Bio Mechanics 2 Shorter

8/6/2019 Bio Mechanics 2 Shorter

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The Bio-mechanics of

Orthodontic ToothMovementD 657

Dr. Shiva ShankerDr. Allen Firestone

D 657

Dr. Shiva ShankerDr. Allen Firestone


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LECTURE READINGLECTURE READING

Contemporary Orthodontics,

Chapter 10,3rd Edition: pp. 337-360

2nd Edition: pp. 302-315

Recommended:

Smith and Burstone, Mechanics of

tooth movement. American Journal of

Orthodontics, 1984; 85:294-307

Contemporary Orthodontics,

Chapter 10,3rd Edition: pp. 337-360

2nd Edition: pp. 302-315

Recommended:

Smith and Burstone, Mechanics of

tooth movement. American Journal of

Orthodontics, 1984; 85:294-307


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LECTURE OBJECTIVESLECTURE OBJECTIVES

1. Definition of terms

2. Mechanics of tooth movement

3. Anchorage in orthodontic appliances





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1. Review Laboratory Procedures:

ArchL

ength AnalysisMolar Uprighting: Preparing

typodont


ArchL

ength AnalysisMolar Uprighting: Preparing

typodont


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DefinitionsDefinitions

Force

Center of Resistance (Cres)

Types of Tooth Movement

Force




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ForceForce

Physical property e.g. distance,

weight, temperature, force.

Physical properties are,mathematically, scalars orvectors

Scalars have a magnitude and no

direction e.g. weight, temperatureVectors have a magnitude and a

direction e.g. force

Physical property e.g. distance,

weight, temperature, force.

Physical properties are,mathematically, scalars orvectors

Scalars have a mag

nitude and no

direction e.g. weight, temperatureVectors have a magnitude and a

direction e.g. force


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VectorsVectors

Line of ActionLine of Action

Point of ApplicationPoint of Application

SenseSense

MagnitudeMagnitude


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Resultant of ForcesResultant of Forces

Common point of applicationCommon point of application

Resolving force into componentsResolving force into components

Different points of applicationDifferent points of application


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Common point of application

Resultant of Forces

Common point of application

Resultant of Forces


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Different points of application

Resultant of Forces

Different points of application

Resultant of Forces


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Resolving Force Into Components

Resultant of Forces

Resolving Force Into Components

Resultant of Forces


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ForceForce

A load applied to an object that will

tend to move it in the direction of the

applied forceDefined in units of Newtons

Orthodontic purposes measured as

grams or ounces

A load applied to an object that will

tend to move it in the direction of the

applied forceDefined in units of Newtons

Orthodontic purposes measured as

grams or ounces


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Force



Force




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Center of ResistanceCenter of Resistance

Free body: center of mass/gravity =

point of balance

Restrained body (tooth): center ofresistance (Cres)

By definition, a force acting through

Cres moves tooth with no change inorientation = translation

Free body: center of mass/gravity =

point of balance

Restrained body (tooth): center ofresistance (Cres)

By definition, a force acting through

Cres moves tooth with no change inorientation = translation


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A point at which resistance to

movement can be concentrated for

mathematical analysis (= Cres)The center of resistance for a tooth is

1/2 - 1/3 (40%) root length apical to

alveolar crest

Cres varies with root length and

alveolar crest height

A point at which resistance to

movement can be concentrated for

mathematical analysis (= Cres)The center of resistance for a tooth is

1/2 - 1/3 (40%) root length apical to

alveolar crest




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Force



Force




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Types of Tooth MovementTypes of Tooth Movement

TranslationTranslation

RotationRotation

Combination/TippingCombination/Tipping

Moment

Couple

Center of Rotation (Crot)

Moment

Couple

Center of Rotation (Crot)


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Translation =

Bodily Tooth Movement

Translation =

Bodily Tooth MovementA force applied in line with the center

of resistance;

the tooth is translated with norotation relative to the force

Orthodontically, the point of

attachment is irrelevant;

the line of action of force

determines the effect on the tooth

A force applied in line with the center

of resistance;

the tooth is translated with norotation relative to the force

Orthodontically, the point of

attachment is irrelevant;

the line of action of force

determines the effect on the tooth


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Translation or


Translation or



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Tipping Tooth MovementTipping Tooth Movement

A force that doesntpass through

Cres causes translation +

rotation = tippingi.e., tends to tip the tooth, movement

with a rotational component.

