Due to the prominence of teeth in oral health, many dentists and students often overlook the periodontium and its anatomy, which turns out to be one of the most important elements for oral well-being, responsible for the functions of protection and support for our teeth.
In this guide, we will discuss all the points that address the periodontium, such as its anatomy, functions, structures, and characteristics.
What is the Periodontium and What Does it Comprise?
The periodontium is a set of structures that surround the teeth, providing the necessary support to maintain their function. It consists of four main structures:
- Gingival Epithelium: the most superficial structure that covers the alveolar bone and root cementum.
- Periodontal Ligament: a fibrous structure that connects the root cementum to the alveolar bone.
- Root Cementum: a layer of calcified tissue that covers the tooth’s root.
- Alveolar Bone: the bony structure forming the base of the oral cavity.
Although they have differing locations and compositions, all four structures work together to maintain the same unit in operation. Thus, when any of these structures undergo any alteration due to pathologies, the other components of the periodontium also experience implications in their functions.
Function of the Periodontium
The primary function of the periodontium is to protect teeth from harmful external agents and ensure their support. In essence, it helps protect the tooth roots, cushioning the forces of chewing, preventing fractures, and serving as a protective barrier against bacteria and other substances that can lead to gum and tooth pathologies.
Gingival Epithelium
The gingival epithelium serves various functions, such as acting as a physical barrier to protect against organisms and infection, providing an attachment for the underlying gum, and, according to recent research, playing an active role in the immune defense by assisting in response and immune signaling when bacteria enter the epithelium, for instance.
It is divided into three types:
- Oral External Epithelium: the part of the epithelium facing the oral cavity, consisting of marginal (or free) gum, attached gum, and interproximal gum.
- Sulcular Oral Epithelium: the area facing the tooth without direct contact with it.
- Junctional Epithelium: one of the most critical regions of the gingival epithelium, responsible for promoting gum-to-tooth contact.
All three types of epithelium serve the same function, maintaining oral homeostasis and participating in the immune defense system.
Marginal Gum
The marginal gum, or free gum, is the portion of the gum that covers the crowns of the teeth. It consists of a keratinized stratified squamous epithelium, a layer of cells that covers the external surface of the gum and is responsible for protection against injuries, infections, and other aggressive agents.
When a pathology affects the gum, it is common for it to become inflamed, and the primary points of bleeding and swelling are usually located in the marginal gum itself.
Free gum also functions to protect the teeth and the bones of the oral cavity, providing a hermetic seal around the tooth. It is separated from the attached gum through the gingival sulcus.
Attached Gum
The attached gum is the portion of the gum that begins just below the gingival groove of the marginal gum and extends to the alveolar mucosa, being connected to the periosteum. It consists of a stratified squamous epithelium that varies between keratinized and parakeratinized, giving it a firm and resilient characteristic to mechanical damage.
One of its primary functions is to protect the teeth and the bones of the oral cavity, making it an important component of what we call the protective periodontium.
It has a firm, pink texture and, like the marginal gum, may have an “orange peel” appearance in healthy individuals due to the insertions of connective fibers.
Interproximal Gum
The interproximal gum is the portion of the gum that lies between two adjacent teeth. It consists of non-keratinized stratified squamous epithelium and serves to protect the teeth and the bones of the oral cavity, making it a component of the protective periodontium.
The interproximal gum also has an important aesthetic function, as it is the part of the gum that forms the “black triangle” or “col” between the teeth. It is separated by an interdental space, which is the region between the teeth.
Sulcular Epithelium
Also known as sulcular epithelium, it is the part of the gingival epithelium that lies between the enamel and the upper layer of the marginal (or free) gum but without direct contact with the tooth. Its epithelium consists of cuboidal cells and is stratified squamous with a keratinized surface.
Its main characteristics include:
- While being less permeable than the junctional epithelium, it can still act as a semipermeable membrane, allowing the passage of some pathogens.
- It is thicker in the coronal region.
- It has a thickness of approximately 0.69 mm, which may vary from person to person.
