Scientists identified a total of almost 400 different species of microbes in the mouths of 100 study participants belonging to four ethnic affiliations: non-Hispanic blacks, whites, Chinese and Latinos.
Only 2% of bacterial species were present in all individuals - but in different concentrations according to ethnicity - and 8% were detected in 90% of the participants.
Researchers found that each ethnic group in the study was represented by a "signature" of shared microbial communities.
"This is the first time it has been shown that ethnicity is a huge component in determining what you carry in your mouth," said Purnima Kumar, associate professor of periodontology at The Ohio State University.
"No two people were exactly alike. That's truly a fingerprint," said Kumar, senior author of the study.
Kumar used a DNA deep sequencing methodology to obtain an unprecedented in-depth view of these microbial communities in their natural setting.
When the scientists trained a machine to classify each assortment of microbes from under the gums according to ethnicity, a given bacterial community predicted an individual's ethnicity with 62% accuracy.
The classifier identified African Americans according to their microbial signature correctly 100% of the time.
The research also confirms that one type of dental treatment is not appropriate for all, and could contribute to a more personalised approach to care of the mouth.
"The most important point of this paper is discovering that ethnicity-specific oral microbial communities may predispose individuals to future disease," Kumar said.
Though it's too soon to change dental practice based on this work, she said the findings show that "there is huge potential to develop chair-side tools to determine a patient's susceptibility to disease."
Kumar and colleagues collected samples of bacteria from the saliva, tooth surfaces and under the gums of the study participants.
More than 60% of bacteria in the human mouth have never been classified, named or studied because they won't grow in a laboratory dish, so the researchers identified the different species - or species-level operational taxonomic units - by sequencing their DNA.
The study was published in the journal PLOS ONE.