Childhood stress can interfere with the development of the teeth to the extent that a traumatic experience leaves a recognisable line in the tooth enamel that remains as a record of past traumas.
I discovered this when reading about a study published in the Annals of the New York Academy of Sciences [pdf] that used these lines to compare the number of childhood traumatic experiences that occured in people diagnosed with schizophrenia and healthy controls.
New approaches to the problem of estimating stress during early brain development are required. In this regard, human enamel has promise as accessible repositories of indelible information on stress between gestation and the age of 13. Stressful experiences induce long-term activation of the sympatho-adrenal system, slowing of tropic [growth-related] parasympathetic functions, and they then induce disrupted secretion of the enamel matrix.
During the brain development (in infancy, childhood and preadolescence), ameloblast activity in human enamel is slowed during 1 to 2 days of extreme stress, and the segment of enamel rods is smaller and often misshapen, making a particular dark line seen by the use of a microscope (we referred this line to Pathological Stress Line, PSL in short). Retzius reported that this line is incremental lines reflecting the layered apposition of enamel during amelogenesis (Retzius, 1937), and after that this line is termed the Retzius line. The line is conceptually akin to tree rings which are markers of environmental adversity in the tree’s life.
Schizophrenia was once thought to be largely caused by genetic factors, but in the last decade a number of studies have shown that childhood trauma contributes to the chance of developing the disorder.
One difficulty with this type of research is that it often relies on people remembering back to their childhood after the onset of psychosis, which could mean that the memories aren’t perfectly reliable in some cases.
Stress-induced lines in tooth enamel are one way of looking at the link between trauma and schizophrenia that doesn’t rely on potentially hazy memories of the past.