Dental Caries: The Microbiology of Tooth Decay

Introduction

Tooth decay, which is commonly known as dental caries, is a contagious disease caused by microbes in the mouth. The microbes damage the dental structure by dissolving the calcified parts of the teeth. This issue is interesting and important because tooth decay is an epidemic affecting millions of people around the world. Besides, dental caries influences the general health of the affected individuals and eminence of life.

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For instance, damaged teeth cause pain and affect how people eat, while discolored teeth may lead to low self-esteem, thus influencing the overall quality of life for the affected individuals. Tooth decay occurs due to several reasons, such as diet, nature of teeth enamel, host physiology, interaction among individuals in the plague community, and the availability of Streptococcus mutans. This paper focuses on the microbial processes involved in tooth decay and the relevant microbes.

Causes and Process of Tooth Decay

In order to understand dental caries or tooth decay, the disease should be defined and addressed from a microbial perspective. According to Yadav and Prakash (2017), dental caries is a “chronic contagious disease caused by a complete interaction of oral microorganism in dental plaque, diet and a broad array of host factors ranging from societal & environmental factors to genetic & biochemical/immunologic host responses” (p. 1). Dental caries occurs in two major types – primary and secondary tooth decay. Primary dental caries lesions start forming on an approximal surface and appear between teeth below the contact area. On the other hand, in secondary caries, damage occurs through the demineralization of the walls of the margin of a dental restoration.

Microbes and tooth decay

The biology of oral microbes within the soft and hard tissue surfaces of the teeth and mouth underline the microbial ecology of tooth decay, which occurs in different microhabitats within this environment. Particularly, “the non-shedding surface of enamel allows the accumulation of a biofilm that provides a protected habitat with a variety of niches that support a wide range of bacterial genera and species” (Yadav & Prakash, 2017, p. 3).

The common microbes that cause tooth decay fall into two broad categories – Streptococcus sobrinus and Streptococcus mutans. However, studies have shown that Actinomyces and Lactobacillus are also involved in dental caries (Yadav & Prakash, 2017). For instance, Actinomyces odontolyticus affects infants even before the formation of teeth (Yadav & Prakash, 2017). Besides, other bacterial species associated with low pH habitats, such as Streptococcus mitis and Bifidobacterium, have been shown to cause dental caries. Additionally, the phenotypic characteristics of bacteria involved in the formation of dental caries can vary for selection and survival reasons depending on the ecology of the plague.

The process of tooth decay

The etiology of dental caries is facilitated through the formation of a biofilm community consisting of diverse bacterial populations. The bacteria in this biofilm community can fall into any of the following three categories – gram-positive or negative cocci, gram-positive or negative rods, and yeasts. However, this section will focus on the most virulent pathogens involved in tooth decay, viz. Mutans streptococci (MS) with the common ones being S. mutans and S. sobrinus. MS pathogens produce large amounts of short-chain acids, which ultimately soften the hard tissues of teeth (Yadav & Prakash, 2017).

After softening the hard teeth tissues, different isozymes catalyze the metabolism of sucrose to form insoluble extracellular polysaccharides. The formed polysaccharides facilitate the adherence of MS to the tooth surface, thus resulting in the formation of biofilm. This process is termed as sucrose-dependent adhesion, which is the first part of bacterial colonization in the mouth. S. mutans has specific cell-surface proteins, which enable its quick adherence to teeth surfaces, and thus it is more virulent as compared to S. sobrinus that lacks such binding proteins.

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The two major microbial processes involved in dental caries are adherence and biofilm formation, which underscore the colonization of teeth by bacteria. The presence of different sugars and glycosides in the mouth facilitates this process (Yadav & Prakash, 2017). The adhesion process occurs through sucrose-dependent and sucrose-independent mechanisms. In sucrose-dependent adhesion, sucrose is metabolized into polysaccharides, which aid in the adhesion process.

On the other hand, sucrose-independent adhesion occurs when components in saliva initiate the attachment process. Normally, vicious saliva facilitates the protection of teeth by ensuring the presence of carbohydrates in the mouth, which act as antibacterial agents by neutralizing acids after ingestion. Therefore, low production of saliva reduces this protective effect, and the bacterial adhesion process is expedited.

Biofilm formation occurs in a series of stages including association, adhesion, proliferation, the creation of micro-colonies, and maturation (Yadav & Prakash, 2017). During association, bacterial attachment surfaces on teeth are created through the formation of a dental pellicle. Bacteria then adhere to these surfaces in the second stage, and the repetition of this step leads to proliferation and multiplication of the microbes. The microbes then secrete a slime layer for protection, thus forming micro-colonies in the fourth stage. The micro-colonies then create complex groups before developing a primitive circulatory system in the final stage of biofilm formation. Biofilm formation is the basic process of tooth decay through bacterial colonization.

Prevention of Dental Caries

The first step of dental caries prevention is to understand the relationship between oral hygiene and microbes and the associated risk factors. As shown earlier, tooth decay can only occur at the presence of harmful microbial plagues in the mouth. Therefore, daily removal of these plagues through oral care, such as brushing and flossing, is important in a bid to prevent tooth decay (Lee, 2013). This aspect underscores the importance of being sterile, as bacteria will not have an enabling environment for colonization.

Besides, applying fluoride prevents the demineralization of the hard teeth surfaces, thus inhibiting the adhesion process of biofilm formation. Pits and fissures should be sealed as they favor the accumulation of plague (Lee, 2013). Additionally, avoiding sugary foods, especially those containing xylitol – a form of sucrose, will prevent tooth decay. Xylitol is metabolized in the sucrose-dependent adherence process to facilitate the formation of biofilm. These practices will get rid of harmful bacteria, such as MS, and protect useful ones including probiotics that help in food digestion.

Conclusion

Dental caries is an epidemic contagious disease caused by the presence of harmful bacteria in the mouth. The most virulent bacteria that cause tooth decay are MS, such as S. mutans and S. sobrinus. The process of tooth decay occurs through the softening of hard teeth surface, thus allowing bacteria to attach themselves and colonize the affected areas. Therefore, daily oral care routines will prevent the formation of dental caries. Such practices clear the plague that might have formed on the teeth. In the future, the focus should be on the creation of commercial vaccines to help people fight against microbial activities in the mouth.

References

Lee, Y. (2013). Diagnosis and prevention strategies for dental caries. Journal of Lifestyle Medicine, 3(2), 107-109.

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Yadav, K., & Prakash, S. (2017). Dental caries: A microbiological approach. Journal of Clinical Infectious Diseases & Practice, 2(1), 1-15. Web.

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