Biology of OrthodonticTooth Movement

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BIOLOGY OF ORTHODONTIC TOOTH MOVEMENT

Prepared By

JEAN MICHAELFinal Year - RDC

Guided By

Dr. Hariprasad MDSDr. Sarath MDSDr. Shaji MDSDr. Yohan Varghese MDS, PhD

Widescreen (16:9)

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Physiologic Tooth Movement

It is the naturally occurring tooth movementsthat take place during and after tooth eruption

1. Tooth eruption2. Migration or drift of teeth3. Changes in tooth position during mastication

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Tooth Eruption

Axial or occlusal movement of the tooth from its developmental position within the jaw to its functional position in the occlusal plane

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Theories Of Tooth Eruption

• Vascular pressure theory• Root formation• Bone Remodeling• Periodontal ligament traction

This theory states that the periodontal ligament is rich in fibroblaststhat contain contractile tissue. The contraction of these periodontal fibers (mainly the oblique group) result in tooth eruption.

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Migration Or Drift Of Teeth• Teeth have the ability to drift through the alveolar

bone • Human teeth have a tendency to migrate in mesial or

occlusal direction • This maintains the inter-proximal and occlusal contact • Aided by bone resorption and deposition by

osteoclasts and osteoblasts respectively

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• Mesial - due to proximal caries (loss of tooth structure)

• Occlusal - Due to premature exfoliation or absence of opposing tooth (supra-eruption)

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Tooth Movement During Mastication• Normal force of mastication – 1 to 50 kg• It occurs in cycles of 1 second duration• Teeth exhibit slight movement within the socket and

return to their original position on withdrawal of the force

• Whenever the force is sustained for more than 1 second, periodontal fluid is squeezed out & pain is felt as the tooth is displaced within the periodontal space

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PERIODONTIUM

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• Thickness of normal PDL – 0.5 mm• Collagenous fibres of PDL connects

the cementum and lamina dura• The fibers run at an angle attaching

farther apically on the tooth than on the adjacent alveolar bone

• PDL space is filled with fluid derived from vascular system

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Periodontal Ligament

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Cellular Elements in the PDL• Fibroblasts – produce and destroys collagen fibers• Osteoblasts –produce new bone• Osteoclasts – aids in bone resorption• Cementoblasts – forms new cementum• Cementoclasts – removes cementum• PDL is vascular and contains nerve endings which

aid in proprioception

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FIBROBLAST

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OSTEOCYTE

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OSTEOBLASTS

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OSTEOCLASTS

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• Is orthodontic movement possible for a tooth that has undergone endodontic treatment ?

YES (the PDL is intact in this case)

• Is it possible to move an ankylosed tooth ?

NO (here there is complete absence of the PDL)

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Piezoelectric Effect• When a force is applied to a

crystalline structure (like bone or collagen), a flow of current is produced that quickly dies away

• When the force is released, an opposite current flow is observed

• The piezoelectric effect results from migration of electrons within the crystal lattice

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Response to Normal Function• Teeth and periodontal structures are subjected to

forces up to 50 kg during mastication• Force is transmitted to the alveolar bone which

bends in response• Generation of piezoelectric currents• It acts as an important stimulus to skeletal

regeneration and repair resulting in adaptation of bony architecture to functional demands

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Response to Continuous Pressure• < 1 second: Fluid in the PDL is incompressible

• 1 – 2 seconds: PDL fluid expressed, Tooth moves within PDL space

• 3 – 5 seconds: PDL fluid squeezed out, Tissue compressed and immediate pain is felt if force is heavy

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Force for Orthodontic Tooth Movement• Forces that bring about orthodontic tooth movement

are continuous and should have a minimum magnitude (threshold)

• Below this threshold limit, the PDL has the ability to stabilize the tooth by active metabolism

• The minimum pressure required is 5 to 10 gm/cm2 (current concept)

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Resting Pressure from Lip & Tongue• Upper Anteriors

Force exerted by LIP > Tongue• Lower Anteriors

Force exerted by TONGUE > LIP• Teeth remain stable in their position as the

unbalanced forces acting on them, are below the threshold limit tolerated by the metabolism in PDL

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Magnitude of Force VS Tooth Movement

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ORTHODONTIC TOOTH MOVEMENT

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Modes of Orthodontic Tooth Movement

Forces created by orthodontic appliances bring about tooth movement by 2 mechanisms.

