Evaluation of masticatory muscles in temporomandibular joint disorder patients using quantitative MRI fat fraction analysis-Could it be a biomarker?

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.

[Ultrasound anatomy of masticatory muscles. (Experimental and clinical study)]. / Ul'trazvukovaya anatomiya zhevatel'nykh myshts. (Eksperimental'no-klinicheskoe issledovanie).

PURPOSE: To describe the ultrasound anatomy of the masticatory muscles based on a comparison of the results of macroscopic and ultrasound studies of the masticatory muscles in vitro. MATERIAL AND METHODS: In the experimental part, a macropreparation of the masticatory muscle was studied; in a clinical example, an ultrasound of the masticatory muscles was performed on a patient with normal occlusion using the author's methods for analyzing echograms. RESULTS: The ultrasound anatomy of the masticatory muscles is described based on a comparison of data from the study of a macroscopic specimen and ultrasound images of the masticatory muscle of an experimental animal. Using a clinical example of a patient with normal occlusion, the results demonstrate the usage of the authors' developments in describing ultrasound images of the masticatory muscles. CONCLUSION: The study resulted in an algorithm for describing ultrasound images of masticatory muscles, including methods for qualitative and quantitative assessment of ultrasound images using proprietary developments involving elements of artificial intelligence technologies.

Assessing thickness and stiffness of superficial/deep masticatory muscles in orofacial pain: an ultrasound and shear wave elastography study.

INTRODUCTION: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Quantitative volume and area assessment of masticatory muscles through magnetic resonance imaging in patients with temporomandibular joint disorders.

OBJECTIVE: To compare volume and surface area measurements of the lateral pterygoid (LPM), medial pterygoid (MPM), and masseter muscles (MM) as calculated on magnetic resonance imaging (MRI) based on the position of the temporomandibular joint disk, mouth position, and patient sex, and to calculate the correlations of the measurements among the muscles. STUDY DESIGN: Measurements of muscle volume and area were performed on the MRIs of 51 patients. Wilcoxon, Kruskal-Wallis, and Mann-Whitney U tests were used to calculate the significance of differences in measurements. The Spearman correlation coefficient calculated the correlation of measurements among the muscles. The significance of difference was established at P < .05. RESULTS: Volume and area of the left MPM in patients with disk displacement without reduction (DDWOR) were larger than in patients with normal disk position (P ≤ .040). MM volumes were smaller with DDWOR than with DD with reduction bilaterally (P ≤ .031). The volume and area of LPM and MM were significantly different between closed and open mouth positions (P < .001). Differences in volume and area between females and males were significant for all muscles in volume (P ≤ .021) and for MPM and MM in area (P ≤ .021). Significant positive correlations were found among all muscles for volume and area. CONCLUSION: Volume and area measurements of the masticatory muscles varied according to disk and mouth position and patient sex and exhibited significant positive correlations.

Quantitative analysis of masticatory muscle changes by Eichner index using diffusion-weighted imaging.

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.

Magnetic resonance imaging evaluation of masticatory muscle changes in patients with primary trigeminal neuralgia before microvascular decompression.

Primary trigeminal neuralgia (PTN) is characterized by chronic neuropathic pain. There are few studies exploring masticatory muscle changes in patients with PTN. This study evaluated the changes in the masticatory muscles using magnetic resonance imaging (MRI) and the predictive factors of masticatory muscle changes in patients with PTN. The radiologic outcomes of 52 patients with PTN and 58 healthy adults were evaluated. The temporalis, lateral pterygoid, medial pterygoid, and masseter muscles were assessed using MRI. Atrophy and edema of the masticatory muscles were noted. Multivariate analyses were conducted to identify factors associated with masticatory muscle atrophy. Among the PTN group, the right side (61.5%) and mandibular branch (53.9%) were the most affected. Muscle atrophy of the temporalis (P < .001), medial pterygoid (P = .016), lateral pterygoid (P = .031), and masseter (P = .001) were significantly higher in the PTN group than in the control group. Lateral pterygoid edema was significantly higher in the PTN group (P < .001). However, no significant difference was found in the temporalis and masseter edema between the two groups. Logistic regression analysis demonstrated that neurovascular conflict (NVC) significantly predicted mastication muscle atrophy (P = .037). Patients with PTN had higher rates of masticatory muscle atrophy and edema. The assessment of NVC may be a preoperative imaging biomarker to predict atrophy in PTN.

