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Report on the treatment of a female patient, now 18 years old, with a bilateral continuous cleft of the lip, jaw and palate, in whom genuine ossification occurred at the jaw clefts. The upper lateral incisors and both upper canines have aligned themselves regularly in this jaw. Until now natural bone formation in a cleft jaw has been considered impossible.
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.
The activity of jaw muscle receptors was studied by recording neurons in the mesencephalic nucleus of the trigeminal nerve in monkeys trained to control the position and movement of their mandible. Jaw position was measured by a weighted lever resting on the mandibular incisors. The force required to maintain the position of the lever was varied; in most cases it was either 25 or 360 g. Firing rates of neurons were related to stationary mandibular positions and to the velocity of movements during intervals when the movement velocity was constant. Of 49 neurons studied in detail, 21 fired at rates that were consistently and linearly related to static incisal openings. This static position sensitivity was typically about 5 spikes/mm of incisal opening. Most position-sensitive neurons fired at higher rates during opening movements and at lower rates during closing movements than would be accounted for by their position sensitivity. This sensitivity to the velocity of movement was not linear, however; slow closing movements sometimes did not produce a decrease in firing rate, and an actual increase during muscle shortening was seen in a few instances. The position sensitivity of eight neurons was evaluated during different loading conditions; in no case did it change substantially. Of the remaining 28 neurons, 26 fired at high rates during all opening movements and either stopped firing or fired at low, sporadic rates during closing movements. The static position sensitivity of these neurons was weak and variable both within and between neurons. The velocity sensitivity of these stretch-sensitive neurons was very nonlinear. Except for a range of slow movements (+/- 5 mm/s), the firing rate was maximal (200 spikes/s or higher) for most opening movements and zero for most closing movements. Maximal firing rates were higher when the loads being moved were increased from 25 to 360 g. The majority of position-sensitive neurons exhibited a large interspike-interval variability at wide incisal opening. In most of these neurons, this interspike-interval variability was periodic, usually at a rate of about 10 periods/s, and took the form of "saw-tooth" modulation on a record of instantaneous firing rate. Neurons that exhibited this modulation in a very prominent form also exhibited, in many instances, a substantial increase in firing rate during closing jaw movements.
Muscle cross-sectional area (CSA) is used as a measure for maximum muscle force. This CSA is commonly determined at one location within the muscle and for one jaw position. The purpose of this study was to establish a method to standardize the analysis of the CSA of the masticatory muscles in vivo, and to compare the CSAs along their entire length for two different jaw positions (opened and closed). The CSAs in the planes perpendicular to the long axes of the masseter, medial, and lateral pterygoid muscles were measured in ten normal young adult subjects by magnetic resonance imaging. Our results showed large differences among the muscles and a non-uniform change in CSA after jaw-opening. The method enables the CSA measurement to be standardized in vivo, and allows for a correct comparison of CSAs in different skull morphologies.
Radiographic and histological investigations were carried out on a total of 15 rabbits after lower-jaw osteotomy and miniplate osteosynthesis. After the removal of the lower jaw (4, 8, 12 and 24 weeks) consolidation of the osteotomy surfaces without complications was observed in all animals. Radiographic examinations showed that callus formation in the operated area increased as the experiment proceeded. Histological observations made clear that only secondary bone-fracture healing resulted which must be attributed to the operation technique. These findings show that the lower jaw of the rabbit is very well suited to experimental research on miniplate osteosynthesis.
Jaw cyst lining cells have an active transporting mechanism for Na+ ion and K+ion, a secreting mechanism and a selecting mechanism, and they allow permeation of electrolytes, lipids and protein into cysts. The components within the cysts have a controlling metabolism, and keep the system stable. Tumour wall cells of cystic ameloblastoma have only a passive transporting mechanism for various substances. Their nature differs from that of jaw cyst lining cells.
During each phase of the pigeon's eating sequence, jaw opening amplitude (gape) is adjusted to the size of the food object; first prior to contact (Grasping), again in positioning the food (Stationing), and finally, during its movement through the oral cavity (Intraoral Transport). Part I of this study examined jaw movement kinematics during ingestion of different size food pellets to determine the relative contribution of velocity and rise time variables. Part II specified the muscle activity patterns mediating each phase of the eating sequence, and determined how these patterns are modulated to produce adjustments of gape size. The relative contribution of velocity and rise time variables to the control of gape differs in each phase of the eating sequence. However, for any pellet size, variations in opening rise time may function in a compensatory manner to minimize gape "undershooting". Each phase of the eating sequence is mediated by a characteristic muscle activity pattern. The adjustment of gape size to pellet size involves systematic modulation of this pattern, and the parameters modulated differ in the different phases in a manner which may reflect the functional requirements of each phase.
