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Periodontal ligament (PDL) Dr / Abdelatif Galal Lecturer of oral Medicine & periodontlogy  The periodental ligaments 2  INTRODUCTION Periodontal ligament is an integral part of periodontium. The periodontium is an attachment apparatus of the teeth. Teeth are atta...

Periodontal ligament (PDL) Dr / Abdelatif Galal Lecturer of oral Medicine & periodontlogy  The periodental ligaments 2  INTRODUCTION Periodontal ligament is an integral part of periodontium. The periodontium is an attachment apparatus of the teeth. Teeth are attached to the bone of the jaws by periodontium. 3 ⚫The periodontal ligament is a soft, fibrous specialized connective tissue which is present in the periodontal space; and situated between the cementum and bone. ⚫The periodontal ligament extends coronally up to the most apical part of connective tissue of gingiva. ⚫Because the collagen fibers are attached to the cementum and alveolar bone, the ligament provides soft tissue continuity between the mineralized connective tissues of periodontium.  PDL has the shape of an hour glass. It ranges in width from 0.15-0.38mm , is thinnest in the mid root area , and decreases slightly in thickness with age. 5  Histological structure of PDL. The periodontal ligament formed from : Intercellular substances Synthetic Fibers Resorptive ground substances Progenitor blood vessels, Defensive nerves & lymphatics. 6  Synthetic fibroblasts, osteoblasts and cementoblasts. cells Resorptive cementoclasts , osteoclasts and fibroblasts. cells Progenitor undifferentiated mesenchymal cells. cells Epithelial cells remnants of the epithelial Defensive macrophage, lymphocytes and mast root sheath of Hertwig cells cells. 7 1-Synthetic cells : They have the ability to produce &secret protein. A – Fibroblasts: are the most common cells( principle cells) in periodontal ligament which found usually running parallel to the collagen fibers of PDL. They constitute about 65% of total population of PDL. they are responsible for formation of ground substance & collagen fibers of PDL. The fibroblast is stellate shaped cell which produces: 1. Collagen fibers 2. Reticulin fibers 3. Oxytalan fibers. The damaged periodontal fibers are replaced and remodeled by newly formed fibers. The “RENEWAL CAPABILITY” is an important characteristic of periodontal ligament. 8  b- Osteoblasts : Although technically situated within the PDL, these cells are responsible for bone formation and growth of bone tissue. They are seen along the surface of the bone lining the dental socket. The osteoblast synthesize collagen and ground substance of bone matrix. C- Cementoblasts : Cementoblasts are responsible for formation of cellular cementum ; found covering the periodontal surface of the cementum. They have ultrastructural characteristics typically of cell activity synthesizing protein (i.e. an abundant endoplasmic reticulum , a well developed Golgyi apparatus and several mitochondria. 9  Cementoblasts Osteoblasts 1 Both are rich in alkaline phosphatase activity. 0  2-Resorptive cells: a- Osteoclasts : - Osteoclast cells resorb bone and tend to be large and multinucleated (Multinucleated osteoclasts are formed by fusion of several cells or by division of the nucleus with out division of the cells ). - it has an eosinophilic cytoplasm rich in acid phosphatase. - They are usually present in depression in bone known as Howship’s lacunae - Resorption occurs in two stages: The mineral is removed at bone margins and then exposed organic matrix disintegrates. 10 b- Cementoclasts: resemble osteoclasts and are occasionally found in normal functioning PDL. but not remodeled like alveolar bone and periodontal ligament. These are found on the surface of cementum.  Resorptive Cells of PDL Osteoclasts Cementoclasts Both are rich in acid phosphatase activity. 11 C-FIBROBLASTS Fibroblasts are capable of both synthesis and resorption (Dual action) of collagen fibers of PDL. The presence of collagen resorbing fibroblasts in a normal functioning periodontal ligament indicates resorption of fibers occurring during remodeling of periodontal ligament. 3-Progenitor cells (U. M. C.): Progenitor cells are the undifferentiated mesenchymal cells Can undergo mitotic devision Can differentiate to different types of cells Have small, closed-face nucleus Little amount of cytoplasm Found close to blood vessels  Epithelial cell rests of Mallassez: These cells are the remnants of HERS and found in the PDL. close to cementum Most numerous in the apical area & cervical area. They are found as a network , strands or tubules. They reduce in number with age and may undergo calcification to form cementicles. 13  Defensive Cells : a- MAST CELLS Small round or oval cell. Contain numerous cytoplasmic ,Contain heparin & histamine. Histamine plays a role in inflammatory reaction. Occasionally seen in healthy PDL. It may cause proliferation of endothelial & mesenchymal cells.  b-Macrophage cells ( Histiocytes): They are predominantly present in PDL, and are embedded adjacent to the B.V. Nucleus has a regular contour and may be kidney shaped with a dense peripheral layer of chromatin. Surface may be raised in microvilli. Role of macrophage in PDL : 1. Phagocytosing dead cells 2. Secreting growth factors that regulate the proliferation of adjacent fibroblasts 14  -Ground substance : It mainly consists of mucopolysuccharides and glycoprotein.The ground substance fills the space between cells , blood vessels and nerves. -Interstitial tissues: They are found between the fibers of the periodontal ligament. *They are areas that contain some of the blood vessels, lymphatic and nerves. *They are surrounded by loose connective tissue. 15  Blood supply The arterial blood supply of the periodontal ligament is derived from 3 sources 1) Branches from the gingival vessels these enter the PDL from the coronal direction. 2) Branches from the intra-alveolar vessels, these branches run horizontally and these constitute the main blood supply. 3) Branches from the apical vessels that supply the dental pulp. Nerve supply: The nerve supply of periodontal ligament comes from either the inferior or superior dental nerves. 1 Bundles of nerve fibers run from the apical region of the root towards the gingival margin. 2 Nerves enter the ligament horizontally through multiple foramina in the bone. The nerve fibers are either of large diameter or a small diameter Small nerve fibers pain sensation Are responsible for Large nerve fibers touch & pressure 17  Principle fibers of the periodontal ligaments The most important element of periodontal ligament -principal fibers. The principal fibers are collagenous in nature and arranged in bundles The periodontal fibers of PDL primarily composed of bundles of type I collagen fibrils. Vitamin C help in formation and repair of collagen Dental implants lack periodontal ligament fibers and they have a rigid connection to bone (Osseointegration). They have been classified into several groups on the basis of their anatomic location.  The following constitute the principle fiber groups of the periodontal ligaments: 1- Alveolar crest fibers. 2- Horizontal fibers. 3- Oblique fibers. 4- Apical fibers. 5- Interradicular fibers. 19 SHARPEY’S FIBERS Collagen fibers bundles are attached in cementum at one end of PDL space and alveolar bone at other end. These fibers do not run in straight line but have a wavy course. 20 Oxytalan Fibers: ❑ Run in axial or oblique direction. ❑ One end being embedded in cementum or bone and the other end in the wall of blood vessels. ❑ The function of the oxytalan fibers has been suggested that they play a part in supporting the blood vessels of the periodontal ligament during mastication i.e., it prevents the sudden closure of the blood vessels under masticatory forces. 21  Functions Of PDL 1. Supportive function. 2. Formative and Remodeling 3. Nutritive 4. Sensory. 22 The Age Changes of periodontal ligament The periodontal ligament through aging shows Vasuclarity Cellularity Thickness 23