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Objectives: Diffusion-weighted imaging (DWI) provides quantitative functional information about the microscopic movement of water at the cellular level. However, few reports have quantitatively evaluated histological changes in masticatory muscles due to changes in occlusal relationships using DWI. This study aimed to assess the changes in masticatory muscles by Eichner index using DWI., Methods: We analyzed magnetic resonance imaging (MRI) studies of 201 patients from November 2017 to April 2018. Each Eichner index group, age, and sex were used as criterion variables, and the average apparent diffusion coefficient (ADC) values of the masticatory muscles were the explanatory variable. The mean ADC value differences were analyzed in each Eichner index group. We analyzed the data using the Kruskal-Wallis test and post hoc Mann-Whitney test with Bonferroni adjustment multiple regression analysis with Shapiro-Wilk test and Spearman's correlation coefficients. P < 0.05 was considered statistically significant., Results: The mean ADC values of each Eichner classification group were significantly different, with the lowest value in group C (P < 0.001). There was a negative correlation between the ADC value of the masseter, lateral pterygoid muscle, and age (P < 0.001). There were significant differences between the sex groups (P < 0.001)., Conclusions: ADC values of masticatory muscles were significantly different in the Eichner index groups. The ADC values of masticatory muscles may be useful for the quantitative evaluation of the masticatory muscles affected by the occlusal state., (© 2022. The Author(s) under exclusive licence to Japanese Society for Oral and Maxillofacial Radiology.)

Purpose: Myalgia of the masticatory muscles is difficult to evaluate quantitatively. The purpose of the present study was to quantitatively assess myalgia of the masticatory muscles in patients with temporomandibular disorders (TMDs) using the apparent diffusion coefficient (ADC) on diffusion-weighted magnetic resonance imaging (MRI)., Patients and Methods: Patients who had undergone MRI with clinically diagnosed TMDs according to the criteria of the American Academy of Orofacial Pain and unilateral temporomandibular joint pain from March 2015 to January 2017 were prospectively enrolled. The MRI techniques used included axial diffusion-weighted imaging (DWI) and short T1 inversion recovery imaging through the neck to the skull base. The regions of interest were drawn to completely include the right and left lateral pterygoid muscles, medial pterygoid muscles, and masseter muscles on a slice demonstrating the largest area of each muscle on the ADC map. We compared each masticatory muscle of the pain side with those of the contralateral side without pain., Results: A total of 106 patients with TMD had met the inclusion criteria (18 males, 88 females; mean age, 48.7 years; range, 16 to 80). The mean ADC values of the masticatory muscles of the pain side were significantly greater than those of the no-pain sides (P < .01), as were those for the lateral pterygoid muscles (1.35 ± 0.79 × 10 -3  mm 2 /second vs 1.13 ± 0.77 × 10 -3  mm 2 /second), medial pterygoid muscles (1.28 ± 0.46 × 10 -3  mm 2 /second vs 1.05 ± 0.69 × 10 -3  mm 2 /second), masseter muscles (1.33 ± 0.78 × 10 -3  mm 2 /second vs 1.09 ± 0.64 × 10 -3  mm 2 /second)., Conclusions: The ADC values of the masticatory muscles on the pain side were significantly greater than those of the contralateral side without pain. Our results suggest that DWI could be used to assess myalgia of the masticatory muscles quantitatively., (Copyright © 2019 American Association of Oral and Maxillofacial Surgeons. Published by Elsevier Inc. All rights reserved.)

Based on an atypical case of squamous carcinoma of the tongue in a young non-alcoholic, non-smoking woman, the authors review the anatomy of the tongue and adjacent spaces. The features of extension and the CT and MRI diagnosis of the tumour are analysed. Extension beyond the oropharynx to the pharyngolarynx and intratemporal fossa and bony involvement changed the stage and modified the treatment.

The management of a broken short 30-gauge hypodermic needle after an inferior alveolar dental nerve block in a 3-year-old child is discussed. Because of the possibility of the needle migrating toward vital structures, and because of the psychologic and medicolegal implications that could arise, we believed that the needle should be immediately removed with surgical procedures.

This wide-ranging, omnivorous lizard of Australia has a very complex adductor muscle mass, with fibers differing in length by a factor of three and in insertion angle by 90 degrees. Stimulated muscles produce maximal moment with the mouth nearly fully open. The opening mechanism appears to involve only simple rotation and no translation of the mandible. EMGs indicate that the entire mass is activated equivalently in crushing and there are no temporal subdivisions, for instance, matching activity to angle of opening. During crushing of hard objects, the chin is brought into contact with the ground so that the subvertebral muscles may aid buccal closure. The lizards also activate the muscles in a pulsatile staircase effect leading to an unfused tetanus that generates forces several times the twitch level. Application in parallel of a maximum number of sarcomeres to the crushing bite appears to be the major design characteristic. Hence, this species offers an ideal case for analysis of the effects of different sarcomere placements on the simple movement generated. For the primary adductor muscles, the angles of fiber insertion relative to the lines connecting each insertion with the jaw joint are equivalent; this relation persists as the mouth opens. Also, fiber lenghts are proportional to the distance between jaw joint and site of insertion so that each sarcomere contributes equally to the movement generated. Complex tendons provide additional space for muscle placement. Some of these also extend beyond the bony attachment sites, producing tendinous "coronoid processes." The fibers of laterally and ventrally placed muscles are short relative to the length of the entire muscle, insert at relatively short moment arms, and undergo short excursion during opening; however, there are many such fibers. Also, muscles with a low incident angle are crossed; they apparently protect the jaw joint from horizontal (disarticulating) forces.

Our propose is to present a case of peripheral ameloblastoma revealed by a glue-ear. This lesion is rare: thirty-one peripheral ameloblastoma have been reported whereas this case seems to be the first case described in the infratemporal fossa. Microscopic examination is necessary for the diagnosis. The resection was realized through the soft palate.

