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Pedo/Ortho II > Lecture 8 > Flashcards

Lecture 8 Flashcards

1
Q

What is it called when a load is applied to an object that will tend to move it to a different position in space?

A

force

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2
Q

point at which resistance to movement can be concentrated for math analysis.

A

Center of Resistance

*For an object in free space, the center of resistance is in the same as the center of mass

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3
Q

Where is the center of resistance when a tooth root is embedded in bone?

A

half way between the root apex and the crest of the alveolar bone

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4
Q

A measure of the tendency of a force to rotate an object around some piont

A

moment

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5
Q

what is a moment generated by?

A

a force acting at a distance to the center of the resistance

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6
Q

what is a couple?

A

two forces equal in magnitude and in opposite directions

*create spinning object

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7
Q

what is the center of rotation?

A

point where the rotation actually occurs

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8
Q

where is the center of resistance for a tooth?

A

approximately at midpoint of the embedded portion of the root

*technically at 6 tenths

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9
Q

where is the moment arm?

A

the perpendicular distance from the point of force application to the center of resistance

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10
Q

using a lingually directed force and a buccally directed force on the crown of a tooth is an example of what?

A

a couple

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11
Q

using an ortho bracket to place a couple force on the crown of a tooth is an example of what?

A

a couple

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12
Q

if the moment arm is small, the force must be _____

A

large to generate the necessary Mc

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13
Q

what determines the type of tooth movement?

A

ratio between the moment produced by the force applied and the counterbalancing moment produced by the couple

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14
Q

what determines where the center of the rotation will be on the tooth?

A

the moment couple ratios

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15
Q

what happens when there is no couple?

A

the tooth rotations around the center of resistance

*creates pure tipping movement

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16
Q

what is it called when the moment-to-force ratio increases and the center of rotation is displaced further and further apically, away from the center of resistance?

A

controlled tipping

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17
Q

loss of alveolar bone height moves the center of resistance closer to the apex or incisal edge?

A

closer to the apex

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18
Q

what is force times distance?

A

magnitude of tipping moment from force

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19
Q

what happens when the center of resistance moves apically?

A

the tipping moment produced by the force (Mf) increases because the moment arm is longer

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20
Q

what is required if root movement in someone with alveolar bone loss is the goal?

A

a fixed appliance

*almost impossible with braces or clear aligners

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21
Q

where is heavy pressure felt when moving teeth?

A

apex and crest of alveolar bone

*ZERO pressure at center of resistance

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22
Q

what is the optimal force to create rotational movement?

A

35-60 grams

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23
Q

a Hawley retainer with finger spring is capable of moving a tooth by which type of movement?

A

tipping

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24
Q

how does a hawley retainer work?

A

finger spring places a single force at a distance from the center of resistance…causing tipping at center of resistance

*what direction of incisal movement

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25
Q

what is it called when the PDL space is loaded uniformly from alveolar crest to apex?

A

translation

  • rectangular diagram
  • twice as much force needed compared to tipping
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26
Q

optimal force for translation?

A

70-120 grams

*twice as much force needed compared to tipping

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27
Q

what kind of tooth movement occurs when a force is concentrated over a small area at the apex?

A

Intrusion

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28
Q

what is the optimal force for intrusion?

A

10-20 grams

*very light!

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29
Q

optimal pressure for extrusion?

A

35-60 grams

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30
Q

what 2 things would an ideal spring do?

A

1-maintain the same amount of force regardless of distance
2-would be the most ideal force system for ortho tooth movement

*but real springs’ force decays as tooth moves away

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31
Q

What is a continuous force in ortho?

A

forces that are maintained between activations, even though force declines

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32
Q

what are interrupted forces?

A

forces drop to zero between activations

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33
Q

what are intermittent forces?

A

forces that fall to zero when a removable appliance is taken out, but resumes when its is reinserted.

*these forces also decay as tooth movement occurs

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34
Q

On a typical force deflection curve, what does the slope of the linear portion represent?

A

the wire stiffness

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35
Q

on a force-deflection curve, what does the range on the x axis represent?

A

permanent deformation

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36
Q

How do you calculate strength on a force-deflection curve?

A

range x stiffness

37
Q

what is the proportional limit on a force-deflection curve?

A

the point where force on the wire is proportional to its deflection

38
Q

what is spring-back?

A

The position the wire will return to after it’s deflected

39
Q

what is the failure point on a force-deflection curve?

A

point where the wire breaks

40
Q

the major elastic properties of an ortho wire are affected by what 2 things?

A

1-length

2-cross section of wire

41
Q

4 points about stainless steal wires

A

1-strong
2-stiff
3-formable
routinely used for years

42
Q

3 points about chromium alloys wires

hint: compare to stainless steel

A

1-softer than stainless steal
2-more formable (because softer)
3-can be heat treated to make it harder

43
Q

4 things about Ni-Ti alloy wires

A

1-very useful in initial ortho
2-light force over large range
3-shape memory and superelasticity
4-poor formability

44
Q

3 things about beta-titanium wires

A

1-great strength/springiness combo
2-good formability
3-between SS and NiTi

45
Q

what are the 2 bracket slot size dimensions?

