgrip (IHG) and post-handgrip muscle ischemia (PHGMI), while in the supine position. Spatially-resolved near-infrared spectroscopy was used to measure relative changes in blood volume and oxygenation (TOI) of the resting masseter and biceps muscles. Cardiac output, heart rate, and arterial blood pressure (ABP) were also monitored. Except apnea, all tests increased ABP. Different response patterns were observed in the 2 muscles: TOI significantly increased during contralateral IHG (1.24 ± 1.17%) but markedly decreased during CPT (−4.84 ± 4.09%) and PHGMI (−6.65 ± 5.31%) in the biceps muscle, while exhibiting consistent increases in the masseter (1.88 ± 1.85%; 1.60 ± 1.75%; 1.06 ± 3.29%, respectively) (p < 0.05). The results allow us to infer differential control of blood flow in head and limb muscles. In general, the masseter appears more prone to dilatation than the biceps, exhibiting opposite changes in response to painful stimuli (CPT and PHGMI). Several mechanisms may mediate this effect, including reduced sympathetic outflow to the extracranial vasculature of the head, generally exposed to lower hydrostatic loads than the rest of the body. • Acute stress differently affected blood flow in head and limb muscles. • Vasoconstrictory responses were generally observed in limbs. • No evidence of vasoconstriction was observed in the masseter muscle. • Masseter perfusion was consistently increased in response to painful stimuli. [ABSTRACT FROM AUTHOR]

Botulinum neurotoxins (BoNT) are used in masticatory muscles for pain relief, unloading of the mandible, and cosmetic facial contouring. Treatment is often repeated every few months as function returns. This study assessed masticatory function and musculoskeletal structure after multiple BoNT treatment of the rabbit masseter. Female rabbits received 3 injections of BoNT (n = 13) or saline (n = 5) into one masseter muscle at intervals of 12 weeks. The contralateral side served as control. Periodic measurements of masticatory electromyography (EMG) and stimulated anterior bite force were made. After the final 12-week recovery interval, neuromuscular connection was investigated by stimulating the masseteric nerve to elicit an evoked EMG response. Mandibular specimens were collected for microCT analysis, and masseters were collected for histomorphometry and counts of replicating cells. Control and saline-injected muscles maintained consistent masticatory EMG and anterior bite force throughout the study. BoNT-injected masseters showed strong declines after each injection; during the 12-week recovery period, masticatory EMG and anterior bite force improved, although only electrical activity reached normal levels. Multiple injection resulted in persistently atrophied muscle fibers with fibrosis, and notable loss of bone from the mandibular body and condyle. The uninjected masseters of the BoNT group also showed evidence of mild toxin-related changes. Although muscle function is mostly regained after each injection, masseters receiving multiple doses of BoNT show extensive damage. In addition, mandibular bone density is decreased on the injected side. • Repeated botulinum treatment of the masseter reduced anterior bite force. • Fiber atrophy and fibrosis were prominent in the injected muscle. • Bone density in the mandibular body and condyle diminished with repeated injections. • After repeated treatment, side effects were seen in the contralateral masseter and condyle. [ABSTRACT FROM AUTHOR]

Objective To examine the effects of imbalance of masticatory muscle activity of the rat mandible on the condylar cartilage and subchondral bone during the growth period. Design Forty 5-week-old male Wistar rats were randomly divided into experimental ( n = 20) and control ( n = 20) groups. In the experimental group, the left masseter muscles were resected. The rats were sacrificed at 7 or 9 weeks of age in both groups. Microcomputed tomography was used to determine the three-dimensional morphology and cancellous bone structure. For histological and histochemical examination, 5-μm-thick serial frontal sections of the condyle were stained with toluidine blue and immunostained with asporin and TGF-β1 to evaluate the promotion and inhibition of chondrogenesis. Results In the experimental group, microcomputed tomography analysis showed asymmetric growth; the resected side condyles showed degenerative changes. Histological analysis showed that the total cartilage in the central region of the resected side was significantly thinner than in the non-resected side in the experimental group, as well as in the control group. Compared with the control group, the expression of asporin was significantly higher in the resected side, and significantly lower in the non-resected side. In contrast, the expression of TGF-β1-immunopositive cells in the non-resected side was significantly higher than in the resected side and the control group. Conclusions These findings imply that lateral imbalance of masseter muscle activity lead to inhibition of chondrogenesis and induce asymmetric formation of the condyle during the growth period. [ABSTRACT FROM AUTHOR]

Objective To study and compare the relationships between mean chewing cycle duration, selected cephalometric variables representing mandibular length, face height, etc., measured in women and in their teenage or young–adult biological daughters. Design Daughters were recruited from local high schools and the University of Michigan School of Dentistry. Selection criteria included healthy females with full dentition, 1st molar occlusion, no active orthodontics, no medical conditions nor medication use that could interfere with normal masticatory motor function. Mothers had to be biologically related to their daughters. All data were obtained in the School of Dentistry. Measurements obtained from lateral cephalograms included: two “jaw length” measures, condylion-gnathion and gonion-gnathion, and four measures of facial profile including lower anterior face height, and angles sella-nasion-A point (SNA), sella-nasion-B point (SNB) and A point-nasion-B point (ANB). Mean cycle duration was calculated from 60 continuous chewing cycles, where a cycle was defined as the time between two successive maximum jaw openings in the vertical dimension. Other variables included subject height and weight. Linear and logistic regression analyses were used to evaluate the mother–daughter relationships and to study the relationships between cephalometric variables and chewing cycle duration. Results Height, weight, Co-Gn and Go-Gn were significantly correlated between mother–daughter pairs; however, mean cycle duration was not ( r 2 = 0.015). Mean cycle duration was positively correlated with ANB and height in mothers, but negatively correlated with Co-Gn in daughters. Conclusions Chewing rate is not correlated between mothers and daughters in humans. [ABSTRACT FROM AUTHOR]

