Oral Biology I: Periodontal Ligament PDF

Course Title: Oral Biology I Course Code: BDS123 Topic of Lecture: Periodontal ligament Structure Lecturer: Prof Samah Mehanny F A C U L T Y O F D e n t i s t r y T h e F u t u r e S t a r t s H e r e S u m m...

Course Title: Oral Biology I Course Code: BDS123 Topic of Lecture: Periodontal ligament Structure Lecturer: Prof Samah Mehanny F A C U L T Y O F D e n t i s t r y T h e F u t u r e S t a r t s H e r e S u m m e r 2 0 2 4 Pepared by Samah Mehanny  Periodontium: Is the investing and supporting attachment system of the teeth. It consists of: Two soft tissues Two hard tissues 1- Gingiva 1- Cementum That part covers the neck of the tooth and part of the alveolar covers the anatomical root bone. 2- Alveolar Bone The bone of the jaw that 2- Periodontal Ligament surrounds the root of the Strong ligament that attaches tooth the tooth to the alveolar bone Pepared by Samah Mehanny ◼ Definition: The periodontal ligament is the dense fibrous connective tissue that occupies the periodontal space between the root of the tooth and the alveolus. Inflammation from the dental pulp and gingiva could spread to involve the PDL and other apical supporting tissues. Pepared by Samah Mehanny Pepared by Samah Mehanny Pepared by Samah Mehanny Width of the periodontal ligament: It ranges from 0.15-0.21 mm. The narrowest area is at the mid-root ( Fulcrum ). The region at the alveolar crest is the widest area followed by the apical region. The width is generally reduced in: Non-functioning teeth. Un-erupted teeth. Bone While increased in: Dentin *Teeth subjected to occlusal stress within the physiological limits. *Deciduous teeth Pepared by Samah Mehanny The periodontal ligament resembles immature, fetal-like connective tissues in the following features: 1- High rate of turnover. 2- Large volume of ground substance. 3- The presence of oxytalan fibers. 4- High cellularity. 5- Similar biomechanical properties. Pepared by Samah Mehanny Development of periodontal ligament Pepared by Samah Mehanny Pepared by Samah Mehanny 1-Dense fibrous and cellular tissues immediately encapsulate the developing tooth. (Cementum) 2-Mesenchyme away from the tooth. (PDL , Alveolar bone) Pepared by Samah Mehanny Pepared by Samah Mehanny Pepared by Samah Mehanny  Histological structure The periodontal ligament is formed of : Intercellular Cells substances Synthetic Fibers, Resorptive Ground substances Progenitor Blood vessels, Defensive Nerves & lymphatics. Pepared by Samah Mehanny Pepared by Samah Mehanny  The Fibers ◼ 1- Collagen fibers type I: They are embedded in both the cementum and bone (Sharpey’s fibers) A- Principal: Prevent intrusive apical as well as lateral tooth movements. B- Accessory: Prevent rotatory tooth movements. ◼ 2- Oxytalan fibers ( immature elastic fibers): Keep the patency of the blood vessels ◼ 3-Elastic fibers are restricted almost entirely to the walls of blood vessels. Pepared by Samah Mehanny Pepared by Samah Mehanny  A- The principal fibers: They are formed of collagen bundles having a wavy course and are arranged in three groups. a) Gingival fibers. b) Transseptal or interdental ligament. c) Alveolodental ligament which is subdivided into the following five subgroups: 1- Alveolar crest group. 2- Horizontal group. 3- Oblique group. 4-Apical group. 5- Interradicular group. Pepared by Samah Mehanny Pepared by Samah Mehanny  a-The gingival fibers: They form a rigid cuff around the tooth. Function: They add stability to the gingiva and resist gingival displacement. Pepared by Samah Mehanny Pepared by Samah Mehanny b- The trans-septal ligament: *It connects two adjacent teeth. *The ligament runs from the Dentin cementum of one tooth over the crest of the alveolus to the cementum of the adjacent tooth. *Function: Bone 1-Maintain the mesiodistal width Dentin and teeth alignment. 2-Prevent tooth rotation. Pepared by Samah Mehanny Pepared by Samah Mehanny c- The alveolo-dental ligament: It resists the masticatory forces and is formed of: 1-Alveolar crest group: radiates from the crest of the alveolar process and Bone Dentin attaches themselves to the cervical part of the cementum. Function: resists vertical and intrusive forces. Pepared by Samah Mehanny Pepared by Samah Mehanny 2-Horizontal group: The fiber bundles run from the cementum to the bone at a right angle to the long axis of the tooth. Bone Dentin Function: 1-Prevent extrusion of teeth. 