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Striae of Retzius

The striae of Retzius are incremental growth lines seen in enamel and are results of enamel's development. When viewed microscopically in cross-section, they appear as concentric rings. In a longitudinal section, they appear as a series of dark bands. The presence of the dark lines is similar to the annual rings on a tree.

Darker lines in the striae of Retzius result from systemic disturbances in the human body. For example, a fever can cause some lines to appear darker than those surrounding it. The neonatal line is the darkest band which represents the enamel formed before and birth.

The formation of the striae of Retzius result from a constriction of Tomes' processes in conjunction with an increasing process of interrod enamel development.