Purpose: The potential relationship between mastication ability and cognitive function in idiopathic normal pressure hydrocephalus (iNPH) patients is unclear. This report investigated the association between mastication and cognitive function in iNPH patients using the gray level of the co-occurrence matrix on the lateral pterygoid muscle. Methods: We analyzed data from 96 unoperated iNPH patients who underwent magnetic resonance imaging (MRI) between December 2016 and February 2023. Radiomic features were extracted from T2 MRI scans of the lateral pterygoid muscle, and muscle texture parameters were correlated with the iNPH grading scale. Subgroup analysis compared the texture parameters of patients with normal cognitive function with those of patients with cognitive impairment. Results: The mini-mental state examination score correlated positively with the angular second moment (P < 0.05) and negatively with entropy (P < 0.05). The dementia scale (Eide's classification) correlated negatively with gray values (P < 0.05). Gray values were higher in the cognitive impairment group (64.7 ± 16.6) when compared with the non-cognitive impairment group (57.4 ± 13.3) (P = 0.005). Entropy was higher in the cognitive impairment group (8.2 ± 0.3) than in the non-cognitive impairment group (8.0 ± 0.3) (P < 0.001). The area under the receiver operating characteristic curve was 0.681 (P = 0.003) and 0.701 (P < 0.001) for gray value and entropy, respectively. Conclusion: Our findings suggest an association between heterogeneity of mastication and impaired cognitive function in iNPH patients and highlight muscle texture analysis as a potential tool for predicting cognitive impairment in these patients. [ABSTRACT FROM AUTHOR]

Temporomandibular joint disorders (TMDs) are closely related to the masticatory muscles, but objective and quantitative methods to evaluate muscle are lacking. IDEAL-IQ, a type of chemical shift-encoded magnetic resonance imaging (CSE-MRI), can quantify the fat fraction (FF). The purpose of this study was to develop an MR IDEAL-IQ-based method for quantitative muscle diagnosis in TMD patients. A total of 65 patients who underwent 3 T MRI scans, including CSE-MRI sequences, were retrospectively included. MRI diagnoses and clinical data were reviewed. There were 19 patients in the normal group and 46 patients in the TMD group with unilateral disc displacement. The TMD group was subdivided into those with and without clenching. The right and left FF values of the masseter, medial, and lateral pterygoid muscles were measured twice by two oral radiologists on CSE-MRI, and the average value was used. FF measurements using CSE-MRI showed excellent intra- and inter-observer agreement (ICC > 0.889 for both). There were no statistically significant differences between the right and left FF values in the masseter, medial pterygoid, and lateral pterygoid of the normal group (p > 0.05). A statistically significant difference was found in the TMD group without clenching, in which the masseter muscle had a statistically significantly lower FF value on the disc displacement side (3.94 ± 1.61) than on the normal side (4.52 ± 2.24) (p < 0.05). CSE-MRI, which can reproducibly quantify muscle FF values, is expected to be a biomarker for objective muscle evaluation in TMD patients. The masseter muscle is expected to be particularly useful compared to other masticatory muscles, but further research is needed. [ABSTRACT FROM AUTHOR]

Sonoelastography has been increasingly used for non-invasive evaluation of the mechanical features of human tissues. The interplay between orofacial pain and regional muscle activity appears clinically paramount, although only few imaging studies have investigated this association. Using shear wave sonoelastography (SWS), this study ascertained whether orofacial pain induced alterations in the stiffness of superficial and deep masticatory muscles. All participants were systematically evaluated for oral/facial-related conditions, including the area and intensity of pain. SWS was applied to measure the stiffness of the bilateral masseter, temporalis, and lateral pterygoid muscles. The association between orofacial pain and muscle stiffness/thickness was investigated using a generalized estimating equation for adjusting the influence of age, sex, laterality, and body mass index on muscle thickness/stiffness. A total of 98 participants were included in the present study: 48 asymptomatic controls, 13 patients with unilateral pain, and 37 patients with bilateral orofacial pain. The reliability, quantified by the intraclass correlation coefficient for muscle stiffness measurement, ranged from 0.745 to 0.893. Orofacial pain at the individual muscle level was significantly associated with masseter muscle stiffness. A trend of increased stiffness (p = 0.06) was also observed in relation to the painful side of the temporalis muscle. No significant correlation was identified between the numeric rating scales for pain and stiffness measurements. SWS provides reliable stiffness measurements for the superficial and deep masticatory muscles. The ipsilateral masseter and temporalis muscles might be stiffer than those on the side without orofacial pain. Future studies using the present sonoelasotography protocol can be designed to investigate the stiffness changes in the target muscles after interventions. Shear wave sonoelastography (SWS) can reliably assess the stiffness of masticatory muscles. Orofacial pain, particularly affecting the ipsilateral masseter muscles, exhibited increased stiffness, with a similar trend observed in the temporalis muscle as revealed by SWS. However, the stiffness of the lateral pterygoid muscle appeared to remain unaffected. These findings establish a foundational framework for the objective and quantitative assessment of orofacial pain and indicate the potential utility of SWS as a tool for evaluating treatment outcomes. [ABSTRACT FROM AUTHOR]

This study evaluated photobiomodulation therapy (PBMT) for treatment of trismus in patients undergoing radiotherapy for head and neck cancer (HNC). Sixteen patients, 10 men and 6 women, who had a mouth opening < 35 mm and underwent RT were included. The patients were evaluated daily before and after the PBMT application, measuring mouth opening and performing pain scores for the masticatory muscles using the visual analog scale (VAS). We used the infrared laser (~ 808 nm) extraorally, 0.1 W power, 3 J energy, 30 s (107 J/cm2) per point, applied to temporalis anterior, masseter muscles, and temporomandibular joints (TMJ). An intraoral point was made in the trigonoretromolar region towards the medial pterygoid muscle. The mean mouth opening of the patients increased by more than 7 mm throughout the treatment. The pain scores on the initial days showed an immediate reduction after PBMT on the ipsilateral side in the muscles and TMJ. Throughout PBMT applications, there was a significant reduction in pain scores in all muscles and the TMJ. The radiation dose of all patients was above 40 Gy, which is the threshold dose for the risk of developing trismus. SPSS software was used and adopted a confidence of 95%. The Kolmogorov–Smirnov normality test, Wilcoxon test, and Spearman correlation were performed. PBMT controls muscular pain and reduced mouth opening limitation in HNC during radiotherapy. Further studies are needed to evaluate the preventive capacity of PBMT protocols for RT trismus-related HNC. [ABSTRACT FROM AUTHOR]

