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
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
Physiological tooth movement and PDL
All components of PDL act
together as a SHOCK
ABSORBER
• Ground substance
• Tissue fluid / blood
• Fibre bundles of PDL
Cementum and Alveolar
bone respond to stresses
at specific sites
Secretion and resorption
Corresponding to areas
of tension / compression
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
tooth movement
Tooth movement under force v time
time
first force
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 -
REMEMBER :–
TOTAL TIME TAKEN FOR A TOOTH TO
RETURN TO ITS ORIGINAL POSITION IS
GREATER THAN THAT TAKEN TO MOVE
UNDER THE IMPOSED FORCE
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
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
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
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
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
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
movement
Tooth movement with second force
time
first force
second force
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
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
So what happens to alveolar bone & cementum?
Alveolar bone
Cementum
In areas of COMPRESSION,
osteoclasts RESORB bone
to accommodate tooth
movement
In areas of TENSION,
cementoblasts increase
SECRETION of cementum
to fill space left
In areas of TENSION
osteoblasts SECRETE
bone to fill space left
In areas of COMPRESSION
cementum is RESORBED
Compression
Tension
Compression
Tension
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