10th Class Flashcards
_______ is the research and analysis of the mechanical properties of living tissues and non-living objects that affect those living tissues.
Biomechanics
The analysis of the non-living component simply follows _______ mechanical principles.
Newtonian
, the biomechanical properties of living or non-living tissue are more complicated and often not thoroughly understood?
Living tissue more complicated
Newton’s three “Laws of Motion” describe the relationship between
the _______ acting on an object and the _____ of that object,
which form the basis for classical mechanics.
external forces; motion
Mechanics is the branch of physics concerned with the behavior of
objects when subjected to _____ or _______
forces; displacements
What is Newton’s first law?
A body at rest remains at rest, and a body in motion continues to move in a straight line with a constant speed unless and until an external unbalanced force acts upon it.
What is Newton’s second law?
The rate of change of momentum of a body is directly proportional to the impressed force and takes place in the direction in which the force acts.
What is Newton’s third law?
Whenever A exerts a force on B, B simultaneously exerts a force of the same magnitude and in the opposite direction on A.
“For every action, there is an equal and opposite reaction”
_____ is an influence that may cause an object to change its velocity (accelerate).
force
It may be experienced as a lift, a push, or a pull, and it has a magnitude and a direction and hence is mathematically represented by a _____
vector
The actual acceleration of the body is determined by the _______ of all forces acting on it.
vector sum
A vector is a concept characterized by a ______ and a _______.
magnitude; direction
_____ is a vector quantity defined as the rate of change of the momentum of
the body that would be induced by that force acting alone.
Force
A ____ has only a magnitude.
scalar
A scalar has only _____
Magnitude
Orthodontic forces are described by their what 3 things?
magnitude, point
of application, and direction.
The ______ of the force is defined by the line of action and the sense (arrowhead).
direction
The ______ of the force is depicted by the length of the line using an arbitrary scale
magnitude
Using the ______ as the horizontal reference of
an orthogonal coordinate system.
occlusal plane
The calculations of magnitude and direction of the
components can be carried out geometrically by using
_____ methods
trigonometric
The ______ describes all the forces involved and allows for
analysis and calculation of resultant forces on a tooth or a group of
teeth.
force system
______ forces depicted as vectors can be added
together to calculate the resultant by using the
parallelogram method or by addition of their
components in a reference system.
Concurrent
The ______ method used to derive resultant forces
entails drawing the two concurrent forces (F1 and F2) to
scale at appropriate angulations.
parallelogram
The diagonal of this parallelogram from the point of force
application, when measured and converted using the
specified scale, gives the _______ of the resultant (R).
magnitude
Forces have what 4 things?
- Line of action.
- Direction.
- Magnitude.
- Point of application.
Force application in orthodontics is analyzed in relation to the ________ of a tooth or group of teeth.
Centre of Resistance
C of Res.
______ is the point on the tooth where if a force is
applied will result in bodily movement or translation.
C of Res
C of Res is located on the ______ of the tooth approx.
30% from the alveolar crest.
long axis
C of Res is located on the long axis of the tooth approx.
___ % from the alveolar crest.
30%
The center of resistance is a constant point for any given tooth and
depends on what 4 things?
- The root length
- Thickness
- Bone
- Periodontal ligament
•The point around which the tooth rotates
Center of Rotation
The location of the center of rotation is dependent on the_______ applied to the tooth
force
system
This force system to determine center of rotation is considered as the _________
Moment to Force
ratio (M/F)
_____ is the tendency for a force to produce rotation or tipping of a tooth.
-determined by multiplying the magnitude of the force (F) by the
perpendicular distance (d) from the center of resistance to the line of action of
this force.
Moment
_____ is a system having two parallel forces of equal magnitude
acting in opposite directions
Couple
Every point of a body to which a couple is applied is under a rotational
effect in the ____ direction and magnitude.
same
T/F: A couple can never move the center of resistance, and with a couple
the center of rotation and the center of resistance will always be
coincident.
True
A couple causes an object to ________
regardless of the point of application.
rotate around its center of resistance
Two forces ____ in magnitude and _____ in direction.
equal; opposite
Perhaps the simplest way to determine how a tooth
will move is to consider:
•The ratio between the moment created when a force is
applied to the crown of a tooth. (moment of the force MF)
•The counter-balancing moment generated by a couple
within the bracket. (moment of the couple MC)
MC/MF ratio
MC/MF = 0
What happens?
•Uncontrolled tipping (tooth rotates around center of resistance)
0 < MC/MF < 1
What happens?
•Controlled tipping (inclination of tooth changes but the center of rotation is
displaced away from the center of resistance, and the root and crown move
in the same direction).
MC/MF = 1
What happens?
•Bodily movement(equal movement of crown and root).
MC/MF > 1
What happens?
•Torque (root apex moves further than crown)
•The simplest form of orthodontic movement is tipping.
•Tipping movements are produced when a single force is applied against the crown
of a tooth.
•When this is done, the tooth rotates around its “center of resistance”.
•Force applied at the bracket causes crown to move one way, and the root the
other.
•Centre of Rotation (C of Rot) point around which the tooth is located at C of Res.
Uncontrolled tipping
To control the M of the F, we must introduce another MOMENT produced by
a ______ which acts in opposition to the M of the F.
COUPLE
Further increasing the Moment of the Couple completely counters the M of
the F and moves the C of Rot to infinity => _____
Translation
Increasing the M of the Couple to exceed the M of the F moves the C of Rot
to the incisal edge => ________
palatal crown torque.
Involves moving the C of Rot away from the C of Res.
•Accomplished by applying a Moment of a Couple to counter
the Moment of the Force.
Controlled tipping
If the force passes through the center of
resistance of the tooth, the tooth will
move ________
•The center of rotation goes to the infinity.
•In this movement the moment caused by
the arch wire is compensating for the
moment of the force.
bodily or translate.
