Biology1

BIOLOGY OF TOOTH MOVEMENT AND
ROOT RESORPTION
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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.
 4 connective tissues
 Two mineralized
-Cementum
-Alveolar bone
Two fibrous
-Periodontal ligament
-Lamina propria of the gingiva.

Cells
 Progenitor cells
 Synthetic cells
a) Osteoblasts
b) Fibroblasts
c) Cementoblasts
 Resorptive cells
A) Osteoclasts
B) Fibroblasts
C) Cementoclasts

Extra cellular elements
 Fibres
-Collagen
-Oxytalan
Ground Substance
-Proteoglycans
-Glycoproteins

Principle Fibres of the Periodontal
Ligament(Collagen Fibres)
1. Alveolar crest group
2. Horizontal group
3. Oblique group
4. Apical group
5. Interradicular group

GINGIVAL FIBRES
1. Circular
2. Alveologingival
3. Dentoperiosteal
4. Dentogingival
5. Transseptal fibres(Accesory fibres)

Alveolar bone
 Two parts
1. Alveolar bone proper
2. Supporting alveolar bone
A.- Cortical Plate
B.- Spongy Bone
 Alveolar process is formed by intramembranous
ossification.
 They can be remodelled owing to the structure.

Active stabilization of teeth against
forces of low magnitude

Response to normal function:
Forces applied on the teeth are-
1-2 kgs when soft
Upto 50 kgs against harder food

Tooth
movement-
Vanarsdall

Peridontally Compromised Teeth

Historical Perspective
1. Celsus
2. Reitan
3. Openheim
4. Norton
5. Burstone
6. Davidovitch

TOOTH MOVEMENT-
 Application of orthodontic force –
tooth movement on account of
resorption on the pressure side and
deposition on the tension side.

Cascade of
activities-
Tooth
movement
(Norton)

Classification of orthodontic
forces- Schwartz
 Four degrees of biologic efficiency.
1st
–Below threshold stimulus.
2nd
-Most favourable 15-20 gms per square cm.Less than the
blood pressure.
3rd
-Medium strength.They stop the blood. flow.Tissues are not
crushed.
4th
–Forces are so high that the tissues are crushed. Irrepairable
damage may be caused to the tissues involved.

Theories of orthodontic tooth movement
1) Bioelectric theory -electric signals produced when
alveolar bone flexes and bends. Also called the
piezoelectric theory.
2) Pressure tension theory(Schwartz1932)-related to
cellular changes produced by chemical messengers.
Bien Hydrodynamic damping of tooth movement, J. D. -
1966.
 Theories are mutually dependent.

Bioelectric theory
 2 unusual characteristics-
1. -quick decay rate
2. -equivalent signal opposite direction

 Crystal deformation-electrons migrate due to distortion
of cross linkages between the collagen fibres in the
bones.
Electropositive response (convexity) –resorption
Electronegetive (concavity) -deposition
 Ions in fluids bathe the bone and cause “streaming
potential”. Similar but not the same.
 No place in natural control of body.
Bioelectric theory

Bioelectric theory
 Stress generated signals important-
astronauts.(can also be explained OB
differentiation)
 Chewing /orthodontic forces.
 Bioelectric signals-active growth, not
exactly known. Exogenous signals –
modify tooth movement-lag phase before
tooth movement.

Effect of Pulsed Electromagnetic Field on Tooth
Movement- Stark and Sinclair Ajo - 1987 Feb
 Simple non invasive pulsed
electromagnetic (25-Hz) field can cause an
effect on the rate and amount of tooth
movement.
 20-experimental,20-control
Guinea pigs
 AFTER 10 DAYS
Tooth movement
Osteoclast cell count

Observations-
1. Protein metabolism indicated by creatinine ,craetinine
phosphokinase, uric acid.
2. Na Ca K which are postulated to be the effect of pulsed
electromagnetic stimulation on the cell membrane are not increased.
3. Exciting possibily for future consideration - Ability to initiate and
enhance the bone deposition-use with functional appliances.

