biomechanics and appliances Flashcards
optimum tooth movement is produced by
1) light continuous force
key terms to remember
1) elastic behavior is dictated by its stress strain response
2) stress is internal distribution of the load (F/A)
3) strain is internal distortion produced by the load (deflection/length)
elastic limit
1) point on stress/stain curve where any deformation occurs
yield point
1) 0.1% deformation occurs
ultimate tensile strength
1) maximum stress a material can withstand while being stretched or pulled before necking (cross section starts to contract)
properties of a good wire
1) high strength
2) low stiffness
3) high range
4) high formability
5) weldable and solderable
stainless steel high chromium contnet
1) stiff, strength
2) bendable and deformable
cobalt chromium alloy
1) bendable, more expensive
NiTi wires
1) nickel, titanium, and naval ordinance lab
2) two major properties
- shape memory
- superelastic
3) originally, it was a springy and strong form, but now it has super elasticity
stress stain curve of NiTi
1) more stress deforms the wire until the strain plateaus
2) then as the teeth straighten, it comes down at a lower force
two more properties
1) resilience
- area under the stress strain curve
out to the proportional limit
- the storage capacity of the wire
- combination of strength and springiness
2) formability
- amount of permanent deformation a wire can withstand before failing
archwire sequence
1) round flexible wire for alignment
2) rectangular flexible wire to fill the slot
3) rectangular formable wire to detail finish
mechanical concepts in ortho
1) force
2) center of resistance
3) center of rotation
4) moment
5) couple
force
1) load applied to object that will tend to move it into a different position in space
- point of application
- magnitude
- line of action
- direction (sense)
center of mass
1) a point in mass that behaves as if the whole mass is concentrated in it
center of resistance
1) point of concentrated resistance to movement
2) applied force must pass through for a free object to move linearly without any rotation
—
1) if the object is embedded in bone, the CR changes to the center of the object that is EMBEDDED
- depends on the alveolar bone height and root length
center of resistance for a tooth
1) midpoint of the embedded portion of the tooth
2) usually furcation area for multirooted