Objective Tooth wear is a basic physiological adjustment mechanism in the masticatory system. Unfortunately, it is not clear what the relationship is between the activity of the masticatory muscles and the tooth hard tissue loss (mainly enamel) in patients with advanced tooth wear. The aims of this study were (1) to compare the occlusion times and (2) to compare the EMG activity in maximal voluntary clench of the masseter and anterior temporalis muscles of patients with advanced tooth wear to the same activity of healthy volunteers. Design 50 (16F, 34M) patients and 30 (12F, 18M) age matched controls were clinically examined to assess the degree of wear (TWI). Each subject underwent electromyographic analysis (bilateral anterior temporalis, superficial masseter, anterior digastric and sternocleidomastoid muscles) and digital occlusal analysis. Results Mean values of the electrical potentials of the mandible elevating muscles during clench were higher in the study group compared to the controls. A negative correlation was found between the temporalis and masseter muscle activities during clench and the mean value of TWI ( r = −0.383, p = 0.009; r = −0.447, p = 0.002). Occlusion time was longer in the study group compared to controls ( p < 0.05). Conclusions Mandibular adductors demonstrated lower muscular activities during clenching in the tooth wear patients; however, the cause of this finding is not certain. Prolongation of occlusion time may exacerbate occlusal surfaces wear or excessive wear may prolong occlusion time. [ABSTRACT FROM AUTHOR]

Objectives The jaw-stretch reflex (JSR) was studied in both patients and healthy participants in order to investigate the possible long-term impact of orthognathic surgery on the motor function of the masticatory system. Design JSR was measured in patients before surgery (PC), 1 year after surgery (PS) and in healthy controls (HC) ( N = 31 in each group). JSR was evoked by a standardized stretch device and recorded bilaterally from masseter and anterior temporalis muscles using surface electromyography (EMG). Results The peak-to-peak amplitude (which was normalized to pre-stimulus EMG activity) of JSRs in PC and PS were significantly smaller than in HC ( P < 0.001; P < 0.001). The onset latency in PS was significantly longer compared with HC ( P < 0.05). The duration of JSR in PS was significantly longer than in HC and PC ( P < 0.001; P < 0.05). Conclusion Patients with dentofacial deformities are characterized by reduced JSR amplitude. The delayed onset and elongated duration of JSR might be potential indicators of a long-term surgical impact on the motor function of the masticatory system. [ABSTRACT FROM AUTHOR]

Objective This study assessed the degree of relationship between masticatory laterality and lateral asymmetry of masticatory performance using silicon pieces enclosed in a latex bag. Design Forty-two young adults with natural dentition participated in this cross-sectional, observational study. They performed four different masticatory assays, each consisting of five trials of chewing three pieces of silicon for 20 cycles. In one assay, they were asked to masticate unbagged silicon free-style, whilst in the three other assays they were asked to masticate bagged silicon free-style, unilaterally on the right-hand side and unilaterally on the left-hand side. The preferred chewing side was determined by calculating the asymmetry index for both the free-style assays. Masticatory performance was determined by sieving the silicon particles and the cycle duration was also recorded. Data were analysed using independent samples or paired t -test and linear regression. Results Masticatory function using the bagged silicon was similar to that using the unbagged silicon. A significant and positive relationship was observed between the preferred chewing side expressed as the asymmetry index and the side with better masticatory performance. Alternate unilateral chewers demonstrated better masticatory performance than unilateral chewers. However, when free-style and unilateral chewing were compared for each subject, unilateral chewing was found to be as efficient as – or even more efficient than – free-style chewing. Conclusions There is a positive association between the preferred chewing side and the more efficient side. Alternate unilateral mastication per se does not promote better masticatory performance than consistently unilateral mastication. [ABSTRACT FROM AUTHOR]

Introduction The aim of this study was to evaluate the reliability of surface electromyography of the masticatory muscles in patients with cerebral palsy. Methods Surface electromyography was performed over the masseter and temporal muscles in 15 patients with cerebral palsy with the mandible at rest and during maximum clenching effort in two sessions. The data were analyzed using the root mean square amplitude, mean frequency, median frequency, zero crossings and approximate entropy. Results In the within-day evaluations, intraclass correlation coefficients were higher (0.80–0.98) for the all electromyography variables and muscles during maximum clenching effort. In the resting position, the coefficients revealed good to excellent reliability (0.61–0.95) for root mean square, mean frequency, median frequency and zero crossings and fair to good reliability (0.53–0.74) for approximate entropy. In the between-day evaluations, the coefficients revealed good to excellent reliability (0.60–0.86) for mean frequency, median frequency, zero crossings and approximate entropy. In the resting position, the coefficients revealed poor to fair reliability (0.23–0.57) for all electromyography variables studied. The root mean square had the highest standard errors during maximum clenching effort (2.37–5.91) and at rest (1.47–6.86). Conclusion Mean frequency, median frequency and approximate entropy are the most reliable variables of surface electromyography signals of the masseter and temporal muscles during maximum clenching effort in individuals with cerebral palsy. These measures can be used to evaluate the function and behaviour of the masticatory muscles in this population following oral rehabilitation and surgical oral procedures as well as for the study the physiology of these muscles. [ABSTRACT FROM AUTHOR]