Aim: The objective of this study is to utilize artificial intelligence for the segmentation of masticatory muscles in ultrasound images. Materials and Methods: The study comprised a cohort of 60 pediatric patients with ultrasonographic images of the masseter, anterior temporal, and lateral pterygoid muscles, 120 images for each muscle, right and left, totaling 360 muscle images. Within the context of this research, the YOLOv8-Seg deep learning model was employed to automatically conduct the segmentation of the masseter, anterior temporal and lateral pterygoid muscles within ultrasonography images. In this study, an artificial intelligence algorithm (Roboflow, Inc., Des Moines, Iowa, USA) was developed to autonomously carry out the segmentation of the masseter, anterior temporal and lateral pterygoid muscles. A total of 120 images for each muscle group were randomly divided into training, validation and test sets. Results: For the muscle segmentations on the test data, the true positive (TP), false positive (FP) and false negative (FN) values were 18, 0, 0 for masseter muscle, 18, 0, 0 for temporal muscle and 16, 1, 1 for lateral pterygoid muscle, respectively. The model's F1 score, precision and sensitivity values are 1.0, 1.0 and 1.0 for masseter muscle, 1.0, 1.0 and 1.0 for temporal muscle and 0.92, 0.94 and 0.94 for lateral pterygoid, respectively. Conclusion: In summary, segmentation techniques based on deep learning for analyzing ultrasonography images of anatomical structures like masticatory muscles have great potential in clinical applications. Precise segmentation of muscles through this technology can play a crucial role in the diagnosis and follow-up of diverse medical conditions and diseases. [ABSTRACT FROM AUTHOR]

Mice are commonly used to study mandibular dynamics due to their similarity in chewing cycle patterns with humans. Adult mice treated unilaterally with botulinum toxin type A (BoNTA) in the masseter exhibit atrophy of this muscle characterized by an increase in the gene expression of atrophy-related molecular markers, and a reduction in both muscle fiber diameter and muscle mass at 14d. However, the impact of this muscle imbalance on the non-treated masticatory muscles remains unexplored. Here, we hypothesize that the unilateral masseter hypofunction leads to molecular and 3D morphometric signs of atrophy of the masseter and its agonist masticatory muscles in adult mice. Twenty-three 8-week-old male BALB/c mice received a single injection of BoNTA in the right masseter, whereas the left masseter received the same volume of saline solution (control side). Animals were euthanized at 2d, 7d, and 14d, and the masticatory muscles were analyzed for mRNA expression. Five heads were harvested at 14d, fixed, stained with a contrast-enhanced agent, and scanned using X-ray microtomography. The three-dimensional morphometric parameters (the volume and thickness) from muscles in situ were obtained. Atrogin-1/MAFbx, MuRF-1, and Myogenin mRNA gene expression were significantly increased at 2 and 7d for both the masseter and temporalis from the BoNTA side. For medial pterygoid, increased mRNA gene expression was found at 7d for Atrogin-1/MAFbx and at 2d–7d for Myogenin. Both the volume and thickness of the masseter, temporalis, and medial pterygoid muscles from the BoNTA side were significantly reduced at 14d. In contrast, the lateral pterygoid from the BoNTA side showed a significant increase in volume at 14d. Therefore, the unilateral hypofunction of the masseter leads to molecular and morphological signs of atrophy in both the BoNTA-injected muscle and its agonistic non-injected masticatory muscles. The generalized effect on the mouse masticatory apparatus when one of its components is intervened suggests the need for more clinical studies to determine the safety of BoNTA usage in clinical dentistry. [ABSTRACT FROM AUTHOR]

Objective: To evaluate alterations in the masticator space due to the dissemination of malignant neoplasms originating from the tonsillar fossa, retromolar trigone, maxillary sinus, or nasopharynx, using computed tomography (CT), as well as to correlate the presence of trismus with the CT findings and the dimensions of the tumor. Materials and Methods: We evaluated the medical records of 65 patients with malignant tumors in the regions described. The images were analyzed by two physician examiners, working independently, who were blinded to the clinical data. In the evaluation of the masticator space, the following parameters were considered: symmetry with the contralateral space; obliteration of the fat plane, retromolar trigone, or pharyngeal space; edema/atrophy of the medial or lateral pterygoid muscles; and destruction of the mandibular ramus. Results: Obliteration of the fat plane was found in 69.2% of the patients. Asymmetry, edema/atrophy, and bone destruction were detected in 27.7%, 26.2%, and 20.0% of the patients, respectively. Trismus was identified in 15.4% of the patients. Of the patients with trismus, 90.0% had stage T4 tumors, compared with only 43.8% of those without trismus. Trismus was 11.6 times more common among the patients with stage T4 tumors than among those with lower-stage tumors. Neoplasms of the tonsillar fossa and retromolar trigone collectively accounted for 95.0% of the cases. The CT scans showed edema/atrophy of the pterygoid muscles in 60.0% of the patients with trismus and in 21.8% of those without. An association was observed between T4 tumor stage and edema/atrophy of the pterygoid muscles. In addition, the risk of trismus was 5.4 times higher among the patients with stage T4 tumors. Conclusion: In our patient sample, the most common finding was obliteration of the fat plane, followed by asymmetry and edema/atrophy. Most of the patients with T4 tumors had trismus, together with edema/atrophy of the pterygoid muscles. [ABSTRACT FROM AUTHOR]

Background: Clinical use of botulinum neurotoxins (BoNTs) in masticatory muscles is usually bilateral, but most studies on the functional consequences of BoNT treatment have used unilaterally treated animals. Objectives: To test the hypothesis that bilateral BoNT treatment of the rabbit masseter hampers mastication and to assess its effects on bone density of the mandibular condyles. Methods: Ten 5‐month‐old female rabbits received injections of BoNT into both masseter muscles and nine sham animals received saline. Body weight, incisor bite force during masseter tetany, and surface and fine‐wire electromyography (EMG) of the masseter and medial pterygoid muscles were assessed at regular intervals. Half the sample was terminated after 4 weeks and the remainder after 12 weeks. Muscles were weighed and mandibular condyles were scanned with microCT to analyse bone density. Results: BoNT rabbits lost weight and required a soft‐food diet. Incisor occlusal force plummeted after BoNT injection and remained lower than the shams. The duration of masticatory cycles was increased in the BoNT rabbits for 5 weeks, with most of the increase due to the adductor burst. Masseteric EMG amplitude began to improve at Week 5, but remained low on the working side throughout the experiment. At the 12‐week endpoint, masseter muscles were smaller in the BoNT rabbits. Medial pterygoid muscles did not compensate. Condylar bone density was reduced. Conclusion: Bilateral treatment of the rabbit masseter by BoNT severely affected chewing performance. Even after a 3‐month recovery period, deficits remained in bite force, muscle size and condylar bone density. [ABSTRACT FROM AUTHOR]

