Several scientific studies have shown that certain pathogenic oral bacteria can translocate by proximity to the upper airways and from there pass on to the lungs. 

Pneumonia, chronic obstructive respiratory disease, and lung cancer are very serious respiratory conditions that may be affected by this circumstance. Once again, this shows how important having good oral health is. 

The oral cavity is colonised by countless microorganisms that, in conditions of health, are in equilibrium with the host. When the environmental conditions change, certain pathogenic species which may be present in very small quantities find a way to grow and cause an increase in the aggressiveness of dental plaque or biofilm in the gums. As a consequence, they cause an inflammatory reaction that is at first limited to the gingival tissue (gingivitis). But if this develops, it may compromise the support of the tooth and its long-term survival (periodontitis). 

Several scientific studies have shown that this type of more pathogenic oral bacteria may be translocated by proximity to the upper airways and from there pass on to the lungs⁽¹⁾. Following on from this model, we should hence discuss three very serious respiratory conditions that may be affected by this dangerous relationship between the presence of periodontal disease and the lungs: pneumonia, chronic obstructive respiratory disease and lung cancer. 

PNEUMONIA 

Pneumonia is an infection of the lungs that may be caused by bacteria, mycoplasmas, viruses, fungi or parasites. Together with the flu, pneumonia is one of the chief causes of death worldwide, especially among the elderly. This disease also contributes to morbidity and a decrease in quality of life, as well as a considerable increase in hospital medical expenses. 

Bacterial pneumonia is made up of several subtypes: community-acquired pneumonia, aspiration pneumonia, hospital-acquired pneumonia (nosocomial), ventilator-associated pneumonia, and nursing home-associated pneumonia. In all cases, correlations have been made with the patient’s state of oral health. 

Of nosocomial pneumonias, those associated with aspiration in patients in intensive care units (ICUs) and with mechanical ventilation are especially severe. 

This type of pneumonia is the most common hospital infection among patients in ICUs, which in many cases leads to the lengthening of their stay in hospital, in turn leading to considerably increased hospitalisation costs. Additionally, it raises the risk of mortality by between 15% and 45%, depending on the study. 

The main cause is the aspiration of oropharyngeal secretions to the lower respiratory tract. This is because, through intubation, the natural barrier between the oropharynx and the trachea is lost. In addition, there may be greater bacterial colonisation in the mouth due to a lack of proper oral hygiene along with decreased salivary secretion, whereby the passage of potentially pathogenic oral bacteria along the breathing tube increases. 

Strategies to reduce the likelihood of pneumonia in these patients should address a reduction of oral microorganisms by mechanical removal of dental plaque and the chemical control of the most pathogenic microorganisms. 

CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD) 

COPD is a chronic obstruction of airflow due to the narrowing of the airways, along with excess production of mucus resulting from chronic bronchitis and/or emphysema. It is estimated that by 2020 it will be the third leading cause of death and the fourth most important cause leading to disability⁽²⁾. 

Chronic bronchitis is defined as the result of irritation of the bronchial airways and sufficient mucus secretion to cause coughing with expectoration for at least three months per year and for two consecutive years. Emphysema consists of the permanent enlargement of the air spaces distal to the terminal bronchioles, together with the destruction of the alveolar walls. 

As in cases of pneumonia, bacteria present in the mouths of patients with periodontal disease may pass into the lungs and cause infection. In addition, both periodontal disease and COPD share risk factors and indicators such as smoking, age, obesity, socio-economic status and living conditions. A recent meta-analysis of several cross-sectional and case-control studies has provided evidence that periodontal disease is associated with an increased risk of developing COPD and that this risk would increase significantly by 2.08 times⁽³⁾. 

LUNG CANCER 

A large number of observational studies carried out over recent years have found associations between periodontal disease and different types of cancer. The biological mechanism would respond to factors such as prior existence of diseases related to the affected organ or tissue, the passage of pathogenic bacteria to the affected tissues, and above all, increased systemic inflammation. A recent meta-analysis of numerous cohort studies found a positive association between the incidence of lung cancer and the presence of periodontal disease⁽⁴⁾. However, these associations should be considered with caution, as the studies used are not always comparable and may be somewhat heterogeneous. Further studies with similar methodologies should be carried out in the future in order to obtain more relevant conclusions. 

CONCLUSIONS 

In the past, the mouth and its diseases were considered totally unrelated to the rest of the body. However, the importance of having good oral health is now becoming increasingly evident, since its impairment may have repercussions in any part of our body. These repercussions may range from a reduction in quality of life to the risk of acquiring potentially fatal diseases.