Periodontium brian
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Periodontium brian

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Periodontium brian Periodontium brian Presentation Transcript

  • PERIODONTIUM Oral mic anatomy and embyrology BEE
  • PERIODONTIUM Cementum PDL Alveolar bone Sharpey's fibers Attachment organ Cementum Periodontal ligament Alveolar bone Apical foramen Pulp cavity Enamel Dentin Gingiva Root canal Alveolar vessels & nerves
  • TEETH IN-SITU
  • Periodontium
    • Four tissue supporting the tooth in the jaw
      • Cementum
      • Periodontal ligament
      • Alveolar bone
      • Gingivae
  • Cementum
    • Thin layer of calcified tissue covering the root in the human teeth
    • Present in the crowns of some mammals
      • Adaptation to herbivorous diet
    • One of four tissues supporting the tooth (periodontium)
    • The least known of
      • Periodontium tissues
      • All mineralized tissues
  • Role of Cementum
    • It covers and protects the root dentin (covers the opening of dentinal tubules)
    • 2) It provides attachment of the periodontal fibers
    • 3) It reverses tooth resorption
  • Cementum
    • Varies in thickness
      • Thick @ apex (50-200 µm) & inter-radicular regions
      • Thin cervically (10-15 µm)
    • Contiguous with PDL
    • Firmly adherent with root dentine
    • Highly responsive mineralized tissue
      • Maintenance of root integrity
      • Maintenance of functional position of tooth
      • Tooth repair & regeneration
  • Varies in thickness: thickest in the apex and In the inter-radicular areas of multirooted teeth, and thinnest in the cervical area 10 to 15  m in the cervical areas to 50 to 200  m (can exceed > 600  m) apically
  • Cementum
    • Slowly-formed throughout life
    • Allowing continual reattachment of PDL fibers
    • Cementum can be regarded as a mineralized component of PDL
    • Precementum - a thin mineralized layer on the surface of the cellular cementum
    • Similar to bone, however -
      • Avascular & not innervated
      • Less rapidly resorbed – orthodontics
  • Cement-enamel junction
    • Pattern I
      • Cementum overlaps enamel for a short distance
      • Most predominant – 60% of sections
    • Pattern II
      • Enamel meet cementum at butt joint
      • Occurs in 30% of sections
    • Pattern III
      • Enamel fails to meet cementum
      • Dentine between them is exposed
      • 10% of sections
  • Physical properties
    • Pale yellow
    • Softer than dentine
    • Permeability
      • Varies with age and type of cementum
      • Decreases with age
      • Cellular is more permeable
      • More permeable than dentine
    • Readily removed by abrasion after gingival recession
  • Chemical properties
    • Hydroxyapatite crystals similar to those in bone
    • More concentration of trace elements (F) at surface
    • F levels higher in acellular
    • Collagenous organic matrix, primarily type I
    • Molecules involved in PDL fiber reattachment &/or mineralization
      • Bone sialoprotein, osteopontin & cementum-specific elements
    Inorganic Organic Water By weight 65% 23% 12% By volume 45% 33% 22%
  • Cellular and Acellular Cementum A: Acellular cementum (primary cementum) B: Cellular Cementum (secondary cementum) Acellular cementum : covers the root adjacent to dentin whereas cellular cementum is found in the apical area Cellular : apical area and overlying acellular cementum. Also common in interradicular areas Cementum is more cellular as the thickness increases in order to maintain Viability The thin cervical layer requires no cells to maintain viability as the fluids bathe its surface
  • A: Acellular cementum B: Hyaline layer of Hopwell-Smith C: Granular layer of Tomes D: Root dentin Cellular: Has cells Acellular: No cells and has no structure Cellular cementum usually overlies acellular cementum
  • Acellular Cellular Variations also noted where acellular and cellular reverse in position and also alternate
  • Dentin GT Lacuna of cementocyte Canaliculus CEMENTUM Acellular cementum Cellular cementum Hyaline layer (of Hopewell Smith) Granular layer of tomes Dentin with tubules
  • Cementoblast and cementocyte Cementocytes in lacunae and the channels that their processes extend are called the canaliculi Cementoid: Young matrix that becomes secondarily mineralized Cementum is deposited in increments similar to bone and dentin
  •  
  • Are acellular and cellular cementum formed from two different sources? One theory is that the structural differences between acellular and cellular cementum is related to the faster rate of matrix formation for cellular cementum. Cementoblasts gets incorporated and embedded in the tissue as cementocytes. Different rates of cementum formation also reflected in more widely spaced incremental lines in cellular cementum
