Physiological properties of the neurons responding to canine tooth pulp stimulation (tooth pulp-driven neurons : TPDNs) were studied by recording single unit activities from the primary somatosensory cortex (SI) in cats anesthetized with α-chloralose. Analysis was focused on the TPDNs receiving excitatory converging inputs from the whisker pad and/or masseteric nerve with special reference to the interaction among these inputs. The results are as follows: (1) Twenty-seven of 51 TPDNs in SI (530) were convergent type neurons. (2) Convergent type TPDNs showed the following characteristics in relation to conditioning and test stimuli applied to the tooth pulp and other peripheral sites: a) When supra- or subthreshold conditioning stimuli were applied to the whisker pad and test stimuli to the tooth pulp, the number of spikes evoked by the test stimuli was decreased. Suprathreshold conditioning stimuli produced a greater decrease than subthreshold ones. On the contrary, no effects were seen when the sites of conditioning and test stimuli were reversed. b) Suprathreshold conditioning stimuli applied to the masseteric nerve exerted no effects on the number of spikes evoked by the tooth pulp test stimuli, whereas it was decreased in the reverse combination of conditioning and test sites. These results suggest that TPDNs in SI play an important role both in the recognition of the sites being stimulated and in processing other pain information, including the referred pain.
Repetitive stimulation of a certain area in the cerebral cortex in the monkey, cat, rabbit and guinea pig is known to induce a rhythmical jaw movement (RJM) accompanied by a coordinated tongue movement as well as salivation. The response is so closely similar to the natural masticatory movement that such a cortical area is called the cortical masticatory area (CMA) . In the cat, the CMA corresponds with the rostral part of the orbital gyrus. The present study was carried out to examine the role of the CMA by making quantitative analyses of the correlation between the unit activity pattern of the CMA neurons and the parameters of the jaw movement during the natural mastication in the unanesthetized chronic cat. The single unit activity was recorded from 134 neurons in the rostral part of the orbital gyrus during the natural masticatory movement. Thirty-two of them showed spike firing related to some aspects of the RJM, but none of them responed with antidromic spikes to the stimulation of the ipsilateral cerebral peduncle. Thirteen neurons changed the firing rate (FR) rather tonically during the natural masticatory movement (non-phasic group) and 12 neurons increased the FR throughout the series of the masticatory strokes (increase type), while 1 neuron decreased the FR during the initial masticatory strokes (decrease type) . The change in the FR started preceding the onset of the RJM by 500-1, 000 ms. The remaining 19 neurons rhythmically modulated the FR at the same rhythm as the RJM (phasic group) and 9 neurons attained the highest FR in the jawopening (JO) phase (opening type), while the other 10 neurons attained it in the jaw-closing (JC) phase (closing type) . The instantaneous firing frequency (IFF) of the 4 opening type neurons showed a positive correlation with the velocity of the JO movement and in 3 of them it was also positively correlated with the jaw position in the JO phase. In 2 of these neurons, one neuron showed also a positive correlation with the jaw position in the JC phase, while the other neuron showed also a negative correlation with both the velocity and jaw position in the JC phase. The IFF of other 2 neurons showed a positive correlation with the jaw position in only the JC phase and another 1 neuron showed a negative correlation only with the velocity of the JC movement. The IFF of each of the 2 closing type neurons showed either a negative or a positive correlation with the jaw pesition in the JC phase. The latter neuron showed also a positive correlation with the jaw position in the JO phase. The IFF of other 2 neurons showed a negative correlation with the velocity of the JO movement. The results suggest that there are neurons in the rostral part of the orbital gyrus of the cat, which participate in the initiation and/or execution of the masticatory jaw movement.
