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IN THE NAME OF GOD
Tooth response to orthodontic force
Biomechanics in orthodontics
Different types of tooth movement
Anchorage and its control
Deleterious effects of orthodontic force
By: Dr. Sepideh Arab
PERIODONTAL AND BONE RESPONSE
TO
NORMAL FUNCTION
Periodontal ligament structure and function
 Response to normal function
 Role of the periodontal ligament in eruption and
stabilization of the teeth
 Periodontal ligament and bone response to
sustained orthodontic force
 Effects of force magnitude
 Force duration and force decay
 Drug effects on the response to orthodontic force

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.
Forces applied to the teeth can also affect the pattern
of bone apposition and resorption at sites distant from
the teeth
PERIODONTAL LIGAMENT STRUCTURE
Approximately 0.5 mm
The major component of the ligament is a network of parallel
collagenous fibers
Cementum
Lamina dura
Two other major components:
 (1) the cellular elements,
including mesenchymal cells of various types along with
vascular and neural elements
UMC
fibroblasts and osteoblasts
Hematogenous origin
osteoblasts & cementoblasts
 (2) the tissue fluids
PERIODONTAL LIGAMENT FUNCTION
ERUPTION:
The phenomenon of tooth eruption makes it plain
that forces generated within the P D L itself can
produce tooth movement.
ACTIVE STABILIZATION
interrupted
intermittent
Different types of forces based on
The force consistency
continuous
RESPONSE TO NORMAL FUNCTION
Since those are intermittent heavy forces, response to these
forces depends on the duration of force exertion
The body of the mandible bends as the mouth is opened and closed
PERIODONTAL LIGAMENT AND BONE RESPONSE
TO SUSTAINEDORTHODONTIC FORCE

Piezoelectric signals

Pressure-Tension Theory
PIEZOELECTRIC SIGNALS:
deformation of the crystal
structure (organic or inorganic)
produces a flow of electric
current
as
electrons
are
displaced from one pan of the
crystal lattice to another
Characteristics:
(1) a quick decay rate
(2) production of an equivalent
signal, opposite in direction
Endogenous electric
signals
Streaming potential: Ions in the
fluids of the living bone interact
with the complex electric field
generated when the bone bends,
causing temperature changes as
well as electric signals.
bioelectric potential: can be
observed in bone that is not being
stressed. Metabolically active bone
or connective tissue cells.
Reverse piezoelectricity
PRESSURE-TENSION THEORY:
•
The
classic
theory
of
tooth
movement
•
Chemical rather than electric
signals
•
Alterations in blood flow create
changes in O2 level & chemical
environment
Pressure side
Tension side
decrease
increase
PERIODONTAL
LIGAMENT
AND
BONE
RESPONSE
TO
SUSTAINEDORTHODONTIC FORCE
Depends on the
magnitude of force
(cAMP), the "second
messenger" for many
important
cellular
functions
including
differentiation, appear
after about 4 hours
of sustained pressure.
what happens between the onset of pressure and tension in the
PDL and the appearance of second messengers a few hours later
Prostaglandin and interleukin-1 beta levels increase within the PDL
within a short time after the application of pressure
prostaglandin E2 is an important mediator of the cellular response.
Changes in cell shape probably play a role. prostaglandins are released
when cells are mechanically deformed (i.e., prostaglandin release may be a
primary rather than a secondary response to pressure).
mobilization of membrane phospholipids, which leads to the
formation of inositol phosphates, is another pathway toward the
eventual cellular response.
Other chemical messengers, particularly members of the cytokine family
but also nitric oxide (NO) and other regulators of cellular activity, also
are involved
Where from are the osteoclasts derived when a light force is
applied?
Osteoclasts appear within the compressed PDL via two waves:
1)some may be derived from a local cell population
2)others (the larger second wave) are brought in from distant
areas via blood flow
These cells attack the adjacent lamina dura, removing bone in
the process of "frontal resorption," and tooth movement
begins soon thereafter.
PERIODONTAL
LIGAMENT
AND
BONE
RESPONSE
TO
SUSTAINEDORTHODONTIC FORCE
Depends
on
the
magnitude of
force
Where from are the osteoclasts derived when a
heavy force is applied?
Complete occlusion of blood vessels lead to a sterile
necrosis ensues within the compressed area.
Remodeling of bone bordering the necrotic area of
the P D L must be accomplished by cells derived
from adjacent undamaged areas.
Osteoclasts appear within the adjacent bone
marrow spaces and begin an attack on the
underside of the bone immediately adjacent to
the necrotic PDL area creating undermining
bone resorption
UNDERMINING RESORPTION
delay in tooth movement
results by
1. a delay in stimulating
differentiation of cells
within the marrow spaces
2. a considerable thickness of
bone must be removed
from the underside before
any tooth movement can
take place.
CLINICAL TOOTH MOVEMENT, STEPWISE
RELATIONSHIP OF TOOTH MOVEMENT
TO FORCE
DRUG EFFECTS ON THE RESPONSE TO ORTHODONTIC
FORCE
Vitamin D
Direct injection of prostaglandin
Enhance OTM rate
OTM rate depressors:
1. Bisphosphonates (alendronate)
2. prostaglandin inhibitors
3. other classes of drugs can affect prostaglandin levels
4. anticonvulsant drug
5. some tetracyclines
OTM rate depressors:
1. Bisphosphonates (alendronate)

synthetic analogues of pyrophosphate that bind to hydroxyapatite in bone

They act as specific inhibitors of osteoclast-mediated bone resorption

explore with her physician for switching to estrogen, at least temporarily.
2. prostaglandin inhibitors

