FUNCTIONS OF THE PERIODONTIUM

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

1. Tooth eruption
2. Adaptation to jaw growth
3. Physiological mesial drift
4. 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 Sharpeys 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
Tension
Compression
Tension
19
CLINICAL IMPLICATIONS

1. Varying structure of alveolar bone means
   different types of movement needed to extract
   different teeth in direction of thinnest bone
2. Direction of PDL fibres means extraction force is
   APICALLY directed (push not pull)
3. Rapid rate of PDL turnover and activity of
   cementoblasts osteoblasts means re-attachement
   of teeth possible
4. Epithelial rests of Malassez can proliferate
   radicular cysts and occasionally more serious
   pathology