A clear understanding of the structure and function of the periodontium is necessary in order to appreciate the disease process and treatment. The periodontium consists primarily of noncalcified and calcified connective tissues covered by a intact layer of epithelium. It is the destruction of the calcified connective tissues due to the host response to the exogenous and endogenous periodontal pathogens that result in loss of periodontal support and eventual tooth
What Are the Functions of the Periodontium?
• Attach the tooth to the alveolar bone proper
• Resist and dissipate the forces generated by mastication, speech, and deglutition
Adjust to changes in functional demands through continuous remodeling, regeneration, and repair
• Defend against the external pathogenic and environmental influences present in the oral cavity
What are the Surface Characteristics marks of the Periodontium?
• Free gingival margin: This is the most coronal edge of the gingiva.
• Free gingival groove: A groove seen on the facial gingiva that approximates the location of the base of the sulcus is one of the mark of periodontium. The free gingival groove is not always present (estimated in only 30% to 40% of adults), nor is it an exact landmark for the base of the sulcus.
• Keratinized tissue: The surface of the tissue that comprises the free and attached gingival. The boundaries are from the free gingival margin to the mucogingival junction on the facial and lingual surfaces. The keratinized tissue is continuous with the rest of the masticatory mucosa of the palate marking the surface characteristic of periodontium. The keratin is found in the stratum corneum of the epithelium and may be parakeratin (cell nuclei remaining) or orthokeratin (thick layer of keratin without remaining cell nuclei). The epithelium covering is also referred to as the oral epithelium.
• Free gingival: The gingival from the free gingival margin to the base of the sulcus. This tissue is continuous with the attached gingiva but is not bound down to any underlying structure of periodontium.
• Attached gingiva of periodontium: Gingiva that is firmly bound down to underlying tooth structure, periosteum, and bone. The boundaries to the attached gingiva are from the base of the sulcus to the mucogingival junction. The width of facial attached gingiva ranges from 1-9 mm and is greatest on the facial surface of the maxillary lateral incisor and narrowest on the facial surfaces of the mandibular canine and first premolar periodontium. On the lingual, attached gingiva was widest near the first and second molars and narrowest adjacent to the incisors and canines. The thickness of attached gingiva averages 1.25 mm ± 0.42 mm.
• Mucogingival junction: The demarcation between the attached gingiva and the alveolar mucosa apical to the attached gingiva. The mucogingival junction often appears as a distinct line between the two structures of periodontium. If the mucogingival junction is difficult to see, it may be identified as the fold area when the alveolar mucosa is gently pushed in a coronal direction.
• Alveolar mucosa: Part of the lining mucosa. The alveolar mucosa is located apical to the attached gingiva on the facial and lingual surfaces. This tissue is loosely attached to the underlying bone, freely moveable, and relatively fragile compared to the gingiva of periodontium. There are more elastic fibers in the alveolar mucosa. This tissue extends into the vestibule of the mouth and is continuous with the labial, buccal, and lingual mucosa. There is no alveolar mucosa on the hard palate.
• Masticatory mucosa: Keratinized tissue including the gingiva and the tissue covering the hard palate.
• Frenum (frenulum): The narrow band of tissue that attaches the labial and buccal mucosa to the alveolar mucosa. There is also a lingual frenum that attaches the anterior part of the tongue to the lingual aspect of the alveolar process and the floor of the mouth in the anterior region of periodontium.
• Rugae: The irregular ridges found on the anterior part of the hard palate adjacent to the incisors, canines, and first premolars.
• Stippling: The irregular surface texture of the attached gingiva, similar to the surface of an orange peel, found in 40% of adults. Stippling in periodontium occurs at the intersection of epithelial ridges that causes the depression and the interspersing of connective tissue papillae between these intersections giving rise to the small bumps.
• Melanocyte: A cell of the basal layer that produces melanin pigment granules (melanosomes) that are transferred to surrounding keratinocytes for transport. There are similar numbers of melanocytes in the epithelium regardless of the skin or gingival pigmentation present.
What Does Clinically-Healthy Gingiva Look Like?
