FUNCTIONS OF THE PERIODONTIUM Attachment
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  • 1. FUNCTIONS OF THE PERIODONTIUM
    • Attachment & support
    • Nutritive
    • Sensation
    • All components of the periodontium form a FUNCTIONAL SYSTEM that provides attachment for the tooth to the bone of the jaw AND permits the tooth to withstand the forces of mastication
  • 2. ATTACHMENT & SUPPORT
    • Principal collagen fibre bundles attach the tooth to the jaw
    • Cementum, PDL and alveolar bone involved in accommodating any tooth movement
    • Teeth held in jaws and supported against functional stresses
    • BUT
    • Allow for tooth movement
    • Intrasocket & Translocatory
  • 3. Physiological tooth movement and PDL
    • All components of PDL act together as a SHOCK ABSORBER
    • Cementum and Alveolar bone respond to stresses at specific sites
    • Ground substance
    • Tissue fluid / blood
    • Fibre bundles of PDL
    • Secretion and resorption
    • Corresponding to areas of tension / compression
  • 4. Intra – socket tooth movements
    • Teeth of opposing jaws come together
    • - APPLYING FORCE -
    • Teeth move within sockets
    • - REMOVING FORCE -
    • Teeth move back to their original position
  • 5. Tooth movement under force v time
  • 6. Intra – socket movements
    • Direction and amount of movement depend on direction and amount of force
    • When force applied – rate of movement rapid initially but DECREASES WITH TIME
    • - no further movement occurs -
    • When force removed – rate of movement rapid and DECREASES WITH TIME
    • - tooth returns to original position -
  • 7.
    • REMEMBER :–
    • TOTAL TIME TAKEN FOR A TOOTH TO RETURN TO ITS ORIGINAL POSITION IS GREATER THAN THAT TAKEN TO MOVE UNDER THE IMPOSED FORCE
  • 8. Physiology during tooth movement OR “whats going on ?”
    • 3 components of PDL in the system of tooth support
    • GROUND SUBSTANCE
    • TISSUE FLUID / BLOOD and BLOOD VESSELS
    • PRINCIPLE FIBRE BUNDLES
    • Operate and function in that order
  • 9. GROUND SUBSTANCE
    • Allows rapid movement
    • Operates first
    • Resistance provided by friction between large individual PG molecules and between PGs and collagen fibres
    • Alterations in molecular structure occur
    • Ground substance - compressed & displaced into other regions of ligament - depending on direction of force
  • 10. BLOOD AND BLOOD VESSELS
    • Blood forced from vessels in ligament to those in alveolar bone marrow
    • Resistance provided by friction between blood and vessel walls
    • Again acts as a damper when force applied as blood displaced through vessels through cribriform plate to alveolar bone marrow
  • 11. PRINCIPLE FIBRE BUNDLES
    • Only involved after ground substance and other tissue fluids have responded to forces
    • Fibres become straightened out and absorb axial stress – can increase in number and thickness
    • Are inelastic – allow no further tooth movement
    • Prevent direct apposition of cementum and bone surfaces so prevents complete closure of periodontal space
  • 12. Other changes
    • Increase in periodontium function :–
    • 50% increase in PDL thickness
    • Alveolar bone increases in thickness
    • Reduction in function :-
    • PDL narrows, fibre bundles decrease thickness
    • Alveolar bone decreases in thickness
  • 13. What happens of we have a second force applied to the tooth after the first force?
    • Occurs during chewing! Forces later than the first occur before teeth have returned to their resting positions
    • Collagen fibres prevent complete closure of periodontal space
    • Proteoglycans become increasingly viscous with increasing rates of loading
    • Teeth move further than after initial force - longer to return to resting position when force removed
  • 14. Tooth movement with second force
  • 15. TRANSLOCATORY TOOTH MOVEMENT
    • Resultant of forces so that tooth moves permanently
    • Socket is remodelled to move with tooth and accommodate new position
    • Tooth eruption
    • Adaptation to jaw growth
    • Physiological mesial drift
    • Orthodontic tooth movement
  • 16.
    • Remodelling of PDL = metabolic turnover across whole width of PDL
    • - FORCE -
    • PDL fibres breakdown – new ones synthesized
    • Anchored to cementum and bone by Sharpey’s fibres
    • New layer of cementum secreted and alveolar socket wall remodelled (resorption and deposition of bone)
    • Staggered replacement of PDL fibres as
    • tooth attachment maintained during any movement
  • 17. So what happens to alveolar bone & cementum?
    • Alveolar bone
    • In areas of COMPRESSION, osteoclasts RESORB bone to accommodate tooth movement
    • In areas of TENSION osteoblasts SECRETE bone to fill space left
    • Cementum
    • In areas of TENSION, cementoblasts increase SECRETION of cementum to fill space left
    • In areas of COMPRESSION cementum is RESORBED
  • 18. Compression Compression Tension Tension
  • 19. CLINICAL IMPLICATIONS
    • Varying structure of alveolar bone means different types of movement needed to extract different teeth – in direction of thinnest bone
    • Direction of PDL fibres means extraction force is APICALLY directed (push not pull)
    • Rapid rate of PDL turnover and activity of cementoblasts & osteoblasts means re-attachement of teeth possible
    • Epithelial rests of Malassez can proliferate = radicular cysts and occasionally more serious pathology