Ioe Elec Periodontum Function

Front 1

what are the 4 functions of the periodontal ligament

Back 1

1. it is the tissue of attachement between the tooth and the alveolar bone,it is responisble for resisting displacing forces on the tooth and in so doing, protects the nerves and the blood vessels at the root apex



2. responsible for the mechanism whereby the tooth attains and maintains its functional position, e.g. eruption and mesial drift

3. it cells maintain and remodel the adjacent bone and cementum

4. it contains mechano receptors which provide sensory input for jaw reflex activity.

Front 2

what does the ligament resist and in doing so what does it protect and prevent

Back 2

how the it resists intrusive loading
on the tooth and in so doing protects the delicate
tissues at the base of the tooth and prevents the root
apex from impacting the bone at the socket base

Front 3

to an uneducated person what may he think occurs when a load is applied to a tooth.




why is this wrong

Back 3

One might expect that when a load is applied to the
tooth, the tooth would intrude a small distance into
the socket and tension would be generated within the
oblique fibre system and further tooth movement
would cease. The ligament would thus act like a
simple suspensory ligament.


However, much of the
experimental data does not support this simple
suspensory ligament form of tooth support

Front 4

how can the pattern of intrusive behaviour of a tooth be determined

Back 4

If tooth position is monitored continuously (in this
case with a sensitivity of approximately 1μm) its
pattern of intrusive behaviour can be determined

Front 5

WHAT HAPPENS WHILST THE TOOTH IS UNLOADED

Back 5

While unloaded the tooth remains static in its socket
and the trace is steady (apart from the small pulsatile
movements in synchrony with the heart beat).

Front 6

EXPLAIN THE 2 PHASE SYSTEM ONCE A LOAD IS APPLIED

WHAT IS THIS SYSTEM TERMED

Back 6

When
a load is applied to the tooth there is an initial rapid
intrusion, the so-called ‘elastic’ phase. However, if
the load is maintained the intrusion continues at a
much slower rate but over a much longer period of
time – this is the so-called ‘creep’ phase. This second
phase, if given time, will produce a much larger
overall intrusion than the initial ‘elastic’ phase. This
biphasic response is termed ‘visco-elastic’.

Front 7

WHAT HAPPENS AFTER THE LOAD IS REMOVED

Back 7

If the load
is then removed, there is an initial rapid (elastic)
recovery and then a much slower extrusion which
again, given time, will restore the tooth to its original
position

Front 8

WHAT IS DIFFICULT TO EXPLAIN

Back 8

It is difficult to explain these characteristic
biphasic responses simply on the basis of tension
generated within the oblique fibre system.

Front 9

OUTLINE ONE OF THE EARLIER EXPERIMENTS CONDUCTED TO INVESTIGATE THE MECHANISM OF TOOTH SUPPORT


WHAT DID THIS MECHANISM SUGGEST

Back 9

One of the early experiments conducted to
investigate the mechanism of tooth support was to
measure the distance (‘A’) between opposing
alveolar crests when a load was applied to the tooth.
The expectation was that when the load was applied
tension would be generated in the oblique fibres, the
crests would be pulled together and therefore
distance ‘A’ should decrease. In fact distance ‘A’
increased, indicating that the crests had been pushed
apart. htt

Front 10

OUTLINE ANOTHER WAY TO STUDY THE MECHANICS OF TOOTH SUPPORT

Back 10

Another way to study the mechanics of tooth support
is to look at the stress/strain curve for the oblique
fibre system and compare it to other well
characterised connective tissues,

Front 11

DESCRIBE WHAT THE STRESS/STRAIN CURVE PLOTS/SHOWS

Back 11

The stress/strain curve plots the %age
increase in length of the tissue (the strain) as the load
applied (the stress) is increased until a point is
reached where damage occurs and the tissue does
not recover when the load is removed – the so-called
failure stress and strain.

Front 12

WHAT IS EXPECTED OF THE ACHILLES TENDON

WHAT DOES THE STRESS STRAIN CURVE SHOW ABOUT THE ACHILLES TENDON

Back 12

In the case of a typical
tendon such as the achilles tendon very large loads
are required to produce little in the way of extension
and failure occurs at only approximately 10% strain.
We would expect this of a tissue who’s function is to
transmit tension generated by a muscle directly to a
bone.

Front 13

HOW DOES THE STRESS/STRAIN CURVE FOR THE ACHILLES TENDON APPEAR IN COMPARISON TO THE SKIN

Back 13

Compare this to the skin, a very elastic and
pliable tissue, where only very modest increases in
load produce large increases in strain with failure
occurring at approximately 45% strain.

Front 14

FROM WHAT DATA WHAS THE STRESS/STRAIN CURVE FOR THE PERIODONTAL LIGAMENT

Back 14

dissected pig jaws were used with the
base of the socket removed. Increasing loads were
then applied to the tooth and the displacement into
the socket recorded until sufficient stress was applied
for the oblique fibres to be ruptured. From these data
the stress/strain curve could be constructed,

Front 15

WHAT DOES THE STRESS STRAIN CURVE SHOW FOR THE % STRAIN AT WHICH FAILURE OCURS IN THE PERIODONTAL LIGAMENT.


WHAT IS IT SIMILAR TO

WHAT IS SIGNIFICANT IN THESE RESULTS

Back 15

both in terms of its shape and failure stress and strain, with failure occurring at approximately 20% strain. Interestingly this is very close the stress/strain failure point for foetal, as
opposed to adult, tendon. This relatively low failure
stress value for periodontal oblique fibres is
significant given the relatively large loads that people are known to apply to teeth during normal
mastication, particularly in certain ethnic groups and cultures.

Front 16

IT IS CLEAR THAT OTHER ELEMENTS WITHIN THE TISSUE PLAY AN IMPORTANT ROLE IN

Back 16

Whilst some of the load applied to the tooth is
probably dissipated through the oblique fibre system,
it is clear that other elements within the tissue play an
important role in this process

Front 17

WHAT OTHER POSSIBILITY IS CONSISTENT WITH MUCH OF THE DATA ALREADY OBTAINED

Back 17

One possibility which
would be consistent with much of the data obtained
so far is that a large part of the load is dissipated by
fluid flow both within the matrix itself and within the
capillary bed. When the tooth is intruded fluid will be
relocated from beneath the tooth ultimately to the
large blood spaces in the surrounding bone and to
regions of the ligament further coronally. This would
lead to increased fluid volume in the crestal region
which in turn would tend to force the alveolar crests
apart.

Front 18

WHAT DOES THE PERIODONTAL LIGAMENT DEMONSTRATE

Back 18

The periodontal ligament demonstrates a
biphasic, ‘visco-elastic’, response to axial
loading

Front 19

WHAT DO THE STRESS STRAIN CURVES FOR THE PERIODONTAL OBLIQUE FIBRES SHOW

Back 19

The failure stress and strain of the periodontal
oblique fibres are more akin to foetal tendon
than either adult tendon or skin

Front 20

WHAT DOES THE LIGAMENT APPEAR TO RESIST

Back 20

The ligament appears to resist intrusive loads
primarily by compression and fluid flow