Our ancient ancestors had better jaw alignment and less tooth decay because they ate more fibre-rich foods, while we eat more sugar and finer food, researchers have concluded after looking at skulls from 4,000 years ago.
The modern-day environment and eating habits have led to a dramatic increase in the occurrence of tooth and jaw misalignment.
People in the past used their face muscles more often in chewing harder food such as roots and leaves, said Dr Zhang Chengfei, clinical associate professor in endodontics at the University of Hong Kong who took part in the Chinese skull study. Endodontics is the branch of dentistry specialising in internal parts of teeth such as roots and nerves.
"We are lazy and don't like to chew hard food," Zhang said. "We should make better use of our jaw, so that it functions better."
The findings did not imply people should adopt ancient diets, but suggested that fibre-rich food would enable more jaw exercise and also give a cleaning effect like brushing the teeth, he said.
Researchers from Peking University and HKU examined skulls from the Xia dynasty unearthed in Henan and Shanxi provinces.
Among the 29 skulls that had both upper and lower jaws, eight had misaligned jaws or teeth, including protruding upper or lower jaws, according to the report published earlier this year in the Chinese Medical Journal.
At 28 per cent, this rate of teeth and jaw misalignment was much lower than the 73 per cent found among Chinese children in the past decade with permanent teeth.
Previous studies showed similar misalignment rates of 26 per cent in the Neolithic age 6,000 to 7,000 years ago and 28 per cent in the Shang dynasty 3,000 years ago.
This change was related to an evolutional decrease in jaw sizes and less wearing off of teeth surfaces. Smaller jaws and larger teeth meant more tooth crowding and problems arising from wisdom teeth in modern people, Zhang said.
In another part of the study, the researchers found that the problem of tooth decay in the skulls was very rare, compared to modern people who consume more sugary food and acidic soft drinks, which damage teeth. Zhang said talking also enhanced jaw health - which should sound an alert those who use computers to communicate.