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The secret lives of baby teeth

Why some are trying to discover more about our bodies’ “little living archives.”

Getty Images; illustration by Amanda Northrop/Vox

Part of the Memory Issue of The Highlight, our home for ambitious stories that explain our world.

Erin Dunn gets baby teeth in the mail, sent by volunteers from across New England. Each tooth arrives at her lab in a tube packed with fluffy cotton balls, usually clean but sometimes flecked with dried blood. Dunn, a psychiatric epidemiologist at Massachusetts General Hospital who brands herself as “the science tooth fairy” to appeal to kids and encourage them to donate their baby teeth for a scientific study, then hands them over to Felicitas Bidlack, a specialist in tooth development at the Forsyth Institute, an oral health research center.

Bidlack inspects each one, noting any coloring, grooves, chips or cracks. She uses X-rays and CT scans to look inside their layers to measure enamel thickness, mineral density, and other characteristics before she slices each one.

Anthropological studies have shown connections between tooth growth patterns and physical stressors such as illnesses or injuries, and a few studies in the life sciences have shown that traces of toxins or pesticides can embed in baby teeth, which could make teeth useful biomarkers for assessing harmful exposures during childhood.

Dunn, Bidlack, and others like them want to know whether the enamel layers could also reveal a record of childhood trauma or adversity. They’re part of a cadre of scientists who are trying to decode the memories recorded in our chompers. If they do, doctors could analyze baby teeth as children lose them, learning about their psychological and social hardships to ensure children are on track for healthy development. In a recent study in JAMA Network Open, Dunn’s and Bidlack’s group found some preliminary support for the idea that teeth could provide a record of stressful psychosocial experiences — events in the home or community that influence mental health and behavior — during early development in particular.

Dunn’s work in the field began fairly recently, after she gave a talk on child development at Brown University and later vented to a colleague about the lack of objective, rigorous measures of adverse childhood experiences. After a pause, that colleague asked Dunn if she had thought to look into teeth, as anthropologists have done. Maybe psychological and emotional memories could be encoded not just in the brain, but in teeth, too.

Dunn immediately dove into the anthropological and archaeological literature about teeth. “What blew me away is that no one had really pieced together the different fields,” said Dunn, and tried to see whether teeth could be a biomarker for childhood traumas. “They might be able to help solve a major problem that we have in the field of childhood adversity.” When Bidlack heard about Dunn’s interests from a colleague, the idea that teeth might record traumas piqued her interest; the two decided to work together to determine the extent of teeth’s record-keeping capabilities.

“When we have intense psychological experiences or stressors, our bodies react,” Bidlack said. “In trauma, that response can get ingrained into your physiology,” for example, by influencing brain development and leaving a mark on our DNA. “Why would it not be in teeth?”

Baby tooth formation begins before birth. Cells build the tooth enamel layer by layer in a daily cycle, depositing prisms of tightly packed crystalline rods that make up the enamel. “It’s like a clock that starts ticking, and it continues throughout the formation of each individual tooth,” said Tanya Smith, a biological anthropologist at Griffith University in Australia, who studies tooth growth and structure.

As primary or baby teeth grow, they capture the conditions of their surroundings, similar to growth rings in a tree. When Bidlack peers into a microscope at a backlit slice of tooth, it reveals a detailed archive of the child’s daily development in the finely striped enamel. A dark line in some of the earliest-laid enamel marks the transition from womb to world. From there, subsequent, lighter growth lines are a record of daily enamel growth, but darker bands may interrupt the record, indicating that something disrupted the tooth’s, and the child’s, development.

“There’s something very precious about that,” said Bidlack. “Seeing those teeth, it’s really somebody’s history.”

A quarter of a million years ago, two young Neanderthals who lived in what’s now southeastern France left behind some baby teeth. Unearthed at an archaeological site, the teeth contained a trove of information. Equipped with this dental data, Smith and her colleagues discovered that one of the Neanderthal children was born during the spring, weaned from breast milk at 2 and a half years old in the fall, and exposed to lead at least twice during intervening winters. A dark, accentuated line, or stress line, interrupting the enamel growth in one Neanderthal tooth signaled to researchers that the child experienced some kind of stressor one winter, perhaps an illness and weight loss.

Anthropologists and archaeologists have been using teeth for decades to learn about evolution and the lives of ancient humans, Neanderthals, and primates. With other information from the teeth and environment, scientists can sometimes identify specific stressors that were present at the time. One well-established stress line serves as a biological birth certificate: Birth, quite a stressful event for the emerging child, leaves a distinct, dark band in the teeth called the neonatal line.

Scientists also know that metals like lead and copper accumulate in teeth. This means they could reveal dangerous levels of metal exposure with more consistency than blood or urine tests, which only offer a snapshot of a child’s exposure.

Even in permanent adult teeth, enamel formation leaves marks every six to 12 days until the teeth finish growing. By cutting the teeth into wafer-thin slices to view under a microscope, scientists can see these fine striations through the enamel. “They’re these little living archives in your body,” said Christine Austin, an environmental health researcher at the Icahn School of Medicine at Mount Sinai in New York, “constantly storing the history of what you’re being exposed to.”

