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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.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.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 /VBoth 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 (CThese 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.

OBJECTIVES To test the hypotheses that (a) the force thresholds at onset of medial pterygoid muscle single motor unit (SMU) activity do not decrease with an increase in the rate of force generation in standardised vertical or horizontal jaw-force tasks, and (b) there is evidence for functional heterogeneity within the medial pterygoid muscle. METHODS In 14 healthy participants, electromyographic recordings of the right medial pterygoid muscle were performed with intramuscular fine-wire electrodes during four isometric force tasks: vertical, horizontal contralateral, horizontal protrusion and horizontal ipsilateral, performed at two rates of force development (slow ramp, fast ramp). Computer tomography scans confirmed electrode location within the muscle, which was divided into medial and lateral parts. Force thresholds of onset of discriminated SMUs were compared between rates in each task; significance accepted at p

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.

Background The infratemporal fossa (ITF) represents an area densely packed with neurovascular structures within irregular boundaries. The goal of this study was to classify the ITF into zones corresponding to its anatomical spaces and the order in which they are encountered during an endonasal approach (anteroposterior axis). Methods Six cadaveric specimens (12 sides) with injected colored latex were dissected. Following an endoscopic medial maxillectomy and Denker's approach, a progressive exploration of the masticator space and upper parapharyngeal space was completed. A classification of the ITF based on well-defined spaces was ascertained. Results The ITF was divided into five zones: Zone 1 (retromaxillary space)-space lying between the posterolateral wall of the maxillary sinus and the temporalis and pterygoid muscles. Zone 2 (superior interpterygoid space)-area including the superior head of the lateral pterygoid muscle, V3 , and foramen ovale. Zone 3 (inferior interpterygoid space)-includes the inferior head of lateral pterygoid muscle, medial pterygoid, and temporalis muscles, and the space enclosed by these muscles. Zone 4 (temporo-masseteric space)-space lateral to the temporalis muscle (comprising fat mostly). Zone 5 (tubopharyngeal space)-includes the Eustachian tube, tensor, and levator veli palatini muscles, and structures in upper parapharyngeal space. Conclusion The ITF can be visualized as five zones based on spaces enclosed by the masticator muscles and upper parapharyngeal structures. This novel classification system is useful to guide endoscopic approaches to the ITF, while decreasing the potential for injury of neurovascular structures and pterygoid muscles.

Hizli, Omer/0000-0001-6822-2679 WOS: 000491220700012 PubMed: 30919461 Objectives To investigate the olfactory fossa depths and lateral lamella lengths of patients with different types of developmental disorders of paranasal sinuses in comparison with normal controls. Study Design Retrospective, archival, radio-anatomical study. Methods We included 58 patients with maxillary sinus hypoplasia, 50 patients with frontal sinus hypoplasia/aplasia, 50 patients with sphenoid sinus hypoplasia/aplasia, and 40 normal controls. Reviewing paranasal computerized tomography scans, we noted the olfactory fossa depths and lateral lamella lengths of all the groups and compared between the hypoplasia groups and the control group. Results Compared with the normal controls, the maxillary hypoplasia group (P < 0.001), frontal hypoplasia/aplasia group (P = 0.004), and sphenoid hypoplasia/aplasia group had significantly deeper olfactory fossa (P = 0.003). The mean lateral lamella lengths in the type 1, type 2, and type 3 hypoplastic maxillary sinus groups were significantly greater compared with that in the control group (P < 0.001). Additionally, the mean lateral lamella lengths in the hypoplastic frontal sinus, aplastic frontal sinus, and hypoplastic sphenoid sinus groups were significantly greater compared with that in the control group (P < 0.001). Conclusion The patients with pneumatization defects of the maxillary, frontal, and sphenoid sinuses had deeper olfactory fossa and longer lateral lamella related to increased risk of skull base injury during endoscopic sinus surgery. Level of Evidence 3 Laryngoscope, 129:2458-2463, 2019

The jaw adductor muscles of extinct mammals are often reconstructed to elucidate paleoecological relationships and to make broad comparisons among taxa. Muscle lever arms, bite load arms, muscle dimensions, and gape are often also reconstructed to better understand feeding. Several different approaches to these and related goals are discussed here. A protocol for reconstructing muscle dimensions and bite force using biomechanically informative skull measurements and osteological proxies of muscle dimensions is described and applied to a case study of subfossil Malagasy lemurs. The results of this case study show that most subfossil lemurs emphasized the masseter and medial pterygoid muscles over the temporalis. This supports the inference that these extinct lemurs depended heavily on tough food like leaves. Exceptions include signals of hard-object feeding in Archaeolemur that vary between A. majori and A. edwardsi. Reconstructions of soft-tissue and function are important for understanding past ecological relationships. Even those based on well-supported osteological proxies from extant analogues have limitations for making precise inferences. Anat Rec, 301:343-362, 2018. © 2018 Wiley Periodicals, Inc.

Published descriptions about the sites of origin of the human medial pterygoid muscle vary and there are few reports on the distribution and density of muscle spindles in this muscle. We aimed to: (1) determine the extent of anatomical variability in the origins and insertions of the superficial and deep heads of the human medial pterygoid muscle and (2) determine the extent of variation in the distribution of spindles in the two heads of the muscle. Thirty-nine human cadaver hemi-heads were dissected and the attachments of the medial pterygoid muscle examined. The whole muscle was removed, weighed, cut into segments and embedded in wax for light microscopy. Sections were stained with Weigert-Van Gieson stain and scanned into digital images. Spindles were manually counted. In seven specimens, the deep head of the muscle arose from the medial surface of the lateral pterygoid plate and the pterygoid fossa. In 28 specimens, the origin extended onto the lateral surface of the medial pterygoid plate. There were abundant muscle spindles in the middle of the muscle, slightly fewer 1 cm toward the insertion, significantly fewer 1 cm toward the origin, and few or no spindles near the origins of the superficial and deep heads or near their insertion. In conclusion, firstly, this study shows that in 72% of the specimens examined, the origin of the medial pterygoid is wider than conventionally described in anatomical textbooks. Secondly, the segmental distribution of muscle spindles is described for the first time. Clin. Anat. 30:1064-1071, 2017. © 2017 Wiley Periodicals, Inc.

