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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

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 Analysis Molar Uprighting: Preparing typodont

LECTURE OBJECTIVES


Definitions
Definitions Analysis Molar Uprighting: Preparing typodont

  • Force

  • Center of Resistance (Cres)

  • Types of Tooth Movement


Force
Force Analysis Molar Uprighting: Preparing typodont

  • 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 Analysis Molar Uprighting: Preparing typodont

  • Line of Action

  • Sense

  • Magnitude

  • Point of Application


Resultant of forces
Resultant of Forces Analysis Molar Uprighting: Preparing typodont

  • Common point of application

  • Different points of application

  • Resolving force into components


Common point of application resultant of forces
Common point of application Analysis Molar Uprighting: Preparing typodontResultant of Forces


Different points of application resultant of forces
Different points of application Analysis Molar Uprighting: Preparing typodontResultant of Forces


Resolving force into components resultant of forces
Resolving Force Into Components Analysis Molar Uprighting: Preparing typodontResultant of Forces


Force1
Force Analysis Molar Uprighting: Preparing typodont

  • 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 Analysis Molar Uprighting: Preparing typodont

  • Force

  • Center of Resistance (Cres)

  • Types of Tooth Movement


Center of resistance
Center of Resistance Analysis Molar Uprighting: Preparing typodont

  • 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 Analysis Molar Uprighting: Preparing typodont

  • 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 Analysis Molar Uprighting: Preparing typodont

  • Cres varies with root length and alveolar crest height


Definitions2
Definitions Analysis Molar Uprighting: Preparing typodont

  • Force

  • Center of Resistance (Cres)

  • Types of Tooth Movement


Types of tooth movement
Types of Tooth Movement Analysis Molar Uprighting: Preparing typodont

  • Translation

  • Rotation

  • Combination/Tipping

  • Moment

  • Couple

  • Center of Rotation (Crot)


Translation bodily tooth movement
Translation = Analysis Molar Uprighting: Preparing typodontBodily 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 Analysis Molar Uprighting: Preparing typodontBodily Tooth Movement


Tipping tooth movement
Tipping Tooth Movement Analysis Molar Uprighting: Preparing typodont

  • 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 Analysis Molar Uprighting: Preparing typodont

  • Force

  • Center of Resistance (Cres)

  • Types of Tooth Movement Moment Couple Center of Rotation (Crot)


Moment
Moment Analysis Molar Uprighting: Preparing typodont

  • 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 Analysis Molar Uprighting: Preparing typodont

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

  • Direction: Clockwise or Counter-cw


Couple
Couple Analysis Molar Uprighting: Preparing typodont

  • 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 Analysis Molar Uprighting: Preparing typodont

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

  • Translational effects cancel each other out


Couple2
Couple Analysis Molar Uprighting: Preparing typodont

  • The moments are in the same direction and are additive


Couple3

+ Analysis Molar Uprighting: Preparing typodont

= 1000 gm mm

Couple

  • The Sum of the Moments =

50 g X 10 mm

50 g X 10 mm


Couple4
Couple Analysis Molar Uprighting: Preparing typodont

  • 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 Analysis Molar Uprighting: Preparing typodont

  • Force

  • Center of Resistance (Cres)

  • Types of Tooth Movement MomentCouple Center of Rotation (Crot)


Center of rotation c rot
Center of Rotation C Analysis Molar Uprighting: Preparing typodontrot

  • 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 C Analysis Molar Uprighting: Preparing typodontrot

  • 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 Analysis Molar Uprighting: Preparing typodont

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 Analysis Molar Uprighting: Preparing typodont

Point of application of force: Closer to Cres Smaller moment Less rotation More translation


Lecture objectives2

1. Definition of terms Analysis Molar Uprighting: Preparing typodont2. Mechanics of tooth movement3.Anchorage in orthodontic appliances

LECTURE OBJECTIVES


Anchorage
Anchorage Analysis Molar Uprighting: Preparing typodont

  • Resistance to unwanted tooth movement

  • Resistance to reaction forces

  • Maximizing tooth movement and minimizing unwanted “reactionary effects”


Strategy 1
Strategy 1 Analysis Molar Uprighting: Preparing typodont

  • Reciprocal space closure

  • Minimum anchorage requirements


Strategy 2 differential anchorage values
Strategy 2 - Differential Anchorage Values Analysis Molar Uprighting: Preparing typodont

  • Differential space closure

  • Intermediate anchorage requirements

1237

706


Strategy 2a differential tooth movement
Strategy 2A - Differential Tooth Movement Analysis Molar Uprighting: Preparing typodont

  • Differential space closure

  • Intermediate anchorage requirements


Strategy 3
Strategy 3 Analysis Molar Uprighting: Preparing typodont

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

  • Reinforced anchorage

  • Maximum anchorage


Frictional effects on anchorage
Frictional Effects on Anchorage Analysis Molar Uprighting: Preparing typodont

  • Frictional resistance to sliding archwires against brackets


Factors affecting friction
Factors Affecting Friction Analysis Molar Uprighting: Preparing typodont

  • 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 terms Analysis Molar Uprighting: Preparing typodont2. Types of tooth movement3. Anchorage in orthodontic appliances

LECTURE OBJECTIVES


Lecture objectives4

1. Review Laboratory Procedures: Arch Length Analysis Molar Uprighting: Preparing typodont

LECTURE OBJECTIVES


Arch length analysis space analysis

Arch Length Analysis = Space Analysis Analysis Molar Uprighting: Preparing typodont

  • Permanent Dentition

  • Mixed Dentition


Space analysis permanent dentition
Space Analysis Analysis Molar Uprighting: Preparing typodontPermanent Dentition

+Arch length available

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

__________________________

= Arch length deficiency or excess


Arch length
Arch Length Analysis Molar Uprighting: Preparing typodont

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.


Measuring Arch Length Analysis Molar Uprighting: Preparing typodont


Space analysis measuring tooth width
Space Analysis Analysis Molar Uprighting: Preparing typodontMeasuring Tooth Width


Space analysis mixed dentition
Space Analysis: Analysis Molar Uprighting: Preparing typodontMixed 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 Analysis Molar Uprighting: Preparing typodontMeasuring ALD

+Arch length available

- M/D width of teeth mesial to first molars

_______________________

= Arch length deficiency or excess


Measuring Arch Length Analysis Molar Uprighting: Preparing typodont


Moyers mixed dentition space analysis
Moyers: Mixed Dentition Space Analysis Analysis Molar Uprighting: Preparing typodont

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 Analysis Molar Uprighting: Preparing typodont

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 Analysis Molar Uprighting: Preparing typodont

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 Analysis Molar Uprighting: Preparing typodont


Molar uprighting teeth

Molar Uprighting Teeth Analysis Molar Uprighting: Preparing typodont


Molar uprighting wax

Molar Uprighting Wax Analysis Molar Uprighting: Preparing typodont


Molar uprighting wax preparation

Molar Uprighting Analysis Molar Uprighting: Preparing typodontWax Preparation


Molar uprighting segment preparation

Molar Uprighting Analysis Molar Uprighting: Preparing typodontSegment Preparation


Molar uprighting segment preparation1

Molar Uprighting Analysis Molar Uprighting: Preparing typodontSegment Preparation


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