To test the dental wash, the scientists gathered several teeth from Brazilian burials dating from 2,800 to 1,805 years ago. All were excavated at a southeastern coastal site called Sambaqui Jabuticabeira II.
The site has yielded several large piles of mollusk shells mixed with other debris, which are associated with human activity.
The researchers swirled recovered teeth in the solution to loosen the tartar. To isolate the particles in the tartar, the scientists strained and spun the solution in a centrifuge.
They found three types of microfossils. Most common were starch grains from tubers. The researchers also found diatoms, microscopic algae used as a food source by marine organisms, and phytoliths, tiny mineral particles produced by plants.
The first two microfossils suggest the individual's last meals likely consisted of shellfish accompanied by some sort of tuber.
"At the moment, we do not know where the phytoliths came from," Eggers said. "They might have been part of a plant eaten or a plant element, such as palm leaves, chewed for the production of ropes, baskets, hammocks or some kind of clothing."
Although the dental wash was successful, it made some of the ancient teeth brittle, while others turned bright white.
Since scientists hope to leave specimens in a condition as close to the original as possible, the researchers suggested the dental wash recipe requires further tinkering. They also said particles might be removed using sound waves.
Sheila Souza, a scientist at Brazil's National School of Public Health, told Discovery News that she and colleague Veronica Wesolowski have also been recovering particulate matter from ancient teeth.
"It is really new to try the washing technique proposed by the researchers," Souza said, adding that the new dental wash technique is "interesting," but problematic for the reasons the inventors cited themselves.
Souza agreed that it is important to analyze ancient teeth, however, particularly in Brazil, where early plant evidence has been sparse in some areas.
"We are really opening a big, new field to improve prehistoric reconstructions about the Sambaquis diet and lifestyle with calculus and microfossils," she said.
