CTPLMABVbCT PL MA BV ccbb CTPLMABVaCT PL MA BV a BVCTPLPLMAEBV CT PL PL MA E FIGURE 16.14 • Ameloblasts in different stages of maturation. a. This black and white photomicrograph of an H&E–stained specimen shows maturation-stage ameloblasts (MA) in demineralized tissue. The maturing enamel has been lost during slide preparation, and the space below the ameloblasts previously occupied by the enamel appears empty. Maturation-stage ameloblasts with a striated border account for 80% of the cell population in the maturation zone. BV, blood vessels; CT, connective tissue; PL, papillary layer. 650. b. This photomicrograph shows smooth-ended maturation-stage ameloblasts (MA), which account for 20% of the cell population in the mature zone. At the basal pole of the ameloblasts are the cells of the papillary layer (PL). A layer of stratum intermedium is no longer present during this stage of ameloblast maturation. 650. c. Colorized scanning electron micrograph of freeze fracture section of the tooth shows layer of smooth-ended maturation-stage ameloblasts (MA, green) on the enamel surface (orange). During slide preparation apical surfaces of ameloblasts were detached from the enamel. Basal surface of ameloblast is attached to connective tissue (CT) containing blood vessels  1,300. (Part C from SPL / Photo Researchers, Inc, with permission.) processes elongate; the longest are surrounded by the mineralized dentin. In newly formed dentin, the wall of the dentinal tubule is simply the edge of the mineralized dentin. With time, the dentin immediately surrounding the dentinal tubule becomes more highly mineralized; this more mineralized sheath of dentin is referred to as the peritubular dentin. The remainder of the dentin is called the intertubular dentin.
FIGURE 16.15 • Electron micrograph of Sharpey’s fibers.
Sharpey’s fibers extend from the periodontal ligament (right) into the cementum. They consist of collagen fibrils. Sharpey’s fibers within the cementum are mineralized; those within the periodontal ligament are not mineralized. 13,000.
The dental pulp cavity is a connective tissue compartment bounded by the tooth dentin.
The central pulp cavity is the space within a tooth that is occupied by dental pulp, a loose connective tissue that is richly vascularized and supplied by abundant nerves. The pulp cavity takes the general shape of the tooth. The blood vessels and nerves enter the pulp cavity at the tip (apex) of the root, at a site called the apical foramen. (The designations apex and apical in this context refer only to the narrowed tip of the root of the tooth rather than to a luminal (apical) surface, as used in describing secretory and absorptive epithelia.)
The blood vessels and nerves extend to the crown of the tooth, where they form vascular and neural networks beneath and within the layer of odontoblasts. Some bare nerve fibers also enter the proximal portions of the dentinal tubules and contact odontoblast processes. The odontoblast processes are believed to serve a transducer function in transmitting stimuli from the tooth surface to the nerves in the dental pulp. In teeth with more than one cusp, pulpal horns extend into the cusps and contain large numbers of nerve fibers. More of these fibers extend into the dentinal tubules than at other sites. Because dentin continues to be secreted throughout life, the pulp cavity decreases in volume with age.