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IODC > Orthodontics > Flashcards

Orthodontics Flashcards

1
Q

What is orthodontics?

A

The branch of dentistry concerned with facial growth, with development of the dentition and occlusion, and with the diagnosis, interception and treatment of occlusal anomalies

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2
Q

What is malocclusion?

A

Variation from ideal occlusion which has dental health and/or psychosocial implications for the individual

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3
Q

What 3 types of orthodontic appliances exist?

A

Fixed, functional and removable

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4
Q

Materials in orthodontics: What is PMMA?

A

PMMA is a vinyl polymer, made by free radical vinyl polymerization from the monomer methyl methacrylate.

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5
Q

Materials in orthodontics: What are heat cured and self cured PMMA used for?

A
  • Heat cured – used for baseplates
  • Self cured – also used for baseplates, it is chemically very similar to heat cured PMMA but contains an activator (dimethyl- p-toluidine).
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6
Q

Materials in orthodontics: What problem can occur with PMMA’s used for baseplates?

A

• Depending on which type of PMMA is used there can be between 0.1% and 5% residual monomer and additives that can be released from the baseplate.

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7
Q

Materials in orthodontics: How do you prevent an allergy to PMMA?

A
  • Use heat cure PMMA
  • Store appliance in water for several hours prior to fit
  • Use light cured ‘acrylic’
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8
Q

Materials in orthodontics: What are the most common allergens for occupationally exposed dental professionals?

A

MMA, dibenzoyl peroxide and the cross- linking agent EGDMA (ethylene glycol dimethacrylate)

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9
Q

Materials in orthodontics: How do you minimise exposure of PMMA?

A
  • Wear gloves
  • Ventilation
  • Use down-draught extraction
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10
Q

Materials in orthodontics: What is a tensile force/compressive force/ shear force?

A
  • A tensile force causes elongation in the direction of load applied.
  • A compressive force causes a contraction in the direction of the load applied.
  • A shear force causes either a sliding displacement of one side of a specimen or a twisting around its axis (torsion
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11
Q

Materials in orthodontics: How are mechanical properties of these wires generally assessed?

A
  • tensile,

* bending, and • torsionaltests

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12
Q

Materials in orthodontics: What are the optimum characteristics of wire?

A
  • The characteristics desirable in an orthodontic wire are:
  • large springback,
  • low stiffness,
  • good formability,
  • high stored energy,
  • biocompatibility and environmental stability,
  • low surface friction, and
  • the capability to be welded or soldered to auxiliaries.
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13
Q

Materials in orthodontics: Why are stainless steel wires popular?

A
  • formability,
  • biocompatibility and environmental stability,
  • stiffness,
  • resilience, and
  • low cost
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14
Q

Materials in orthodontics: What is the formula for force and deflection of stainless steel springs?

A 
F = k d r4 / l3
r = radius of the wire
d = deflection of the wire
l = length of the spring
k = stiffness of the wire (Young’s Modulus)
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15
Q

Materials in orthodontics: What does heat treatment of Co-Cr result in?

A

a wire with properties similar to those of stainless steel.

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16
Q

Materials in orthodontics: What are the properties of NiTi wires?

A
  • Nitinol wires have a good springback and low stiffness.

* This alloy, however, has poor formability and ‘joinability’

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17
Q

Materials in orthodontics: What are the properties of Beta-titanium wires?

A

• Beta-titanium wires provide a combination of adequate springback, average stiffness, good formability, and can be welded to auxiliaries.

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18
Q

Materials in orthodontics: What are the properties of multi-strand wires?

A
  • Multi-stranded wires have a high spring-back and low stiffness when compared with solid stainless steel wires.
  • Used as a cheap substitute for NiTi and for bonded retainers
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19
Q

Materials in orthodontics: How do you assess the elastic properties of a wire?

