The dense, flat and crushing teeth of sharks contain fluoride keeping that is an active component of most toothpastes and dental care mouthwashes, an in-dept look at their teeth has found.
This helps to explain why sharks are so effective at either tearing or cutting their prey.
According to the study, their teeth are perfectly designed for such tasks, never suffering from cavities.
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,” Discovery News quoted Epple, a professor of inorganic chemistry at the University of Duisburg-Essen, as saying.
“In the surface of human teeth after brushing, a small amount — much less than 1 percent — of hydroxide is exchanged by fluoride.
“In contrast, (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,” he said.
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,” he said.
He continued that if the teeth of any animal, including humans, were all mineral and super hard, they would be more brittle and prone to shattering.
Nature therefore has ways of circumventing this problem, with teeth “built up from small crystals that are arranged in a special ‘architecture’ to make them mechanically stronger.”
The small amount of protein in teeth, also present in other hard structures like bone and shells, makes these things more elastic.
The study has been published in the Journal of Structural Biology.