Appearance
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.
In the longitudinal section of a tooth. these lines appear near the dentin. They bend obliquely near the cervical region. They curve occlusally near the cuspal regions or the incisal regions.
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 or lip side of anterior or front teeth as horizontal lines on the tooth crown, also known as "imbrication lines" .
Evenly spaced Retzius lines indicate a 6-11 day cycle of enamel formation.
Read more about this topic: Striae Of Retzius
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—Mason Cooley (b. 1927)
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—Bible: Hebrew, 1 Samuel 16:7.
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—Aldous Huxley (1894–1963)