Little is known about the dendritic architectures of trigeminal motoneurons innervating antagonistic muscles. Thus, the aim of the present study was to provide a quantitative description of jaw-closing (JC) and jaw-opening (JO) alpha motoneurons and to determine geometrical similarities and differences of the dendritic tree between the two. Seven JC alpha motoneurons and four JO alpha motoneurons were intracellularly labeled with horseradish peroxidase (HRP) in the cat and quantitatively analyzed with a computer-assisted three-dimensional system. The dendritic tree of JC alpha motoneurons was confined within the JC motor nucleus, despite locations of the cell body. In contrast, JO alpha motoneurons generated extensive extranuclear dendrites in the reticular formation. The branching pattern of proximal dendritic segments was simpler in the JC than in the JO alpha motoneurons. Despite these differences, the mean values of dendritic parameters examined per neuron were not different between the two kinds of alpha motoneurons, and the stem dendrite diameter was positively correlated with several dendritic parameters in a linear manner. The present study provides new evidence that underlying design principles of the geometry of the dendritic tree are not concerned with the differences in configuration and branching pattern of the dendritic tree of trigeminal alpha motoneurons innervating antagonistic muscles. In addition, we estimated the number of excitatory and inhibitory synapses covering dendrites of single JC alpha motoneurons.
Oromandibular dystonia (OMD) is a form of focal dystonia that affects masticatory, lower facial, and lingual muscles. We compared the clinical variables and response to treatment between patients with idiopathic jaw-closure C-OMD (n = 11) and jaw-opening dystonia O-OMD (n = 12) seen in our Movement Disorders clinic over the last 10 years. The co-existence of dystonia in other regions and sensory tricks were significantly more prevalent in O-OMD (P = 0.049 and 0.03, respectively). Male gender, orobuccolingual dyskinesias (facial grimacing, lip biting, tongue dyskinesias, platysma contractions and bruxism) and better response to botulinum toxin injections were more frequent in C-OMD but remained a trend.
Extreme animal movements are usually associated with a single, high-performance behavior. However, the remarkably rapid mandible strikes of the trap-jaw ant, Odontomachus bauri, can yield multiple functional outcomes. Here we investigate the biomechanics of mandible strikes in O. bauri and find that the extreme mandible movements serve two distinct functions: predation and propulsion. During predatory strikes, O. bauri mandibles close at speeds ranging from 35 to 64 m.s-1 within an average duration of 0.13 ms, far surpassing the speeds of other documented ballistic predatory appendages in the animal kingdom. The high speeds of the mandibles assist in capturing prey, while the extreme accelerations result in instantaneous mandible strike forces that can exceed 300 times the ant's body weight. Consequently, an O. bauri mandible strike directed against the substrate produces sufficient propulsive power to launch the ant into the air. Changing head orientation and strike surfaces allow O. bauri to use the trap-jaw mechanism to capture prey, eject intruders, or jump to safety. This use of a single, simple mechanical system to generate a suite of profoundly different behavioral functions offers insights into the morphological origins of novelties in feeding and locomotion.
Formant frequency data were gathered for four English vowels (i, ae, a, u) as produced by 15 male Caucasian subjects. There were 5 moderately articulatory disordered children aged 5.9 to 8.1 yr., 5 normal articulatory children aged 6.8 to 7.0 yr., and 5 normal adults aged 19.3 to 23.1 yr. All groups produced vowels under two conditions including with the mandible unconstrained in a normal or free condition and with the mandible fixed by a bite block. All subjects produced formant patterns within the ranges accepted for normal vowels in both jaw unconstrained and jaw fixed conditions. This finding suggests that articulation is a creative and context-sensitive behavior for normally matured, maturing, and developmentally immature systems. Also, it suggests that, if there are neurophysiological differences between groups, the vowel task is too simple to tease them out. The implication of these findings for consideration of tasks of motor equivalence is discussed.
Neural controlling mechanisms between the digastric (jaw-opening) and masseter (jaw-closing) muscles were studied in the cat. High threshold afferent impulses from the anterior belly of the digastric muscle to masseteric montoneurons in the trigeminal motor nucleus induced an EPSP-IPSP sequence of potentials with long latency, and high threshold afferent impulses from the masseter muscle also exerted a similar effect on digastric motoneurons in the same nucleus innervating the anterior belly of the digastric muscle. These results suggest that reciprocal inhibition via Ia interneurons as observed between the flexor and extensor muscles in the spinal cord does not exist between the digastric and masseter muscles in the cat. However, the respective motoneurons innervating the masseter and digastric muscles receive inputs of early excitation-late inhibition via high threshold afferent nerve fibers from each antagonistic muscle. As such, since EPSPs preceding IPSPs are recognized, these high threshold afferent impulses may exert not only a reciprocal inhibitory effect, but also a synchronous excitatory or inhibitory effect on the antagonistic motoneurons.