A
  • Strength = Stiffness X Range
  • Strength is the quality or state of being strong, relating to tensile strength.
  • Stiffness is the quality of being rigid; not easily bent.
  • Range is the distance a wire travels before permanent deformation.
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20
Q

Materials in orthodontics: What is stiffness?

A

Is the slope of the strength-range graph and is equal to the product of the elastic modulus of the material (E) times its area moment of inertia (I). The value, I, is geometry dependent. Thus, with a change in shape of the same material you will change the stiffness.

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21
Q

Materials in orthodontics: What are round cross section wires used for?

A

• Wires that are round in cross-section fit loosely in the brackets and are used for initial stages and only TILT teeth. They do not move the root, the root is dragged along passively through the bone into an approximate position in the arch

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22
Q

Materials in orthodontics: What are rectangular wires used for?

A

Rectangular wires are used in the second stage of movement and engage the bracket much more firmly such that a torque force is placed on the tooth.

This torque acts on the long-axis of the tooth such that the root moves into an angle parallel with masticatory forces.

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23
Q

Materials in orthodontics: What is strength and what are the 3 ways it can be viewed?

A

Strength is the measure of the force a material can withstand before the material permanently deforms. Strength may be viewed in these three ways

1 Proportional Limit
the point at which any permanent deformation first
occurs.
2 Yield Strength
the point at which 0.1% deformation is measured.
3 Ultimate Tensile Strength
the maximum load that the wire can sustain

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24
Q

Materials in orthodontics: What is range?

A

Range is the deflection the material will encounter before any permanent deformation occurs - from zero to the proportional limit.

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25
Q

Materials in orthodontics: What is the slope of the stress/strain curve? (check slide)

A

The elastic modulus (E) - proportional to the stiffness

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26
Q

Materials in orthodontics: What is resilience?

A

the area under the curve out to the proportional limit. Resilience represents the energy capacity of the material that is a combination of the strength and stiffness.

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27
Q

Materials in orthodontics: What is formability?

A

the amount of permanent deformation that a material can withstand before breaking.

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28
Q

Materials in orthodontics: What unique properties does nitinol exhibit?

A

“Shape Memory” and “Super- elasticity”.

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29
Q

Materials in orthodontics: What is shape memory?

A

the process of restoring the original shape of a plastically deformed sample by heating it.
• This is a result of a crystalline phase change known as “thermoelastic martensitic transformation”.
• The shape memory effect is repeatable

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30
Q

Materials in orthodontics: What is superelasticity?

A

Superelasticity assumes a reversible response to stress caused by a phase transformation.
• Superelasticity (or pseudoelasticity,) shows us the type of deformational behaviour, traditionally an elastic one.

• Shape memory denotes the possibility of a body to return to its original configuration, unlike superelastic materials it can do this without applying temperature

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31
Q

Materials in orthodontics: What is the constancy of stress?

A

Super-elastic Nitinol has an unloading curve that stays flat over large strains, i.e. Nitinol archwires can apply a constant stress over a wide range. Orthodontic archwires were the first medical application of super- elastic Nitinol. Nitinol archwires “move with the teeth”, applying a constant force over a broad treatment time and tooth position.

  • don’t move teeth too quickly
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32
Q

Materials in orthodontics: What type of bonding do brackets use?

A

most successful - mechanical retention

  • have to make sure you can get them off so don’t use the strongest material
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33
Q

Materials in orthodontics: What is adhesion?

A

• The force of attraction between the molecules or atoms on two different surfaces as they are brought into contact.

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34
Q

Materials in orthodontics: What are the different types of adhesion?

A

Mechanical adhesion
Two materials may be mechanically interlocked. Sewing forms a large scale mechanical bond, velcro forms one on a medium scale, and some textile adhesives form one at a small scale.
• Chemical Adhesion
Two materials may form a compound at the join. The strongest joins are where atoms
of the two materials swap (ionic bonding) or share (covalent bonding) outer electrons.
• Dispersive Adhesion
Also known as adsorption. Two materials may be held together by van der Waals
forces.
• Electrostatic Adhesion
Some conducting materials may pass electrons to form a difference in electrical charge at the join. This results in a structure similar to a capacitor and creates an attractive electrostatic force between the materials. The electrons are passed if one conducting material binds its electrons less strongly than the other does.
• Diffusive Adhesion
This may occur when the molecules of both materials are mobile and soluble in each other. It is also the mechanism involved in sintering. When metal or ceramic powders are pressed together and heated, atoms diffuse from one particle to the next. This joins the particles into one.