  • Classification of cementum
    • Presence or absence of cells
      • Cellular cementum
      • Acellular cementum
    • Nature & origin of organic matrix
      • Extrinsic fiber cementum
      • Intrinsic fiber cementum
      • Mixed fiber cementum
    • Combinations
  • Acellular cementum
    • Most common pattern- adjacent to dentine
    • Structureless
    • Afibrillar cementum
      • Exists between
        • Acellular cementum
        • Hyaline layer (of Hopewell-Smith)
      • Mineralized GS
      • Covers cervical enamel
      • Results following loss of REE
  • Acellular cementum
    • Root dentine
    • Fibres of Periodontal Ligament
    • Cementum
    • Epithelial Rests
  • Cellular cementum
    • Most common pattern
      • Apical area
      • Inter-radicular areas
      • Overlying acellular dentine
    • Cementocytes
      • Inactive
      • In lacunae – appear dark in GS
      • Processes present in canaliculi
      • Processes connected via gap junctions
  • Cellular cementum
  • Cementum simulates bone
    • Organic fibrous framework, ground substance, crystal type, development
    • Lacunae
    • Canaliculi
    • Cellular component
    • Incremental lines (also known as “resting” lines; they are produced by continuous but phasic, deposition of cementum)
  • Clinical Correlation Cementum is more resistant to resorption: Important in permitting orthodontic tooth movement
  • Cementocytes vs. osteocytes
    • Cementocytes
      • More widely dispersed
      • Randomly arranged
      • Canaliculi oriented towards PDL – nutrition
    • Osteocytes
      • Osteon – Haversian system
      • Organized cells
      • Circumferential lamellae
  • Relationship between acellular & cellular cementum
    • More common pattern
      • Acellular – cervically
      • Acellular closer to dentine
      • Cellular – apically
      • Cellular covers acellular
    • Less common patterns
      • Alternating
      • Acellular overlies cellular
  • Extrinsic & intrinsic fiber cementum
    • Extrinsic fiber cementum
      • Fibers derived from inserting Sharpy’s fibers of PDL
    • Intrinsic fiber cementum
      • Run parallel to root surface at right angles to extrinsic fibers
      • Fibers derived from cementoblasts
  • Acellular extrinsic fiber cementum
    • AEFC
    • Over cervical half – 2/3s of the root
    • Bulk of cementum in premolars
    • First formed cementum - acellular
    • Thickness of 15 µm
    • All collagen are from Sharpy’s fibers
    • Though GS from cementoblasts
    • Fibers well-mineralized
  • Cellular intrinsic fiber cementum
    • CIFC
    • Fibers deposited by cementoblasts
    • Fibers run parallel to root surface
    • No role of tooth attachment
    • In apical 1/3 & inter-radicular areas
    • May be
      • Temporary – extrinsic fibers gain reattachment
      • Permanent – without attaching fibers
  • Acellular intrinsic fiber cemetum
    • If cementum forms slowly in CIFC
  • Cellular mixed stratified cementum
    • Alternating AEFC with CIFC
    • Root apex
    • Furcation areas
  • Mixed-fiber cementum
    • Collagen fibers derived from
      • Extrinsic fibers
      • Intrinsic fibers
    • Intrinsic fibers run between the extrinsic fibers
    • Two types – rate of formation
      • Acellular mixed-fiber cementum
        • Well mineralized fibers
      • Cellular mixed-fiber cementum
        • Less well mineralized fibers
  • Cemental incremental lines
    • Irregular rhythm of deposition
    • Not related to activity & quiescence
    • Related to
      • Difference in the degree of mineralization
      • Composition of organic matrix
    • Imprecise periodicity
    • Acellular – closer, thinner & regular lines
    • Cellular - farther apart, thicker & irregular lines
  • Development of Cementum Cementum formation occurs along the entire tooth Hertwig’s epithelial root sheath (HERS) – Extension of the inner and outer dental epithelium HERS sends inductive signal to ectomesen- chymal pulp cells to secrete predentin by differentiating into odontoblasts HERS becomes interrupted Ectomesenchymal cells from the inner portion of the dental follicle come in with predentin by differentiating into cementoblasts Cementoblasts lay down cementum
  • How cementoblasts get activated to lay down cementum is not known
    • 3 theories:
    • Infiltrating dental follicle cells receive reciprocal signal from
    • the dentin or the surrounding HERS cells and differentiate
    • into cementoblasts
    • HERS cells directly differentiate into cementoblasts
    • What are the function of epithelial cell rests of Malassez?
