Dental Caries as a Non-Communicable Disease: Pathophysiological Insights

Summary

Recent advances in science that support our knowledge of both the onset of dental caries and the subsequent behavior of lesions over time provide us with a solid foundation to understand caries differently.

Advances in understanding the human and oral microbiome have occurred in parallel with recognition of the importance of balancing protective and pathological risk factors.

Caries prevention and management now involves controlling risk factors to maintain a balanced intraoral biofilm ecology that protects against continued low pH caused by frequent consumption of sugars.

Therefore, caries control is no longer about trying to eradicate any specific microorganism. Furthermore, current knowledge leads to the classification of dental caries as a non-communicable disease (NCD), which is of vital importance from a policy perspective (both globally and nationally).

Caries shares similar risk factors with other chronic/systemic diseases, providing opportunities to develop common prevention strategies and promote health equity through action on the social determinants of health. Therefore, caries prevention and control should be integrated at the so-called upstream, intermediate and downstream levels, and these activities can also help control other NCDs.

Tooth decay is a major health problem in most industrialized countries, with the majority of children and adults suffering from the disease. In the Global Burden of Disease Study, untreated caries was the most prevalent of the 291 medical conditions evaluated, affecting 3.1 billion people (44%) worldwide, with a major impact on quality of life and high costs. for individuals, families and society. The disease is distributed unevenly in populations with a strong socioeconomic gradient.

Like other conditions described as non-communicable diseases (NCDs), dental caries develops as a result of a combination of genetic, physiological, environmental and behavioral factors. 5A serious concern is that, although dental caries is largely a preventable disease, its prevalence has barely decreased in the last 30 years.

This paper argues that recognizing dental caries as an NCD rather than an infectious disease will allow caries to be integrated into oral health promotion, prevention and treatment strategies, and into general NCD policies.

The human microbiome

Human beings are composed of equal numbers of eukaryotic and microbial cells. These microorganisms, called the human microbiome , are natural and colonize all surfaces of the body exposed to the environment, from where they perform essential functions for our well-being. The human microbiome plays a fundamental role in digestion and energy production, the normal development of host defenses and many of our physiological systems. It also acts as a barrier to colonization by exogenous and often pathogenic microbes.

Generally, we live in harmony with our microbiome, but sometimes this relationship can be broken and diseases can appear. The disruption is called dysbiosis and is usually the result of a major change in habitat that disrupts the delicate balance between the microbiome and the host. Imbalance can lead to a number of diverse conditions along the microbiome-gut-brain axis, such as autoimmune and inflammation-mediated diseases, malnutrition, obesity, and neurological disorders.

The oral microbiome

The mouth hosts a complex microbiome that persists and grows on oral surfaces as multispecies biofilms; These biofilms are called dental plaque when they develop on the teeth. The unique properties of the oral cavity make the composition of the oral microbiome characteristic of the site but distinct from that of neighboring habitats, such as the skin and digestive tract.

These observations emphasize an important principle, namely the decisive role that the local environment plays in determining which species can colonize, grow, and become major or minor components of the microbiome in a specific niche. The oral microbiome has a symbiotic relationship with the host. Resident oral microbes exhibit pathogen exclusion, downregulate undesirable and potentially proinflammatory responses to beneficial resident organisms, and promote cardiovascular health through the enterosalivary nitrate-nitrite-nitric oxide pathway.

The relationship between the microbiome and the host is dynamic and is susceptible/vulnerable to change if substantial changes occur in the habitat. This includes the social determinants of health that shape the distribution of the four main behavioral risk factors for NCDs: unhealthy diet, physical inactivity, smoking and excessive alcohol consumption.

The oral microbiome and dental caries

Early culture-based cross-sectional studies found a correlation between mutans streptococci and caries, but these bacteria are also present in caries-free sites and caries could occur in the apparent absence of these bacteria. However, longitudinal trials provide the best evidence of causality, as they can detect temporal changes in the microbiota before caries diagnosis.

To date, a common observation is that dental biofilms show a divergent microbial composition over time, with clear differences between caries-active and apparently “cavity-free” children. Studies have confirmed the discriminatory role of S. mutans, although these organisms represent only a small fraction of the bacterial community. Furthermore, new species and phyla, such as Scardovia wiggsiae, Slackia exigua, Granulicatella elegans and Firmicutes, are described in children who develop dental caries, while other commensal bacteria (Streptococcus mitis, S. gordonii and S. sanguinis) appear in the dental biofilm. of the kids. Non-carious tooth surfaces.

