Analysis of histochemically and morphometrically in the anterior belly digastric muscle of osteopetrotic (op/op) mice.
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The fibers of the anterior belly digastric muscle of mice, fed a granulated diet for various periods, have been studied histochemically and morphometrically. The diameters of the anterior belly digastric fibers in normal mice fed only a granulated diet were smaller than those in mice fed a solid diet. Differences in the succinate dehydrogenase (SDH) activity of muscle fibers between op/op and normal mice gradually appeared in the anterior belly digastric muscle and, by the age of 90 days, under-development of muscle fibers was observed in the mild-belly region of the anterior belly digastric muscle of op/op mice fed a granulated diet. These results indicate mechanical stress in mastication plays an important role in the development of the anterior belly digastric muscle structures. (+info)
Temporomandibular disorders in relation to craniofacial dimensions, head posture and bite force in children selected for orthodontic treatment.
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The present study examined the associations between craniofacial dimensions, head posture, bite force, and symptoms and signs of temporomandibular disorders (TMD). The sample comprised 96 children (51F, 45M) aged 7-13 years, sequentially admitted for orthodontic treatment of malocclusions entailing health risks. Symptoms and signs of TMD were assessed by 37 variables describing the occurrence of headache and facial pain, clicking, jaw mobility, tenderness of muscles and joints, and the Helkimo Anamnestic and Dysfunction indices. Craniofacial dimensions (33 variables), and head and cervical posture (nine variables) were recorded from lateral cephalometric radiographs taken with the subject standing with the head in a standardized posture (mirror position). Dental arch widths were measured on plaster casts and bite force was measured at the first molars on each side by means of a pressure transducer. Associations were assessed by Spearman correlations and multiple stepwise logistic regression analyses. The magnitudes of the significant associations were generally low to moderate. On average, temporomandibular joint (TMJ) dysfunction was seen in connection with a marked forward inclination of the upper cervical spine and an increased craniocervical angulation, but no firm conclusion could be made regarding any particular craniofacial morphology in children with symptoms and signs of TMJ dysfunction. Muscle tenderness was associated with a 'long face' type of craniofacial morphology and a lower bite force. Headache was associated with a larger maxillary length and increased maxillary prognathism. A high score on Helkimo's Clinical Dysfunction Index was associated with smaller values of a number of vertical, horizontal, and transversal linear craniofacial dimensions and a lower bite force. (+info)
Temporomandibular disorders in adults with repaired cleft lip and palate: a comparison with controls.
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The purpose of this study was to investigate the prevalence of temporomandibular disorders (TMD), and assess psycho-social distress in adult subjects with repaired complete cleft lip and palate (CLP). Sixty-three adults (42 males and 21 females, mean age 24.2 years, range 19.5-29.2) with repaired CLP (CLP group) were compared with a group of 66 adults without cleft (non-cleft group, 49 males and 17 females, mean age 25.5 years, range 20.2-29.9). All subjects underwent a clinical TMD examination, which followed the guidelines in the Research Diagnostic Criteria for TMD (RDC/TMD). Jaw function was assessed by evaluating answers to the mandibular function impairment questionnaire (MFIQ). Tension-type headache was diagnosed according to the International Headache Society (IHS) classification. Psychological status was assessed using the depression score and the non-specific physical symptom score with subscales of the Revised Symptom Checklist-90 (SCL-90-R). The prevalence of reported pain in the face, jaws and/or TMJs was 14 and 9 per cent for the CLP and non-cleft group, respectively, and did not differ significantly between the groups. The CLP group exhibited a significantly reduced jaw-opening pattern (P < 0.001) and a higher frequency of crossbites (P < 0.05) compared with the non-cleft group. Whilst jaw function was similar in both groups, a few items, e.g. speech and drinking, were significantly more impaired (P < 0.01) in the CLP group than in the non-cleft group. There were no significant differences between the two groups concerning tension-type headache or psycho-social distress. The study found that overall TMD pain or psycho-social distress was not more common in this CLP group than in a non-cleft group. (+info)
Evidence for a monosynaptic mechanism in the tonic vibration reflex of the human masseter muscle.
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Vibration of the masseter and temporalis muscles in normal human adult subjects elicits a tonic vibration reflex with unexpected features. The electromyographic response is not asynchronous as in the limb muscles, but involves well-defined spikes with a one-to-one temporal relation to the vibration cycles. The effect of various parameters such as muscle stretch, vibration frequency or amplitude, etc, has been investigated. The small latency fluctuation of the vibration-induced spikes is compatible with a monosynaptic reflex mechanism which is considered to be assisted by a polysynaptic facilitatory background of proprioceptive origin. (+info)
Morphological, functional and aesthetic criteria of acceptable mature occlusion.
