biomechanics and appliances

Question 1

optimum tooth movement is produced by

Answer 1

1) light continuous force

Question 2

key terms to remember

Answer 2

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)

Question 3

elastic limit

Answer 3

1) point on stress/stain curve where any deformation occurs

Question 4

yield point

Answer 4

1) 0.1% deformation occurs

Question 5

ultimate tensile strength

Answer 5

1) maximum stress a material can withstand while being stretched or pulled before necking (cross section starts to contract)

Question 6

properties of a good wire

Answer 6

1) high strength
2) low stiffness
3) high range
4) high formability
5) weldable and solderable

Question 7

stainless steel high chromium contnet

Answer 7

1) stiff, strength
2) bendable and deformable

Question 8

cobalt chromium alloy

Answer 8

1) bendable, more expensive

Question 9

NiTi wires

Answer 9

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

Question 10

stress stain curve of NiTi

Answer 10

1) more stress deforms the wire until the strain plateaus
2) then as the teeth straighten, it comes down at a lower force

Question 11

two more properties

Answer 11

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

Question 12

archwire sequence

Answer 12

1) round flexible wire for alignment
2) rectangular flexible wire to fill the slot
3) rectangular formable wire to detail finish

Question 13

mechanical concepts in ortho

Answer 13

1) force
2) center of resistance
3) center of rotation
4) moment
5) couple

Question 14

force

Answer 14

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)

Question 15

center of mass

Answer 15

1) a point in mass that behaves as if the whole mass is concentrated in it

Question 16

center of resistance

Answer 16

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

Question 17

center of resistance for a tooth

Answer 17

1) midpoint of the embedded portion of the tooth
2) usually furcation area for multirooted

Question 18

moment

Answer 18

1) if force doesn’t pass through the CR, there will be rotation around the center of rotation, which can be at the CR or apical to it or at the apex
2) rotational + linear movement
3) moment (M) = force (F) x perpendicular distance (D) from CR

Question 19

clinical examples of moments of a force

Answer 19

1) mesial at the molar bracket tends to rotate the tooth, mesial in
2) expansion force on a molar tips the crown buccally
3) intrusive force at the molar creates a moment tipping the crown buccally

Question 20

couple

Answer 20

1) created by two parallel forces equal in magnitude and opposite in direction
2) moment
- magnitude of one of the forces multiplied by the perpendicular distance between two forces
- pure rotation around CR regardless of point of application of the couple

Question 21

couple of second order

Answer 21

1) engaging a wire in an angulated bracket
- causes spinning motion of the tooth
2) can upright a molar and close diastema

Question 22

couple in the third order

Answer 22

1) engaging a rectangular wire in a bracket slot
- inclination of root (torque)

Question 23

round arch wire vs rectangular wire

Answer 23

1) moment of the force = moment of couple
- only works when wire contacts the bracket in 2 points!

Question 24

ribbon arch

Answer 24

1) taller

Question 25

edgewise

Answer 25

1) wider

Question 26

types of toot hmovment

Answer 26

1) tipping 2) translation 3) root movement 4) rotation 5) intrusion and extrusion

Question 27

uncontrolled tipping

Answer 27

1) cannot control amount of rotation 2) a retainer - contacts at one point, not counteracting force 3) Mc/Mf = 0

Question 28

moment to force ratio

Answer 28

1) moment of the force and the counterbalancing generated by the bracket (couple) --- Mc/Mf = 0 (uncontrolled) - center of rotation at CR 01 (torqueing) - center of rotation approaches incisal edge

Question 29

intrusion movement

Answer 29

1 )force is concentrated over a small area at the apex 2) light force is required 10-20 gm - or tooth would get shorter

Question 30

extrusion

Answer 30

1) ideally no areas of compression within PDL 2) only tension 3) same force as tipping

Question 31

forces for different movements

Answer 31

1) tipping 25-60 gm 2) bodily movement 70-120 3) root uprighting 50-100 4) rotation 35-60 5) extrusion 35-60 6) intrusion 10-20

Question 32

edward angle

Answer 32

1) four appliance designs - e-arch - pin and tube - ribbon arch - edgewise appliance

Question 33

e-arch appliance

Answer 33

1) ligatures form a heavy labial arch were used to bring malposed teeth to the line of occlusion 2) ONLY capable of tipping 3) very painful

Question 34

ribbon arch

Answer 34

1) vertical slot appliance 2) well adapted to bring teeth into alignment, butt too flexible to allow precise positioning of roots

Question 35

edgewise appliance

Answer 35

1) horizontal slop appliance 2) arch wire inserted at 90 degree angles

Question 36

bracket slot dimension

Answer 36

1) 22 slot 2) 18 slot 3) how tall the slot for the wire is

Question 37

bracket placement is important

Answer 37

1) where the tooth move 2) how long the treatment last 3) final look

Question 38

indirect bonding

Answer 38

1) you place it on the study models where you want them 2) make a suckdown, then use the template and light cure it

Question 39

bands

Answer 39

1) restrict to second molars 2) things that cause a lot of force 3) more secure for surgeries 4) the separator is painful and more plaque

Question 40

clear or ceramic brackets

Answer 40

1) more expensive 2) more friction, can slow movement a little

Question 41

lingual braces

Answer 41

1) you cannot see them 2) restricts tongue space

Question 42

1) self ligating brackets

Answer 42

1) self-closing and holds wire in position 2) offer better hygiene

Question 43

invisalign

Answer 43

1) clear trays that help move teeth