for National Geographic News
Teeth rotted by sugar could be made whole again with a new dental filling derived from bile.
Modern dental fillings contain either mercury or a chemical called bisphenol A. Both substances help the fillings harden but are potentially toxic to humans and the environment.
The new filling uses bile acids in place of these ingredients.
Bile acids are components of bile produced during the breakdown of cholesterol in the liver. The acids are in the gall bladder and released during digestion of fatty foods.
(Find out more about the human digestive system.)
Chemist Julian Zhu at the University of Montreal in Canada and colleagues mixed bile acids with chemical fillers to form a resin that hardens into a tough plastic upon exposure to blue light. Blue wavelengths provide enough heat to induce the chemical reaction without harming the components.
Zhu's team initially developed the bile composite to be a hydrogel for biomedical applications, such as tissue repair and drug delivery. But the scientists found that the substance became too rigid.
"We had to add in a lot of other things to make it soft, and at that point we thought, Why don't we use this for dental resin?" he said.
Preliminary tests suggest the bile-acid filling is just as durable as conventional fillings and even more resistant to cracking.
And since bile acids are naturally found in the human body, the filling should be completely safe.
"Even if it decomposes, it's still a part of the body," Zhu said.
Human bile acids are chemically identical to those found in pigs, cattle, and many other animals, so farms could provide a cheap and abundant supply of the filling ingredient, Zhu added.
Although he acknowledges the potential "yuck factor" of filling cavities with a product of animal digestion, Zhu thinks bile-based fillings beat the alternative.
"Would you rather put a mercury-containing material into your body, knowing that some of it could end up in a vital organ?" he said.
"Bile acids are a natural compound. They are in our bodies all the time."
Findings detailed in a recent issue of the journal ACS Applied Materials & Interfaces.
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