The bio mechanics of orthodontic tooth movement
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The Bio-mechanics of Orthodontic Tooth Movement. D 657 Dr. Shiva Shanker Dr. Allen Firestone. Contemporary Orthodontics , Chapter 10, 3rd Edition:pp. 337-360 2nd Edition:pp. 302-315

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The Bio-mechanics of Orthodontic Tooth Movement

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The bio mechanics of orthodontic tooth movement

The Bio-mechanics of Orthodontic Tooth Movement

D 657

Dr. Shiva Shanker

Dr. Allen Firestone


Lecture 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

LECTURE READING


Lecture objectives

1. Definition of terms2. Mechanics of tooth movement3. Anchorage in orthodontic appliances

LECTURE OBJECTIVES


Lecture objectives1

1. Review Laboratory Procedures:Arch Length AnalysisMolar Uprighting: Preparing typodont

LECTURE OBJECTIVES


Definitions

Definitions

  • Force

  • Center of Resistance (Cres)

  • Types of Tooth Movement


Force

Force

  • Physical property e.g. distance, weight, temperature, force.

  • Physical properties are, mathematically, scalars or vectors

  • Scalars have a magnitude and no direction e.g. weight, temperature

  • Vectors have a magnitude and a direction e.g. force


Vectors

Vectors

  • Line of Action

  • Sense

  • Magnitude

  • Point of Application


Resultant of forces

Resultant of Forces

  • Common point of application

  • Different points of application

  • Resolving force into components


Common point of application resultant of forces

Common point of applicationResultant of Forces


Different points of application resultant of forces

Different points of applicationResultant of Forces


Resolving force into components resultant of forces

Resolving Force Into ComponentsResultant of Forces


Force1

Force

  • A load applied to an object that will tend to move it in the direction of the applied force

  • Defined in units of Newtons

  • Orthodontic purposes measured as grams or ounces


Definitions1

Definitions

  • Force

  • Center of Resistance (Cres)

  • Types of Tooth Movement


Center of resistance

Center of Resistance

  • Free body: center of mass/gravity = point of balance

  • Restrained body (tooth): center of resistance (Cres)

  • By definition, a force acting through Cres moves tooth with no change in orientation = translation


Center of resistance1

Center of Resistance

  • 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


Center of resistance2

Center of Resistance

  • Cres varies with root length and alveolar crest height


Definitions2

Definitions

  • Force

  • Center of Resistance (Cres)

  • Types of Tooth Movement


Types of tooth movement

Types of Tooth Movement

  • Translation

  • Rotation

  • Combination/Tipping

  • Moment

  • Couple

  • Center of Rotation (Crot)


Translation bodily tooth movement

Translation = Bodily Tooth Movement

  • A force applied in line with the center of resistance;the tooth is translated with no rotation relative to the force

  • Orthodontically, the point of attachment is irrelevant; the line of action of force determines the effect on the tooth


Translation or bodily tooth movement

Translation or Bodily Tooth Movement


Tipping tooth movement

Tipping Tooth Movement

  • A force that doesn’t pass through Cres causes translation + rotation = tipping

    i.e., tends to tip the tooth, movement with a rotational component.


Definitions3

Definitions

  • Force

  • Center of Resistance (Cres)

  • Types of Tooth MovementMomentCoupleCenter of Rotation (Crot)


Moment

Moment

  • If the line of action of a force is at a distance from the Cres the force will produce some rotation. The potential for rotation is measured as a moment


Moment magnitude

Moment - Magnitude

  • Magnitude = perpendicular distance from Cres to the line of action X magnitude of force (unit = gram mm)

  • Direction: Clockwise or Counter-cw


Couple

Couple

  • No single force can cause pure rotation

  • Only a couple can

  • Two forces: equal magnitude; parallel and non-collinear; opposite sense

  • Couple is a ‘free vector’


Couple1

Couple

  • Two forces; equal magnitude; parallel and non-collinear; opposite sense

  • Translational effects cancel each other out


Couple2

Couple

  • The moments are in the same direction and are additive


Couple3

+

= 1000 gm mm

Couple

  • The Sum of the Moments =

50 g X 10 mm

50 g X 10 mm


Couple4

Couple

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

  • Only a couple can cause pure rotation


Definitions4

Definitions

  • Force

  • Center of Resistance (Cres)

  • Types of Tooth MovementMomentCoupleCenter of Rotation (Crot)


