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PubMed2002

The upper dentition and face of Pondaungia cotteri from central Myanmar.

A specimen of Pondaungia from the late middle Eocene Pondaung Formation in central Myanmar includes maxillary fragments and parts of the dentition, some hitherto undocumented, including the upper central incisor, canine, premolars and molars. Pondaungia has a large spatulate I1 closely resembling that of crown anthropoids. It possesses a stout projecting upper canine (like anthropoids) but differs from that tooth of crown anthropoids in lacking a strong mesial groove. There are three upper premolars of which P2 is distinctly smaller than P3 or P4. P3 has a buccolingually oriented mesial profile and an inflated distal profile resembling that of parapithecids and crown anthropoids. The distolingual molar cusp is a hypocone and is not homologus with the "pseudohypocone" of notharctines because the cusp is neither twinned with the protocone nor attached to a Nannopithex-fold. Pondaungia has a stout zygomatic root with a strongly demarcated muscle scar for the superficial masseter situated well above the occlusal plane. The inferior orbital margin is not preserved but the inflated suborbital region allows for the inference that the orbit was small. This specimen is not sufficiently well preserved to identify if there was postorbital closure. However, a specimen of the frontal bone of Amphipithecus shows that its orbital septum was absent or poorly developed. If, as commonly supposed, Pondaungia andAmphipithecus are sister taxa, postorbital closure was probably absent in Pondaungia. The large incisors, molars with poorly developed crests and thick enamel, together with the stoutly developed and strong dorsal component of the force vector of the superficial masseter muscle suggest that Pondaungia had a diet low in fiber, but that included hard food objects like nuts or seeds. The present material adds to the structural similarities between Pondaungia and anthropoids, but whether these similarities are due to shared descent or functional and adaptive convergence remains unresolved.

Adaptation, Physiological↗
PubMed2002

The sites of origin of projection fibers from the cerebral cortex to the jaw region of the striatum of the rat.

Electrical microstimulation of the jaw region of the rat striatum (SJR) has been reported to provoke clear electromyographic activity in the anterior digastric muscle but not in the masseter muscle (Neurosci. Lett., 252 (1998) 79-82). Thus, in the present study, we examined the sites of origin of cortico-SJR fibers by the retrograde labeling. The SJR, identified by electrical microstimulation, was injected electrophoretically with cholera toxin B subunit. In the cerebral cortex ipsilateral to the injection, there existed two foci of retrograde labeling: One focus was centered on the lateral part of the sensorimotor area, while the other on the insular cortical area around the middle cerebral artery. These foci appeared to correspond to the reported two cortical areas, where two different types of rhythmical jaw movements were induced by repetitive electrical stimulation (Jap. J. Oral Biol., 32 (1990) 57-68).

Animals↗
PubMed1993

Coordination of cortically induced rhythmic jaw and tongue movements in the rabbit.

1. Rhythmic movements of the jaw, tongue, and hyoid that were induced by stimulation of the cortical masticatory area (CMA) were recorded cineradiographically in the anesthetized rabbit. Jaw movements were also recorded by a laser position detector. 2. The evoked jaw movements were classified into four types: small circular (type A), large circular (type B), large vertical (type C), and crescent-shaped (type D). Among these, types B and D resembled the jaw movements of the food transport cycle and those of the chewing cycle in a masticatory sequence. 3. Each type of jaw movement was associated with a particular pattern of tongue and hyoid movements. In general, the tongue protruded during jaw opening and retracted during jaw closure. The hyoid generally moved upward and forward during jaw opening but downward and backward during jaw closure. 4. Electromyograms (EMGs) were recorded from jaw muscles [masseter (Ma) and digastric (Di) muscles], extrinsic tongue muscles [styloglossus (Sg) and genioglossus (Gg) muscles], and hyoid muscles [sternohyoid (Sh) and geniohyoid (Gh) muscles] during cortically induced rhythmic jaw and tongue movements (CRJTMs). These muscles were classified into two groups: group 1 was activated mainly in the jaw opening phase, and group 2 was activated mainly in the jaw closing and power phases. The Di, Gg, and Gh were included in the former, and the Ma, Sg, and Sh were included in the latter. 5. The timings of EMG activation to a jaw movement cycle were relatively constant for the muscles of group 1, irrespective of the types of CRJTMs, whereas those for the muscles of group 2 altered considerably with the different types of CRJTMs. 6. Relationships of the integrated muscle activity between the Di and Gg and between the Di and Gh were significant, whereas those between the Ma and Sg and between the Ma and Sh were not. 7. When a small strip of polyurethane form of various degrees of hardness was inserted between the opposing molars during CRJTMs, EMG activity of the muscles of group 2 increased with the hardness of the strip. On the other hand, EMG activities of the muscles of group 1 were less affected by the same intraoral stimuli. 8. Two conclusions were reached: first, physiological properties of the CRJTMs and cortically induced rhythmic movements of the hyoid were essentially similar to those observed in natural mastication. This fictive mastication might thus be regarded as a suitable model for simulating natural mastication.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Expression of endogenous receptors for neoglycoproteins, especially lectins, that allow fiber typing on formaldehyde-fixed, paraffin-embedded muscle biopsy specimens. A glycohistochemical, immunohistochemical, and glycobiochemical study.

