Lecture 8

Question 1

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

Answer 1

force

Question 2

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

Answer 2

Center of Resistance

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

Question 3

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

Answer 3

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

Question 4

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

Answer 4

moment

Question 5

what is a moment generated by?

Answer 5

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

Question 6

what is a couple?

Answer 6

two forces equal in magnitude and in opposite directions

*create spinning object

Question 7

what is the center of rotation?

Answer 7

point where the rotation actually occurs

Question 8

where is the center of resistance for a tooth?

Answer 8

approximately at midpoint of the embedded portion of the root

*technically at 6 tenths

Question 9

where is the moment arm?

Answer 9

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

Question 10

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

Answer 10

a couple

Question 11

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

Answer 11

a couple

Question 12

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

Answer 12

large to generate the necessary Mc

Question 13

what determines the type of tooth movement?

Answer 13

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

Question 14

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

Answer 14

the moment couple ratios

Question 15

what happens when there is no couple?

Answer 15

the tooth rotations around the center of resistance

*creates pure tipping movement

Question 16

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?

Answer 16

controlled tipping

Question 17

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

Answer 17

closer to the apex

Question 18

what is force times distance?

Answer 18

magnitude of tipping moment from force

Question 19

what happens when the center of resistance moves apically?

Answer 19

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

Question 20

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

Answer 20

a fixed appliance

*almost impossible with braces or clear aligners

Question 21

where is heavy pressure felt when moving teeth?

Answer 21

apex and crest of alveolar bone

*ZERO pressure at center of resistance

Question 22

what is the optimal force to create rotational movement?

Answer 22

35-60 grams

Question 23

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

Answer 23

tipping

Question 24

how does a hawley retainer work?

Answer 24

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

Question 25

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

Answer 25

translation * rectangular diagram * twice as much force needed compared to tipping

Question 26

optimal force for translation?

Answer 26

70-120 grams *twice as much force needed compared to tipping

Question 27

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

Answer 27

Intrusion

Question 28

what is the optimal force for intrusion?

Answer 28

10-20 grams *very light!

Question 29

optimal pressure for extrusion?

Answer 29

35-60 grams

Question 30

what 2 things would an ideal spring do?

Answer 30

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

Question 31

What is a continuous force in ortho?

Answer 31

forces that are maintained between activations, even though force declines

Question 32

what are interrupted forces?

Answer 32

forces drop to zero between activations

Question 33

what are intermittent forces?

Answer 33

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

Question 34

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

Answer 34

the wire stiffness

Question 35

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

Answer 35

permanent deformation

Question 36

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

Answer 36

range x stiffness

Question 37

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

Answer 37

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

Question 38

what is spring-back?

Answer 38

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

Question 39

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

Answer 39

point where the wire breaks

Question 40

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

Answer 40

1-length | 2-cross section of wire

Question 41

4 points about stainless steal wires

Answer 41

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

Question 42

3 points about chromium alloys wires hint: compare to stainless steel

Answer 42

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

Question 43

4 things about Ni-Ti alloy wires

Answer 43

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

Question 44

3 things about beta-titanium wires

Answer 44

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

Question 45

what are the 2 bracket slot size dimensions?

Answer 45

1- .022 in (.55mm) | 2- .018 in (.45mm)

Question 46

each bracket has what 3 things prescribed?

Answer 46

1-torque 2-angulation 3-offset

Question 47

what is a Begg bracket?

Answer 47

narrow slot for loose fitted wire. Held with locking pin

Question 48

what is an edgewise appliance system?

Answer 48

most common. rectangular archwire *gets teeth in the ball park

Question 49

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

Answer 49

- lingual max incisors and canines should be level | - buccal mand incisors and canines should be level

Question 50

What is indirect bonding of brackets?

Answer 50

fabrication of a splint on a model which contains the brackets

Question 51

5 advantages to indirect bracket bonding

Answer 51

``` 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 ```

Question 52

2 disadvantages to indirect bracket bonding

Answer 52

1-technique sensitive | 2-Clean up of excess bond can be difficult

Question 53

3 advantages to direct bracket bonding

Answer 53

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

Question 54

2 disadvantages to direct bonding

Answer 54

1-longer chair time | 2-some brackets difficult to place

Question 55

class 1 elastics

Answer 55

vertical direction, no ant. post. forces

Question 56

class 2 elastics

Answer 56

Anterior maxillary teeth to posterior mandibular teeth

Question 57

class 3 elastics

Answer 57

lingual of maxillary teeth to buccal of mand teeth

Question 58

what is anchorage?

Answer 58

resistance to unwanted tooth movement

Question 59

what is traction?

Answer 59

used to create space *headgear to distalize tooth

Question 60

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

Answer 60

true

Question 61

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

Answer 61

True

Question 62

What is the goal of anchorage?

Answer 62

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

Question 63

how do you determine anchorage value?

Answer 63

roughly the root surface area

Question 64

example of reciprocal tooth movement?

Answer 64

pulling 8 and 9 together to close diastema. | equal force on each tooth

Question 65

what is reinforced anchorage?

Answer 65

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

Question 66

what are the 4 possible places for skeletal anchorage?

Answer 66

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

Question 67

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

Answer 67

3 week intervals

Question 68

how much time does undermining resorption requrie?

Answer 68

7-14 days *longer for PDL

Question 69

average bone loss during ortho

Answer 69

less than .5mm *rarely exceeds 1mm

Question 70

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

Answer 70

false, it stays the same

Question 71

T/F there in increased mobility in ortho patients?

Answer 71

true * thickened ligament * will go away when force does

Question 72

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

Answer 72

False * pain my last 2-4 days * some say to chew gum

Question 73

T/F ortho can cause pulpitis

Answer 73

true *may contribute to pain

Question 74

Ortho has more to do with pulp or PDL?

Answer 74

PLD *endo teeth can be treated normally

Question 75

category 1 root resorption

Answer 75

slight blunting

Question 76

cat. 2 root resorption

Answer 76

moderate resorption, up to 1/4 root length

Question 77

cat. 3 root reorption

Answer 77

sever resorption, greater than 1/4 root length

Question 78

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

Answer 78

90, half *length is clinically insignificant

Question 79

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

Answer 79

3% adolescence, 4% adults

Question 80

what 2 things have studies indicated might cause root resorption?

Answer 80

1-hyalinization | 2-sterile necrosis

Question 81

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

Answer 81

continuous

Question 82

T/F root resorption continues after ortho tx

Answer 82

false *unless you continually use a retainer

Question 83

what are the 4 variables to root resorption?

Answer 83

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

Question 84

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

Answer 84

True

Question 85

Generally speaking, does more force=more root resorption?

Answer 85

yes

Question 86

many adverse effects of ortho are caused by what?

Answer 86

poor patient compliance

Question 87

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

Answer 87

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

Question 88

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

Answer 88

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

Question 89

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

Answer 89

NO! Prophylactic sealing did not significantly reduce decalcification