There is limited information of the normal function of the human medial pterygoid muscle (MPt). The aims were to determine whether (i) the MPt is active throughout horizontal jaw movements with the teeth apart and (ii) whether single motor units (SMUs) are active during horizontal and opening-closing jaw movements. Intramuscular electrodes were placed in the right MPt of 18 participants who performed five teeth-apart tasks: (i) postural position, (ii) ipsilateral (i.e. right) jaw movement, (iii) contralateral movement, (iv) protrusive movement and (v) opening-closing movement. Movement tasks were guided by a target and were divided into BEFORE, OUT, HOLDING, RETURN and AFTER phases according to the movement trajectories recorded by a jaw tracking system. Increased EMG activity was consistently found in the OUT, HOLDING and RETURN phases of the contralateral and protrusive movement tasks. An increased RETURN phase activity in the ipsilateral task indicates an important role for the MPt in the contralateral force vector. Of the 14 SMUs active in the opening-closing task, 64% were also active in at least one horizontal task. There were tonically active SMUs at the postural jaw position in 44% of participants. These new data point to an important role for the MPt in the fine control of low forces as required for stabilisation of vertical mandibular position not only to maintain postural position, but also throughout horizontal jaw movements with the teeth apart. These findings provide baseline information for future investigations of the possible role of this muscle in oro-facial pain conditions.

Masticatory muscle activity during teeth clenching is affected by occlusal pattern. However, few studies have performed simultaneous evaluation of all masticatory activities during teeth clenching under various occlusal conditions. The aim of this study was to use muscle functional magnetic resonance imaging (mfMRI) to evaluate the effects of changes in occlusal point on masticatory activity during single tooth clenching. Changes in mean proton transverse relaxation time (∆T2) as an index of activity in all masticatory muscles during left unilateral clenching at the first molar or first premolar for 1 min were examined in nine healthy volunteers. Bite force was maintained at 40% of the maximum voluntary clenching force. The ∆T2 values of the masseter and lateral pterygoid muscles were analysed separately for superficial and deep layers, and for superior and inferior heads. The ∆T2 values for the ipsilateral deep masseter were significantly lower, and for the superior head of the ipsilateral lateral pterygoid muscles were significantly higher, after left first premolar clenching compared to left first molar clenching. These results quantitatively demonstrate a significant increase in activity of the superior head of the ipsilateral lateral pterygoid muscle and a significant decrease in activity of the ipsilateral deep masseter muscle with forward displacement of the occlusal contact point during unilateral tooth clenching.

Objectives/Hypothesis Surgery of the paranasopharyngeal space is very hazardous due to the position of the internal carotid artery, which is surrounded by soft tissue with few anatomical landmarks. Study Design Fresh cadaveric study. Methods In this study, we used the maxillary swing procedure to have a broad view of the internal carotid artery using an anterior approach. We sought to establish surgical landmarks, make measurements, and compare them to other imagery and cadaveric studies in the literature. Results We performed the maxillary swing procedure in 10 subjects (six female and four male, mean deceased age 81 years). The internal carotid artery was found to be in the same sagittal plane as the lateral pterygoid plate, the foramen ovale, and the eustachian tube isthmus. It was always located behind the stylopharyngeal fascia and immediately lateral to the longus capitis muscle. The artery was measured on average 10.7 mm from the pharyngeal recess, 7.3 mm from the eustachian tube isthmus, and 22.8 mm from the torus tubarius. Conclusions The eustachian tube isthmus, the longus capitis muscle, and the stylopharyngeal fascia are the main surgical landmarks of the internal carotid artery. The artery can also be found in an oblique sagittal plane including the eustachian tube isthmus, the foramen ovale, and the lateral pterygoid plate. The pharyngeal recess remains a very dangerous area, only millimeters away from the carotid artery. Level of Evidence NA Laryngoscope, 2016

Background Conventional approaches for removing parapharyngeal space tumors require a cervical skin incision and resection of soft tissues between the skin and parapharyngeal space. The surgical visual field for this conventional approach is limited. Methods To decrease invasiveness during removal of benign parapharyngeal space tumors and to enhance the visual field, we devised a new approach called the modified endoscopic transnasal-transmaxillary-transpterygoid approach (MENMAP). The "surgical corridor" to the parapharyngeal space consists of the maxillary sinus, submucous tunnel under the lateral nasal wall, and the space created by removing the pterygoid process. Results We successfully performed en bloc removal of a parapharyngeal space tumor using the MENMAP approach. The only surgical complication was hypoesthesia of the right hard palate and maxillary gingiva, which gradually improved. Conclusion The MENMAP approach is a viable alternative for removing parapharyngeal space tumors, as it is safe, feasible, and less invasive. © 2016 Wiley Periodicals, Inc. Head Neck 38: 933-938, 2016.

The mandible has a property to flex inwards around the mandibular symphysis with change in shape and decrease in mandibular arch width during opening and protrusion of the mandible. The mandibular deformation may range from a few micrometres to more than 1 mm. The movement occurs because of the contraction of lateral pterygoid muscles that pulls mandibular condyles medially and causes a sagittal movement of the posterior segments. This movement of mandible can have a profound influence on prognosis and treatment outcome for various restorative, endodontics, fixed, removable and implant-related prosthesis. The review unfolds the causes, importance and clinical implications of median mandibular flexure in oral rehabilitation. This review also highlights the appropriate preventive measures and techniques that should be adopted by clinicians to minimise the effect of flexural movement of the jaw during oral rehabilitation. This would not only help clinicians to achieve a good prosthesis with accurate fit and longevity but also maintain the health of the surrounding periodontal or periimplant gingival tissues and bone.

Subjects with/without temporomandibular joint disorders (TMJD) were tested for differences in muscle forces.School of Dental Medicine, University at Buffalo. Ninety-one subjects were classified in four groups based on the presence/absence (±) of chronic myofascial and/or TMJ pain (P) and bilateral disc displacement (DD).Validated numerical models employed an organizational objective and subjects' anatomy to calculate masticatory muscle forces during static biting. anova and Holm's step-down procedure post hoc tests assessed group differences. Theoretical geometries, representing the range of subjects' muscle orientations, were surveyed via numerical models to identify key combinations resulting in high muscle forces. Effect size (Cohen's d) and anova/post hoc tests assessed group differences in key muscle orientations.+P-DD subjects had significantly higher muscle forces, especially for lateral pterygoid muscles, compared to the other groups (p0.01) for bite forces that were directed posteromedially or posterolaterally on mandibular molars and posteriorly and slightly medially on mandibular incisors. Key muscle orientations for peak lateral pterygoid muscle forces were identified, and group comparisons showed mean orientation in +P-DD compared to other diagnostic groups was ≥5° more upright for masseter and ≥3° more posteriorly directed for temporalis muscles (all Cohen's d≥0.8).Predicted lateral pterygoid muscle forces were significantly higher in +P-DD compared to other groups for specific biting conditions and were attributable, in part, to differences in masseter and temporalis muscle orientations.

