Study explains why our ancestors did not have cavities in their teeth and the reason is surprising

Two teeth from a man who lived around 4,000 years ago were found, full of bacteria that commonly cause cavities and gum disease. This unique discovery could help scientists understand how changes in the human diet have resulted in the current prevalence of cavities.

The teeth were discovered during two excavations carried out in 1993 and 1996, along with several other human teeth and remains found in a limestone cave in County Limerick, Ireland. The two molars, dated between 2280 and 2140 BC, belonged to an individual who lived during the Bronze Age, as reported in an article published March 27 in the journal Molecular Biology and Evolution.

One of the teeth had a surprising amount of Streptococcus mutans (S. mutans), an oral bacteria responsible for causing cavities. This bacterium is rarely found in ancient genomic records, probably because its acidogenic nature causes DNA degradation in teeth, making it difficult to preserve, explained Lara Cassidy, lead author of the paper and assistant professor in the department of genetics at Trinity College Dublin.

Researchers also believe the bacteria is not commonly found in old teeth due to the human diet at the time, which included less refined sugar and fewer processed foods than are consumed today, Cassidy said. A significant change in diet was observed with the advent of agriculture around 10,000 years ago, but the last few hundred years have seen even more significant changes with the popularization of sugar.

Relationship between dietary changes and cavities

It’s still unclear why the bacteria in the newly discovered tooth were so well preserved, but Cassidy suggested that the cave’s cool, dry conditions may have contributed to it.

Although cavities have been observed in other finds of ancient teeth, S. mutans has only been found in very small quantities in some remains, such as an older tooth from the Neolithic period from southwestern France (dated between 3400 and 2900 BC) or a chewed resin from the Scandinavian Mesolithic period (dated between 9890 and 9540 BC). Observations of cavities in other old teeth become more common after the adoption of cereal agriculture, the cultivation of grains such as wheat and barley, according to the article.

By analyzing bacteria found in Bronze Age teeth and comparing them to modern samples, researchers discovered that the ancient evolutionary tree of S. mutans was more complex than initially thought, and found traits of the ancient bacteria, such as virulence (ability to cause harm), evolving along with changes in the human diet, including the popularization of sugar and grains, Cassidy said.

“The last few centuries have seen a huge amount of change (in the human diet), so understanding particularly how this has impacted the microbiome (the microorganisms, like bacteria, that naturally live in and on the human body), not just the oral microbiome, but also the intestinal microbiome, can help us understand a little why certain diseases have become so prevalent in Western or Westernized populations in recent centuries”, he added.

Bronze Age oral health

Although no cavities have been detected in the Bronze Age teeth, Cassidy suggests that if the adult man they belonged to had lived longer, the large amount of bacteria present indicates that he would likely have developed cavities.

Additionally, both teeth contained traces of DNA from Tannerella forsythia (T. forsythia), a bacteria associated with gum disease and commonly found in ancient genomic records. However, researchers identified two distinct strains of the bacteria in teeth, whereas today only one strain is commonly observed. This suggests that ancient microbiomes were more diverse than today’s, a loss of biodiversity that is worrying due to possible negative impacts on human health, as mentioned in a press release from Trinity College Dublin.

Other teeth found in the cave showed signs of tooth decay. However, it is not known whether these teeth belonged to the same person or to other members of the community, as they were found disarticulated, separated from other skeletal remains, as explained by Cassidy. She added that it is possible that other teeth in the mouth of the same person or other members of the community also had cavities.

Cassidy also mentioned that analysis of ancient S. mutans suggests that the bacteria’s prevalence has increased in recent centuries due to sugar consumption, providing a favorable environment for the species in human mouths. Understanding the strains of modern bacteria that cause cavities can help scientists better understand how dietary changes can affect oral health today.

Analysis of ancient S. mutans compared to modern S. mutans “revealed a significant change in the last few centuries linked to increased sugar consumption” and supports previous research that found higher rates of cavities after refined sugar became widely available in the 19th century, said Louise Humphrey, research leader at the Human Evolution Research Center at the Natural History Museum in London, who was not involved. in the study.

“The oral microbiome has implications for many areas of human health and disease. Ancient teeth can help us understand how the human oral microbiome (range of microorganisms) has evolved over time and the impact of these changes on human health in the past and today,” Humphrey said in an email.

With information from CNN