Periodontics. Fernando Suarez

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      As in the formation of the PDL, cementum starts developing in a prefunctional stage prior to the eruption of the tooth. After the crown is formed, the cells of the inner and outer enamel epithelium that constitute the cervical loop will proliferate deeper into the ectomesenchyme driving the development of the dental root. This structure is known as the Hertwig epithelial root sheath (HERS). The most apical portion of the HERS, which encloses the dental papilla, is known as the epithelial diaphragm. Cells from the HERS induce the differentiation of the dental papilla cells in a coronoapical direction to become odontoblasts that will form the dentin of the root. The number and morphology of the dental roots will be determined by the disposition of the HERS. The cementum, the mineral portion of the root facing the PDL, is formed by cementoblasts that are believed to originate from the ectomesenchymal cells of the dental follicle after the disintegration of the HERS. Cells from the HERS produce different proteins and mediators to induce the differentiation of the dental follicle cells into cementoblasts. Fibroblasts in the area produce bundles of collagen fibrils that form fringe fibers, and these are anchored to the tooth by the deposition of a mineral matrix by cementoblasts.

      When the tooth is near to entering its functional stage, a shift in the formation of cementum can be seen from acellular extrinsic fibrillar cementum to mixed stratified cementum. The rate of growth of cementum is 1.5 to 3 µm per year.¹²

      Even though the previously described formation of cementum is the most accepted theory, an alternative hypothesis has been proposed. This theory suggests an enhanced role of the HERS in the formation of cementum through the differentiation of HERS cells to become cementoblasts.¹³

      The chemical composition of cementum is similar to bone with approximately one-third organic material, one-third mineral phase, and one-third water. The primary inorganic structure of cementum is also hydroxyapatite crystals. The organic material is composed of collagen, glycoproteins, and proteoglycans (Box 1-1).

BOX 1-1 Organic chemical composition of cementum

      GINGIVA

      The oral mucosa is composed of the mucosal tissues that cover the mouth, and it can be classified as masticatory mucosa (gingiva and hard palate), lining mucosa (alveolar mucosa, floor of the month, and internal surface of lips), and specialized mucosa (tongue). The lining or alveolar mucosa extends inside the cheeks, floor of the mouth, as well as soft palate, and it is characterized by the presence of a basal layer (which is positive to the expression of keratin 5, 14, and 19), an intermediate layer, and a superficial layer expressing keratin 13 and 4.¹⁴

      The gingiva (masticatory mucosa) is composed of free gingiva and attached gingiva, and it is characterized by the presence of keratin in the most superficial layer. Histologically, four layers of cells have been described (Fig 1-1):

      Fig 1-1 Layers of keratinized gingiva.

      1 Stratum basale, which is characterized by the expression of keratin 5 and 14

      2 Stratum spinous, named due to the spinous morphology of the cells in this layer

      3 Stratum granulosum, characterized by the presence of round cytoplasmic granules

      4 Stratum corneum with cornified cells

      Gingiva has different names and presents with slight morphologic differences depending on the tissue that it covers (ie, free gingiva or attached gingiva; Fig 1-2).

      Fig 1-2 The gingiva.

      Free gingiva

      Free gingiva is the portion of the gingival epithelium that extends from the free gingival margin to the gingival groove (see Fig 1-2). The gingival groove is defined as the “shallow linear depression on the gingiva surface that demarcates the free gingiva and the attached gingiva.”¹ The free gingiva covers the teeth at the vestibular and lingual sites following the contour of the tooth and the dental papilla. In normal conditions, the free gingiva presents as a coral pink color. The location of the gingival groove is determined by the position of the CEJ, and it is present in 4% to 54% of teeth with differences based on tooth type.^15,16

      Attached gingiva

      Attached to the tooth and/or alveolar bone, the attached gingiva is delimited by the gingival groove at the coronal end and the mucogingival junction at the apical end. In healthy conditions, it also presents with a coral pink color. A morphologic characteristic of the attached gingiva is the stippling or orange peel appearance. The stippling corresponds to small epithelial ridges and is developed in areas of high keratinization. When the attached gingiva is inflamed, it loses the superficial stippling, and the color turns to a darker red.^15,17,18

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