Purpose The purpose of this study was to test the null hypothesis that there was no relationship between increased vertical overlap (vertical overlap ≥4 mm) with minimal horizontal overlap (horizontal overlap ≤2 mm) and the signs of temporomandibular disorders. Materials and Methods Thirty participants (20 women, aged 20 to 45 years) with increased vertical overlap and minimal horizontal overlap, and 30 participants (20 women, aged 20 to 45 years) with no contact between the anterior teeth (control group) were examined. Diagnoses, psychological status (depression and nonspesific physical symptoms), and chronic pain severity were judged according to the Research Diagnostic Criteria for Temporomandibular Disorders and then compared. For statistical analysis of quantitative data, along with the descriptive statistical methods (mean, standard deviation, frequency), Student's t-test was used to compare parameters that reflected a normal distribution. Comparison of qualitative data between groups was performed using Chi-square and Fisher's exact tests. The level of significance was set at p < 0.05. Results In this study, deviation upon maximum opening was found significantly more frequently in the increased vertical overlap group than in the control group (p < 0.05). Tenderness upon palpation of lateral pterygoid muscles was observed more often in the increased vertical overlap group compared with the control group (p < 0.05). Opening-closing joint sounds occurred significantly more often in the increased vertical overlap group than in the control group (p = 0.050). Conclusion Within the limitations of this study, deviation upon maximum opening, tenderness of lateral pterygoid muscles (upon palpation), and opening-closing joint sounds occurred more often in the increased vertical overlap occlusions with minimum horizontal overlap compared to the control groups. These results indicated that clinicians should pay special attention to the tempormandibuar joint status of patients with significant vertical overlap anteriorly and position of the incisors when performing dental treatments that require reestablishment of incisor relationships.

The objective of this study is to clearly and precisely describe the topography and contents of the infratemporal fossa. Ten formalin-fixed, adult cadaveric specimens were studied. Twenty infratemporal fossa were dissected and examined using micro-operative techniques with magnifications of 3-40×. Information was obtained about the inter-relationships of the contents of the infratemporal fossa. The infratemporal fossa lies at the boundary of the head and neck, and the intracranial cavity. It is surrounded by the maxillary sinus anteriorly, the mandible laterally, the pterygoid process anteromedially, and the parapharyngeal space posteromedially. It contains the maxillary artery and its branches, the pterygoid muscles, the mandibular nerve, and the pterygoid venous plexus. The course and the anatomic variation of the maxillary artery and the branches of the mandibular nerve were demonstrated. The three-dimensional (3D) relationships between the important bony landmarks and the neurovascular bundles of the infratemporal fossa were also shown. The skull base anatomy of the infratemporal fossa is complex, requiring neurosurgeons and head and neck surgeons to have a precise knowledge of 3D details of the topography and contents of the region. A detailed 3D anatomic knowledge is mandatory to manage benign or malignant lesions involving the infratemporal fossa without significant postoperative complications.

The midfacial deep fatty tissue has been divided into the buccal and parapharyngeal fat pads although the former carries several extensions in adults. Using histological sections of 15 large human fetuses, we demonstrated that the parapharyngeal fat pad corresponds to the major content of the prestyloid compartment of the parapharyngeal space or, simply, the prestyloid fat. The buccal and prestyloid fatty tissues were separated by the medial and lateral pterygoid muscles. In these tissues, superficial parts, corresponding to the lower body and the masseteric extension of the adult buccal fat pad, were well encapsulated and showed the most advanced stage of histogenesis. As the sphenoid bone was not fully developed even in the largest specimens, the temporal, infratemporal, and pterygopalatine fossae joined to provide a large space for a single, large upper extension of the buccal fat pad. In the intermediate part of the extension course, the larger specimens carried a narrower part between the maxilla and the temporalis muscle. The single, upper extension appeared to divide into several extensions, as seen in adults. The periocular fat was clearly separated from the upper extension of the buccal fat pad by the sheet-like orbitalis muscle. A communication between the prestyloid fat and the buccal fat pad likely occurred through a potential space along the lingual nerve immediately superior to the deep part of the submandibular gland. At this site, therefore, the prestyloid fat may be injured or infected when the buccal fat pad is treated surgically.

Background The infratemporal fossa anatomy, from an endoscopic standpoint, is poorly understood. Our purpose was to design an anatomic model that illustrates the anatomy of the infratemporal fossa from the endoscopic standpoint and serves as a training model for surgeons interested in pursuing this endeavor. Methods Red and blue silicone dyes were respectively injected into the great vessels of the neck. Digital data acquired from a high resolution CT scan was imported to a navigational system. An endoscopic endonasal dissection of the infratemporal fossa was completed under conditions that mimicked our operating suite. Results A detailed anatomic dissection of the infratemporal fossa was correlated to the image guidance (navigation) system. This provided a surgical map highlighting critical neurovascular structures and illustrating the potential surgical corridors. Conclusion A thorough understanding of the anatomy of infratemporal fossa from the endoscopic perspective allows the surgeon to plan an adequate corridor. © 2011 Wiley Periodicals, Inc. Head Neck, 2012

Rodents are defined by their unique masticatory apparatus and are frequently separated into three nonmonophyletic groups--sciuromorphs, hystricomorphs, and myomorphs--based on the morphology of their masticatory muscles. Despite several comprehensive dissections in previous work, inconsistencies persist as to the exact morphology of the rodent jaw-closing musculature, particularly, the masseter. Here, we review the literature and document for the first time the muscle architecture noninvasively and in 3D by using iodine-enhanced microCT. Observations and measurements were recorded with reference to images of three individuals, each belonging to one of the three muscle morphotypes (squirrel, guinea pig, and rat). Results revealed an enlarged superficial masseter muscle in the guinea pig compared with the rat and squirrel, but a reduced deep masseter (possibly indicating reduced efficiency at the incisors). The deep masseter had expanded forward to take an origin on the rostrum and was also separated into anterior and posterior parts in the rat and squirrel. The zygomaticomandibularis muscle was split into anterior and posterior parts in all the three specimens by the masseteric nerve, and in the rat and guinea pig had an additional rostral expansion through the infraorbital foramen. The temporalis muscle was found to be considerably larger in the rat, and its separation into anterior and posterior parts was only evident in the rat and squirrel. The pterygoid muscles were broadly similar in all three specimens, although the internal pterygoid was somewhat enlarged in the guinea pig implying greater lateral movement of the mandible during chewing in this species.