Effect of Pulsed Electromagnetic Field on Tooth
Movement- Stark and Sinclair Ajo - 1987 Feb
PRE AND POST EXPERIMENT

CONTROL AND EXPERIMENTAL
GROUP

INCREMENTAL MOVEMENT

Structure of the bone

Pressure -Tension Theory
 Relies on chemical signals and not
electrical signals for cellular differentiation
and tooth movement.

Cells causing remodeling of bone
1. OB
2. OC
 ORIGIN OF THE CELLS
1) OB-Neural crest cells(OB)- Pre Osteoblasts
a) Contact inhibition.
b) G1,G2 blocked cells.

Differentiation of cells under
mechanical influence

2) OC- Hematogenous in origin
 Monocytes have been suggested to be the
predecessors. Progenitors ???
 Blocked cells local preosteoclasts &
circulating preosteoclasts.
Cells causing remodeling of bone

Differentiation of cells under
mechanical influence-OB & OC

Vit D metabolites
 They are known to effect bone formation and
deposition via the differentiation of the comitted
progenitor cells into mature cells.

OSTEOBLASTS
 RESORPTIVE FUNCTION
 1) OB-Physical barrier-layer of cells on the bone surface.
If these cells are stimulated by PTH they change shape
(round) thus exposing the underlying mineral of the tooth
– only affects already differentiated cells.
.

Shape change in cells: mechanism for the
transduction of mechanical forces ( Sandy-
Bdj;1992)
 Relationship exists bw cell shape and metabolic
activity.
 Flattened cells synthesize more DNA than rounded
cells.
 PG and PTH induce change in shape.
 Suggested – in pressure sites the cells are rounded
and have catabolic effects-tension sites the cells are
flattened and in a synthetic mode.

 2) Release certain mediators –cytokines-Bring about
osteoclastic resorption.
 They are defined as short range soluble
mediators,released from the cells which modulate the
activity of other cells - ( Bone remodeling- Sajeda
Meghji 1992; Bdj ) - lymphokines.
OSTEOBLASTS

Cytokines:Mediators of bone remodeling( -Sandy-
Bdj;1992
-Biology of tooth movement- Norton and Burstone)
 Osteoclasts don’t work
independently -signal
transmitted to the
osteoclast by an
Osteoblast Cytokine.

 3)Osteiod layer covering
the bone is removed by
OB - secrete
collagenase.
• P TIMP
Cytokines:Mediators of bone remodeling ( Sandy-
Bdj;1992,-Biology of tooth movement- Norton and Burstone)
TIMP-TISSUE INHIBITOR OF
METTALOPROTEINASES
TIMP-TISSUE INHIBITOR OF
METTALOPROTEINASES

FORMATIVE-
 1)Pressure
 2)Production of first messenger( physical/
chemical)
a) Deformation may lead to ca influx
b) Hormones(PTH)
c) Prostaglandins( macrophages )
d) Neurotransmitters(SP)
OSTEOBLASTS
They bind to the cell
surface receptors.
They bind to the cell
surface receptors.

 3)Second messengers
a. c AMP
b. c GMP
c. Ca
 4)Increased bone activity
OSTEOBLASTS

Trans membrane signaling pathway
PHOSPHOINOITIDASE
INOSITOL
TRIPHOSOHATE
PHOSPHOINOITIDASE
INOSITOL
TRIPHOSOHATE

 Discovered by VON
EULER –1934
 Prostate gland
 Yamasaki –injection of
exogenous PG increased
osteoclast numbers.
Role of Prostaglandins (Tooth eruption and
orthodontic movement:Sandy-Bdj,1992)
Phospholipids
phopholipase
Arachidonic acids
Prostaglandin's
c AMP
Ca+2

ARACHIDONIC ACID METABOLISM

 Leukotrienes and HETE (Leucocytes)
(Hydroxyeicosatetraenoic Acid) , produced
from the same substrate.
 Since PGs do not fully account for bone
remodeling associated with tooth movement ,
lipoxygenase products may be involved.

