In the Maltese language, the word for both ‘teeth’ and ‘years’ sounds the same – ‘snin/snien’. The words are connected. Although we can tell how old horses are by the rings on their teeth, human teeth are a little bit more difficult to understand until now.

In 2015, Daniela Santucci and Nikolai Attard wrote about the conditions of teeth among older Maltese in institutions.

The authors found that in nine State institutions, out of 278 older adults, only six people had healthy teeth. Nearly half had tooth loss, a rate higher than any other European country. The problem is that infections in the mouth not only cause heart problems but we are also finding that it can cause dementia.

In 2017 the Japanese researcher Kenji Takeuchi and his colleagues reported that people in their 60s who lost their teeth were more likely to get dementia five years later. And there was a dose effect, with those having fewer teeth suffering a higher rate of dementia, peaking at nearly twice as high. Only when older people completely had no teeth did this rate of dementia drop slightly. Controlling for other effects is difficult.

For example, Takeuchi also reported that teeth loss was related to having less than 10 years formal education. After age, lack of formal education by itself remains the best predictor of dementia. Education has a protective function, perhaps delaying rather than eliminating dementia.

Ageing makes us less able to cope with diseases, and the best attack is to prevent diseases from infecting us in the first place

Related to education is also income, as Nora Donaldson with King’s College London and her colleagues reported in 2008. She found that richer people made better use of preventive care and also independently had better teeth. Even among identical twins, the twin who had tooth loss before the age of 35 was 5.5 times more likely to develop Alzheimer’s disease.

Even among centenarians – those who have lived to a 100 years and older – better oral health was reported than their respective peers when they were in their early 60s. So we are seeing a pattern that good teeth translate to longer life and a healthier brain.

Tooth loss can be caused by many factors, but the main contender seems to be periodontal disease. Periodontal disease is caused by bacteria that initially forms a sticky ‘plaque’ which, if not removed by brushing, can harden and form ‘tartar’. This in turn can attack the gum causing ‘gingivitis’ and eventually infects the tooth and bone as ‘periodontitis’.

The association of periodontal disease with dementia has been reported in many studies. In one recent 2017 review by Spanish researchers, Yago Leira Feijóo and his colleagues concluded that those with severe forms of periodontal disease are nearly three times more likely of getting dementia.

The cause of periodontal disease is primarily bacteria. There are some 400 bacterial species populating the mouth, together with some viruses and fungi, a concoction that is also capable of invading the brain.

In 2011 Judith Miklossy confirmed these associations when she found that in four out of five autopsied brains of Alzheimer’s patients there were spirochetal bacteria that originate in the mouth. This initial infection can cause inflammation in the brain. It is this inflammation that attacks the brain from inside.

Ruth Utzhaki and her colleagues, in a 2016 review, came up with incontrovertible evidence that Alzheimer’s disease has a microbial component.

In fact, the hallmarks of Alzheimer’s disease – plaques and tangles – are observed in mice and in cell culture after an infection with bacteria. These plaques and tangles have been found to have anti-microbial function against multiple bacteria, yeast and viruses.

It is biologically feasible for oral bacteria to go through the bloodstream, reach the brain and either initiate or promote existing lesions and cause an inflammatory response. The brain reacts by protecting itself through inflammation and surrounding the toxic substance with plaques and tangles. If this inflammation mechanism is the cause of dementia, then perhaps simple medication can lower the inflammation in the brain.

Unfortunately, it is not that simple. Studies that look at anti-inflammation medication (like paracetamol for example) have had mixed results. Through these studies we are learning how much we depend on other organisms in our bodies – bacteria in this case.

There are both good and bad bacteria for our bodies. The best way to prevent the bad bacteria from invading us is by cleaning our teeth regularly and visiting the dentist to clear away the tartar that has grown where we miss with the toothbrush.

Ageing makes us less able to cope with diseases, and the best attack is to prevent diseases from infecting us in the first place. The mouth is the best place to start. Who knows, we might enjoy a few more smiles and that’s always good for our mental health as well.

Mario Garrett was born in Malta and is currently a professor of gerontology at San Diego State University in California, US.