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connective tissue, the lamina propria, and a thick, mostly parakeratinized or keratinized epithelium. The lamina propria provides a firm attachment for the tooth by the orientation of its fibers, which radiate from the tooth and encircle it. Its function is to resist the mechanical forces of mastication. The epithelium encircles the tooth like a collar or cuff and is actually attached to the tooth's surface by a layer of mucopolysaccharides. The epithelium, which is called either the epithelial attachment or the attached epithelial cuff, seals the dentogingival junction, preventing the invasion of bacteria, their toxins, and the products of food decay.

The dentogingival junction is formed as the tooth erupts, and its location on the tooth's surface depends upon the tooth's stage of eruption. Before the tooth erupts, its entire enamel surface clown to the cementoenamel junction is covered with a thin membrane, called the reduced dental epithelium, which is organically attached to the enamel. As the tip of the crown nears its emergence point, this thin mem-

brane fuses with the oral epithelium, and the epithelium over the emergence point degenerates. As the crown erupts through this defect, the attached epithelium is gradually separated from its surface. The shallow groove marking the separation point of the epithelial attachment from the tooth is the gingival sulcus.

As the tooth continues to erupt, more of the attached epithelium separates from the enamel, and the dentogingival junction shifts further away from the tip of the crown. The shift of this junction to-ward the cementoenamel junction is fairly rapid until the tooth reaches its occlusal plane. At this stage, the end of active eruption of the tooth, about one-third to one-fourth of the enamel crown is still covered by the gingiva (Fig. 3-17). Further expo-sure of the tooth brought about by wear is gradual and may take many years. Because external forces help determine the duration of this stage, it is called passive eruption.

As wear continues, the gingiva recedes and more

Fig. 3-18. The level of the gingival sulcus may vary around the same tooth, as shown in these three sections. EA, Epithelial attachment; E, enamel. (From Sicher, H., editor: Orban's oral histology and embryology, ed. 6, St. Louis, 1966, The C. V. Mosby Co.)