CHANGES IN PERIODONTAL LIGAMENT
DURING ORTHODONTIC TOOTH MOVEMENT

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INDIAN DENTAL ACADEMY
Leader in continuing dental education

www.indiandentalacademy.com

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CONTENT
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INTRODUCTION
PERIODONTAL LIGAMENT
CELLS OF THE PERIODONTAL LIGAMENT
EXTRACELLUL...
INTRODUCTION
Orthodontic treatment is based on the principle that if
prolonged pressure is applied to a tooth, tooth movem...
The periodontium comprises
four connective tissues :
1.two mineralized connective
tissues :
alveolar bone and cementum
2. ...
Periodontal ligament
- approximately 0.25mm wide
- Is the soft, richly vascular and cellular connective tissue.
- It surro...
-It contains connective tissue polysaccharides, salts and water.
-The connective tissue as well as the ground substance va...
Development :
The periodontal ligament develop
from the dental follicle. Cells of the
dental follicle that differentiate i...
The true periodontal ligament fibers, the principal fibers, develops
in conjunction with the eruption of the tooth.
www.in...
FIBERS OF PERIODONTAL LIGAMENT:

1 ALVEOLAR CRESTAL FIBERS
2 HORIZONTAL
3. OBLIQUE
4. APICAL
5. INTERRADICULAR

www.indian...
Development of Sharpey’s fibers
Collagen fibers are embedded into cementum on one side of the
periodontal space and into a...
Root cementum

fine fibrils join in
periodontal space

www.indiandentalacademy.com

bone surface

12
CELLS OF PERIODONTAL LIGAMENT
The principal cells of the healthy, functioning periodontal ligament
are:
1. DIFFERNTIATED C...
A) SYNTHETIC CELLS:

OSTEOBLASTS: The osteoblasts covering the periodontal
surface of the alveolar bone constitutes a modi...
FIBROBLASTS:
Fibroblast in various stages
of differentiation, and their
progenitor, are found in the
periodontal ligament,...
CEMENTOBLASTS: Soon after Hertwig’s sheath breaks up,
undifferentiated mesenchymal cells from adjacent connective
tissue d...
B) RESORPTIVE CELLS:
• OSTEOCLASTS:
osteoclasts are cells that
resorb bone and tend to be
large and multinucleated
cells. ...
FIBROBLASTS:
Periodontal ligament can be
resorbed under physiologic
conditions by mononuclear
fibroblasts.
These cells exh...
CEMETOCLASTS:
They resemble osteoclast and are occasionally found in
normal functioning periodontal ligament. Cementum is ...
C) PROGENITOR CELLS: (Undifferentiated mesenchymal cells)
-All connective tissues, including periodontal ligament, contain...
FUNCTIONS OF MAJOR COMPONENTS OF PDL :
1.The cellular elements
2.The tissue fluids

Both play an important role in normal ...
The collagen of the ligament is constantly being remodeled
and renewed during normal function. The same cells can serve
as...
Bone and cementum are removed by specialized Osteoclasts and
cementoclasts, respectively. These multinucleated giant cells...
Finally, function of tissue fluid
PDL space is filled with fluid; this fluid is that same as that
found in all other tissu...
PERIODONTAL LIGAMENT RESPONSE TO NORMAL
FUNCTION:
TOOTH IS SUBJECTED TO HEAVY LOADS
PDL & INCOMPRESSIBLE TISSUE FLUID IN P...
PHYSIOLOGICAL RESPONSE TO HEAVY RESPONSE
TIME ( sec )

EVENTS

<1

PDL fluid incompressible , alveolar bone bends,
piezoel...
WHAT MAKES THE TISSUE RESPOND ?
HOW APPLICATION OF SUSTAINED FORCE
TRANSFORMS INTO CELL REACTION NECESSARY FOR
REMODELLING...
THEORIES OF TOOTH MOVEMENT
The bioelectric theory relates to changes in bone metabolism
controlled by the electric signals...
ORTHODONTIC TOOTH MOVEMENT AS RELATED TO
BONE DEFORMATION;
BIOELECTRICITY: First suggested by Farrar (1888)
Bones have a r...
TOOTH IS SUBJECTED TO SUSTAINED FORCE
PDL & INCOMPRESSIBLE TISSUE FLUID IN PDL
ALVEOLAR BONE
BONE BENDS
PIEZOELECTRIC CURR...
Piezoelectricity signals have two unusual characteristics:

A quick decay rate (i.e., when a force is applied, a piezoelec...
PRESSURE
CRYSTAL LATTICE E.g. Bone, Collagen
DEFORMED LATTICE
MIGRATION OF ELECTRONS
FORMATION OF ELECTRIC CURRENT
QUICKLY...
Cells are sensitive to these strain-generated potential
(piezoelectric effect).
Zengo in his experiments on dogs alveolar ...
Zengo et al (1973) in his vivo experiment observed the
electrical potentials highest at the enamel surface of the tooth
mo...
Some investigators have reached highly diverging conclusions as
regards the stimulus required for producing bone deformati...
Baumrind and Buck et al investigated the changes in rat
periodontium at varying periods up to 72 days by injecting
radioac...
There is no longer doubt that stress-generated signals are
important in the general maintenance of the skeleton. Without
s...
A second type of endogenous electric signal, which is called the
“bioelectric potential” can be observed in bone that is n...
The external electric signals probably affect cell membrane
receptors, membrane permeability, or both.
Both animal and hum...
Electromagnetic fields also can affect cell membrane
potentials and permeability and thereby trigger changes in
cellular a...
ORTHODONTIC TOOTH MOVEMENT AS
RELATED TO BIOCHEMICAL REACTION
PRESSURE TENSION THEORY:
The pressure-tension theory, the cl...
• 1. Alteration in blood
flow associated with
pressure with in the
PDL
• 2. Formation andor
release of chemical
messengers...
PRESSURE TENSION THEORY
SUSTAINED PRESSURE
TOOTH DISPLACEMENT WITHIN PDL SPACE
PDL COMPRESSED

PDL STRETCHED

PDL SIZE RED...
FORMATION AND RELEASE OF CHEMICAL
MESSENGERS:
Mechanical stresses alter the structural and functional properties of
cells ...
EXTRACELLULAR SIGNALING:
Cell-surface receptor proteins water-soluble extracellular
signaling molecules (ligands) referred...
INTRACELLULAR SIGNALING:
There seems to be two ways in which the signals are generated into
intracellular signals.
-One is...
The protein kinases are special enzymes that phosphorylate a
great number of inactive enzymes and thereby activate them to...
Synthesis of prostaglandins takes place in cellular membranes
where fatty acids are cleared from membrane phospholipids by...
Davidovitch and Shanfeld (1975) reported findings indicating that
the levels of cAMP and cGMP increased in PDL cells and a...
Lear and Moorreess et al in their histochemical study found that the
macrophages of the new blood vessels that penetrate t...
Yamasaki et al (1980) have shown that prostaglandins that
were produced during orthodontic tooth movement may
increase bon...
Results of experiments performed by Davidovitch et al (1988) and
Kvinnsland (1990) indicate the that increase in second me...
Also immune systems play a regulatory part in orthodontic tissue
reactions.
Pronounced vasodilatation has been reported in...
It has been reported in experimental studies that stress produced by
orthodontic forces would cause a marked increase in t...
SUSTAINED PRESURE [ MECHANICAL STRESS ]
DEFORMATION OF CELLS
PEPTIDES, PG,AMINO ACID, EPINEPHRINE
(LIGANDS, act as 1st mes...
RESPONSE OF THE PERIODONTAL LIGAMENT ON
THE PRESSURE SIDE:
- It is the side towards which a tooth is being moved.
-The per...
Histological studies :
Shows resorption of the alveolar bone surface on the
side towards which the tooth is moving.
In phy...
Orthodontics forces elicit more dramatic
changes.
Such changes can be categorized broadly into
“direct resorption” where t...
DIRECT RESORTION
Osteoclasts appear in the PDL along the alveolar bone
surface, some hours after the application of orthod...
• Garant et al observed Fibroblasts with increased
amounts of intracellular collagen profiles near
osteoclasts in PDL.
• T...
The precise pathway by which degraded collaged collagen is
removed is unknown.
1. Extracellular breakdown by fibroblasts-l...
The rich blood supply to the PDL may play a role
concerning the reactions of the periodontal vasculature to
moderate press...
Under non-pathological conditions, the width of the
PDL will give an indication of its capacity for
remodeling during the ...
HYALINIZATION
• Increased pressure in all localized region of the PDL can
easily exceed the optimum force and inhibit the
...
•
•
•