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35
Q

Extractions: What three ways can you expand the arch?

A

lateral, anterior, posterior, buccal segments back distally

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36
Q

Extractions: What does anterior movement during expansion do to the incisors?

A

Bimaxillary proclincation

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37
Q

Extractions: What are the problems with bimaxillary proclination?

A

appearance
stability
periodontal health - forces won’t go through the tooth properly

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38
Q

Extractions: What can happen in non extraction cases?

A

Bimaxillary proclincation

7 and 8s impacted

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39
Q

Extractions: What are the reasons for extraction in orthodontics?

A 
Relieve crowding
Correct incisor relationship 
  -  Reduce an overjet(Class II)
  -  Camouflage in Class III
Overbite correction 
To correct centrelines - can shift teeth round 
 Anchorage
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40
Q

Extractions: What are the principles of extractions in orthodontics?

A
  1. Condition of the teeth - always opt to take out teeth with poorest prognosis
  2. Location of the crowding - extract teeth close to the crowding
  3. Position of the teeth (crowns/apices)
  4. Appliance treatment proposed
41
Q

Extractions: What teeth are most common for extraction?

A

Premolars (most common)
 first premolar
 second premolar

 Third molars (for a mandibular osteotomy)

42
Q

Extractions: What would you do in cases of previous loss of upper central incisor? (previous trauma usually)

A

Preserve space
–space maintainer - can put in a prosthetic tooth into the brace
Close space
–crown lateral incisor - don’t tend to move lateral into the space due to poor aesthetics and poor gingival condition

43
Q

Extractions: What are the problems with lower incisor extractions?

A
  • Compromise the occlusion - 3 lower incisors against 4 upper incisors
  • Increased overjet and overbite (if patient is already class 1)
  • Increased upper crowding
44
Q

Extractions: When are canines extracted?

A

In cases of gross displacement - usually surgical

- quicker treatment

45
Q

Extractions: What are the problems with canine extractions?

A

Upper arch

  • space between 2 and 4 opens
  • Poor aesthetics

Lower arch
poor contact between 2 and 4 - black triangle in the area

46
Q

Extractions: Why is extraction of first premolars good?

A
  • give space to relieve crowding at front and can move buccal segments
  • can retract anterior teeth or bring posterior teeth forward
47
Q

Extractions: What can headgear do to molars?

A

hold upper molars where they are or move them distal

finger springs keep the 6’s back

48
Q

Extractions: What are the problems with first premolar extractions?

A

May give too much space
 7mm per tooth

(Possible effect on patient profile)
 poor treatment planning
 poor mechanics
 No evidence

49
Q

Extractions: What are the effects of second premolar extraction?

A
  • doesn’t give as much space as the first premolars

but more meisial movement of buccal segments (closes space from behind)

50
Q

Extractions: What are the effects of molar extraction?

A

Removes teeth of poor prognosis

Extended treatment time

51
Q

Extractions: What are the effects of second molar extraction?

A

Third molars are impacted
7s of poor prognosis
Ca not be used to resolve crowding anteriorlymolar extraction?
- rarely done as doesn’t give enough space

52
Q

Treatment of class 1 malocclusion: What is a class 1 incisor relationship?

A
  • can never get a class 1 if you have an overbite

Lower incisor occludes at or below the upper incisor cingulum plateau

53
Q

Treatment of class 1 malocclusion: What malocclusions occur in class 1’s?

A

crowding
spacing
displaced teeth

54
Q

Treatment of class 1 malocclusion: Why can crowding happen?