A panel of biotinylated (neo)glycoproteins was used for specific detection of endogenous sugar receptors, especially lectins, in formaldehyde-fixed, paraffin-embedded muscle biopsy specimens from human deltoid, quadriceps, and biceps muscles, tibial and quadriceps muscles of rat, and bovine masseter muscle. The glycohistochemical probes used consisted of conjugates of a labeled, histochemically inert carrier protein and various covalently linked, histochemically crucial sugar moieties. Specific binding of alpha-L-fucoside, beta-D-galactoside, beta-D-xyloside, and alpha-D-mannoside to muscle sections was detected, showing no species-specific differences. The presence of receptors for the N-acetylated sugars in natural glycoconjugates, and for sugars with a phosphate group, i.e., mannose-6-phosphate and galactose-6-phosphate, was demonstrated glycohistochemically. However, these binding specificities revealed species-specific differences, e.g., the absence of N-acetyl-D-galactosamine-specific receptors or galactose-6-phosphate-specific receptors in rat muscle. Other charged sugars included glucuronic acid and sialic acid, which bound only to ox and rat muscle or failed to reveal their respective receptors in all types of muscle investigated. This different extent of staining with anionic probes served as a further control to ascertain carbohydrate binding specificity. Positive glycohistochemical reaction developed within sarcomeres only at the level of A-bands. Granular staining was observed in the sarcoplasm among the myofibrils and also in the subsarcolemmal regions. Differences in expression of glycohistochemically detectable sugar receptors were noted between type 1, type 2A, and type 2B fibers. The molecular properties of one type of glycohistochemically detectable sugar receptor were inferred both immunohistochemically and biochemically. An antiserum against an endogenous beta-galactoside-specific lectin from muscle tissue localized this lectin within sections consistently similar to (neo)glycoproteins, detecting beta-galactoside-specific receptor(s). This similarity of binding patterns strongly supports the assumption that (neo)glycoproteins with beta-galactoside termini indeed bind to the respective endogenous lectin. The lectin-specific antiserum enabled us to ascertain that glycohistochemical fiber typing corresponds to enzyme histochemical typing. Moreover, biochemical purification using affinity chromatography and subsequent affinity elution revealed only the immunohistochemically detectable beta-galactoside-specific lectin. Consequently, use of a panel of neoglycoproteins, when frozen sections for histochemical analysis are not available, co

Acetylation↗
PubMed2000

Referred craniofacial pain patterns in patients with temporomandibular disorder.