•

•

With pronounced pressure tissue changes within the PDL are
characterized by :
Edema, gradual obliteration of ...
• All tooth movement stops until the adjacent bone is
resorbed by cells that differentiate on spongiosa surface of
the bon...
• RESPONSE ON THE PERIODONTAL LIGAMENT
ON TENSION SIDE:
• The tooth is drawn away from the alveolar bone on tension
side.
...
•

A number of cellular processes are activated within the PDL.
There is an increase in the number of connective tissue by...
• It ha been thought that PDL fibers at the alveolar bone surface became
entrapped passively by the advancing front of new...
• Areas of experimental tension of the PDL, great increase in
vascular activity could be observed by an increase in the
sp...
TYPES OF TOOT MOVEMENT:
For the purposes of illustration, forces and
movements are often discussed in terms of tipping,
to...
• A tipping movement nearly
always results in the
formation of a hyalinized
zone slightly below the
alveolar crest, partic...
• In most young orthodontic patients, bone resorption
result form a moderate tipping movement is usually
followed by compe...
TORQUE :
• During the initial movement of torque the pressure areas
is usually located close to the middle region of the r...
• The force exerted during light
wire torque in of the continuous
type. Reitan and Kvam found
in experimental study that t...
BODILY MOVEMENT
• Bodily movement is obtained by
establishing a couple of force along
parallel lines and distributing the ...
• The short duration of the hyalinization
result from an increased bone
resorption on both sides of the
hyalinized tissue,...
ROTATION:
• In rotation of a tooth around its long axis the force can be
distributed over the entire PDL rather than over ...
• Most teeth to be rotated
create two pressure sides
and two tension sides.
Rotation may cause
certain variations in the
t...
• In the marginal region rotation usually causes
marked displacement of fibrous structure. The free
gingival fiber groups ...
EXTRUSION:
• Extrusive tooth movements
ideally produce no areas of
compression within the
PDL, only tension. Varying
with ...
• In young individual,
extrusion of a tooth
involves a more prolonged
stretch and displacement
of the supraalveolar fiber
...
INTRUSION:
• Intrusion requires careful control of force magnitude. Light force is
required because the force is concentra...
OPTIMUM FORCES FOR OTHODONTIC
TOOTH MOVEMENT
TYPE OF MOVEMENT

FORCE (gms)

•
•
•
•
•
•

•
•
•
•
•
•

TIPPING
TRANSLATION
...
EFFECTS OF FORCE DURATION
AND FORCE DECAY
• Animal studies suggest that only after forces is
maintained for approximately ...
ORTHODONTIC FORCE
DURATION IS CLASSIFIED BY
RATE OF DECAY AS
• CONTINUOUS – Forces that are maintained
between activation ...
• INTERMITENT- Forces level declines abruptly to zero
intermittently.
- when orthodontic appliance is removed by the
patie...
Effects of continuous force:
Effects of light continuous force:
- Smooth tooth movement will result from
frontal resorptio...
Effects of light interrupted force:
• the tooth will move a small amount by frontal
resorption and then remain in that pos...
EFFECTS OF FORCE MAGNITUDE:
• It is generally considered lighter forces moves tooth rapidly with less
injuries to supporti...
• Generally, the magnitude of the force determines the
duration of the hyalinization.
• This is shorter with the light for...
DRUG EFFECT ON THE RESPONSE TO ORTHODONTICS FORCE:

Two types of drugs are known to depress the response of
orthodontic fo...
• Corticosteroids inhibits the phospholipase activity.
• Indomethacin inhibits cyclo-oxygenase and may also
inhibit the to...
• BISPHONATES, used in osteoporosis bind to hydroxyapatite in
bone. They acts as a specific inhibitors of osteoclast-media...
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Changes in periodontal ligament during orthodontic tooth movement /certified fixed orthodontic courses by Indian dental academy

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Changes in periodontal ligament during orthodontic tooth movement /certified fixed orthodontic courses by Indian dental academy

