Oral anatomy and microbiome

Key points

Cavities (caries) and periodontitis are among the most common diseases in humans, with 90% of the global population experiencing an oral health issue during their lifetime. In this lesson, you will learn about the anatomy of the mouth and teeth, the essential functions of saliva, and how oral health affects your overall well-being.

​

​

The teeth

Tooth development involves over 200 genes, and even before birth, the foundations of both primary (baby) and permanent teeth are formed. Young children, typically between the ages of 2 and 3, develop 20 baby teeth, which are gradually replaced by permanent teeth starting at around age 6.

In a child’s jaw, there isn’t enough space for permanent teeth yet, so baby teeth act as placeholders, aiding in speech development and chewing until the jaw grows to accommodate adult teeth.

32 permanent teeth

An adult has a total of 32 teeth, including the wisdom teeth. Each type of tooth (incisors, canines, premolars, and molars) serves a specific function.

incisor	canine	molar

The teeth are grouped as follows: 28 teeth, plus four possible wisdom teeth (6.). Behind the wisdom teeth are the molars (5.), followed by the premolars (4.), the canines (3.), and the incisors (2.) at the front of the mouth. Bacteria in the mouth process sugar, producing acids that attack the tooth enamel, which can lead to cavities (caries). At the center of the oral cavity, surrounded by the teeth, is the palate (1.).

The structure of teeth

The basic structure of a tooth is always the same.

​1. Crown (Corona dentis): The visible part of the tooth above the gum line. ​ 2. Neck (Cervix dentis): The transition area between the crown and the root. ​ 3.  Root  (Radix dentis): The part of the tooth embedded in the jawbone. The root is covered by cementum, a hard, bone-like substance that is continually formed throughout life.​

What does a tooth look like on the inside?

1. Enamel: The hardest material in the human body. It forms the durable, insensitive outer surface of the crown. Enamel is made up of enamel prisms, which are rods composed of large hydroxyapatite crystals. These crystals contain a mixture of calcium, phosphate, hydroxide ions, and other trace elements like carbonate, magnesium, sodium, zinc, and fluoride. Enamel cannot regenerate once it is damaged.
   
   
2. Dentin: The sensitive inner layer of the tooth, located beneath the enamel. It is harder than bone but softer than enamel. Dentin consists of a dense network of collagen fibers embedded with calcium salts in the form of hydroxyapatite. Unlike enamel, dentin is a living tissue and can regenerate. Tiny nerve fibers in the dentin tubules transmit sensations like heat, cold, or sweetness, which can cause pain.
   
   
3. Pulp (Pulpa): The innermost part of the tooth, housing the nerves, blood vessels, and connective tissue. The pulp supplies the tooth with nutrients and transmits sensations like heat or cold to the nervous system. Inflammation of the pulp can lead to severe tooth pain.
   
   
4. Cementum: A thin, hard layer that covers the root of the tooth.
   
   
5. Periodontium: Also known as the supporting structure of the tooth, it includes the gum tissue, the jawbone, the periodontal ligament, and the cementum. The periodontium anchors the tooth securely in the jawbone.
   
   
6. Alveolus: The bony socket in the jaw where the roots of the tooth are anchored.
   

The gums (gingiva) and the periodontium form the protective and supportive structures around the teeth. The gums are a part of the oral mucosa and surround the teeth like a collar, while the periodontium ensures the teeth are firmly anchored in the jawbone. This detailed overview of tooth anatomy provides the foundation for understanding dental health and its role in overall well-being.

Saliva

Humans produce between 0.75 and 1.5 liters of saliva daily. Saliva has antibacterial, antiviral, and antifungal properties. It also neutralizes and dilutes acids in the mouth, helping to maintain a balanced pH level of 6.2–7.6. Additionally, the enzymes in saliva aid digestion and support the crucial process of tooth remineralization. Its viscosity acts as a protective layer for teeth and gums and enhances the sense of taste. Saliva is secreted by the parotid, submandibular, and sublingual glands, along with approximately 600 minor salivary glands.

