The periodontium, defined as tissues supporting and fixing the tooth, comprises root cementum, periodontal ligament, bone lining the tooth socket (alveolar bone) and part of the gingiva facing the tooth (dentogingival junction) (Fig. 1.21.).
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The periodontium GINGIVA
The gingiva is part of the oral mucosa that covers the alveolar processes of the jaws and surrounds the cervical portion of the teeth.
Functions
• covering the cervical portions of the teeth and the alveolar processes of the jaws
• composed of a thin outer layer of epithelium and an underlying core of connective tissue
• provides a tissue seal around the cervical portions of the crowns Macroscopic anatomy of the gingiva (Fig. 1.22.)
• Free gingiva (marginal gingiva):unattached portion of the gingiva that surrounds the tooth in the region of the cementoenamel junction
• Gingival sulcus: V-shaped, shallow space between the free gingiva and the tooth surface. The depth is 1-3 mm for a clinically normal gingival sulcus and is measured using a periodontal probe around the tooth. The base of the sulcus is formed by junctional epithelium.
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• Attached gingiva: Gingiva that is tightly connected to the cementum on the cervical third of the root and to the periosteum (connective tissue cover) of the alveolar bone. It lies between the free gingiva and the alveolar mucosa.
• Interdental gingiva:the portion of the gingiva that fills the area between two adjacent teeth apical to the contact area
1. Papilla/Papillae:the interdental (or interproximal) gingiva consists of two interdental papilla (one facial, one lingual)
2. Col area:Valley-like depression in the interdental gingiva. It lies directly apical to the contact area. The col is not present if the adjacent teeth are not in contact or if the gingiva has receded.
• Mucogingival junction:The clinically visible boundary where the pink attached gingiva meets the red, shiny alveolar mucosa. •Alveolar mucosa: Movable tissue loosely attached to the underlying bone. Nonkeratinised, thin, smooth and shiny epithelium. The underlying vessels may be seen through the epithelium. It also covers the vestibule and the floor of the mouth and continues in the buckle and labial mucosa.
Macroscopic anatomy of theperiodontium
The colour of the attached and marginal gingiva is generally described as "pale pink" and is produced by the vascular supply and the thickness and degree of keratinisation of the epithelium. The alveolar mucosa is nonkeratinised red, smooth and shiny rather than pink and stippled. The connective tissue of the alveolar mucosa is loosely arranged and the blood vessels are more numerous. The attached gingiva may exhibits varying degrees of brownish pigmentation due to synthesis f melanin by melanocytes locatedin the basal cell layer of oral epithelium (Fig. 1.23.).
Pigmented gingiva
The contour or shape of the gingiva varies considerably and depends on different factors (the shape of the teeth and their alignment in the arch, the location and size of the area of proximal contact). The marginal gingiva envelops the teeth in a collar-like fashion and has a scalloped outline on the facial and lingual surfaces.
The gingiva is firm and resilient and, with the exception of the movable free margin, tightly bound to the underlying bone. It presents a textured surface similar to an orange peel and is referred to as being stippled (the attached gingiva). Stippling is best viewed by drying the gingiva. It is absent in infancy, first appears in children at about 5 years of age, increases until adulthood and frequently begins to disappear in old age.
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The position of the gingiva refers to the level at which the gingival margin is attached to the tooth (normally strongly attached to the cementoenamel junction).
Microscopic anatomy of the gingiva
The gingiva consists of epithelium and connective tissue (lamina propria). The epithelium covering the free gingiva may be classified into three types:
1. Oral epithelium (OE)which faces the oral cavity
2. Oral sulcular epithelium (OSE)covering the gingival crevice or pocket
3. Junctional epithelium (JE)which provides the contact between the gingiva and the root
The attached gingiva covered by oral epithelium. Characterisation of cell layer (OE, OSE) from basal layer to granular cell layer:
• height of cells decrease
• the number of desmosomes and the number of tonofilaments in the cytoplasm increase
• the number of cell organells decrease The connective tissue (CT) consists of
• collagen fibers (60%)
• cells (5%) – fibroblasts, PMN, macrophages, lymphocytes
• matrix (35%) vessels and nerves are embedded in an amorphous ground substances
The supraalveolar gingival fiber bundles attach the gingiva to the tooth surface and to the alveolar bone.
Functions of the gingival fibers:
• maintaining of resistance and resiliency of the gingiva
• resistance to force
• stabilizing of the tooth
• supporting of junctional epithelium
The gingival fibers are: circular, semicircular, interpapillary, intercircular, intergingival, transseptal fibers.
The biological width is defined as the dimension of the soft tissue, which is attached to the portion of the tooth coronal to the crest of the alveolar bone. Biologic width is the distance established by "the junctional epithelium and connective tissue attachment to the root surface" of a tooth. The biologic width is essential for preservation of periodontal health and removal of irritation that might damage the periodontium (prosthetic restorations, for example).
