Orthodontic Materials / Physical Principles 8% 5Q Flashcards
Equation for stress =
force / area
Equation for strain =
deflection / unit strength
Equation for strength =
stiffness x range
Equation for springiness =
1 / stiffness
The stress strain curve shows the __________ behavior of a material
elastic
the point at which any permanent deformation is first observed:
elastic limit / proportional limit
Deformation of 0.1% is observed
yield strength
Maximum Load / Ultimate Tensile Strength
maximum load the wire can sustain after some permanent deformation
area of the curve up to the proportional limit. (Energy Storage)
Resilience
amount of permanent bending a wire can stand before breaking
Formability
distance a wire will bend elastically before permanent deformation
Range
Ideal AW properties:
( High / Low ) strength
( High / Low ) Stiffness
( High / Low ) Range
( High / Low ) Formability
High strength
Low Stiffness
High Range
High Formability
In terms of surface roughness which AW materials have the most asperities
NiTi > TMA > SS
Which AWs have the most friction to sliding mechanics
TMA > NiTi > SS
Frictionless mechanics with closing loops is done with which material?
TMA
An increase in wire length x 2 has what effect on strength?
decrease x 2
1/X
An increase in wire length x 2 has what effect on stiffness?
decrease x 8
1/X3
An increase in wire length x 2 has what effect on springiness?
increase x 8
X3
An increase in wire length x 2 has what effect on range?
increase x 4
X2
An increase in wire diameter x 2 has what effect on range?
decrease x 2
1/X
An increase in wire diameter x 2 has what effect on strength?
increase x 8
X3
An increase in wire diameter x 2 has what effect on stiffness?
increase x 16
X4
An increase in wire diameter x 2 has what effect on springiness?
decrease x 16
1/X4
what is another name for the material Elgiloy
cobalt chromium
Elgiloy can be softer and thus more:
formable
Elgiloy can be heat treated, which would increase its strength to that of _________________ by increasing the UTS and resilience
stainless steel
Nitinol has no phase change, is not superplastic and is also known as
M-NiTi
NiTi is superplastic, meaning it has shape ___________; it ( does / does not ) have the ability to change molecular structure
memory
does
Name the 2 ways to get a phase change in NiTi
Pseudoelasticity/Superelasticity
Thermoelasticity
Due to the thermoelasticity of NiTi, heat induces change from the ___ → ___ state while cold induces change from the ___ → ___ state.
heat: M → A
cold: A → M
Due to the superelasticity of NiTi, stress induced martensite (SIM) induces change from the ___ → ___ state while deactivation induces change from the ___ → ___ state.
SIM A → M
Deactivation M → A
NiTi is formed at high temps (state ___ ), when cooled (state ___ ) can then be plastically deformed.
This means its original shape restored when ( cooled / heated )
A
M
heated
- ( A / M ) NiTi is the stabilized form of NiTi with no application of phase transition effects
M (Martensitic)
Flexibility: A-NTi ___ M-NiTi
A < M
Stiffness: A-NTi ___ M-NiTi
A > M
what is manifested by very large reversible strains and a non-elastic stress-strain or force-deflection curve
superelasticity
In A-NiTi wires, the initial archwire should exert (more / less / same ) force whether it were deflected a relatively small or large distance
the same
The unique force-deflection curve for A-NiTi wire occurs because of a ______________________ in grain structure from austenite to martensite in response to an applied force (not to a temperature change).
phase transition
Beta NiTi is aka
Copper NiTi
which material guarantees Temperature Transition Range (TTR) so you know exactly at what temperature the phase transition occurs?
Beta NiTi
the ideal temperature for the phase transition of Beta NiTi
35° C
Bending moment vs deflection plot for 16 mil orthodontic wires
Note that after an initial force is reached, ___-NiTi has a considerably flatter load-deflection curve and greater springback than ___-NiTi, which has greater springback than steel
A
M
The concept that the unloading force is different (less) than the loading force. After untyting, retying increases the amount of force delivered.
Hystersis
Small-round NiTi wires should be ___-NiTi, while larger rectangular ones often perform better if made from ___-NiTi. M-NiTi which remains useful, primarily in the later stages of treatment when flexible but larger and somewhat stiffer wires are needed
A
M
TMA is aka
Titanium Molybdenum
Compared to Nitonol, TMAis, ( smoother / rougher ), ( can / cannot ) be welded, has good formability
smoother
can
What AW material offers remarkable strength and springiness, making it an excellent choice for auxiliary springs and for intermediate and finishing wires
TMA
