Biology of tooth movement (2)

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.
www.indiandentalacademy.com

“When an orthodontic force is applied, Tooth
moves thro the bone carrying its attachment
apparatus (Periodontal ligament) with it , as
the socket of the Tooth migrates.”So before
going in detail about the Tooth movement, it
will be appropriate to know the Basis about
periodontal ligament (Attachment apparatus)
and the alveolar Bone.

PERIODONTAL LIGAMENT
 1. PDL is a connective tissue organ, which
attaches cementum of the Tooth to the
alveolar bone.
 2. Normally it occupies a space approximately
0.5mm in width around all parts of the root .

COMPOSITION
Cellular elements
Extracellular matrix

Synthetic cells Resorptive cells
Epithelial rests of
malassez
Cellular elements

Extracellular matrix
Fires
Ground substance
collagen Oxytalan
proteoglycans glycoprotein Mucopolysaccharides

Transseptal
fibers
Alveolar
crest
Oblique fibers
Horizontal fibers

 STRUCTURES PRESENT
 Blood vessels
 Nerves
 Unmyelinated free Nerve Endings: - pain
perception
 Myelinated, complex Nerve Endings:
-proprioception (pressure)
 Cementicles
 Lymphatics

FUNCTIONS OF PDL
 SUPPORTIVE
 SENSORY: by nerve supply
 Free nerve endings – pain sensation
 Myelinated fibers – proprioception
 NUTRITION:
 HOMEOSTATIC

Alveolar bone
 Bone consists of about 65% inorganic and 35%
organic material .The inorganic material consists
of calcium and inorganic orthophosphate in the
form of hydroxyapatite crystals while the organic
material is type I collagen which lies in the
ground substance of glycoprotein and
proteoglycans.

Composition
 INORGANIC =65%
 ORGANIC = 35%
 COLLAGEN= 88-89%
 NONCOLLAGEN = 11-12%
 GLYCOPROTEINS= 6.5%-10%
 PROTEOGLYCANS = 0.8%
 SIALOPROTEINS = 0.35%
 LIPIDS= 0.4%

Structure of alveolar
process
 As a result of adaptation to its function , two
pats of alveolar process can be distinguished
Alveolar bone proper Supporting alveolar bone
Cortical plate Spongy bone

PHYISOLOGICAL CHANGES IN
ALVEOLAR BONE
 The internal structure of Bone is adapted to
mechanical stresses. It changes continuously
during growth and alteration of functional
stresses. These changes are correlated to the
Growth, eruption, movements, and loss of
teeth.


 Al l these processes are made possible only
by a coordination of Destructive and
formative activities.
The cells responsible for these all
 (1) Osteoblasts – formation / Deposition
 (2) Osteoclasts – Destruction –Resorption

Structure Of Osteoblast
 Ovoid cells, Basophilic cytoplasm and oval
nucleus
 Function: secretes organic matrix (osteoid) in
the Tension side, which is then calcified
resulting in the Formation of Bone Lamella.

Precursors of osteoblasts are
(1) Fibroblasts in PDL
(2) Perivascular stem cells

Structure of Osteoclasts
 Multinucleated giant cells have 12 / more
nucleus Irregularly oval / club shaped with
branching process
 _ Occur in Bay like depressions in Bone
called“ Howship's lacunae”
 _ The part of the osteoclasts in contact with
the resorbing bone has a ‘Ruffled Border’.
 Osteoclasts (Bone Resorbing cells) are more
in number in the compression side of PDL

How the orthodontic tooth movement differs
from physiological dental drift or tooth
eruption
 The former is uniquely characterized by the
abrupt creation of compression and tension
regions in the PDL.
Physiological tooth movement is a slow
process that occurs mainly in the buccal
direction into Cancellous bone or because of
growth into cortical bone.

 Physiological tooth movement1
Tooth eruption Migration or drift of teeth During
mastication
1. Blood pressure theory
2.Root growth theory
3.Hammock ligament theory
4.Periodontal ligament traction theory

 BIOCHEMICAL PRINCIPLES OF TOOTH
MOVEMENT
 (Yoshikava – Dental clinics of South America
1981)

Orthodontic force application
Periodontal ligament
compression tension
Decreased
blood supply Increased blood
supply
Decreased o
supply Rich nutrient
supply
Tissue injury
Production of Ist
messenger
Metabolites washed
out easilywww.indiandentalacademy.com

Production of 2nd
messenger
osteoclasts
Bone resorption
Stimulation of progenitor
cells
osteoblasts
Bone deposition
Orthodontic tooth
movement