Corticosteroids (chronic steroid therapy)

NSAIDs (especially potent prostaglandin inhibitors like indomethacin)

agents that have mixed agonistic and antagonistic effects on various
prostaglandins
3. other classes of drugs can affect prostaglandin levels

Tricyclic antidepressants (doxepin, amitriptyline,imipramine)

anti-arrhythmic agents (procaine)

antimalarial drugs (quinine, quinidine, chloroquine)

methyl xanthines
4. anticonvulsant drug (phenytoin)
5. some tetracyclines (e.g., doxycycline) inhibit osteoclast recruitment, an effect
similar to bisphosphonates.
BIOMECHANICS, BASIC DEFINITIONS

Force

Moment

Centre of resistance

Centre of rotation
DIFFERENT TYPES OF TOOTH MOVEMENT

Tipping

Bodily

Root torque

Rotation

Intrusion

extrusion
TIPPING
The simplest form of orthodontic
movement.
 Tipping
movements
are
produced when a single force
(e.g., a spring extending from a
removable appliance) is applied
against the crown of a tooth.
 Maximum pressure in the P D L
is created at the alveolar crest
and at the root apex
 The loading diagram, therefore,
consists of two triangles as
shown.

BODILY MOVEMENT
(TRANSLATION)



the root apex and crown
move in the same
direction and with the
same amount.
the total PDL area is
loaded uniformly
rectangular loading
diagram
INTRUSION




Light force is required for
intrusion because the force will
be concentrated in a small area
at the tooth apex
As with extrusion, the tooth
probably will tip somewhat as it
is intruded
the
loading
diagram
nevertheless will show high
force concentration at the
apex.
Only if the force is kept very
light can intrusion be expected.
EXTRUSION
ROTATION
ROOT MOVEMENT
(ROOT TORQUE)
TABLE 9-3 Optimum Forces for Orthodontic Tooth Movement
'Values depend in part on the size of the tooth; smaller values
appropriate for
incisors, higher values for multirooted posterior teeth.
ANCHORAGE: RESISTANCE TO UNWANTED
TOOTH MOVEMENT
For every (desired) action there is an equal and
opposite reaction. Inevitably, reaction forces can
move other teeth as well if the appliance contacts
them.
 Anchorage, then, is the resistance to reaction
forces
 provided (usually) by other teeth, or (sometimes)
by the palate, head or neck (via extraoral force),
or implants in bone.

RECIPROCAL TOOTH MOVEMENT.



In a reciprocal situation, the
forces applied to teeth and to
arch segments are equal, and
so is the force distribution in
the PDL .
example is what would occur if
two maxillary central incisors
if a spring were placed across a
first premolar extraction site,
pitting the central incisor,
lateral incisor, and canine in
the anterior arch segment
against the second premolar
and first molarposteriorly.
REINFORCED ANCHORAGE.


reinforcing anchorage by adding
more
resistance
units
is
effective because with more
teeth (or extra oral structures)
in the anchorage, the reaction
force is distributed over a larger
PDL area.
if it was desired to differentially
retract the anterior teeth, the
anchorage of the posterior teeth
could be reinforced by adding
the second molar to the
posterior unit
STATIONARY ANCHORAGE.

can be obtained by pitting
bodily movement of one
group of teeth against tipping
of another to differentially
retract the anterior teeth, the
anchorage of the posterior
teeth could be reinforced by
adding the second molar to
the posterior unit
oexample of a premolar extraction site, if the appliance were
arranged so that the anterior teeth could tip lingually while the
posterior teeth could only move bodily
DIFFERENTIAL EFFECT OF VERY LARGE
FORCES.

If tooth movement were actually impeded by very high
levels of pressure, it might be possible to structure an
anchorage situation so that there was more movement
of the arch segment with the larger PDL area.
Not
recommended
CORTICAL ANCHORAGE.