Objective The aim of the study was to evaluate and correlate masticatory efficiency (ME) and maximum bite force (MBF) in adult individuals of both genders with normal occlusion. Design The study was conducted in a university research centre. ME and MBF were evaluated in 55 adults (27 men and 28 women) with normal occlusion. All subjects chewed four fuchsin capsules (two on the right and two on the left molar region) for 15 chewing cycles with a 3-min interval between capsules. The concentration of fuchsin in the capsules was determined by spectrophotometry and stratified by gender and chewing side. Bite force (BF) was measured three times on both the left and right molars; the highest value of the three measurements on each side was taken as the MBF. Results ME was higher in women (right side, 1.17 ± 016 μg/mL; left side, 1.20 ± 0.15 μg/mL) than in men (right side, 0.92 ± 0.24 μg/mL; left side, 0.89 ± 0.24 μg/mL). The MBF was higher in men (right side, 632 ± 174 N; left side, 627 ± 170 N) compared with women (right side, 427 ± 140 N; left side, 420 ± 112 N). No significant differences in chewing efficiency and BF were found between sides for both genders. Conclusions Women showed the highest ME, while men had the highest MBF, with no correlation between these two parameters among genders. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: Biomechanical forces, such as those produced during mastication, are considered a primary agent in stimulating craniofacial growth and development. There appears to be a strong connection between the strength of the masticatory muscles and the dimensions of the craniofacial complex, with changes in biomechanical force and muscular strength influencing and altering the underlying bony tissues. This is markedly apparent in the mandible and it is possible to infer that changes to mandibular form are due in part to dietary changes. This study aims to investigate this idea by using an archaeological sample from a period that experienced important dietary changes as a result of the Industrial Revolution. Design: 279 skeletons from the mediaeval and post-mediaeval periods in London were selected for analysis, and a detailed metric examination of each mandible was carried out. Results: Males and females were analysed separately and statistically significant reductions were observed in nearly all post-mediaeval measurements. This effect was most pronounced in the areas of the mandible associated with masticatory muscles attachment, including the gonial angle, ramus height and width, bi-gonial breadth and bi-condylar breadth. Conclusions: These recorded changes in mandibular morphology of mediaeval and post-mediaeval Londoners are most likely the result of a shift in diet (and associated decrease in masticatory function) observed in the period surrounding the Industrial Revolution. [Copyright &y& Elsevier]

Abstract: Objective: The purpose of this study was to test the hypothesis that jaw clenching induces co-contraction and low-level long-lasting tonic activation (LLTA) of neck muscles in the supine position. Design: Ten healthy subjects developed various feedback-controlled submaximum bite forces in different bite-force directions in supine position. The electromyographic (EMG) activity of the semispinalis capitis, semispinalis cervicis, multifidi, splenius capitis, levator scapulae, trapezius, sternocleidomastoideus, masseter and infra/supra-hyoidal muscles was recorded. For normalization of EMG data, maximum-effort tasks of the neck muscles were performed. Results: Co-contractions of the posterior neck muscles varied between 2% and 11% of their maximum voluntary contraction. Different bite forces and bite-force directions resulted in significant (p <.05) activity differences between the co-contraction levels of the neck muscles. In addition, LLTA of specific neck muscles, provoked by the jaw clenching tasks, was observed. Conclusions: This study demonstrated for the first time moderate co-contractions of jaw and neck muscles in the supine position under controlled submaximum jaw clenching forces. LLTA of most neck muscles was observed, outlasting clenching episodes and indicating an additional neuromuscular interaction between the two muscle groups. [Copyright &y& Elsevier]

Abstract: Introduction: Certain periods of development of the nervous system are critically vulnerable to environmental insults because of the processes involved that cycle very quickly. Morphologic and functional development of mastication occurs coincidently during these stages. Early environmental insults during critical periods can cause permanent effects on both structures and functions of organic systems that can have lasting repercussions in adulthood. Objective: In this study, we investigated, through a literature review, the possible effects of perinatal calorie and/or protein low diet on structural and physiological development of mastication. Design: A systematic literature search was conducted from in the PUBMED electronic database. In collecting literature we used the keywords: “undernutrition” and “stomatognathic system”. Criteria used in the selection of articles for inclusion were: studies evaluating the effects of perinatal calorie and/or protein low diet on masticatory morphology and function. Exclusion criteria included, short communications and nonavailability in full text format. Conclusion: Undernutrition during critical periods of life causes changes in the key structures of masticatory function. This fact can affect the selection of essential nutrients, thereby interfering with the process of satiation. [Copyright &y& Elsevier]

