Ecological Plaque Hypothesis: How Microbial Imbalance Causes Tooth Decay?

What Is the Complexity of Enamel Hydroxyapatite Structure?

When we explore the structure of the tooth enamel, there are multiple functions it performs because of its strong and potent mineralization that coats the exterior surface of your teeth. Further, because enamel appears white, giving your tooth an aesthetic look, enamel alterations or regressions owing to its demineralization or cariogenic susceptibility or attack, can create both esthetic and functional issues for individuals. Since tooth enamel contains a remarkable concentration of calcium hydroxyapatite crystals, its function is also to help the tooth withstand the forces involved in chewing and grinding food, playing a crucial role in digestion. Hence, tooth enamel also plays an extremely pivotal role in digestion. According to the current histologic research, the complexity of the enamel structure is such that the tooth enamel has several dimensions, within it that range from its basic atomic level of hydroxyapatite (HAP) units to the micrometer level of its crystalline structures, and then subsequently to the millimeter level of its hierarchy comprising enamel rods.

How Does the Ecological Plaque Hypothesis Explain Dental Caries Formation and Enamel Demineralization?

One of the most accepted and accurate dental hypothesis that has been testified by dental research is the ecological plaque hypothesis. Let us explore in this article, the structural hierarchy and the organic-inorganic balance that is maintained by your tooth enamel, which is the most important part of your tooth, that resists cariogenic microorganisms or attacks, and also preserves your tooth enamel to prevent the risk of dental caries. According to the detailed description of this hypothesis, dental caries mainly occur as an exposure to acidogenic microorganisms, wherein bacterial pathogens can tend to create an imbalance in your oral microbiota. This phenomenon is called the "ecological stress" that is exerted on the otherwise healthy oral microbiome. When the existence of certain oral pathogens or dental decay-causing microorganisms present in the enamel biofilm is further enriched with dietary acids, poor oral hygiene, lack of timely dental management, or even because of certain systemic diseases, dental caries is seen as a multifactorial disease process.

Further, when the individual consumes more sugary or fermentable carbohydrates, that can feed the acidogenic and aciduric bacteria or the oral pathogens, induces acid production and creates a cariogenic environment.

According to the hypothesis, the inorganic components mainly the OH− and PO43− ions that are essential for enamel remineralization are greatly reduced, resulting in enamel dissolution.

The rationale of the ecological plaque hypothesis is that enamel remineralization is affected when there is a clear oral microbiome imbalance, leading to the counteractive cariogenic microorganisms eventually demineralizing and breaking the structure of the potent tooth enamel.

How Does the Demineralisation Process Start According to the Ecological Plaque Hypothesis?

According to the ecological plaque hypothesis, because a healthy oral cavity itself harbors an aqueous or semiliquid environment, there are several local risk factors like oral hygiene, the flow of saliva (major immune defense and liquid that protects your tooth), the number of bacterial pathogens present in your mouth, and also the type of diet you incorporate plays the role of dietary acids. When these factors that influence the remineralization of dental enamel are challenged or face a detrimental impact, then definitely the integrity of tooth enamel can be compromised. While the formation of dental biofilm takes place on the enamel surface soon after the bacterial attack or ingress, it can take several days for the biofilm to progress to incipient caries or white spot lesions eventually when left untreated. These lesions can even get extensive creating a break in the enamel and dentinal tissues, involving the vascular root canal or tooth pulp.

What Is the Histological Structure of Enamel?

The histologic structure or the hierarchy of enamel is a mineralized calcium-based structure of the tooth that forms the resistant outer layer. It is composed mainly of around 17.7 weight (wt) percent phosphorus, 36.5 wt percent of calcium (majorly), 3.5 wt percent carbonate, 0.5 wt percent sodium, approximately 0.01 percent fluoride, and 0.44 wt percent magnesium.

There are also several enamel proteins, such as amelogenin, ameloblastin, and enamelin that form the crux or structure of tooth enamel.

Hence, enamel is one of the most resistant and tough biological materials that are the main defense mechanisms as well for your tooth apart from their innumerable functions for support and structural esthetics.

Enamel is mainly formed from specialized cells known as ameloblasts and further comprises several enamel rods or prisms, interrods, that would be histologically seen as the building blocks of mineralization (usually measuring around five to eight μm micrometer) in diameter, spanning the width of the enamel to the dentin junction (DEJ), or the other tooth surfaces). These cylindrical rods are composed of HAP crystallites or crystals.

What Is the Need for Fluoride Treatment for Healthy Enamel?

Current research shows that the use of professionally formulated and recommended fluoride products, with the capacity for fluoride ions to fit into the HAP crystal structure, that is, by replacing calcium hydroxyapatite after brushing with fluorapatite crystals, is one of the basic steps to counteracting dental caries.

Given that most of the dentist-recommended toothpaste products available in commercial stores typically contain approximately 1000 to 1500 parts per million (ppm), sodium fluoride (NaF) or sodium mono fluorophosphate (MFP) are used in these formulations. Also, dental research demonstrates that the use of professionally applied gels, trays, or products that are dentally recommended either for in-office or home application, along with proper oral hygiene practices can help circulate salivary fluoride effectively into different oral compartments, balancing the oral microbiome effectively.

Conclusion

Several dental researchers over the decades have proposed the concept of the symbiotic relationship between oral bacteria and dental caries formation on tooth enamel. However, it is to be noted that the ecological plaque hypothesis remains one of the most accepted and near-accurate testifications that has been relatable from a histological observation of the tooth enamel and dental caries formation in it. Further because of the structural hierarchy of enamel. Its demineralization-remineralization mechanisms are explained well in this hypothesis, and fluoride management can be the cornerstone for strengthening, or sustaining the health of tooth enamel.