Overview

Have you ever wondered why some people seem to battle frequent tooth decay? Well, your mouth is home to countless microbes, and this plays a surprising role in tooth decay. These bacteria form a sticky coating over the teeth, called dental plaque. When the balance tips in the oral microbiome by frequent intake of sugary foods, the bacteria in dental plaque produce acids. This weakens tooth enamel (the hard cover protecting your teeth). Over time, weakened enamel can lead to cavities in your teeth.

What is oral microbiome?

The oral microbiome refers to the combined genome of microorganisms in the oral cavity. It is the second-largest microbial community within the human body, following the gut.¹ The areas like the gingival sulcus, the tongue, the cheek, the hard and soft palates, the floor of the mouth, the throat, the saliva and the teeth provide a platform for the colonisation of microbes. Antony van Leeuwenhoek known as the "Father of Microbiology," identified the oral microbiome by his initial examination of dental plaque.¹

The normal microbiome is formed by bacteria, fungi, viruses, and protozoa. It is composed of gram-positive bacteria such as Peptostreptococcus, Streptococcus, Actinomyces, Bifidobacterium, Corynebacterium, Lactobacillus, etc and gram-negative species like Neisseria, Veillonella, Campylobacter, Capnocytophaga, Fusobacterium, Prevotella, Treponema, etc. The fungi in the healthy oral microbiome include Candida, Cryptococcus, Fusarium, Aspergillus, etc.^2,3 The most commonly found protozoa are Entamoeba gingivalis and Trichomonas tenax.³

The composition of the oral microbiome is influenced by factors such as genetic predisposition, salivary flow, maternal transmission, dietary patterns, oral hygiene practices, medications, introduction of external microbes, and systemic health conditions.

Understanding dental plaque

Formation of Dental plaque

Dental plaque is a yellowish-white biofilm, that consists primarily of bacteria. The bacteria are embedded in a matrix of exfoliated epithelial cells and salivary proteins. Shortly after the teeth are cleaned, an acquired pellicle forms on the tooth surfaces primarily composed of glycoproteins in saliva. While this pellicle aids in lubrication, it also serves as an adhesive and provides binding sites for bacteria.

Subsequently, bacteria such as Streptococcus and Actinomyces species (early colonisers) stick to this pellicle layer. They form microcolonies and mature on the tooth surface. Streptococcus species produce extracellular polysaccharides like glucans and fructans. These aid the bacteria to stick together, facilitating plaque growth and maturation. As the plaque matures, it becomes more anaerobic. This allows the colonisation of anaerobic bacteria like Prevotella and Porphyromonas species, etc (late colonisers). These bacteria interact via co-aggregation, forming complex structures.^2,3

Composition of dental plaque

Plaque consists of approximately 80% water and 20% solids. Among the solids, half of the dry weight comprises bacterial and salivary proteins. Another 25% of the plaque's dry weight is attributed to the plaque matrix. The matrix is made up of organic materials like carbohydrates, proteins and lipids and inorganic components like calcium, sodium, phosphorus, potassium and fluorides.⁴

Types of dental plaque

Dental plaque can be classified as supra-gingival (above or along the gum line) and subgingival (below the gum line) plaque. Supra-gingival and tooth-associated subgingival plaque could contribute to dental caries. Dental plaque usually accumulates in the gingival thirds of the tooth surface, pits and fissures in teeth, areas around misaligned teeth and overhanging restorations. While it’s normal to produce plaque, if it’s not removed with regular oral hygiene practices like daily brushing and flossing, and periodic dental cleanings, it can lead to tooth decay and other oral health issues.

Understanding tooth decay

Tooth decay (dental caries) is a dynamic disease influenced by biofilms, driven by sugar consumption, and characterised by the phasic demineralization and remineralization of dental hard tissue.⁵ Tooth decay is the breakdown of teeth due to acids produced by bacteria when they break down food debris accumulated on the tooth surface.

The symptoms of tooth decay vary, depending on the extent of the damage to the tooth. Initially, there are no symptoms except white or blackish-brown discolouration of the tooth. As the decay progresses, it may cause symptoms such as toothache, tooth sensitivity, and holes or pits in the teeth.

The interplay between dental plaque and tooth decay

An imbalance in the resident dental microbiome causes the onset of tooth decay or dental caries. This shift primarily occurs due to frequent sugar consumption. In the healthy state, both plaque biofilm and adjacent tissues maintain a delicate balance with a harmonious relationship between the two. However, changes occur during tooth decay that transform this 'healthy' dental plaque into a 'pathogenic' biofilm. This breakdown in the balance of microbial populations is known as dysbiosis.

