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The objectives of this study were to observe with the electron microscope ( a ) the epithelial cell types found in the neck and isthmus of the gastric fundic gland of the rat, and ( b ) the effects of hypuphysectomy on the gland. The following cell types were distinguished in the neck of the fundic gland of the rat: nondifferentiated cell, immature surface cell, mucous neck cell, and neck parietal cell. In the normal gland, these cell types resembled each other in the possession of a ground cytoplasm and nucleoplasm of low density, a poorly developed endoplasmic reticulum, few mitochondria and numerous free ribosomes. The most important structural difference between mucous neck and immature surface cells was the contrasting density of the secretory granules; both cell types differed from the nondifferentiated cell primarily in the presence of their characteristic secretory granules. The neck parietal cell appeared to be a developmental form between the immature surface cell and the mature parietal cell. No changes were observed in these cells to result from hypophysectomy.Hypophysectomy caused marked involutional changes in the chief cell which involved mainly the organelles most directly concerned with protein synthesis, i.e., the ergastoplasm and Golgi apparatus. These effects were correlated with the loss of basophilia and secretory granules and with the reduction in cell size and capacity to secrete pepsinogen which were described previously. In contrast, the parietal cell, which is concerned with electrolyte transport, was affected much less.

In situ remineralization of early enamel lesions by a fluoride chewing gum was studied. Human enamel specimens with subsurface lesions were mounted in removable lower appliances for 6 adults. Subjects used a F-free dentifrice 3 ×/day and chewed five sticks/day for the F gum group (0.1 mg F/stick) or five sticks of sugarless gum. No gum was chewed for controls. Surface microhardness was performed on: (1) sound enamel; (2) lesions; (3) after intraoral exposure, and (4) after acid-resistance testing (ART). Separate specimens were etched and measured for F uptake and image analyses on microradiographs were performed for all regimens. ΔZ values were calculated and converted to percent of mineralization. Values for F gum were significantly higher (p > 0.05) than non-F gum and controls for ART, percent remineralization, and F uptake up to 70 μm depth.

The purpose of this investigation was to study the nerves in mouse molar teeth during their development to observe their distribution and their relationship to the odontoblast and its process. The specimens were first assessed by light microscopy using silver staining techniques. It was found that by nine days after birth, major nerves appeared in the pulp organ and extended to the basal region of the odontoblasts. At 15 days, a subodontoblastic neural plexus had developed, and by 25 days, isolated nerves penetrated into the predentin of the pulpal horns. From 25-70 days, a highly organized subodontoblastic plexus was apparent with branches extending into the odontoblastic layer, predentin and inner dentin.Ultrastructural study revealed small, nonmyelinated nerves at the basal region of the odontoblasts by nine days. Both myelinated and small, nonmyelinated nerves appeared in the subodontoblastic plexus. Small nerves closely associated with the odontoblastic process were found within the predentinal tubules by 25 days. These processes contained occasional mitochondria, numerous microvesicles and small dark granules. From 35-50 days of age, similar nerves which exhibited alternate constrictions and dilations along their lengths were found in the tubules of circumpulpal dentin. By 60 days, both Schwann cell covered and naked axons appeared among the odontoblasts, and by 70 days Schwann cell covered axons appeared in predentin.The pattern of development of pulpal nerves has been observed by light microscopy in silver impregnated sections of teeth by Arwill ('58), Fearnhead ('57, '61), Kubota et al. ('60) and Bernick ('59a). Arwill ('58) utilized both silver and iron trioxyhematoxylin staining and observed no nerve fibers in developing dentin of 13-32 week old human fetuses nor in mineralized dentin of erupted human permanent teeth. A few nerve fibers were observed in predentin of the erupted teeth, but such fibers did not appear intratubular in location. Fearnhead ('57) reported that the subodontoblastic nerve plexus did not appear until root formation was nearly complete, and that innervation of coronal dentin followed only after the tooth had been in functional occlusion for several years.Occasional nerve fibers in the predentin of human teeth have been reported by Fearnhead ('57, '61), Rapp et al. ('57 ('59b, '64). Fearnhead ('57) noted that small intratubular nerves about 0.2 in diameter extended through the predentin and into the dentin for a short distance. In no instance were such nerves found to traverse the entire thickness of the dentin or terminate near the dentino-enamel junction. On the other hand, Stella and Fuentes ('65) reported intratubular nerves which terminated in the peripheral dentin. However they used iron hematoxylin which is a nonspecific stain for neural elements.More recently, the increased magnification and resolution of the electron microscope have yielded further information concerning intradentinal nerves. Frank ('68b) identified intratubular nonmyeli- nated nerve fibers appr...

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