OSTEOCLASTS
 Resorptive action
PTH- systemic factor
Cytokines
Mechanical
Ruffled border
Lysosomal enzymes

 Osteocytes – cytoplasmic processes which help to gauge
the pressure changes and signal the OB.
Osteocytes

Events during bone remodelling

PDL and bone response to sustained
forces on pressure side-
1. Undermining resorption
2. Fontal resorption

Oteoclast differentiation
 2 waves
-1st
wave –local cell population.
-2nd
wave-blood flow.
 Optimal force-frontal resoption on pressure
side
 Excess force would cause –undermining
resorption.

Pattern of bone deposition and resorption

Tooth movement
 Tooth movement may be divide into (Graber .Vanarsdall)
- Initial –Undermining resorption
- Secondary period-Frontal resorption
 Initial phase- 3 main stages
1. Degeneration
2. Elimination of destroyed tissue
3. Establishment of new attachment

 1.Degeneration
1. Blood flow
2. Degradation of vessel walls
3. Cellular changes
-Swelling of mitochondria
-Rupture of cytoplasmic membrane leaving only isolated nuclei
between the fibrous elements
 The source of cells which differentiate into osteoclasts is
lost. Area is cell free.
 Glassy appearing sterile necrotic area caused due to
excessive pressure application -HYALINIZATION
Tooth movement

Tooth movement
2.Elimination of destroyed tissue
 Adjacent undamaged areas give rise to the osteoclasts
(multinucleated giant cells) which cause remodeling of
the bone on the peripheral areas.
 Invasion of the hyalinized areas by the cellular elements.
 Adjacent alveolar bone-undermining resorption
3.Establishment of new attachment
 Synthesis of new tissue once the hyalinized tissue is
removed - Fibroblasts.

Macrophages adjacent to
hyalinized areas

Tooth movement
 In secondary phase
Osteoclasts differentiate and cause frontal resorption.
Osteoblasts deposit on the tension surface.
On the tension side resorption occurs on the spongiosa
surface of the alveolar bone.
On pressure apposition takes place on the spongiosa
surface.
 Remodelling also takes place on the on the periosteal
surface of the bone - helps to maintain the thickness of the
alveoar bone.

Differential Time Course Bw Frontal and
Undermining Resorption

 Initial loading leads to some amount of
tooth movement- movement increases with
time-light forces.
 Movement takes place in a stepwise
fashion with heavy forces.
Differential Time Course Bw Frontal and
Undermining Resorption

Effects of Tooth Movement and Force
Distribution
 Distribution of forces and tooth movement
differ depending upon the type of tooth
movement.
 Tipping
-Forces used to
tip the teeth
must be kept low
50gms.

Distribution
 Tipping-hyalinization
 Caution -alveolar
crest.

Distribution
 Bodily tooth movement-uniform loading of
the teeth is seen.
.

Bodily tooth movement
 Slight tipping due to the
hyalinized zone formed and
resorption adjacent to it.
Further tipping prevented by
the stretch of the fibres.
Effects of Tooth Movement and
Force Distribution

Rotation
 Practically
impossible to bring
about pure rotation
tipping is the
actual mechanism
 2 pressure sites and 2 tention sites.usually 1 side shows
frontal and other undermining resorption.After 3-4 weeks
frontal resorption prevails.
 Supracrestal fibres-gingival fibres, trans gingival fibres.
 Long retention period, supracrestal fibrotomy.
Distribution

TRANSSEPTAL FIBRES

Effects of Tooth Movement and Force Distribution
 Intrusion –light forces are actually needed for intrusion as the
forces are highly concentrated over a very small area.
 If bone compact
as in adults-interrupted
force maybe better.
allows time for cell
proliferation.
 Gingival fibres are relaxed
- cause formation of
bony spicules - crestal areas.

Ditribution(Proffit)
1. Tipping –35-60gms
2. Bodily –70-120gms
3. Uprighting –50-100gms
4. Rotation –35-60gms
5. Extrusion –10-20gms
6. Intrusion-10-20gms

Effects of force duration and decay
 Duration – the second messenger
produced only after 4 hours.
 Forces –
1. Continuous
2. Interrupted light and heavy
3. Intermittent

Force Duration and Decay
 Ideal to have light
continuous forces but
heavier forces can be
allowed if a period of
regeneration and repair
is allowed.
 4 week appointment
cycle.

