Smoking is a habit that is extremely damaging to health and that continues to be widespread throughout society. It is the leading preventable cause of premature death in the world, and it is estimated that in 2020 it will be directly related to some 10 million deaths, mainly in developing countries¹. 

According to the most recent INE (Spanish National Institute of Statistics) 2011-12 survey data, approximately 1 in every 3 adults in Spain is a regular smoker. 

The mechanism of action of tobacco smoke and its components can be seen both at the local and at the systemic level. At the local level, the mouth is the gateway for tobacco smoke to enter our bodies, and therefore is a direct irritant on oral mucosa. Nicotine also has direct effects on the gums. At the systemic level, smoking alters the innate and adaptive defense mechanisms and interferes with multiple cellular processes. 

Smoking is associated with a long list of systemic diseases and disorders, several of which have an impact on oral health. A clear example of these impairments is delayed oral wound healing, whether these are caused by accidents or periodontal surgery and tooth extraction². Smoking can also cause bad breath, from the odour of tobacco itself or from changes in the bacterial microbiota in the oral cavity³. 

Nevertheless, the main oral diseases associated with smoking and which we will discuss in this article are periodontal disease and oral cancer. 

Smoking and periodontal disease 

Smoking is the leading environmental risk factor and the second most important modifiable risk factor, following plaque control, for periodontal disease development⁴. One of the mechanisms by which smoking favours its development seems to be the reduction and impairment of immune defenses against periodontal pathogens. Smokers tend to show increased peripheral blood monocytes with impaired functionality. Impaired phagocytic activity can lead to poor pathogen elimination from the oral cavity. 

Also, B- lymphocytes and T-lymphocytes, when exposed to tobacco smoke, show reduced capacity for proliferation and production of immunoglobulins that protect against oral pathogens⁵. 

A typical characteristic of smoking-related periodontal disease is tooth-support tissue destruction, with signs of bone loss, periodontal pocket formation and, on occasion, tooth loss. 

Smoking increases the risk for periodontal disease by 5 to 20 times, depending on the definition of disease, compared to non-smokers⁶. This increase depends on the time of tobacco smoke exposure. The cause may be related to changes in the oral microbiota or vascular and inflammatory phenomena. Nicotine and carbon monoxide from tobacco smoke also have a negative impact on wound healing⁶. Smokers have an increased prevalence of periodontal diseases, as well as a higher incidence of tooth loss⁷.

Most studies also show that smokers with periodontitis respond less favourably to periodontal treatment, whether surgical or non-surgical, and regenerative and mucogingival surgery is not recommended in these patients. Long-term studies have proven that smokers have a higher probability of experiencing periodontal disease recurrence during the periodontal maintenance phase, while people who smoke more than 10 cigarettes per day show the most severe disease progression⁷. 

Some studies have even shown that second-hand smoke can have greater periodontal effects, although this is more difficult to determine. Smokers also are at higher risk for experiencing dental implant-related complications, both on the short and the long term. 

Smoking and oral cancer 

Tobacco in all of its different forms and uses is, along with alcohol consumption and certain nutritional deficiencies, the leading cause of oral cancer. Tobacco cigarettes contain over 60 carcinogenic combustion products, capable of binding to and impairing DNA. They also increase oxidative stress on tissues, and in turn, the release of free radical species that damage proteins, lipids, carbohydrates and DNA itself. 

Studies have shown that the risk for oral cancer in smokers is 3 to 5 times higher than in non-smokers, that the effect is dose-dependent and that this dramatically increases when alcohol consumption is added to the equation⁸. 

Lesions that can be detected in the mouth, and that are at higher risk of becoming malignant, include leukoplakias, described as whitish patches that cannot be scraped off, that form part of the epithelium and that are growing. These are mainly caused by tobacco and are precursors of oral cancer in approximately 10% of all cases. 

Conclusion 

In short, we must keep in mind that the mouth is particularly susceptible to the effects of smoking and that the risk of suffering from highly disabling diseases such as periodontitis or even deadly such as oral cancer, greatly multiplies among smokers. Therefore, the role of healthcare professionals is crucial for encouraging smokers to reduce their consumption or to quit smoking altogether.