• Tooth decay is closely associated with specific bacteria in the mouth. Among these bacteria, Streptococcus mutans, and Lactobacilli are strongly linked to the development of caries
• S. mutans, in particular, ferments sugars like sucrose to produce lactic acid as a byproduct
• This leads to the acidification of the environment around the teeth and the breakdown of tooth enamel
• Other bacteria like Veillonella, Bifidobacterium spp., Actinomyces, and Candida albicans have also been identified as being associated with different stages of caries progression
• When fermentable carbohydrate intake (eg: sweet foods) is moderate, the presence of these bacteria is clinically insignificant
• When the frequency of acidic exposure increases, dental plaque spends more time below the critical pH threshold of approximately 5.5, which enhances the risk of tooth demineralization. The shift in pH has a dual effect on the microbial ecology of the plaque
• This shifts the balance towards demineralization

Cariogenic dental plaque contributes to tooth decay and is particularly abundant in glucan and fructan polysaccharides.

Preventive strategies for dental plaque and tooth decay

Plaque control

Plaque control refers to the consistent removal and prevention of dental plaque buildup on both the teeth and the nearby gingival surfaces. It can be done in two ways:

Mechanical

1. Manual Toothbrush
2. Electric Toothbrush
3. Interdental brush
4. Dental Floss
5. Superfloss
6. Triangular tooth pics
7. Perio-Aid
8. Irrigators⁴

Chemical

1. First-generation anti-plaque agents (eg: Antibiotics, phenols, etc.)
2. Second-generation anti-plaque agents (eg: Chlorhexidine)
3. Third-generation anti-plaque agents (eg: Delmopinol)

Antiplaque agents can be delivered in oral hygiene aids like dental floss, mouth rinses, toothpaste, dental gels, chewing gums, herbal extracts, periodontal dressing, pulsated jet irrigators, etc.⁴

Prevention of tooth decay

The initial indication of the disease is demineralisation on the tooth surface. Early-stage tooth decay can be addressed through preventive and minimally invasive dental procedures. Failure to manage the initial decay allows it to advance, leading to cavities that require more invasive treatments.

Caries risk assessment 

Caries risk assessment is crucial for personalised management of tooth decay, determining the likelihood of developing new decay over time. Factors such as previous caries experience, dental education, socioeconomic status, and age at the time of colonisation by cariogenic microbes play key roles in assessing caries risk.⁵

Fluoride

Community water fluoridation, topical fluoride application, and fluoride kinds of toothpaste have been instrumental in reducing caries prevalence.⁵

Sealants

By preventing food accumulation in tooth pits and fissures, sealants effectively prevent tooth decay. Moreover, placing sealants over carious lesions halts the disease process and proves cost-effective compared to routine restorative care.⁵

Remineralisation

Incipient tooth decay could be repaired by saliva when combined with fluoride application and plaque removal. Promising new therapies are focused on calcium-containing preparations like amorphous calcium phosphate (ACP), but none have been proven more effective than fluoride in clinical trials.⁵

Diet

When free sugar intake is less than 15 kg/person/year, the incidence of tooth decay tends to be low. It's recommended to limit the frequency of sugar intake to four times or less per day.⁷ Reducing the amount and frequency of sugar consumption, especially processed foods and soft drinks, is crucial. Foods that stimulate salivary flow, including wholegrain foods, peanuts, hard cheeses and sugar-free chewing gum protect against decay. A variety of sugar substitutes like sucralose and xylitol with low or no cariogenic potential are available.⁶

FAQs

What is dental plaque?

Plaque is a yellowish-white sticky microbial layer that constantly forms on our teeth.

Is dental plaque normal?

Dental plaque is a natural occurrence in the mouth, but it's crucial to eliminate it through daily brushing, flossing, regular dental check-ups and professional dental cleaning.

How to spot dental plaque?

Initially, dental plaque may be hard to spot, but with accumulation, it becomes more noticeable. It typically presents as a soft, white or yellowish film, particularly along the gum line and between teeth. Apart from its visual presence, dental plaque can induce symptoms such as halitosis, tooth sensitivity, and gum bleeding.

How does plaque affect our teeth?

The bacteria in the dental plaque when exposed to sugary or starchy foods frequently, produce acids that harm tooth enamel. Continuous acid exposure gradually wears down enamel, leading to tooth decay and eventually cavities.

How to know if a tooth is decaying?

Indications of decay include discolouration in white, brown, or black hues on the tooth surface. In advanced stages, decay may manifest as cavities or holes accompanied by tooth hypersensitivity and pain. During routine dental examinations and radiographic investigations, dentists can identify tooth decay.

Summary

The oral microbiome, comprising diverse microorganisms, plays a crucial role in dental plaque formation and tooth decay. Influenced by factors like diet, genetics, and oral hygiene, the balance within the microbiome impacts oral health. Understanding the dynamic interplay between the oral microbiome and tooth decay informs personalised approaches to caries management. Preventive strategies such as plaque control, fluoride application, dietary modifications, and sealants aim to disrupt plaque formation, inhibit bacterial growth, and promote remineralisation of enamel.