Body size and food properties account for much of the variation in the hard tissue morphology of the masticatory system whereas their influence on the soft tissue anatomy remains relatively understudied. Data on jaw adductor fiber architecture and experimentally determined ingested food size in a broad sample of 24 species of extant strepsirrhines allows us to evaluate several hypotheses about the influence of body size and diet on the masticatory muscles. Jaw adductor mass scales isometrically with body mass (β = 0.99, r = 0.95), skull size (β = 1.04, r = 0.97), and jaw length cubed (β = 1.02, r = 0.95). Fiber length also scales isometrically with body mass (β = 0.28, r = 0.85), skull size (β = 0.33, r = 0.84), and jaw length cubed (β = 0.29, r = 0.88). Physiological cross-sectional area (PCSA) scales with isometry or slight positive allometry with body mass (β = 0.76, r = 0.92), skull size (β = 0.78, r = 0.94), and jaw length cubed (β = 0.78, r = 0.91). Whereas PCSA is isometric to body size estimates in frugivores, it is positively allometric in folivores. Independent of body size, fiber length is correlated with maximum ingested food size, suggesting that ingestive gape is related to fiber excursion. Comparisons of temporalis, masseter, and medial pterygoid PCSA in strepsirrhines of different diets suggest that there may be functional partitioning between these muscle groups.

Objectives: Endoscopic endonasal approaches to the pterygopalatine and infratemporal fossae are technically challenging due to the complex anatomy of these areas. This project attempts to develop an anatomic and surgical model to enhance the understanding of these spaces from the endonasal endoscopic perspective. Methods: Eight pterygopalatine and infratemporal fossae were dissected in four adult human specimens in accordance with institutional protocols. All specimens were prepared with vascular injections using colored latex. Both the pterygopalatine and infratemporal fossae were accessed using a transpterygoid approach, which included a medial maxillectomy. Rod lens endoscopes (with 0°, 30°, and 45° lenses), surgical microscope, microsurgical and endoscopic instruments were used to complete the dissections. Results: Endoscopic endonasal approaches provided adequate access to the pterygopalatine and infratemporal fossae. Dissection of the internal maxillary artery and its terminal branches, and detachment of the medial and lateral pterygoid muscles were critical steps to access deeper structures of the infratemporal fossa. The lateral pterygoid plate was the most useful landmark to locate foramen ovale, and the mandibular branch of the trigeminal nerve. The Eustachian tube, medial pterygoid plate, and styloid process were the most useful landmarks to locate parapharyngeal poststyloid structures (parapharyngeal segment of the internal carotid artery, internal jugular vein, cranial nerves IX and X). Conclusions: A medial maxillectomy coupled with a transpterygoid endoscopic approach, provides adequate access to the pterygopalatine and infratemporal fossae. The complex anatomy of the infratemporal fossa requires precise identification of surgical landmarks to assure preservation of neurovascular structures. Laryngoscope, 2011

Oral Diseases (2011) 17, 407–413 Objective: Quantitative analysis of the activities of all masticatory muscles is required to elucidate the mechanism of stomatognathic dysfunction. Electromyography can be used to record the activity of masticatory muscles, but quantification of the overall activity of every masticatory muscle has not been accomplished because of methodological limitations. In this study, we used muscle functional magnetic resonance imaging for simultaneous quantification of the overall activities of the masseter, medial pterygoid and lateral pterygoid muscles during unilateral gum chewing. Methods: Seven healthy male volunteers participated in the study. We evaluated changes in the mean proton transverse relaxation time in the bilateral masseter, medial pterygoid and lateral pterygoid muscles before and after unilateral gum chewing, and to quantify the overall activity of these muscles simultaneously during unilateral gum chewing. Results: After 5 min of chewing, the activity of the ipsilateral masseter was highest among the six muscles, followed by the ipsilateral medial pterygoid, contralateral lateral pterygoid and contralateral masseter muscles. Conclusion: These results affirm the importance of the ipsilateral masseter muscle and quantitatively demonstrate the important contribution of the ipsilateral medial pterygoid and contralateral lateral pterygoid muscles during unilateral mastication.

Do closely related marsupial herbivores (Diprotodontia) conserve a common masticatory motor pattern or are motor patterns linked to the structure and function of the masticatory apparatus? We recorded the sequence and duration of activity of the individual jaw closing muscles during rhythmic chewing in koalas and then compared their motor pattern with that of their closest extant relatives, wombats, and their more distant marsupial relatives, macropodoids. These three lineages prove to have fundamentally different motor patterns and jaw movements during mastication. Each motor pattern represents independent modifications of an earlier motor pattern that was probably present in an ancestral diprotodontian. We show that koalas evolved a motor program that is in many aspects similar to that of placental herbivores with a fused mandibular symphysis (artiodactyls, perissodactyls, and higher primates) and almost identical to one artiodactyl, viz. alpacas. Anatomically, koalas are convergent on placental herbivores because they lost the inflected mandibular angle and large external part of the medial pterygoid muscle characteristic of other marsupials. We support the view that many different motor programs evolved for the control of transverse jaw movements, but identical motor programs for the control of transverse jaw movements can evolve independently in distantly related taxa. Refereed/Peer-reviewed