• FRONTAL Resorption• UNDERMINING Resorption

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Frontal Resorption

• Accomplished by Light Orthodontic Forces• least painful • least harmful to the periodontium• Most desirable

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• Caused by Heavy Orthodontic Forces• Painful• More harmful to the periodontium• Occurs in a small scale even in the most careful

orthodontic treatment• The dentist should always try to minimize this

Undermining Resorption

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Role of Piezoelectric Current • Piezoelectric currents produced on application of force

on tooth and alveolar bone dies off quickly and play little role in orthodontic tooth movement

• Orthodontic tooth movement requires sustained forces which does not produce continuous piezoelectric current

• But these signals which are produced while normal chewing are required for proper maintenance of normal bony architecture

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The Pressure – Tension Theory• When force is applied on the tooth, PDL is

compressed on one side and stretched on the other side

• Blood flow is decreased on the pressure side where PDL is compressed

• Blood flow is increased on the tension side where PDL is stretched

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• The process of initiation of tooth movement has 3 stages1. Alternation of blood flow associated with

pressure within the PDL2. The formation and release of chemical

messengers3. Activation of cells which causes deposition and

resorption of bone

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• BONE RESORPTION (osteoclastic activity) takes place at the side of the PDL where there is PRESSURE

• BONE FORMATION (osteoblastic activity) takes place at the side where there is TENSION

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Maintenance of Thickness of Alveolar Bone• In an ideal treatment, the attachment level is

maintained • Resorption and deposition of bone maintains its

thickness in the facial and lingual side irrespective of the type of movement the tooth has undergone on the alveolar bone

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Chemical Regulation of OTM• Within the 1st hour

Increase in Prostaglandin E & Interleukin – 1Increase in Cytokines & Nitric oxide (NO)

• After 4 hours of pressure applicationIncrease in cAMP (chemical mediator for differentiation)

PROSTAGLADINS can stimulate formation of both OSTEOBLAST & OSTEOCLAST

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• It takes a minimum of 4 to 6 hours of continuous force to initiate orthodontic tooth movement

• So removable appliance worn for less than this minimum period of time is of no use

Maximum efficiency is obtained if the appliance is worn for 24/7

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Types of Orthodonic Forces

• LIGHT Force – Frontal resorption• HEAVY Force – undermining resorption

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Effect of Magnitude of Force on PDL

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Application Of Continuous Light Force• < 1 second: PDL fluid is incompressible, alveolar bone

bends, piezoelectric signal generated

• 1 – 3 seconds: PDL fluid expressed & tooth moves within the socket

• 3 – 5 seconds: Blood vessels within PDL partially compressed on pressure side & dilated on tension side. PDL fibers and cells are mechanically distorted

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• Minutes: Blood flow altered & oxygen tension begins to change. Prostaglandins and cytokines released

• Hours: Metabolic changes ocures. Chemical messengers affects cellular activity. Enzyme levels change

• 4 Hours: Iincreased cAMP levels are detectable & cellular differentiation begins within PDL

• 2 Days: Tooth movement begins as osteoclasts & osteoblasts remodel bony socket

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No pressure – Normal perfusion of blood vessels

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Light pressure – blood vessels constricted

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Tension side – Fibers stretched & Vessels open wide

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Result of Continuous Light Force• Osteoclasts initiates resorption of lamina dura from

the side of PDL• The osteoclasts arrive in 2 waves

1st wave derived from the PDL itself2nd wave (larger) from distant areas via blood flow

• All these events lead to FRONTAL RESORPTION

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Application of Continuous Heavy Force• < 1 second: PDL fluid is incompressible, alveolar bone

bends, piezoelectric signal generated

• 1 – 3 seconds: PDL fluid expressed & tooth moves within the socket

• 3 – 5 seconds: Blood vessels with in PDL occlude on the pressure side

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• Minutes: Blood flow gets cut off to compressed PDL area

