In a fascinating discovery, two teeth dating back approximately 4,000 years have been found to harbor an unusually high concentration of bacteria responsible for tooth decay and gum disease. The findings, which could help scientists understand the connection between changes in human diet and the prevalence of cavities today, were published in the journal Molecular Biology and Evolution.

Unearthed during excavations in Ireland's County Limerick between 1993 and 1996, the two molars belonged to an individual who lived during the Bronze Age, around 2280 to 2140 BC. Notably, one of the teeth contained an unexpected abundance of Streptococcus mutans (S. mutans), a bacterium known to cause cavities. According to Lara Cassidy, senior author of the study and an assistant professor at Trinity College Dublin, S. mutans is rarely found in ancient genetic records due to its acid-producing nature, which leads to decay and DNA degradation within teeth.

The researchers also attribute the rarity of S. mutans in ancient teeth to differences in diet. The human diet of the time consisted of minimal refined sugar and processed food compared to current consumption patterns. However, the advent of agriculture around 10,000 years ago marked a significant shift, and more recent centuries witnessed major changes with the rise in popularity of sugar.

The exceptionally preserved condition of the teeth is thought to be due to the cool and dry environment of the limestone cave where they were discovered. While cavities have been observed in other ancient teeth, S. mutans has only been found in small amounts in a handful of cases.

By analyzing the ancient bacteria and comparing it to modern samples, researchers have discovered a more complex evolutionary tree for S. mutans than previously believed. The bacteria's traits, including its ability to cause damage (virulence), have evolved alongside changes in human diet, including the introduction of sugar and cereal grains.

Understanding how the modern diet impacts the microbiome, both in the mouth and the gut, can shed light on the prevalence of certain diseases in Western populations. The study also highlights the loss of biodiversity in ancient microbiomes and its potential negative implications for human health.

Although no signs of tooth decay were found on the Bronze Age teeth, the high concentration of bacteria suggests that cavities would have developed had the individual lived longer. Further examination of other teeth found in the cave revealed signs of tooth decay, raising the possibility that dental disease affected other individuals in the community.

These findings underscore the impact of dietary changes on oral health. The comparison of ancient and modern S. mutans reveals a significant shift correlated with the consumption of sugar. Higher rates of cavities have been observed since the widespread availability of refined sugar in the 19th century, supporting previous research.

Louise Humphrey, a research leader at the Centre for Human Evolution Research at the Natural History Museum in London, who was not involved in the study, emphasized the crucial role of the oral microbiome in human health and disease. Ancient teeth provide valuable insights into the evolution of the oral microbiota and its historical and current impacts on human health.

This groundbreaking research paves the way for a better understanding of how dietary changes affect oral health today. By delving into the lineage of cavity-causing bacteria, scientists can unravel the repercussions of dietary shifts and enhance oral hygiene practices for the present and future populations.