A

1- .022 in (.55mm)

2- .018 in (.45mm)

46
Q

each bracket has what 3 things prescribed?

A

1-torque
2-angulation
3-offset

47
Q

what is a Begg bracket?

A

narrow slot for loose fitted wire. Held with locking pin

48
Q

what is an edgewise appliance system?

A

most common. rectangular archwire

*gets teeth in the ball park

49
Q

in the edgewise straight wire theory, what is the labio-lingual direction?

A
  • lingual max incisors and canines should be level

- buccal mand incisors and canines should be level

50
Q

What is indirect bonding of brackets?

A

fabrication of a splint on a model which contains the brackets

51
Q

5 advantages to indirect bracket bonding

A 
1-place brackets all at once
2-reduct chair time
3-more precise location
4- control thickness of resin
5-can be delegated to staff
52
Q

2 disadvantages to indirect bracket bonding

A

1-technique sensitive

2-Clean up of excess bond can be difficult

53
Q

3 advantages to direct bracket bonding

A

1-don’t have to make a splint2
2-don’t have errors on splint placement
3-easy excess bond cleanup

54
Q

2 disadvantages to direct bonding

A

1-longer chair time

2-some brackets difficult to place

55
Q

class 1 elastics

A

vertical direction, no ant. post. forces

56
Q

class 2 elastics

A

Anterior maxillary teeth to posterior mandibular teeth

57
Q

class 3 elastics

A

lingual of maxillary teeth to buccal of mand teeth

58
Q

what is anchorage?

A

resistance to unwanted tooth movement

59
Q

what is traction?

A

used to create space

*headgear to distalize tooth

60
Q

T/F reciprocal effects though the dental arches must be analyzed, evaluated, and controlled?

A

true

61
Q

T/F a major part of tx planning is maximizing desired movement and minimizing undesirable movement

A

True

62
Q

What is the goal of anchorage?

A

concentrate movement on desired tooth, while keeping pressure off PDL of anchored tooth

63
Q

how do you determine anchorage value?

A

roughly the root surface area

64
Q

example of reciprocal tooth movement?

A

pulling 8 and 9 together to close diastema.

equal force on each tooth

65
Q

what is reinforced anchorage?

A

adding additional teeth to the unit ti distribute force over larger root surface area

66
Q

what are the 4 possible places for skeletal anchorage?

A

1-palate
2-head or neck
3-cortical anchorage
4-temporary anchorage (implants)

67
Q

What is the shortest space of time ortho appliances can be reactivated?

A

3 week intervals

68
Q

how much time does undermining resorption requrie?

A

7-14 days

*longer for PDL

69
Q

average bone loss during ortho

A

less than .5mm

*rarely exceeds 1mm

70
Q

T/F biologic width changes when a tooth in intruded or extruded with ortho?

A

false, it stays the same

71
Q

T/F there in increased mobility in ortho patients?

A

true

  • thickened ligament
  • will go away when force does
72
Q

T/F all patients will feel pain when ortho force is applied

A

False

  • pain my last 2-4 days
  • some say to chew gum
73
Q

T/F ortho can cause pulpitis

A

true

*may contribute to pain

74
Q

Ortho has more to do with pulp or PDL?

A

PLD

*endo teeth can be treated normally

75
Q

category 1 root resorption

A

slight blunting

76
Q

cat. 2 root resorption

A

moderate resorption, up to 1/4 root length

77
Q

cat. 3 root reorption

A

sever resorption, greater than 1/4 root length

78
Q

over ____% max incisors and over ________ of al teeth show some loss of root length form ortho

A

90, half

*length is clinically insignificant

79
Q

what percent of ortho patients will have moderate to severe root resorption?

A

3% adolescence, 4% adults

80
Q

what 2 things have studies indicated might cause root resorption?

A

1-hyalinization

2-sterile necrosis

81
Q

What is worse for root resorption, continuous or intermittent forces?

A

continuous

82
Q

T/F root resorption continues after ortho tx

A

false

*unless you continually use a retainer

83
Q

what are the 4 variables to root resorption?

A

1-pre-tx resorption is visable
2-duration of ortho tx
3-premolar extraction cases
4-family history of root resorption

84
Q

T/F genetic screening in the future may help id px who are predisposed to resorption?

A

True

85
Q

Generally speaking, does more force=more root resorption?

A

yes

86
Q

many adverse effects of ortho are caused by what?

A

poor patient compliance

87
Q

what 4 things must ortho pxs do to cair for teeth and gums?

A

1-proper brushing and flossing
2-reduce sugar
3-quickly report any loose brackets
4-dental visits every 3-6 months

88
Q

what 3 other things must an ortho px do to be considered compliant?

A

1-wear headgear and/or elastics
2-stop tongue and finger habits
3-keep appointments

89
Q

Proseal is an example of a fluoride releasing sealant that is placed around brackets to prevent decay. Does it work?

A

NO! Prophylactic sealing did not significantly reduce decalcification

Pedo/Ortho II (11 decks)

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