• Hours: Cell death in compressed area• 3 to 5 days: Cell differentiation in adjacent marrow

spaces; undermining resorption begins• 7 to 14 days: Undermining resorption removes

lamina dura adjacent to compressed PDL & tooth movement occurs

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Heavy Pressure – Blood flow totally cut off

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Compressed PDL after Sterile Necrosis

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Cellular Changes• Loss of blood flow causes sterile necrosis of the PDL• A “Hyalinized” area devoid of cells and vasculature

develops• Osteoclasts appear within the adjacent bone marrow

spaces and begins an attack on the underside of the bone immediately adjacent to the necrotic PDL area

• An initial delay in tooth movement ocures

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• This delay is due to 2 reasons• The delay in stimulating differentiation of cells

within the marrow space • A considerable thickness of bone has to be

removed from the underside before any tooth movement can take place

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Undermining Resorption

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Frontal Resorption VS Undermining Resorption

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Centre Of Resistance

• It is the point on the tooth when a single force is passed through it, would bring about its translation along the line of action of the force

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• Factors affecting Centre of Resistance1. Number of roots2. Degree of Alveolar Bone loss3. Degree of Root Resorption

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ANCHORAGE• It is the Resistance to Unwanted Tooth Movement

Or

• It is the nature and degree of resistance to displacement offered by an anatomic unit for the purpose of effecting tooth movement

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Absolute Anchorage

1. Appliances gaining anchorage from extraoral structures – Extraoral appliances (eg – Head Gear)

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2. Titanium screws implanted into the alveolar bone through the gingiva to act as anchorage

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Intraoral Anchorage

• Anchorage value of a tooth is proportional to the surface area of the root

• The tooth with larger root surface area requires greater force to move

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Anchorage Value Of Each Tooth

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• Teeth that are ANKYLOSED or DILACERATED are very good sources of anchorage

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Different Types of OTM

CONTROLLED TIPPING

UNCONTROLLED TIPPING

BODILY MOVEMENT

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ROTATION ROOTUPRIGHTING

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EXTRUSIONINTRUSION

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Optimum Forces For OTMsTYPE OF MOVEMENT FORCE REQUIRED (gm)

Tipping 35-60 Bodily movement (translation) 70-120Root uprighting 50-100Rotation 35-60 Extrusion 35-60Intrusion 10-20

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Forces Delivered by Appliances

• Continuous Force (ideal spring)• Interrupted Force (removable active plates)• Intermittent Force (removable appliances)

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Continuous Force

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Interrupted Force

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Intermittent Force

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Deleterious Effects of Orthodontic Force• Pain• Allergic reactions• Mobility • Gingival Inflammation• Loss of vitality of pulp• Root Resorption

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Pain• If appropriate force (not heavy) is applied, the patient

feels little pain immediately• Pain develops after several hours• The patient feels mild aching sensation and the teeth

are quite sensitive to pressure• The pain usually lasts for 2 – 4 days and disappears

until the appliance is reactivated

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• For most of the patients, the pain associated with the initial activation of the appliance is most severe

• Pain is due to the development of ischemic areas in the PDL

• The pain is directly proportional to the area of PDL that has undergone sterile necrosis (hyalinization)

• So heavier forces produce larger areas of hyalinization and greater pain

• Pain can be managed using analgesics like ACETAMINOPHEN

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Allergic Reactions• Some patients may develop allergic reactions

to Stainless steel which contains NICKEL• Allergic reactions manifest as widespread

erythema and swelling of oral tissue which develops 1 – 2 days after starting the treatment

• In such patients, Stainless steel appliances (brackets, bands, wires etc) should be substituted with TITANIUM appliances

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Mobility• Mobility is due to–Widening of PDL space during orthodontic

treatment– Temporary disorganization of the fibers in the PDL

• Moderate increase in mobility is an expected response of orthodontic treatment

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• Heavier Force causes greater degree of Undermining Resorption which leads to Excessive mobility