THEORIES OF TOOTH MOVEMENT
 Numerous theories have been put forward to
explain the mechanism of tooth movement ,
when orthodontic force is applied.
 The theories that are accepted and have
stood the test of time are
 1. Pressure tension theory
 2.Bone bending piezoelectric theory
 3.Blood flow theory

Pressure tension theory
 Author - Schwarz 1932
whenever a tooth is subjected to an orthodontic
force, it results in areas of pressure and
tension
 The area of periodontium in the direction of
tooth movement is under pressure show
“Bone Resorption"
 The area of periodontium opposite the tooth
movement is under Tension show “Bone
Deposition" www.indiandentalacademy.com

 schwarz concluded that the forces delivered
as part of orthodontic treatment should not
exceed the capillary bed blood pressure (20-
25 g/cm2 of root surface).
 If one exceeds this pressure, compression
Could cause tissue necrosis through“suffocation
of the strangulated periodontium.”

 Baumrind reconsidering the propriety of the
pressure-tension hypothesis, pointed out a
conceptual flaw in it. He considered the PDL
to be a continuous hydrostatic system and
suggested that any force delivered to it would
be transmitted equally to all regions.
 He drew support for this concept from
Pascal’s law, a basic law in physics.

 Current concepts by Massella and
meisler(AJO APRIL 2006)
 They are divided into:
 1.Molecular genetics of osteoblast
differentiation and function
 2.neurotransmitters
 3.osteoclasts differentiation and function
 4.hormonal control of bone formation and
resorption
 5.intracellular and extracellular environment
 6.signal input and genetic output

 2 osteoblasts specific m rna transcripts are
known:
Cbfa1 transcription factor
Enhancing or supression
gene expression
osteocalcinin
Inhibitor of osteoblast
function

Mesenchy
mal stem
cells
T f genes
cbfa1
Col
type 1
BSP
Preosteoblasts
T f gene osteocalcinin
osteoblasts
Bone matrix secretion
inhibit
10 hrs post force
48 hours post force

NEUROTRANSMITTERS
Due to application of physiological
orthodontic force
PDL peripheral nerve fiber
CGRP SUBSTANCE P
DOCKING
OSTEOBLASTS
(VASODILATORS)
Release of cytokine
Orthodontic tooth movement

Osteoclasts differentiation
and function

Endocrine regulation of bone physiology

Mechanical force induced reciprocal communication between 5 microenvironments

Bone bending theory
 Farrar (1876), First noted deformation /
Bending of interseptal alveolar walls.
 What is piezoelectricity?
e- -e-e-e
Small electric current
is generated

What is the source of
electric current
 1.collagen
 2.Hydroxyapatite
 3.collagen –hydroxyapatite interface

force
-e-e -e-e-e-e-
force
-e-e -e-e-e-e-
As long as the force is maintained ,crystal structure is stable and no further
electric effect is observed
Ions in
the ECF
Streamig
potential

Reassessment of force magnitude in orthodontics
Ken Yoshikawa, AJO-1985 Sep

Fluid dynamic theory
 (Bien 1966- Arch oral Biology)
 According to this theory
 Tooth movement occurs as a result of
alternations in fluid dynamic in the PDL.

When force is applied
Interstitial fluid is squeezed and moved towards apex and cervical
margins known as squeeze film effect
Blood vessels trapped in
the fibers
Stenosis and
aneurysm(balloons)
Decreased o supply(anoxia)
Alteration in the chemical
environment Bone
remodellingwww.indiandentalacademy.com

PHASES OF ORTHODONTIC TOOTH
MOVEMENT
Tooth movement progress thro
three stages:
1. Initial Strain
2. Lag Phase
3.Progressive Tooth Movement / Post Lag
Phase


MELSEN’S HYPOTHESIS
 Acc to this hypothesis the indirect bone
resorption at the pressure side is not a
reaction to force but an attempt to remove
ischemic bone lying adjacent to the
hyalinized tissue.

Signaling molecules and
metabolites in orthodontic
tooth movement
 1.Arachidionic acid metabolites
 2.Prostaglandins
 3.intracellular second messenger system
a.cyclic nucleotide pathway
b.Phosphatidyl inositol (PI) pathway

Arachidonic acid pathway
 Arachidonic acid is the main component of
the phospholipids of cell membrane is
released due to the action of phospholipase
enzymes.