Assessment of the masseter stiffness in patients during conservative therapy for masticatory muscle disorders with shear wave elastography.

BACKGROUND: The complex structure of the stomatognathic system plays a vital role in chewing, digestion, speaking, breathing, facial expression and swallowing. Its complexity is the primary reason for creating multidisciplinary teams to manage temporomandibular disorders (TMD). We aimed to assess the masseter stiffness in patients undergoing conservative therapy for masticatory muscle disorders and evaluate the efficacy of manual therapy and stabilization occlusal splint in the treatment of masticatory muscle disorders. METHODS: This uncontrolled prospective cohort study included 35 patients with masticatory muscle disorders. The study lasted for eight weeks. The patients were treated with manual therapy and stabilization occlusal splint and evaluated using shear wave elastography of the masseter muscles and patient-reported outcome measures (PROMs) to assess pain, anxiety, quality of sleep, satisfaction with life and perceived stress. RESULTS: After the treatment, the stiffness of both masseter muscles decreased significantly (by 4.21 kPa). The patients reported a significant reduction in pain. At baseline, the median scores ranged from 5 to 8; after treatment, they ranged from 0 to 1 (p < 0.0001). The patients also reported significant improvement in terms of all patient-reported outcome measures. The reduction in stiffness corresponded to the improvement in pain and PROMs, as shown by correlations which were insignificant for all measures. CONCLUSIONS: Conservative therapy of masticatory muscle disorders involving manual therapy and stabilization occlusal splint is effective. It reduces the masseter stiffness as objectively shown in shear wave elastography and improves subjective PROMs scores, including numerical pain assessment and selected questionnaires. Shear wave elastography has the potential for broad application in clinical practice to monitor masticatory muscle disorders treatment effects due to its objectivity and non-invasive character. Further research is recommended on larger patient populations and longer follow-up. TRIAL REGISTRATION: The study was registered at clinicaltrials.gov ( NCT03844854 ). First posted date: 19/02/2019.

Functional magnetic resonance imaging evaluation of masticatory muscle dysfunction in unilateral exodontia rabbits.

OBJECTIVE: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Bite Force, Thickness, and Thermographic Patterns of Masticatory Muscles Post-Hemorrhagic Stroke.

OBJECTIVE: Stroke is a neurological deficit of cerebrovascular origin, considered a 21st-century epidemic that causes functional changes in the human body. This study aimed to evaluate the stomatognathic system of patients after hemorrhagic stroke through the bite force, thickness, and skin temperature in the region of the masseter and temporalis muscles. MATERIAL AND METHODS: Twenty-four subjects were divided into groups: post-hemorrhagic stroke; with right side of the affected body (n = 12) and without the neurological disorder (n = 12). Maximum molar bite force was verified using a digital dynamometer. Muscle thickness was measured using ultrasound images obtained at rest and during maximal voluntary contraction of the masseter and temporalis muscles. Thermographic camera was used to record the thermographic patterns of the masseter and temporalis muscles. Data were subjected to Student's t-test (P < .05). RESULTS: The maximum molar bite force showed significant differences in the right (P = .04) and left (P = .03) sides, with a reduction in force in the post-hemorrhagic stroke group on the affected and unaffected sides. There was a significant difference (P < .05) in the thickness of the left temporal muscle at mandibular rest (P = .01) between groups. The post-hemorrhagic stroke group clinically presented greater muscle thickness in almost 100% of the muscles evaluated in both clinical conditions. There were no significant differences in skin temperature in the masseter and temporal muscles between the groups. CONCLUSIONS: Our results suggest functional changes in the stomatognathic system of subjects after a hemorrhagic stroke, especially concerning molar bite force and masticatory muscle thickness in the temporal muscle (unaffected side).