  1. 1. CHANGES IN PERIODONTAL LIGAMENT DURING ORTHODONTIC TOOTH MOVEMENT www.indiandentalacademy.com 1
  2. 2. INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com 2
  3. 3. CONTENT • • • • • • • • • • • • • • • • • INTRODUCTION PERIODONTAL LIGAMENT CELLS OF THE PERIODONTAL LIGAMENT EXTRACELLULAR SUBSTANCE FIBERS OF THE PERIODONTAL LIGAMENT PERIODONTAL LIGAMENT FUNCTION PERIODONTAL LIGAMENT RESPONSE TO NORMAL FUNCTION THEORIES OF TOOTH MOVEMENT ORTHODONTIC TOOTH MOVEMENT AS RELATED TO BONE DEFORMATION ORTHODONTIC TOOTH MOVEMENT AS RELATED TO BIOCHEMICAL REACTION BIOLOGIC MECHANISMS INVOLVED IN THE TRANSFORMATION OF EXTERNAL STIMULI TO SPECIFIC TISSUE REACTIONS RESPONSE OF PERIODONTAL LIGAMENT ON: PRESSUE SIDE & TENSION SIDE TYPES OF TOOTH MOVEMENT OPTIMUM FORCES FOR ORTHODONTIC MOVEMENT EFFECTS OF FORCE DURARTION AND FORCE DECAY EFFECTS OF FORCE MAGITUDE www.indiandentalacademy.com 3 DRUG EFFECT ON RESPONSE TO ORTHODONTIC FORCE
  4. 4. INTRODUCTION Orthodontic treatment is based on the principle that if prolonged pressure is applied to a tooth, tooth movement will occur as the bone around the tooth remodels. Bone is selectively removed in some areas and added in others. In essence, the tooth moves through the bone carrying its attachment apparatus with it, as the socket of the tooth migrates because the periodontal ligament mediates the bony response, tooth movement is primarily a periodontal ligament phenomenon. www.indiandentalacademy.com 4
  5. 5. The periodontium comprises four connective tissues : 1.two mineralized connective tissues : alveolar bone and cementum 2. the two fibrous connective tissues : periodontal ligament and lamina propria of the gingiva. The periodontal ligament occupies the periodontal space, which is located between the cementum and the www.indiandentalacademy.com periodontal surface of the 5
  6. 6. Periodontal ligament - approximately 0.25mm wide - Is the soft, richly vascular and cellular connective tissue. - It surrounds the roots of the teeth and joins the root cementum with the lamina dura or the alveolar bone proper. - It functions as a shock absorber during mastication -The fibrils of the PDL are embedded in a ground substance, which is the amorphous structure left after all the cells, capillaries and fibers have been removed. www.indiandentalacademy.com 6
  7. 7. -It contains connective tissue polysaccharides, salts and water. -The connective tissue as well as the ground substance varies in different species as well as with age. -For instance, the tissue response to orthodontic forces, including both cell mobilization and conversion of collagen fibers, is considerably slower in elderly individual than in children and adolescent. -The ground substance has a more rapid turnover than the collagen fibers. - It is also essential for movement of teeth in orthodontic treatment www.indiandentalacademy.com 7
  8. 8. Development : The periodontal ligament develop from the dental follicle. Cells of the dental follicle that differentiate into fibroblasts synthesis the fibers and ground substance of the periodontal ligament. The fibers of the periodontal ligament are embedded in newly developed cementum and bone as tooth erupts. www.indiandentalacademy.com 8
  9. 9. The true periodontal ligament fibers, the principal fibers, develops in conjunction with the eruption of the tooth. www.indiandentalacademy.com 9
  10. 10. FIBERS OF PERIODONTAL LIGAMENT: 1 ALVEOLAR CRESTAL FIBERS 2 HORIZONTAL 3. OBLIQUE 4. APICAL 5. INTERRADICULAR www.indiandentalacademy.com 10
  11. 11. Development of Sharpey’s fibers Collagen fibers are embedded into cementum on one side of the periodontal space and into alveolar bone on the other. The embedded fibers are termed as sharpey’s fibers. www.indiandentalacademy.com 11
  12. 12. Root cementum fine fibrils join in periodontal space www.indiandentalacademy.com bone surface 12
  13. 13. CELLS OF PERIODONTAL LIGAMENT The principal cells of the healthy, functioning periodontal ligament are: 1. DIFFERNTIATED CELLS for -Synthesis and resorption 2. PROGENITOR CELLS. -The differentiated cells are concerned with the synthesis and resorption of alveolar bone and the fibrous connective tissue of the ligament and cementum. Consequently the cells of the periodontal ligament can be divided into three main categories: SYNTHETIC CELLS -Osteoblasts, fibroblast, cementoblast RESOPTIVE CELLS -Osteoclasts, fibroblasts, cemetoblast PROGENITOR CELLS www.indiandentalacademy.com 13
  14. 14. A) SYNTHETIC CELLS: OSTEOBLASTS: The osteoblasts covering the periodontal surface of the alveolar bone constitutes a modified endosteum. Osteoblasts secrete the type I collagen as well non-collagenous matrix of bone. Osteoblasts differentiate from progenitor cells of the connective tissue at site of bone formation. As the osteoblasts secrete the organic matrix of bone, it is at first devoid of mineral salts and is called osteoid tissue and after mineraliztion of osteoblasts, they become embedded in it and form osteocytes and www.indiandentalacademy.com 14 are important in deposition of bone.
  15. 15. FIBROBLASTS: Fibroblast in various stages of differentiation, and their progenitor, are found in the periodontal ligament, they are surrounded by fibers and ground substance. In longitudinal section, the cells of the ligament appear to be oriented parallel to the oriented bundles of collagen. They are important in synthesis of collagen. www.indiandentalacademy.com 15
  16. 16. CEMENTOBLASTS: Soon after Hertwig’s sheath breaks up, undifferentiated mesenchymal cells from adjacent connective tissue differentiate into cementoblasts. Cementoblasts synthesis collagen and protein, which constitutes the organic matrix of cementum. Uncalcified matrix is called cementoid. They are unimportant in synthesis of cementum. This cementoid is lined by cementoblasts. Connective tissue fibers from the periodontal ligament pass between the cementoblasts into the cementum. Numerous collagen fibrils embedded into the cementum are called Sharpey’s fibers. www.indiandentalacademy.com 16
  17. 17. B) RESORPTIVE CELLS: • OSTEOCLASTS: osteoclasts are cells that resorb bone and tend to be large and multinucleated cells. These multinucleated osteoclasts are formed by their precursor, the circulating monocytes, but they may also differentiate from the mesenchymal cells in situ. www.indiandentalacademy.com 17
  18. 18. FIBROBLASTS: Periodontal ligament can be resorbed under physiologic conditions by mononuclear fibroblasts. These cells exhibit lysosomes that contain fragment of collagen that appear to be undergoing digestion. Fibroblast is capable of both synthesis and resorption. Collagen-resorbing fibroblasts are inhabitants of normal functioning periodontal ligament, and their presence, like that of osteoclast in relation to bone, indicates resorption of fibers occurring during physiologic turnover or remodeling of periodontal www.indiandentalacademy.com ligament. 18
  19. 19. CEMETOCLASTS: They resemble osteoclast and are occasionally found in normal functioning periodontal ligament. Cementum is not remodeled in the fashion of alveolar bone and periodontal ligament but that it undergoes continual deposition during life. However, resorption of cementum can occur under certain circumstances, and in these instances mononuclear cementoclasts or multinucleated giant cells, often located in howship’s lacunae, are found on the surface of the cementum. The origin of cementoclast is similar to that of osteoclasts from ciruclating monocytes. www.indiandentalacademy.com 19
  20. 20. C) PROGENITOR CELLS: (Undifferentiated mesenchymal cells) -All connective tissues, including periodontal ligament, contain progenitor cells that have the capacity to undergo mitotic division. If they were not present, there would be no cells available to replace differentiated cells dying at the end of their life space or as a result of trauma. - It is believed that generally, after division, one of the daughter cells differentiates into functional type of connective tissue cell (i.e., any one of cell types as described above ) while the other remains an undifferentiated progenitor cell retaining the capacity to divide when stimulated appropriately. EXTRACELLULAR SUSBSTANCE: A. FIBERS -Collagen (predominantly type I and also type III) -Oxytalan B. GROUND SUBSTANCE -Proteoglycans www.indiandentalacademy.com 20 -Glycoproteins
  21. 21. FUNCTIONS OF MAJOR COMPONENTS OF PDL : 1.The cellular elements 2.The tissue fluids Both play an important role in normal function and in making orthodontic tooth movement possible. www.indiandentalacademy.com 21
  22. 22. The collagen of the ligament is constantly being remodeled and renewed during normal function. The same cells can serve as both fibroblasts, producing new collagenous matrix materials, and fibroblasts, destroying produced collagen. Remodeling and recontouring of the bony socket and the cementum of the root is also constantly being carried out, though on a smaller scale, as a response to normal function. Fibroblasts in the PDL have properties similar to osteoblasts, and new bone probably is formed by osteoblasts that differentiated from the local cellular population. www.indiandentalacademy.com 22