Center of rotation c rot

Center of Rotation Crot

  • The point around which rotation occurs when an object is being moved

  • This point will vary depending on the force/moment/couple being applied

    Bodily movement or translation

    Tipping movement


Determining c rot

Determining Crot

  • Connect the before and after positions of 2 points

  • The intersection of the perpendicular bisectors of these lines is Crot


Tooth movement and c rot

Type of Movement

Translation

Uncontrolled tipping

Controlled tipping

Root movement

Center of Rotation

Infinity

Slightly apical to Cres

Apex

Incisal edge

Tooth Movement and Crot


Control of center of rotation

Control of Center of Rotation

Point of application of force:Closer to Cres Smaller momentLess rotationMore translation


Lecture objectives2

1. Definition of terms2. Mechanics of tooth movement3.Anchorage in orthodontic appliances

LECTURE OBJECTIVES


Anchorage

Anchorage

  • Resistance to unwanted tooth movement

  • Resistance to reaction forces

  • Maximizing tooth movement and minimizing unwanted “reactionary effects”


Strategy 1

Strategy 1

  • Reciprocal space closure

  • Minimum anchorage requirements


Strategy 2 differential anchorage values

Strategy 2 - Differential Anchorage Values

  • Differential space closure

  • Intermediate anchorage requirements

1237

706


Strategy 2a differential tooth movement

Strategy 2A - Differential Tooth Movement

  • Differential space closure

  • Intermediate anchorage requirements


Strategy 3

Strategy 3

  • Dissipate reactionary forces over as many teeth (or as widely) as possible

  • Reinforced anchorage

  • Maximum anchorage


Frictional effects on anchorage

Frictional Effects on Anchorage

  • Frictional resistance to sliding archwires against brackets


Factors affecting friction

Factors 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 exhibit greater frictional resistance


Lecture objectives3

1. Definition of terms2. Types of tooth movement3. Anchorage in orthodontic appliances

LECTURE OBJECTIVES


Lecture objectives4

1. Review Laboratory Procedures:Arch Length AnalysisMolar Uprighting: Preparing typodont

LECTURE OBJECTIVES


Arch length analysis space analysis

Arch Length Analysis = Space Analysis

  • Permanent Dentition

  • Mixed Dentition


Space analysis permanent dentition

Space AnalysisPermanent Dentition

+Arch length available

- M/D width of 12 teeth: first molar to first molar

__________________________

= Arch length deficiency or excess


Arch length

Arch 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 bio mechanics of orthodontic tooth movement

Measuring Arch Length


Space analysis measuring tooth width

Space Analysis Measuring Tooth Width


Space analysis mixed dentition

Space Analysis: Mixed Dentition

  • The same procedure in themixed dentition but

  • Need to estimate the size of unerupted permanent teeth (premolars and canines)

    • Moyers proportionality tables, Tanaka and Johnston


Space analysis measuring ald

Space Analysis Measuring ALD

+Arch length available

- M/D width of teeth mesial to first molars

_______________________

= Arch length deficiency or excess


The bio mechanics of orthodontic tooth movement

Measuring Arch Length


Moyers mixed dentition space analysis

Moyers: Mixed Dentition Space Analysis

To estimate the width of unerupted canines and premolars in a quadrant:

1. Get sum of the mesial-distal width of the 4 mandibular permanent incisors.

2. Locate value in Table and look up predicted width of maxillary and mandibular teeth.


Tanaka johnston mixed dentition space analysis

Tanaka-Johnston: Mixed Dentition Space Analysis

To estimate the width of unerupted canines and premolars in a quadrant:

1. Get sum of the mesial-distal width of the 4 mandibular permanent incisors.

2. Divide by 2 and add

11.0 for max. canine + premolars

10.5 for mand. canine + premolars.

Tanaka &Johnston, JADA 88:798, 1974


Rule of thumb mixed dentition space analysis

Rule of Thumb: Mixed Dentition Space Analysis

To estimate the width of unerupted canines and premolars in a quadrant:

23mm for maxillary quadrant

22mm for mandibular quadrant


Molar uprighting typodont

Molar Uprighting Typodont


Molar uprighting teeth

Molar Uprighting Teeth


Molar uprighting wax

Molar Uprighting Wax


Molar uprighting wax preparation

Molar Uprighting Wax Preparation


Molar uprighting segment preparation

Molar UprightingSegment Preparation


Molar uprighting segment preparation1

Molar UprightingSegment Preparation


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