A

 Imbalance in:

 jaw size
 tooth size
 arch perimeter

55
Q

Treatment of class 1 malocclusion: How can crowding be solved?

A
  1. Expansion - expand the arch (not distillasization) - removable or fixed appliances
  2. Distal movement
  3. Enamel stripping 4. Extraction
56
Q

Treatment of class 1 malocclusion: What are the problems with expansion?

A

 Relapse -  Average expansion = 3.7mm  Average relapse = 2mm
Fenestration of labial plate
 Aesthetics

57
Q

Treatment of class 1 malocclusion: How does a quad helix work?

A

bands on molars
2 arms to 5 and 4
quad in the roof of mouth
expanded outside of mouth and pushed into mouth when fitted - provides force on palette

58
Q

Treatment of class 1 malocclusion: What is the Damon system?

A

self ligating system
- everything expands to automatically accommodate all teeth
no long term studies to check it

59
Q

Treatment of class 1 malocclusion: What is the % success of non extraction arch development?

A

10% long term success

premolar extraction - 30% long term success

60
Q

Treatment of class 1 malocclusion: What are the limits of expansion?

A

buccal segements - 3mm max stable
incisors - 2mm forward max stable
canine - cannot be moved buccally without relapse

61
Q

Treatment of class 1 malocclusion: What is fenestration of labial plate?

A

move roots of the teeth out of bone

62
Q

Treatment of class 1 malocclusion: What may happen if you signifcantly procline or retrocline teeth?

A

recession

relapse

63
Q

Treatment of class 1 malocclusion: how does distal movement solve crowding?

A

Retract upper 6 and 7 if erupted
retract premolars and canine
align canine

headgear for upper arch
 non-compliance appliances
 Temporary Anchorage Devices

(Lower arch)
 lip bumper

64
Q

Treatment of class 1 malocclusion: what are mid palatal plants/ TADs?

A

pushes 6’s back

TADS - screws in-between roots of teeth, push coil between 4 and 6 to distalise the 6 without other teeth moving?

65
Q

Treatment of class 1 malocclusion: When do you consider distal movement of upper buccal segments?

A

 Well-aligned lower arch  Half-unit Class II molars  Co-operative patient

66
Q

Treatment of class 1 malocclusion: How does enamel stripping work?

A

 abrasive metal strips  air-rotor stripping

Remove up to 0.25mm enamel from contact points

causes inter proximal reduction

need to strip after alignment

67
Q

Treatment of class 1 malocclusion: What are the 3 types of spacing?

A

Upper midline diastema - prominent labial frenum
Generalised spacing
Missing teeth

68
Q

Treatment of class 1 malocclusion: Why may generalised spacing happen?

A

jaws too big
teeth too small
can be restored with restorative work

69
Q

Treatment of class 1 malocclusion: What tooth is most likely to be missing?

A

lateral incisors most common missing teeth

70
Q

Treatment of class 1 malocclusion: What 3 things are considered when teeth are missing and you want to open or close space?

A

 malocclusion
 molar relationship
space present

71
Q

Treatment of class 1 malocclusion: When would you open or close the space?

A 
clASS 1 MOLARS - open space
class 2 molars - close space
72
Q

Treatment of class 1 malocclusion: What is the general rule for missing upper lateral incisors?

A 
class 2 incisors - close space
class 3 incisors - open space
73
Q

Treatment of class 1 malocclusion: What is the most common displaced tooth?

A

upper permanent canine

74
Q

Treatment of class 1 malocclusion: Where are canines most likely to impact?

A

Palatal 85%

buccal - 15%

75
Q

Treatment of class 1 malocclusion: What do you do with palatal impaction?

A
  1. Leave in situ, monitor
  2. Extract
  3. Expose and align
  4. Transplant
76
Q

Treatment of class 1 malocclusion: What do you do with buccal impaction?

