Test #2 Flashcards
Flush Plane
- pretty much an end to end class II relationship of the primary molars
- considered to be “normal”
- after eruption of permanent teeth, the leeway space allows mandibular teeth to come forward into class I relationship
mesial step
- mandibular molar is mesial to the flush plane
- If it is greater than 1 mm, they have an increased chance of developing a class III relationship
distal step
- mandibular molar is distal to the flush plane
- if the patient has this, they have a 100% chance of developing a class II relationship
Tooth’s center of resistance
about halfway up the root, but depends on periodontal support
vertical distance from the bracket to the center of resistance (CR) is…
about 10 mm
“moment”
tendency to rotate
the center of resistance moves how during a force?
the CR only moves in the direction of the force, (usually not up or down)
what is the formula for the magnitude of a moment?
M=Fd,
unit is g-mm
-F=magnitude of the force and d is the perpendicular distance of the Force from CR
A COUPLE always causes..
pure rotation around the center of resistance, regardless of its location on the tooth
-and it produces a pure moment
1st order view
viewed in the occlusal plane
-in-out bends
causing buccal-lingual movement and
rotation called “rotation”
2nd order
-viewed from the facial or lingual
-up-down bends
causing vertical movement and
rotation called “tipping”
3rd order
Viewed from the mesial or distal
-torquing bends causing buccal-lingual rotation called “torque”
What is the Moment/Force ration to get pure translation?
10/1
what is a couple?
- two equal and opposite non-colinear forces
- when 2 equal forces are applied in opposite directions, they both contribute a tendency to rotate but the forces to move the tooth are cancelled out
if the moment to force ratio is 0 what occurs?
tipping (rotation from a buccal or lingual view), but the center of rotation will be above the center of resistance
what is the M/F ratio that puts the center of rotation at the apex of the root?
7/1
during pure translation, where is the center of rotation?
at “infinity” because there is no center of rotation
if the M/F ratio is 13/1, what occurs?
the root will move in the direction of the root, while the crown stays.
-the center of rotation is at the crown
what is the M/F for pure rotation?
M/F=undef, the center of rotation is at the center of resistance
what type of device/appliance is used for simple attachment?
a button or hook,
-a bracket can also be used for simple forces, but can also do more complicated stuff
if a wire has a higher slope what properties does it have?
higher slope (E=modulus of elasticity)=increased stiffness
lower slope (modulus of elasticity)=
increased springiness
what is the “strength” of a wire?
strength=the max FORCE that a wire can deliver before deforming or breaking
what is the “range” of a wire?
range=the maximum deflection a wire can undergo before deforming (or breaking)
what were the three materials discussed that are used for wires?
- stainless steel
- beta-titanium
- nickel titanium
rank the wire materials in order of stiffness, from most stiff to least
- stainless steel
- beta-titanium
- nickel titanium
how does changing the diameter of the wire affect the stiffness?
- increasing the diameter affects stiffness by the change in diameter to the 4th power
- thus doubling the diameter makes it 16 times stiffer
how does changing the length of a wire affect its properties?
- increasing the length of the wire affects the springiness to the third power
- doubling the length of a wire makes it 8 times springier
E is proportional to …. (formula)
d^4/l^3
what is anchorage?
resistance to unwanted tooth movement
increasing anchorage…
involves increasing the resistance to unwanted tooth movement
reciprocal anchorage (reciprocal tooth movement)
-two (equal) teeth or sets of teeth move equally in the desired directions
the anchorage value of a tooth is roughly equal to what?
root surface area
“stationary” anchorage
making one side undergo a hard tooth movement while the other has easy movement
- translation vs crown movement
- crown movement vs root movement
what are some of the ways/devices that you can increase anchorage?
- headgear
- Nance (palatal) appliance
- interarch elastics
- ortho TADs
class II elastics
the posterior portion of the elastic is on mandibular teeth
class III elastics
the posterior portion of the elastic is on the maxillary teeth
what is an ortho TAD(s)
- temporary anchorage device(s)
- DIRECT and INDIRECT
- like the screw into the alveolar bone with the spring and wire attached to it
when is the only time that a tooth will undergo pure rotation?
when M/F=undef,
-I think it’s when there is only a moment
