 FOLDER 16.3 Clinical Correlation: Dental Caries aabba b EEEEDDDDEE CLCLCL D D DDD FIGURE F16.3.1 • Photomicrographs of carious lesions. a. Photomicrograph of an unstained ground section of a tooth showing a carious lesion (CL) that has penetrated the entire thickness of the enamel (E) and spread laterally at the amelodentinal junction. D, dentin. b. The lesion here is more advanced. The enamel (E) has been undermined and weakened, causing fracture and a resulting cavity. At this point, bacteria can invade and penetrate down the exposed dental tubules, resulting in destructive liquefaction foci in the dentin (D) and, ultimately, exposure of the pulp. 16. (From Eveson JW, Scully C. Color Atlas of Oral Pathology. London: Times Mirror International Publishers, 1995.) major salivary glands are distinguished. Thus, three types of acini are described:  Serous acini, which contain only serous cells and are generally spherical Mucous acini, which contain only mucous cells and are usually more tubular  Mixed acini, which contain both serous and mucous cells. In routine H&E preparations, mucous acini have a cap of serous cells that are thought to secrete into the highly convoluted intercellular space between the mucous cells. Because of their appearance in histologic sections, such caps are called serous demilunes [Fr., half-moon].
Serous demilunes are artifacts of the traditional fixation method.
As noted above, each mixed acinus, such as those found in the sublingual and submandibular glands, contains serous and mucus-producing cells. In routine preparation for both light and electron microscopy, serous cells have traditionally been regarded as the structures that make up the demilune. Recent electron microscopic studies now challenge this classic interpretation of the demilune. Rapid freezing of the tissue in liquid nitrogen, followed by rapid freeze substitution with osmium tetroxide in cold acetone, reveals that both mucous and serous cells are aligned in the same row to surround the lumen of the secretory acinus. No serous demilune is found. Sections prepared from the same specimen by conventional methods show swollen mucous cells with enlarged secretory granules. The serous cells form typical demilunes and are positioned in the peripheral region of the acinus with slender cytoplasmic processes interposed between the mucous cells. These findings indicate that the demilune observed in light or electron microscopy is an artifact of the routine fxation method (Fig. 16.22). The process of demilune formation can be explained by the expansion of mucinogen, a major component of secretory granules, during routine fixation. This expansion increases the volume of the mucous cells and displaces the serous cells from their original position, thus creating the demilune effect. A similar phenomenon is sometimes seen in the intestinal mucosa, in which swollen goblet cells displace adjacent absorptive cells.
FIGURE 16.21 • Diagram comparing the components of the salivon in the three major salivary glands. The four major parts of the salivon–the acinus, intercalated duct, striated duct, and excretory duct—are color-coded. The three columns on the right of the salivon compare the length of the different ducts in the three salivary glands. The red-colored cells of the acinus represent serous-secreting cells, and the yellow-colored cells represent mucus-secreting cells. The ratio of serous-secreting cells to mucus-secreting cells is depicted in the acini of the various glands.
Serous cells are protein-secreting cells.
Serous cells have a pyramidal shape, with a relatively wide basal surface facing the basal lamina and a small apical surface facing the lumen of the acinus. They contain large amounts of rER, free ribosomes, a prominent Golgi appara-