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
2
Q
What is malocclusion?
A
Variation from ideal occlusion which has dental health and/or psychosocial implications for the individual
3
Q
What 3 types of orthodontic appliances exist?
A
Fixed, functional and removable
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.
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).
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.
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’
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)
9
Q
Materials in orthodontics: How do you minimise exposure of PMMA?
A
- Wear gloves
- Ventilation
- Use down-draught extraction
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
11
Q
Materials in orthodontics: How are mechanical properties of these wires generally assessed?
A
- tensile,
* bending, and • torsionaltests
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.
13
Q
Materials in orthodontics: Why are stainless steel wires popular?
A
- formability,
- biocompatibility and environmental stability,
- stiffness,
- resilience, and
- low cost
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)
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.
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’
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.
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
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.
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.
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
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.
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
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.
25
Materials in orthodontics: What is the slope of the stress/strain curve? (check slide)
The elastic modulus (E) - proportional to the stiffness
26
Materials in orthodontics: What is resilience?
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.
27
Materials in orthodontics: What is formability?
the amount of permanent deformation that a material can withstand before breaking.
28
Materials in orthodontics: What unique properties does nitinol exhibit?
"Shape Memory" and "Super- elasticity".
29
Materials in orthodontics: What is shape memory?
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
30
Materials in orthodontics: What is superelasticity?
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
31
Materials in orthodontics: What is the constancy of stress?
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
32
Materials in orthodontics: What type of bonding do brackets use?
most successful - mechanical retention
- have to make sure you can get them off so don't use the strongest material
33
Materials in orthodontics: What is adhesion?
• The force of attraction between the molecules or atoms on two different surfaces as they are brought into contact.
34
Materials in orthodontics: What are the different types of adhesion?
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.
35
Extractions: What three ways can you expand the arch?
lateral, anterior, posterior, buccal segments back distally
36
Extractions: What does anterior movement during expansion do to the incisors?
Bimaxillary proclincation
37
Extractions: What are the problems with bimaxillary proclination?
appearance
stability
periodontal health - forces won't go through the tooth properly
38
Extractions: What can happen in non extraction cases?
Bimaxillary proclincation
| 7 and 8s impacted
39
Extractions: What are the reasons for extraction in orthodontics?
```
Relieve crowding
Correct incisor relationship
- Reduce an overjet(Class II)
- Camouflage in Class III
Overbite correction
To correct centrelines - can shift teeth round
Anchorage
```
40
Extractions: What are the principles of extractions in orthodontics?
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
Extractions: What teeth are most common for extraction?
Premolars (most common)
first premolar
second premolar
Third molars (for a mandibular osteotomy)
42
Extractions: What would you do in cases of previous loss of upper central incisor? (previous trauma usually)
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
Extractions: What are the problems with lower incisor extractions?
* Compromise the occlusion - 3 lower incisors against 4 upper incisors
* Increased overjet and overbite (if patient is already class 1)
* Increased upper crowding
44
Extractions: When are canines extracted?
In cases of gross displacement - usually surgical
| - quicker treatment
45
Extractions: What are the problems with canine extractions?
Upper arch
- space between 2 and 4 opens
- Poor aesthetics
Lower arch
poor contact between 2 and 4 - black triangle in the area
46
Extractions: Why is extraction of first premolars good?
- give space to relieve crowding at front and can move buccal segments
- can retract anterior teeth or bring posterior teeth forward
47
Extractions: What can headgear do to molars?
hold upper molars where they are or move them distal
finger springs keep the 6's back
48
Extractions: What are the problems with first premolar extractions?
May give too much space
7mm per tooth
(Possible effect on patient profile)
poor treatment planning
poor mechanics
No evidence
49
Extractions: What are the effects of second premolar extraction?
- doesn't give as much space as the first premolars
| but more meisial movement of buccal segments (closes space from behind)
50
Extractions: What are the effects of molar extraction?
Removes teeth of poor prognosis
| Extended treatment time
51
Extractions: What are the effects of second molar extraction?
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
Treatment of class 1 malocclusion: What is a class 1 incisor relationship?
- can never get a class 1 if you have an overbite
Lower incisor occludes at or below the upper incisor cingulum plateau
53
Treatment of class 1 malocclusion: What malocclusions occur in class 1's?
crowding
spacing
displaced teeth
54
Treatment of class 1 malocclusion: Why can crowding happen?
Imbalance in:
jaw size
tooth size
arch perimeter
55
Treatment of class 1 malocclusion: How can crowding be solved?
1. Expansion - expand the arch (not distillasization) - removable or fixed appliances
2. Distal movement
3. Enamel stripping 4. Extraction
56
Treatment of class 1 malocclusion: What are the problems with expansion?
Relapse - Average expansion = 3.7mm Average relapse = 2mm
Fenestration of labial plate
Aesthetics
57
Treatment of class 1 malocclusion: How does a quad helix work?
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
Treatment of class 1 malocclusion: What is the Damon system?
self ligating system
- everything expands to automatically accommodate all teeth
no long term studies to check it
59
Treatment of class 1 malocclusion: What is the % success of non extraction arch development?
