3. Orthodontic tooth movement (OTM) is a
complex
biomechanical process which
is initiated by the clinician with the
application of a force. The applied force
moves the tooth beyond its range of
physiologic tooth movement.
4. Several
factors affect and modify the
nature and amount of orthodontic tooth
movement.
The
most
significant
mechanical
factors
are:
magnitude, direction and nature of the
force. The inherent biological factors
include bone density, age of the
person, systemic health, hormones and
factors that influence the bone
turnover.
5. Physiologic tooth movement designates
primarily the slight tipping of the
functioning tooth in its socket and
secondarily,the changes in tooth position
that occur in young persons during and
after tooth eruption.It is of three
types:
1. Movement during mastication
2. Eruption of tooth
3. Tooth migration
6. Tooth
movement during masticatory
function depends upon the location of
neutral axis of the functioning tooth.
Neutral axis is located between the
middle and apical regions of the roots in
an adult tooth.
For younger persons,the neutral axis is
either located in the marginal region or
closer to the middle of the root ,if the
root is fully developed.
7. During
chewing , the teeth tips slightly
around the neutral axis as fulcrum.
Tooth is displaced because of bending of
the alveolar process
Movement during mastication is
transient. Once the occlusal load is
removed, it reverts back to normal
position
8. Different
teeth move in different
directions during eruption
During eruption, upper molar teeth move
mainly in mesial direction
Lower molar teeth show variations in
direction of movement. Sometimes even
a distal direction of movement is
observed
Premolars sometimes show lingual
movement during eruption
9. Migration
of teeth is a slow tooth
movement
Direction of movement is usually mesial
and occlusal
This corresponds to the adult
equilibrium stage of tooth eruption
These movements take place to
compensate interproximal attrition and
occlusal wear
10. Each tooth is attached to and
separated from the adjacent alveolar
bone by a heavy collagenous supporting
structure , the periodontal ligament
(PDL). The width of the PDL is
approximately 0.5mm.
13. The
major component of the PDL is a
network of parallel collagenous
fibers, inserting into cementum of the
root surface on one side and into a
relatively dense bony plate, the lamina
dura,on the other side
14. These
supporting fibers run at an
angle, attaching farther apically on the
tooth than on the adjacent alveolar bone
This arrangement resists the
displacement of the tooth expected
during normal function
15. The
principle cellular elements in the
PDL are undifferentiated mesenchymal
cells and their progeny in the form of
fibroblasts and osteoblasts
16. Nerve
endings are found within the
ligament, both the unmyelinated free
endings associated with perception of
pain and the more complex receptors
associated with pressure and positional
information
17. The
PDL space is filled with fluid and is
derived from the vascular system
Tissue fluids acts as a shock absorber
18. During masticatory function, the teeth and
periodontal structures are subjected to
intermittent heavy forces. Tooth contact
lasts for one second or less, forces are
heavy and tooth is subjected to heavy
loads, quick displacement of the tooth
within the PDL space is prevented by the
incompressible tissue fluid and the force is
transmitted to the alveolar bone ,which
bends in response and formation of
piezoelectric signals.
19. .
Pain is normally felt after 3 to 5 seconds
of heavy force application ,indicating that
the fluids are expressed and crushing
pressure is applied against the PDL in this
amount of time. The resistance provided by
tissue fluids allows normal mastication with
its force applications of 1 second or
less, to occur with out pain. Orthodontic
tooth movement is made possible by
application of prolonged forces.
20. TIME (SECONDS)
EVENT
LESS THAN 1
PDL fluid incompressible, alveolar
bone bends, piezoelectric signal
generated
1-2
PDL fluid expressed, tooth moves
with in PDL space
3–5
PDL fluid squeezed out, tissues
compressed;immediate pain if
pressure is heavy
21. The phenomenon of tooth eruption makes it
plain that forces generated within the PDL
itself can produce tooth movement
The eruption mechanism appears to depend
on metabolic events with in the PDL
including but perhaps not limited to
formation, cross-linkage and maturational
shortening of collagen fibres.and it
continues at a reduced rate into adult life
22. This
mechanism also indicates active
stabilization of the teeth against
prolonged forces of light magnitude
Active stabilization implies a threshold
for orthodontic force
24. The bioelectric theory relates tooth
movement at least in part to changes in
bone metabolism controlled by the
electric signals that are produced when
alveolar bone flexes and bends. This
bending and flexing generates electric
signals that alter the metabolism of
bone.