BACKGROUND: Referred pain is prevalent in the craniofacial region, and it would be helpful for dental practitioners to have drawings delineating regions with a high probability for a patient's referred pain source. METHODS: The author applied firm pressure for approximately five seconds to trigger points, nodules of spot tenderness, and selected masticatory structures within the head and neck region on 230 patients with temporomandibular disorder, or TMD. As firm pressure was being applied, subjects were asked whether pain was developing or intensifying in a location different than that being palpated. RESULTS: One hundred ninety-six subjects (85 percent) reported that referred pain was being generated. The cheek area, ear and forehead were the most frequently reported sites of referred pain generation; palpation over the trapezius muscle, lateral pterygoid area and masseter muscle were the most common sources of referred pain to the craniofacial region. The author provides figures displaying common referred pain sites and their sources. CONCLUSIONS: Patients with TMD often report referred craniofacial pain arising from palpation of the head and neck region. The author found that the pattern between referred pain source and site was consistent and predictable. PRACTICE IMPLICATIONS: Practitioners should consider craniofacial pain's propensity for referral when treating patients with TMD. Practitioners can use the figures presented to determine regions of high probability for a patient's referred pain source.

Adolescent↗
PubMed1979

Motor nuclear representation of masticatory muscles in the rat.

Representation of the masticatory muscles within the motor trigeminal nucleus was studied in rats by the horseradish peroxidase (HRP) method and the antidromic field potential method. The motor trigeminal nucleus of the rat could be divided cytoarchitecturally into a dorsolateral and a ventromedial division. Within the dorsolateral division, the temporal muscle was represented dorsomedially, the masseter muscle dorsolaterally and laterally, and the lateral and medial pterygoid muscles ventrolaterally. Within the ventromedial division, the anterior digastric muscle was represented dorsomedially and the mylohyoid muscle ventrolaterally. Distribution of antidromic field potentials evoked by stimulation of the mylohyoid and masseteric nerves coincided with the results from the HRP investigation.

Animals↗
PubMed1999

[Study on masticatory muscles and tooth long axis of miniature pigs].

OBJECTIVE: The similarities of masticatory muscles and teeth orientations between miniature pigs and human beings were studied in order to evaluate the use of miniature pigs in oral biomechanics research. METHODS: By means of anatomy, the shapes, start-stop points and orientations of muscle of major masticatory muscles of miniature pigs were measured. Inclination of upper and lower teeth long axis was studied with lateral xray film of mandibles. RESULTS: The main masticatory muscles of miniature pigs include masseter muscle, temptory muscle, lateral pterygoid muscle, medial pterygoid muscle and zygomaticomandibular muscle. The angles of masticatory muscles and base plane are 63.9 degrees in massater muscle, 114.55 degrees in temple muscle, 64.4 degrees in medial pterygoidp muscle. The long axises of miniature pigs teeth are 6.1 degrees in the upper first molar, 6.5 degrees in the lower first molar, 7.3 degrees in the upper third premolar, 3.8 degrees in the lower third premolar. CONCLUSION: The masticatory muscles of miniature pigs are similar with human being in the shape, start-stop point and orientation of muscle force. The third premolar and the first molar of miniature pigs inclinate mesially, and are similar with the first premolar and the first molar of the human beings. Miniature pigs can be used as an animal models which can explain some problems of gnathostomatic system of human beings.

Animals↗
PubMedDate not supplied

Combat and warfare in the early paleolithic and medically unexplained musculo-facial pain in 21st century war veterans and active-duty military personnel.

In a series of recent articles, we suggest that family dentists, military dentists and psychiatrists with expertise in posttraumatic stress disorder (especially in the Veterans Health Administration) are likely to see an increased number of patients with symptomatic jaw-clenching and early stages of tooth-grinding (Bracha et al., 2005). Returning warfighters and other returnees from military deployment may be especially at risk for high rates of clenching-induced masticatory muscle disorders at early stages of incisor grinding. The literature we have recently reviewed strongly supports the conclusion that clenching and grinding may primarily be a manifestation of experiencing extreme fear or severe chronic distress (respectively). We have recently reviewed the clinical and paleoanthropological literature and have noted that ancestral warfare and ancestral combat, in the early Paleolithic Environment of Evolutionary Adaptedness (EEA) may be a neglected factor explaining the conservation of the archaic trait of bite-muscle strengthening. We have hypothesized that among ancestral warriors, jaw clenching may have rapidly strengthened the two primary muscles involved in biting, the masseter muscles and the much larger temporalis muscles. The strengthening of these muscles may have served the purpose of enabling a stronger, deeper, and therefore more lethal, defensive bite for early Paleolithic humans. The neuroevolutionary perspective presented here may be novel to many dentists. However, it may be useful in patient education and in preventing progression from jaw-clenching to chronic facial pain.

