MF BIOMECHANICS

Question 1

Which properties are ideal for alignment?

Answer 1

Low load deflection rate (NiTi)

Question 2

Which properties are ideal for leveling?

Answer 2

High load deflection rate (SS)

Question 3

Which wire has low modulus of elasticity?

Answer 3

NiTi (more flexible)

Question 4

Which wire to use for nickel sensitivity?

Answer 4

TMA

Question 5

What is the composition and properties of SS?

Answer 5

• 18-8 (18% chromium and 8% nickel)
• HIGH modulus of elasticity

Question 6

________ is defined as the distance that the wire will bend elastically before permanent deformation.

Answer 6

Range
(If deflected past yield point, will not return to original shape)

Question 7

Still clinically useful until point of arbitrary clinical loading (no hope of going back to original shape); Will work until failure point

Answer 7

Spring back

Question 8

Which wire has more friction?

Answer 8

TMA

Question 9

Which wire has more asparities?

Answer 9

NiTi

Question 10

T/F: properties of SS, TMA, and martensitic NiTI?
- SS has higher strength than TMA
- TMA has a higher strength and stiffness than martensitic NiTI
- SS has a higher stiffness than TMA
- TMA has a wider range than SS
- Martensitic NiTi has a longer range than TMA

Answer 10

All true

Question 11

What is the equation for strength?

Answer 11

Stiffness x range

Question 12

What happens to the ability of a rectangular archwire to deflect, if the size is doubled? Strength if diameter is doubled?

Answer 12

• If you double the size of an archwire, the deflection is going to be 1/8.
• If you double the diameter of the wire, you will increase the strength by 8

Question 13

How is the transformation from A-NiTi to M-NiTi induced?

Answer 13

Thermally induced (phase transformation)

Question 14

Which NiTi has high stress, low temp (flexible outside the mouth)?

Answer 14

Martensitic

Question 15

Which NiTi is low stress, high temp (in mouth, restores original shape), good range and constant force, initial wire?

Answer 15

Austentic

Question 16

What is the effect of 1st, 2nd, and 3rd order bends?

Answer 16

• 1st: in/out (correcting rotations)
• 2nd: up/down (correcting marginal ridges)
• 3rd: torque (correcting marginal ridges)

Question 17

Does bone increase with intrusion?

Answer 17

No

Question 18

Where is the center of rotation in uncontrolled tipping?

Answer 18

1/3 from the apex

Question 19

What does not affect the location of center of resistance of a single tooth?

Answer 19

Magnitude of force application

Question 20

Optimum force to retract a canine?

Answer 20

100-150g

Question 21

What is hysteresis?

Answer 21

• Force delivered to the periodontal structures is lower than the force necessary to activate the wire.
• It is the difference in force of a wire between loading and unloading (loading is always higher).
• Low hysteresis is desired.

Question 22

What is the affect on the wire with lingual crown torque on LR6?

Answer 22

Wire will be above the bracket on the opposite side

Question 23

What happens to strength, springiness, and range if you double the Diameter? Length?

Answer 23

Diameter:
- Strength: 8
- Springiness: 1/16
- Range: 1/2

Length:
- Strength: 1/2
- Springiness: 8
- Range: 4