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The treatment of dentofacial deformities generally includes orthognathic surgery in which mandibular condyle changes following surgery are a common cause of relapse. This study investigated the changes in the mandibular condyle and related muscles to identify the factors that affected the changes in the mandibular condyle after orthognathic surgery in skeletal class II patients. This research studied 60 joints in 30 patients with skeletal class II dentofacial deformities who received surgical orthodontic treatment, including bilateral sagittal split ramus osteotomy, and underwent computed tomography before and after orthodontic treatment. The mandibular condyle, masseter, and medial pterygoid muscles were reconstructed and measured in 3D. Condylar positional and morphology changes, masseter and medial pterygoid muscle volume, temporomandibular joint (TMJ) pain, and distal segment movement were analyzed. The study observed that both the masseter and medial pterygoid muscle volumes decreased with statistical significance. The changes in the horizontal direction were positively correlated with the amount of movement. The findings indicated that mandibular condyle changes were significantly affected by the movement of the distal segment, the medial pterygoid muscle volume, and the direction of the distal segment, which influenced the treatment's long-term stability after orthognathic surgery. [ABSTRACT FROM AUTHOR]

There is still considerable controversy surrounding the impact of mastication on obesity. The aim of this study was to identify the interplay between the masticatory muscles, teeth, and general muscular fitness and how they contribute to body adiposity in a general German population. This cross-sectional study included 616 participants (300 male, 316 female, age 31–93 years) from the population-based Study of Health in Pomerania. The cross-sectional areas of the masseter, medial and lateral pterygoid muscles were measured using magnetic resonance imaging (MRI), muscular fitness assessed by hand grip strength (HGS) and body fat distribution was measured by bioelectrical impedance analysis (BIA) and MRI. The overall prevalence of obesity was high in our cohort. The cross-sectional area of the masseter muscles was positively associated with the number of teeth, body mass index (BMI) and HGS, and negatively associated with the BIA-assessed body fat when adjusted for age, sex, teeth, and BMI. Especially the correlation was strong (p < 0.001). Analogous relationships were observed between the masseter, HGS and MRI-assessed subcutaneous fat. These associations were most pronounced with masseter, but also significant with both pterygoid muscles. Though the masticatory muscles were affected by the number of teeth, teeth had no impact on the relations between masseter muscle and adiposity. Physical fitness and masticatory performance are associated with body shape, controlled and directed by the relevant muscles. [ABSTRACT FROM AUTHOR]

Summary: Regional and systemic disorders of myopathic or neurogenic cause affecting the masticatory muscles have been reported or suspected in horses. The primary masticatory muscles include the masseter, temporalis, lateral and medial pterygoid muscles. The masseter muscle is the largest of the primary masticatory muscles and the most affected based on sporadic reports. This is a brief review of disorders involving the masseter muscle. [ABSTRACT FROM AUTHOR]

Objectives: The purpose of this study was to elucidate how masticatory muscles are involved in the generation of occlusal force. Materials and Methods: The experiment was conducted by fabricating an experimental apparatus for a unilateral occlusion model with the masticatory muscles imparted. The experimental apparatus was fabricated by enlarging the lateral photograph of a dried adult skull specimen 3.5 times larger than that of a standard adult and drawing the outlines of the maxilla and mandible, canines and molars of the upper and lower jaws, and temporomandibular joint on a wooden board. The masticatory muscles used in the experiment were the masseter muscle, the temporalis muscle (anterior and posterior muscle bundles), and the lateral pterygoid muscle. For the measurement of the contractile force of the masticatory muscle, we used the spring scale. For the food, we used cut plastic cylinders. Results: The results of the experiment revealed the following: First, the occlusal force was generated under the condition that the contraction forces of all the masticatory muscles were balanced. Second, when the occlusal force was applied to food, the occlusal planes of the upper and lower jaws were parallel. Third, the occlusal force occurred perpendicular to the occlusal plane. Fourth, the occlusal force was generated with a force greater than the contraction force of the individual masticatory muscles. And finally, even if occlusal force was applied to the food, the occlusal force did not load the temporomandibular joint. Conclusion: Occlusal force is not generated by the action of a single masticatory muscle but under the balanced contractile force of all masticatory muscles. The occlusal force then emerges with a force greater than the contraction force of all the masticatory muscles, and its direction occurs perpendicular to the occlusal plane. [ABSTRACT FROM AUTHOR]

Background: Temporomandibular joint disorders (TMDs) are the most common cause of non-odontogenic pain in the maxillofacial region. Internal derangement (ID) is one of the most prevalent causes of TMDs, and disc displacement is recognized as the most common ID. The masticatory muscles are among anatomical structures involved in TMDs that may be affected by ID. Objectives: This study aimed to evaluate the correlation between the masticatory muscle dimensions and ID of temporomandibular joints using magnetic resonance imaging (MRI). Patients and Methods: This cross-sectional study was conducted on the MRI images of 145 patients, retrieved from the archives of the MRI diagnostic and research center during 2020 - 2021. The patients were categorized into three main groups of normal disc position (NP) (n = 42), disc displacement with reduction (DDR) (n = 54), and disc displacement without reduction (DDWR) (n = 49). The maximum width and height of the masseter and medial pterygoid muscles and the maximum height and length of the superior and inferior heads of the lateral pterygoid muscle were measured on MRI images for each of the groups. Data were analyzed using t-test, Pearson's correlation test, ANOVA test, and Tukey's test (alpha < 0.05). Results: Significant differences were observed between the NP, DDR, and DDWR groups regarding the height (P < 0.001) and length (P< 0.001) of the superior head of the lateral pterygoid muscle; both parameters were significantly higher in the NP group, followed by the DDR and DDWR groups (P < 0.05). The dimensions of masticatory muscles were significantly greater in males than females (P < 0.05), except for the width of the medial pterygoid muscle (P = 0.064). The height of the masseter muscle (r = 0.190, P = 0.022) and the medial pterygoid muscle (r = 0.166, P = 0.046) was significantly correlated with age. Conclusion: Significant correlations were found between the height and length of the superior head of the lateral pterygoid muscle and ID of TMJ; the corresponding values were lower in the DDWR group compared to the DDR and NP groups, respectively. [ABSTRACT FROM AUTHOR]