Mechanical stimulus
Arachidonic acid
Cyclo-oxygenase
pathway Lipo-oxygenase pathway
PGG2,PGH2 5HETE LECOTRIENS

Prostaglandins
 prostaglandins
PGE1
PGE2

IST
MESENGER
PG,
CYTOKINES,
HORMONES
CYTOPLASMIC
ATP
CYCLIC
AMP
CYCLIC
GMP
2nd
MESSENGERS
Interacts
with
cellular
enzyme
Protein
synthesis

Cyclic nucleotide pathway
 Cyclic AMP and Cyclic GMP
Activate enzyme protein kinase c
present on the cell membrane
Opening of calcium channels
Increase in the ca conc in the cells
Trggering a number of protein
phosphorylation agents
Protein synthesis

PI dual signaling pathway
 This pathway was given by Hokin and Hokin
in 1953.
 Interest in this system started with the
demonstration of an increase in the
phosphate concentration into cell membrane
phospholipids

Activation of cell surface
receptors
PI 4,5 Biphosphate present in
the cell membrane
H20
IP3
Release of calcium
from the intracellular
stores
IP4
Controls the ca
entry at plasma
membrane through
ca channels

CALCIUM HOMEOSTASIS
 1. Rapid[Instantaneous] flux of calcium from
bone fluids[seconds]
 2. Short term response of osteoclasts &
osteoblasts.[minutes to days]
 3. Long term[weeks to months] control of
bone turnover.

Cytoskeltal-extracellular
matrix interactions
 The dental and paradental cellular responses
to applied mechanical loads involve interplay
between intra- and extracellular structural
elements, and among biochemical
messengers.

ECM includes
collagen,proteo
glycan,laminin ,
and fibronectin
transduction
Reorganization of
cytoskeleton ,secretion
of stored
cytokines,ribosomal
activation and gene
transcription
Integrin
receptors
Na+
Na+
K+ ,k+

Signaling molecules involved
in load induced tissue
remodeling
 The PDL is abundantly supplied with 2 kinds
of nerve terminals:
 Ruffini-like endings and nociceptive endings.
 Both endings can change their structures in
response to external stimuli, such as
orthodontic force

Pain and tooth movement
Tooth movement-associated tissue
remodeling, an inflammatory process, might
induce painful sensations, particularly after
activation of the orthodontic appliance.

After 24 hours of force
application
Nociceptive endings in
PDLare stimulated
Trigeminal subnucleus
caudalis
C-fos neurons are
stimulated
Activate pain control system
descending monoaminergic
pathwaywww.indiandentalacademy.com

Cytokines in orthodontic
tooth movement

 The different types of cytokines which take part in
orthodontic bone remodeling are:-
 1. Interteukin - 1 alpha[IL - 1 alpha]
 2. Interieukin - 1 beta(lL - 1 beta)
 3.Tumor Necrosis Factor – alpha(TNF –alpha) or
Cachectin
 4. Tumor Necrosis Factor - beta(TNF -beta] or
Lymphotoxin
 5. Interieukin - 6[IL-6] www.indiandentalacademy.com

Orthodontic force
Distotion of PDL and
alveolar bone
Distortion of axonal nerve
endings
Peripheral release of
neurotransmitters
Dilation of
PDLcapillaries
Extravascular migration of
macrophages and
lymphocytes
Production of IL-1,IL-
1,TNF,Monokines&PG’s
Production of IL-2,other
lymphokines
Production of fibroblasts
Alveolar bone cell
response &bone
remodeling

Growth factors
 Bone contains the abundant amount of
growth factors:
 Fibroblasts like growth factor
 Platelet derived growth factor
 Transforming growth factor
 Connective tissue like growth factor

Recent model of tooth
movement by Jones et al
 stress in any form—compressive, tensile, or
shear—will evoke many reactions in the cell,
leading to the development of strain.

K+
K+
k+
Ca2+
Ca2+
Ca2+
stress
Activation of
phospholipase C
Inositol
triphosphate
Increased levels
Phospholipase
A
STORES OF
ARACHIDONIC
ACID

Bone remodeling and tooth
movement
 MUNDY AND ROODMAN HYPOTHESIS: This
is the most widely accepted hypothesis.
According to this hypothesis, osteoclasts are
derived from stem cells in haemopoietic
organs, and granulocyte macrophage colony
forming units are the earliest identifiable
precursors of osteoclasts

Granulocyte macrophage
colony forming units
promonocytes
Early preosteoclasts
Late preosteoclasts
osteoclasts
MUNDY AND ROODMAN HYPOTHESIS

Factors affecting bone
remodeling process
 Hormones
 Growth factors
 Cytokines
 Colony stimulating factors
 others

Gingival effects of
orthodontic force
 Accordingly, 2 disparate processes occur in
the gingiva after transduction of orthodontic
force. First, there is an injury of the gingival
connective tissue, manifested by torn and
ripped collagen fibers.
second, the genes for both collagen and elastin
are activated, whereas those for tissue
collagenases are inhibited.

Biology of tooth movement (2)

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