Biological Evolution↗
PubMed1984

Nocturnal muscle activity in the edentulous patient with and without dentures.

Nocturnal oral activity was evaluated in four complete denture wearers by means of masseter muscle EMG measurements. Patients who had worn dentures that were judged satisfactory for at least a 1-year period were selected. EMG levels were compared when subjects slept with and without the dentures in the mouth. All subjects showed a decrease in the integrated muscle activity while wearing the dentures. Additional studies need to be directed at understanding the mechanism of the effect of denture wearing on nocturnal muscle activity.

Denture, Complete↗
PubMed1979

Muscle spindle supply to the masticatory muscles in the Japane ermine (Carnivora).

Histological examination of the jaw muscles of the Japanese ermine showed that 4 jaw-closing muscles have 13 muscle spindles on one side of the face. The temporal muscle has 99 muscle spindles, 68 being in the anterior vertical and 31 in the posterior horizontal belly. The masseter muscle has 33 muscle spindles, 23 being in the profound and 10 in the superficial belly. The medial pterygoid muscle has 7 muscle spindles and the zygomaticomandibular muscle contains 4 muscle spindles. The lateral pterygoid and the jaw-opening muscles have no spindles.

Animals↗
PubMed2006

An impact of masticatory muscle function on IL-1beta and SOX9 expression in condyle.

The importance of masticatory muscle function on the growth and differentiation of condyle was examined. The aim of this study was to investigate how reduced masticatory muscle function influences intrinsic regulatory factors which govern growth and differentiation of condylar cartilage. Masseter muscles of 3-week-old Wistar rats were resected bilaterally. Masseteric resected animals and corresponding control animals were sacrificed at 3, 6, 12 and 21 days post-resection. The condyles were then processed for histological and immunohistochemical analysis. The expression patterns of an inhibitory regulator (IL-1beta) and a master regulator (Sox9) of chondrogenesis in condylar cartilage of growing rats were investigated. Quantitative analysis shows that masseteric resection significantly increased the number of IL-1beta positive cells in proliferative layer. In contrast, the number of Sox9 positive cells was significantly decreased compared to the control animals. It can be concluded that the reduced articular function due to masseteric resection decreased condylar cartilage cell differentiation which led to the decrease in the thickness of condylar cartilage.

Animals↗
PubMed2005

A three-dimensional in vitro model system to study the adaptation of craniofacial skeletal muscle following mechanostimulation.

The aim of this study was to investigate the in vitro response of human craniofacial muscle-derived myotubes (primitive/nascent muscle fibres), in three-dimensional constructs, to strain in vitro to mimic clinical scenarios, using expression of the mechanoresponsive gene gelatinase-A/matrix metalloproteinase-2 (MMP-2) as a marker of remodelling of muscle extracellular matrix. Three-dimensional (3D) constructs of cells derived from explants of human masseter muscle (human craniofacial muscle-derived cells; hCMDC) in collagen sponges were subjected to mechanical, uniaxial strain using the Bio-Stretch system. 3D myotube constructs were exposed to the strain regimes of rapid ramp stretch (RRS) or cyclical ramp strain (CRS) with 7.5% and 15% strain. The activity of MMP-2 was assessed by zymography of construct-conditioned medium, whilst lysates of the constructs were used to measure creatine phosphokinase (CPK) activity to confirm the presence of myotubes in the strained constructs. Scanning electron microscopy of the collagen sponges and the CPK assays confirmed the presence of myotubes. MMP-2 was expressed by all the samples and controls, but expression was found to be significantly higher in those cultures strained continuously (RRS), compared to cyclical strain (CRS), and in those strained at 15% compared to 7.5%. Thus, MMP-2 expression, and hence extracellular matrix remodelling, is up-regulated in response to strain and is dependent upon the amount and type of strain to which the muscle is subjected.

