biology of tooth movement-ortho / orthodontic courses by indian dental academy

INDIAN DENTAL ACADEMYLeader in continuing dental education

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BIOLOGY OF TOOTH

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 group2. Horizontal group3. Oblique group4. Apical group5. Interradicular group

GINGIVAL FIBRES

1. Circular2. Alveologingival3. Dentoperiosteal4. Dentogingival5. Transseptal fibres(Accesory fibres)

Alveolar bone

Two parts1. 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. Openheim4. Norton5. 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 rate2. -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

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 MOVEMENTwww.indiandentalacademy.com

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. OB2. 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.

RESORPTIVE FUNCTION 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.

RESORPTIVE FUNCTION 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

FORMATIVE-

1)Pressure 2)Production of first messenger( physical/

chemical)

a) Deformation may lead to ca influxb) Hormones(PTH)c) Prostaglandins( macrophages )d) Neurotransmitters(SP)

OSTEOBLASTS

They bind to the cell surface receptors.

3)Second messengersa. c AMPb. c GMPc. Ca 4)Increased bone activity

OSTEOBLASTS

Trans membrane signaling pathway

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

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 stages1. Degeneration

2. Elimination of destroyed tissue

3. Establishment of new attachment

1.Degeneration1. Blood flow2. Degradation of vessel walls3. 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

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. www.indiandentalacademy.com

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 low50gms.

Effects of Tooth Movement and Force Distribution Tipping-hyalinization Caution -alveolar

crest.

Effects of Tooth Movement and Force 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.

TRANSSEPTAL FIBRES

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 ofbony spicules - crestal areas.

Effects of Tooth Movement and Force Ditribution(Proffit)1. Tipping –35-60gms2. Bodily –70-120gms3. Uprighting –50-100gms4. Rotation –35-60gms5. Extrusion –10-20gms6. Intrusion-10-20gms

Effects of force duration and decay

Duration – the second messenger produced only after 4 hours.

Forces –1. Continuous2. 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 repairis allowed. 4 week appointmentcycle.

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 www.indiandentalacademy.com

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 effect1. 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

www.indiandentalacademy.comLeader in continuing dental education

biology of tooth movement-ortho / orthodontic courses by indian dental academy

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