lecture 8

Question 1

Mechanics:

Answer 1

the science that deals with the action of forces on the form and motion of bodies

Question 2

1. Center of mass:

Answer 2

balance point of a system

Question 3

center of mass with gravity

Answer 3

• Free body in space
• All the points move the same amount in the same
  direction
• called TRANSLATION or BODILY MOVEMENT

Question 4

force
Measured in?

Answer 4

Measured in ounces or grams
– A: Point of application = Origin of the arrow
– Line of action: Body of the arrow
– Direction: Body of the arrow and the arrowhead
– Magnitude: length of the arrow

Question 5

where would point of application be in ortho?

Answer 5

crown

Question 6

what movement happens here?

Answer 6

rotation with translation, point of application is away from the center of mass

Question 7

center of resistance of a free body

Answer 7

• One point in a free body on which it can be perfectly
  balanced (center of gravity)
• Mathematical point at which all resistance to
  displacement may be thought of as concentrated

Question 8

Center of resistance of a tooth

Answer 8

roughly 2/3 from the apex, tooth is not a free body (embedded in bone)

Question 9

tooth as a constrianed body

Answer 9

• A tooth is a constrained body.
• The center of resistancewill vary with alveolar height

Question 10

what does decreased alveolar bone support cause in regards to ortho tx?

Answer 10

longer distance from center of mass to the point of application

Question 11

types of force systems

Answer 11

single point force and force couple

Question 12

Simple Force

Answer 12

Question 13

types of simple forces

Answer 13

push, pull, intrusion and extrusion

Question 14

Force systems in orthodontics

Answer 14

Point of application of the force: almost always at the crown level
* Direction of the force (3 planes of space)
* Amplitude of the force(varies)
Remember that we must also move the roots

Question 15

simple forces in relation to the center of resistance at the tooth

Answer 15

will cause rotation and tipping, need force systems for better movement

Question 16

If the line of force goes through the center of
resistance, what occurs?

Answer 16

If the line of force goes through the center of
resistance, pure translation will take place
* translation = all points on a tooth move the
same amount in the same direction

Question 17

what will occur

Answer 17

pure translation

Question 18

can we apply a simple force to the center of resistance?

Answer 18

usually not

Question 19

In orthodontics, a simple force applied to the crown of a tooth will result in?
* crown/apex directions?

Answer 19

In orthodontics, a simple force applied to the crown of a tooth will result in tipping of the crown.
* The crown will tip in the direction of the force, the apex will tip in the opposite direction

Question 20

how can we get translation in ortho?

Answer 20

• Two forces equal in magnitude and opposite in direction act on an object
• The result is a pure moment, since translatory effect of the forces cancel
• The object will spin around its center of resistance (rotation

Question 21

moment of force

Answer 21

• Line of action of a force does not pass through the center of resistance
• The force will produce some rotation of the object
• This potential of rotation is called a moment

Question 22

Moment of a force calc

Answer 22

Mf = F x d
F: magnitude of the force
d: perpendicular distance between the line
of the force and the centre of resistance

Question 23

moment of force is a measure of?

Answer 23

rotational tendency

Question 24

Translation

Answer 24

• In orthodontics, translation is often the
  movement of choice
• You need a combination of a simple force and
  a moment of force to obtain translation