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Microscopic anatomy of the gingiva
A: Enamel, B: Cementum, C: Alveolar bone, D: Gingiva, E: Periodontal ligaments, f: dentogingival fibers, g:
gingival fibers, h: alveologingival fibers, i: periostogingival fibers, j: JE, k: OSE, l: OE, p: oral mucosa, q:
attached gingiva, r: marginal gingiva, s: sulcus gingivae (gingival crevice) IG: intergingival fibers, TG:
transgingival fibers, IC: intercircular fibers, C: circular fibers, DG: dentogingival fibers PERIODONTAL LIGAMENTS
The periodontal ligament is the connective tissue that surrounds the root and connects it with the bone. It is continuous with the connective tissue of the gingiva and communicates with the marrow spaces through vascular channels in the bone. The average width is about 0.2 mm.
Principal fibres of the periodontal ligament: they are classified into several groups on the basis of their anatomical location. Oblique fibres are the largest group among the periodontal ligaments; they extend from the cementum in a coronal direction obliquely to the bone. They bear the brunt of vertical masticatory forces and transform them into tension on the alveolar bone (Fig. 1.25.).
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The periodontal ligaments Functions of the Periodontal Ligament
Physical functions
• Transmission of occlusal forces to the bone.
• Attachment of the teeth to the bone.
• Resistance to the impact of occlusal forces (shock absorption) Formative and Remodelling Function
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The periodontal ligament is constantly undergoing remodelling. The cells of the periodontal ligament participate in the formation and resorption of cementum and bone, which occur:
• in physiological tooth movement;
• in the accommodation of the periodontium to occlusal forces
• in the repair of injuries.
Nutritional and Sensory Functions
It supplies nutrients to the cementum, bone and gingiva by way of blood vessels and provides lymphatic drainage. It contains sensory nerve fibres capable of transmitting tactile, pressure and pain sensations. Nerve bundles pass into the periodontal ligament from the periapical area and through channels from the alveolar bone that follow the course of the blood vessels.
CEMENTUM
Cementum is calcified mesenchymal tissue that forms the outer covering of the anatomic root. There are for main types of root cementum:
1. Acellular, afibrillar cementumIt is found as coronal cementum
2. Acellular, extrinsic fiber cementumThis cementum is located in the cervical two-thirds of the root 3. Cellular, intrinsic fiber cementumIt is located in the lacunas of the root at sites of cementum repair.
4. Cellular, mixed fiber cementumIt is found on the apical third of the root and in furcations Both consist of a calcified interfibrillar matrix and collagen fibrils.
Thickness of the cementum is increase from the coronal part (50-150 micrmeter) to the apical portion (200-600 micrometer). Cementum deposition is a continuous process, most rapid in the apical part of the root.
Hypercementosis is prominent thickening of cementum layer.
Cementum resorption may be due to local or systemic causes (trauma from occlusion, orthodontic movement, cysts and tumours, replanted and transplanted teeth) •Cementum resorption is not continuous, it may alternate with periods of repair
ALVEOLAR PROCESS
The alveolar process is the portion of the maxilla and mandible that forms and supports the tooth sockets. It consists of compact bone and cortical bone. The existence of the alveolar bone is dependent on the presence of teeth. When teeth are extracted, in time the alveolar bone resorbs so only basal bone remains.
The alveolar process consists of (Fig. 1.26):
• Alveolar bone proper (it is perforated by numerous small canals through wich blood and lymph vessels as well as nerve enter the periodontal space)
• Trabecular bone (relatively small amount , often missing at lower incisors, upper canines and upper premolars)
• Compact bone (meet with alveolar bone at margin to form the alveolar crest)
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The alveolar process
Anatomical areas of the alveolar bone (Fig.1.27.):
• Alveolar crest (the most coronal portion of the alveolar process, located 1-2 mm apical to the CEJs of the teeth)
• Interproximal bone (the area of bone that lies between the proximal surfaces of two adjacent teeth)
• Interradicular bone (bone between the roots of the same tooth)
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The contour of the bone normally conforms to the prominence of the roots. The height and thickness of the facial and lingual bony plates are affected by the alignment of the teeth, by the angulation of the root to the bone and by occlusal forces.
Isolated areas in which the root is denuded of bone and the root surface is covered only by periosteum and overlying gingiva are termed fenestrations. In these instances the marginal bone is intact. When the denuded areas extend through the marginal bone, the defect is called a dehiscence (Fig. 1.27.). Fenestration and dehiscence are important, because they may complicate the outcome of periodontal surgery.
The anatomical areas of the alveolar bone. Fenestration and dehiscence