Periodontal Ligaments PDF - Oral Histology

Periodontal Ligaments Oral Histology Ass. Prof. Dr/ Baleegh A. Alkadasi -----------------------------------------------------------------------------------------------------------------------------------------------------...

Periodontal Ligaments Oral Histology Ass. Prof. Dr/ Baleegh A. Alkadasi ----------------------------------------------------------------------------------------------------------------------------------------------------- Periodontal Ligaments Definition: The periodontal ligament is the dense fibrous connective tissue that occupies the periodontal space between the root of the tooth and the alveolus.  Width of PDL = 0.15 to 0.38 mm (the narrowest width at bellow the mid root and the widest width is the alvelor crest followed by the apical region)  PDL width decreases with age.  The PDL extends coronally up to the most apical of the connective tissue of the gingiva.  It consists of the blood vessels, various cells & extracellular matrix. Functions of the Periodontal Ligament 1- Physical: - Attachment of the teeth to the bone, 132  Periodontal Ligaments Oral Histology Ass. Prof. Dr/ Baleegh A. Alkadasi ----------------------------------------------------------------------------------------------------------------------------------------------------- - Transmission of the occlusal forces and - Resistance to the impact of these forces and - Maintenance of the gingival tissue in their proper relationship to the teeth. 2- Formative and Remodelling: Cells of the P. Ligament participate in the formation and resorption of cementum and bone. 3- Sensory function: The PDL nerve fibers transmit sensation of touch, pressure and pain to higher centers. 4-Nutritive function: Blood vessels of ligament provide essential nutrients for the ligament’s vitality and hard tissue of cementum and alveolar bone. Development: - Shortly after the beginning of root formation & the formation of the outer dentinal layer of root, the PDL is formed. - The external & internal dental epithelia proliferate from the cervical loop of dental organ to form a Hertwigs epithelial root sheath, which then fragments to form the discrete clusters of the epithelial cells called as " epithelial cell rests of Malassez" - The enamel organ & root sheath are surrounded by dental sac which is formed by condensed cells. -A thin layer of cells lying adjacent to the dental organ, known as dental follicle, divide & differentiate into cementoblasts, fibroblasts & osteoblasts. - The fibroblasts synthesize the fibers & ground substance of the PDL. 133  Periodontal Ligaments Oral Histology Ass. Prof. Dr/ Baleegh A. Alkadasi ----------------------------------------------------------------------------------------------------------------------------------------------------- - These fibers initially occupy the periodontal space without any specific orientation, but just before tooth eruption acquire an orientation oblique to the tooth towards the coronal portion. - Similar fibers appear on the side of bone also. - They fibers elongate, meet & fuse in the middle. - They mature progressively towards the root apex as the eruption progresses & with the establishment of occlusal contact the proper arrangement of the principle fibers of the PDL occurs. - The damaged periodontal fibers are replaced & remodeled by newly formed fibers. 134  Periodontal Ligaments Oral Histology Ass. Prof. Dr/ Baleegh A. Alkadasi ----------------------------------------------------------------------------------------------------------------------------------------------------- Histological structure of the periodontal ligaments: The PDL consists: A- Cells B- Extracellular substances A- Cells: 1-Synthetic cells: Fibroblasts, Osteoblasts, Cementoblasts. 2-Resorpative cells: Fibroblasts, cementoclasts, osteoclasts. 3- Progenitor cells: undifferentiated mesenchymal cells. 4- Epithelial cells: epithelial rest of malassez. 5- Defensive cells: macrophages, lymphocytes and mast cells (see lecture of dental pulp) B- extracellular substances: 1- Fibres The fibers of the periodontal ligament are mainly collagen. They are divided into: A) The principal fibers. B) The accessory fibers. C) The oxytalan ( elastic ) fibers. 2- ground substances 3- blood vessels 4- lymphatic vessels 5- nerves 135  Periodontal Ligaments Oral Histology Ass. Prof. Dr/ Baleegh A. Alkadasi ----------------------------------------------------------------------------------------------------------------------------------------------------- CELLS: Synthetic Cells 1. Osteoblasts: - Derived from the multipotent mesenchymal cells. - They cover the periodontal surface of the alveolar bone. - The collagen fibers of ligament that penetrate the alveolar bone are present between the the cells. 2. Fibroblasts:- - it consider the Principal cells of PDL - Ovoid or elongated cells oriented along the principal fibers & exhibiting pseudopodia like processes. - The collagen turnover is regulated by fibroblasts. - Have different functions such as secretion of collagen of different types or production of collagenase. 3- Cementoblasts:- - Found on the surface of the cementum. - Help in cementum formation. - Produce cementoid layer which undergoes mineralization. - Some of these cells get embeded in the cementum as cementocytes. 136  Periodontal Ligaments Oral Histology Ass. Prof. Dr/ Baleegh A. Alkadasi ----------------------------------------------------------------------------------------------------------------------------------------------------- Resorptive Cells: 1. Osteoclasts:- - Multinucleated cells which resorb bone. - Helps in remodeling, which allows functional changes in the position of tooth. 2. Fibroblasts:- -help in both synthesis & resorption of collagen. - The collagen fibers can be resorbed by the mononuclear fibroblasts. 137  Periodontal Ligaments Oral Histology Ass. Prof. Dr/ Baleegh A. Alkadasi ----------------------------------------------------------------------------------------------------------------------------------------------------- - help in remodeling process of PDL. They exhibit lysosomes, which contain collagen fragments undergoing digestion. 