Temporomandibular disorder is a musculoskeletal disease with complex, multifactorial etiology regarding improper functioning of the stomatognathic system (masticatory muscles, temporomandibular joints, and surrounding structures). This article presents medical emergencies occurring among patients treated for temporomandibular disorders, which tend to constitute a severe difficulty for practitioners during their clinical practice. Examples of the most common emergencies of this type are disc displacement without reduction and a sudden contraction of the inferior part of the lateral pterygoid muscle. The latter occurs in cases of uncontrolled and incorrect use of the anterior repositioning splints and the hypertrophy of the coronoid process of the mandible. The sudden attacks of pain of secondary trigeminal neuralgia are also discussed in this article, together with their specific nature, which is significantly different from the nature of the pain of primary trigeminal neuralgia, yet the two types of neuralgia can be easily confused when the primary one takes the painful form. Subsequent emergencies discussed are myofascial pain syndrome, traumatic and inflammatory states of the temporomandibular joints, subluxation, and the consequences of intense occlusive parafunctions. Finally, the recommended therapeutic methods, which are used as part of the treatment in the cases of aforementioned emergencies, are described in this mini-review article, emphasizing that the implementation of the incorrect treatment and rehabilitation for emergencies of temporomandibular disorders may lead to permanent damage to the soft tissue structures of the temporomandibular joints. [ABSTRACT FROM AUTHOR]

Background: Speaking depends on refined control of jaw opening and closing movements. The medial pterygoid muscle (MPT), involved in jaw closing, and the lateral pterygoid muscle (LPT), involved in jaw opening, are two key mandibular muscles in mastication and are likely to be recruited for controlled movements in speech. Objectives: Three hypotheses were investigated, that during speech the MPT and LPT: (1) were both active, (2) but exhibited different patterns of activity, (3) which fluctuated with the vowels and consonants in speech. Methods: Intramuscular EMG recordings were made from the right inferior head of the LPT and/or the right MPT in five participants during production of 40 target nonsense words (NWs) consisting of three syllables in the form /V1C1V2 C2ə/ (V = vowel; C = consonant; ə = unstressed, reduced vowel), spoken by each participant 10 times per NW; analysis focussed on the target syllable, C1V2. Results: Both MPT and LPT exhibited robust increases in EMG activity during utterance of most NWs, relative to rest. Peak LPT activation was time‐locked to the final part of the target consonant (C1) interval when the jaw begins opening for the target vowel (V2), whereas peak MPT activation occurred around the temporal midpoint of V2, when the jaw begins closing for C2. EMG amplitude peaks differed in magnitude between "high" vowels, i.e., for which the tongue/jaw are high (e.g., in SEEK), and "low" vowels, i.e., for which the tongue/jaw are low (e.g., in SOCK). Conclusions: These novel findings suggest a key role for the LPT and MPT in the fine control of speech production. They imply that speech may impose major synergistic demands on the activities of the MPT and the LPT, and thereby provide insights into the possible interactions between speech activities and orofacial activities (e.g. mastication) and conditions (e.g. Temporomandibular Disorders) that involve the masticatory muscles. [ABSTRACT FROM AUTHOR]

The study of bulbar functions, particularly chewing, in patients with Duchenne muscular dystrophy (DMD) is an emerging field; various markers, such as fatty infiltration, have been explored. Increased fatty infiltration of masticatory muscles has been observed in muscle ultrasonography (MUSG), however, this technique has several limitations. Our aim was to measure the fat fraction (FF) of masticatory muscles using quantitative muscle resonance in DMD patients and its correlation with maximum masticatory force (MMF). Multicenter cross-sectional study in 17 healthy men (median age 16 years (interquartile range (IQR) 14-19 years), and in 11 DMD patients (median age 17, IQR 13-21 years). Bilateral MMF was measured with an oral dynamometer and MRI was performed in T1 and mDixon sequences and in the masseter, pterygoid and temporal muscles. The patients were enrolled in the study Magnetic Resonance of Orofacial and Cardiac Muscles as Biomarkers in Children and Adults with DMD. The MMF was 526 Newton (N) in controls and 156N in DMD patients (p<0.05). The muscle volumes of the muscles were 19,883 mm3 in healthy males and 19,392 mm3 in DMD patients. The mean FF was 4% in healthy men and 55% in DMD patients. Both differences were statistically significant (p<0.05). A negative correlation was observed between fatty infiltration and muscle strength (r=-0.78) in healthy patients and in DMD patients. The DMD children in this study presented significantly higher FF and lower MMF than controls. FF correlates with a lower MMF, which could be applied in the clinic and as a biomarker in clinical trials. [ABSTRACT FROM AUTHOR]

Occlusal alteration due to tooth loss may cause overload of masticatory muscle and promote muscle dysfunction. This study explored the feasibility of using functional magnetic resonance imaging (fMRI) to evaluate muscle dysfunction in an established unilateral exodontia animal model. 6 rabbits were extracted right maxillary molars. T2 mapping, T2* mapping and Iterative Decomposition of water and fat with Echo Asymmetry and Least Square Estimation (IDEAL-IQ) were performed one day before extraction and every 2 weeks (2th~12th week) after extraction. The T2 and T2* values and fat fraction (FF) of bilateral temporal muscle (TM), masseter muscle (MM) and medial pterygoid muscle (MPM) were measured and compared between the extraction side and the contralateral side. Parameters of three monitoring time points (0th, 6th, 12th week) were also analyzed. T2 values of MM on extraction side were significantly higher than those of contralateral side-from fourth week to 12th week after extraction (p < 0.05). T2 values of MM and MPM on extraction side and TM on contralateral side were significantly higher in 12th week than those in 0th week (p < 0.05). And FF of bilateral MM was significantly higher in 12th week than those in 0th week (p < 0.05). T2* value showed no significant difference between extraction side and contralateral side and also at above three time points. T2 and T2* value and FF can be used as indicators of masticatory muscle dysfunction. fMRI is expected to be a non-invasive method for in vivo and real-time evaluation of masticatory muscle functional abnormality. [ABSTRACT FROM AUTHOR]

Abstract Objective The lateral pterygoid is vital in coordinating multidimensional jaw movements. Since a vector in three‐dimensional (3D) space is defined by two 3D points, the role of the lateral pterygoid in 3D jaw movements is defined by its origin and insertion. Reportedly, the lateral pterygoid is inserted into not only the pterygoid fovea but also into the medial surface of the condylar process. The objective was to investigate the morphological features of the region of the lateral pterygoid that inserted into the medial surface of the condylar process. Material and Methods Ten head halves of seven cadaveric donors were analyzed. In all specimens, the insertion area on the medial surface of the condylar process was measured based on microcomputed tomography images. Muscle fibers were separated into ≥50 small bundles, and positional relationships between the origins and insertions were investigated. Results Overall, 28.8 ± 5.0% of the insertion area of the lateral pterygoid was situated on the medial surface of the condylar process. Moreover, muscle fiber arrangement revealed that origins of the muscle bundles inserting into the medial surface in seven specimens posteriorly occupied the lateral plate of the pterygoid process longitudinally, whereas those in three specimens mainly occupied the posteroinferior portion. Conclusions Muscle bundle inserting on the medial surface of the condylar process had a broad insertion area and a distinct origin on the posterior region of the lateral plate of the pterygoid process. This muscle bundle could act as one of the significant subunits within the lateral pterygoid. Therefore, anatomical coordination mechanisms underlying jaw movement cannot be elucidated without considering this subunit.

