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BIOLOGICAL BASIS OF ORTHODONTIC THERAPY
Orthdontic therapy is based on interaction between mechanics and biology.
Inflammation is a major part of the biologic response to orthodontic forces. Ref:American Journal of Orthodontics & Dentofacial Orthopedics Volume 135, Issue 2,
Pages 222-231 February 2009.Teeth can be moved by mean of orthodonticappliances because of certain fundamental properties of bone tissue.Principalchanges resulting from tooth movement are seen within the dentoalveolar system
and other areas like sutures and TMJ area.
The Periodontium
Periodontium is a connective tissue organ covered by epithelium, that attaches the
teeth to the bones of the jaws and provides a continually adapting apparatus for
support of teeth during function. It have 4 connective tissues.
Two fibrous
- Lamina propria of the gingiva.
- Periodontal ligament
Two mineralized
-Cementum
-Alveolar bone
Gingiva Group (Principal fibers) : .
A) Circular fibres:
Run in free gingiva and encircle the tooth.
B) Dentogingival fibres:
Embedded in cementum of supraalveolar
portion of root and project from cementun in a fan like configuration into free gingival tissue.
C) Dentoperiosteal fibres:
Embedded in same portion of cementum as
dentogingival fibres but terminate in tissue of
attached gingiva.
D) Trans-septal fibres:
Run straight across the interdental septum and
are embedded in the cementum of adjacent teeth.
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Alveolar Group (Principal fibers):
Primary cementum:
Secondary cementum:
Alveolar crest fibres.
Horizontal fibre.
Oblique fibre.
Apical fibre.
Inter-radicular fiber.
Individual bundles have wavy
course, allows the tooth tomove within socket
(physiologic mobility) despite
the inelastic nature of collagen
fibres.
Formed during root
formation.
Acellular
During formation of primary
cementum, principal fibres in
PDL get embedded and
mineralised
Sharpeys fibres are regarded as
direct continuation of collagen in PD
Formed after tooth
eruption and in
response to functional
demands
Contain cells.
More pronounced in
a ical ortion of root.
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Alveolar bone:
Osteoid:
Physiologic tooth migration:
Surrounds the tooth to
approx 1mm apical to
CEJ
Part of alveolar bone
that covers the alveolar
is lamina dura.
Principal fibres of PDL
are embedded in
alveolar bone, called
contains.
Collagen
Matrix proteoglycans,
glycoproteins
is found on all bone surfaces
where new bone is deposited.
Not attacked by osteoclasts.
Under goes mineralisations by
deposition ofcalcium and
phosphate.
Transformed to hydroxyapatite
Remodeling of PDL and
alveolar bone.
Resorptive surface &
depository surface
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Orthodontic tooth movements:
No greater difference exists between tissue reaction in physiologic tooth
migration and ortho tooth movement except that the tissue changes elicited
by ortho forces are more marked and extensive.
Theories of tooth movement:
Pressure-tension:
This hypothesis explained that, on the pressure side, the PDL displays
disorganization and diminution of fiber production. Here, cell replication decreases
seemingly due to vascular constriction
Pressure- Tension theory
Fluid Dynamic theory
Bien
Squeeze- Film effect
Oxygen tension
Bone bending piezoelectric
theory
Sandstedt
(1904),
Oppenheim
(1911),and
Schwarz
(1932).
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Osteoclastic activity :
Undermining resorption
This hypothesis explained that, on
the pressure side, the PDL displays
disorganization and diminution of
fiber production. Here, cellreplication decreases seemingly due
to vascular constriction. On the
tension side, stimulation produced
by stretching of PDL fiber bundles
results in an increase in cell
replication
Hyalinization-
remodeling of bone
around Necrotic
connective tissue-
derived from adjacent
undamaged area
Osteoclasts appear
adjacent bone marrow
spaces- attack on
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Fluid Dynamic theory:According to this theory , alternation in the chemical environment ,
interstitial fluid squeezed out , decreased oxygen level , compressionoccour.
Bone Bending theory:
Piezoelectricity:
Farrar- (1888) was the first to
suggest-alveolar bone bending
plays a pivotal role- tooth
movement.This hypothesis-confirmed with the experiments of
Baumrind (rats) and Grimm
(humans).