3. Cementoclasts:- - found on surface of cementum. - cementum is not remodeled like alveolar bone & PDL progenitor cells - are the undifferentiated mesenchymal cells. - have the capacity to undergo mitotic division & replace the differentiated cells dying at the end of their lifespan. - located in perivascular region. 138  Periodontal Ligaments Oral Histology Ass. Prof. Dr/ Baleegh A. Alkadasi ----------------------------------------------------------------------------------------------------------------------------------------------------- Epithelial cell rests of malassez:- - remnants of the epithelium of hertwig's epithelial root sheath. -found close to the cementum. - arranged parallel to the root surface. - formed at the time of cementum formation. - when stimulated these cells undergo rapid proliferation & produce a variety of cysts & tumours. - Defensive cells (see lecture of pulp) -Extracellular substances: 1-fibers: The fibers of the periodontal ligament are mainly collagen. They are divided into: a) The principal fibers. b) The accessory fibers. c) The oxytalan ( elastic ) fibers. 2- Ground Substance (a) Glycosaminoglycans (b) Glycoproteins 139  Periodontal Ligaments Oral Histology Ass. Prof. Dr/ Baleegh A. Alkadasi ----------------------------------------------------------------------------------------------------------------------------------------------------- a) The principal fibers: A- the principal fibers of periodontal ligament are formed of collagen bundles, which are wavy in course and are arranged in three ligaments. a) Gingival fibers. b) Transseptal or interdental ligament. c) Alveolodental ligament which is subdivided into the following five groups: 1- Alveolar crest group. 2- Horizontal group. 3- Oblique group. 4-Apical group. 5- Interradicular group. A-The Gingival Fibers: 1- Dentogingival group : extend from the cervical cementum into the lamina propria of the gingival. 2- Alveologingival group: extends from the alveolar crest into the lamina propria. 3- Circular group: a small group of fibers that encircles the tooth and interlaces with the outer fibers of bone. 4- Dentoperiosteal fibers: they extend from the cementum direct over the crest and then incline apically between the periosteum of the alveolar bone to the lamina propria of the gingiva. 140  Periodontal Ligaments Oral Histology Ass. Prof. Dr/ Baleegh A. Alkadasi ----------------------------------------------------------------------------------------------------------------------------------------------------- Functions of the gingival fibers They hold the marginal gingiva against the tooth. They provide the marginal gingiva with enough rigidity to withstand the forces of mastication without distorting. B- The Transseptal Ligament: *It connects two adjacent teeth. *The ligament runs from the cementum of one tooth over the crest of the alveolus to the cementum of the adjacent tooth. 141  Periodontal Ligaments Oral Histology Ass. Prof. Dr/ Baleegh A. Alkadasi ----------------------------------------------------------------------------------------------------------------------------------------------------- C- The Alveolodental Ligament: 1-Alveolar crest group: The fiber bundles radiate from the crest of the alveolar process and attach to the cervical part of the cementum. 2-Horizontal group: The fiber bundles run from the cementum to the bone at right angle to the long axis of the tooth. 3- Oblique group: The fiber bundles run obliquely. Their attachment in the bone is somewhat coronal than the attachment in the cementum. It is the greatest number of fiber bundles found in this group. They perform the main support of the tooth against masticatory force. 4- Apical group: The bundles radiate from the apical region of the root to the surrounding bone. 5- Interradicular group: The bundles radiate from the interradicular septum to the furcation of the multirooted tooth. 142  Periodontal Ligaments Oral Histology Ass. Prof. Dr/ Baleegh A. Alkadasi ----------------------------------------------------------------------------------------------------------------------------------------------------- The Alveolodental Ligament: (1 & 2) 3) 4) 5) 143  Periodontal Ligaments Oral Histology Ass. Prof. Dr/ Baleegh A. Alkadasi ----------------------------------------------------------------------------------------------------------------------------------------------------- B- Accessory fibers: It is 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 C- Oxytalan Fibers -Immature elastic fibers. - Run in axial or oblique direction. - One end being embedded in cementum or bone and the other end in the wall of blood vesseles -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. Interstitial Tissue -Some of the blood vessels ,lymphatics, and nerves of the PDL are surrounded by loose C.T. These areas have termed interstitial tissue. -Fibroblasts histiocytes, UMC, and lymphocytes are also found in interstitial tissue. -Biological significance: unknown. 144  Periodontal Ligaments Oral Histology Ass. Prof. Dr/ Baleegh A. Alkadasi ----------------------------------------------------------------------------------------------------------------------------------------------------- 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 these constitue 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 formatina in the bone. 145  Periodontal Ligaments Oral Histology Ass. Prof. Dr/ Baleegh A. Alkadasi ----------------------------------------------------------------------------------------------------------------------------------------------------- The age changes of periodontal ligament 1-The periodontal ligament through aging shows decrease in: -Vascularity -Cellularity -Thickness 2- It may contain cementicles. The cementicles appear near the surface of cementum may be free , attached or embedded in the cementum. They have nidus favoring the deposition of concentric layers of calcosphrite as degenerated cells, area of hemorrhage and epithelial rest's of Malassez. Cementicles are usually seen in periodontal ligament by aging but in some cases they may be seen in a younger person after local trauma. 146