imbrication
(im-brĭ-ka′shun) 1. An overlapping of the free edges of tissue in the closure of a wound or the repair of a defect. 2. A regular overlapping of a surface, such as the slight, horizontal, scalelike ridges on the cervical third of the labial surface of some anterior teeth.
The striae of Retzius are incremental growth lines seen in enamel and are the result of enamel 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. They are named after Swedish anatomist Anders Retzius.
Produced during the second stage of enamel calcification, also known as the maturation stage, ameloblasts produce matrix and enamel at the rate of 4 micrometers per day; however every fourth day there is a change in development. Brownish lines, the striae of Retzius, develop as a result of a change in the growth process. Macroscopically, these lines can be seen on the labial surface of anterior teeth as horizontal lines on the crown, aka imbrication lines.[1]
Occasional darker 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 them. The neonatal line is the darkest band, which represents the disrupted enamel formation due to the stress of being born.
The formation of the striae of Retzius results from a constriction of Tomes’ processes in conjunction with an increasing process of interrod enamel development.
Lines of Retzius: (Stria) (A) (Think Age Bands like a tree)
Artifacts in enamel (not found in dentin) created by incremental steps of Ameloblasts
Analogous to Contour Lines of Owen in Dentin
Have increased organic content and are indicative of the rhythmic variation in the calcification of the enamel matrix
They follow the appositional growth pattern
Several diagrams and photographs of these lines (and others) appears in a document published by the Max Plank Institute for Evolutionary
.
