Enamel Organ and Matrix Development

Teeth develop from tooth buds, an aggregation of cells derived from the ectoderm of the first branchial arch and ectomesenchyme of the neural crest. The tooth bud is divided into enamel organ (EO), dental papilla (DP), and dental follicle. An enamel organ has four layers outer and inner enamel epithelium, stratum intermedium (SI), and stellate reticulum (SR). The inner enamel epithelium induces the development of odontoblasts from the opposing mesenchymal cells of the dental papilla. As dentin forms, the inner enamel epithelium becomes converted to ameloblasts (Fig. 9.9). 

The ameloblasts develop a tall columnar shape in which the nuclei move toward the stratum intermedium. On the dentinal side, a Tome s process appears and enamel matrix is 

A portion of the dental papilla (DP) shows odontoblasts (Ob) adjacent to early dentine (D). E enamel, DF dental follicle outside the outer epithelium, AB alveolar bone. Scale bar = 70 pm (From Fig. 1 in Cerri PS, de Faria FP, Villa RG, et al. (2004) Light microscopy and computer three-dimensional reconstruction of the blood capillaries of the enamel organ of rat molar tooth germs. Journal of Anatomy 204 191-195. 

With copyright permission from Wiley-Blackwell, PO Box 805, 9600 Garsington Road, Oxford OX4 2DQ, UK) 

Finally, the ameloblasts secrete an unusual basal lamina, which partially mineralizes into the surface enamel crystals, the enamel cuticle. By this time, the enamel organ has shrunk so that its outer layers have merged with the ameloblast layer at the completed enamel surface postmaturation stage). This reduced enamel epithelium is rubbed off as the teeth erupt, but the enamel cuticle is abraded more slowly and gradually replaced by proteins from saliva, the acquired pellicle (Sect. 12.1.3). 

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