Tissue Changes1

7/27/2019 Tissue Changes1

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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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Tissue Changes1