• Excessive mobility indicates that there is heavy force acting on the tooth

• If the tooth becomes extremely mobile, force should be discontinued until the mobility decreases to moderate levels

• Excessive mobility will usually correct itself without permanent damage

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Insults to the Pulp• There will be a modest inflammatory response

within the pulp at the beginning of the treatment• It may cause an initial mild pulpitis which has no

long term significance

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Loss of Vitality of Pulp• Loss of vitality may be encountered if there is– History of previous trauma to the tooth – Poor control of orthodontic forces

• Heavy forces cause abrupt movement of root apex causing obstruction of the blood flow to the pulp

• Relatively heavy forces applied for intrusion can also give rise to the same situation

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Root Resorption• Cementum adjacent to the hayalinized PDL undergo

resorption by cementoclast cells• This can progress to the extend of dentin destruction• Once orthodontic forces are removed, repair occurs

by the deposition of new cementum in the area of previous destruction

• Dentin once lost will not be replaced

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Craters of Root Resorption in Dentin

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Types of Resorption• Slight Blunting• Moderate resorption – up to ¼ of the root length• Severe resorption – more than ¼ of the root length• Moderate Generalized Resorption• Severe Generalized Resorption • Severe Localized Resorption

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Slight Blunting

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Moderate Resorption

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Severe Resorption

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Moderate Generalized Resorption• Most of the teeth show some loss of root length • Greater in patients whose treatment duration

was longer• Shortening of root length is more for maxillary

incisors • In most cases, this type of resorption is clinically

insignificant

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Severe Generalized Resorption• This is mostly of unknown etiology• In case of patients with thyroid deficiency, chances

of developing severe generalized resorption is high• To prevent this, thyroid supplementation is

indicated

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Severe Localized Resorption

• Caused by excessive forces and prolonged duration of treatment

• Risk of severe resorption is much greater for maxillary incisors

• Very high risk is noted if roots of maxillary incisors are forced against the lingual cortical plate

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Effect of DRUGS on OTM

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Drugs which Enhance OTM

• Vitamin D administration

• Direct injection of Prostaglandin into PDL(disadvantage – It is very painful)

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Synthesis of Prostaglandins

PHOSPHOLIPIDS ARACHIDONIC ACID PROSTAGLADINS

CORTICOSTEROIDS NSAIDS

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Drugs which Impede OMT• BISPHOSPHONATES – for Osteoporosis– Alendronate

• PROSTAGLADIN INHIBITORS– Indomethacin

• TETRACYCLINES– Doxycycline

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• TRICYCLIC ANTIDEPRESSANTS– Doxepine– Imipramine

• ANTIARRHYTHMIC agents– Procaine

• ANTIMALARIALS Drugs–Quinine– Chloroquine

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Patient with Osteoporosis• This condition is encountered in case of post-

menopausal females• The patient may be using BISPHOSPHONATES which

binds to Hydroxyapatite in bone and inhibits Osteoclast mediated Bone Resorption

• BEFORE ORTHODONTIC TREATMENT,– Consult the patient’s physician and temporarily

switch to estrogen therapy (Evista)

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Pain killers – Do they Inhibit OTM ?• Common analgesics used during treatment– IBUPROFEN– ASPIRIN

• At the dose level used during orthodontic treatment, they do not impede tooth movement

• Acetaminophen is a better option as it is a centrally acting agent which does not reduce inflammation

NSAIDS

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Prostaglandin Inhibitors in Microspheres• If Prostaglandin Inhibitors were placed in mini-

spheres and could be maintained in the sulcus around tooth (like antibiotics in periodontal therapy) which has to serve as anchorage, the efficiency of the orthodontic treatment can be improved.

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Conclusion• A dentist should thoroughly understand the biological

factors and principles behind Orthodontic Tooth Movement. He should achieve the desired aesthetic and functional result using the optimum amount of force. He should also give consideration to the health of the periodontium and thus try to minimize the deleterious effects of the treatment.

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REFERENCE

• Contemporary Orthodontics 4/e• Orban’s Oral Histology and Embryology 11/e• Ten Cate’s Oral Histology 7/e• Orthodontics – The Art and Science 4/e

THANK YOU

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