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At least 775 records · Page 43Linked to original sources
PubMed1998

[Methods proposed for the determination of external forces applied to the mandible during mastication. Initial results].

The purpose of this study is to determine the external forces that are brought to bear on the mandible during various masticatory exercises. An analysis is presented of a static two-dimensional mandibular model taking into account projections in the sagittal plane of the forces exerted by six muscle groups and the joint reaction. In calculating the external forces, two working hypotheses are adopted: the existence of a linear relationship between cross-sectional surface of the muscle and its maximum force of contraction; the existence of a linear relationship between the electrical signal emitted by a muscle and the force the muscle then develops. It follows that, in order to calculate, the muscle forces, there is a need to measure the intensity of masticatory effort, the cross-sectional surface and the electromyographic activity of the different muscles involved. These values are then used for working out the equations of equilibrium. Results are provided for 14 masticatory exercises effected in three different mandibular positions and compared with data from literature. Individual variations recorded in the measurement of the different parameters involved in the equilibrium equations are such that they must be taken into account for the calculation of the forces. Moreover, the functional value of the muscles appears to be closely dependent on the mandibular position with which they are associated, which is not brought out in earlier studies. Finally, intra-joint action proves to be intense, although its direction varies according not only to the mandibular position but also the type of exercise performed.

Algorithms↗
PubMed1998

Evidence that trigeminal brainstem interneurons form subpopulations to produce different forms of mastication in the rabbit.

To determine how trigeminal brainstem interneurons pattern different forms of rhythmical jaw movements, four types of motor patterns were induced by electrical stimulation within the cortical masticatory areas of rabbits. After these were recorded, animals were paralyzed and fictive motor output was recorded with an extracellular microelectrode in the trigeminal motor nucleus. A second electrode was used to record from interneurons within the lateral part of the parvocellular reticular formation (Rpc-alpha, n = 28) and gamma- subnucleus of the oral nucleus of the spinal trigeminal tract (NVspo-gamma, n = 68). Both of these areas contain many interneurons projecting to the trigeminal motor nucleus. The basic characteristics of the four movement types evoked before paralysis were similar to those seen after the neuromuscular blockade, although cycle duration was significantly decreased for all patterns. Interneurons showed three types of firing pattern: 54% were inactive, 42% were rhythmically active, and 4% had a tonic firing pattern. Neurons within the first two categories were intermingled in Rpc-alpha and NVspo-gamma: 48% of rhythmic neurons were active during one movement type, 35% were active during two, and 13% were active during three or four patterns. Most units fired during either the middle of the masseter burst or interburst phases during fictive movements evoked from the left caudal cortex. In contrast, there were no tendencies toward a preferred coupling of interneuron activity to any particular phase of the cycle during stimulation of other cortical sites. It was concluded that the premotoneurons that form the final commands to trigeminal motoneurons are organized into subpopulations according to movement pattern.

Animals↗
PubMed1982

Contractile properties of the muscles of mastication of rhesus monkeys (Macaca mulatta) following increase in muscle length.

The hypothesis was tested that increasing the resting length of the masseter and temporalis muscles by a bite-opening appliance with or without detachment and re-attachment of the masseter would not affect the contractile properties of these muscles. Appliances opened the bite of 10 adult female monkeys 20 mm. Five received the appliance alone (Group A); five received the appliance and in addition the masseter was detached and re-attached (Group ADR). Comparisons were made 48 weeks later. Small bundles of fibres were excised from the masseter and temporalis muscles of experimental animals and from 8 control animals. Isometric and isotonic contractile properties were measured in vitro and fibre classification and fibre areas were determined histochemically. No significant differences were observed within either masseter or temporalis muscles between animals in Groups A and ADR. In both groups, the bundles of fibres from the masseter had prolonged contraction and relaxation times compared to control masseter muscles but no difference was observed in the percentage of Type II fibres. As detachment and re-attachment had no significant effect on morphological or physiological characteristics, other than those due to lengthening, this procedure may be useful in decreasing the passive tension induced when orthognathic surgery increases muscle length. The significant prolongation of the contractile response of the masseter is similar to the adaptation induced by long-term stimulation at low frequency.

Adaptation, Physiological↗
PubMed1986

Bilateral lung abscess associated with a severe masticator space infection.

The clinician should be constantly aware of the danger of aspiration in cases of prolonged sepsis with profuse suppuration. In such cases, it might be wiser to establish dependent extraoral drainage, rather than relying solely on intraoral means. The chances of aspirating septic material and the resultant occurrence of pulmonary abscesses will be lessened.

