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. Intrasocket & Translocatory
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?
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
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