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Even with all the brushing, flossing and rinsing, many people still suffer from toothache and rotting teeth. Researchers have now found that bacteria that cause dental cavities have evolved with changing diets and left the human mouth in, as Alan Cooper, lead author of the study puts it, a "permanent disease state".

The study was conducted by a research team led by researchers from the University of Adelaide's Centre for Ancient DNA (ACAD). Researchers created a kind of genetic record that mapped the way bacteria in the mouth have changed their behavior to continue living in our mouths. Researchers found that the numbers of bacteria in the mouth declined over time, but in the last few decades, cavity-causing bacteria grew due to unhealthy eating habits.

The DNA material for the study came from tartar, which is calcified dental plaque, from 34 human skeletons from prehistoric Europe.

"Dental plaque represents the only easily accessible source of preserved human bacteria," says lead author Dr. Christina Adler, from the University of Sydney.

Researchers then documented the growth and evolution of dental bacteria through history - from the very first farmers, to people living in the Bronze Age, to those in the Medieval Age.

"Oral bacteria in modern man are markedly less diverse than historic populations and this is thought to contribute to chronic oral and other disease in post-industrial lifestyles," said professor Alan Cooper, ACAD director and lead author of the study.

"The composition of oral bacteria changed markedly with the introduction of farming, and again around 150 years ago. With the introduction of processed sugar and flour in the Industrial Revolution, we can see a dramatically decreased diversity in our oral bacteria, allowing domination by caries-causing strains. The modern mouth basically exists in a permanent disease state," Cooper said in a news release.

The study is published in the journal Nature Genetics.