We examined the shapes and sizes of dermal bones of the palate of selected Palaeozoic tetrapods in order to identify the ancestral states of palatal bone morphologies in the earliest tetrapods, to learn how the composition of the palate varies within and among early tetrapod radiations, and to recognize evolutionary correlations among the size and shapes of skeletal elements in this important group of animals. We find that whereas the palatal bones themselves and their arrangements are usually conserved, considerable correlated evolutionary change occurs in the shapes and sizes of the bones. Some of the changes in the bones are allometrically linked to overall palate size, which varies more than 100-fold among the taxa in our sample. Often, these allometries were only hinted at in traditional independent contrasts-based regressions of log transformed data, particularly because many allometries are subtle, their slopes may vary among subclades, and the scatter around some trendlines is high. Rather, the allometries showed up in analyses of size-standardized palatal bone dimensions investigated using independent contrasts, bivariate phylomorphospace plots, and mirrored character reconstructions on the phylogenetic tree. We find negative allometry for parasphenoid lengths and widths essentially across the entire tree of Palaeozoic tetrapods, but with different trajectories characterizing the two largest clades, the temnospondyls and the lepospondyls. The lengths of several other elements may show positive allometries, either across the entire tree or in just a subclade. One possible positive allometry exists for the ectopterygoid, which appears to shorten allometrically in temnospondyls that evolve small body and palate size, and, as in Doleserpeton can be lost altogether. Both shortening and loss could be by the same developmental change, paedomorphosis, a form of heterochrony. Paedomorphosis might also account for evolution of relatively large parasphenoids in both lepospondyls and diminutive temnospondyls, but does not seem to explain evolution of ectopterygoid loss in lepospondyls. A regularity observed across nearly all taxa in our study set is an inverse correlation between the lengths of the vomer and pterygoid, bones that lie adjacent to one another along the long palatal axis. Further work is needed to learn whether such correlated evolution might be due to adaptation and/or to developmental bias, and particularly to learn how correlations and allometries themselves evolve.

The hypothesis was that the superior head of human lateral pterygoid muscle (SHLP) plays a similar role in jaw movement as the inferior head of human lateral pterygoid muscle (IHLP). The aims were to determine the functional properties of SHLP single motor units (SMUs) and root mean square activity (RMS) of the SHLP during contralateral and protrusive jaw movement tasks and to compare these features with those identified previously for the IHLP. In 22 human subjects, SMUs were recorded intramuscularly from computer tomography-verified sites within the SHLP during standardized contralateral and protrusive jaw movement tasks recorded by a jaw-tracking device. Of the 50 SMUs discriminated, 39 were active during contralateral and 29 during protrusive jaw movements. The firing rates and RMS of the SHLP motor units increased with an increase in jaw displacement. The RMS activity across the entire trial during contralateral jaw movement was significantly greater than that during protrusion. Similarly to conclusions previously identified for the IHLP, the data are consistent with an important role for the SHLP in the control of contralateral and protrusive jaw movements. The similarities in SHLP and IHLP functional properties support the proposal that both heads should be regarded as a system of fibers acting as one muscle.

The report describes oromandibular dystonia (OMD) in four women with involuntary activity of the lateral pterygoid muscles (LP), causing incapacitating protrusive and lateral jaw movements and displacements, and treatment with botulinum toxin type A (BTX). For initial survey and treatment control, OMD was analyzed with several, independent, and standardized methods. OMD severity and functional difficulties were evaluated subjectively and scored from videotapes. Jaw movements were assessed graphically with a magnetic tracking system, and electromyographical activity (EMG) of LP was recorded with needle electrodes using an intraoral approach, whereas activity of masseter muscles was recorded with surface electrodes. EMG-guided BTX injections (25-40 units Botox per muscle) into the muscles were performed with cannula electrodes. Compared with reference values for LP, OMD was associated with a markedly increased level of spontaneous activity, but almost normal level of maximum voluntary activity. The central pattern generator for mastication seemed to override the dystonic activity, as all patients were able to chew despite some distortion. BTX reduced both the spontaneous and the maximum activity for 3-9 months. Concomitantly, a marked reduction of the OMD severity, mandibular movements and functional disturbances were also present with the best effect in localized OMD with late onset.

In an earlier dry-skull study (Dias et al. [2001] Int J Osteoarchaeol 11:241–248), a hitherto undescribed groove was observed in the infratemporal region of the greater wing of the sphenoid bone in the cranial base, passing laterally from the foramen ovale onto the squamous temporal bone. We found a very high incidence of this groove, 81% on one side at least, in modern South-Asian Indian adult crania, but much less so, 50%, in a Polynesian sample of both New Zealand Maori and Moriori adult crania. This article reports our finding of the groove, at least on one side, in 85% of a modern Portuguese skeletal population, and our dissection study on twenty European cadavers confirms that the groove, present in all, is formed by the posterior deep temporal nerve. Clin. Anat. 20:126–130, 2007. © 2006 Wiley-Liss, Inc.

Objective Pathology within a lateral recess of a widely pneumatized sphenoid sinus is difficult to access with the use of traditional open and current endoscopic surgical approaches. A new surgical procedure, the endoscopic transpterygoid approach, directly accesses this region. A clinical experience over several year with this approach is reported as well as a refined and updated description of the technique. Setting Tertiary care center. Methods Retrospective review of medical records of patients treated with the endoscopic transpterygoid approach to the lateral sphenoid recess. Results An endoscopic transpterygoid approach was performed in 9 patients, 6 to resect a middle fossa meningoencephalocele and repair the CSF leak and associated skull base defect, 2 for possible invasive fungal sinusitis, and 1 to marsupialize a symptomatic epidermoid cyst. Patients tolerated the approach well and no significant complications occurred. Conclusions and significance In selected cases, the endoscopic transpterygoid approach enables the otolaryngologist to meet modern demands to treat conditions in the lateral sphenoid using minimally invasive techniques that are well-tolerated by patients. The surgical approach and the initial experience described herein is presented in the hopes that it can aid fellow otolaryngologists to help patients with challenging conditions in this region of the body.

Background. Metastatic adenocarcinoma of the colon is a frequently encountered medical situation. Metastasis to the mandible from adenocarcinoma of the colon is very unusual and rarely reported. We report the case of a 73-year-old man with metastatic adenocarcinoma to the mandible. Methods. The patient was referred for evaluation of a mass of 2 months' duration in the right parotid gland. He gave a history of watery bowel movements of unknown duration. Physical examination revealed a 7- × 6-cm hard mass, which seemed to be fixed to the right mandible. A CT scan revealed a destructive process involving the ramus and condyle of the right mandible that invaded the pterygopalatine fossa, pterygoid muscles, and middle cranial fossa. CT scans of the abdomen and pelvis revealed a 5-cm mass in the sigmoid colon with metastases to the liver. Results. A biopsy of the mass in the mandible was performed, and metastatic adenocarcinoma of colonic origin was diagnosed. Colonoscopy and biopsy of the colonic mass substantiated that the sigmoid colon was the primary site of the cancer. Because the patient had disseminated disease, he declined treatment, and he died shortly thereafter. Conclusions. Although rare, metastatic adenocarcinoma from the colon to the mandible and parotid area should be included in the differential diagnosis of masses in this area. After analysis of our case and a review of the literature, we conclude that metastasis from adenocarcinoma of the colon is quite rare and represents incurable disseminated disease. © 2005 Wiley Periodicals, Inc. Head Neck27: XXX–XXX, 2005