The different response of cortical compared with medullary
bone
If a root is persistently forced against either of these cortical
plates, tooth movement is greatly slowed and root resorption
is likely
ABSOLUTE ANCHORAGE.
DETRIMENTAL EFFECTS OF ORTHDONTIC
FORCES

Mobility
Reorganization of the PDL itself
Radiographically, it can be observed that the P D L space widens during
orthodontic tooth movement

Excessive mobility is an indication that excessive forces

may occur because the patient is clenching or grinding against a tooth that has
moved into a position of traumatic occlusion
Pain
Caused by ischemia of PDL


If heavy pressure is applied to a tooth, pain develops almost immediately
If appropriate orthodontic force is applied, the patient feels little or nothing
immediately

Allergy (soft tissue)

Latex
Nickel
EFFECTS OF ORTHDONTIC FORCES ON PULP

Necrotic tooth
1) If a tooth is subjected to
heavy continuous force
2) Root apex, moving outside
the alveolar process
What about the teeth with
RCT?
Moving endodontically
treated teeth is perfectly
feasible

EFFECTS OF ORTHDONTIC FORCES ON ROOT STRUCTURE
Types of root resorption:
cementum adjacent to hyalinized (necrotic) areas of the PDL is "marked" by
this contact and that clast cells attack this marked cementum

Moderate generalized resorption
Individuals who have undergone comprehensive orthodontic treatment shows
that most of the teeth show some loss of root length, and this is greater in
patients whose treatment duration was longer

severe generalized resorption
At this point the etiology of severe generalized resorption must be considered
entirely unknown. Orthodontic treatment is not the major etiologic factor

severe localized resorption
excessive force during orthodontic treatment
SUBDIVISIONS OF ROOT RESORPTION

1, slight blunting

2, moderate resorption, up to 1/4 of root length

3, severe resorption, greater than 1/4 of root
length
EFFECTS OF ORTHODONTIC FORCE ON
ALVEOLAR BONE HEIGHT
Since the presence of orthodontic appliances increases the amount of
gingival inflammation, this potential side effect of treatment might
seem even more likely. Fortunately, excessive loss of crestal bone
height is almost never seen as a complication of orthodontic
treatment. Loss of alveolar crest height in one large series of
patients averaged less than 0.5 mm and almost never exceeded 1
mm, with the greatest changes at extraction sites.

Lateral missing

Extrusion and intrusion

Intrusion of teeth with periodontal problem
SKELETAL EFFECTS ORTHODONTIC FORCES

Effects of Orthodontic Force on the Maxilla and
Midface : amount of force, duration of force
Because tooth movement is an undesirable side effect, it would be
convenient if part-time application of heavy force produced relatively
more skeletal than dental effect.


Acceleration: facemask
Prevention : Headgear
PREVENTION : HEADGEAR
Force of 500 to 1000 gm
total (half that per side)
Force direction slightly
above the occlusal plane
Force duration at least
12 hours per day
ACCELERATION: FACEMASK
Suitable age? 7 years
(before interdigitation of
sutures)
An ankylosed tooth or
implant/onplant would
provide
perfect
anchorage
Maxillary soft tissue is
the most preventing
factor
EFFECTS OF ORTHODONTIC FORCE
ON THE MANDIBLE

Prevention : Chin cup

Acceleration: functional
Attachment of the mandible to the rest of the facial skeleton
via the temporomandibular joint is very different from the
sutural attachment of the maxilla
PREVENTION : CHIN CUP

Animal experiments, in which
quite heavy and prolonged forces
can be used, suggest that
restraining forces can stop
mandibular growth
A.
The duration of the chin cup force
(hours/day) may be an important
difference between children and
experimental animals.
B.
the presence of the articular disk
complicates the situation, making
it difficult to determine exactly
what areas in and around the
temporomandibular joint
It is fair to say that controlling
excessive mandibular growth is
an important unsolved problem
in contemporary orthodontics.
At this point, we simply cannot
restrain mandibular growth
It is possible to use a chin cup to
deliberately rotate the mandible
down and back, redirecting
rather than directly restraining
mandibular growth
ACCELERATION: FUNCTIONAL

Passive

active
MC/MF, TYPES OF MOVEMENT
Mechanical Principles in Orthodontic
Force Control

The Basic Properties of Elastic Materials
Springiness = 1/Stiffness
Strain
MECHANICAL PRINCIPLES IN ORTHODONTIC
FORCE CONTROL
Deflection
THREE MAJOR PROPERTIES OF BEAM
MATERIALS FOR ORTHODONTIC PURPOSES:
 Strength

stiffness (or its inverse, springiness)

range
These three major properties have an important relationship:
Strength = Stiffness X Range
ORTHODONTIC ARCH WIRE MATERIALS

Precious Metal Alloys

Stainless Steel (18% chromium and 8% nickel)

Beta Titanum

Cobalt-Chromium (Elgiloy)

Nickel-Titanium (NiTi) Alloys.
NITI ALLOYS SPECIAL FEATURES




shape memory:
Shape memory refers to the ability of the material to
"remember" its original shape after being plastically
deformed while in the martensitic form. In a typical
application, a certain shape is set while the alloy is
maintained at an elevated temperature, above the
martensite-austenite transition temperature. When
the alloy is cooled below the transition temperature, it
can be plastically deformed, but when it is heated
again the original shape is restored.
superelasticity
A-NiTi wires do not undergo plastic deformation until
remarkably high force is applied. The wires can be
shaped and their properties can be altered, however,
by heat-treatment.
COMPARISON OF CONTEMPORARY
ARCHWIRES
Stiffness
 formability

EFFECT OF LENGTH AND DIAMETER