A force that doesntpass through

Cres causes translation +

rotation = tippingi.e., tends to tip the tooth, movement

with a rotational component.


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Force


Types of Tooth MovementMoment

Couple

Center of Rotation (

Crot)

Force



Couple


Crot)


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MomentMoment

If the line of action of a force is at a

distance from the Cres the force will

produce some rotation. The potentialfor rotation is measured as a moment

If the line of action of a force is at a

distance from the Cres the force will

produce some rotation. The potentialfor rotation is measured as a moment


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Moment - MagnitudeMoment - Magnitude

Magnitude = perpendicular distance

from Cres to the line of action X

magnitude of force (unit = gram mm)Direction: Clockwise orCounter-cw

Magnitude = perpendicular distance

from Cres to the line of action X

magnitude of force (unit = gram mm)Direction: Clockwise orCounter-cw


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CoupleCouple

No single force can cause pure

rotation

Only a couple canTwo forces: equal magnitude;

parallel and non-collinear; opposite

senseCouple is a free vector

No single force can cause pure

rotation

Only a couple canTwo forces: equal magnitude;

parallel and non-collinear; opposite

senseCouple is a free vector


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CoupleCouple

Two forces; equal magnitude; parallel and

non-collinear; opposite sense

Two forces; equal magnitude; parallel and

non-collinear; opposite sense

Translational effects cancel each other out Translational effects cancel each other out


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CoupleCouple

The moments are in the same direction and

are additive

The moments are in the same direction and

are additive


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CoupleCouple

The Sum of the Moments = The Sum of the Moments =

50 g X 10 mm50 g X 10 mm 50 g X 10 mm50 g X 10 mm++ = 1000 gm mm= 1000 gm mm


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Only a couple can cause pure rotation Only a couple can cause pure rotation

The moment of a couple is equal to the magnitude of oneof the forces X distance between them (50g X 20 mm) The moment of a couple is equal to the magnitude of oneof the forces X distance between them (50g X 20 mm)

CoupleCouple


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Force



Couple


Crot)

Force



Couple


Crot)


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Center of Rotation CrotCenter of Rotation Crot

The point around which rotation

occurs when an object is being

movedThis point will vary depending on the

force/moment/couple being applied

Bodily movement or translationTipping movement

The point around which rotation

occurs when an object is being

movedThis point will vary depending on the

force/moment/couple being applied

Bodily movement or translationTipping movement


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Determining CrotDetermining CrotConnect the

before and after

positions of 2

pointsThe intersection of

the perpendicular

bisectors of theselines is Crot

Connect the

before and after

positions of 2

pointsThe intersection of

the perpendicular

bisectors of theselines is Crot


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Tooth Movement and CrotTooth Movement and Crot

Type of Movement

Translation

Uncontrolled tipping

Controlled tipping

Root movement

Type of Movement

Translation

Uncontrolled tipping

Controlled tipping

Root movement

Center of Rotation

Infinity

Slightly apical to Cres

Apex

Incisal edge

Center of Rotation

Infinity

Slightly apical to Cres

Apex

Incisal edge


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Control ofCenter of

Rotation

Control ofCenter of

RotationPoint of application of force:

Closer to Cres

Smaller momentLess rotation

More translation

Point of application of force:

Closer to Cres

Smaller momentLess rotation

More translation


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AnchorageAnchorage

Resistance to unwanted tooth

movement

Resistance to reaction forcesMaximizing tooth movement and

minimizing unwanted reactionary

effects

Resistance to unwanted tooth

movement

Resistance to reaction forcesMaximizing tooth movement and

minimizing unwanted reactionary

effects


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Strategy 1Strategy 1

Reciprocal space closure

Minimum anchorage requirements

Reciprocal space closure

Minimum anchorage requirements


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Strategy 2 - Differential

Anchorage Values

Strategy 2 - Differential

Anchorage ValuesDifferential space closure

Intermediate anchorage requirements

Differential space closure


12371237 706706


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Strategy 2A - Differential

Tooth Movement

Strategy 2A - Differential

Tooth MovementDifferential space closure


Differential space closure



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Strategy 3Strategy 3

Dissipate reactionary forces over asmany teeth (or as widely) as possible

Reinforced anchorage

Maximum anchorage

Dissipate reactionary forces over asmany teeth (or as widely) as possible

Reinforced anchorage

Maximum anchorage


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Frictional Effects on

Anchorage

Frictional Effects on

AnchorageFrictional resistance to sliding

archwires against brackets

Frictional resistance to sliding

archwires against brackets


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Factors Affecting FrictionFactors Affecting Friction

