Periodontitis is one of the most common inflammatory diseases, affecting approximately half of the adult population worldwide. The link between periodontitis and systemic diseases, such as heart disease or diabetes, is already well known.

However, something that is not yet discussed is the fact that generalised inflammation is also a risk factor for mental health conditions such as depression and anxiety; and conversely, that the likelihood and severity of gum disease can be affected by mental health status.

Periodontitis

Periodontitis is a chronic, multifactor inflammatory disease. Periodontitis is associated with elevated markers of inflammation throughout the body, such as the pro-inflammatory cytokines TNF-alpha, IL-6 and IL-1beta, CRP (a measure of inflammation), and gamma-glutamyltransferase (a marker of oxidative stress). 

Possible mechanisms by which periodontitis may affect distant organs include direct migration and colonisation of bacterial species to distant areas, resulting in a local inflammatory immune response in the new region; and the transmission of inflammatory agents from the oral cavity. The presence of elevated chronic systemic pro-inflammatory cytokines and systemic dissemination of periodontal bacterial products support the theory of the already known link between periodontitis, heart disease, and diabetes.

Periodontitis-related diseases

Scientific evidence suggests that inflammation related to periodontal disease may also be linked to rheumatoid arthritis, some types of cancer, premature birth and dementia. Although the link between mental illness and poor oral health has long been established, it is generally interpreted as a result of the lack of self-care and poor lifestyle often seen in people with mental health problems. 

More recent research shows that chronic systemic inflammation directly affects the neurological system and human behaviour in very specific ways, suggesting that the link with mental and dental health is likely to be both physiological and psychosocial. The increase in peripheral cytokines directly affects the brain (such as the hypothalamus, hippocampus and prefrontal cortex), which is related to depression, and reduces levels of serotonin, dopamine and norepinephrine in the brain, changes often correlated with mental illness.

In addition, inflammation reduces the production of brain-derived neurotrophic factor, which is crucial for the creation of new neurons and synaptic connections. Experimental studies in mice have shown that the administration of inflammatory agents leads directly to ‘depressive behaviour’, such as social withdrawal, reduced motivation and motor activity, and increased anxiety. This type of behaviour has also been observed in cases of high levels of inflammatory markers in humans. 

It is important to note that not all people with clinical levels of depression have inflammation and, conversely, not all people with inflammation are depressed. Therefore, systemic inflammation should be seen as a trigger for depression, among other factors.

Implications

The idea that immunological processes may play a key role in the development of psychiatric conditions and influence their treatment is a current area of interest. Generalised inflammation may be a risk factor for depression and stress-induced behavioural changes. However, although periodontitis causes systemic inflammation and several clinical studies imply a link between periodontitis and depression, the idea that periodontitis is a risk factor for depression is not fully demonstrated and further studies are needed. Currently, it is also being studied that infections in the oral cavity, such as dental cysts, may also be a risk factor for depression and dementia.

Clinical implications: the link between periodontitis and depression

The importance of oral health should be more closely monitored in patients with mental health problems. Effective treatment of periodontal disease is capable of reducing the systemic inflammatory burden, which may support recovery from mental illness. Effective treatment of periodontitis in people under stress (e.g. a recent bereavement) can reduce susceptibility for mental illness and improve psychological wellbeing.

Psychological stress is one of the main risk factors for exacerbating inflammatory processes. Through a complex cascade, the release of epinephrine and norepinephrine leads to the positive regulation of pro-inflammatory cytokines. Stress has been directly linked to the progression of periodontitis. Chronic conditions, such as depression and anxiety, are also associated with physiological changes that can directly accelerate the progression of periodontal disease. One of the most common side effects of psychotropic drugs is xerostomia (dry mouth). Medication can alter both the volume and composition of saliva, reducing its protective function and contributing to an increase in the levels of oral bacteria.

Although it is not within the dentist’s competence to provide mental healthcare, it is important to know how to identify these types of patients and refer them to health professionals who can accompany them.

*Dr. Ana Paz, Science, Research and Daily Practice at White Clinic

*Originally published in O Jornal Dentistry.