  23. 23. Bone and cementum are removed by specialized Osteoclasts and cementoclasts, respectively. These multinucleated giant cells are quite different from the osteoblasts and cementoclasts that produce bone and cementum. Despite years of investigation, their origin remains controversial. Most are of hematogenous origin; some may be derived from the pluripotent stem cells in the local area . www.indiandentalacademy.com 23
  24. 24. Finally, function of tissue fluid PDL space is filled with fluid; this fluid is that same as that found in all other tissues, ultimately derived from the vascular system. A fluid-filled chamber with retentive but porous walls could be a description of SHOCK ABSORBER, and in normal function, the fluid allows the PDL space to play just this role. www.indiandentalacademy.com 24
  25. 25. PERIODONTAL LIGAMENT RESPONSE TO NORMAL FUNCTION: TOOTH IS SUBJECTED TO HEAVY LOADS PDL & INCOMPRESSIBLE TISSUE FLUID IN PDL ALVEOLAR BONE [ Prevents tooth displacement ] BONE BENDS PIEZOELECTRIC CURRENT STIMULUS FOR SKELETAL REGENERATION & REPAIR www.indiandentalacademy.com 25
  26. 26. PHYSIOLOGICAL RESPONSE TO HEAVY RESPONSE TIME ( sec ) EVENTS <1 PDL fluid incompressible , alveolar bone bends, piezoelectric signal generated. [ the resistance provided by tissue fluid allow normal mastication, with its force application of 1sec or less to occur without pain.] 1 -2 PDL fluid expressed, tooth moves within PDL space 3-5 PDL fluid squeezed out, tissue compressed; immediate pain if pressure is heavy. www.indiandentalacademy.com 26
  27. 27. WHAT MAKES THE TISSUE RESPOND ? HOW APPLICATION OF SUSTAINED FORCE TRANSFORMS INTO CELL REACTION NECESSARY FOR REMODELLING OF TOOTH SUPPORTING STRUCTURE ? Two possible control elements, biologic electricity and pressure tension in the PDL that affects blood flow, are explained in two major theories of orthodontic tooth movement www.indiandentalacademy.com 27
  28. 28. THEORIES OF TOOTH MOVEMENT The bioelectric theory relates to changes in bone metabolism controlled by the electric signals that are produced when alveolar bone flexes and bends The pressure tension theory relates to cellular changes produced by chemical messengers, traditionally thought to be generated by alteration in blood flow through the PDL. Pressure and tension with the PDL, by reducing (pressure) or increasing (tension) the diameter of blood vessels in the ligament space, could certainly alter blood flow. The two theories are neither incompatible nor mutually exclusive. From a contemporary perspective, it appears that both mechanisms may play a part on the biologic control of tooth movement. www.indiandentalacademy.com 28
  29. 29. ORTHODONTIC TOOTH MOVEMENT AS RELATED TO BONE DEFORMATION; BIOELECTRICITY: First suggested by Farrar (1888) Bones have a remarkable ability to remodel their structure such a way that stress is optimally resisted (WOLFF’S LAW) Electric signals that might initiate tooth movement initially were thought to be piezoelectric. Piezoelectricity is a phenomenon observed in many crystalline materials in which deformations of the crystalline materials in flow of electric currents are displaced from one part of the crystal lattice to another. The piezoelectricity of inorganic crystal has been recognized and now organic crystal structure can also have a piezoelectric property. Not only bone mineral a crystal structure with piezoelectric properties; collagen itself is piezoelectric, and stressgenerated potentials in dried bone specimens can be attributed to www.indiandentalacademy.com 29 piezoelectricity.
  30. 30. TOOTH IS SUBJECTED TO SUSTAINED FORCE PDL & INCOMPRESSIBLE TISSUE FLUID IN PDL ALVEOLAR BONE BONE BENDS PIEZOELECTRIC CURRENT TOOTH MOVEMENT STARTS www.indiandentalacademy.com 30
  31. 31. Piezoelectricity signals have two unusual characteristics: A quick decay rate (i.e., when a force is applied, a piezoelectric signal is created in response that quickly dies away to zero even though the force is maintained) and The production of an equivalent signal, opposite in direction, when the force is released. www.indiandentalacademy.com 31
  32. 32. PRESSURE CRYSTAL LATTICE E.g. Bone, Collagen DEFORMED LATTICE MIGRATION OF ELECTRONS FORMATION OF ELECTRIC CURRENT QUICKLY DECAYS WHEN PRESSURE IS RELEASED OPPOSITE CURRENT FLOWS www.indiandentalacademy.com 32
  33. 33. Cells are sensitive to these strain-generated potential (piezoelectric effect). Zengo in his experiments on dogs alveolar bone showed that bending of bone may create negative fields occurring in the concave aspects of the bone surface leading to deposition and positive fields occuring on the convex bone surface leading to bone resorption. Zengo et al 1973- 74 ) It has been suggested that ions in the fluids surrounding living bone interact with the electrical fields generated when the bone is bent. These currents of small voltages are called streaming potentials. www.indiandentalacademy.com 33
  34. 34. Zengo et al (1973) in his vivo experiment observed the electrical potentials highest at the enamel surface of the tooth moved, less in the cementum and dentin and least in the alveolar bone. At the same time a bioelectric effect could be observed in the gingiva as well as in the proximal teeth and their supporting tissues. Observation has shown that not only bone deformation but also tension may create bioelectrical signals. Thus in vivo experiments conducted by Roberts et al (1981) have revealed that a negative electrical field is created in areas where the periodontal ligament is widened. www.indiandentalacademy.com 34
  35. 35. Some investigators have reached highly diverging conclusions as regards the stimulus required for producing bone deformation. Baumrind et al conducting experiments on 99 rats concluded, “bone deflection can be produced by forces lower than those required to produce consequential changes in the periodontal ligament width.” Contrary to this statement, Murphy et al using the tetracycline microfluorescent technique, observed no bending of the alveolar bone during retraction of teeth in the monkey. Obviously deflection of thin bone lamellae occurs quite frequently during treatment, but in most cases deformed bone walls tend to move back to their former position as a result of bone elasticity and fiber contraction as soon as space has been created by resorption. www.indiandentalacademy.com 35
  36. 36. Baumrind and Buck et al investigated the changes in rat periodontium at varying periods up to 72 days by injecting radioactive precursors that labeled individual cellular and connective tissue elements to be investigated: 1. CELL STUDY :Tritiated thymidine for observation of cell replication as indicated by the presence of DNA, tritiated uridine for RNA assessment. 2. COLLAGEN STUDY : Tritiated proline for observation of collagen formation. The auto radiographic findings showed significant increase in cell division adjacent to the roots of the experimental teeth as compared with those of the nondisplaced control teeth. Collagen synthesis seemed to decrease in areas adjacent to the experimental teeth. On the pressure side there was an increase in the number of labeled cells fairly similar to that on the tension side. It was suggested that the major physiologic and mechanical changes might occur not in the www.indiandentalacademy.com 36 periodontal ligament but rather in the alveolar bone.
  37. 37. There is no longer doubt that stress-generated signals are important in the general maintenance of the skeleton. Without such signals, bone mineral is lost and general atrophy ensues. Signals generated by the bending of the alveolar bone during normal chewing almost surely are important for maintenance of the bone around the teeth. On the other hand, sustained force of the type used to induce orthodontic tooth movement does not produce prominent stressgenerated signals. It appears that stress-generated signals, important as they may be for normal skeletal function, probably have little if anything to do with the response of orthodontic tooth movement. www.indiandentalacademy.com 37
  38. 38. A second type of endogenous electric signal, which is called the “bioelectric potential” can be observed in bone that is not being stressed. 1. Electronegative charges are observed in areas of metabolically active bone or connective tissue where bone growth or remodeling is occurring. 2. Inactive cells and areas are nearly electrically neutral. Although the purpose of this bioelectric potential is not known, adding exogenous electric signals can modify cellular activity. The effects, presumably, are felt at cell membranes. Membrane depolarization triggers nerve impulses and muscle contraction, but changes in membrane potentials accompany other cellular response as well. www.indiandentalacademy.com 38