Surface of wires/bracket -

1) Stainless steel slides well on

stainless steel;2) Nickel titanium alloy wires have

greater frictional resistance

3) Ceramic brackets also exhibitgreater frictional resistance

Surface of wires/bracket -

1) Stainless steel slides well on

stainless steel;2) Nickel titanium alloy wires have

greater frictional resistance

3) Ceramic brackets also exhibitgreater frictional resistance


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2. Types of tooth movement



2. Types of tooth movement



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Arch Length Analysis

Molar Uprighting: Preparing

typodont


Arch Length Analysis

Molar Uprighting: Preparing

typodont


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ArchL

ength Analysis =Space AnalysisArchL

ength Analysis =Space Analysis

Permanent Dentition

Mixed Dentition

Permanent Dentition

Mixed Dentition


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Space Analysis

Permanent Dentition

Space Analysis

Permanent Dentition+Arch length available

- M/D width of 12 teeth:

first molar to first molar

__________________________

= Arch length deficiency or

excess

+Arch length available

- M/D width of 12 teeth:

first molar to first molar

__________________________

= Arch length deficiency or

excess


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Arch LengthArch Length

The arch circumference:

measured at the proximal

contacts of posterior teeth and

the incisal edges of anterior

teeth i.e., the widest part of the

tooth.

The arch circumference:

measured at the proximal

contacts of posterior teeth and

the incisal edges of anterior

teeth i.e., the widest part of the

tooth.


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Measuring Arch LengthMeasuring Arch Length


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Space AnalysisMeasuring Tooth Width

Space AnalysisMeasuring Tooth Width


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Space Analysis:

Mixed Dentition

Space Analysis:

Mixed Dentition

The same procedure in the mixed

dentition but

Need to estimate the size ofunerupted permanent teeth

(premolars and canines)

Moyers proportionality tables, Tanaka

and Johnston

The same procedure in the mixed

dentition but

Need to estimate the size ofunerupted permanent teeth

(premolars and canines)

Moyers proportionality tables, Tanaka

and Johnston


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Space Analysis

Measuring ALD

Space Analysis

Measuring ALD


- M/D width of teeth mesialto first molars

_______________________

= Arch length deficiency orexcess


- M/D width of teeth mesialto first molars

_______________________

= Arch length deficiency orexcess


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Measuring Arch LengthMeasuring Arch Length


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Moyers: Mixed Dentition

Space Analysis

Moyers: Mixed Dentition

Space Analysis

To estimate the width ofunerupted

canines and premolars in a quadrant:

1. Get sum of the mesial-distal width ofthe 4 mandibularpermanent incisors.

2. Locate value in Table and look up

predicted width of maxillary and

mandibular teeth.




2. Locate value in Table and look up

predicted width of maxillary and

mandibular teeth.

T k J h Mi dT k J h Mi d


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Tanaka-Johnston: Mixed

Dentition Space Analysis

Tanaka-Johnston: Mixed





2. Divide by 2 and add

11.0 formax. canine + premolars10.5 formand. canine + premolars.




2. Divide by 2 and add

11.0 formax. canine + premolars10.5 formand. canine + premolars.

Tanaka &Johnston, JADA 88:798, 1974Tanaka &Johnston, JADA 88:798, 1974


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Rule of Thumb: Mixed


Rule of Thumb: Mixed

Dentition Space AnalysisTo estimate the width ofunerupted


23mm for maxillary quadrant

22mm for mandibular quadrant



23mm for maxillary quadrant

22mm for mandibular quadrant


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Molar Uprighting TypodontMolar Uprighting Typodont


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Molar Uprighting TeethMolar Uprighting Teeth


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Molar Uprighting WaxMolar Uprighting Wax


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Molar Uprighting

Wax Preparation

Molar Uprighting

Wax Preparation


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Molar Uprighting

Segment Preparation

Molar Uprighting

Segment Preparation


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Molar Uprighting

Segment Preparation

Molar Uprighting

Segment Preparation


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