Synaptic basis of the rhythmical activity induced by repetitive stimulation of the masticatory area of the cerebral cortex was studied by intracellular recording from hypoglossal motoneurons in cats, with the following results: (1) Repetitive cortical stimulation induced rhythmical tongue movements coordinated with rhythmical jaw movements. After the animal was paralyzed, the cortical stimulation still induced a rhythmically alternating efferent burst activity in the medial and lateral branches of the hypoglossal nerve; the bursts in the medial and lateral branches were in and out of phase with that of the digastric nerve, respectively. (2) In all of the recorded 36 hypoglossal motoneurons, repetitive cortical stimulation induced a rhythmical depolarizing potential superimposed by spike bursts corresponding with the rhythmical efferent burst in the hypoglossal nerve. No hyperpolarizing potential was present between the consecutive depolarizing potential. (3) Synaptic activation noise was increased coincidentally with the depolarizing potential, indicating that EPSPs were involved in the generation of the depolarizing potential. By intracellular application of either DC current or Cl-, no evidence was obtained for existence of IPSPs during the inter-excitatory phase. It was concluded that rhythmical bombardment of excitatory impulses to hypoglossal motoneurons was responsible for their rhythmical activity induced by repetitive stimulation of the cortical masticatory area.
The effect of the system speed on the radiographic performance by seven dentists reading the positions of the endodontic file in the root canal and of the root apex was studied. Two nonscreen dental films and four screen-film combinations, whose relative speeds ranged between 1 and 40, were used. The results showed that the differences from the true positions and the standard deviations of the seven performances were relatively small and both ranged between 0.2 and 0.3mm for the root apex and 0.1 and 0.8mm for the file tip, depending on the system speed. The components of the variance associated with the position of the file tip and root apex were compared for the effects of speed and dentists. The variances associated with the speed were five times and twice larger compared to those observed among the dentists for the file tip and root apex, respectively. These findings indicated that a substantial reduction in the exposure would have a relatively small effect, although the diagnostic accuracy depends on the system speed and diagnostic task.
In order to understand the phylogenetic change of the jaw movement mode of the mammals, it is quite necessary to define the neuromuscular mechanism relative to the feeding habit proper to the toothless animals (e. g. Pangolin) . Three specimens were examined. The serial celloidin frontal and horizontal sections, 30 to 40μm thick, were stained with hematoxylin and eosin. 1. The masseter arises from the incomplete zygomatic arch, consisting of the maxillary bone, connective tissue cord and squamosal bone. It passes downwards and backwards to the cylindrical jaw bone (to the neck of the condyle) . The muscle is composed of 2 bellies, the superficial and profound, which contain 48 muscle spindles (52%) and 34 spindles (36%), respectively. 2. The temporalis is rudimentary, composed only of the small vertical belly, arising from the posterior part of the zygomatic arch and the wall of the temporal fossa, being inserted into the jaw above the mandibular foramen. It contains 11 spindles (12%) . 3. The pterygoideus lateralis arises from the wall of the infratemporal fossa. It passes backwards and is inserted into the condyle, forming two heads. It is devoid of spindles. 4. The pterygoideus medialis is absent. 5. The intermandibularis is well developed, forming the floor of the mouth and extending backwards beyond the TMJ. It is devoid of spindles.
Developmental changes of the buccal teeth segments on the longitudinal dentitions during the period of buccal teeth exchange and the factors having effect on their dimensional changes were investigated by using three groups: normal group, group with good alignment in spite of the premature loss of the second deciduous molar and the group resulting ultimately in bad alignment. The dimensional changes were observed as the positional changes of each buccal teeth, first permanent molars and permanent lateral incisors on the three dimensional coordinate, which was defined by the rugae, median raphe and papilla on the palate of the plaster model. As the result, the increment of the buccal arch segment placed between the permanent lateral incisor and the first permanent molar occurred mainly by the eruption of the permanent canine as well as of the first premolar in consequence of the forward and mesial migration of the permanent lateral incisor and in some cases backward migration of the first permanent molar by the eruption of the first premolar caused by the eruptive force of these permanent teeth. The decrement, on the contrary, was observed mainly by the eruption of the second premolar with the large forward migration of the first permanent molar. In the cases with a premature loss of the second deciduous molars, the increment of the segmental dimension was observed by the eruption of the second premolar, contrary to the normal group.