Orthodontics Flashcards
(145 cards)
1
Q
How much space, on average, is required for the mandibular arch from mesial of 6 to distal of 2?
A
21mm
2
Q
How much space, on average, is required for the maxillary arch from mesial of 6 to distal of 2?
A
22mm
3
Q
What is there an increased risk of with peg shaped lateral incisors?
A
That the canines will be ectopic
4
Q
By what age should the upper 3’s definitely be palpable?
A
11 years old
5
Q
What are the three reasons for premature loss of deciduous teeth?
A
- Caries
- Balancing and compensating extractions
- Trauma
6
Q
What is the most frequent complication of premature loss of deciduous teeth?
A
Mesial drifting of 6’s resulting in premolar crowding
7
Q
What 4 dental features can you typically get with a long-term habit such as thumb-sucking?
A
- proclined upper incisors
- retroclined lower incisors
- buccal segment crossbites
- reduced overbite or anterior open bite
8
Q
Why can you get buccal segment cross bites from sucking your thumb?
A
Because sucking of the thumb puts pressure on the palate and can cause the upper arch to narrow
9
Q
How can habits such as thumb sucking be managed?
A
- Deterrent devices/habit breakers
- Elastoplast on finger (check allergy)
- Encouragement
- Nail varnish (doesn’t taste nice)
10
Q
What % of 6-year olds have a median diastema?
A
98%
11
Q
If median diastema is minimal (<3mm) what is the management?
A
Nothing. Likely to reduce on its own as permanent teeth erupt
12
Q
If median diastema is large (>3mm) what is the management?
A
A fixed appliance or permanent retention of midline diastema
13
Q
What is the management for impacted central incisors?
A
- Remove obstruction
- Expose
- URA to align
14
Q
If extracting primary incisors, is there a need for balancing extractions?
A
No
15
Q
If extracting primary canines, is there a need for balancing extractions?
A
Balancing extraction only if the dentition is deemed very crowded, as this will have an effect on centre line if only unilateral extraction.
16
Q
If extracting primary first molars, is there a need for balancing extractions?
A
Yes, this may necessitate a balancing extraction in a crowded arch due to risk of centre-line shift.
17
Q
If extracting primary second molars, is there a need for balancing extractions?
A
No balancing extraction required as this will have no significant effect on centreline
18
Q
Why should consideration be given to fitting a space maintainer when a primary second molar has to be extracted?
A
Because this extraction may allow forward movement and tilting of the adjacent first permanent molar.
19
Q
What is a key contra-indication to fitting a space maintainer?
A
Poor OH
20
Q
Describe a balancing extraction.
A
Removal of a first permanent molar from the opposite side of the same dental arch
21
Q
Describe a compensating extraction.
A
Removal of a first permanent molar from the opposing quadrant
22
Q
What arch should compensating extractions not be carried out on?
A
Lower arch
23
Q
Why are compensating extractions needed?
A
If unopposed, upper molars may overupt and prevent the favourable mesial movement of the lower second permanent molar due to malocclusion.
24
Q
How can thumb sucking lead to an increased risk of dental trauma?
A
Cause an increased overjet which in turn can be linked to an increased risk of trauma to the maxillary incisors
25
What are the 4 management options for ectopic first permanent molars?
1. Monitoring
2. Separation
3. Active appliance
4. Extraction of the second primary molar and appliance therapy
26
If ectopic first permanent molars have a mild degree of angulation causing impaction. What is the most appropriate treatment?
Placement of a separator to cause disimpaction
27
If ectopic first permanent molars are not accessible and the degree of impaction is more severe. What is the most appropriate treatment?
Active appliance placement, to produce a force to distalize the first permanent molar.
28
If ectopic first permanent molars are not accessible and the degree of impaction is more severe, and the second primary molar has poor prognosis with severe resorption, caries or abscess. What is the most appropriate treatment?
Extraction of the second primary molar and appliance therapy
29
How is an anterior dental cross-bite treated?