The clinical notion that some disturbance to the activity of the lateral pterygoid muscle plays a role in the aetiology of temporomandibular disorders (TMD) is still widely accepted and influences management strategies. However, there is no rigorous scientific evidence to support this clinical notion and the role of the lateral pterygoid muscle in normal function is still controversial. The classically defined functions of each head of the muscle are that the superior head is active on closing, retrusion, and ipsilateral jaw movements, while the inferior head is active on opening, protrusion and contralateral jaw movements. However, recent data indicate that these concepts are too simplistic. For example, recent evidence suggests that parts of the superior head may also be active on opening, protrusion and contralateral jaw movements, and that the superior head may consist of three mediolaterally arranged functional zones. Given these complexities, the proposal that clicking and/or locking conditions arise in the temporomandibular joint through some form of lack of co-ordination between the two heads of the muscle needs re-evaluation. Despite earlier reports to the contrary, both heads of the lateral pterygoid muscle appear to be electrically silent at the postural or resting jaw position, and therefore appear to play no role in the anteroposterior positioning of the jaw at the postural position. An important role has also been demonstrated electromyographically for progressive changes in activity in the inferior head as the direction of horizontal jaw force shifts from one side to the other. This suggests an important role for the lateral pterygoid muscle in the generation of side-to-side and protrusive jaw forces. The lateral pterygoid muscle is likely therefore to play an important role in parafunctional excursive jaw movements and also possibly a role in influencing jaw position in patients where the maxillomandibular relationship records change from session to session. The above data provide new insights into the normal function of the lateral pterygoid muscle. The proposal that the lateral pterygoid muscle plays some role in the aetiology of TMD needs now to be rigorously tested.

Masticatory muscle contraction causes both jaw movement and tissue deformation during function. Natural chewing data from 25 adult miniature pigs were studied by means of time series analysis. The data set included simultaneous recordings of electromyography (EMG) from bilateral masseter (MA), zygomaticomandibularis (ZM) and lateral pterygoid muscles, bone surface strains from the left squamosal bone (SQ), condylar neck (CD) and mandibular corpus (MD), and linear deformation of the capsule of the jaw joint measured bilaterally using differential variable reluctance transducers. Pairwise comparisons were examined by calculating the cross-correlation functions. Jaw-adductor muscle activity of MA and ZM was found to be highly cross-correlated with CD and SQ strains and weakly with MD strain. No muscle's activity was strongly linked to capsular deformation of the jaw joint, nor were bone strains and capsular deformation tightly linked. Homologous muscle pairs showed the greatest synchronization of signals, but the signals themselves were not significantly more correlated than those of non-homologous muscle pairs. These results suggested that bone strains and capsular deformation are driven by different mechanical regimes. Muscle contraction and ensuing reaction forces are probably responsible for bone strains, whereas capsular deformation is more likely a product of movement.

Displacement of root fragments into adjacent anatomical areas is an uncommon complication of the removal of teeth. This paper describes the management of a mandibular third molar root fragment that was forced into the antero-inferior aspect of the pterygomandibular space. The importance of tomographical radiographs in the visualization of the displaced root is also discussed.

– This study investigated the characteristic of bifid condyle secondary to temporomandibular joint (TMJ) trauma, aiming to analyse the pathogenesis of post-traumatic bifid condyle. Four cases identified as having bifid condyle secondary to TMJ trauma were involved in this study. The relative information extracted from the case records included patients’ complaint, history of injury and radiographic appearance, which were used to analyse the characteristic and pathogenesis of post-traumatic bifid condyle. The results indicated that there was a correlation between condylar trauma degree and bifid condylar head appearance after trauma. For severe condylar fracture, it might result in Y-shaped condyle associated with TMJ ankylosis; and condylar groove could be associated with the slight trauma in condyle articulating surface. In conclusion, as a specific entity, post-traumatic bifid condyle may develop in cases with insufficient remodelling capacity after condyle trauma, and it seems that the severity degree of trauma, the site of trauma and its relation to the insertion of the lateral pterygoid muscles are factors associated with the appearance and orientation of bifid condyle.

The aim of this study is to compare phosphocreatine (PCr) concentrations of human masseter and medial pterygoid muscles by a recently developed localized magnetic resonance spectroscopy (MRS) method, chemical shift imaging (CSI). The characteristic spectra of phosphorous metabolites including PCr and beta-ATP from the superficial part of the masseter (SM) and the deep part of the masseter (DM) and the medial pterygoid muscles (MPt) from 11 volunteers, 20-27-year-old were obtained. The study clearly demonstrated higher PCr/beta-ATP in the SM and MPt than in the DM both in mean values (P < 0.01) and in individual subjects. The results indicate that SM and MPt are power producers. There were no significant differences in the mean values of the PCr/beta-ATP ratios in SM and MPt, however, the PCr/beta-ATP ratios varied individually and the subjects could be divided into three distinct groups: values of MPt higher than SM (group A, 4 subjects); values of MPt almost equal to SM (group B, 3 subjects); and values of MPt lower than SM (group C, 4 subjects). There appears to be a close relationship between the PCr content as determined in the groups here and occlusal guidance.

Oromandibular dystonia is a focal dystonia that manifests as involuntary masticatory and/or tongue muscle contractions. Jaw opening, jaw deviation, and jaw protrusion types of oromamdibular dystonia are caused by involuntary contraction of the lateral pterygoid muscles. The medial pterygoid can be very hyperactive in jaw closing dystonia as a result of the so‐called “whack‐a‐mole phenomenon,” after repeated botulinum toxin injections into the masseter and temporalis muscles. The more accurately the botulinum toxin is injected into the muscles, the more likely the improvement in the patient's symptoms, and the lower the risk of complications, such as hematoma or arterial bleeding. Both pterygoid muscles can be accessed by intra‐ and extraoral routes. Safe and correct injection of botulinum toxin into both pterygoid muscles is described in this video. With understanding of the anatomy of the muscles, indications for injection, and technique of needle placement, injection of botulinum toxin into the lateral and medial pterygoid muscles is safe and effective for oromandibular dystonia.

