Causes
Occasional darker striae or grooves of Retzius result from systemic disturbances in the human body. For example, a fever can cause some lines to appear darker than those surrounding them. Normally, amelogenesis involves a period of enamel matrix formation and a rest period. In case of any disturbance, the rest periods are prolonged and occur close to one another. Consequentially, the line of Retzius appears broader and much more prominent, often presenting a brownish colour under the microscope.The neonatal line is the darkest band, which represents the disrupted enamel formation due to the stress of being born.
It is also said to occur due to periodic bending of enamel rods.
The formation of the striae of Retzius results from a constriction of Tomes' processes when the activity of ameloblasts – cells only present in laying down enamel – is narrowed in conjunction with an increasing process of interrod enamel development.
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