Tipping the affected maxillary incisors labially over the opposing mandibular tooth until stable relationship is reached
30
How is a posterior dental cross-bite treated?
Tipping the affected tooth or can involve arch expansion
31
What are the three tx options for anterior dental crossbite?
1. inclined bite planes
2. Removable appliance with bite plane and a spring or screw in place to procline the incisor
3. Fixed appliance bonded to anterior teeth and molars
32
What are the 4 treatment option for posterior dental cross-bite?
1. Extraction of over-retained primary teeth
2. Elastics can be used to correct single molar posterior cross-bites
3. Palatal expansion
4. Removable appliances such as hawley appliance with a jack screw
33
What is an eruption cyst?
An accumulation of fluid or blood in the follicular space overlying the crown of an erupting tooth
34
What is the rationale of balancing extractions?
To avoid centreline shift problems
35
What is the rationale for compensating extractions?
To maintain occlusal relationships between the arches
36
How do infra-occluded teeth ankylose?
“Resorption of deciduous teeth is not a continuous process. Resorption is interchanged with periods of repair. If repair has temporary predominance, this can result in akylosis.”
37
Where a permanent successor exists, is extraction of an infra-occluded primary tooth necessary? Under what conditions is it necessary?
Not always necessary.
Necessary under following conditions:
1. Danger of tooth disappearing sub-gingivally
2. Root formation of permanent tooth is near completion (eruption tends to slow at this point)
38
What is the most common reason for non-appearance of a maxillary central incisor?
Supernumerary tooth
39
At what point do you know a midline diastema is likely to persist?
After eruption of the canines, it is unlikely to close spontaneously
40
Define an appliance used to utilise, eliminate or guide the forces of muscles of mastication, tooth eruption and growth to correct a malocclusion.
Functional appliance (e.g. twin block)
41
How do functional appliances work?
By posturing the mandible forwards in the growing patient
42
What skeletal discrepancy and malocclusion can a functional appliances treat?
Most commonly mild to moderate class II skeletal discrepancy, and class II div I malocclusion.
With minor alterations can be used to treat class II div II
43
Why does use of a functional appliance often involve a phase of fixed appliances?
Because functional appliances are most effective at changing the anteroposterior occlusion between the upper and lower arches, they are not as effective at correcting tooth irregularities and improving arch alignment- so fixed appliances are often needed.
44
What are the 3 key aims of functional appliance treatment with fixed appliances?
1. Growth modification to improve skeletal pattern
2. Camouflage any remaining skeletal discrepancy with fixed appliances
3. Align the teeth and close the spaces
45
What is a typical dental feature after use of a twin-block appliance for many months?
Posterior lateral open bite
46
How high do the bite blocks on twin blocks need to be? And why?
At least 5mm high, to prevent the patient from both blocks on top of the other.
47
How often should a twin blocks be worn?
Can be worn full time, including during eating. Needs cleaned after meals.
48
Why is posterior lateral open bite at the end of functional appliance use a common side effect? How is it fixed?
Because the posterior teeth are prevented from erupting by the occlusal coverage of the bite blocks.
Any remaining lateral open bites are closed down in the fixed appliances phase of tx.
49
When should a functional appliance be reviewed?
2-3 weeks after fitting
Once the clincian is confident that the patient is wearing the appliance as instructed, reviewed can be 6-10 week intervals
50
Why might it be sensible, at the end of functional appliance treatment, to slightly over correct the overjet reduction to edge-to-edge?
Due to risk of relapse
51
What is the average failure rate for functional appliances?
20-30%
52
What is the most common reason for functional appliances failure?
Lack of compliance
53
What are the two types of bone formation in the face?
1. Intramembranous ossification
2. Endochondral ossification
54
What type of ossification leads to formation of the maxilla and mandible (except condylar cartilage)?
Intra-membranous ossification
55
What type of ossification leads to formation of condylar cartilage and nasal septal cartilage?
Endochondral ossification
56
What part of the mandible does a functional appliance utilise to lengthen the mandible?
