WHEN A BABY TOOTH FALLS OUT IT IS TYPICALLY COLLECTED FOR THE TOOTH FAIRY. But for some researchers, teeth are far more valuable than a dollar under the pillow. A bit of additional scrutiny, they say, can reveal a great deal about past environmental risks—and what the future might hold.

“Teeth are like a hard drive on a computer,” says Manish Arora, an environmental epidemiologist and exposure biologist at the Icahn School of Medicine at Mount Sinai in New York City. “They store and preserve everything in a kind of sequence. It’s our job to crack the encryption.”

Arora became interested in baby teeth about 20 years ago while working on his master’s in public health at the University of Sydney in Australia. He had been studying research by pediatrician Herb Needleman, who back in the 1970s was looking for a way to measure lead exposure in children. Analyzing teeth was far preferable to invasive biopsies of bone, which also stores evidence of exposure to lead. By grinding baby teeth and measuring lead content, Needleman was able to provide the first evidence that low-level lead exposure can significantly affect a child’s development.

Arora wondered whether there was a way to fine-tune this process to show environmental exposures year by year, or even month by month. During early development, a new tooth layer forms each day, with each layer capturing and reflecting environmental toxins, nutrient deficiencies and other facts about a child’s life.

In 2011 he teamed up with analytical chemist Christine Austin, now at the Icahn School of Medicine at Mount Sinai, to develop a “laser ablation” technique that blasted baby teeth with a high-energy laser beam. This method enables them to sample micron-level amounts of material to trace prenatal and early-life exposures to nutrients and toxic elements that might play a role in the development of several diseases, including cancer, schizophrenia and ALS. Understanding these exposures, and the biological responses to them, could lead to an early warning system for neurodevelopmental disorders.

More recently Arora, Austin and their team tested a hypothesis that children with autism spectrum disorder (ASD) may not absorb and metabolize certain metals and nutrients properly—a phenomenon known as elemental dysregulation. The researchers compared teeth from ASD-affected children and their non-ASD twins (including both identical and fraternal pairs), measuring concentrations of zinc, copper and other elements in layers of the baby teeth corresponding to the children’s development from the second trimester of pregnancy to approximately one year of age.

They found abnormalities in the metabolism of zinc and copper in the teeth of the children who ultimately developed ASD, and their findings suggested that these altered concentrations were present prenatally, preceding the emergence of the condition. Using these novel biomarkers, the researchers were then able to create a predictive model that was 90% accurate in distinguishing those who would be diagnosed with ASD in childhood from those who did not develop the disorder.

Arora and Austin are also studying two-million-year-old teeth from early human ancestors to learn about ancient breastfeeding habits. In a study published in July 2019 in Nature, the researchers were able to measure tooth concentrations of barium, an element found in human milk, to show when children were weaned and started to eat solid food. “Seeing this progression can inform best practices for modern humans,” says Austin.

Other researchers have turned to teeth as well. Erin Dunn, an epidemiologist based at Massachusetts General Hospital, was finding it difficult to measure childhood exposure to adversity and stress. She needed an objective record that could tell her when these life events occurred to help her identify those at risk for future mental health problems.

“If teeth can provide a history of environmental exposures, that is, people’s experiences in the physical world,” says Dunn, “they might also contain clues about people’s social experiences, including their exposure to trauma and the timing of those stressors.”

In February, Dunn and her colleagues presented a study at the American Association for the Advancement of Science in which they examined baby teeth collected from six-year-olds in California. The team used high-resolution imaging, among other tests, to assess the thickness of the teeth’s enamel, and compared this characteristic to behavioral reports from the children’s teachers and parents. They found that children whose teeth had thinner enamel were more likely to have behavioral and emotional problems—an association that could be related to the way that cortisol, a stress hormone, affects developing teeth.

While her work is still in the early stages, Dunn hopes that one day parents will be able to take their child’s baby teeth to a pediatrician, who could then, based on what the teeth reveal, make recommendations to help avoid potential health problems.

“We have a long way to go, but teeth represent a promising new tool that can record not just environmental toxins but possibly trauma exposures as well,” says Dunn. “Teeth are one of the few tissues in the body that permanently record the history of life experiences. We need to take advantage of this untapped resource to help guide us toward the ultimate goal of preventing disease.”