26. It is a phenomenon observed in crystalline
materials in which deformation of a
crystal structure produces a flow of
electric current as electrons from one
part of the crystal lattice are displaced
to another. Bone and collagen and stress
generated potentials in dried bone
specimens have piezoelectricity
27. 1.
2.
Quick decay rate:- When a force is
applied a piezoelectric signal is created
in response that quickly dies away to
zero even though the force is
maintained
The production of an equivalent
signal, opposite in direction when the
force is released
29. Ions in the fluids that bathe living bone
interact with the complex electric field
generated when the bone bends, causing
temperature changes as well as electric
signals. The small voltages that are
observed are called streaming potential.
30. Application
of orthodontic force by the
appliance will cause physical distortion
of the alveolar bone which is
accompanied by bending of bone . Bone
which is deformed by stress becomes
electrically charged
Concave surfaces take a negative
polarity and convex surfaces a positive
polarity
31. Alterations
in blood flow associated with
pressure with in the periodontal
ligament
Formation
and/or release of chemical
messengers
Activation of cells
32. Orthodontic force
Tissue trauma
Release of Ist messengers (PG)
(Extracellular signals are activated)
Conversion into intracellular signals by 2 pathways
Synthesis of cAMP
IInd messengers
Protein kinase enzymes
within the cell
Cellular changes
Remodeling of bone
Activation of Ca++
IIIrd messengers
33. Tissue reactions to orthodontic forces
were first described by Sandstedt in
1904,1905 and later by Oppenheim in
1930,1935,1936
34. Light continuous force
Compression of blood vessels + PDL
Blood flow altered
Prostaglandins (Ist messenger) are released
Synthesis of cyclic AMP activation of Ca++
Metabolic activity
Activation of osteoclasts
35. The
bone was deposited on the tension
side of the tooth both with heavy and
light forces while on the pressure side
with light forces alveolar bone was
resorbed directly by multinucleated
osteoclast cells called frontal resorption
or direct resorption
36. With
the
application
of
heavy
forces, the periodontal tissues are
compressed leading to a cell free zone
called the hyalinised tissue, which
occurs due to thrombosis of vessels and
cell death. on histologic sections, this
zone resembles hyaline connective tissue
and the process is called hyalinisation
The ideal orthodontic force should not
exceed the capillary pulse pressure
,which is about 20-26gm/cm2
37.
In hyalinised areas ,resorption of the alveolus
takes place far from the cell free zone in the
bone marrow spaces and is called undermining
resorption or rear resorption
Tooth movement is delayed because of
hyalinization and undermining resorption and
the reasons are :
differentiation and activation of osteoclasts
from marrow space take more time
the thickness of bone to be removed from
the underside is more
38. Cellular
activity is delayed in areas of
tension when compared to pressure
zones
It takes 30 hours for increased cellular
activity to be seen in tension zone
The stretched periodontal fibers are
reconstructed by changes of the original
fibrils
Macrophages are found in great
numbers in tension zone
39. There
is inflammatory like breakdown and
rebuilding of fibrous elements in areas of
tension
New unmineralised matrix is laid down
around the parts of the fibers that are
close to the alveolar wall
After sometime ,osteoid is laid on the
whole of the alveolar wall on the tension
side
Osteoblasts synthesize the osteoid
,subsequently mineralization of osteoid
takes place
Rate of bone deposition is about 30micro
meter/day
40. Orthodontic tooth movement consequent
to application of force is outcome of
complex chains of events ,eventually
leading to bone resorption and bone
formation
41. Contemporary Orthodontics Fourth
Edition – WILLIAM R PROFFIT
Orthodontics Diagnosis and
Management of Malocclusion and
Dentofacial Deformities OM PRAKASH KHARBANDA
Orthodontics – Exam Preparatory
Manual for Undergraduates Second
Edition – SRIDHAR PREM KUMAR