  39. 39. The external electric signals probably affect cell membrane receptors, membrane permeability, or both. Both animal and human experiment indicate that when low voltage direct current is applied to the alveolar bone, modifying the bioelectric potential, a tooth moves faster than its control in response to an identical spring.(Davidovitch et al AJO 1980 ) www.indiandentalacademy.com 39
  40. 40. Electromagnetic fields also can affect cell membrane potentials and permeability and thereby trigger changes in cellular activity. In animal experiments, a pulsed electromagnetic field increased the role of tooth movement; apparently by shortening the initial “lag phase” before tooth movement begins. ( Sinclair at al AJO 1987 ) Electromagnetic fields can be induced within tissues by adjacent magnets, without the contact required by electrodes, and bone healing has been shown to be enhanced by certain types of fields. It is possible that this effect can be utilized in the future to enhance orthodontic tooth movement and or alter jaw growth. www.indiandentalacademy.com 40
  41. 41. ORTHODONTIC TOOTH MOVEMENT AS RELATED TO BIOCHEMICAL REACTION PRESSURE TENSION THEORY: The pressure-tension theory, the classic theory of tooth movement, relies on chemical rather than electric signals as the stimulus for cellular differentiation and ultimately tooth movement. Chemical messengers are important in the cascade of events that lead to remodeling of the alveolar bone and tooth movement.. In essence, this view of tooth movement shows three stages: 1. Alteration in blood flow associated with pressure with in the PDL www.indiandentalacademy.com 2. Formation andor release of chemical messengers, and 3. Activation of cells. 41
  42. 42. • 1. Alteration in blood flow associated with pressure with in the PDL • 2. Formation andor release of chemical messengers, and • 3. Activation of cells. www.indiandentalacademy.com 42
  43. 43. PRESSURE TENSION THEORY SUSTAINED PRESSURE TOOTH DISPLACEMENT WITHIN PDL SPACE PDL COMPRESSED PDL STRETCHED PDL SIZE REDUCED PDL SIZE INCREASED BLOOD VESSEL COMPRESSED BLOOD VESSEL DILATES BLOOD FLOW OXYGEN LEVEL METABOLITES BLOOD FLOW OXYGEN LEVEL METABOLITES www.indiandentalacademy.com STIMULATES RELEASE OF CHEMICAL MESSANGER 43
  44. 44. FORMATION AND RELEASE OF CHEMICAL MESSENGERS: Mechanical stresses alter the structural and functional properties of cells at cellular, molecular, and genetic levels, leading to both rapid responses in the neighboring tissues. Cellular responses to mechanical stresses involve interplay between structural elements and biochemical second messengers. www.indiandentalacademy.com 44
  45. 45. EXTRACELLULAR SIGNALING: Cell-surface receptor proteins water-soluble extracellular signaling molecules (ligands) referred to as first messenger. -The endocrine cells secrete hormones that travel through the bloodstream to influence target organs. -Nerve cells from junction (synapses) with the target cells and secrete chemical neurotransmitters, which act on the target cells. -Local chemical mediators are produced by many cells and act only on cells in the local environment, since they are rapidly destroyed (chemotatic factors, histamine, prostaglandin’s). www.indiandentalacademy.com 45
  46. 46. INTRACELLULAR SIGNALING: There seems to be two ways in which the signals are generated into intracellular signals. -One is activation of a membrane- bound enzyme (adenylate cyclase) that acts upon adenosine phosphate (ATP) to increase (in some cells to decrease) the synthesis of the adenosine monophosphate (cAMP) serves as a universal signaling molecule within cells and controls many different intracellular signals. -Other way in which extracellular signals are generated into extracellular signals: that the surface receptors may open and close gated ion channels in the plasma membrane and in turn change the flux of ions into the cell. Particularly important in the influx of Ca+. Both cAMP and Ca+(though not the only intracellular mediators for extracellular signals) activate intracellular protein kinases and are www.indiandentalacademy.com 46 referred to as second messengers.
  47. 47. The protein kinases are special enzymes that phosphorylate a great number of inactive enzymes and thereby activate them to become third messengers. When this cascade of enzyme is in increased, a high cellular activity can be the result. Among the extracellular local chemical mediators the prostaglandins (PG) are known to bind to cell receptors. They have different biologic effect and are very potent. On a general basis prostaglandins are very vasoactive and influence the Ca+ concentration in the cellular cytosol. Another important effect of prostaglandins is regulation of the intracellular concentration of cAMP through an effect on the enzyme adenylate cyclase On the other hand Ca+ liberation in cells may influence prostaglandin synthesis directly or through cAMP www.indiandentalacademy.com 47
  48. 48. Synthesis of prostaglandins takes place in cellular membranes where fatty acids are cleared from membrane phospholipids by enzymes (phospholipase) into arachidonic acids. By a change of arachidonic acid from an extended into a folded conformation and by further oxidation steps by different enzymes (cyclo-oxygenases) one of the prostaglandins will be produced. Experimental evidence proves that the open state of ion channels seen in most cells depends on stress exerted at the membrane, a finding that again is influenced by the maintenance and composition of the extracellular matrix. When an orthodontic force displace the periodontal ligament, such a movement may result in cell perturbation, altering the influx of Ca+ and other ions, which in turn has been believed to alter the synthesis of cAMP. www.indiandentalacademy.com 48
  49. 49. Davidovitch and Shanfeld (1975) reported findings indicating that the levels of cAMP and cGMP increased in PDL cells and alveolar bone following the application of orthodontic forces to teeth. Somjen et al (1980) demonstrated that the synthesis of cAMP coincident with the stretching of the cells is prostaglandin dependant. This report and others led to the assumption that what happens to the cellular structures during transduction of orthodontic mechanical forces, which results in physical deformation of cell membranes with resultant prostaglandin synthesis. This would result in activation of membrane-bound adenylate or guanylate cyclases responsible for converting the respective substrates to cAMP and cGMP. Which would have a effect upon the amount of collagen synthesized and degraded intracellularly and perhaps phagocytosis of extracellular collagens. www.indiandentalacademy.com 49
  50. 50. Lear and Moorreess et al in their histochemical study found that the macrophages of the new blood vessels that penetrate the tissues of a hyalinized are could be identified by their high aryly-sulfatase and aminopeptidase-M activity, enzymes known as markers of macrophage activity. These cells also revealed high prostaglandin synthetase (PgS) activity. This prostaglandin synthetase enzyme converts arachidonic acid to prostaglandin. It has been assumed that macrophages invading and removing hyalinized tissue, may release prostaglandins and also stimulate the formation of osteoclast. On the other hand osteoclast-like cells showed typical high acid phosphatase activity, which are in contact with bone. Davidovitch and Shanfield et al showed a rise of prostaglandin E2 (PGE2) levels in the periodontal ligament and alveolar bone, both in sites of tension and compression in orthodontically treated animals. www.indiandentalacademy.com 50
  51. 51. Yamasaki et al (1980) have shown that prostaglandins that were produced during orthodontic tooth movement may increase bone resorption activity. These author performed series of experiments in rats, monkeys, and humans; Prostaglandin E was injected in the gingiva of the teeth to be moved. They reported enhanced rate of tooth movement. Now increasing evidence proves that although Prostaglandin E is involved in the transduction of mechanical stress on the PDL and alveolar bone during orthodontic tooth movement, several other inflammatory mediators are active. It appears that orthodontic forces may activate the nervous as well as immune systems. www.indiandentalacademy.com . 51
  52. 52. Results of experiments performed by Davidovitch et al (1988) and Kvinnsland (1990) indicate the that increase in second messengers (cAMP, cGMP) in periodontal cells do not result solely from the direct effects of the mechanical forces but also caused by endogenous signaling agents Mechanical stress alter the level and distribution of the neurotransmitter substances in PDL. Neuropeptide: Substance P (SP), vasoactive intestinal polypeptides (VIP), calcitonin gene related peptide (CGRP) and other neurotransmitters from sensory nerve fibers in the PDL supply a link between physical stimulus and the biochemical response. Pain sensitive nerve endings release stored substance P into the PDL, leading to binding of SP to specific cellular receptor. Through interaction with endothelial cells there will be a rapid vasodilatation and migration of leucocytes from blood vessels. www.indiandentalacademy.com 52