Adaptation, Physiological↗
PubMed1988

The effects of muscle fatigue on the silent period of the masticatory muscles.

Thirteen healthy adults performed sustained clenching at 50% maximum clenching level judged electromyographically. Electromyograms were recorded from both anterior temporal and masseter muscles during clenching and the silent period latency and duration were measured. As the result of muscle fatigue, the silent period latency significantly decreased, whilst the duration significantly increased up to 3 min from the beginning of clenching.

Adult↗
PubMed2003

Effects of experimental nasal obstruction on human masseter and suprahyoid muscle activities during sleep.

The effect of nasal obstruction on nocturnal masseter and suprahyoid muscle activities using a newly developed portable electromygram (EMG)-recording unit was examined. Ten healthy Japanese males participated in this study. EMG activities of both the right masseter and bilateral suprahyoid muscles were recorded with a portable EMG-recording unit. At midnight, the subject was asked to lie on a bed after complete preparation with surface electrodes. After maximal clenching and jaw-opening effort (100% maximum voluntary contribution), the subject was allowed to fall asleep. In the first half of the night, EMG activities were recorded for about three hours of sleep without nasal obstruction. In the second half of the night, EMG activities were recorded for about three hours of sleep with nasal obstruction. In both muscles, there were no significant changes in either the maximal EMG activities or the number of events beyond 40% MVC with nasal obstruction. But in an evaluation based on the distribution of muscle activities, the EMG activity of the masseter muscle tended to decrease (P = .07) and that of the suprahyoid muscles increased significantly (P = .02) with nasal obstruction. These results suggest that nasal obstruction could modulate the activities of the masseter and suprahyoid muscles during sleep.

Adult↗
PubMed1989

An exteroceptive reflex in the sternocleidomastoid muscle produced by electrical stimulation of the supraorbital nerve in normal subjects and patients with spasmodic torticollis.

We examined suppression of EMG activity in the contracting sternocleidomastoid muscles, produced by electrical stimulation of the supraorbital nerve in 10 normal subjects and 9 patients with spasmodic torticollis. This exteroceptive reflex in the sternocleidomastoid muscle consisted of 2 or 3 phases: (1) an early, small, and unstable phase of facilitation, followed by (2) a period of suppression beginning 35 msec after the stimulus, lasting for 35 msec with a reduction in EMG activity to approximately 40% of the prestimulus level, and (3) a further phase of facilitation at a latency of 70 msec, with duration 35 msec and an increase in EMG activity to approximately 35% above prestimulus levels. The latency and duration of the suppressive phase of this reflex were similar to the exteroceptive suppression of EMG activity in the masseter muscle after supraorbital nerve stimulation (masseter silent period). In patients with spasmodic torticollis, the depth of this exteroceptive suppression in the sternocleidomastoid muscles was less than that observed in an age-matched cohort of normal subjects, although the latency and duration were normal. In contrast, exteroceptive suppression in the masseter muscle was normal. These findings suggest abnormal function of inhibitory interneuronal networks between the 5th cranial nerve and the motor neurons of the spinal accessory and upper cervical nerves which mediate exteroceptive suppression in the sternocleidomastoid muscle in patients with spasmodic torticollis.

Adult↗
PubMed1993

An electromyographic study of whether the digastric muscles are controlled by jaw-closing proprioceptors in man.

Whether in the oral system the digastric muscles (which lack muscle spindles) are under the control of proprioceptive information from the masseter muscles (which contain muscle spindles) was investigated by analysing whether and how the masseters and digastrics showed coordinated behaviour during a static, forceful bite. Subjects were asked to maintain a 100-N force for 15 s with and without visual guidance; bite force exerted, and masseter and digastric electromyograms (EMGs) were recorded. Under visual guidance all subjects co-contracted their digastric muscles during the isometric bite. They held the force for a short time, followed by periods with fluctuations (peak-to-peak force amplitude about 15-20 N). Fluctuations in bite force correlated with the masseter EMGs, the maximum in the correlogram occurring at about -50 ms with the force lagging the masseter. In 75% of the subjects a significant periodic component in the masseter and in the force spectra was found at about 4 Hz. This was also seen in the amplitude spectra of the forces, which showed in 80% of the subjects a significant elevation between 7-10 Hz as well. No correlation between the digastric EMGs and the bite forces, and between the EMGs of masseter and digastric could be detected. Spectra of digastric EMGs showed no prominent maxima. When subjects were deprived of visual feedback, maxima at -50 ms in the cross-correlation functions of the masseters and the forces were reduced considerably; periodicities of +/- 250 ms disappeared.(ABSTRACT TRUNCATED AT 250 WORDS)

