The Biomechanics of Orthodontic Tooth Movement Flashcards
Forces are what
vectors
What is the measurement(s) of the magnitude of force
Newton (N) is the common unit clinical orthodontics; often measures in grams or ounces
Resultant force is calculated by what
the parallelogram law
Vector resolution is the opposite of what
vector addition
What does this image represent
addition of forces when they have a common point of application
What does this image represent
Addition of forces when they have different points of application
What does this image represent
resolving a force into components
This is the point at which resistance to movement can concentrated for mathematical analysis
center of resistance (C res)
Where is the center of resistance in a free object
center of mass/gravity, or point of balance
Where is the center of resistance of a partially restraint object (like teeth)
it is determined by the nature of the external constraints (like for a tooth; alveolar bone)
Where is the center of resistance of a tooth
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)
The center of resistance of a tooth can vary with what two parameters
alveolar bone hieght and root length; more specifically, the part of the root embedded in the alveolar bone
Does the center of resistnce vary with orthodontic force?
No, unless force causes a change in alveolar bone height
What happens to the center of resistance with alveolar bone loss
it moves apically
What happens to the center of resistance when there is root resportion
it moves coronally
If the line of action of a force does not pass through the center of resistance, the force will produce some what
rotation of the tooth
The potential for rotation is measured as what
a moment
What is magnitude
magnitude of force x perpendicular distance from center of resistance to the line of action
This is two forces of equal magnitude; parallel and non-colinear in the opposite direction producing pure rotation
couple
A single force (not passing the center of resistance) produces what types of force
rotational and translational effect; not a pure rotation
The translational effects produced by the two forces of a couple do what to each other
cancel each other out
This is the point around which an object is rotating
center of rotation
Unlike the center of resistance, center of rotation is what
not at a fixed point and varies with the force/moment/couple applied to the tooth
In orthodontics, the center of rotation can be changed to acheive what
different types of tooth movement and clinical goals
What are the three types of orthodontic tooth movement
translation
pure rotation
combination of translation and rotation (tipping); majoirty of the movements
During translation, all points on an object move where
in the same direction at the same rate
To produce translation, what needs to occur
the line of action of a single force needs to pass through the center of resistance
What determies whether translation is produced
line of action
When a force is not passing through the center of resistance, translation is still acheivable how
by cancelling the moment produced by this force using an opposite moment producs by a couple (torsion of archwire)
When some points on an object move differently than other points on the same objest, the overall movement of the object is what
tippine
When does tipping occur
when the line of action of a single force does not pass through the center of resistance the force will produce a tipping
A tipping movement can be resolved into what
translational and rotational components
What are the five types of tooth movement
translation
uncontrolled tipping
controlled tipping
root movement (torque)
pure rotation
Where is the center of rotation in translation
infinity; no rotation, no center
Where is the center of rotation involving uncontrolled tipping
slightly apical to the center of resistance
Where is the center of rotation involving controlled tipping
apex
Where is the center of rotation involving root movement (torque)
incisal edge
Where is the center of rotation involving pure rotation
center of resistnce
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)
uncontrolled tipping
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
controlled tipping
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
A. at the apex
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
D. 1/3 the root length from the apex