Cone shaped cartilage on end of condyle. This cartilage is not yet bone in growing stages so can be activates and help mandible lengthen.
57
Which growth spurt is most important/ideally utilised in orthodontic treatment?
Pre-pubertal growth spurt
58
What are the 4 skeletal effects of a functional appliance?
- causes forward displacement of mandible
- places a backwards force on the maxillary arch
- accelerates condylar growth
- redirects condylar growth
59
What are the 3 dentoalveolar effects of functional appliances?
1. Retracts upper teeth
2. Proclined lower teeth
3. Different rates of tooth eruption
60
On average, how much skeletal correction will take place following functional appliance use?
30-40%
61
On average how much dental correction will take place following functional appliance use?
60%
62
What are the 3 active components that can be used on a functional appliance? State their functions.
1. Adam’s clasp for retention
2. Labial bow for retention and space closure
3. Expansion screw to widen upper arch
63
63
What are 5 contraindications to a functional appliance?
1. Poor motivation
2. Age >14
3. Poor dental health
4. Condylar disease e.g. juvenile RA
5. Proclined lower incisors
64
What is the treatment for class II maxillary excess?
Headgear
65
What is the treatment for class III maxillary deficiency?
Face mask (which pull maxilla forward, rotates mandible downwards and backwards)
66
Long term, post tx, what is the minimum a patient should wear their retainer for per week?
1-2 nights per week
67
After adjustment, how long can the patient expect to feel some pain/discomfort from their fixed appliance?
3-5 days after each adjustment
68
How often should a patient with a fixed appliance be brushing their teeth per day?
3x daily
69
How often will a patient with a fixed appliance need an appointment?
Every one to two months
70
Why do patients feel pain/discomfort for a few days after a fixed appliance is fitted or adjusted?
As a result of the physiological changes occurring within the PDL. The PDL is compressed and stretched which causes the cells to release chemical messengers that initiate an inflammatory cascade to cause the pattern of bone resorption and deposition required for tooth movement.
71
If components of the brace start to irritate soft tissues, what can be done as an immediate measure in general practice?
Placement of orthodontic relief wax to cover prominent components
72
What is the most common allergy in orthodontics?
Nickel allergy
73
How can an orthodontic problem list be classified into 6 sections?
1. The patients concerns
2. Facial and smile aesthetics
3. Alignment and symmetry within each arch
4. Skeletal and dental relationships in the transverse plane
5. Skeletal and dental relationships in the anteroposterior plane
6. Skeletal and dental relationships in the vertical plane
74
Define, the process of determining the amount of space required.
Space analysis
75
What does treatment with “orthodontic camouflage” mean?
That the skeletal discrepancy is accepted, but the labial teeth are moved into a class 1 relationship
76
If teeth are extracted in the upper arch, but not in the lower, what relationship will the molars be in?
Class II relationship
77
If teeth are extracted in the lower arch, but not in the upper, what relationship will the molars be in?
Class III relationship
78
Why are planned extractions needed in the upper arch?
To allow retraction of the upper labial segment to camouflage the underlying skeletal pattern
79
Why are planned extractions needed in the lower arch?
To allow retraction of the lower labial segment
80
What is anchorage planning?
It is about resisting unwanted tooth movement of other teeth in an arch that do not need to move as part of ortho tx
81
How much space is required in the dental arch for every millimetre of incisor retraction?
2mm of space
82
What are often the teeth of choice to extract when space requirement is moderate to severe?
First premolars
83
What can be a consequence of early loss of second deciduous molars?
Crowding of the second premolars palatally in the upper and lingually in the lower
84
How much space is created in the dental arch for every 1mm of posterior arch expansion?
0.5mm
85
How can space be created in an arch? Name 5 ways.
1. Extractions
2. Distal movement of molars in the upper arch
3. Enamel stripping
4. expansion
5. Proclination of incisors
86
How wide is a premolar on average?
7mm
87
What is the most commonly used active component?
