Introduction to Orthodontic Biomechanics

Question 1

Mechanics:

Answer 1

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

Question 2

Center of mass:

Answer 2

balance
point of a system

Question 3

Center of mass (gravity)
(3)

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
– A:
– Line of action:
– Direction:
– Magnitude:

Answer 4

ounces or grams
Point of application = Origin of the arrow
Body of the arrow
Body of the arrow and the arrowhead
length of the arrow

Question 5

Center of resistance of a free body
(2)

Answer 5

• 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 6

Constrained body
(2)

Answer 6

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

Question 7

Force Systems
(2)

Answer 7

1. Single-point force (simple force)
2. Force couple

Question 8

Simple Force
– Point of application:
– Line of action:
– Direction:
– Magnitude:

Answer 8

Origin of the
arrow ( at crown level)
Body of the arrow
Body of the arrow and the
arrowhead (in 3 plane of space)
length of the arrow
(variable)

Question 9

Simple Force
Ex (4)

Answer 9

➢Pull (tension)
➢Push (pressure)
➢Extrude
➢Intrude

Question 10

Force systems in orthodontics
* Point of application of
the force: almost always
at the — level
* — of the force (3
planes of space)
* — of the force
(varies)

Answer 10

crown
Direction
Amplitude

Question 11

If the line of force goes through the center of
resistance, pure — will take place

Answer 11

translation

Question 12

translation =

Answer 12

all points on a tooth move the
same amount in the same direction

Question 13

However, in clinical practice, a — force
can rarely be applied through the center of
resistance

Answer 13

simple

Question 14

Single force
* In orthodontics, a
simple force applied
to the crown of a
tooth will result in
— of the crown.

Answer 14

tipping
* The crown will tip in
the direction of the
force, the apex will
tip in the opposite
direction

Question 15

Tooth Movement needing more
than a simple force
(2)

Answer 15

• Translation
• Rotation

Question 16

Force Couple
(3)

Answer 16

• 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 17

Rotation
(2)

Answer 17

• Steering wheel
  effect
• So you need
  enough contact
  and or rotational
  attachments

Question 18

Moment of force
(3)

Answer 18

• 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 19

Moment of a force
equation

Answer 19

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

Question 20

Moment of a force
* a measure of — tendency

Answer 20

rotational

Question 21

In orthodontics, — is often the
movement of choice

Answer 21

translation

Question 22

• You need a combination of a (2) to obtain translation

Answer 22

simple force and
a moment of force