• Sulcus: This is the space in periodontium bounded by the free gingival margin, the tooth, and the most coronal attachment of the junctional epithelium. In health, the sulcus usually measures from 1-3 mm deep. In disease, this space is referred to as a pocket.
• Col: This is the saddle-like depression in the interdental gingiva as seen from buccal to lingual apical to the contact of two adjacent posterior teeth.
What Are the Layers of Cells That Comprise the Oral Epithelium? What Are a Keratinocyte, Langerhans Cell, and a Melanocyte?
The oral epithelium consists of four layers of cells of periodontium:
1. Stratum basale: Basal layer of cuboidal cells along the basement membrane. This is where epithelial cell replication occurs. Melanocytes are found in this layer.
2. Stratum spinosum: These cells appear to have cytoplasmic spines when viewed by light microscopy. Langerhans cells, involved in the processing of antigens, are found in this layer. Keratin synthesis begins in the stratum spinosum.
3. Stratum granulosum: Keratohyalin granules may be seen in this layer of periodontium. Keratin synthesis is ongoing. Cells appear to be flattened.
4. Stratum corneum: This is the layer where para- or orthokeratinization are found.
Keratinocyte: A cell of the epidermis and parts of the mouth that produce keratin. Because of their ability to produce keratins, epithelial cells are referred to as keratinocytes. Keratins are a family of approximately 30 proteins that form the intermediate filaments of the epithelial cell cytoskeleton of periodontium. Keratins may be found extracellularly in the stratum corneum and contribute to the protective function of epithelium.
• Langerhans cell: A dendritic cell in the epidermis. These cells are found in the suprabasal layers of the epithelium. They do not have desmosomal attachments to adjacent cells of periodontium. They move in and out of the epithelium, are derived from bone marrow, and probably have an immunologic function for recognizing and processing antigens.
• Color: The normal color of gingiva is often described as coral pink. Gingiva may also have slight to significant brown pigmentation from the melanocytes located in the basal layer of the epithelium of periodontium.
• Size: Gingival contours generally follow the cementoenamel junctions of the teeth. Tissue thickness is in the 0,25-0.5 mm range. A wider zone of gingiva is normally seen in the maxillary anterior region, with the narrowest zone of gingiva on the buccal surface of the mandibular first premolars. On the lingual, it is narrowest in the mandibular region and widest in the molar area.
• Contour: Gingiva has been described as being either thin and scalloped, or thick and flatter in contour. The contour of the gingiva periodontium depends on the contour of the cementoenamel junction of the teeth, the amount of embrasure space, and the nature of the contact between teeth. The gingiva appears prominent over the tooth root and may have a slightly concave appearance in the inter- proximal area.
• Consistency: Gingiva is generally firm to the touch and attached to the underlying bone and/or tooth.
• Surface texture of periodontium: Gingiva may have either a smooth or stippled surface. Stippling is not an indicator of health nor is the absence of stippling an indicator of disease. The reappearance of stippling during therapy may be an indication of tissue returning to health.
What Supporting Structures Lie Beneath the Gingiva?
• Sclcular epithelium: The epithelium that lines the sulcus in health, secular epithelium does not have ridge formation.
Functional epithelium: The epithelium that attaches the surface of the tooth periodontium, or to compatible restorative materials. The special part of the functional epithelium that actually provides the attachment is called the epithelial attachment. This attachment consists of a lamina Lucida, lamina dense, and hemidesmosomes.
Connective tissue in periodontium: The predominantly collagenous tissue found beneath the epithelium. The connective tissue contains collagen fibers (60%), fibroblasts (5%), and interfibrillar substance composed of noncollagenous proteins and mucopolysaccharides, small numbers of neutrophils and lymphocytes, blood vessels, lymphatics, and nerves (the remaining 35%). The overlying epithelium must have intact connective tissue in order to survive. Most of the collagen found in the periodontium is type I collagen.
Gingival fibers: These are specially oriented fibers in the connective tissue of periodontium. Also known as the supracrestal connective tissue fibers, these fibers are designated by their orientation: Dentogingival, dentoperiosteal, circular, and transseptal (connecting two adjacent teeth) fibers. Some authors include the transseptal fibers in the principal fibers of the periodontium ligament, although they are actually tooth-to-tooth and not tooth-to-bone fibers.