Fig: Hypothetical model of the role of
stress-induced bioelectric potentials in
regulating alveolar bone remodeling.Ref: Om Prakash Kharbanda First
Edition-2009 Page: 89
Bone- Organic crystal
Two unusual
characteristics :
Quick decay and
equal & opposite signal
Ref: William R. Proffit
Fourth Edition Page:
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Tissue response in periodontium:
Continuous force
application on tooth
leads to tooth
movement which is
marked initially by
narrowing of PDL,
particularly in marginal
area.
After 30 40 hours,
osteoclasts differentiate
along the alveolar bone
wall.
Direct bone resorption
is found in secondary
period, when hyalinized
tissue has disappeared
after undermining
bone resorption
Initial direct bone
resorption can be
observed during
rotation of teeth, when
the root is moved
parallel to bone surface
without causin an
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Figure 2 Light macroscopic images of the effect of different orthodontic
forces on the multinucleate osteoclasts (haematoxylin and eosin:original magnification 400). Osteoclasts (thin arrows) appeared on the
alveolar bone surface in both groups on days 3 (c and e) and 7 (d and f).
Odontoclasts (thick arrows) on the cementum in the 50 g group was
more than that of the 10 g on day 7 (f). AB: alveolar bone, PDL:
periodontal ligament, C: cementum, and D: dentine; bar = 50 m. The
direction of applied force is indicated by the dotted arrow. Ref: Eur J
Orthod (2010) 0(2010): cjq068v1-cjq068
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Figure 4 Effect of different orthodontic forces on RANKL- and RANK-positive
odontoclasts by immunohistochemistry on days 7 (Figure 4A) and 10
(Figure 4B; original magnification 400). Immunoreactivity of RANKL and
RANK was observed in the odontoclasts (arrow) on the cementum in the 50
g group (4AB-e, f), but not in the 10 g (4AB-c, d) on days 7 and 10. PDL:
periodontal ligament, C: cementum, D: dentine; bar = 50 m. The directionof applied force is indicated by the dotted arrow. Ref: Eur J Orthod
(2010) 0(2010): cjq068v1-cjq068
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1. Initial application of force:
Hyalinization:
Sterile necrotic area
Clear, Eosinophilic
Glass like structure (1-2mm)
Cellular struture Indistinct
Displays mainly 3 stages:
a. Degeneration
b. Elimination of destroyed tissue
c. Establishment of new tooth attachment
Compression in limited
areas of membrane
impedes vascular
circulation and cell
differentiation causing
degradation of cells and
vascular structures.
In light microscopy
reveals a glass like
appearance i.e.hyalinization.
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2. Secondary period of tooth movement:
Osteoclasts attack the bonesurface over a much wider
area.
Fibrous attachment apparatus
is reorganised by production
ofnew PDL fibres
Ref: i) C.C Teixeira, E. Khoo, J. Tran,
Y. Liu, L.P. Gart JDR
October 2010 vol. 89 no. 10 1135-
1141 ii) RANKL icrease in
compressed periodontal ligament
cells from root resorption.
Yamaguchi M, Aihara N, Kojima T,
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Secondary remodeling changes:
Biochemical Reaction:
(Mechanical force - cellular change)
Alveolar process drifts
with the tooth
Bony changes also takes
place else where to
maintain the with of the
supporting alveolar proces
(Ref: Q. Xing, P. deVos, M.M. Faas, Q. Ye, and Y. Ren J DENT
RES, February 2011; vol. 90, 2: pp 157-
162)
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Inflammation like reaction:
Root Resorption:
Small area of root resorption are universally found on orthodontically
tooth movement, (Linge & Linge, 1983).
During ortho tooth
movement extracellularbreak down of collagen by
collagenases, produced by
leukocyte/ fibroblasts
interaction. Ref: i) J.K.
Maclaive, A.B. Rabie, R.
Wong Eur J Orthod (2010)
32(4): 435-440 ii) D.
BayarsaihanJ DENT RES,
January 2011; vol. 90, 1: pp.
9-17.
Ref: Om Prakash Kharbanda
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CONCLUSION:
Light continuous forces produce the most efficient tooth movement,.
Heavier forces that produce this response are physiologically acceptable
only if the forces levels decline so that there is period of repair and
regeneration before the next activation.
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