Abstract: Objective: The study investigated modulation of fast and slow opening (FO, SO) and closing (FC, SC) chewing cycle phases using gum-chewing sequences in humans. Design: Twenty-two healthy adult subjects participated by chewing gum for at least 20s on the right side and at least 20s on the left side while jaw movements were tracked with a 3D motion analysis system. Jaw movement data were digitized, and chewing cycle phases were identified and analysed for all chewing cycles in a complete sequence. Results: All four chewing cycle phase durations were more variant than total cycle durations, a result found in other non-human primates. Significant negative correlations existed between the opening phases, SO and FO, and between the closing phases, SC and FC; however, there was less consistency in terms of which phases were negatively correlated both between subjects, and between chewing sides within subjects, compared with results reported in other species. Conclusions: The coordination of intra-cycle phases appears to be flexible and to follow complex rules during gum-chewing in humans. Alternatively, the observed intra-cycle phase relationships could simply reflect: (1) variation in jaw kinematics due to variation in how gum was handled by the tongue on a chew-by-chew basis in our experimental design or (2) by variation due to data sampling noise and/or how phases were defined and identified. [Copyright &y& Elsevier]

Abstract: Objective: The effect of experimental jaw-muscle pain and stress on masticatory muscle activity in TMD-patients has been discussed. Furthermore, associations between TMD and deep bite patients have been studied. Accordingly in the present study, comparison of EMG responses at rest, maximal clenching, during evoked pain and stress between deep bite patients and controls was investigated. Design: In 30 deep bite patients and in 30 sex-/age-matched controls with neutral occlusion EMG activity was recorded bilaterally from masseter and anterior temporalis muscles before and during evoked pain and before and during a stress task. Evoked pain was induced by injections of glutamate into the masseter (local pain) and brachioradialis (remote pain) muscles and resting EMG activity was recorded before and after 1, 2, 3, 4, 5 and 10min. A precision task was used to simulate a stressful condition and EMG activity was recorded twice during the task. Maximal EMG activity was recorded during maximal clenching. Results: Resting and maximal EMG activity were significantly different between groups and age with no gender differences. EMG activity during local pain and during the precision task were significantly different between groups, gender, age and time, whereas no time effect was found for the EMG activity during remote pain. Conclusions: Patients with deep bite have significantly different jaw motor responses to painful stimulation of the trigeminal region and manual precision tasks suggesting a differential integration of both somatosensory and behavioural stimuli. [Copyright &y& Elsevier]

Abstract: Transcranial magnetic stimulation (TMS) has been used to assess corticomotor control of jaw muscles, but few studies have examined cortical plasticity of the masticatory system and potential modification by jaw muscle training. Objectives: To determine if a 1-h jaw muscle training task would be sufficient to induce signs of neuroplastic changes in the corticomotor excitability of the masseter muscle. Materials and methods: Corticomotor excitability was assessed by changes in electromyographic activity evoked by TMS in 15 healthy participants. Motor evoked potentials (MEPs) recorded in the masseter and the first dorsal interosseos (FDI – as a control) muscle were assessed at four time points: at baseline, immediately after the 1-h training, 1h after training and 1 day follow-up (n =7). MEPs were assessed by stimulus–response curves and corticomotor mapping. Results: All participants successfully performed the task (mean success rate: 47.0±4.1%) which increased significantly during the 1-h training. However, no significant effect of jaw muscle training on masseter and FDI MEPs or corticomotor maps were observed. Conclusion: The present finding showed that 1-h jaw muscle training is insufficient to evoke neuroplastic changes in corticomotor excitability. The potential for training-induced neuroplasticity may vary among different cranial muscles which may have therapeutic consequences. [Copyright &y& Elsevier]

Abstract: Objective: The aim of this study was to evaluate the maximal bite force (MBF), electromyographic (EMG) activity and thickness of the masseter, anterior part of the temporalis and sternocleidomastoid (SCM) muscles in a group of young adults with and without temporomandibular disorders (TMDs). Design: Nineteen individuals comprised the TMD group (6 males/13 females, aged 25.4±3.8 years), classified based on the Research Diagnostic Criteria for TMD (RDC/TMD), and 19 comprised the control group (6 males/13 females, aged 24.1±3.6 years). The MBF was determined with a transducer placed between the dental arches at the first molars level (N). The muscles were evaluated bilaterally at rest and during maximal voluntary clenching (MVC) by assessing EMG activity and performing ultrasonography (USG). The mean values of these measures for both sides of the mouth were used. The normality of the distributions was assessed by the Shapiro–Wilks test. Variables between groups and genders were compared using two-way factorial ANOVA test and correlated using the Spearman coefficient (α =0.05). Unpaired t test was used to compare variables between TMD subgroups. Logistic regression analysis was used to identify the variables associated with the presence of TMD. Results: MBF, EMG and USG data were similar among clinical groups and among TMD subgroups. The thickness of masseter and SCM muscles in the relaxed and clenching states were significantly higher in males than females. On the other hand, the EMG of the temporalis muscle in the rest state was significantly higher in females than males. Additionally, the MBF was positively correlated with the USG characteristics of masseter and SCM muscles, as well as with the EMG activity of masseter and temporalis muscles in the TMD group. In this group, there was also a positive correlation between the thickness of the masseter muscle and its activity. On the other hand, the thickness of the SCM muscle was negatively correlated with its activity. A lower MBF was independently associated with the presence of TMD. Conclusions: Subjects with TMD exhibited similar values of MBF, thickness and electrical activity of masticatory and cervical muscles when compared with controls; positive correlations observed between these variables may suggest a muscular alteration in TMD patients and a co-activation of masticatory and cervical muscles during mandibular movement. This fact may also be confirmed by the negative association between bite forces and presence of TMD. [Copyright &y& Elsevier]