This retrospective case-series study aimed to elucidate the three-dimensional attachment morphometric features and to quantify the volumetric changes of the masticatory muscles following free fibular flap reconstruction of the mandibular condyle. Navigation software (iPlan, version 3.0; Brainlab) was used to perform delineation and volumetric measurement of the masticatory muscles using DICOM data. In total, 30 patients were included in this retrospective case series. In 25 cases (83.33%), the lateral pterygoid muscle achieved reattachment within 6 months postoperatively. The medial pterygoid muscles on the affected side achieved ectopic attachment in all cases. However, masseter reattachment on the affected side was achieved in only three cases. On the normal side, the volumes of lateral pterygoid muscle, medial pterygoid muscle, and masseter had recovered to almost preoperative levels at 1 year postoperatively. On the affected side, the volume of medial pterygoid muscle had decreased significantly (p = 2.4e-04) at 3 months postoperatively. The volumes of lateral pterygoid muscle and masseter showed mild decreases at 3 months postoperatively, but these were not significant (p = 0.52 and p = 0.05 for the pterygoid muscle and masseter, respectively). At 6 months after surgery, with the exception of the volume of the lateral pterygoid muscle (p = 0.06), the total volume of the masticatory muscles decreased significantly on the affected side. The volumes of lateral pterygoid muscle, medial pterygoid muscle, and masseter showed significant decreases at 1 year postoperatively (p = 0.03, p = 4.7e-08, and p = 1.1e-05, respectively) on the affected side. The postoperative volumes of the masseter, medial pterygoid, and lateral pterygoid muscles showed significant decreases due to the loss of reattachment. The results of this study may not help to ascertain whether reattachment of masticatory muscles will lead to better function. As a consequence, clinical trials of higher quality are needed. [ABSTRACT FROM AUTHOR]

Both the masseter and medial pterygoid muscles elevate the mandible, raising the lower jaw by acting simultaneously on the lateral and medial surfaces of the mandibular ramus. Nevertheless, electromyographic studies indicate that these muscles, as well as the superficial and deep heads of the masseter, act in a different way during mastication. We have analyzed by real time quantitative polymerase chain reaction (RT-qPCR) the expression of myosin heavy chain (MHC) isoforms in the masseter and medial pterygoid muscles in humans in order to identify possible differences in the expression patterns that may be related to functional differences identified with electromyography. Our findings indicate that the expression pattern of MHC isoforms in the two muscles is characteristic of fast and powerful phasic muscles. We have also observed a high percentage of expression of the MHC-IIx isoform and the expression of the MHC-M isoform at the mRNA level in both muscles, an isoform that does not translate into protein in the masticatory muscles of humans. The high percentage of expression of the MHC-IIx isoform in humans can be related to a high contractile speed of the masseter and medial pterygoid in humans. On the other hand, the low percentage of expression of the MHC-M isoform at the mRNA level in both muscles can be related to the complex evolutionary process that has reduced the size and force of the masticatory muscles in humans. [ABSTRACT FROM AUTHOR]

Background: The pterygoid fovea on the mandibular neck is superomedial to the mandibular notch and serves to attach the lateral pterygoid muscle.Clinical presentation: During a retrospective cone beam computed tomography study, a 67-year-old male patient was found to exhibit a peculiar variant that contradicted normal anatomy. The patient's mandibular condyles were asymmetrical in terms of their shapes and sizes, although their lateral poles (lateral condylar tubercles) were both prominent. On the left side, the lateral condylar tubercle had a second, or accessory, pterygoid fovea, which was located outside the mandibular notch. Further, the left lateral pterygoid muscle was attached to the entire width of the mandibular condyle, including the accessory fovea.Clinical significance: Such rare anatomical variants lead to asymmetrical temporomandibular joints, although their occurrence has not previously been reported. Thus, they should be further documented in clinical studies of temporomandibular joint dysfunction.Abbreviations: LPM: Lateral pterygoid muscle; MC: Mandibular condyle; PF: Pterygoid fovea; TMJ: Temporomandibular joint; MCC: Mandibular condylar cartilage; MPR: Multiplanar Reconstruction; VC: Vascular canal. [ABSTRACT FROM AUTHOR]

The article focuses on investigating sex-related differences in the lateral pterygoid muscle (LPM) characteristics in patients with anterior disk displacement (ADD), highlighting higher fat infiltration and fibrotic tendencies in female patients compared to males. Topics include the need for clarification regarding the presence of bruxism in the studied patients, that demographic information about bruxism could enhance the understanding of the impact of temporomandibular joint disorders.

Age-related craniofacial morphology: Assessing the effect of muscle action on the bony orbit in subjects with long-standing flaccid unilateral facial nerve paralysis Although we have tried to isolate the effects of muscle contraction, the subjects with unilateral facial nerve paralysis still have normal function of the muscles of mastication because these are innervated by the trigeminal nerve. Since these muscles of mastication are unaffected in facial paralysis patients, patients would still be expected to demonstrate some changes of the bony structure at and around the orbital bones due to muscle contraction not associated with the facial nerve. [Extracted from the article]