Acute Disease↗
PubMed1987

Comparison of arthrographic findings of the temporomandibular joint with palpation of the muscles of mastication.

Two hundred five patients were examined for temporomandibular joint pain and dysfunction and specifically for tenderness to muscle palpation. Arthrograms were performed on 222 joints (188 unilateral and 17 bilateral). Significant findings were ascertained for the middle portion of the temporal muscle in "normal" patients versus "with and without meniscus reduction" patients. The superficial masseter muscle was more tender in "normal" patients and in "reducing meniscus" patients than in "without meniscus reduction" patients. The medial pterygoid muscle was more tender in "normal" patients and in "without meniscus reduction" patients than in "reducing meniscus" patients. Though there are some significant findings with respect to muscle palpation, by itself muscle palpation is not a specific indicator of temporomandibular joint internal derangement.

Arthrography↗
PubMed2006

The volume of muscles of mastication in patients receiving mandibular contouring surgery: a comparative study.

PURPOSE: As the management of prominent mandibular angle and masseter muscle hypertrophy becomes increasingly popular, proper understanding of the volumetric component of the related structures becomes important but is currently lacking. MATERIALS AND METHODS: Three-dimensional computed tomographic (CT) scans of 18 female and eight male adult patients with square-face appearance were used for volumetric measurement of the osseous hemi-mandible, masseter, medial and lateral pterygoid muscles. CT scans of 28 female and 17 male adult patients without square-face appearance were selected from the imaging laboratory archive to serve as controls. RESULTS: Compared with the sex-matched controls, the square-faced patients had significantly higher volume of the osseous hemi-mandible as well as the masseter and medial pterygoid muscles. There was no significant difference in the volume of the lateral pterygoid muscle between the two groups. This study confirms a significantly greater volume in the osseous mandible and masseter muscle in patients complaining of square-face appearance. The implication of this information on treatment is discussed.

Adult↗
PubMed2001

Differential expression of myosin heavy-chain mRNA in muscles of mastication during functional advancement of the mandible in pigs.

Surgical and orthodontic treatment of retrognathia aims to improve orofacial function by adaptation and training of muscle capacity, which is connected with a change in muscle fibre-type proportions. The aim here was to analyse the proportion of myosin-heavy chain (MyHC) gene expression in type I (slow twitch/ST) and type IIb (fast twitch/FT) fibres during sagittal advancement of the mandible by reverse transcriptase-polymerase chain reaction (RT-PCR). The experiments were carried out on 10-week-old pigs (six test animals, six controls) over a 28-day period. Six pigs were fitted with acrylic bite blocks for sagittal advancement of the mandible. Tissue was taken from seven different regions of the masseter, temporal, medial pterygoid, and geniohyoid muscles. The 84 samples were used for histological fibre differentiation with ATPase staining and for isolation of total RNA. To measure the two MyHC isoforms, RT-PCR (in a single tube reaction with MyHC I, MyHC IIb, and GAPDH primers) was used. A significant increase was registered in the percentage of ST fibres and in mRNA from MyHC I in the anterior region of the masseter and in the posterior region of the temporal muscle of the treated animals. The proportion of ST fibres to FT fibres was increased by up to 12% after functional advancement of the mandible. The histological findings corresponded with the data for fibre mRNA generated by RT-PCR.

Acrylic Resins↗
PubMed1997

Mastication of verruca vulgaris associated with esophageal papilloma: HPV-45 sequences detected in oral and cutaneous tissues.

Human papillomaviruses (HPVs) are double-stranded, circular, epitheliotropic DNA viruses of which nearly 70 types have been identified. Specific HPV types exhibit a predilection to infect certain sites; however, occurrence is not unique or restricted to these sites. HPV typing may also be helpful in determining the oncogenic potential of HPV lesions. The most common HPV types, 6 and 11, are associated with benign mucosal lesions, whereas types 18, 16, 31, and 33 are thought to confer a high rate of malignant transformation. We describe a patient with both palmar verrucae and esophageal papillomatosis that proved to be HPV type 45 by polymerase chain reaction. HPV 45 has a high homology to HPV 18 and is a member of the relatively new "high-risk" mucosal HPV family in terms of cervical oncogenic potential. To our knowledge, HPV 45 has never been reported in cutaneous warts or esophageal lesions.

DNA, Viral↗