Junctional Epithelium
As mentioned earlier, the junctional epithelium promotes contact between the tooth and the gum. Like the sulcular and oral epithelia, it is constantly renewed through the cell division of the basal layer.
Some of its main characteristics include:
- It tapers from the coronal region to the apical region.
- In healthy tissues, the junctional epithelium is located at the cementoenamel junction.
- It has a low protective effect against the biofilm that comes from the gingival sulcus.
- One of its functions is to allow access for gingival fluid, inflammatory cells, and immune components to the marginal gum.
- Its cells have a rapid turnover, renewing every 6 to 7 days.
- It has endocytic capacity, capturing, isolating, and degrading cellular debris and microbial agents.
Periodontal Ligament
The periodontal ligament is a fibrous structure that connects the root cementum to the alveolar bone. It is responsible for cushioning the forces of mastication and helping to keep the teeth firmly in place. Additionally, the periodontal ligament is responsible for nourishing the root cementum and the alveolar bone.
These fibers are organized into six groups:
- Transseptal fibers: These are present in the interproximal spaces between teeth and insert into the cementum of one tooth to the cementum of the adjacent tooth. Since they do not make contact with the alveolar bone, they are considered gingival fibers.
- Alveolar crest fibers: These fibers extend obliquely from the cementum to the alveolar bone crest. Sometimes, they may also pass over the crest and insert into the periosteal layer covering the alveolar bone.
- Horizontal fibers: These fibers extend perpendicularly from the tooth’s cementum to the alveolar bone.
- Oblique fibers: These are the most numerous fibers and extend obliquely from the cementum to the alveolar bone. Like the larger group, they play an important role in supporting the impact of occlusal forces and converting them into tension for the alveolar bone.
- Apical fibers: They extend apically and irregularly from the cementum to the alveolar bone, near the base of the alveolus. For this reason, apical fibers are not found in teeth that are still developing.
- Inter-radicular fibers: As the name suggests, these fibers fan out from the cementum to the furcation areas in multi-rooted teeth.
Root Cementum
The root cementum is a layer of mineralized, calcified, and avascular tissue that covers the root surface of the tooth. It is divided into two main types, cellular (primary) root cementum and acellular (secondary) root cementum.
Like other mineralized tissues, both types consist of calcified interfibrillar matrix and collagen fibers embedded in an organic matrix.
The primary source of collagen fibers in cementum is mainly the Sharpey’s fibers, which are produced by fibroblasts and have their ends inserted into both the cementum and the alveolar bone. Thanks to these fibers present in acellular root cementum, it becomes an essential element in the supportive periodontium, as it facilitates the connection between the tooth and the alveolar bone.
Alveolar Process
The alveolar process, also known as the alveolar bone, is the portion of the maxilla or mandible that forms the tooth sockets and provides support for the teeth. It develops during tooth eruption and, barring pathological changes, exists until the tooth’s loss, after which it gradually diminishes.
The alveolar process consists of:
An outer layer of cortical bone. An inner wall formed by thin and compact bone. Spongy trabeculae, which are located between the two layers of bone mentioned above and are responsible for supporting the alveolar bone.
The alveolar process, together with the other structures of the supporting periodontium, which include the root cementum and the periodontal ligament, constitutes the apparatus for tooth support and attachment. Its primary function is to distribute the occlusal forces generated during mastication and other dental contacts, such as those occurring during oral parafunction.
Histology of the Periodontium
As previously mentioned, the periodontium is composed of various structures, and to better explain its histology, it’s necessary to break it down into several topics.
Histology of the Oral Epithelium
Since the oral epithelium is made up of a keratinized stratified squamous epithelium, the majority of its cells (around 90%) are keratin-producing cells. However, summarizing its histology in this way would be a significant mistake, as the other 10% are also crucial for its functioning. (2)
These cells are:
- Keratinocytes: These make up about 90% of all cells in the oral epithelium, and their function is to produce keratin, a fibrous protein that waterproofs and acts as a protective layer for the epidermis.
