Mature enamel contains very little organic material. Despite its hardness, enamel can be decalcified by acid-producing bacteria acting on food products trapped on the enamel surface. This is the basis of the initiation of dental caries. Fluoride added to the hydroxyapatite complex makes the enamel more resistant to acid demineralization. The widespread use of fluoride in drinking water, toothpaste, pediatric vitamin  supplements, and mouthwashes significantly reduces the incidence of dental caries.
Enamel is produced by ameloblasts of the enamel organ, and dentin is produced by neural crest–derived odontoblasts of the adjacent mesenchyme.
The enamel organ is an epithelial formation that is derived from ectodermal epithelial cells of the oral cavity. The onset of tooth development is marked by proliferation of oral epithelium to form a horseshoe-shaped cellular band of tissue, the dental lamina, in the adjacent mesenchyme where the upper and lower jaws will develop. At the site of each future tooth, there is a further proliferation of cells that arise from the dental lamina, resulting in a rounded, cellular, budlike outgrowth, one for each tooth, that projects into the underlying mesenchymal tissue. This outgrowth, referred to as the bud stage, represents the early enamel organ (Fig. 16.10a). Gradually, the rounded cell mass enlarges and then develops a concavity at the site opposite where it arose from the dental lamina. The enamel organ is now referred to as being in the cap stage (Fig. 16.10b). Further growth and development of the enamel organ results in the bell stage (Fig. 16.10, c and d). At this stage the enamel organ consists of four recognizable cellular components:  Outer enamel epithelium, made up of a cell layer that forms the convex surface  Inner enamel epithelium, made up of a cell layer that forms the concave surface  Stratum intermedium, a cell layer that develops internal to the inner enamel epithelium Stellate reticulum, made up of cells that have a stellate ap pearance and occupy the inner portion of the enamel organ
The neural crest–derived preodontoblasts lined up within the “bell” adjacent to the inner enamel epithelial cells become columnar and have an epithelial-type appearance. They will become odontoblasts and form the dentin of the tooth. The inner enamel epithelial cells of the enamel organ will become ameloblasts. Along with the cells of the stratum intermedium, they will be responsible for enamel production. At the early stage, just before dentinogenesis and amelogenesis, the dental lamina degenerates, leaving the developing tooth primordium detached from its site of origin.
Dental enamel is formed by a matrix-mediated biomineralization process known as amelogenesis. These are the major stages of amelogenesis:
FIGURE 16.9 • Structure of young enamel. a. This electron micrograph shows enamel rods cut obliquely. Arrows indicate the boundaries between adjacent rods. 14,700. b. Parts of two adjacent rods are seen at higher magnification. Arrows mark the boundary between the two rods. The dark needlelike objects are young hydroxyapatite crystals; the substance between the hydroxyapatite crystals is the organic matrix of the developing enamel. As the enamel matures, the hydroxyapatite crystals grow, and the bulk of the organic matrix is removed. 60,000.