It’s this archival capacity of teeth that captivates Dunn and Bidlack. Dunn’s research into childhood experiences and mental health previously relied on imperfect human memories for accurate reports of major stressors. “Seeing the gap that exists in the field of childhood adversity and learning more about the potential of teeth, I was just completely floored,” she said.

Scientists have long known that trauma and chronic stress leave physical marks on the body, particularly the brain. During the first few years of life, the brain rapidly grows, forging foundational connections between neurons and pruning expendable ones. But when violence, neglect, or other hardships interrupt that growth, children can become more sensitive to stress, develop cognitive issues, and struggle to regulate their emotions. It even raises the risk of health problems later in life, such as heart disease and cancer.

Researchers have been searching for an objective biomarker of childhood adversity that could ensure children who need help are getting it before problems arise. “Biomarkers have the capacity to tell us earlier in time whether or not someone is experiencing a biological activation that’s potentially problematic,” said Nicole Bush, a psychologist studying developmental stress science at the University of California San Francisco.

While pediatricians screen children for exposure to adverse childhood experiences, they rely on questionnaires, which hinge on the imperfect, subjective nature of human memory. Sometimes people forget or don’t want to talk about these events, but that doesn’t mean that person is unscathed. Biomarkers can serve as a more objective, physiological memory. Commonly, researchers use blood, urine, or salivary samples to measure levels of cortisol, the “stress hormone,” to gauge someone’s stress levels. These, however, reflect only a person’s current distress.

A handful of studies have looked for signatures of psychological and social distress in the baby teeth of monkeys. Some have shown that stressors like separation from the group or the mother may correlate with growth disruptions in tooth enamel of nonhuman primates.

In a 2016 study, for example, Austin and Smith collaborated to explore whether social stressors left structural and chemical marks in the teeth of nine young monkeys in captivity. Six of the monkeys were temporarily removed from their group for behavioral assessments at a young age, a stressful separation. Austin and Smith saw that subtle stress lines appeared in the teeth on the same day as those assessments, although that relationship was less consistent in teeth from a couple of the animals.

Fewer people have studied these patterns in humans. In a recent, preliminary study, Dunn’s team analyzed images of 70 baby teeth from 70 children who lost the teeth between ages 5 and 7. The researchers looked to see whether stressors during pregnancy made the neonatal line thicker or thinner. That kind of stress can also influence the fetus’s brain development.

As it turned out, children born to mothers with mental health issues — including a history of severe depression, depression, or anxiety when 32 weeks pregnant, and other psychiatric disorders — tended to have thicker birth lines. Children with mothers who had lots of social support after pregnancy tended to have thinner lines. These findings persisted even when they controlled for factors such as obesity, age of the mother, and whether they took iron supplements during pregnancy.

The results are intriguing, but far from conclusive. Stress lines alone don’t reveal what specific kind of stressor disturbed tooth development. “It’s certainly a structural and a chemical disturbance that changes the way that people look microscopically,” said Smith. “The rub is, how do you know what it is?” In this case, the researchers had to survey the parents and children to understand what was going on in their lives.

And researchers still need to figure out which pathways in the body — possibly hormone pathways involving cortisol — might link stressors with teeth. “You’re not just looking at when a stress response occurred, but what also was happening” in the body at the same time, Austin said. Scientists need that information to rule out other factors that affect teeth.

Because so many factors can influence birth lines, and because different people react differently to stressors, it’s still difficult to link them to stress, especially when studying a small number of people. One of the few other studies of maternal stress and infant birth lines, which focused on 53 children, didn’t find any relationship between stress and teeth.

If teeth are found to serve as a biomarker in children who have experienced traumas, “the implications could be huge,” said Bidlack.

In December 2019, Dunn and Bidlack began collecting baby teeth donated by parents and their children born around the time of the Boston Marathon bombing in 2013. The event created a tragic natural experiment. With the aid of medical and dental records, researchers hope to pinpoint any stress lines associated with that traumatic event. So far, they’ve enrolled 250 children and their mothers, including a control group that had little exposure to the bombing and manhunt that followed. “If it turns out we can see that stress exposure in the children’s teeth, it would be somewhat mind-blowing,” said Bidlack.

Adverse childhood experiences raise the risks of psychiatric and other illnesses, and exposure to more adversity means bigger risks. On average, low-income children and children of color have more of these experiences than their white, wealthier peers, and those health consequences can follow them throughout their life. Dunn says that finding more detailed and precise markers for these experiences is key to closing those gaps.

Ideally, a biomarker could show how much stress affected a child, and when. It could show whether a stressor occurred during a sensitive period when important neural circuitry is forming. Teeth have the potential to offer that timeline, logging exposures in the body from the very start. Clinicians could then intervene before the child develops mental health issues, like PTSD or depression.

Researchers are still trying to show definitively that teeth could be that sought-after biomarker. Knowing how trauma physically manifests elsewhere in the body, however, Bidlack said she believes it makes sense that such scars could appear in teeth too. “There is a beauty to that — how your body keeps a memory and knows the truth.”

Jackie Rocheleau is a science journalist who writes about brain science and public health. Her work has appeared in Forbes, Medscape, Science News, and other outlets.

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