Abstract: Objective: To evaluate the association between oral conditions, masticatory performance (MP) and oral health-related quality of life (OHRQoL) in 8–12 year-old children. Design: 150 Brazilian scholars were examined for caries and malocclusions. MP was evaluated based on the ability to comminute an artificial test food followed by the determination of the median particle size (X 50) and particle distribution in different-sized sieves (“b”). OHRQoL was measured using the Brazilian versions 8–10 and 11–14 of the child perceptions questionnaire (CPQ), considering the following domains: oral symptoms (OS), functional limitations (FL), emotional well-being (EW) and social well-being (SW). Higher scores indicated worse OHRQoL. Data were submitted to Spearman's correlation test and multiple linear regression analysis. Results: There were significant positive correlations between the psychosocial and OS domains scores of the CPQ8–10 and the number of decayed and missing teeth, respectively. The number of decayed teeth positively correlated with the number of missing teeth and the CPQ11–14 scores. The number of decayed and missing teeth was significantly associated with higher CPQ8–10 scores. Higher CPQ11–14 overall scores were associated with female gender, higher FL domain scores were associated with the number of missing teeth, and higher X 50 values and EW domain scores were associated with female gender and the number of decayed teeth. Conclusions: A higher number of missing teeth correlated with an inferior MP in older children. Children with a higher number of caries rated their oral health less favourably. Older females and those who broke the test material into smaller sizes were also more likely to report a worse OHRQoL, suggesting that the time allowed to reduce food appears to be a more influential factor on children’ perception of oral health than their ability to break down the test material into smaller sizes. Moreover, the subjectivity of functional domain and artificial nature of chewable test material could have influenced the test sensitivity. [Copyright &y& Elsevier]

To sequentially track mandibular defect repair by using radiographic and histological techniques, so as to compare repair patterns of sensory denervated versus innervated mandibles. Forty Sprague-Dawley rats were subjected to unilateral inferior alveolar nerve (IAN) axotomy and bilateral 3 mm full-thickness circular osteotomy of their mandibles. Micro-CT and histological staining were applied to track the repair process of the mandibular defects at 1, 2, 4, and 8 weeks after surgery. The bone volume of both sides increased by 2 weeks post-operation, and then gradually decreased. The new bone volumes of the axotomy side were significantly less than that of the sham side at 1, 2, and 4 weeks post-surgery, whereas no significant differences were detected at 8 weeks post-surgery. Meanwhile, there were no significant differences in bone mineral density between the two sides during repair. Noteworthy, the repaired bone remained more vertically than horizontally aligned throughout the repair process. IAN axotomy decreases the quantity of bone calluses during the early stage of mandibular defect repair, but with no effect on the degree of mineralization. The shape of the defect area appeared to be aligned with the direction of local mechanical force produced by masticatory muscles. • Sensory denervation decreased the quantity of new bone in mandibular defect repair. • Visualization of mandibular defect repair was first achieved by Echarts. • Force from masticatory muscles affected direction of mandibular defect repair. • The critical size of full-thickness circular mandibular defect seemed ≤ 3 mm. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: Few studies have evaluated the relationship between morphological and functional characteristics of the masticatory apparatus in young subjects. Thus, the aim of this study was to evaluate masticatory performance (MP), maximal bite force (BF), orthodontic treatment need and orofacial dysfunction in children and adolescents. Design: The sample consisted of 316 subjects of both genders, with an age range 6–16years divided into 4 groups: early mixed, intermediate mixed, late mixed and permanent dentition. MP was evaluated by the individual''s ability to comminute a chewable test material in order to determine median particle size (X 50) and distribution of particles in different sieves (“b”). BF was determined using a digital gnatodynamometer with fork strength of 10mm. Orofacial function and orthodontic treatment need were screened using the Nordic Orofacial Test-Screening (NOT-S) protocol and Index of Orthodontic Treatment Need (IOTN), respectively. The results were submitted to descriptive statistics, normality test, analysis of variance and stepwise multiple linear regression to test relationship between MP and studied independent variables. Results: Variance of X 50 and b between groups was statistically significant. But evaluation of variables that significantly contributed to MP variation showed that age, body mass index (BMI), BF and the presence of sleep bruxism were negatively related to X 50 and the NOT-S clinical exam scores showed a positive relationship with X 50. Conclusion: In the studied sample, age, BMI, BF and the presence of sleep bruxism were related to better MP; but the increase in NOT-S scores was significantly related to poorer MP. [Copyright &y& Elsevier]