During examination of the positional relationships between the lateral pterygoid and the temporalis muscles and the innervating nerves, an aberrant muscle was observed in three of 66 head halves. The aberrant muscle originated from the medial surface of the anteromedial muscle bundle of the temporalis (Shimokawa et al. 1998, Surg. Radiol. Anat. 20:329–334) and inserted into the inferolateral surface of the lower head of the lateral pterygoid. Due to its location, origin and insertion this aberrant muscle slip is considered to correspond to the pterygoideus proprius described by Henle (1858, Handbuch der Anatomie des Menschen). Based on the innervation findings, the present aberrant muscle might be considered as a remnant muscle bundle between the anteromedial muscle bundle of the temporalis and the lateral pterygoid during differentiation of the lateral masticatory muscle anlage. Clin. Anat. 14:288–291, 2001. © 2001 Wiley-Liss, Inc.

For an accurate assessment of jaw movement, it is crucial to understand the comprehensive formation of the masticatory muscles with special reference to the relationship to the disc of the temporomandibular joint. Detailed dissection was performed on 26 head halves of 14 Japanese cadavers in order to obtain precise anatomical information of the positional relationships between the masticatory muscles and the branches of the mandibular nerve. After complete removal of the bony elements, the midmedial muscle bundle in all specimens and the discotemporal muscle bundle in 6 specimens, derivatives of the temporalis, which insert into the disc were observed. On the anterior area of the articular capsule and the disc of the temporomandibular joint, the upper head of the lateral pterygoid, the midmedial muscle bundle of temporalis and the discotemporal bundle of temporalis were attached mediolaterally, and in 3 specimens the posterosuperior margin of the zygomaticomandibularis was attached to the anterolateral area of the disc. It is suggested that these muscles and muscle bundles contribute to various mandibular movements. Although various patterns of the positional relationships between the muscles and muscle bundles and the their innervating nerves are observed in the present study, relative positional relationships of the muscles and muscle bundles and of nerves of the mandibular nerve are consistent. A possible scheme of the developmental formation of the masticatory muscles based on the findings of the positional relationships between the muscles and the nerves is presented.

A 46-year-old man who had been suffering from palmoplantar pustulosis (PPP) for 3 years had anterior chest pain and left temporal pain from six months after the onset of his disease. A bone scan revealed abnormal uptake at the sternoclavicular joint and left temporal region. The head CT and MRI gave the diagnosis of temporal osteomyelitis with meningitis and myositis. His headache continued even after tonsillectomy and was effectively treated with cyclosporine A (3 mg/kg/day). Oral cyclosporine A was beneficial for the osteomyelitis and skin lesions. Sterile lytic bone lesions occurring most often at the sternocostoclavicular joint have been associated with PPP. However, there have been no reports of a PPP patient with temporal osteomyelytic involvement.

This review shows that human jaw muscles not only have unique fibre type and myosin heavy chain (MyHC) compositions but also undergo muscle and region-specific changes in fibre composition during ageing. Alterations in the masseter and the lateral pterygoid muscles in the elderly are opposite to those reported for limb and trunk muscles, whereas changes in the anterior and posterior bellies of the digastric muscle resemble those of limb and trunk muscles. We conclude that age-related alterations in fibre type composition and MyHC expression are muscle and region specific, probably reflecting muscular differences in genetic programs and epigenetic influences.

The actions of masticatory muscles in relation to transverse grinding, associated with forward masticatory movement of the mandible, were investigated by using a mechanical model in the two murid rodents, the Japanese field mouse (Apodemus speciosus: subfamily Murinae) and the gray red-backed vole (Clethrionomys rufocanus: subfamily Arvicolinae). Furthermore, statics of the masticatory system on a sagittal plane while chewing is taking place were also analyzed in these rodents. The inward grinding movements of hemimandibles are generated by the posterior temporalis and internal and external pterygoids in both species. In addition to these muscles, the anterior temporalis also moves the hemimandibles lingually in Apodemus speciosus. The area of origin of the external pterygoid seems more advantageous for transverse grinding in A. speciosus than in Clethrionomys rufocanus. On the basis of the static analysis, the anterodorsal area of origin of the external pterygoid to the upper second and third molars in Clethrionomys rufocanus appears to be an adaptive character to prevent the jaw joints from dislocation during occlusion at a posterior point on the elongated row of cheek teeth.

We carried out a computerised tomographic (CT) examination to elucidate the modifications in the head related to orbital enlargement in the Baikal seal. Transverse CT images showed that (1) the external frontal contours and the frontal sinuses are compressed medially and ventrally by the orbital enlargement; (2) the caudal part of the nasal cavity and nasopharynx are compacted ventrally; and (3) the cranial cavity is displaced caudally. The neurocranium is obviously separated from the facial part in the transverse plane at the caudal region of the orbit. The disposition of the mandible, zygomatic arch, temporal bone, and the masseter, temporal, digastric and pterygoid muscles is changed by the enlarged orbit in the 3-dimensional reorganisation of the head in this species. It is suggested that adaptation for the Lake Baikal environment primarily resulted in orbital enlargement, and that the altered orbital design may subsequently have influenced the form and function of the masticatory and respiratory system.

Masticatory and tongue muscle activity was examined polysomnographically in 14 patients with sleep apnea syndrome and six snorers. The all-night polysomnographic recordings included electromyograms (EMG) of the genioglossal, the masseter and the inferior head of the lateral pterygoid muscles, nasal airflow and thoracoabdominal respiratory effort. The apneas were defined and classified into three types (obstructive, central and mixed). EMG amplitudes of each muscle were measured before, during and after the obstructive and central apneas. In the apnea patients the three muscles showed significantly lower EMG amplitudes during the obstructive apnea than before the apnea, and then significantly higher amplitudes after the apnea. These findings indicate that the hypotonia of the muscles during sleep can result in obstructive apnea. There was no significant difference in the pattern of muscle activity during obstructive apnea between the apnea patients and the snorers. On the other hand, a decrease in the mean EMG amplitude during the central apnea was not observed. It is suggested that central apnea occurs independently of masticatory and tongue muscle activity.