Development of the upper dentition in Alligator mississippiensis was investigated using a close series of accurately staged and aged embryos, hatchlings, and young juveniles up to 11 days posthatching, as well as some young and old adult specimens. Studies from scanning electron microscopy, light microscopy, acetate and computer reconstructions, radiography and macroscopy were combined to elucidate the details of embryonic dental development, tooth initiation pattern, dentitional growth, and erupted functional dentition. The results were compared with those from the lower jaw and related to the development of other craniofacial structures. Approximately 17 early teeth in each jaw half develop as surface teeth, of which 13 project for 1 to 12 days before sinking into the mesenchyme. The first three teeth initiate directly from the oral epithelium at Ferguson stages 14-15 (days 15-19 after egg laying), before there is any local trace of dental lamina formation. All other teeth develop from a dental prolamina or lamina; and with progressive lamina development, submerged teeth initiate from the aboral end leading to the formation of replacement teeth. All teeth form dentin matrix, but 12 early teeth do not form enamel. Approximately 20 embryonic teeth are resorbed, 6 are transitional, and 42 function for longer periods after hatching. The embryonic tooth initiation pattern (illustrated by defining a tooth position formula) does not support the previous models of Odontostichi, Zahnreihen, and Tooth Families, each of which postulates perfect regularity. Up to three interstitial tooth positions develop between sites of primary tooth initiation, and families with up to five generations at hatching are at first arbitrarily defined.
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.
The activities of acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) in rat masticatory motoneurones were measured. Anterior digastric (jaw-opening) and masseter (jaw-closing) motoneurones were retrogradely labelled with the fluorescent tracers nuclear yellow and bisbenzimide, respectively. The animals were pretreated with an irreversible AChE inhibitor, diisopropyl fluorophosphate, for the measurement of AChE activities. After transcardial perfusion, serial frozen sections, 20-microm thick, of the brainstem were prepared and processed for AChE histochemical analysis. Sections of 30-microm thickness were also prepared and processed for ChAT immunohistochemical analysis using anti-ChAT antibodies and the peroxidase-antiperoxidase complex. The AChE and ChAT activities in motoneurones identified by their fluorescence were determined by measuring their absorbance in the cytoplasm at 470 and 450 nm, respectively. Each of the enzymatic activities was significantly higher in the anterior digastric than in masseter motoneurones (p < 0.001, student t-test).
Analysis was made of 44 solid casts of toothless lower jaws. Stereophotogrammetry, a measurement procedure in photogrammetry, was used as a method in the measurement of solid casts. Adequate instruments and method of measurement made it possible to objectify anatomical and morphological structures of toothless lower jaws. The anterior width of the ridge in the region of canines was 22.70-35.50 mm. The posterior width in the first molars region was 43.30-59.10 mm, with statistically significant difference between the genders. The width at the level of posterior ridge of mandibular tubercle was 52.10-70.00 mm, with statistically significant difference between the genders. The length of the alveolar ridge between the symphysis and the tangent line of posterior ridge of mandibular tubercle in the medial line was 34.70-49.00 mm, without statistically significant difference between the genders. The surface of the toothless ridge is at the same time the surface of the total lower prosthesis bed. The size of the surface depended on the resorption and relation between the alveolar ridge and the surrounding active structures; it ranged between 103.21-205.50 mm2. The mean value being 145.99 mm2. The values obtained in our study are in approximate accordance with the reference literature data. They are the results of accurate measurements of solid casts.
The effect of each stimulus pulse to the digastric and masseter muscles activities was examined during the rhythmic jaw movement evoked by repetitive electrical stimulation of the cortical masticatory area and amygdala in the rabbit. The stimulus pulse evoked facilitation and suppression in the digastric muscle activity, and suppression and slight facilitation in the masseter muscle activity. No obvious difference in the pattern of the modulation was appeared between the stimulation of the anterior and posterior cortical masticatory area in the digastric muscle activity. In masseter muscle, the stimulation of the anterior cortical masticatory area showed remarkable suppression only, whereas the stimulation of the posterior cortical masticatory area evoked both suppression and facilitation. Lager motor units were received conspicuous modulation than smaller motor units in both muscles. The time course of these modulation was resembled with those of the masseteric and digastric reflexes by stimulation of the cortical masticatory area. We concluded that the modulation evoked by repetitive electrical stimulation of the cortical masticatory area might be occurred by stimulation of the same pathway as evoking the modulation of reflexes. The repetitive electrical stimulation of the amygdala induced rhythmical jaw movement. In the digastric and masseter muscles, the stimulus pulse evoked facilitation, whereas no obvious suppression was appeared. Lager motor unit was modulated remarkably than smaller unit.
A total of 125 students, aged from 6 to 18, with dysplasia of the permanent teeth were examined by a qualified pediatric stomatologist and orthodontist. Dental-jaw deformities (DJD) were established in 74.40% of all examined students. Most frequent proved to be the combination of DJD with hypomineralization in mixed dentition (34.41%) and with hypoplasia in permanent dentition--20.45% and hypomineralization--10.75%. The analysis with a view to the type of DJD revealed that the combination between dysplasias of the permanent teeth and deformities in the proportion of the jaws was most frequent (56.84%). The highest relative share of deep bite was established (27.89%) with no tendency to selfregulation in the permanent dentition. The authors underlined the necessity of follow-up care of the students with dysplasia in combination with DJD in connection with the joint therapeutic and orthodontic treatment.