1. Date of download: 5/30/2016 Copyright © 2016 McGraw-Hill Education. All rights reserved. Stages in crown development. A. Dental lamina stage. Localized bands of proliferating cells in the basal layer of the stratified oral epithelium, peripheral to the developing tongue, form two (one per jaw) horseshoe-shaped epithelial ridges, or dental laminae, over the mesenchyme of the future mandibular and maxillary arches. B. Bud stage. Stimulated by local clusters of neural crest–derived mesenchyme cells, proliferation increases in the base of each dental lamina at the 10 sites of future deciduous teeth. These epithelial tooth buds enlarge and bulge into the underlying mesenchyme. C. Early cap stage. With further proliferation, the deep bud surfaces invaginate and widen to form solid caps over mesenchymal clusters. In the cap's core, the cell density decreases as internal cells become stellate and the interstices accumulate tissue fluid. The peripheral cells, which contact the basal lamina, form a simple epithelial shell and continue to divide, increasing the cap's size. A stalk of dental lamina connects each cap to the oral epithelium. The mesenchyme under the cap proliferates and condenses, indenting the cap's base. D. Late cap stage. Mesenchyme within the indentation forms the dental papilla, further indenting the cap's base. The epithelial cells over the papilla (inner enamel epithelium) become columnar, whereas those forming the rest of the shell (outer enamel epithelium) remain low cuboidal. The stellate cells and fluid inside the shell make up the stellate reticulum. Between the stellate reticulum and the inner enamel epithelium lies a layer of epithelial cells called the stratum intermedium. Together, the inner and outer epithelia, stratum intermedium, and stellate reticulum constitute the enamel organ. The outer enamel epithelium is continuous with the narrowing stalk of the dental lamina; this gives rise to another tooth bud that will subsequently form a permanent tooth (IV.F). E. Bell stage. As the cap grows, the indentation deepens, the inner enamel epithelium expands around the enlarging papilla, and the developing tooth becomes bell- shaped. Mesenchyme cells near the inner enamel epithelium condense, differentiate into a layer of columnar odontoblasts, and begin forming predentin. Mesenchyme in the papilla's core forms the dental pulp. Columnar cells of the inner enamel epithelium differentiate into ameloblasts and begin producing enamel soon after the dentin begins to calcify. After the enamel layer is complete, the ameloblasts shorten and become inactive. The ringlike junction of the inner and outer enamel epithelium at the rim of the bell is termed the cervical loop. Capillaries indent the outer enamel epithelium, and it loses its connection with the oral epithelium as the dental lamina degenerates. (Revised and redrawn, with permission, from Warshawsky H. The teeth. In: Weiss L, ed. Histology: Cell and Tissue Biology. 6th ed. New York: Elsevier; 1988.) Legend : From: Chapter 15. Digestive Tract Histology & Cell Biology: Examination & Board Review, 5e, 2010 From: Chapter 15. Digestive Tract Histology & Cell Biology: Examination & Board Review, 5e, 2010