Objective: The lateral pterygoid is vital in coordinating multidimensional jaw movements. Since a vector in three‐dimensional (3D) space is defined by two 3D points, the role of the lateral pterygoid in 3D jaw movements is defined by its origin and insertion. Reportedly, the lateral pterygoid is inserted into not only the pterygoid fovea but also into the medial surface of the condylar process. The objective was to investigate the morphological features of the region of the lateral pterygoid that inserted into the medial surface of the condylar process. Material and Methods: Ten head halves of seven cadaveric donors were analyzed. In all specimens, the insertion area on the medial surface of the condylar process was measured based on microcomputed tomography images. Muscle fibers were separated into ≥50 small bundles, and positional relationships between the origins and insertions were investigated. Results: Overall, 28.8 ± 5.0% of the insertion area of the lateral pterygoid was situated on the medial surface of the condylar process. Moreover, muscle fiber arrangement revealed that origins of the muscle bundles inserting into the medial surface in seven specimens posteriorly occupied the lateral plate of the pterygoid process longitudinally, whereas those in three specimens mainly occupied the posteroinferior portion. Conclusions: Muscle bundle inserting on the medial surface of the condylar process had a broad insertion area and a distinct origin on the posterior region of the lateral plate of the pterygoid process. This muscle bundle could act as one of the significant subunits within the lateral pterygoid. Therefore, anatomical coordination mechanisms underlying jaw movement cannot be elucidated without considering this subunit. [ABSTRACT FROM AUTHOR]

This article from Neurology India discusses a case of masticator muscle atrophy in a 53-year-old man. The patient initially presented with a headache and right-lower-motor-neuron facial palsy, and a CT scan revealed a small intracerebral hemorrhage. After being discharged, the patient returned three months later with facial deformity and difficulty opening his mouth fully. MRI scans showed atrophy and hyperintensities in the right masseteric muscles, corresponding to the location of the motor nucleus of the trigeminal nerve. The article concludes that a strategic trigeminal motor nuclear lesion can result in unilateral lower motor neuron masticator muscle atrophy, which can be detected on MRI. [Extracted from the article]

Introduction. Myositis ossificans traumatica (MOT) refers to a benign, localized ectopic bone formation within skeletal muscle bundles related to a traumatic injury. MOT rarely affects masticatory muscles, and it represents a major diagnostic and therapeutic problem for clinicians. Currently, the treatment of choice is complete excision of the calcified mass after bone maturation and resection of the affected bone. Case report. A 47-year-old male presented with a month-long severe restriction of mouth opening that was followed by extraction of the right lower third molar tooth under local anesthesia. A computed tomography (CT) scan revealed ectopic bone formation in the right temporal muscle extending to the right coronoid process. Surgical excision of the calcified mass was performed. Six years after the surgery, the patient reported the same symptoms. The CT scan revealed a calcified mass of the right temporal muscle extending to the medial pterygoid muscle. The patient was reoperated, and sent for the postoperative physical treatment. Conclusion. MOT represents a major diagnostic and therapeutic challenge for surgeons due to unclear etiology and frequent recurrences after surgical treatment. Further research is needed to clarify the mechanisms of ossification in MOT in order to develop conservative treatment approaches. [ABSTRACT FROM AUTHOR]

The causes of dentofacial deformities include various known syndromes, genetics, environmental and neuromuscular factors, trauma, and tumors. Above all, the functional effects of muscles are important, and deformation of the mandible is often associated with a mechanical imbalance of the masticatory muscles. With the vertical position of the face, weakness of the sling of the masseter muscle and medial pterygoid muscle causes dilatation of the mandibular angle. In patients with a deep bite, excessive function of the masticatory muscles is reported. Myosin heavy chain (MyHC) properties also affect jawbone morphology. In short-face patients, the proportion of type II fibers, which are fast muscles, is high. The proportions of muscle fiber types are genetically determined but can be altered by postnatal environmental factors. Orthognathic surgery may results in the transition of MyHC to type II (fast) fibers, but excessive stretching enhances the release of inflammatory mediators and causes a shift toward a greater proportion of slow muscle fibers. This feature can be related to postoperative relapse. Bones and muscles are in close crosstalk, and it may be possible to use biochemical approaches as well as biomechanical considerations for the treatment of jaw deformities. [ABSTRACT FROM AUTHOR]

Objectives: Temporomandibular joint dysfunction (TMD) results in changes in anatomical structures. The aim of this study was to examine the morphological changes using magnetic resonance imaging (MRI) and evaluate the effectiveness of different treatment methods in patients with TMD. Methods: 34 TMD patients (18-62 years of age) were randomly divided into two treatment groups. Group A (n=18) was subjected to dry needling (DN) and mobilization for 10 sessions, Group B (n=16) was instructed to use occlusal splint with home exercises for one month. The control group included MRIs of 17 healthy adults that were randomly selected from the archives of Radiology Department of Mustafa Kemal University. The length and width of the masseter, lateral and medial pterygoid muscles and the depth of the mandibular fossa were measured and mandibular condyle types were recorded. Range of motion of each temporomandibular joint was evaluated in pre- and post-treatment periods to test the effectiveness of the treatment methods. Results: The size of the masticatory muscles in TMD group was significantly smaller than the control group (p<0.05). The depth of the mandibular fossa was significantly shallower in the TMD group (p<0.05). The most commonly encountered condylar shape was convex in the TMD group (63.6%), but flat (58.8%) in the control group. No statistically significant relationship was observed between condyle type and fossa depth (p>0.05). However, the fossa depth showed a significant correlation with muscle size (p<0.05) and this correlation decreased with dysfunction. Dry needling and mobilization significantly decreased pain and increased mandibular movements (p<0.05); however, there was no significant change for Group B. Conclusion: The anatomical structures associated with the temporomandibular joint seems to be affected in patients with TMD. We suggest that the limited movement of the temporomandibular joint may cause atrophy of the masticatory muscles, affecting the range of motion of the joint. Dry needling and mobilization techniques might be a more effective alternative than occlusal splint in the treatment of TMD. [ABSTRACT FROM AUTHOR]

Background: Temporomandibular disorders (TMDs) are pathological conditions affecting the temporomandibular joint and/or masticatory muscles. The current diagnosis of TMDs is complex and multi-factorial, including questionnaires, medical testing and the use of diagnostic methods, such as computed tomography and magnetic resonance imaging. The evaluation, like the mandibular range of motion, needs the experience of the professional in the field and as such, there is a probability of human error when diagnosing TMD. The aim of this study is therefore to develop a method with infrared cameras, using the maximum range of motion of the jaw and four types of classifiers to help professionals to classify the pathologies of the temporomandibular joint (TMJ) and related muscles in a quantitative way, thus helping to diagnose and follow up on TMD.Methods: Forty individuals were evaluated and diagnosed using the diagnostic criteria for temporomandibular disorders (DC/TMD) scale, and divided into three groups: 20 healthy individuals (control group CG), 10 individuals with myopathies (MG), 10 individuals with arthropathies (AG). A quantitative assessment was carried out by motion capture. The TMJ movement was captured with camera tracking markers mounted on the face and jaw of each individual. Data was exported and analyzed using a custom-made software. The data was used to identify and place each participant into one of three classes using the K-nearest neighbor (KNN), Random Forest, Naïve Bayes and Support Vector Machine algorithms.Results: Significant precision and accuracy (over 90%) was reached by KNN when classifying the three groups. The other methods tested presented lower values of sensitivity and specificity.Conclusion: The quantitative TMD classification method proposed herein has significant precision and accuracy over the DC/TMD standards. However, this should not be used as a standalone tool but as an auxiliary method for diagnostic TMDs. [ABSTRACT FROM AUTHOR]