Drivers of dysbiosis in dental caries

For many decades, dental caries was described as a transmissible infectious disease and S. mutans was called the ’arch-criminal’ . It was believed that these bacteria were infectious agents and that babies acquired this pathogen from their mothers only after the eruption of primary teeth. Consequently, clinical strategies to prevent or delay the transmission of these organisms have been suggested, along with attempts to suppress or even kill mutans streptococci in the oral cavity with topical antibacterial substances and vaccines.

However, the ’one pathogen, one disease’ paradigm of dental caries has now been replaced by a holistic concept of a microbial community as the entity of pathogenicity. Studies of people of different ages and with different diets from around the world have shown substantial differences in the composition of the microbiota in the biofilms covering caries lesions, with an enrichment of species with an acid-producing and acid-tolerant phenotype. Therefore, the development of a caries lesion is associated with a change in the balance of the resident dental microbiota , so that normally minor components of the biofilm become more prevalent.

The main driver of such a dysbiotic change is the frequent consumption of sugars.

The inevitable low pH generated by your metabolism is driving the selection of acid-producing and acid-loving microorganisms at the expense of beneficial oral bacteria that prefer a pH close to neutrality. Similarly, a reduction in saliva flow and non-daily mechanical alteration (dental cleaning) of the dental biofilm will generate similar changes.

Dental caries has therefore been described as a microbial ’ecological catastrophe’ ; Implicit in this concept and the ’ecological plaque hypothesis’ is that interference from drivers of dysbiosis is necessary to prevent or control disease. In this way, dental caries is not an example of a classic infectious or communicable disease. An appreciation and acceptance of this concept will have implications for dental practice and public health.

ENT: what are they and why are they important?

Prevention and control of caries as an NCD will require coordinated action at national, community and clinical levels.

At the global/national level, oral diseases have been identified in the United Nations Political Declaration on the Prevention and Control of Noncommunicable Diseases as "a major health burden for many countries and these diseases share common risk factors and can benefit from common responses to non-communicable diseases.’

This included two objectives: 1) ’reduce modifiable NCD risk factors and underlying social determinants by creating health-promoting environments’; and 2) ’Health systems and universal health coverage: strengthen and guide health systems to address the prevention and control of NCDs and underlying social determinants through people-centred primary health care and coverage universal health.

The WHO Oral Health Resolution 2021, adopted by the World Health Assembly in May 2021, reinforces these objectives in relation to oral diseases and dental caries. Urges countries to reorient the traditional curative approach and move towards a ’promotional preventive approach with risk identification for timely, comprehensive and inclusive care, taking into account all actors to contribute to the improvement of the oral health of the population with a positive impact on general health’.

Additionally, the WHO resolution emphasizes green, less invasive dentistry that could help countries implement the Minamata Convention on Mercury, including supporting preventive programs and establishing national targets for the prevention of caries and Health promotion. This should be based on and aligned with our knowledge and understanding that bacteria play a crucial role in oral and general health.

Implications for the future of practice and policy and patient care

Caries prevention and health promotion have traditionally relied on fluoride exposure, dietary control, complete oral hygiene, and antibacterial measures. Recognizing dental caries as an NCD certainly does not disqualify these measures but rather places them in a broader context. An important step is that oral health professionals must adopt and implement the concept of a balanced microbiome as a basis for caries prevention and that maintaining or restoring symbiosis is the result throughout life.

Dietary advice should focus on limiting the intake of free sugars and fruit juices.

Here, the updated WHO sugar recommendations for children and adults are helpful. 33 To prevent both dental caries and obesity, there is a strong recommendation that the intake of free sugars does not exceed 10% of total daily energy intake, which corresponds to less than 50 grams per day. A conditional recommendation is to limit intake to below 5%. Subjects with this low sugar consumption have fewer caries-related species in their saliva and supragingival plaque than those who consume more sugar.

Free sugars are all types of sugar, added by the producer during food preparation and by the consumer while eating. In particular, several ’natural’ products such as honey, syrup and fruit juices are de facto sugar-free. Oral hygiene instructions should focus on gentle and regular disruption of biofilm rather than meticulous eradication. The presence of fluoride in the biofilm throughout the day plays a critical role in biofilm control.

Fluoride may reduce sugar stress in biofilm by lowering the critical pH for enamel dissolution, limiting demineralization. Additionally, fluoride can inhibit many traits associated with dental caries, including enzymes associated with biofilm matrix production and enolase, directly slowing glycolysis and indirectly reducing bacterial sugar transport systems.

Inhibition of acid production eliminates environmental conditions that are responsible for the suppression of beneficial oral bacteria essential for the enrichment of acid-tolerant species.