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At present, there are no generally accepted criteria that could easily be applied to the evaluation of occlusal acceptability in clinical examinations at population level. The present study analyses the opinions of Finnish orthodontists and general practitioners on the characteristics required for acceptable occlusion in the full permanent dentition. A questionnaire was sent to all 37 health centres where at least one orthodontist was employed, 31 regionally comparable health centres without an orthodontist, 12 private orthodontists, and 13 orthodontists working at university dental clinics. Seventy-four orthodontists returned the questionnaire giving a response rate of 80 per cent. They were asked to give their views on the importance of morphology, function, long-term stability, and dental appearance as elements of acceptable occlusion. They were also encouraged to indicate other significant characteristics and requested to assess the relative significance of these features. In general, the respondents expressed the need to assess morphological, functional and aesthetic aspects of occlusion as a whole. Good function, rather than morphology, was considered to be the most important feature of an acceptable occlusion, with a relative significance of 40 per cent (range 20-90 per cent). According to the respondents, the acceptability of occlusion is determined not only by morphological features, but also by the functional status and long-term stability, as well as by the patient's opinion of the dental appearance. (+info)
Extraocular muscle is defined by a fundamentally distinct gene expression profile.
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Skeletal muscle fibers are defined by patterned covariation of key traits that determine contractile and metabolic characteristics. Although the functional properties of most skeletal muscles result from their proportional content of a few conserved muscle fiber types, some, typically craniofacial, muscles exhibit fiber types that appear to lie outside the common phenotypic range. We analyzed gene expression profiles of three putative muscle classes, limb, masticatory, and extraocular muscle (EOM), in adult mice by high-density oligonucleotide arrays. Pairwise comparisons using conservative acceptance criteria identified expression differences in 287 genes between EOM and limb and/or masticatory muscles. Use of significance analysis of microarrays methodology identified up to 400 genes as having an EOM-specific expression pattern. Genes differentially expressed in EOM reflect key aspects of muscle biology, including transcriptional regulation, sarcomeric organization, excitation-contraction coupling, intermediary metabolism, and immune response. These patterned differences in gene expression define EOM as a distinct muscle class and may explain the unique response of these muscles in neuromuscular diseases. (+info)
The examination and recording of the occlusion: why and how.
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Before presenting 'how' the examination and recording of the occlusion may be achieved, some attempt should be made to justify 'why' it is necessary. It may appear to be a strange way of justifying the need to examine the patient's occlusion, but this will initially involve a study of the influences of mandibular movements. (+info)
Putative feed-forward control of jaw-closing muscle activity during rhythmic jaw movements in the anesthetized rabbit.
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When a thin plastic test strip of various hardness is placed between the upper and lower teeth during rhythmical jaw movements induced by electrical stimulation of the cortical masticatory area (CMA) in anesthetized rabbits, electromyographic (EMG) activity of the masseter muscle is facilitated in a hardness-dependent manner. This facilitatory masseteric response (FMR) often occurred prior to contact of the teeth to the strip, and thus preceded the onset of the masticatory force. Since this finding suggests involvement of a feed-forward mechanism in the induction of the FMR, the temporal relationship between the onset of the FMR and that of the masticatory force was analyzed in five sequential masticatory cycles after application of the strip. The FMR was found to precede the onset of masticatory force from the second masticatory cycle after application of the strip, but never did in the first cycle. This finding supports the concept of a feed-forward control mechanism that modulates FMR timing. Furthermore, the FMR preceding the force onset disappeared after making a lesion of the mesencephalic trigeminal nucleus (MesV) where the ganglion cells of the muscle spindle afferents from the jaw-closing muscles are located. In contrast, no such change occurred after blocking periodontal afferents by transection of both the maxillary and the inferior alveolar nerves. The putative feed-forward control of the FMR is therefore dependent mainly on sensory inputs from the muscle spindles, but little on those from the periodontal receptors, if any. We further examined the involvement of the CMA with the putative feed-forward control of the FMR via the transcortical loop. For this purpose, rhythmical jaw movements were induced by stimulation of the pyramidal tract. No significant change in the timing of the FMR occurred after the CMA ablation, which strongly suggests that the CMA is not involved in the putative feed-forward control of the FMR. The FMR was also noted to increase significantly in a hardness-dependent manner even after the MesV lesion, although the rate of increment decreased significantly. Contribution of muscle spindles and periodontal receptors to the hardness-dependent change of the FMR is discussed. (+info)