Springs
88
What is the formula for the force exerted by an orthodontic spring?
F=dr^4/l^3
89
In this formula:
F=dr^4/l^3
What does F, d, r and l stand for?
F= force exerted by orthodontic spring
D= deflection of the spring on activation
R= radius of the wire
L= length of the spring
90
By how much is the force delivered by a spring increased if you double the radius of the wire?
By a factor of 16
91
How much space is created between the two sections of an appliance for each quarter turn of an expansion screw?
0.25mm
92
What limits the activation of an expansion screw?
The width of the PDL, to exceed the would result in crushing the ligament cells and cessation of tooth movement
93
Define, a clasp that engages undercuts present on a fully erupted first permanent molar at the junctions of the mesial and distal surfaces with the buccal aspect of the tooth.
Adam’s clasp
94
What width of wire and material is used for an Adam’s clasp? What amount of undercut should it engage?
0.7mm stainless steel wire, should engage about 1mm of undercut
95
What was the “Southend clasp” designed to engage?
Utilise the undercut beneath the contact point between two incisors
96
What was the “ball-ended clasp” designed to engage?
The undercut interproximally
97
What was the “plint clasp” designed to engage?
Under the tube assembly on a molar band or bracket
98
What is the function of a labial bow?
Anterior retention
99
What are the two indications for a bite-plane to be prescribed?
1. When the overbite needs to be reduced by eruption of the lower buccal segment teeth
2. Elimination of possible occlusal interferences is necessary to allow tooth movement to occur
100
What type of spring is commonly used to move a single incisor buccaly?
Z-spring
101
What width of wire should be used to fabricate a z-spring?
0.5mm
102
How is a z-spring activated?
By pulling the spring about 1-2mm away from the baseplate at an angle approximately 45 degrees in the direction of desired movement
103
How often in the monitoring process should patients wearing an active removable appliance be seen?
Around every 4 weeks
104
What should normal tooth movement during orthodontic treatment per month be for a child?
Approximately 1mm per month
105
Via what mechanisms do fixed orthodntic appliances adhere to teeth?
Chemical or micro-mechanical attachment
106
What type of additional movement is achieved by using rectangular arch wire in rectangular slot on a fixed appliance?
Control of the root apex in the buccal-lingual direction, known as torque.
107
What type of movements are achieved by using round arch wire in rectangular slot on a fixed appliance?
Tipping (bucco-lingually) and vertical tooth movements
108
What is the relationship between the fit of the arch wire and bracket slot, and the degree of control of movement?
“The closer the fit between the arch wire and the bracket slot, the greater the degree of control”
109
Individual bends can be placed into orthodontic wires to induce desired tooth movements. What is meant by a first-order bend?
“In/out bends to compensate for the varying thickness of the individual teeth”
110
Individual bends can be placed into orthodontic wires to induce desired tooth movements. What is meant by a second-order bend?
“Angulation or tip bends placed in the vertical plane relative to the long axis of the tooth to allow better mesio-distal angulation/tilt.”
111
Individual bends can be placed into orthodontic wires to induce desired tooth movements. What is meant by a third-order bend?
“Inclination or torque bends relative to the true vertical and can only be produced with rectangular arch wire. They are generated by twisting the plane of the wire where it inserts into the bracket slot, resulting in buccolingual force on the root apex.”
112
What are the 6 indications for use of a fixed appliance?
1. Correction of mild to moderate skeletal discrepancies
2. Intrusion/extrusion of teeth
3. Correction of rotations
4. Overbite reduction by intrusion of incisors
5. Multiple tooth movements required within one arch
6. Active closure of extraction spaces (or Hypodontia spaces)
113
What is now the one use of orthodontic bands?
“Only routinely used on molars when the bond strength of direct attachments is insufficient for the planned forces to be applied or where additional customised laboratory made components need to be utilised”
114
What is an orthodontic band?
“A metal ring which encompasses the tooth onto which an orthodontic attachment is welded/soldered”
115
What is the purpose of elastomeric modules?