Relationship Between Masticatory Muscle Size and Bone Regeneration After Mandibular Angle Osteotomy.

ABSTRACT: Mandibular angle osteotomy with outer cortex grinding has become the preferred cosmetic procedure for correcting square faces. After surgery, bone hyperplasia at the mandibular angle affects the operation result. This study evaluated the effect of the masticatory muscles on bone repair. From January 2016 to January 2019, patients who underwent mandibular angle osteotomy with outer cortex grinding were retrospectively reviewed. Computed tomography data of these patients were collected, and the bone volume of the mandibular angle changes and its correlation with masticatory muscle morphology were analyzed. Computed tomography data measurement results showed that a large amount of bone in the mandibular angle area was removed by the operation; however, the long-term follow-up results showed that there was bone hyperplasia in the mandibular angle areas. Compared with the immediate postoperative bone volume, the difference was statistically significant (P < 0.01). The thickness and cross-sectional area of the masseter muscle were significantly related to bone regeneration (P < 0.01). This study suggests that mandibular angle osteotomy with outer cortex grinding could ablate the symptoms of a prominent mandibular angle; however, muscle-related bone hyperplasia in the mandibular angle area after surgery was a non-negligible event, which may significantly compromise surgical outcomes.

Multicompartmental Epidermoid Cyst Causing Chronic Parotid Gland and Masticator Space Muscle Atrophy.

Epidermoid cysts are rare benign intracranial tumors of congenital origin. They are slow-growing and are seen to insinuate between brain structures. These are commonly located in cerebello-pontine angle and parasellar regions. The symptoms produced are primarily due to mass effect. Hearing loss, facial nerve palsy, and trigeminal neuralgia are reported when cranial nerves are involved; motor palsy of trigeminal nerve is uncommon. Here, we present an interesting case of an extensive multicompartmental epidermoid cyst causing atrophy of trigeminal nerve with radiologic evidence of chronic motor trigeminal nerve palsy characterized by atrophy of masticator space muscles and parotid gland.

Diagnosis of Temporomandibular Disorders Using Thermovision Imaging.

Temporomandibular joint dysfunction (TMD) is a chronic disease of various etiologies. Correct TMD diagnosis enables to apply effective treatment and significantly improves the quality of patients' lives. One of the diagnostic methods subjected to evaluation in recent years is thermography, which enables safe, noninvasive, and quick imaging of the temperature distribution of temporomandibular joint-associated tissues. This paper, based on Medline, Dentistry & Oral Sciences Source, Academic Search Ultimate, Medline Complete databases, presents basic information related to thermovision imaging and outlines the direction of research conducted in recent years which fight with difficulties in the interpretation of thermograms that require specialized, dedicated analysis and processing of the obtained images. The problem concerns also no standardized protocol for measuring masticatory muscle temperature.

Ultrasound measurements of superficial and deep masticatory muscles in various postures: reliability and influencers.

Masticatory muscle thickness provides objective measurements of the oral motor function, which may change in patients with oral myofascial pain. In this study, we aimed to establish a reliable ultrasound (US) protocol for imaging the superficial and deep masticatory muscles and to identify the potential influencers of the measurements. Forty-eight healthy participants without orofacial pain were enrolled. The intra-and inter-rater reliabilities of US measurements for masseter, temporalis, and lateral pterygoid muscles were assessed. Intraclass correlation coefficients for all muscles were greater than 0.6. The generalised estimating equation was used to analyse the impact of age, gender, laterality, and body mass index on the measurements, whereby age and body mass index were likely to be associated with an increase in masticatory muscle thickness. The thickness tended to be lesser in females. Laterality seemed to exert minimal influence on masticatory muscle thickness. Our study shows acceptable reliability of US in the evaluation of superficial and deep masticatory muscle thickness. Future studies are warranted to validate the usefulness of US imaging in patients with oral myofascial pain syndrome.

