THE GIST
- The outside of shark teeth is made
up of fluoride, the active component of most toothpaste.
- Although human teeth are covered in
a different mineral, both shark and human teeth are equally hard.
- Sharks never get cavities, and are
able to replace their teeth multiple times throughout their lives.An in-depth look at shark teeth has found that they contain fluoride, the active ingredient of most toothpaste and dental care mouthwashes.
It helps to explain why sharks are so
effective at either tearing or cutting prey. Their teeth are perfectly designed
for such tasks, never suffering from cavities, according to the study, recently
published in the Journal of Structural Biology,
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| A close look at shark teeth found them full of flouride as well as a bit more flexible than previously imagined. |
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While shark teeth contain the mineral
fluoroapatite (fluorinated calcium phosphate), the teeth of humans and other
mammals contain hydroxyapatite, which is an inorganic constituent also found in
bone, explained co-author Matthias Epple.
"In order to make teeth more
acid resistant, toothpaste often contains fluoride," Epple, a professor of
inorganic chemistry at the University of Duisburg-Essen, told Discovery News.
"In the surface of human teeth after brushing, a small amount -- much less
than 1 percent -- of hydroxide is exchanged by fluoride."
"In contrast," he added,
"(the surface of) shark teeth contains 100 percent fluoride. In principle,
sharks should not suffer from caries. As they live in water and as they change
their teeth regularly, dental protection should not be a problem for
sharks."
For the study, Epple and colleagues
Joachim Enax, Oleg Prymak and Dierk Raabe used a multitude of high tech
investigative techniques, including scanning electron micrographs, to look at
the teeth of two different sharks: the shortfin mako (Isurus oxyrinchus) and
the tiger shark (Galeocerdo cuvier). These sharks were chosen because of their
different eating habits. Shortfin makos tear the flesh of prey, while tiger
sharks cut flesh.
Despite these differences, the teeth
of the both sharks were found to have a similar chemical and crystalline
composition. In addition to the highly mineralized enamel exterior, the
interior of shark teeth was determined to contain a soft material known as
"dentin," which contains more protein and is more elastic. Human
teeth also have dentin.
Mechanical measurements and tests on
the micro and nano-scales determined that shark teeth are not harder than human
teeth.
"This finding is surprising,
because the mineral fluoroapatite is harder than the mineral hydroxyapatite, so
if a tooth were to consist of the mineral alone, a shark tooth would be harder
than a human tooth," Epple said. "It seems as if the human tooth
makes up for the less hard mineral by the special arrangement of the enamel
crystals and the protein matrix, and ends up being as hard as a shark
tooth."
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Andrew Gillis, a Dalhousie University
Peter Fratzl, a professor at the Max
Planck Institute of Colloids and Interfaces, told Discovery News that he was
interested to learn that shark teeth are covered with the mineral
fluoroapatite.
"It is quite interesting to see
that this repeats a very similar and very recent observation about the crayfish
mandible, which also turns out to be covered with fluoroapatite although the
two species, shark and crayfish, are totally unrelated, but both living under
water."
Fratzl said it's possible that
fluoroapatite coatings are much less water soluble than hydroxyapatite and are
therefore "more stable in water and more resistant against bacterial
attack."In addition to the unique structure of their teeth, sharks also have the handy ability to replace their teeth several times during their lives. This is not due to cavities, but rather because their teeth sometimes wind up stuck in prey or are otherwise forced out.
Discovery News
By Jennifer Viegas