​

Health starts in the mouth

The health of your teeth and gums has a profound impact on your overall health. The mouth is home to a wide variety of bacteria, most of which are harmless. However, as the entry point to both the digestive and respiratory systems, some bacteria can migrate to other areas of the body and cause diseases. All organs in the body are interconnected with the mouth in various ways, which is why oral health and general health influence one another.

The primary entry points for bacteria living in the biofilm are the teeth. Bacteria can enter the body through the hard structures of the teeth, such as enamel or dentin, via cavities. These bacteria convert simple sugars and starches into acids that dissolve minerals from the enamel, weakening it over time. Another critical entry point is the sulcus, the space between the teeth and the surrounding gum tissue. If the gum tissue is inflamed and bleeding (gingivitis), bacteria can easily enter the bloodstream. Gingivitis can often be reversed with proper brushing. Without intervention, gingivitis may progress over years into periodontitis, a chronic inflammatory disease. This condition is particularly dangerous as it can worsen systemic diseases like diabetes.

Certain diseases can be identified early through changes in the oral cavity. Infections or inflammation in the teeth or gum pockets can significantly increase the risk of heart attack and stroke. Poor oral health and untreated oral diseases are associated with various systemic conditions, including cardiovascular disease, elevated stroke risk, and diabetes. Periodontitis during pregnancy has also been linked to low birth weight and preterm births.

Oral microbiome

The entirety of microorganisms in the oral cavity is referred to as the oral microbiome, which plays an essential protective role. It includes bacteria, fungi, viruses, and protozoa. Up to 700 different bacterial species live in the mouth, forming a complex ecosystem. These microorganisms protect against harmful environmental influences and fend off dangerous pathogens. A single mouth can host more than 6 billion bacteria. Did you know that during a 10-second kiss with tongue contact, approximately 80 million bacteria are exchanged?

The oral microbiome also helps maintain barrier functions in the lungs and gut. Additionally, the gut microbiome performs vital metabolic functions, such as producing certain vitamins (like B vitamins and vitamin K) and breaking down indigestible fibers into short-chain fatty acids that benefit the host. The gut microbiota also has diverse metabolic activities, ranging from metabolizing drugs, environmental chemicals, and bile acids to producing neurotransmitters like serotonin, dopamine, and GABA.

Dental plaque – a bacterial biofilm

Dental plaque, also known as biofilm, is a sticky, soft, yellowish layer made up of microorganisms, proteins, polysaccharides, and electrolytes that forms on teeth. Plaque is the primary cause of cavities and periodontitis. Over time, it can harden into tartar as minerals accumulate within it.

Biofilms are complex, multi-cellular communities of microorganisms enclosed in a slimy, sticky matrix of extracellular polymeric substances. These communities thrive on surfaces that provide moisture and nutrients. The biofilm on teeth is highly resistant to antibiotics and antimicrobial agents, and it resides on the gums, teeth, and dental restorations, contributing to cavities and periodontal diseases.

How Can We Combat Biofilms? A landmark clinical study conducted in 1965 by Norwegian professor Harald Löe demonstrated the direct relationship between plaque accumulation and gum inflammation. In the study, participants with healthy gums and excellent oral hygiene stopped brushing their teeth and performing interdental cleaning for three weeks. During this time, plaque began to accumulate. Initially, it consisted of gram-positive cocci and rods. Over time, filamentous organisms and, eventually, gram-negative spirochetes appeared. Within days, mild gingivitis with gum bleeding developed. The increase in gram-negative bacteria was primarily responsible for the gingivitis. However, when participants resumed effective oral hygiene practices, their gums quickly returned to a healthy state, typically within a week.

The Solution to Biofilm Problems? The only recognized, evidence-based solution to biofilm is mechanical plaque control, which involves brushing and flossing. These methods reduce and disrupt plaque formation. The goal is to eliminate the excessive, structured biofilm that causes gum and tooth issues while maintaining the thin layer of beneficial bacteria that provides protection.