2- Resist lateral tooth movements. Pepared by Samah Mehanny 3- Oblique group: The fiber bundles run obliquely. Their attachment in the bone is somewhat coronal (higher) than the attachment in the cementum. bone The greatest number of fiber dentin bundles are found in this group. Function: *Performs the main support of the tooth against masticatory forces. *Resists vertical and intrusive forces. Pepared by Samah Mehanny  dentin 4- Apical group: The bundles radiate from the apical region of the root to bone the surrounding bone Function: Resists vertical force. bone Pepared by Samah Mehanny Pepared by Samah Mehanny 5- Interradicular group: dentin The bundles radiate from the interradicular septum to the furcation of the multirooted tooth. Function: bone resists vertical and lateral forces. Pepared by Samah Mehanny Pepared by Samah Mehanny Pepared by Samah Mehanny Pepared by Samah Mehanny  B- Accessory fibers: They are collagenous in nature and run from bone to cementum in different planes, more tangentially to prevent rotation of the tooth and found in the region of the horizontal group. Pepared by Samah Mehanny Pepared by Samah Mehanny 2- Oxytalan fibers These are immature elastic (pre- elastic) fibers. They need special stains to be demonstrated. They tend to run in an axial direction, one end being embedded in bone or cementum and the other in the wall of the blood vessels. At the apical region, they form a complex network. Pepared by Samah Mehanny Pepared by Samah Mehanny The functions of oxytalan fibers: 1-Support nerves. 2- Support blood vessels. 3- Help fibroblasts migration. Pepared by Samah Mehanny Pepared by Samah Mehanny  Histological structure The periodontal ligament is formed of : Intercellular Cells substances Synthetic Fibers, Resorptive Ground substances Progenitor Blood vessels, Defensive Nerves & lymphatics. Pepared by Samah Mehanny Pepared by Samah Mehanny  The cells Synthetic fibroblasts, osteoblasts and cementoblasts. cells cementoclasts , osteoclasts and fibroclasts. Resorptive Note that fibroblasts perform both synthetic cells and resorptive activities. Progenitor undifferentiated cells mesenchymal cells Defensive macrophage, lymphocytes cells and mast cells Epithelial cells remnants of the epithelial root sheath of Hertwig Pepared by Samah Mehanny Pepared by Samah Mehanny  Synthetic Cells of PDL ◼ Fibroblasts (predominate cells) ◼ Cementoblasts ◼ Osteoblasts Pepared by Samah Mehanny Pepared by Samah Mehanny PDL Fibroblasts Oriented parallel to collagen fibers Are motile due to contractile properties Show numerous microtubules & microfilaments Perform fibroclastic function Ingestion collagen fibers Contains intracellular collagen profiles & vacoules Contains lysosomal system Pepared by Samah Mehanny Pepared by Samah Mehanny  Cementoblasts Osteoblasts Both are rich in alkaline phosphatase activity. Pepared by Samah Mehanny Pepared by Samah Mehanny  Resorptive Cells of PDL Osteoclasts and Cementoclasts * Multi-nucleatd giant cells with ruffled border. *Rich in acid phosphatase enzymes. *Characterized by presence of many mitochondria and lysosomes. *Attached to the resorped bone at its peripheries. Pepared by Samah Mehanny Pepared by Samah Mehanny  Progenitor cells U. M. C. 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 Pepared by Samah Mehanny Pepared by Samah Mehanny  Defensive Cells of PDL Macrophages Mast cells lymphocytes Note: There are no plasma cells. Pepared by Samah Mehanny Pepared by Samah Mehanny Epithelial Cells: remnants of the epithelial root sheath of Hertwig. They are separated from the surrounding connective tissue by a basal lamina. They show low cells turnover, although they may proliferate to form cysts or tumors. Pepared by Samah Mehanny Pepared by Samah Mehanny  Blood supply The arterial blood supply of the periodontal ligament is derived from 3 sources: 1- Branches from the gingival vessels. 2- Branches from the intra-alveolar vessels, these branches run horizontally, and constitute the main blood supply. 3- Branches from the apical vessels that supply the dental pulp. Pepared by Samah Mehanny Pepared by Samah Mehanny  Perforating arteries are more abundant in the PDL of posterior teeth than in that of anterior. In the cervical region of PDL there are coiled fenestrated capillaries Many arteriovenous anastomosis occur in the PDL Venous blood directed from the gingival region to the apical area and bone (opposite direction of the arterial blood) Pepared by Samah Mehanny Pepared by Samah Mehanny 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. Pepared by Samah Mehanny Pepared by Samah Mehanny  Nerve fibers are either large or small fibers: Small nerve fibers Are responsible for pain sensation Myelinated or unmyelinated Large nerve fibers Are responsible for touch & pressure myelinated (mechanoreceptors) Stimulation