At the start of his career, neuroscientist Allyson mackey started to think about molars. As a researcher who studies brain development, she wanted to know if the arrival of these teeth could indicate early maturation in children.
“I have long feared that if children grow up too fast, their brains will mature too quickly and lose plasticity at a younger age. Then they will go to school and have a hard time learning at the same pace as their peers.” , he added. said Mackey, assistant professor in Penn’s psychology department. “Of course, all children who experience stress or [is] low income will show this model of accelerated development. ”
What would help, she thought, was an evolutionary, objective way – a physical manifestation, of sorts – of indicating how children embodied and responded to stresses in their world. The timing of the eruption of the first permanent molars turned out to be exactly that.
In the Proceedings of the National Academy of Sciences, Mackey, with doctoral student Cassidy McDermott and colleagues at Penn’s School of Dental Medicine and the University of Missouri-Kansas City, shows that children from disadvantaged backgrounds and those with more unfavorable childhood experiences get their first permanent molars earlier. The results, initially generated from a small study and replicated using a nationally representative dataset, align with a larger pattern of accelerated development often seen under stressful conditions in early childhood. life.
“It’s really important for us to understand how to spot early ripening earlier,” Mackey says. “Right now, we’re relying on seeing when kids hit puberty, which might be too late for meaningful interventions. If we can inexpensively see that a child is experiencing this maturation sooner, we could perhaps devote more intervention resources to it. ”
A new scoring system
Broadly speaking, Mackey’s lab studies how the brain changes and develops as people learn. It is well established that stress during childhood accelerates maturation and that children who reach puberty earlier are at greater risk for physical and mental health problems in adulthood.
Beyond that, in studies of primate species, molar rash has been used to measure the duration of childhood and correlates with a number of other developmental events. Likewise, for humans, the timing of dental events often plays a role in estimating biological age.
“All of this made molar rash a compelling indicator of development,” says McDermott, who is trained as a clinical psychologist.
It helped that more than 100 children, ages 4 to 7, participated in two Penn studies of brain development, which included structural and functional MRI scans. “There’s a type of MRI called a T2-weighted scan where you can visualize the morphology of the tooth quite well,” McDermott says. These scans, typically used to examine the brain, showed researchers how close these molars were to a ruptured gum line.
Once Mackey and McDermott realized this, they teamed up with Katherine Hilton, then a Penn dental student, and Muralidhar Mupparapu, a professor in the department of oral medicine, who developed a new scale to accurately assess the position of each patient. tooth.
“The scale goes from 1 to 4,” says McDermott. “At the lower end of the scale is 1, which is before the tooth has really grown. As the tooth emerges there are intermediate stages, and the highest score, a 4, is when the tooth is completely in the mouth and parallel to the other teeth. “Four molars were each scored. , which was then averaged, leaving a single score per individual.
By controlling for factors such as age and gender, the researchers then looked for associations between the early environment and the molar eruption. “What we found is that income and adverse childhood experiences are both individually associated with molar rash status,” McDermott explains.
Reproduce the conclusions
These results came from only 117 participants, so while the correlation was clear, Mackey and McDermott hoped to replicate what they saw.
Collaborators from the University of Missouri-Kansas City told them about a large, population-representative dataset called the National Health and Nutrition Examination Survey (NHANES), which is publicly available and includes dental data, demographic data and family income, among other measures.
“Because our sample is only from one city and is much smaller than a representative population study like this,” McDermott says, “we saw it as an opportunity to verify that the results exist in apart from what we had collected in Philadelphia. ”
Although some facets differ – the NHANES measures tooth development a little differently, for example – models showed similar results, indicating a link between lower family income and earlier first molars.
Whether this general trend is new or just emerging is something Mackey wants to explore further. She is also curious when the ripening rate is set. “Is it already in utero or is it dynamically adjusted according to the stressors in the world? ” she says. “If it’s the latter, that tells you that there are more opportunities to intervene.”
Current implications, future work
There are still significant unknowns, as well as results that require further examination, Mackey says. For example, the research team found racial disparities in this timeline, with first molars appearing earlier in black children than in white children.
“These racial differences in molar rash have been known for a long time, but no one has thought critically about their origin,” she says. “This corresponds to higher stress levels due to structural racism. It is a clear indication that it is not just speculation that experiences with racism can cause stress and premature aging. They have an effect. on the children we cannot ignore. ”
For all children, more than a year of grief and social isolation over a pandemic has most certainly amplified stress levels, making it even more important to understand who is most at risk of early maturation, says Mackey .
Still, she and McDermott stress that molar timing shouldn’t become another parental fear. “What I really don’t want is for parents to worry or feel complacent just about when their kids have had their molars,” Mackey explains. “We don’t have that data yet.”
Penn researchers are working on it. In the future, they hope to collaborate with dental offices to recruit children into studies based on their molar rash status. The goal would be to follow them into adulthood, to get more information on what precisely early first molars can indicate. “If this is the significant discovery I think it is,” said Mackey, “I would like a lot of scientists to join us and test these hypotheses.”
Funding for this research comes from the Jacobs Foundation, the National Institute on Drug Abuse (Grant 1R34DA050297-01) and the National Science Foundation.
Allyson Mackey is an Assistant Professor in the Department of Psychology in the School of Arts & Sciences at the University of Pennsylvania. She runs The Changing Brain Lab and is a MindCORE researcher at Penn.
Cassidy McDermott is a second year doctoral student in the Department of Psychology at the School of Arts & Sciences at Penn.
Other contributors to this work included Muralidhar Mupparapu, professor in the department of oral medicine at Penn dental school; Katherine Hilton, then Penn’s dental student; current graduate students from Penn Anne Park, Austin Boroshok and Ursula Tooley; and JoAnna Scott and Erin Bumann of the School of Dentistry at the University of Missouri-Kansas City.