In order to examine the functional significance of intraoral somatosensory input to the cerebral cortex, I studied the cortical projections of tongue and periodontal neurons in the VPM of the cat.
Experiments were carried out on cats anesthetized with urethane and chloralose. Single unit activities were recorded from the thalamus using glass capillary microelectrodes filled with 2% pontamine sky blue in 0.5M sodium acetate. The lingual nerve was stimulated electrically and the chorda tympani was cut to exclude gustatory input.
Cortical potentials evoked by electrical stimulation to the lingual nerve were recorded from SI, SII and SIII of the somatosensory areas, and a part of the gyrus coronalis. Neurons activated by the innocuous mechanical stimulation of intraoral structures were located in the lateral subdivision of the nucleus ventralis posteromedialis parvocellularis (VPMpcl) and the medial part of the VPM proper. Neurons in the VPMpcl responded primarily to the tongue, ipsilateral to the recording site, whereas those in the VPM proper responded to contralateral intraoral structures.
Neurons in the VPMpcl, as well as those in the VPM proper of the SI, were antidromically excited by electrical stimulation of the gyrus coronalis. Repetitive electrical stimulation of the gyrus coronalis induced jaw opening movements resembling mastication.
These experiments indicated that there are projections from the VPMpcl and the VPM proper to the cerebral cortex, and suggested that somatosensory inputs from intraoral structures play an important role in masticatory control.

View full abstract

We cultured 200 strains of human pulpal fibroblasts (HPF), and found two types (HPF-1 and HPF-2), which showed a different response in alkaline phosphatase (ALPase) activity for 1,25(OH)₂D₃.
HPF and human gingival fibroblasts (Gin 1) were cultured for varying time periods in Dulbecco's modified Eagle medium supplemented with 10% fatal calf serum or a conditioned medium obtained from HPF, and the cell proliferation, protein content and alkaline phosphatase activity were measured. In addition, fibroblast chemotaxis induced by the conditioned medium was measured by the membrane filter method.
The daily dynamic course of HPF-1 proliferation was more active than that of HPF-2, and higher levels of spontaneous ALPase activity were observed. When cultured with 1,25(OH)₂D₃, ALPase activity was 5 times higher for HPF-1 and more than 10 times higher for HPF-2. However, there was no increase in activity when Gin 1 was cultured with 1,25(OH)₂D₃.
When cultured with the conditioned medium, HPF-1 proliferation increased markedly, followed by HPF-2 and Gin 1. However, there was no difference in total protein content among the three cell strains. ALPase activity in HPF-1 increased twofold with addition of the conditioned medium, while that of HPF-2 increased 3.5-5 fold that of the control. In addition, the conditioned medium induced the same levels of chemotactic migration for all three cell strains.
These data suggest that when cultured in 1,25(OH)₂D₃, the ALPase activity of human pulpal fibroblasts is more sensitive than that of human gingival fibroblasts. Furthermore, there are more than two types of fibroblasts in pulpal tissue, and they are different not only in their ALPase activity when cultured with 1,25(OH)₂D₃, but also in the ratio of cell proliferation and protein synthesis. These different and specific qualities may be significant in the defense of pulpal tissue against various foreign stimuli.

View full abstract

Intraoral fluoride releasing devices (IFRD) can maintain a low fluoride concentration in saliva, permitting effective action of the fluoride on the enamel. Fluoride released from the IFRD has two mechanisms of action. The first is exposure of the enamel to fluoride prior to demineralization and the second is the continuous exposure during the demineralization process. This study investigated the effect of fluoride exposure on acid solubility of enamel especially during the demineralization process.
The fluoride concentrations tested were 0.3ppm, 1.0ppm, 10.0ppm, and 100.0ppm. These are concentrations which can manitained by IFRD. Enamel slabs prepared from bovine permanent incisors were immersed in various fluoride solutions for 30, 60 and 90 days and then dissolved in acetate buffers having various fluoride concentrations. The dissolved calcium was measured and the demineralized enamel slabs were analyzed with X-ray microanalysis and X-ray diffractometry. The distribution of fluoride in the demineralized enamel was measured by the abrarive method.
The results were a follows :
1. The acid solubility of the enamel decreased with an increase in the fluoride concentration in demineralizing solution.
2. Fluoride uptake in the enamel during demineralization increased with an increase in the fluoride concentration in the demineralizing solution.
3. Calcium fluoride was deposited on the suface of the enamel demineralized by acetate buffer with 100.0ppm fluoride.
4. The combination of fluoride in the immersing and demineralizing solutions was very effective in reducing the acid solubility of the enamel.

View full abstract

We performed a computer analysis of the pulpal threshold of pain predicted for thermal stimuli (cold air and intake of hot and cold foods) using the finite element method. The correlation of pulpal pain was studied in the mandibular second primary molar for various restorative materials for point application of thermal (hot and cold) stress to the restorative material and tooth, with changes in the depth of the cavity preparation and thermal conductivity of the restorative material.
1. Our computer simulation showed that hot stimuli applied to the occlusal surface produced pain at 56℃ and cold stimuli at about 21℃. The pain occurred near the pulp horn.
2. We found that restorative materials with lower thermal conductivity induced less pulpal pain for the same thermal stimuli. This was true for both shallow and deep cavity preparations.

View full abstract

Two cases of myxofibroma arising from mandibular gingiva were studied ultrastructurally and cytochemically. Tumors were histologically composed of stellate or spindle cells associated with the mucous substances in the matrix. Two types of cells, pale and dark ones, were identified by electron microscopy. The pale cells contained several mitochondria, r-ER and Golgi apparatuses while the dark ones had very few organellae.
We concluded that the pale cells were secretory cells of mucous substances due to their positive alkaline phosphatase activity.

View full abstract