of the mechanoreceptors initiates a reflex jaw opening. This reflex is a protective mechanism to prevent forces applied to the teeth from reaching damaging levels. Pepared by Samah Mehanny Pepared by Samah Mehanny  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. *They are designed to withstand the impact of masticatory forces Pepared by Samah Mehanny Pepared by Samah Mehanny Kindly figure out is it possible to regenerate PDL and cementum. Pepared by Samah Mehanny Pepared by Samah Mehanny Knocked out tooth The length of time before a tooth is re-implanted (within half an hour) and how it is transported to the dentist (in saline) are critical in successfully saving and re-implanting the tooth. The periodontal ligament will regenerate and revascularize. A tooth that is replaced within half an hour has a 90% chance of successful re-implantation. Pepared by Samah Mehanny  Functions of the periodontal ligament: 1- Supportive and protective functions: a-During masticatory forces: These functions are achieved by collagen fibers, blood vessels, and nerves (mechanoreceptors). b-During mesiodistal orthodontic tooth movement: These functions are achieved by collagen fibers, blood vessels, and ground substances. Pepared by Samah Mehanny Role of the collagen fibers: *As the masticatory force is applied to the teeth, the wavy course of the collagen fibers gradually straightens out and then acts as inelastic strings. The fibers then transform the masticatory pressure exerted on the tooth into tension on the cementum and bone. This allows formative cell differentiation (Healthy bone and cementum). *If the masticatory force is transmitted as a pressure this will lead to the differentiation of osteoclasts in the pressure area and resorption of the bone will be induced. Pepared by Samah Mehanny Pepared by Samah Mehanny *Role of the blood vessels and the whole components of the ligament: They act all together as a hydraulic damper or shock absorber reducing the transmitted compressive force and thus allowing internal remodeling. The nutritive source of PDL is continuously provided due to the criteria of its vasculatures which are: 1-Capillaries form a rich network. 2-They are arranged in a coil form. 3-They are patent all of the time as they are attached to bone and cementum through the oxytalan fibers. Pepared by Samah Mehanny Pepared by Samah Mehanny The supportive and protective function of the PDL during mesiodistal orthodontic tooth movement: There are two sides: Compressive side: where the PDL acts as a cushion that protects the alveolar bone from excessive direct compressive forces by allowing internal remodeling rather than the resorptive effect of the directly applied forces. In this way, the architecture and thickness of the alveolar bone are preserved. Pepared by Samah Mehanny Internal remodeling preserves the architecture and thickness of bone. Osteoclasts Osteoblasts Osteoblasts Osteoclasts Pepared by Samah Mehanny Pepared by Samah Mehanny Tension side: where the PDL fibers straighten out initiating osteoblastic differentiation thus allowing changing the position of teeth. Understanding the biology of orthodontic tooth movement augmented the concept of bone movement, not tooth movement. Pepared by Samah Mehanny Pepared by Samah Mehanny  2- Sensory: The PDL mechanoreceptors contribute to the sensation of touch and pressure on the teeth. proprioceptive reflex Sudden overload Inhibition of the activity of the masticatory muscles Lead to Opening the mouth thus reduces the initially applied forces. Pepared by Samah Mehanny 3- Nutritive: The blood vessels in the periodontal ligament provide nutrient supply required by the cells of the ligament and to the cementocytes and the most superficial osteocytes. 4- Formative: The fibroblasts are responsible for the formation of new periodontal ligament fibers and dissolution of the old fibers Cementoblasts and osteoblasts are essential in building up cementum and bone. Pepared by Samah Mehanny  The Age Changes of periodontal ligament *The periodontal ligament through aging shows Vasuclarity Cellularity Thickness *It may contain cementicles. Pepared by Samah Mehanny The cementicles that appear near the surface of the cementum may be free , attached or embedded in the cementum. They are formed due to calcific deposition on; -Degenerated cells. -Area of hemorrhage. -Epithelial rests of Malassez. Pepared by Samah Mehanny Cementicles are usually seen in the periodontal ligament by aging but in some cases, they may be seen in a younger person after local trauma. Pepared by Samah Mehanny Thank you & good luck Pepared by Samah Mehanny