The Biomechanics of Orthodontic Tooth Movement

Question 1

Forces are what

Answer 1

vectors

Question 2

What is the measurement(s) of the magnitude of force

Answer 2

Newton (N) is the common unit clinical orthodontics; often measures in grams or ounces

Question 3

Resultant force is calculated by what

Answer 3

the parallelogram law

Question 4

Vector resolution is the opposite of what

Answer 4

vector addition

Question 5

What does this image represent

Answer 5

addition of forces when they have a common point of application

Question 6

What does this image represent

Answer 6

Addition of forces when they have different points of application

Question 7

What does this image represent

Answer 7

resolving a force into components

Question 8

This is the point at which resistance to movement can concentrated for mathematical analysis

Answer 8

center of resistance (C res)

Question 9

Where is the center of resistance in a free object

Answer 9

center of mass/gravity, or point of balance

Question 10

Where is the center of resistance of a partially restraint object (like teeth)

Answer 10

it is determined by the nature of the external constraints (like for a tooth; alveolar bone)

Question 11

Where is the center of resistance of a tooth

Answer 11

it is not the center of gravity, rather, it is the approximate midpoint of embedded portion of the root (or halfway between the apex and alveolar crest)

Question 12

The center of resistance of a tooth can vary with what two parameters

Answer 12

alveolar bone hieght and root length; more specifically, the part of the root embedded in the alveolar bone

Question 13

Does the center of resistnce vary with orthodontic force?

Answer 13

No, unless force causes a change in alveolar bone height

Question 14

What happens to the center of resistance with alveolar bone loss

Answer 14

it moves apically

Question 15

What happens to the center of resistance when there is root resportion

Answer 15

it moves coronally

Question 16

If the line of action of a force does not pass through the center of resistance, the force will produce some what

Answer 16

rotation of the tooth

Question 17

The potential for rotation is measured as what

Answer 17

a moment

Question 18

What is magnitude

Answer 18

magnitude of force x perpendicular distance from center of resistance to the line of action

Question 19

This is two forces of equal magnitude; parallel and non-colinear in the opposite direction producing pure rotation

Answer 19

couple

Question 20

A single force (not passing the center of resistance) produces what types of force

Answer 20

rotational and translational effect; not a pure rotation

Question 21

The translational effects produced by the two forces of a couple do what to each other

Answer 21

cancel each other out

Question 22

This is the point around which an object is rotating

Answer 22

center of rotation

Question 23

Unlike the center of resistance, center of rotation is what

Answer 23

not at a fixed point and varies with the force/moment/couple applied to the tooth

Question 24

In orthodontics, the center of rotation can be changed to acheive what

Answer 24

different types of tooth movement and clinical goals

Question 25

What are the three types of orthodontic tooth movement

Answer 25

translation
pure rotation
combination of translation and rotation (tipping); majoirty of the movements

Question 26

During translation, all points on an object move where

Answer 26

in the same direction at the same rate

Question 27

To produce translation, what needs to occur

Answer 27

the line of action of a single force needs to pass through the center of resistance

Question 28

What determies whether translation is produced

Answer 28

line of action

Question 29

When a force is not passing through the center of resistance, translation is still acheivable how

Answer 29

by cancelling the moment produced by this force using an opposite moment producs by a couple (torsion of archwire)

Question 30

When some points on an object move differently than other points on the same objest, the overall movement of the object is what

Answer 30

tippine

Question 31

When does tipping occur

Answer 31

when the line of action of a single force does not pass through the center of resistance the force will produce a tipping

Question 32

A tipping movement can be resolved into what

Answer 32

translational and rotational components

Question 33

What are the five types of tooth movement

Answer 33

translation
uncontrolled tipping
controlled tipping
root movement (torque)
pure rotation

Question 34

Where is the center of rotation in translation

Answer 34

infinity; no rotation, no center

Question 35

Where is the center of rotation involving uncontrolled tipping

Answer 35

slightly apical to the center of resistance

Question 36

Where is the center of rotation involving controlled tipping

Answer 36

apex

Question 37

Where is the center of rotation involving root movement (torque)

Answer 37

incisal edge

Question 38

Where is the center of rotation involving pure rotation

Answer 38

center of resistnce

Question 39

This is force to the crown causing a tooth to rotate around a center near the middle of the root, the apex and crown move in opposite directions to each other (incisal edge moves more than the apex)

Answer 39

uncontrolled tipping

Question 40

This is a force, together with a moment to the crown, causes the tooth to rotate around its apex; the crown moves the greatest distance and the apex moves the least

Answer 40

controlled tipping

Question 41

When a simple (single or controlled) tipping force is applied to the crown of a single-rooted tooth, the center of rotation is usually located
A. at the apex
B. at the cervical line
C. 5mm beyond the apex
D. 1/3 the root length from the apex
E. 2/3 root length from the apex

Answer 41

A. at the apex

Question 42

When an uncontrolled tipping force is applied to the crown of a single-rooted tooth, the fulcrum is usually located
A. at the apex
B. at the cervical line
C. 5mm. beyond the apex
D. 1/3 of the root length from the apex

Answer 42

D. 1/3 the root length from the apex