Periodontal ligament (PDL): This is the collagenous periodontium tissue that surrounds the tooth root and attaches the tooth to the alveolar bone proper. The principal fibers of the periodontal ligament have been classified as the alveolar crest, horizontal, oblique, apical, and interradicular (in the furcation area of multirooted teeth) fibers. The oblique fibers of periodontium are the most numerous. Fibroblasts, osteoblasts, cementoblasts, osteoclasts, epithelium, and nerve cells are also found in the periodontal ligament space. The width of the PDL space is about 0.25 mm in normal function. A tooth in hypofunction may have a narrower PDL space and a tooth in hyperfunction may have a considerably wider PDL space.
• Alveolar bone: Also known as the alveolar process, this is the portion of the maxilla and mandible that form and support the tooth sockets. The alveolar process gives support to the alveoli and consists of cortical bone, cancellous trabeculae, and the alveolar bone proper.
• Alveolar bone proper: That part of the alveolar bone that lines the tooth socket. It is a perforated cribiform plate through which vessels and nerves pass between the PDL and marrow.
• Basal bone of periodontium: That part of the maxilla and mandible that supports the alveolar process. Basal bone is all that remains once all of the alveolar process is resorbed after the teeth are lost from the arch.
• Cementum in periodontium: The thin, calcified tissue of ectomesenchymal origin covering the roots of teeth in which embedded collagen fibers attach the teeth to the alveolus. There are two types of cementum: Acellular and cellular cementum. Acellular cemented does not contain cementocytes and is found on the coronal half of the tooth root. Cellular cementum contains cementocytes and is found primarily on the apical third of the root. It is continuously deposited throughout life.
What is the Blood Supply to the Periodontium?
The blood supply to the periodontium arises from the terminal branches of the internal maxillary artery. Locally, the blood supply to the gingiva consists of supraperiosteal vessels. Vessels from the alveolar bone and periodontal ligament also contribute to the coalescence of vessels in the gingival papillae, known as the gingival plexus. The alveolar bone of periodontium is supplied by branches of the anterior, middle, and posterior superior arteries to the maxilla and branches of the inferior alveolar artery in the mandible. Intra-alveolar or interdental vessels supply the interdental bone. Arterial blood generally flows in an apical-to-coronal direction. Large numbers of capillary loops that resemble renal glomeruli are beneath the junctional epithelium and sulcular epithelium near the surface of the gingiva.
Nerve supply to the periodontium is derived from terminal branches of the maxillary and mandibular branches of the trigeminal nerve. The periodontium contains sensory receptors for pain, touch, and pressure as well as proprioceptors in the periodontal ligament but not in the gingiva. The sensory nerves have their center in the semi lunar ganglion and other nerves are centered in the mesencephalic nucleus.
The biologic width is the apicocoronal distance that the junctional epithelium and supracrestal connective tissue fibers are attached to the tooth periodontium. This distance is measured histologically from the most coronal part of the junctional epithelium (base of the sulcus) to the crest of the alveolar bone. The average measurement of the biologic width is 2.04 mm, approximately 1 mm for the junctional epithelium and 1 mm for the supracrestal connective tissue fibers. The sulcus depth of periodontium is not part of the biologic width.
The body maintains the biologic width as a stable dimension. When the biologic width is encroached upon and injured by extension of restorative preparations and materials into this area, uncontrolled inflammation may result as the body tries to reestablish this dimension. In areas of thin gingiva of periodontium, this may result in recession or bleeding upon gentle probing even when the patient has good plaque control and recession.
The attachment apparatus is the alveolar bone proper, periodontium ligament fibers, and cementum that attach the root to the alveolar bone Regeneration of the attachment apparatus is one of the surgical goals in periodontal therapy.
In periodontium health, gingival crevicular fluid (GCF) is a fluid that emerges from the gingival sulcus. The gingival crevicular fluid may contain a variety of enzymes and cells, desquamating epithelium and neutroplils. flat are bang shed through the sulcus. An increase in gingval crevicuar fluid flow is the first detectable sign of inflammation. Once inflammation has occurred, the GCF is refined as an inflammatory exudates. This exudates contains serum proteins and leukocytes for periodontium.