Abstract: The aim of this study was to examine the effect of chewing efforts on sensory and pain thresholds of the orofacial skin of symptom-free subjects. Fourteen healthy volunteers were recruited. Using a stair-case method, the tactile detection threshold (TDT) and the filament-prick pain detection threshold (FPT) on the cheek skin (CS) and the skin overlying the palm side of the thenar skin (TS) were measured before and after chewing gum for 5min (Time 1: T1) and keeping the jaw relaxed for 5min (Time 2: T2) as a control. Both for the test and control situation, the TDT was higher in all measurement sites after 5min. As for the FPT, the reactions between T1 and T2 were quite opposite: the FPT increased and/or remained stable in T1, while, it decreased at all sites in T2. There were significant session effects (T1–T2) on the FPT at the left CS (P <0.01), right CS (P <0.05) and TS (P <0.05). The increase of TDT after chewing/no chewing could be due to habituation, while the decrease of FPT observed in the control situation might be due to sensitization, respectively. This potential sensitization, however, was not observed after chewing efforts. Further studies are needed to clarify the modulating effect of masticatory function on the trigeminal sensory system. [Copyright &y& Elsevier]

Abstract: Previous studies have investigated the effects of increasing the occlusal vertical dimension (OVD) with an oral appliance on masticatory muscle EMG activity during oral behaviours in humans and animals. The present study investigated whether a short-term and reversible increase in OVD, followed by a reduction in OVD to the normal level, resulted in a time-correlated change in the EMG activities of the masseter and digastric muscles during chewing. To do this, a guinea pig model in which an increased OVD was established with natural tooth contacts was used. In the control group, in which no bite-raising treatment was applied, OVD gradually increased with a natural growth during the experimental period whilst the masseter and digastric EMG activities, burst duration, and chewing rhythm were unchanged. When the increase in OVD was established in the bite-raised group, the EMG activities of the masseter and digastric muscles were significantly increased by 88.6 and 55.2% from those before bite-raising treatment, respectively. However, during the following 11 days, the increased EMG activities of both muscles did not show changes associated with the subsequent decrease in the OVD to a normal level. The burst durations of both muscles and chewing rhythm were not significantly affected by the change in OVD during the experimental period. Within the limited recording period of the study, the return of OVD from increased to normal levels did not reverse the increased chewing-related masticatory muscle EMG activity that was induced by the bite-raising treatment. [Copyright &y& Elsevier]

Abstract: Introduction: The vascularisation of the peri-implant tissue represents the key factor in obtaining a successful result in implantology, since an adequate vascular supply allows wound healing and the presence of numerous growth factors that promote osteogenesis. The aim of this study was to analyse “in vivo” the vascular pattern of the peri-implant mucosa in subjects that received implant treatment. Materials and methods: In the study 22 subjects were examined, 11 of whom (test group) received dental implants (Straumann Dental Implant System®) while 11 were in the control group; the analysis was performed in the peri-implant masticatory mucosa. The evaluation of the microcirculation was performed “in vivo” using the optical probe videocapillaroscopy technique equipped with 200× lenses. The following parameters were recorded: capillary density, vascular areas, microhaemorrhages and angioarchitecture. Results: The values indicating the capillary density were significantly different in the test group compared to the control group, indicating an angiogenic process taking place “in vivo”. In the test group the capillary loops were arranged parallel (30%) as well as perpendicular to the surface; in contrast, in the control group the gingival margin was always perpendicular to the surface (100%). Conclusions: The peri-implant vascular pattern exhibits special characteristics that differ both in morphology and density from the gingival one. [ABSTRACT FROM AUTHOR]

Abstract: Jaw movement affects masticatory muscles during the postnatal period. Prenatal jaw movement has also been implicated in the development of the temporomandibular joint; however, its effect on prenatal development of the masticatory muscles has not been extensively analysed. In the present study, we examined the effects of the restriction of fetal jaw movement on the temporalis muscle, a major masticatory muscle, in mice by suturing the maxilla and mandible (sutured group) using an exo utero development system. We compared the morphology of the temporalis muscle between sutured, sham-operated and normal in utero groups. At embryonic day (E) 18.5, the volume of muscle fibres, but not that of connective tissue, in the temporalis muscle was decreased in the sutured group. The E18.5 temporalis muscle in the sutured group appeared morphologically similar to that of the E17.5 in utero group, except for frequent muscle fibre irregularities. By transmission electron microscopy, in the sutured group, the myofibrils were immature and scattered, the nuclei appeared comparatively immature, the mitochondria were expanded in volume with fewer cristae, and cytoplasmic inclusion bodies were frequently observed. Expression of Myf-6, a late myogenic transcription factor, by real-time RT-PCR was not significantly different between the sutured and sham-operated groups. These findings demonstrated approximately 1-day delay in the morphological development of the temporalis muscle in the sutured group, and some abnormalities were observed, although Myf-6 level was not affected in the sutured group. The present study revealed that the prenatal jaw movement influences the development of the temporalis muscle. [ABSTRACT FROM AUTHOR]