  • Cementoblasts
    • Derive from dental follicle
    • Transformation of epithelial cells
  • Incremental lines
    • Cementum is formed rhythmically and can be seen as being composed of layers
  • Resorption & repair of cementum
    • Less susceptibility to resorption than bone
    • Localized resorption areas occur
    • Could be caused by microtrauma
    • May continue to root dentine
    • By multinucleated odontoclasts
    • Resorption filled by mineralized tissue (resembles cellular cementum)
    • Reversal line
  • Reparative cementum vs. cementum
    • Wider uncalcified zone
    • Less mineralized
    • Smaller crystals
    • Calcific globules are present
    • Differences are related to different speed of formation
  • Clinical considerations
    • Cemental callus
      • Root fracture
      • No remodeling to original dimensions of the root
    • Cementicles
      • Free or attached pieces in PDL
      • Microtrauma
      • Apical & middle 1/3s of root
      • Root furcation
  • Clinical considerations
    • Supra-eruption of teeth
    • Tooth wear
    • Local hypercementosis
      • Reaction to PA inflammation
      • Difficulty in extraction
      • Paget’s disease – multiple teeth with hypercementosis
    • Cementum narrowing root canal and shifting the junction between dental pulp & PDL cervically
      • Pulp removal in RCT up to that point
  •  
  • Periodontal ligament PDL
    • Dense fibrous connective tissue
    • Occupies the area between the root of the tooth and the walls of the alveolar socket
    • Derived from the dental follicle
    • Continuous with
      • the connective tissue of the gingiva above the alveolar crest
      • The dental pulp at the apical foramen
  • Periodontal ligament space
    • Variable in width, average 0.2 mm
    • looks hourglass in shape
    • Reduced in unerupted & non-functional teeth
    • Increased in teeth subjected to heavy occlusal stress
    • Narrows slightly with age
    • Narrower in permanent teeth
  • Functions of PDL
    • Attachment
    • Has a role in tooth eruption and support
    • Its cells repair the alveolar bone & cementum
    • Neurological control of mastication through its mechanoreceptors
  • Components of PDL
    • Fibers
    • Ground substance
    • Cells
  • Fibers of PDL
    • Collagen
      • Type I (70% of fibers)
      • Type III (20% of fibers)
        • Found in the periphery of Sharpy’s fibers attachment into alveolar bone
      • Small amounts of type V, VI as well as basement membrane collagen IV & VII associated with the epithelial rests
      • Highest turnover of collagen is in PDL
        • Higher near apex
        • Even across the width of PDL
        • Rate could be related to the amount of occlusal stress
    • Oxytalan (in humans) or elastin
      • Attached into cementum
      • May have a role in tooth support
  • Principal fibers of PDL
    • Fibers exist as bundles (principal fibers) running in different orientations in different regions
      • Dentoalveolar crest fibers
      • Horizontal fibers
      • Oblique fibers
      • Apical fibers
      • Interradicular fibers
        • From crest of interradicular septum to furcation
  • Principal fibers of PDL
  • Sharpy’s fibers
    • Principal fibers embedded into cementum and bone
    • More numerous but smaller at cemental end
    • Mineralized and unmineralized parts
  • Ground substance of PDL
    • 60% of PDL by volume
    • Main components
      • Hyaluronate GAGs
      • Proteoglycans
      • Glycoproteins
    • Functions of GS
      • Ion and water binding & exchange
      • Control of collagen fibrillogenesis & fiber orientation
      • Tooth support & eruption - high tissue fluid pressure
  • Cells of PDL
    • Fibroblasts
      • Fusiform cells with many processes
      • Functions – secretion and turnover of fibers
        • Regeneration of tooth support apparatus
        • Adaptive responses to mechanical loading
    • Cementoblasts
      • Cement-forming cells lining cemental surface
      • Cuboidal cells
    • Osteoblasts
      • Bone-forming cells lining tooth socket
      • Resemble cementoblasts
  • Cells of PDL
    • Cementoclasts & osteoclasts
      • Resorbing cells
      • Howship’s lacunae
    • Epithelial rests cells
      • Cuboidal cells that stain deeply
      • Close to cemental surface
    • Defence cells
      • Macrophages
      • Mast cells
      • Eosinophils
  • Blood vessels of PDL
    • Separate from those entering pulp
    • Some from alveolar bone through foramina
    • Some from pulp through accessory canals
    • Major vessels lie between principal fiber bundle close to alveolar bone
    • Capillary plexus around the tooth
    • Crevicular plexus of capillary loops
    • Veins do not follow arteries but drain into intraalveolar venous networks
  • Innervation of PDL
    • Sensory
      • Nociception
      • Mechanoreception
        • Sensitivity to occlusal loads
        • Guidance to intercuspation
    • Autonomic
      • Associated with blood vessels
  • Alveolar process
    • The alveolar process develops during the eruption of teeth
    • Grows at a rapid rate at the free border
    • Proliferates at the alveolar crest
    • No distinct boundary exists between the body of the maxilla or mandible and the alveolar process
    • If teeth are lost the alveolar bone disappears
  • Development of bony crypt
    • Deciduous tooth & permanent successor initially share crypt
    • Bone subsequently forms to encase permanent tooth