What Makes Chiton Teeth So Tough? A Rare Mineral From Rocks
Researchers discovered a rare mineral hidden inside the teeth of a chiton, a large mollusk found along rocky coastlines. Before this strange surprise, the iron mineral, called santabarbaraite, only had been documented in rocks.
Chitons are ocean mollusks that feed by scraping algae off rock, and the cutting tips of their teeth are among the hardest materials made by any animal. A 2021 study from Northwestern University looked at the stalk that attaches each tooth to its flexible base and found a mineral called santabarbaraite, which had been seen before only in rocks. Its structure appears to help the stalk stay strong while staying light.
This is a Lined Chiton, Tonicella lineata. This picture was taken at about 50 feet depth on the west side of Whidbey Island, Washington.Attribution:
Kirt L. Onthank
What is a chiton?
Chitons are flat, oval mollusks with eight overlapping shell plates. They cling to rocks along coastlines. Instead of jaws, they have a radula, a flexible, tongue-like ribbon lined with rows of small teeth. As the teeth wear down from scraping rock, new ones move forward to replace them.
What question did the researchers ask?
The hard caps of chiton teeth had been studied for years. Less was known about the stylus, the long stalk that connects each hard tooth head to the soft radula. Joining a very hard material to a very soft one without the joint failing is a difficult engineering problem, and the team wanted to know how the chiton does it.
They studied the giant Pacific chiton, Cryptochiton stelleri, using high-energy X-ray methods at Argonne National Laboratory along with electron microscopy.
What did they find?
The upper part of the stylus is a mineralized tissue, not just soft protein.
The mineral is santabarbaraite, an iron phosphate with a disordered, non-crystal structure. It had never been found in a living thing.
A second iron phosphate in a similar disordered form sits nearby. Keeping two such forms side by side requires tight biological control.
Over a distance of a few hundred micrometers, about the width of a few hairs, the mineral content and stiffness of the stylus change three- to eightfold. This gradual change lets the stalk blend from soft at one end to hard at the other.
Santabarbaraite is low in iron and high in water, which may make the stylus strong for its weight.
The team then used these ideas to make inks for 3D printing composite materials whose stiffness can be tuned.
What are the limits?
This is basic materials science on one species. It explains how a structure is built. It does not test anything in people.
Why would a dentist care about mollusk teeth?
Human teeth face a similar problem. Hard enamel sits on softer dentin, and teeth are held in bone by a flexible ligament. Where hard and soft materials meet is often where fillings, crowns and bonded restorations fail. Studying how animals grade one material into another gives dental materials researchers ideas for stronger joins between a restoration and the tooth.
If you are curious how printing is already used in dental care, see our post on 3D printing and dentistry. For another look at teeth in the animal world, read about shark teeth and human dental biology.
Sources
Stegbauer L, Smeets PJM, Free R, et al. Persistent polyamorphism in the chiton tooth: from a new biomineral to inks for additive manufacturing. Proc Natl Acad Sci U S A. 2021;118(23):e2020160118. doi:10.1073/pnas.2020160118. Retrieved via PubMed.
Northwestern University. Press release on santabarbaraite in chiton teeth, May 2021.
About the author. CJ Henley, DMD, is a general dentist in Jacksonville whose practice focuses on cosmetic and restorative dentistry, dental implants and dental care around head and neck cancer. Meet Dr. Henley.
CJ Henley, DMD, PA · 3675 Hendricks Avenue, Jacksonville, FL 32207 · 904-398-1549
Updated October 2026.
Can Childhood Stress Make Molars Come In Earlier?
Research shows that children from lower-income backgrounds and those who go through greater adverse childhood experiences get their first permanent molars sooner. The findings align with a broader pattern of accelerated development often seen under conditions of early-life stress.
A 2021 study suggests it may be linked. Researchers at the University of Pennsylvania found that children from lower-income families and children who had more adverse childhood experiences tended to get their first permanent molars earlier. It's an association, not proof of cause, and the researchers stress that the timing of a child's molars says nothing useful about that individual child. For parents, nothing about routine dental care changes.
What did the study look at?
The researchers wanted an inexpensive, early sign of whether stress speeds up a child's development. Earlier puberty is a known marker, but it comes too late to be much help. In other primates, the timing of molar eruption tracks the length of childhood, so the team looked at teeth.
They started with 117 children aged 4 to 7 who were already in brain-imaging studies at Penn. The MRI scans happened to show the developing molars clearly. Working with Penn Dental Medicine, the team rated how far each first permanent molar had come in, then compared those ratings with family income and the number of adverse childhood experiences each child had, after accounting for age and sex.
To check the result, they repeated the income analysis with 1,973 children in the National Health and Nutrition Examination Survey, a national U.S. dataset.
What did they find?
In the Penn group, both lower family income and more adverse childhood experiences were linked with earlier eruption of the first permanent molars.
In the national dataset, the link between lower income and earlier molars held up.
The team also saw differences by race, which they said need further study.
What are the study's limits?
The first group was small and came from one city. The national dataset measured teeth differently and could only test income. Most importantly, the study shows that two things tend to occur together across groups of children. It doesn't show that stress causes earlier molars, and it can't predict anything for a single child. The researchers were clear that parents shouldn't worry, or feel reassured, based on when their child's molars arrived.
What does this mean for your child's teeth?
First permanent molars usually come in around age six, behind the last baby teeth, and children often don't notice them. Whenever they arrive, they need the same care:
Brush them twice a day with fluoride toothpaste. They sit far back and are easy to miss.
Ask your child's dentist whether sealants make sense once the molars are in. The deep grooves on these teeth are where many childhood cavities start.
Keep up regular dental visits.
If you'd like more on what teeth can record about early life, read about growth marks in baby teeth. For young children's care in general, see our parent's guide to early childhood dental problems.
Sources
McDermott CL, Hilton K, Park AT, et al. Early life stress is associated with earlier emergence of permanent molars. Proc Natl Acad Sci U S A. 2021;118(24):e2105304118. doi:10.1073/pnas.2105304118. Retrieved via PubMed (PMID 34103399).
Penn Today. A link between childhood stress and early molars. June 7, 2021. Retrieved 2026-10-06.
About the author. CJ Henley, DMD, is a general dentist in Jacksonville whose practice focuses on cosmetic and restorative dentistry, dental implants and dental care around head and neck cancer. Meet Dr. Henley.
CJ Henley, DMD, PA · 3675 Hendricks Avenue, Jacksonville, FL 32207 · 904-398-1549
Updated October 2026.