A Greenland Fossil Jaw and the Origin of Molars: Summary
Scientists have described the earliest known example of dentary bone with two rows of cusps on molars and double-rooted teeth. The new findings offer insight into mammal tooth evolution, particularly the development of double-rooted teeth.
In 2020, researchers described a fossil jaw from eastern Greenland, about 215 million years old, that has the oldest known molar-like teeth with two roots and two rows of cusps. It belonged to Kalaallitkigun jenkinsi, a mouse-sized close relative of the first mammals.
The study, published in the Proceedings of the National Academy of Sciences, also used engineering models to show that teeth with two roots withstand the forces of biting better than teeth with one root. That may help explain why broad chewing teeth and divided roots evolved together, a design human molars still carry.
For the full explanation, including what the researchers found, the study's limits and what it means for your own molars, read What a Tiny Jaw From Greenland Shows About the Origin of Molars.
Sources
Sulej T, Krzesiński G, Tałanda M, et al. The earliest-known mammaliaform fossil from Greenland sheds light on origin of mammals. Proc Natl Acad Sci U S A. 2020;117(43):26861-26867. doi:10.1073/pnas.2012437117. Retrieved via PubMed.
About the author. CJ Henley, DMD, is a general dentist in Jacksonville whose practice focuses on cosmetic and restorative dentistry, dental implants and dental care around head and neck cancer. Meet Dr. Henley.
CJ Henley, DMD, PA · 3675 Hendricks Avenue, Jacksonville, FL 32207 · 904-398-1549
Updated October 2026.
Is Gum Disease Linked to Stomach and Esophageal Cancer?
People with history of gum disease appear to have higher risk of developing oesophageal and gastric cancer, suggest researchers
A large Harvard study found that adults who reported a history of gum disease were more likely to develop adenocarcinoma of the esophagus or stomach over the next two decades. The increase was roughly 40% to 50% in relative terms, but these cancers are uncommon, so the added risk for any one person is small. The study shows an association, not proof that gum disease causes these cancers.
What did the study look at?
Researchers at the Harvard T.H. Chan School of Public Health used two long-running studies of US health professionals: 98,459 women in the Nurses' Health Study and 49,685 men in the Health Professionals Follow-up Study. Participants reported on questionnaires whether they had gum disease and how many teeth they had lost. Researchers then followed them for 22 to 28 years and confirmed cancer diagnoses from medical records. [1]
During that time, 199 people developed esophageal adenocarcinoma and 238 developed stomach adenocarcinoma.
What did it find?
History of gum disease: about 43% higher risk of esophageal adenocarcinoma and about 52% higher risk of stomach adenocarcinoma, compared with people without gum disease. [1]
Tooth loss: people who had lost two or more teeth also showed higher risk, but these results were weaker and less certain, especially for stomach cancer. [1]
The researchers adjusted for smoking and for other lifestyle and dietary factors that could affect both the mouth and the digestive tract.
What are the limits?
Self-reported gum disease. No one examined participants' gums.
Small numbers of cancers. Fewer than 450 cases across nearly 150,000 people make the estimates less precise.
A research letter, not a full paper. The findings were published as a short letter in the journal Gut. The authors noted that earlier studies on this question had mixed results. [1]
Observational design. The study can't rule out other shared causes.
Researchers suspect oral bacteria or long-term inflammation could play a role, but that remains a hypothesis.
What does this mean for you?
These cancers are uncommon, and the steps that lower risk are mostly the same steps that protect your mouth: don't smoke, limit alcohol, and treat gum disease when it is found. If you have ongoing heartburn, trouble swallowing or unexplained weight loss, see your physician. Those symptoms matter more than your gum history.
Related research and where to get care
Gum disease has also been linked with breast cancer and with overall cancer risk in older women. A comprehensive dental exam at our Jacksonville office includes a full gum evaluation. Contact us or call 904-398-1549 to schedule.
Sources
Lo CH, Kwon S, Wang L, et al. Periodontal disease, tooth loss, and risk of oesophageal and gastric adenocarcinoma: a prospective study. Gut. 2021;70(3):620-621. doi:10.1136/gutjnl-2020-321949 (retrieved via PubMed; full text via PubMed Central)
About the author. CJ Henley, DMD, is a general dentist in Jacksonville whose practice focuses on cosmetic and restorative dentistry, dental implants and dental care around head and neck cancer. Meet Dr. Henley.
CJ Henley, DMD, PA · 3675 Hendricks Avenue, Jacksonville, FL 32207 · 904-398-1549
Updated October 2026.