Dental Enamel Development: Proteinases and Their Enamel Matrix Substrates

Figure 1

Ameloblast changes during enamel formation. The epithelial cells of the inner enamel epithelium (1) rest on a basement membrane containing laminin. These cells increase in length and become differentiating ameloblasts above the predentin matrix (2). Presecretory ameloblasts send processes through the degenerating basement membrane as they initiate the secretion of enamel proteins on the villous surface of mineralizing dentin (3). After establishing the dentin-enamel junction and mineralizing a thin layer of aprismatic enamel, secretory ameloblasts develop a secretory specialization or Tomes’ process. Along the secretory face of the Tomes’ process, in place of the absent basement membrane, secretory ameloblasts secrete proteins at a mineralization front where the enamel crystals grow in length (4). Each enamel rod follows a retreating Tomes’ process from a single ameloblast. At the end of the secretory stage, ameloblasts lose their Tomes’ process and produce a thin layer of aprismatic enamel (5). At this point, the enamel has achieved its final thickness. During the transition stage, the ameloblasts undergo a major restructuring that diminishes their secretory activity and changes the types of proteins secreted (6). KLK4 is secreted, which degrades the accumulated protein matrix. During the maturation stage ameloblasts modulate between ruffled and smooth-ended phases (7). Their activities harden the enamel layer. The histology of the developing tooth was adapted from The histology of the developing tooth was adapted from Uchida et al. Arch Histol Cytol 54:527-538, 1991 and the schematic plus tooth was published in: Hu et al., Cells Tissues Organs 186:78-85, 2007. DOI: 10.1159/000102683.