- Merkel Cells: Located in the basal layer, Merkel cells have a sensitivity function.
- Langerhans Cells: These cells participate in the epithelium’s defense system, reacting to antigens that penetrate it. They are responsible for initiating an immune response to prevent these antigens from reaching deeper layers.
- Melanocytes: As the name suggests, these cells are responsible for producing melanin, providing protection from UV radiation to the epithelium.
Connective Tissue of the Gingiva
The connective tissue of the gingiva is divided into the papillary layer, which is adjacent to the epithelium, and the reticular layer, which is contiguous with the periosteum of the adjacent alveolar bone.
- Papillary Layer: This is a loose connective tissue with papillae responsible for adhering to the epithelium.
- Reticular Layer: This is a dense, unmodeled connective tissue, essentially the proper connective tissue. It is much thicker than the papillary layer.
Extracellular Compartment
In addition to these two layers, this connective tissue consists of a cellular component and an extracellular compartment. Therefore, the main components of this tissue, based on volume, are:
- Collagen fibers (about 60% of the volume).
- Fibroblasts (5% of the volume).
- Blood vessels, nerves, and matrix (approximately 35% of the volume).
Connective Tissue Fibers
This connective tissue has three types of fibers, which include:
- Collagen fibers: As the name suggests, they are made of collagen, giving them a thick and resistant character, preventing the tissue from tearing when stretched.
- Reticular fibers: These are branched fibers that connect the connective tissue to adjacent tissues.
- Elastic fibers: Made of elastin, they provide elasticity to the loose connective tissue, complementing the strength of collagen fibers. They are responsible for returning the tissue to its initial position after being stretched.
Ground Substance
However, all these components do not directly contact each other in the connective tissue; something needs to fill the space between them, and the substance responsible for this is called the ground substance.
The ground substance is responsible for filling the spaces between the fibers and cells, and it has a high water content. It consists of proteoglycans and glycoproteins.
Glycoproteins and Proteoglycans
Among the proteoglycans in the ground substance, the most prominent is hyaluronic acid. And among its glycoproteins, the main ones are:
- Fibronectin: It binds fibroblasts to the fibers and many other components of the cell matrix, aiding in cell adhesion, migration, and mediating functions like phagocytosis, and coagulation.
- Laminin: Among many other roles, laminin’s primary function is to connect the basement membrane to the epithelium. It plays a role in cell adhesion, migration, differentiation, and growth.
Gingival Fibers
Continuing to discuss the connective tissue of the gingiva, there are gingival fibers that have specific functions: to promote the adhesion of the gingiva to the tooth, provide resistance to the forces of mastication without apical displacement, and connect the marginal, inserted, and cementum gingiva. These fibers are divided into:
- Dentogingival fibers: They have a fan shape and extend from the cementum to three directions, the marginal crest, inserted gingiva, and periosteum. In the region between the teeth, they are directed toward the interdental gingiva.
- Circular fibers: These pass through the connective tissue without any contact with the tooth, forming a ring-like fiber.
- Interproximal (transseptal) fibers: These fibers extend from the root cementum of one tooth to insert into the root cementum of the adjacent tooth.
- Dentoperiosteal fibers: They extend from the root cementum to the periosteum.
Were you able to absorb the knowledge?
It is of utmost importance for a dentist or dental student to understand the structures and their respective functions in the periodontium, as it is through it that the tooth will enjoy essential protection and support for its development and health. In the same way, if a dentist or student does not understand these structures, they may inadvertently harm the patient. Therefore, share this post with anyone you believe needs to know more about this subject.
Source of Information
(1) Newman M. G. Takei H. H. Klokkevold P. R. & Carranza F. A. (2019). Newman and Carranza’s Clinical Periodontology (Thirteenth). Elsevier. Retrieved June 23, 2023, from https://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nlabk&AN=1903217.
(2) Lindhe J. Lang N. P. & Karring T. (2008). Clinical Periodontology and Implant Dentistry (5th ed.). Blackwell Munksgaard.