Computed tomography (CT), due to its excellent resolution capacity, is a suitable method to examine the soft and bony structures of the masticatory system. The aim of this study was to compare densities and sizes of the masseter and medial and lateral pterygoid muscles obtained by CT between the symptomatic and asymptomatic side in patients with internal derangement of the temporomandibular joint (TMJ). The aim was also to correlate these variables to sex and age, duration of the symptoms, diagnosis and dentition. The material consisted of 33 patients (26 women, 7 men, mean age 37 years, range 14-74 years) whose TMJs were examined by CT and whose coronal CT scans were available. Diagnosis in the symptomatic TMJ was confirmed in operation. No statistically significant difference was seen in mean densities and sizes of the masticatory muscles between the symptomatic and asymptomatic side. The duration of the symptoms, however, correlated positively to the density of the lateral pterygoid muscles in patients with complete dentition. The age of the patients in this group correlated negatively to the size of the masseter muscles. It can be concluded that patients with internal derangements of TMJ with a long duration of symptoms have structural changes in their masticatory muscles which are detectable by CT.

Background In the mallard duck, functionally distinct groups of jaw muscles are each innervated by a different subnucleus of the main trigeminal (mV) or facial (mVII) motor nucleus. The other subnuclei of mV and mVII innervate several head muscles, including lingual muscles. The reticular premotor cells of the trigeminal and facial jaw motor subnuclei occupy different areas in the parvocellular reticular formation (RPc). The cell bodies of jaw muscle spindle afferents are situated in the mesencephalic nucleus (MesV). In the present study, the central connections of MesV with jaw motor subnuclei and their premotor areas are investigated. Methods In a first series of experiments, horseradish peroxidase (HRP) injections were made in electrophysiologically identified trigeminal and facial subnuclei. In a second series of experiments, HRP was delivered iontophoretically at different parts of RPc. Anterograde tracing with tritiated leucine was used to confirm the central connections of MesV. Double labeling with fluorescent tracers was used to investigate whether MesV collaterals reach both the rostral and caudal parts of RPc. Results MesV projects to only two of the five different subnuclei of the trigeminal motor nucleus. The subnuclei that receive spindle afferents innervate jaw adductor muscles (mV2) or pro- and retractors of the mandible (pterygoid muscles; mV1). The three other subnuclei innervate jaw-opener muscles or other head muscles. MesV fibers also project to the rostral part of the dorsolateral RPc (RPcdl), which serves as a premotor area for the motor subnuclei of adductor and pterygoid muscles. The intermediate part of RPcdl does not contain premotor cells of mV or mVII, and a clear projection of MesV to this area is absent. The caudal part of RPcdl projects to the mV and mVII subnuclei that innervate jaw-opener muscles. This part of RPc receives a projection from the same MesV cells as the rostral RPcdl. The MesV projection to RPc does not include premotor cells of mV and mVII in the ventromedial part of RPc (RPcvm). Conclusions Spindle afferents from jaw-closer muscles project only to mV subnuclei innervating jaw-closer muscles (mV1, mV2) and to a population of premotor cells in the rostral RPcdl that innervates these subnuclei. The mixed population of premotor cells in RPcvm, which innervates both jaw-opener and jaw-closer subnuclei, does not receive a MesV projection. However, a premotor area for jaw-opener subnuclei in the caudal part of RPcdl does receive MesV input and may serve as a relay through which proprioceptive information from jaw closer spindles can reach jaw opener muscles. Anat. Rec. 248:554-565, 1997. © 1997 Wiley-Liss, Inc.

Patients with chronic periodontal disease sometimes complain of difficulty in masticating hard foods. Computed tomography (CT) was used to investigate the cross-sectional area (CSA) and density of the masseter and medial pterygoid muscles in a pilot study of 12 healthy female subjects aged 30-39 years. Six subjects (the 'diseased' group) had suffered from chronic periodontal disease and had, on average, 40% bone loss. Their disease had been treated by scaling and root planning and had remained clinically stable for at least 6 months before their inclusion in the study. The six age-matched 'control' subjects had no history of periodontal disease. All bone-loss measurements were evaluated as a percentage of root length. At defined scan planes, sections of both muscles were readily identified. Results from the 'diseased' group as compared with the 'control' group revealed that in the former the CSA of masseter and medial pterygoid was reduced significantly by 25% and 10%, respectively. There were no significant differences in the X-ray density of both muscles between the two groups, which indicated a similar fibro-fatty content. These findings indicate a reduction in the masticatory force that may be utilized by patients with reduced periodontal support and may help explain their masticatory difficulties.

The distribution of the endomysium, perimysium, and epimysium and their constituent connective tissue fiber types in the mature rat lateral pterygoid muscle was examined with the light microscope. The endomysium and perimysium were relatively thin and consisted mainly of reticular fibers. The epimysium was thicker than the intramuscular sheaths and consisted of both collagen and reticular fibers; however, the thickness and constitutent connective tissue fiber types of these sheaths varied regionally. Near the articular capsule and disc, the endomysium, perimysium, and epimysium were all thicker than in other regions of the muscle and consisted of collagen, reticular, and elastic fibers. The perimysium bound the bundles of muscle fibers together and frequently included blood vessels and nerves. As the superior head of the pterygoid muscle approached its insertion, sheaths of perimysium divided this head into smaller and smaller bundles of muscle fibers. In the inferior head, some of the perimysial sheaths and part of the epimysium were aponeurotic, and many muscle fibers attached to them. There were few such aponeurotic regions in the superior head.

Background: The effects of biomechanical stress on the growth and development of the mandibular condyle have been studied by many investigators. However, the role of the lateral pterygoid muscle in this development is not clear. Methods: Hyperfunction of the lateral pterygoid muscles of male 3-weekold Sprague-Dawley rats was induced by electrical stimulation, and the responses of the mandibular condyles were compared to control tissues by a double-fluorescent staining technique using polyclonal antibodies against type I and type II collagen. Electrical stimulation consisted of repeated application (5 seconds on/5 seconds off) of a Hz current for up to 7 days. Results: In the first 2 days, cartilaginous tissues rich in type II collagen disappeared in the anterior and posterior areas, which were loaded by tensional force due to direct and indirect attachment of the lateral pterygoid muscles. Tissues in these areas were replaced by intramembranous bone that was reactive for type I collagen at 7 days. By the end of the experiment, the trabecula of the condyle was remodled more perpendicularly, thus resisting the compressive force due to hyperfunction of the lateral pterygoid muscles. Conclusions: These results suggest that the activity of the lateral pterygoid muscle might play a significant role in the differentiation of progenitor cells and in the maturation and calcification of chondrocytes in mandibular condyles. © 1995 Wiley-Liss, Inc.