Abstract: The present study aimed investigate the age and gender influence on maximal molar bite force and at outlining the criteria for normal masticatory muscle development in a sample of 177 Brazilian Caucasian dentate individuals aged 7–80 years divided into five age groups: I (7–12 years), II (13–20 years), III (21–40 years), IV (41–60 years), and V (61–80 years). Except for Group V, which comprised nine women and eight men, all groups were equally divided in respect to gender (20 M/20 F). Bite force was recorded with a mouth-adapted 1000N dynamometer and the highest out of three records was regarded as the maximal bite force. The data were submitted to multivariate statistical analysis (SPSS 17.0 p <0.05). Effects of group and gender were found, but no interactions between them. The ANOVA showed significant differences between groups bilaterally. Bonferroni''s test showed that group I had significantly lower bite force means at both sides as compared to all groups, except group V. No differences were found between the left and right sides. In all the groups, gender was found to be a significant factor associated with maximal bite force. A global comparison including all the subjects and measures showed that the means of men were approximately 30% higher than those of women. Within-group comparisons yielded similar results in all groups. Muscle thickness was measured with a SonoSite Titan ultrasound tool using a high-resolution real-time 56mm/10MHz linear-array transducer. Three ultrasound images were obtained from the bilateral masseter and temporal muscles at rest and at maximal voluntary contraction. The means of the three measures in each clinical condition were analyzed with multivariate statistical analysis (SPSS 17.0 p <0.05). A gradual increase in thickness of the masseter and temporal muscles was found both at rest and maximal voluntary contraction for groups I to IV, whereas a decrease in muscle thickness was observed in group V. Multivariate analysis showed that in both conditions there was an effect of group and gender. The study of the development of the stomatognathic system in relation to age and gender can provide useful data for the identification of normal and impaired functioning patterns. The results of this study indicate that age and gender are associated with structural and functional alterations in the muscles of the stomatognathic system. [Copyright &y& Elsevier]

Abstract: Objective: Duchenne muscular dystrophy (DMD) patients have distorted dentofacial morphology that could be a result of changed force balance of masticatory muscles due to unequal dystrophic changes in various masticatory muscles. Skeletal muscles of DMD patients and those of murine model of DMD – mdx mice – are both characterized by Ca2+ induced muscle damage, muscle weakness and characteristic histological changes. Therefore, to determine the pathological changes in this animal model of DMD, we examined the masticatory muscles of the mdx mice for histological abnormalities including nuclei localization, fibre diameters, and collagen expression. Design: Muscle sections from masseter (MAS), temporal (TEM), tongue (TON) and soleus (SOL) of mdx and control normal mice were stained with hemalaun/eosin or with Sirius Red and morphometrically analysed. Levels of collagen staining in normal and mdx muscles were measured using image analysis and the mean optical density (mod) was determined. Results: Dystrophin deficient masticatory muscles contained 11–75% fibres with centralised nuclei. In mdx mice an increased mean fibre diameter was observed as compared to the age-matched control muscles (control vs. mdx; MAS: 33.44±0.49μm vs. 37.76±0.68μm, p <0.005; TEM: 32.93±0.4μm vs. 42.93±0.68μm, p <0.005; SOL: 33.15±0.29μm vs. 40.62±0.55μm, p <0.005; TON: 13.44±0.68μm vs. 15.63±0.18μm, p <0.005). Increased expression of collagen was found in MAS (mod control vs. mdx: 1.34 vs. 3.99, p <0.005), TEM (mod control vs. mdx: 3.11 vs. 4.73, p <0.01) and SOL (mod control vs. mdx: 2.36 vs. 3.49, p <0.01). Conclusion: Our findings revealed that mdx masticatory muscles are unequally affected by the disease process. The masticatory muscles of the mdx mice could present a useful model for further investigating the influence of dystrophin deficiency on muscles function. [Copyright &y& Elsevier]

Abstract: Aim: To investigate effect of capsaicin-evoked masseter-muscle pain on intramuscular blood-flow (BF) at rest and during contractions. Methods: Eight healthy men (22–31 years) participated. BF was measured with Laser Doppler (Moor Instruments, UK) using a single-fibre probe inserted into the right masseter. Three BF probes were attached to the skin above right and left masseter and the right-middle finger. Subjects performed 30s isometric contractions at 5%, 15%, and 25% of maximal voluntary contraction. After the contractions, capsaicin (0.1mL, 100μg/mL) was injected into the right masseter close to the fibre probe. When the pain sensation had disappeared, the series of submaximal contractions were repeated. BF data were sampled continuously, processed in 10s bins, and analyzed with repeated-measures ANOVAs. Results: Intramuscular BF significantly increased immediately after capsaicin injection (P <0.050) and rapidly (30s) decreased to pre-injection values. A significant increase in cutaneous BF above the right masseter was observed (P <0.050) and lasted for 10min, while a significant BF decrease in the finger (P <0.050) was observed. The contractions were associated with increases in intramuscular BF before and after the injection (P <0.022) and the contraction levels were also associated with increase in intramuscular BF before injection (P =0.008) but not after injection (P =0.314). Conclusions: This study demonstrated BF increased by muscle contraction but failed to show effects of contraction levels on BF in a muscle exposed to nociceptive stimuli. Neurogenic inflammation in muscles could possibly be mediated via antidromical effects and local release of vasoactive substances. The decreased BF in the finger could be due to involvement of central regulatory mechanisms. [Copyright &y& Elsevier]