Bite Force↗
PubMed2003

Development of a behavioral assessment of craniofacial muscle pain in lightly anesthetized rats.

In this study, a new behavioral assessment of craniofacial muscle pain in the lightly anesthetized rat is described. Intramuscular injections with algesic agents in lightly anesthetized rats evoked a characteristic ipsilateral hindpaw shaking behavior for several minutes similar to previously described orofacial pain-induced grooming behavior in awake rats (Neurosci Lett 103 (1989) 349, Pain 62 (1995) 295). Eighty-two male Sprague-Dawley rats were used in a series of experiments to study whether this behavior could serve as a valid measure of craniofacial muscle pain. First, we demonstrated that different algesic chemicals, mustard oil (20%), formalin (3%) or hypertonic saline (5%) injected in the mid-region of the masseter muscle effectively elicited the hindpaw shaking behavior. The behavior was only minimally evoked with vehicle injection. Repeated administrations of hypertonic saline, a short duration non-sensitizing algogen, demonstrated reproducibility of the assay. Second, we showed that the peak and overall magnitude of the shaking behavior evoked by injections with different concentrations of mustard oil (1 and 5%) changed in a concentration dependent manner. Finally, we showed that systemic administration of morphine sulfate (3 and 0.3 mg/kg, i.p.) dose dependently attenuated mustard oil induced hindpaw-shaking behavior. Lidocaine injected locally 5 min prior to mustard oil injection also significantly decreased the hindpaw shaking behavior. Based on these results we concluded that ipsilateral hindpaw shaking in lightly anesthetized rats is a stereotypical behavior evoked by noxious muscle stimulation and can be used as a reliable behavioral measure to assess craniofacial muscle pain.

Adjuvants, Anesthesia↗
PubMed1990

Non-reciprocal facilitation of trigeminal motoneurons innervating jaw-closing and jaw-opening muscles induced by iontophoretic application of serotonin in the guinea pig.

Effects of iontophoretically applied serotonin (5-HT) and its antagonist, methysergide (MS), on masseter (a jaw-closer, MA.MNs) and anterior digastric motoneurons (a jaw-opener, AD.MNs) were studied in paralyzed guinea pigs, chloralose-anesthetized or decerebrate. Unitary activity was recorded with multibarrel capillary electrodes from MA.MNs and AD.MNs identified by antidromic spikes evoked by stimulation of the masseter and anterior digastric nerves, respectively. Under chloralose anesthesia, both MA.MNs and AD.MNs were almost quiescent, and application of 5-HT alone induced no changes in discharge of either of them. However, iontophoretically applied 5-HT increased the frequency of discharge induced by iontophoretic application of glutamate in 26 of 34 MA.MNs (76%) and 17 of 30 AD.MNs (59%) tested. MS depressed the glutamate-induced activity in 17 MA.MNs and 3 AD.MNs, respectively, in which 5-HT exerted a facilitatory effect on the glutamate-induced activity. In decerebrate preparations, the firing index of spikes of MA.MNs monosynaptically evoked by stimulation of the trigeminal mesencephalic nucleus was increased by 5-HT and decreased by MS. 5-HT also enhanced the discharge of MA.MNs induced by a ramp-and-hold stretch of the masseter muscle. We conclude that 5-HT alone does not excite either MA.MNs or AD.MNs, but potentiates the effect of excitatory inputs to them: 5-HT exerts a modulatory facilitatory action on trigeminal motoneurons.

Action Potentials↗