Dental problems reflected in “Stone Age chewing gum”

A piece of chewed birch pitch (middle) from the Swedish site of Huseby Klev with casts depicting the upper and lower tooth profile. © Verner Alexandersen

Archaeological finds of a special kind: DNA traces in chewed birch pitch have provided insights into the diet and dental health of people who lived in Scandinavia around 10,000 years ago. Apparently these hunter-gatherers were already affected by tooth decay and other dental problems, as can be seen from the genetic traces of certain types of bacteria. In one case, the analysis results even reflected particularly severe gum disease, the scientists report.

These are surprisingly common finds at Stone Age excavation sites in Eurasia: pieces of birch pitch, which our ancestors once extracted from the resin-rich bark of the trees using a heating process. They used this viscous mass as a kind of glue, for example to attach stone blades to spears. In order to keep the substance in a smooth consistency for use, it was apparently chewed. This is evidenced by tooth marks discovered on many pieces of birch pitch found. Such former chewing masses were also found 30 years ago at the archaeological site of Huseby Klev on the island of Orust near Gothenburg. They were discovered in connection with the remains of stone tools and other human traces that were dated to around 9,700 years old.

Researchers have previously come up with the idea of ​​using the ancient chewing material from Huseby Klev as a source for ancient DNA. Above all, they hoped that human genetic traces were transferred to the material via saliva and were preserved in it. This was confirmed: Using the chewing material, which was around 10,000 years old, they were able to gain insight into the genetic makeup of three people who, according to the characteristics of the tooth impressions, were teenagers. Based on this oldest known DNA from former Scandinavians, clues emerged about the family relationships of these hunter-gatherers to other population groups in Europe.

On the trail of food and oral health

As part of the current study, the international research team has now explored the extent to which genetic traces of food have been preserved in the chewing material. They also set out to search for genetic relics of the oral flora – the beneficial or harmful microorganisms that once lived on teeth and gums. Basically, the investigations initially revealed: “The chewed mastic from Huseby Klev actually contains a wealth of DNA sequences that come from bacteria and also from plant and animal tissues that were previously chewed,” says first author Emrah Kırdök from the Turkish University Mersin, who was already involved in the previous studies at Stockholm University.

As far as plant and animal traces are concerned, the team identified, among other things, hazelnut, deer, trout, red fox and various bird species. The genetic findings match fossil remains that were discovered at the excavation site. The researchers explain that these were substances that people ate before chewing pitch or that they used their teeth to help process.

Tooth decay and gum disease

However, the focus of their study results is on the genetic evidence of the microbes in the mouths of hunter-gatherers. One might think that they had a fairly “healthy” profile. But apparently that wasn't the case: the results of the DNA analyzes showed that several types of bacteria that are associated with tooth decay and gum disease were more common. Based on the relative abundance of the microbes and using machine learning models, the authors estimated that the likelihood of poor dental health was between 70 and 80 percent.

One of the chewing materials in particular is particularly exposed to heavy strain: the teenager who chewed on the substance around 10,000 years ago probably suffered from periodontitis - a severe inflammation of the gums that can lead to tooth loss and bone loss. The authors suggest that fairly intensive use of the teeth for tasks such as holding, cutting or tearing various materials may have played a role in poor dental health. This could also have exposed people to the microbes that cause gum disease.

In addition to providing insight into the life and suffering of the group of hunter-gatherers in southwestern Scandinavia, the study results once again illustrate the potential of investigating the widespread finds of chewing material. The authors conclude: “The bottom line is that we have shown that chewed birch pitch can represent an excellent source of ancient DNA that can contribute to understanding the diet, raw material use and oral health of prehistoric populations.”

Source: Stockholm University, specialist article: Scientific Reports, doi: 10.1038/s41598-023-48762-6

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