Intense Increased 18F-FDG Uptake of Masticator Muscles After Cocaine Use.

F-FDG is the most widely used PET tracer worldwide. Before the examination, recommendations are given to patients to avoid muscular activities, with the goal to limit F-FDG uptake in muscles. Here, we report the case of a 36-year-old man with Hodgkin disease referred to our department to perform an F-FDG PET/CT for immunotherapy assessment. The PET images showed a homogeneous, symmetric, and very intense uptake of the masticatory muscles. The medical examination exhibited a trismus, and the patient revealed to have been using cocaine 15 minutes before injection of F-FDG.

Deep learning vs. atlas-based models for fast auto-segmentation of the masticatory muscles on head and neck CT images.

BACKGROUND: Impaired function of masticatory muscles will lead to trismus. Routine delineation of these muscles during planning may improve dose tracking and facilitate dose reduction resulting in decreased radiation-related trismus. This study aimed to compare a deep learning model with a commercial atlas-based model for fast auto-segmentation of the masticatory muscles on head and neck computed tomography (CT) images. MATERIAL AND METHODS: Paired masseter (M), temporalis (T), medial and lateral pterygoid (MP, LP) muscles were manually segmented on 56 CT images. CT images were randomly divided into training (n = 27) and validation (n = 29) cohorts. Two methods were used for automatic delineation of masticatory muscles (MMs): Deep learning auto-segmentation (DLAS) and atlas-based auto-segmentation (ABAS). The automatic algorithms were evaluated using Dice similarity coefficient (DSC), recall, precision, Hausdorff distance (HD), HD95, and mean surface distance (MSD). A consolidated score was calculated by normalizing the metrics against interobserver variability and averaging over all patients. Differences in dose (∆Dose) to MMs for DLAS and ABAS segmentations were assessed. A paired t-test was used to compare the geometric and dosimetric difference between DLAS and ABAS methods. RESULTS: DLAS outperformed ABAS in delineating all MMs (p < 0.05). The DLAS mean DSC for M, T, MP, and LP ranged from 0.83 ± 0.03 to 0.89 ± 0.02, the ABAS mean DSC ranged from 0.79 ± 0.05 to 0.85 ± 0.04. The mean value for recall, HD, HD95, MSD also improved with DLAS for auto-segmentation. Interobserver variation revealed the highest variability in DSC and MSD for both T and MP, and the highest scores were achieved for T by both automatic algorithms. With few exceptions, the mean ∆D98%, ∆D95%, ∆D50%, and ∆D2% for all structures were below 10% for DLAS and ABAS and had no detectable statistical difference (P > 0.05). DLAS based contours had dose endpoints more closely matched with that of the manually segmented when compared with ABAS. CONCLUSIONS: DLAS auto-segmentation of masticatory muscles for the head and neck radiotherapy had improved segmentation accuracy compared with ABAS with no qualitative difference in dosimetric endpoints compared to manually segmented contours.

Paramyotonia Congenita with Persistent Distal and Facial Muscle Weakness: A Case Report with Literature Review.

BACKGROUND: Paramyotonia congenita (PC; OMIM 168300) is a non-dystrophic myotonia caused by mutations in the SCN4A gene. Transient muscle stiffness, usually induced by exposure to cold and aggravated by exercise, is the predominant clinical symptom, and interictal persistent weakness is uncommon. CASE REPORT: We report a family with a history of PC accompanied by persistent hand muscle weakness with masticatory muscle involvement. Persistent weakness was exacerbated with age, and MR analysis showed marked atrophy of temporal, masseter, and finger flexor muscles with fatty replacement. The PC causative mutation T1313M in the SCN4A gene was prevalent in the family. Administration of acetazolamide chloride improved clinical symptoms and the results of cold and short exercise tests. Phenotypic variation within the family was remarkable, as the two younger affected patients did not present with persistent weakness or muscle atrophy. CONCLUSIONS: PC associated with the T1313M mutation is a possible cause of persistent distal hand weakness.

Could mastication modify the shape of the orbit? A scannographic study in humans.

