Philias R. Garant - Oral Cells and Tissues

Nidogen Nidogen (also called entactin ) is a rod-shaped protein consisting of a single polypeptide chain, approximately 30 nm long, with globular domains at each end and one centrally located domain. 106,107Because nidogen binds with high affinity to collagen IV and laminin, it has an organizing role in assembly of the basal lamina. Nidogen also binds perlecan, the large heparan sulfate proteoglycan of the basal lamina.

The coexpression of laminin 1 and nidogen results in a relatively stable basal lamina. In general, laminin is produced by epithelial cells and nidogen by mesenchymal cells. Temporospatial differences in the expression of laminin and nidogen are thought to have significance in epithelial-mesenchymal tissue remodeling because of resulting changes in the stability of the basement membranes. 108

Basal lamina The basal lamina is a supramolecular aggregate of type IV collagen, laminin, fibronectin, nidogen, and perlecan. They form a macromolecular network with the dual function of supporting epithelial cells and providing for a permeability barrier or filter. Meyer et al 109have reviewed the role of the basal lamina in tooth development and odontoblast differentiation. The basal lamina is discussed in detail in chapter 4.

Clinical Correlation: The Human Dentition

The primary (deciduous) dentition consists of 20 teeth, five in each quadrant ( Fig 1-22). 74 , 110The permanent incisors, canines, and premolars form from successional laminae that extend lingually from the primary precursors toward the midline (see Fig 1-22). The permanent molars develop from a distal extension of the dental lamina, the accessional lamina ( Fig 1-23). Some dental embryologists consider the permanent molars to be members of the first dentition. Their microscopic successors undergo an aborted development.

Fig 1-22Developing primary teeth and the primordia of the permanent teeth in a 28-week human fetus. Maxillary quadrant. (i1) Primary central incisor; (i2) primary lateral incisor; (c) primary canine; (m1) primary first molar; (m2) primary second molar; (I1) permanent central incisor; (I2) permanent lateral incisor; (C) permanent canine; (P1) permanent first premolar; (P2) permanent second premolar; (M1) permanent first molar. (Adapted from Ooe 74with permission.)

Fig 1-23Mandibular molar region in a 159-mm fetus (at 20 weeks old), depicting the formation of the permanent first molar (M1) from a distal extension of the primordia of the primary second molar (m2). (m1) Primary first molar. (Adapted from Ooe 74with permission.)

During the development of primary teeth, the central incisor and canine are positioned labial to the lateral incisor ( Fig 1-24). This arrangement is noted very early in the formation of the enamel organ from the dental lamina. The buds of the permanent teeth have a similar position, so that the lateral incisor is positioned lingual to the central incisor and canine. During normal postnatal development, space is created in the dental arch for the alignment of all anterior teeth. Often, the space created is insufficient, and the central incisor and the canine crowd out the lateral incisor.

Fig 1-24Epithelial portion of the anterior tooth germs and adjacent structures in a 144-mm fetus. (i1) Primary central incisor; (i2) primary lateral incisor; (c) primary canine. (Adapted from Ooe 74with permission.)

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