  53. 53. Also immune systems play a regulatory part in orthodontic tissue reactions. Pronounced vasodilatation has been reported in areas of tension and in the periphery of compressed of the PDL in experimental tooth movement. Macrophages have been identified near the blood vessels. It is generally accepted that vasodilatation leads to migration of macrophages, lymphocytes, proteins and fluid into the extracellular space. These inflammatory cell as well as fibroblasts and osteoblasts, produce signaling molecules, cytokines: interleukins 1a and 1b that attract leucocytes, stimulate fibroblast proliferation and enhance bone resorption and so called tumor necrosis factors A which induces interleukin 1 production ofwww.indiandentalacademy.com monocytes, enchances PGE2 and collagenous 53 production, and increase the number of osteoclasts.
  54. 54. It has been reported in experimental studies that stress produced by orthodontic forces would cause a marked increase in the staining intensity of interleukin 1a in all cell types of the PDL, in particular osteoblasts in tension sites and PDL cells and osteoclasts at compression. Similarly, orthodontic forces would produce a marked increase in the cellular staining intensity of interleukin beta particularly in the osteoblasts at PDL tension sites and osteoclasts at compression site. Even TNF-alpha and gamma Interferon were observed in the PDL in experiment tooth movement. (Davidovitch and Shanfeld et al) www.indiandentalacademy.com 54
  55. 55. SUSTAINED PRESURE [ MECHANICAL STRESS ] DEFORMATION OF CELLS PEPTIDES, PG,AMINO ACID, EPINEPHRINE (LIGANDS, act as 1st messenger ) BIND TO CELL SURFACE RECEPTOR PROTEIN ACTIVATES ENZYMES INCREASED OR DECREASED CONC. OF INTRACELLULAR SIGNALING COMPOUND ( 2nd messenger, e.g. cAMP, cGMP ) www.indiandentalacademy.com 55
  56. 56. RESPONSE OF THE PERIODONTAL LIGAMENT ON THE PRESSURE SIDE: - It is the side towards which a tooth is being moved. -The periodontal space becomes narrower -The crest of the alveolar bone is slightly deformed. -Cellular changes occur within the PDL and on the surface of the alveolar bone. -Similar cellular changes and remodeling of the supporting tissue of teeth occur with physiological migration. -Difference being the rate of changes www.indiandentalacademy.com 56
  57. 57. Histological studies : Shows resorption of the alveolar bone surface on the side towards which the tooth is moving. In physiological tooth movement (where tartarateresistant acid phosphatase-TRAP – is used to identify osteoclast), a few osteoclast can be observed resorbing the alveolar bone wall. Vascular activity is low and few leucocytes and macrophages are seen (Brudvig and Rygh). However, whereas with physiological migration the number of osteoclasts is usually low (indicating slow process). www.indiandentalacademy.com 57
  58. 58. Orthodontics forces elicit more dramatic changes. Such changes can be categorized broadly into “direct resorption” where the pressure is relatively light, and “hyalinization”, where the pressure is large enough to produce degenerative changes. www.indiandentalacademy.com 58
  59. 59. DIRECT RESORTION Osteoclasts appear in the PDL along the alveolar bone surface, some hours after the application of orthodontic force In children aged between 10-13years, Reitan et al found occasional evidence of resorption after 12 hours, and resorption was invariably seen by 40 hours. Within optimal force after 3-4 days, numerous osteoclasts are present along the alveolar wall. In light microscopical sections: A clear zone often separate resorbing cells from the bone. This artifact appears to be related to the destruction of both alveolar bone and sharpey’s fibers. Electron microscope: Shows the ruffled border of osteoclasts in close contact with the resorbing bone surface and both crystals and collagen fibers may be found between www.indiandentalacademy.com 59 the cell processes.
  60. 60. • Garant et al observed Fibroblasts with increased amounts of intracellular collagen profiles near osteoclasts in PDL. • These fibroblasts also play a role in bone resorption and formation of new collagen, which becomes attached to the alveolar bone by localized bone deposition. • There is extensive remodeling of collagen throughout the PDL with possible exception of Sharpey’s fibers at the root surface. • Collagen detached from alveolar bone during resorptive activity may become reattached to bone or to pre-existing periodontal collagen fibers by local activity of osteoblasts or fibroblasts respectively. www.indiandentalacademy.com 60
  61. 61. The precise pathway by which degraded collaged collagen is removed is unknown. 1. Extracellular breakdown by fibroblasts-like cells occurs. 2.Compressed necrotic tissue in hyalinized zones is removed to a considerable extent by macrophages. The ground substance appears to be the major water-binding constituent of connective tissues. Even though it is presumed that both bound and unbound water are present in the PDL, it is not known whether there is movement of water between the vascular and extravascular compartments during loading and unloading of a tooth. www.indiandentalacademy.com 61
  62. 62. The rich blood supply to the PDL may play a role concerning the reactions of the periodontal vasculature to moderate pressure. However, unless an adequate vascular supply is present, the differentiation of specialized cells will not take place. The width of the periodontal space seems to be important in determining the reaction of the PDL to load. Recently erupted teeth in children have a wider PDL than those in adults. This may help explain why children’s teeth are more easily moved orthodontically than adult’s teeth. www.indiandentalacademy.com 62
  63. 63. Under non-pathological conditions, the width of the PDL will give an indication of its capacity for remodeling during the initial phase of increased loading of the tooth. With extensive direct resorption forces, within the PDL is increased. During the initial phase of orthodontic tooth movement and reactivation of an applied force is there a narrowing of the PDL on the pressure side. www.indiandentalacademy.com 63
  64. 64. HYALINIZATION • Increased pressure in all localized region of the PDL can easily exceed the optimum force and inhibit the differentiation of osteoclasts. • As a result, the direct resorption of alveolar bone, which would relieve the pressure in the PDL, cannot occur. • Instead a series of degenerative tissue reactions takes place, commencing within a few hours. The term ‘hyalinization’ is used to describe these tissue reactions, owing to the fact that the degenerated tissue has a “glassy appearance”. • The presence of hyalinization has been interpreted as representing a change in consistency of the collagenous matrix rather than its regeneration www.indiandentalacademy.com 64
  65. 65. • • • • • With pronounced pressure tissue changes within the PDL are characterized by : Edema, gradual obliteration of blood vessels, and breakdown of walls of veins. Leakage of blood constituents into the extravascualar space occurs. Changes in fibroblasts are also seen. These often begin with moderate swelling of the endoplasmic reticulum. More extensive swelling and the formation of vacuoles occur later, followed by rupture of cytoplasmic membrane and loss of cytoplasm. These leaves isolated nuclei, which undergo lysis over a period of several weeks. Mostly the collagen undergoes a longitudinal splitting. The degenerative processes of the different tissue components persist as long as the pressure is maintained and, by doing so they prevent recolonization of the damaged tissue by cells from the adjacent, undamaged PDL. With time accumulated erythrocyte breakdown products in the www.indiandentalacademy.com 65 pressure region may undergo crystallization
  66. 66. • All tooth movement stops until the adjacent bone is resorbed by cells that differentiate on spongiosa surface of the bone or subperiosteally. Where there is no cancellous bone between lamina dura and the external cortical bone. This indirect (’undermining ‘) resorption occurs at the same time as invasion of phagocytosing cells from the peripheral undamaged ligament and from the marrow spaces. All tissue components damaged during compression are eventually removed. Extracellular breakdown by fibroblast-like cells occurs locally in some areas of PDL (i.e. removed of surface cementum in pressure zone and compressed necrotic tissue in hyalinized zones is removed by macrophages • Hyalinized areas are normally removed after a 3-5 week period, provided that, if any further force is to be applied, should be gentle reactivation. The ‘post-hyalinized’ PDL under pressure is markedly wider than before, perhaps in www.indiandentalacademy.com order to withstand the greater mechanical influences 66