Force Magnitude(Heavy pressure)

Force Magnitude(Light pressure)

AJO-DO 1985 Step Reassessment of force magnitude - Quinn and
Yoshikawa
Modifying the force magnitude as suggested by Storey and Smith

Pressure Versus Response
 pressure - movement
 Platue
 Decline at the
end
 Optimum force-
lightest force
producing
maximum
or near maximum movement

Pressure Versus Response
 A1-anchor teeth
 M1- teeth to be moved

Stationary anchorage
 Bodily versus tipping movement- anchor
teeth would move less but if the force is
really high enough to bring posterior teeth
into optimum movement rage they would
move the same amount.
 Large forces

Drug Effect on the Response of
Orthodontic Forces
 +ve effect
PG
 -ve effect
1. Bisphosphanates-act as specific inhibitors of
osteoclast mediated bone resorption.
2. PG inhibitors –NSAIDS, indomethacin ,
tricyclic antidepressants,anti arrhythmic
agents,anti malarial drugs, methyl xanthines.
3. Corticosteroids (reduce the inflamation)

Phospholipids
phopholipase Corticosteroids
Arachidonic acids
NSAIDS
Prostaglandins
Drug Effect on the Response of
Orthodontic Forces

The effect of acetaminophen on tooth movement in rabbits
-1997 Angle Orthodontist John J. Roche et al
 It is a weak prostaglandin inhibitor - recommended
for use to relieve pain during orthodontic tooth
movement.
 14 rabbits were used.
 Lower first molar and incisor teeth on one side were
prepared with a perforation hole buccolingually.
 Maxilla was excluded from the study-21-day period.
 Over the 21 day period, each rabbit was force-fed
1000 mgs of Tylenol (10 ml of solution) per day

 On day 21, the rabbits were sacrificed
Impressions of the final interdental distance were
obtained and poured in stone for future examination.
 Acetaminophen does not seem to retard orthodontic tooth
movement, related to its lack of anti-inflammatory
properties
 Concentrated in the central nervous system
The effect of acetaminophen on tooth movement in
rabbits -1997 Angle Orthodontist John J. Roche,
George J. Cisneros, George Acs.

The effect of acetaminophen on tooth movement in rabbits
-1997 Angle Orthodontist John J. Roche, George . Cisneros,
George Acs.

Role Of Prostaglandins In Orthodontic Tooth
Movement- Dr Anand Patil
 1microgram (µgm) / injection (inj) of PG-E1 along with lignocaine
as a vehicle was injected on three different days in the vestibular
region distal to the right upper canine in 15 Patients.
 The left side was the controlled side with injection of vehicle alone.
 Occlusograms of pre and 60 days post canine retraction was obtained
and distal canine movement was calculated by using stable land
marks such as 1st rugae area .
 The results showed statistically significant 57% increase in
orthodontic distal canine tooth movement on prostaglandin injected
side as compared with matched controlled left side.

Pre & post
Retraction
Occlusograms

AJO-DO 1983 Jan (62-75): Histochemistry of enzymes
associated with tissue degradation incident to orthodontic
tooth movement - Lilja, Lindskog, and Hamm
 Acid phosphatase
 LDH as indicators of bone activity.
 Activity of prostaglandin synthetase since some
prostaglandins - important local activators of bone
resorption.
 The maxillary right first molar in each rat was
moved in a buccal direction.

 A tipping movement had been produced by the
orthodontic forces, and thus two pressure zones-
buccal and lingual.
 Acid phosphatase activity Cells randomly
distributed along the bone surface in the alveoli in
non treated cases.
 Prostaglandin synthetase - found exclusively in
the bone marrow-not in PDM.

 Low force - rapid redistribution to the pressure zones of cells with a
high acid phosphatase activity.
 Accompanied by a high enzyme activity in the adjacent osteocytes.
 Low forces caused no change in the distribution and activity of LDH at
any time during the treatment.
 After 1 day of high force a zone devoid of LDH activity developed in
the buccal pressure zone
 No change in the activity of this enzyme was found in the bone
marrow during the treatment

 Pressure areas
 Tension areas

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