1699656310_The Periodontal Ligaments (1).pdf
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Periodontal ligament Dr. Nawal Khalifa Babikir Periodontal ligament This is a connective tissue structure that surrounds the root and connect it to the bone. It is continuous with the gingival fibres, and it communicate with bone by vascular channels. In a healthy tooth it covers the root up...
Periodontal ligament Dr. Nawal Khalifa Babikir Periodontal ligament This is a connective tissue structure that surrounds the root and connect it to the bone. It is continuous with the gingival fibres, and it communicate with bone by vascular channels. In a healthy tooth it covers the root up to the cemento-enamel junction. In radiograph periodontal ligament appears as a radiolucent line paralleling the root surface. The width of PDL vary from tooth to tooth and within the same tooth. The width of the periodontal ligament is approximately 0.25 mm (range 0.2-0.4 mm). The width of PDL show progressive decrease with age. The shape of PDL is an hourglass, and is narrowest at the mid-root level. The most important thing to consider about the PDL that it is always in state of remodeling. Functions of PDL SUPPORT: PDL supports teeth in their socket. It prevents loosening of teeth. MASTICATORY LOAD: PDL permits teeth to withstand the considerable forces of mastication. SENSORY: PDL is supplied by abundant receptors and nerves that sense the movement when teeth are in function. Helps in the proper positioning of the jaws during normal function. NUTRITIVE: Blood vessels of ligament provide essential nutrients for the ligament’s vitality and hard tissue of cementum and alveolar bone. Microscopic Feature The periodontal ligament is formed of: Cells. The extracellular component. Microscopic Feature ▪ The extracellular compartment consists of : -Well defined collagen fibers bundles embedded in; -The ground substance which comprising of Glycosinaminoglycans, Glycoproteins, and Glycolipids. PDL Fibers Fibers mainly formed of collagen fibers. Other fibers :Oxytalan fiber ,Indifferent fiber plexus. The predominant collagens of PDL are types I, III. They are arranged in distinct and definite fiber bundles. They are able to adapt to the continual stresses placed on them. PDL Fibers ▪ The most important elements of the periodontal ligament are the principal fibers. Terminal portions of the principal fibers that insert into cementum and bone are termed Sharpey's fibers. The principal fiber bundles consist of individual fibers that form a continuous anatomizing network. PRINCIPAL FIBER BUNDLES OF PDL 1. Fibers are grouped into: Transeptal fibers: They run from the cementum of one tooth to the cementum of an adjacent tooth. They are lost & regenerated during and after diseases at more apical area. These fibers may be considered as belonging to the gingiva because they do not have osseous attachment. 2. Alveolar crest fibres: They extend obliquely just apical to junctional epithelium to the alveolar crest. They prevent extrusion of the tooth & resist lateral movement. 3. Horizontal fibres: Extends at right angles to the long axis of the tooth. 4. Oblique fibers: The largest group. Extends from the cementum in a coronal direction obliquely to the bone. Withstand the masticatory forces. 5.Interradicular fibers: in multirooted teeth, fan-out. 6.Apical fibers. They do not occur on incompletely formed roots. The true periodontal ligament fibers(the principal fibers), develop in conjunction with the eruption of the tooth.. The orientation of the collagen fiber bundles alters continuously during the phase of tooth eruption. Although the periodontal ligament does not contain mature elastin, two immature forms are found (Oxytalan and eluanin). In addition to these fiber types, small collagen fibers associated with the larger principal collagen fibers have been described. These fibers run in all directions, forming a plexus called the indifferent fiber plexus. Cellular elements Cells can be grouped into four groups: 1. C.T cells: fibroblast, cementoblast, osteoblast. The former is the most common. 2. The epi. Cells: rest of malassez, they are distributed close to the cementum(lattice work) , more at apical and cervical area. Associated with periapical and lateral root cyst. 3. Defence cells: macrophages, mast cells. 4. Cells associated with neurovascular elements. Ground substance: Has two main components; -Glycosaminoglycans ( hyaluronic acid & protoglycans. -Glycoprotein ( fibronictin& laminin). Water content 70%. The periodontal ligament also may contain calcified masses called cementicles, which are adherent to or detached from the root surfaces Physical Function The physical functions of the periodontal ligament entail the following: 1. Provision of a soft tissue “casing” to protect the vessels and nerves from injury by mechanical forces. 2. Attachment of the teeth to the bone. 3. Maintenance of the gingival tissues in their proper relationship to the teeth. 4. Transmission of occlusal forces to the bone. 5. Resistance to the impact of occlusal forces (shock absorption) Nerve and blood supply Nerves of periodontal ligament: Nerve are responsible for pain, tactile sensation, proprioception & pressure. Innervated by IV cranial nerve. ( Revise the cranial nerves). Blood vessels come from supra-alveolar and infra-alveolar artery.. References Newman & Carranza, Clinical Periodontology, 13 th edition. Periodontics Revisited, Shalu Bhatla