10% long term success
premolar extraction - 30% long term success
60
Treatment of class 1 malocclusion: What are the limits of expansion?
buccal segements - 3mm max stable
incisors - 2mm forward max stable
canine - cannot be moved buccally without relapse
61
Treatment of class 1 malocclusion: What is fenestration of labial plate?
move roots of the teeth out of bone
62
Treatment of class 1 malocclusion: What may happen if you signifcantly procline or retrocline teeth?
recession
| relapse
63
Treatment of class 1 malocclusion: how does distal movement solve crowding?
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
Treatment of class 1 malocclusion: what are mid palatal plants/ TADs?
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
Treatment of class 1 malocclusion: When do you consider distal movement of upper buccal segments?
Well-aligned lower arch Half-unit Class II molars Co-operative patient
66
Treatment of class 1 malocclusion: How does enamel stripping work?
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
Treatment of class 1 malocclusion: What are the 3 types of spacing?
Upper midline diastema - prominent labial frenum
Generalised spacing
Missing teeth
68
Treatment of class 1 malocclusion: Why may generalised spacing happen?
jaws too big
teeth too small
can be restored with restorative work
69
Treatment of class 1 malocclusion: What tooth is most likely to be missing?
lateral incisors most common missing teeth
70
Treatment of class 1 malocclusion: What 3 things are considered when teeth are missing and you want to open or close space?
malocclusion
molar relationship
space present
71
Treatment of class 1 malocclusion: When would you open or close the space?
```
clASS 1 MOLARS - open space
class 2 molars - close space
```
72
Treatment of class 1 malocclusion: What is the general rule for missing upper lateral incisors?
```
class 2 incisors - close space
class 3 incisors - open space
```
73
Treatment of class 1 malocclusion: What is the most common displaced tooth?
upper permanent canine
74
Treatment of class 1 malocclusion: Where are canines most likely to impact?
Palatal 85%
| buccal - 15%
75
Treatment of class 1 malocclusion: What do you do with palatal impaction?
1. Leave in situ, monitor
2. Extract
3. Expose and align
4. Transplant
76
Treatment of class 1 malocclusion: What do you do with buccal impaction?
open exposure - apically repositioned flap
| closed exposure - attach gold chain
77
Treatment of class II Malocclusions: What is a class II malocclusion?
Lower incisor occludes behind upper incisor cingulum plateau
78
Treatment of class II Malocclusions: What is the main limiting factor in class 2 treatments?
Skeletal pattern
79
Treatment of class II Malocclusions: What appliance is used for a growing patient with a class II div 1?
functional appliance
orthodontic camouflage
80
Treatment of class II Malocclusions: What appliance is used for a non-growing patient with a class II div 1?
orthodontic camouflage
Orthognathic surgery
81
Treatment of class II Malocclusions: Which type of appliance is good at reducing overjets?
Functional appliances
then straight wire can be used
82
Treatment of class II Malocclusions: What sort of functional appliances exist and for what cases?
Activators - mild non crowded cases
Twin block - severe or crowded cases
83
Treatment of class II Malocclusions: What is anchorage?
Control of unwanted tooth movement
84
Treatment of class II Malocclusions: What are the keys to planning anchorage?
lower arch crowding
molar and canine relationship
85
Treatment of class II Malocclusions: What are non-compliance appliances?
pendulum appliance
distal jet
Mid palatal implant
Miniscrew implant
86
First permanent molar: What are the implications for the loss of first permanent molars?
* Disturbs occlusion - especially if lower arch extraction
* Orthodontic treatment prolonged
* Treatment maybe more difficult
* Patients unsuitable - high caries, doubtful cooperation
87
First permanent molar: What factors do you need to consider when extracting first permanent molar to determine success?
* Degree of crowding
* Upper or lower
* Timing of extraction
* Balancing (same arch) or compensating extractions (opposite arch)?
88
First permanent molar: Why are lower 6 eruptions more of a problem than upper 6?
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
First permanent molar: What are the options for one or more poor quality first permanent molars? (timing of extraction)
* Immediate extraction?
| * Retain - orthodontics later?
90
First permanent molar: What can happen if lower 6 is extracted too late?
Minimal spontaneous space closure
91
First permanent molar: What happens if lower 6 is extracted too early?
Lower 5 can become ectopic or drift distally
92
First permanent molar: When is the ideal time to extract lower 6's?
•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
First permanent molar: What does balancing or compensating extractions mean?
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
First permanent molar: How can a class II affect first molar extraction?
• 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
First permanent molar: How can a class III affect first molar extraction?
• 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
First permanent molar: What are the general guidelines for extracting first permanent molar?
if they have:
* Class I occlusion
* Mild incisor crowding
* All permanent teeth present
97
What is alveolar necking? LOOK UP
a lot of bone loss - less tendency for the teeth to move forward, get some resorption
98
What may extraction of 6's may also prevent?
impacted 8's