A

open exposure - apically repositioned flap

closed exposure - attach gold chain

77
Q

Treatment of class II Malocclusions: What is a class II malocclusion?

A

Lower incisor occludes behind upper incisor cingulum plateau

78
Q

Treatment of class II Malocclusions: What is the main limiting factor in class 2 treatments?

A

Skeletal pattern

79
Q

Treatment of class II Malocclusions: What appliance is used for a growing patient with a class II div 1?

A

functional appliance

orthodontic camouflage

80
Q

Treatment of class II Malocclusions: What appliance is used for a non-growing patient with a class II div 1?

A

orthodontic camouflage

Orthognathic surgery

81
Q

Treatment of class II Malocclusions: Which type of appliance is good at reducing overjets?

A

Functional appliances

then straight wire can be used

82
Q

Treatment of class II Malocclusions: What sort of functional appliances exist and for what cases?

A

Activators - mild non crowded cases

Twin block - severe or crowded cases

83
Q

Treatment of class II Malocclusions: What is anchorage?

A

Control of unwanted tooth movement

84
Q

Treatment of class II Malocclusions: What are the keys to planning anchorage?

A

lower arch crowding

molar and canine relationship

85
Q

Treatment of class II Malocclusions: What are non-compliance appliances?

A

pendulum appliance

distal jet

Mid palatal implant

Miniscrew implant

86
Q

First permanent molar: What are the implications for the loss of first permanent molars?

A
  • Disturbs occlusion - especially if lower arch extraction
  • Orthodontic treatment prolonged
  • Treatment maybe more difficult
  • Patients unsuitable - high caries, doubtful cooperation
87
Q

First permanent molar: What factors do you need to consider when extracting first permanent molar to determine success?

A
  • Degree of crowding
  • Upper or lower
  • Timing of extraction
  • Balancing (same arch) or compensating extractions (opposite arch)?
88
Q

First permanent molar: Why are lower 6 eruptions more of a problem than upper 6?

A
  1. 7 Tilts mesially
  2. 7 Rotates mesio-lingually
  3. 7 Leans lingually
  4. Over-eruption of upper 6, prevents 7 from drifting forwards
89
Q

First permanent molar: What are the options for one or more poor quality first permanent molars? (timing of extraction)

A
  • Immediate extraction?

* Retain - orthodontics later?

90
Q

First permanent molar: What can happen if lower 6 is extracted too late?

A

Minimal spontaneous space closure

91
Q

First permanent molar: What happens if lower 6 is extracted too early?

A

Lower 5 can become ectopic or drift distally

92
Q

First permanent molar: When is the ideal time to extract lower 6’s?

A

•Bifurcation of lower 7 visible - will drift forward to fit space

Possible other favourable factors:
• Lower 5 engaged in birfurcation of E
• Lower 7 mesially angulated
• Lower 8 present

93
Q

First permanent molar: What does balancing or compensating extractions mean?

A

Balancing – Extraction in the same arch on the opposite side (don’t balance 6s - consider extraction of upper molar if lower is extracted to avoid problems with 7’s )

Compensating – Extraction in the opposite arch on the same side

94
Q

First permanent molar: How can a class II affect first molar extraction?

A

• Extract first molars early to reduce the overjet
if needed extract 4’s
• Correct Class II with functional appliance OR
• Maintain and incorporate into ortho Rx

95
Q

First permanent molar: How can a class III affect first molar extraction?

A

• Seek opinion, orthodontic treatment can be delayed to assess mandibular growth. Timing of extraction can alter if orthognathic surgery is planned.
- 6’s may be needed to attach the brace to

96
Q

First permanent molar: What are the general guidelines for extracting first permanent molar?

A

if they have:

  • Class I occlusion
  • Mild incisor crowding
  • All permanent teeth present
97
Q

What is alveolar necking? LOOK UP

A

a lot of bone loss - less tendency for the teeth to move forward, get some resorption

98
Q

What may extraction of 6’s may also prevent?

A

impacted 8’s

IODC (8 decks)

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