To secure the arch wire into the arch wire slot
116
What archwire is describe:
0.016 inches (0.4mm)
Round arch-wire
117
What arch-wire is described:
0.016 x 0.022 inches (0.4 x 0.55mm)
Rectangular arch-wire
118
What is the effect of increasing the diameter of an arch-wire on force applied to teeth?
increases force against teeth
119
Why do removable appliances inherently provide more anchorage than fixed appliances?
Because they cover the palate
120
What shape of wire allows for more apical control of teeth?
Rectangular wire
121
What is orthodontic tooth movements reliant on?
Activity of the bone cells (osteoclasts and osteoblasts) which are responsible for the bone resorption and deposition
122
What are the 8 advantages of removable appliances?
1. Can be removed for OH and sports
2. Increased anchorage
3. Easy to adjust
4. Less iatrogenic damage
5. Baseplate can be modified
6. Good at moving blocks of teeth
7. Can be passive
8. Lower cost
123
What are the 6 disadvantages of removable appliances?
1. Need good patient compliance
2. Limited movements- tipping
3. Affects speech
4. Technician required
5. Lower appliances difficult to tolerate
6. Inefficient at multiple tooth movements
124
What material are springs constructed from?
18/8 Austenitic stainless steel
125
Increasing the radius of the wire by 2 will result in what increase in force applied?
16 times increase in force applied
126
Increasing the length of the spring by 2 will result in what reduction in force applied?
8x reduction in force applied
127
How much force does it take for a spring to induce single tooth movement?
Between 25-40 grams per tooth
128
When considering placement of a spring, how could you place it to reduce the tipping tendency to a minimum?
Apply force close to the gingival margin of the tooth
129
How can we reinforce anchorage with URA’s? Name 5 ways
1. Clasp more teeth
2. Move only one or two teeth at a time
3. Use lighter forces
4. Occlusal capping
5. Add headgear
130
Define, clear removable plastic appliances which can produce small tooth movements?
Aligned
131
Where canines are buccaly placed, what active component can be used to push them palatally/distally back into the line of the arch?
Buccal canine retractors
132
What position should the helix of a spring be placed?
It must be placed half-way between the starting position of the tooth and the desired finishing position
133
What will happen if the helix of a clasp is placed too far anteriorly?
The tooth will move Palatally
134
What will happen if the helix of a clasp is placed too far distally?
The tooth will move buccaly
135
Why is it necessary to reduce the overbite before reducing the overjet?
Because as incisors tip, the lower incisors prevent further overjet reduction due to increasing overbite.
By incorporating an anterior bite plane, the overjet can be successfully reduced without increasing the overbite as incisors tip palatally.
136
What is ligation?
“The process of tying the brackets and wires together with modules or metal wires
137
What is the need for ligation?
It helps to distribute occlusal forces used to straighten teeth
138
What are the 5 indications for fixed appliance?
1. Multiple tooth movements needed
2. Rotations
3. Bodily movement
4. Space closure
5. Lower arch treatment
139
What are the 4 contra-Indications for a fixed appliance?
1. Poor oral hygiene
2. Active caries
3. Poor motivation
4. Poor dietary control- hard/sticky foods, sugars and acids
140
What is the difference between standard edgewise brackets and and straight wire pre-adjusted brackets?
Standard edgewise requires arch wire bends to produce ideal “tip” on teeth
Straight wire have slots cut diagonally across face to build in ideal tooth position (reduces need to put bends in arch wires and provides torque control)
141
What are the three phases to active treatment for fixed appliance?
1. Levelling and aligning
2. Major tooth movement
3. Finishing (detailed alignment)
142
What are the 3 key advantages of NiTi wires?
1. High flexibility
2. Deliver a low force over a long range
3. Shape memory
143
How do you manage a protruding archwire in general practice?
Place brace wax or cut short if possible, until pt can see orthodontist
144
How do you manage a protruding ligature wire in general practice?
Tuck in if possible or place brace wax, until pt can see orthodontist