  67. 67. • RESPONSE ON THE PERIODONTAL LIGAMENT ON TENSION SIDE: • The tooth is drawn away from the alveolar bone on tension side. • When continuous force is applied to the crown of tooth, the periodontal space will become wider on the side where the tooth is drawn away from the alveolar bone. Bundles of fibers are stretched and the alveolar crest is pulled in the same direction. The blood vessels appear to be distended. • In areas of experimental tension of the PDL, a great increase in vascular activity could be observed. This was indicated by an increase in the space occupied by the blood vessels most commonly seen in the middle of the PDL and towards the alveolar bone. www.indiandentalacademy.com 67
  68. 68. • A number of cellular processes are activated within the PDL. There is an increase in the number of connective tissue by cell division. For young humans, incipient cell proliferation is seen after 30-40hours, particularly near the socket wall. Osteoid tissue will be deposited on the socket wall shortly after. Where the fibrous bundles are thick, new bone appears to be deposited along them. If bundles are thin, a more uniform layer is deposited along the root surface. Calcification in deeper layers of the osteoid starts shortly afterwards, while the superficial parts remain uncalcified. • In longitudinal sections of the tooth, fibroblasts in the PDL are oriented in the same direction as the principal fibers: in the direction of strain. The fibroblasts appear spindle shaped. The cells adjacent to the alveolar wall often appear more spherical www.indiandentalacademy.com 68
  69. 69. • It ha been thought that PDL fibers at the alveolar bone surface became entrapped passively by the advancing front of new bone formation to form Sharpey’s fibers. However findings suggest that new Sharpey’s fibers or new fibrils are secreted simultaneously with new bone deposition. As the fibroblasts migrate with the bone, they may deposit either entirely new Sharpey’s or new fibrils, which are incorporated into existing fibers. While part of the newly synthesized collagen will be incorporated into the new osteoid, some will be incorporated in to the PDL, perhaps associated with increase in width on the tension side. Lengthening of fibers seems also to occur by incorporation of new fibrils into existing fibers. • Observation by Ten Cate et al that fibroblast were able both to break down and to produce collagen fibrils led to the assumption that, in the healthy PDL, assumption that, all collagen degradation was intracellular. Rapid remodeling of the periodontal tissue during experimental or therapeutic tooth movement would be characterized www.indiandentalacademy.com 69 by a very high ratio of internalized collagen or fibroblasts volume.
  70. 70. • Areas of experimental tension of the PDL, great increase in vascular activity could be observed by an increase in the space occupied by the blood vessels, most commonly in the middle of the PDL and towards the alveolar bone. • Macrophage and other leucocytes that migrate out of the PDL blood vessels simultaneously with proteins and fluids are known to be capable of producing and releasing a variety of factors. • In fact, these cells are not only active removers of tissues that have been altered by pathological conditions, but, mostly importantly, they are producers of numerous signal molecules from chemoattraction to stimulation of mitogensis and cytodifferentiation. • Experiments revealed that in local areas of tension, the volume of the collagen fibers running from tooth alveolar bone was reduced as the volume of blood vessels increased www.indiandentalacademy.com 70
  71. 71. TYPES OF TOOT MOVEMENT: For the purposes of illustration, forces and movements are often discussed in terms of tipping, torque, bodily movement, rotation, extrusion and intrusion. TIPPING: • Tipping of a tooth leads to a concentration of pressure in limited areas of PDL. A fulcrum is formed, which enhances root movement in the opposite direction. If the fulcrum is located in the coronal part, the apex o the root is torque. www.indiandentalacademy.com 71
  72. 72. • A tipping movement nearly always results in the formation of a hyalinized zone slightly below the alveolar crest, particularly when the tooth has a short, underdeveloped root. If the root is fully developed, the hyalinized zone is located a short distance from the alveolar crest. Tipping of a tooth by light continuous force results in a greater movement within a shorter time than that obtained by any other method. www.indiandentalacademy.com 72
  73. 73. • In most young orthodontic patients, bone resorption result form a moderate tipping movement is usually followed by compensatory bone formation. The degree of such compression varies individually and depends primarily on the presence of bone forming osteoblasts in the periosteum. Compensatory periosteal bone apposition occurs in the apical region. • Tipping of adult teeth in labial direction may result in bone destruction of the alveolar crest, with little compensatory bone formation. Such undesirable bone resorption has been observed even in young patients. In addition after a prolonged movement of the bone plate in the apical region may occur so rapidly that the root is finally moved through the bone. www.indiandentalacademy.com 73
  74. 74. TORQUE : • During the initial movement of torque the pressure areas is usually located close to the middle region of the root. • This occurs because of the PDL in normally wider in the apical third than the middle third. After resorption of bone areas corresponding to the middle third, the apical surface of the root gradually begins to compress adjacent periodontal fibers and a wider pressure area in established. • Direct bone resorption was observed on the pressure side. However, if more torque in incorporated in the arch wire, the magnitude of force may be considerably increased. A cell free area of short duration may be created adjacent to the middle third of the root. www.indiandentalacademy.com 74
  75. 75. • The force exerted during light wire torque in of the continuous type. Reitan and Kvam found in experimental study that the tissue reaction caused hyalinization and root resorption in two areas. The first was in the middle third of the root and the second, which was formed after the first undermining resorption has terminated, was all along the apical third of the root. www.indiandentalacademy.com 75
  76. 76. BODILY MOVEMENT • Bodily movement is obtained by establishing a couple of force along parallel lines and distributing the force over the whole bone surface. This is favorable method of displacement provided the magnitude of force does not exceed a certain limit. • Hyalinization during an initial bodily movement occurs largely as a result of mechanical factors. Shortly after the movement is initiated, no bodily movement of the tooth is a mechanical sense is observed, but instead a slightly tipping is noticed. The result is compression on the pressure side with formation of a hyalinized zone between the marginal and middle region of the root. www.indiandentalacademy.com 76
  77. 77. • The short duration of the hyalinization result from an increased bone resorption on both sides of the hyalinized tissue, especially in the apical region of the pressure side. • This leads to rapid elimination of the hyalinized zone. The PDL on the pressure side is usually considerably widened by the resorption process. • Further tooth movement, in most cases, produces only minor hyalinized reaction on the pressure side is partly caused by gradually increased stretching of fiber bundle on the tension side, which tends to prevent the tooth from further tipping. New bone layer along these bundles. www.indiandentalacademy.com 77
  78. 78. ROTATION: • In rotation of a tooth around its long axis the force can be distributed over the entire PDL rather than over a narrow vertical strip, whereas forces can be applied than in other tooth movements. • Histologically, however the tissue transformation that occurs during the rotation is largely influenced by the anatomic arrangement of the supporting structure. • In the marginal region most of the periodontal fiber bundles consist of free gingival and transseptal fiber group. Although the principal fibers of the middle and apical thirds are anchored to the root surfaces and the alveolar bone, the supralveolar fibers are connected to the whole fiber system of the supralveolar structure. • This difference in the attachment of fiber bundles has proved to be of great importance, particularly during the retention period. www.indiandentalacademy.com 78