PURPOSE: Since prehistory, changes of the facial skeleton have been related to the modification of diet. More recent studies have shown changes in the morphology of the mandible and maxilla due to variations of strain during mastication. The temporal muscle (TM) is a strong masticatory muscle, with its insertions extending through the temporal fossa. Our objective is to observe the relations between the TM and the lateral orbital wall (LOW) which could indicate an influence of mastication on the shape of the LOW. METHODS: We conducted a retrospective study using 100 CT scans. The length of the lateral orbital wall (LLOW), the angle between LOW and the medial orbital wall (MOW), the cross-sectional areas of LOW and of the TMs were measured on both sides of each CT scan. The correlation between TMs and other three parameters was studied by Pearson correlations. RESULTS: A correlation was found between TMs and LOWs, a lower with LLOW, and a very weak and negative correlation between LOW/MOW angle. CONCLUSIONS: Anatomical knowledge about TM and investigation of masticatory strains lead us to think that mastication have minimal effect on the morphology of the LOW, only on the frontal process of zygomatic. This may explain, in part, why the LOW is the strongest wall of the orbit.

Effects of wear time differences of removable functional appliances in class II patients: prospective MRI study of TMJ and masticatory muscle changes.

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.

Orofacial muscles may be affected in early stages of Becker muscular dystrophy: A preliminary study.

BACKGROUND: Dysphagia is reported in patients with Duchenne or Becker muscular dystrophy. Our clinical experience suggests that, compared with Duchenne patients, impaired mastication and swallowing occur early in Becker patients relative to their skeletal muscle involvement. The aim of this study was to assess dysphagia in Duchenne and Becker patients in relation to ambulatory capacity. METHODS: In patients in the early ambulatory stage, clinical symptoms, quantitative muscle ultrasound of the orofacial muscles, and maximum bite force were assessed. The 6-Minute Walk Test (6MWT) was used to measure ambulatory capacity. RESULTS: Eleven Duchenne and 11 Becker patients were included. Although Becker patients had a greater 6MWT distance than Duchenne patients, the occurrence of mastication and swallowing difficulties was similar. The temporalis muscle was significantly thicker in Becker patients. CONCLUSIONS: Clinicians should be aware of dysphagia in both groups, even when ambulation is still well preserved.

DiceCT Analysis of the Extreme Gouging Adaptations Within the Masticatory Apparatus of the Aye-Aye (Daubentonia madagascariensis).

Relative to all other primates, the aye-aye (Daubentonia madagascariensis) exists at the extremes of both morphology and behavior. Its specialized anatomy-which includes hypselodont incisors and highly derived manual digits-reflects a dietary niche, unique among primates, which combines tap-foraging with gouging to locate and extract wood-boring larvae. Here, we explore the impact of this extreme dietary ecology upon the masticatory musculature of this taxon with reference to a second, similarly sized but highly generalist lemuriform-the mongoose lemur (Eulemur mongoz). Using non-destructive, high-resolution diffusible iodine-based contrast-enhanced computed tomography techniques, we reconstruct the three-dimensional volumes of eight masticatory muscles, and, for the first time in strepsirrhines, isolate and visualize their constituent muscle fascicles in situ and in three dimensions. Using these data, we report muscle volumes, forces, and fascicle lengths from each muscle portion, as well as their orientation relative to two standardized anatomical planes. Our findings demonstrate the overbuilt nature of the aye-aye's masticatory apparatus, in which each muscle possesses an absolutely and relatively larger muscle volume and PCSA than its counterpart in the mongoose lemur. Likewise, for several adductor muscles, aye-ayes also possess relatively greater fascicle lengths. Finally, we note several unusual features within the lateral pterygoid of the aye-aye-the muscle most responsible for jaw protrusion-that relate to force maximization and reorientation. As this jaw motion is critical to gouging, we interpret these differences to reflect highly specific specializations that facilitate the aye-aye's extreme subsistence strategy. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:282-294, 2020. © 2019 American Association for Anatomy.