Abstract: The quantification of biomechanical response of mandibular bone to mastication is an integral component for a key in understanding the biological consequence of masticatory functions. Understanding the response of mandibular bone to external loading may also well explain the mechanisms of bone turnover. In this study, three finite element (FE) models simulating the lower second premolar, first and second molars along with their supporting structures were developed to determine stress/strain levels and distribution under different occlusal loading. The changes in stress/strain values and profiles have been investigated in three scenarios: pre-extraction of the lower first molar, post-extraction and after full healing of the extracted socket. The mastication induced equivalent strains within the supporting mandibular bone at each of these three scenarios were quantified and compared against the Frost''s mechanostat theory. The results of stress/strain profiles show considerably lower magnitudes in the post-extracted and healed scenarios compared with the pre-extraction case. Following the Frost''s MES hypothesis, the initial equivalent strains are related to local bone remodelling. It is found that in the extracted case the bone near the tooth socket undergoes resorption from lingual respect whilst filling the cavity, whereas in the healed case bone turnover reaches equilibrium. The results provide important data for clinical assessment of constructing dentures or other restorative devices. [Copyright &y& Elsevier]

Abstract: Objective: This study aimed to investigate the effect of masticatory functional changes on the lateral view morphology of the mandible in adult rats. Design: Sixty 21-day-old male Sprague–Dawley rats were divided into two groups. Sixteen received ordinary (hard) food during the whole experimental period (normal group). The remaining 44 received a soft diet during 21 weeks to develop a hypofunctional masticatory system. Then, the now adult animals were divided into two equal groups: one continued on a soft diet (hypofunctional group), and the other changed to an ordinary diet with the aim of functionally rehabilitating their masticatory system (rehabilitation group). After another 6 weeks all animals were sacrificed and their left mandible was dissected, photographed and customised cephalometric software was used to perform morphometric measurements. Results: The area of the mandible was smaller in the hypofunctional compared to the normal group. Interestingly, the alveolar process was shorter in the normal group. Morphometric analysis revealed significant differences such as the area of the angular process and the inclination of the condylar process. The rehabilitation group was only marginally different compared to the hypofunctional group, although a general tendency to approach (catch-up) the normal group was observed, and one morphometric variable (condylar base inclination) was indeed significantly different. Conclusions: Morphometric analysis revealed only marginal changes of the adult rat mandibular morphology during a 6-week period of masticatory function rehabilitation. However, the observed catch-up tendency might suggest that a longer rehabilitation period may have significant effect on mandibular morphology. [Copyright &y& Elsevier]

Abstract: Temporomandibular joint and masticatory muscle forces generated during bilateral biting on an experimental device simulating a symmetrically balanced maximum intercuspation, are unknown. The basic motor control strategies during such tasks, executed either strictly controlled or developed rather habitually, are also quite unclear. The main goal of this study was to compare muscle and joint forces at various magnitudes of force under two experimental conditions: (1) generation of a bite force vector perpendicular to the maxillary occlusal plane, (2) development of a directionally unrestricted (quasi-habitual) bite force, both with identical magnitude. Additionally, the experimental results were evaluated on the basis of optimisation strategies displaying physiologically reasonable neuromuscular objectives for coordinated muscle contraction. In 10 normal subjects, the electric activities of all jaw muscles were recorded bilaterally. Intraoral force transfer and force measurement were achieved by a measuring device with one anterior and two posterior force transmission points. Prior to the experiments, the force transmission was balanced at a directionally unrestricted resultant bite force of 100N. Under visual feedback-control, the subjects generated resultant forces of 50, 100, 150, 200, 300, and 400N, respectively. Joint and muscle forces were calculated based on the electromyograms of all jaw muscles, lines of action, geometrical data of the skull, and physiological cross-sectional areas acquired from all subjects. To identify possible motor control strategies, various physiologically reasonable objective functions were applied. The results revealed significant differences in force patterns generated under the two experimental conditions. Directionally unrestricted biting created higher forces in nearly all muscles and in the jaw joints. Muscle forces normalised with the magnitude of the inherent resultant force, and the findings from the optimisation calculations indicate variable central control mechanisms under the two experimental conditions, both minimizing energy consumption. [Copyright &y& Elsevier]

Abstract: The superior head of the human lateral pterygoid muscle (SHLP) has been classically considered to have functions that are independent of the inferior head of the lateral pterygoid (IHLP). Recent evidence however suggests that some of the functional properties of the SHLP are similar to those of the IHLP. The aim was to determine whether the functional properties in terms of single motor unit (SMU) firing rates within the SHLP vary with horizontal isometric force (400–800gwt) and direction (i.e., contralateral (CL), protrusive (P), ipsilateral (IL) and intermediate directions, CL-P, IL-P) in a manner similar to those identified for the IHLP, and as would be expected if both SHLP and IHLP should be regarded as one muscle. In eight subjects, the firing rates of 40 SMUs were recorded from computer tomography (CT)-verified SHLP sites while each subject exerted horizontal isometric forces with their lower jaw onto a force transducer in the five directions. Firing rates increased significantly with horizontal isometric force from 400 to 800gwt. Firing rates also changed significantly (p <0.01) with direction with CL, CL-P and P having comparable firing rates (13.3, 12.6 and 12.6impulses/s, respectively) which were significantly higher than IL-P. The similarity of these data to previous IHLP data, provide additional support for the hypothesis that the SHLP and the IHLP should be regarded as two parts of one muscle. [Copyright &y& Elsevier]