  79. 79. • Most teeth to be rotated create two pressure sides and two tension sides. Rotation may cause certain variations in the type of tissue response observed on the pressure side. Occasionally, hyalinization and undermining resorption takes place in one pressure zone while direct bone resorption occurs in the other. www.indiandentalacademy.com 79
  80. 80. • In the marginal region rotation usually causes marked displacement of fibrous structure. The free gingival fiber groups are arranged obliquely from the root surface, because these fibers bundles interlace with the periosteal structure and the whole supraalveolar fibrous system, rotation also causes displacement of the fibrous tissue located some distance from the rotated tooth. • On the tension side of the middle third, new bone spicules are formed along stretched fiber bundles arranged more or less obliquely. In addition, the new bone on the tension sides consists partly of uncalcified bone spicules. www.indiandentalacademy.com 80
  81. 81. EXTRUSION: • Extrusive tooth movements ideally produce no areas of compression within the PDL, only tension. Varying with the individual reaction, the periodontal fiber bundles elongate and new bone is deposited in areas of alveolar crest as a result of the tension exerted by these stretched fiber bundles. www.indiandentalacademy.com 81
  82. 82. • In young individual, extrusion of a tooth involves a more prolonged stretch and displacement of the supraalveolar fiber bundles than of the principal fibers of the middle and apical thirds. • In adult, the fibers bundles also are stretched during extrusion, but they are less readily elongated and rearranged after treatment. www.indiandentalacademy.com 82
  83. 83. INTRUSION: • Intrusion requires careful control of force magnitude. Light force is required because the force is concentrated in a small area at the tooth apex. Primarily the anterior teeth intruded a light continuous force, such as that obtained in the light wire technique, has proved favorable for intrusion in young patient. In other cases the alveolar bone may be closer to the apex, increasing the risk for apical root resorption. If the bone of the apical region is fairly compact, as is some adults, a light interrupted force may be preferable. • Unlike extruded teeth, intruded teeth in young patients undergo only minor positional changes. Stretched in exerted primarily on the principal fibers. As intruding movement may therefore cause formation of new spicules in the marginal region. These new bone layers occasionally become slightly curved as a result of tension exerted by stretched fiber bundles. Such tension is also seen in the 83 middle of the roots. www.indiandentalacademy.com
  84. 84. OPTIMUM FORCES FOR OTHODONTIC TOOTH MOVEMENT TYPE OF MOVEMENT FORCE (gms) • • • • • • • • • • • • TIPPING TRANSLATION TORQUE ROTATION EXTRUSION INTRUSION 35-60 70-120 50-100 35-60 35-60 10-20 www.indiandentalacademy.com 84
  85. 85. EFFECTS OF FORCE DURATION AND FORCE DECAY • Animal studies suggest that only after forces is maintained for approximately 4 hrs, second messengers are produced, which are required to stimulate cellular differentiation. • Continuous forces produced by fixed appliance produce more tooth movement than removable appliance unless removable appliance is present almost all the time. www.indiandentalacademy.com 85
  86. 86. ORTHODONTIC FORCE DURATION IS CLASSIFIED BY RATE OF DECAY AS • CONTINUOUS – Forces that are maintained between activation of orthodontic appliance. • INTERUPPTED – Forces level declines to zero between activations. when a fixed appliance is temporarily deactivated . www.indiandentalacademy.com 86
  87. 87. • INTERMITENT- Forces level declines abruptly to zero intermittently. - when orthodontic appliance is removed by the patients. - intermittent forces are produced by all patient activated appliances. Such as removable appliance, headgear, elastics. It must be admitted that intermittent and interrupted are more or less synonymous, but they are used for differenent types of tooth movement, e,g interrupted designates movement of short duration elicited by fixed appliance, intermittent is used mainly to designate removable appliances. www.indiandentalacademy.com 87
  88. 88. Effects of continuous force: Effects of light continuous force: - Smooth tooth movement will result from frontal resorption. Effects of heavy continuous force : - Tooth movement will be delayed until undermining resorption can remove the bone necessary for tooth movement. Tooth will change its position rapidly. - Constant heavy force will prevent repair of PDL and create the need for further undermining resorption. - It is destructive for both the tooth and PDL. www.indiandentalacademy.com 88
  89. 89. Effects of light interrupted force: • the tooth will move a small amount by frontal resorption and then remain in that position until the appliance is activated again. Effects of heavy interrupted force : • Heavy forces produce undermining resorption, tooth will move when undermining resorption is eliminated. Since the force has dropped to zero, the tooth will remain in same position until next activation. • Although the original force is heavy, after the tooth moves there is a period of regeneration and repair of the PDL before force is applied again. www.indiandentalacademy.com 89
  90. 90. EFFECTS OF FORCE MAGNITUDE: • It is generally considered lighter forces moves tooth rapidly with less injuries to supporting tissue than heavy ones. What is considered to light or heavy forces depends on the mode of application and the mechanical arrangement of the recipient tooth units. In addition to any applied force, the chewing forces are always present. • In a study by Rygh et al 1986, reaction to heavy, continuous loads (50cN) experimenting tipping of first molar in rats was performed. • The result indicated a pattern in the action of PDL and bone on tensional stress: 1. Up to certain level of stress, the reaction of PDL with increasing vascualization,cell proliferation, fiber formation, osteoid formation occurred. 2. Beyond certain level of stress, decreased vascular supply in the PDL and destruction of cell stretched occurred. Removal of bone was marked with undermining resorption of Sharpey’s fibers occurred 3. Stronger force of long duration resulted in vertical reduction of the alveolar bone www.indiandentalacademy.com 90
  91. 91. • Generally, the magnitude of the force determines the duration of the hyalinization. • This is shorter with the light force levels, although the tendency is towards a longer initial hyalinization period, and also formation of secondary hyalinized zones when excessively strong forces are applied. • Another reason for applying light forces is that it results in less discomfort and pain to the patient. Unmyelinated nerve endings persist in the hyalinized tissue, and they are more or less compressed during the initial stage. www.indiandentalacademy.com 91
  92. 92. DRUG EFFECT ON THE RESPONSE TO ORTHODONTICS FORCE: Two types of drugs are known to depress the response of orthodontic forces 1.Prostaglandin inhibitors 2. Bisphosphonates PROSTAGLANDIN INHIBITORS: • If prostaglandins E plays an important role in the cascade of signals that leads to tooth movement, so inhibitors of its activity affects tooth movement. • Drugs that affects prostaglandins are activity fall in two categories: 1. Corticosteroids and 2. Non-steroidal anti-inflammatory drugs(NSAID) www.indiandentalacademy.com 92
  93. 93. • Corticosteroids inhibits the phospholipase activity. • Indomethacin inhibits cyclo-oxygenase and may also inhibit the total homeostasis in the body, provided the dose are high. • Aspirin and other acetylsalicylic acids inhibits the cyclo-oxygenases irreversibly. • Both children and adult on Steroids and NSAID may encounter possibilities of difficulties in tooth movement. The fact that analgesics often are prostaglandin inhibitors raises the possibility that the medication used for pain after orthodontic treatment could interfere with tooth movement. www.indiandentalacademy.com 93
  94. 94. • BISPHONATES, used in osteoporosis bind to hydroxyapatite in bone. They acts as a specific inhibitors of osteoclast-mediated bone resorption, so the bone remodeling is slower in this medication. If orthodontic treatment is necessary in older woman's taking medication for osteoporosis it’s worthwhile to explore to her physician the possibility of switching to estrogen as replacement for drug which inhibits tooth movement. • • • • • Other drugs which inhibits prostaglandin synthesis: TRICYCLIC ANTIDEPRESSANTS(impramine,amitryptin) ANTI-ARRHYTHMIC AGENTS (procaine) MALARIAL DRUGS(quinine,quinidine,chlorquine) ANTICONVULSANT (phenytoin) TETRACYCLINES(doxycycline) inhibits osteoclast recruitement similar to biphosphonates. www.indiandentalacademy.com 94
  95. 95. www.indiandentalacademy.com Leader in continuing dental education www.indiandentalacademy.com 95

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