The Bathyergidae, commonly known as blesmols or African mole-rats, is a family of rodents well-known for their subterranean lifestyle and tunnelling behaviour. Four of the five extant bathyergid genera (Cryptomys, Fukomys, Georychus and Heliophobius) are chisel-tooth diggers, that is they dig through soil with their enlarged incisors, whereas the remaining genus (Bathyergus) is a scratch-digger, only using its forelimbs for burrowing. Heterocephalus glaber, the naked mole-rat, is also a chisel-tooth digger and was until recently included within the Bathyergidae (as the most basally branching genus), but has now been placed by some researchers into its own family, the Heterocephalidae. Given the importance of the masticatory apparatus in habitat construction in this group, knowledge and understanding of the morphology and arrangement of the jaw-closing muscles in Bathyergidae is vital for future functional analyses. Here, we use diffusible iodine-based contrast-enhanced microCT to reveal and describe the muscles of mastication in representative specimens of each genus of bathyergid mole-rat and to compare them to the previously described musculature of the naked mole-rat. In all bathyergids, as in all rodents, the masseter muscle is the most dominant component of the masticatory musculature. However, the temporalis is also a relatively large muscle, a condition normally associated with sciuromorphous rodents. Unlike their hystricomorphous relatives, the bathyergids do not show an extension of the masseter through the infraorbital foramen on to the rostrum (other than a very slight protrusion in Cryptomys and Fukomys). Thus, morphologically, bathyergids are protrogomorphous, although this is thought to be secondarily derived rather than retained from ancestral rodents. Overall, the relative proportions of the jaw-closing muscles were found to be fairly consistent between genera except in Bathyergus, which was found to have an enlarged superficial masseter and relatively smaller pterygoid muscles. It is concluded that these differences may be a reflection of the behaviour of Bathyergus which, uniquely in the family, does not use its incisors for digging. [ABSTRACT FROM AUTHOR]

Aims: The purpose of this study is to develop a FE model of the temporomandibular joint (TMJ) to investigate a musculoskeletal System of forces able to taking into account the effect of all the muscles on the TMJ in terms of stress evaluated on the bone. Methods: A 3-dimensional finite element model of the mandible was constructed from the images generated by cone-beam computed tomography of a patient undergoing fixed orthodontic treatment. In order to define the loading force system an exustive study was developed to investigated the entity of the Lateral pterygoid, Masseter, medial pterygoid, Temporalis, and Geniohoid digastric, muscles. Results: Stresses in the TMJ components (disc, mandible condyle and the fossa eminence on the skull) were obtained. The results have shown stress distribution during normal occlusion. Conclusion: An appreciation of the anatomical and mechanical features associated with the TMJ can serve as a foundation for understanding a patient's clinical presentation. Performance of a thorough patient history and clinical examination can guide the clinician toward an improved diagnostic process. [ABSTRACT FROM AUTHOR]

The article presents a case study of a 5-year-old neutered male West Highland White Terrier who was suffering with acute unilateral masticatory muscle wasting. Topics include diagnosis of a swollen and stenotic external right ear canal, cytologic examination of swab specimens from both ear canals that revealed yeast and cocci, and use of stereotactic radiotherapy for treatment of dogs with intracranial tumors.

Objectives: The aim of this prospective study was to evaluate the short-term effects of full-time and night-time wear of functional appliances on the temporomandibular joint (TMJ) and masticatory muscles and to compare the differences in craniofacial structures, TMJ, and masticatory muscles with magnetic resonance imaging (MRI). Methods: The study was carried out using cephalometric radiographs and MRI of 20 Class II patients who were treated with monoblock/twin-block appliances. The patients were divided into 2 groups: ten patients in Group 1 used their appliances all day, while ten patients in Group 2 were instructed to wear the appliances during sleep. After at least 6 months of uninterrupted treatment, post-treatment cephalograms and MRI were obtained for patients whose molar relationship improved by at least a half cusp width. Signal intensity ratios (SIR) of TMJ structures and morphological evaluations of masticatory muscles were done for all patients. Results: It was found a significant increase in SIR values of the condylar process, articular disc, retrodiscal tissue, and masticatory muscles for all treatment groups. Length of the masseter and medial pterygoid muscles increased to varying degrees which left side of Group 2 was significantly increased (P < 0.05). The volume of all muscles also increased to varying degrees. Conclusions: The cephalometric and MRI findings of this study show that the treatment effects were similar for both wear schedules. [ABSTRACT FROM AUTHOR]

The article focuses on muscular control and denture stability. Topic include ffectively control the dentures with muscles of the lips, cheeks and tongue; and the labial, lingual and palatal parts of the denture base together with nonarticulating buccal and lingual parts of prosthetic teeth surfaces form the polished surface of the denture.

By using three-dimensional (3-D) CT imaging, the maxillofacial bones and muscles can be observed from any desired angles and analyzed the bone and muscles simultaneously. However, no studies have investigated the three dimensional analysis of muscles in jaw deformity. The purpose of this study was to examine the relationship between the morphology of the masticatory muscles and the craniofacial skeleton in the patients with facial asynmetry. Eight Japanese normal female adults and 10 female adult patients with laterognqthism were participated in this study. The 3-D CT images of their craniofacial skeleton and masseter, medial pterygoid and lateral pterygoid muscles were recon-structed. Then, 6 skeletal and 7 muscle variables were measured for each subject. Significant positive correlations were found among the volume of the masti-catory muscles in the normal adults, but not found in patients with mandibular laterognathism. The muscular variables showed significant positive correlations with skeletal variables in normal subjects, but few significant correlations were found in the patients with laterognathism. This study suggestted that the balance between masticatory muscles and the balance between muscles and skeleton collapsed in the patients with mandibu-lar laterognathism. [ABSTRACT FROM AUTHOR]