Orthodontics

Question 1

How is hard stainless steel wire made?

Answer 1

By drawing the metal in a cold state through a series of dies of successively smaller diameter. This process also causes work hardening, which gives the wire its spring properties.

Question 2

Describe the Bauschinger Effect

Answer 2

When a coil is bent in a wire, it is differentially stretched so that the other surface becomes more work hardened and thus has better spring properties than the inner surface. If the coil is activated in the same direction as the previous bending, its elastic recovery is greater than if it is deflected in the opposite direction

Question 3

What are the four causes of fracture of a stainless steel wire?

Answer 3

*overworking *mechanical abraision *fatigue *weld decay

Question 4

What causes a stainless steel wire to become overworked?

Answer 4

The wire has been excessively overworked by bending and then straightening the wire at the same point creating extreme stresses within the immediate area which can result in fracture

Question 5

What causes mechanical abraision of a stainless steel wire?

Answer 5

This can occur if the wire has been damaged by burs or stones in the finishing process of removable appliances or if the wire has been marked or crushed during the fabrication of components.

Question 6

What are the causes of fatigue in a stainless steel wire?

Answer 6

This can be caused by a repeated straining action eg continually strained to engage a deep undercut with an Adams clasp

Question 7

What causes weld decay in a stainless steel wire?

Answer 7

This is an intergranular corrosion created by overheating the alloy. This causes the chromium carbides to precipitate at the grain boundaries. The oral fluids can now access the surface of the other metals resulting in a galvanic action which weakens the area sufficiently to result in fracture

Question 8

What type of stainless steel wire is commonly used in orthodontics, and what is it composed of?

Answer 8

18/8 austenitic stainless steel wire. *72% iron *18% chromium *8% Nickel *1.7% titanium 0.3% carbon

Question 9

What is the difference between austenite and martensite?

Answer 9

In austenite the average unit cell is a perfect cube. The transformation to martensite sees this cube distorted by interstitial carbon atoms that do not have time to diffuse out during displacive transformation (quenching), so that it is a tiny bit longer than before in one dimension and a little shorter in the other two. A microscopic crystallite of steel is millions of unit cells long. Since all these units face the same direction, distortions of even a fraction percent become magnified into a major mismatch between neighbouring materials. This creates crystal defects within the material similar to work hardening; these defects prevent atoms from sliding past one another in an organised fasion, causing the material to become harder.

Question 10

When writing a lab prescription for an orthodontic appliance, in what order should you make your requests?

Answer 10

*Aim *Active components *Retention *Anchorage *Baseplate

Question 11

Define retention

Answer 11

Retention is the resistance to displacement forces. ie the tongue, mastication, gravity, talking, active components (applied forces can cause displacement)

Question 12

Define anchorage

Answer 12

resistance to unwanted tooth movement

Question 13

List four signs of a digit sucking habit

Answer 13

*proclined upper incisors *retroclined lower incisors *anterior open bite or incomplete open bite *narrow upper arch *unilateral posterior cross bite

Question 14

what causes signs of a digit sucking habit?

Answer 14

the patients thumb/digits are postitioned in the mouth in such a way that they result in the mandible to drop open. This causes the patients tongue to occupy an area that is not deemed normal. The sucking action initiated by the muscular forces in the cheeks narrows the maxillary arch, causing a unilateral posterior cross bite

Question 15

List four ways in which a digit sucking habit can be prevented or stopped

Answer 15

*URA *behavioural management therapy *sock/gloves on hands *plaster on thumb *foul tasting nail polish/hand cream *the use of a dummy

Question 16

Describe the local causes of malocclusion

Answer 16

Localised problem within either arch, usually confined to 1, 2 or several teeth. Can be due to number, size/form, position, soft tissue or a pathology

Question 17

Name four conditions of tooth number that can result in malocclusion

Answer 17

*supernumery *hypodontia *retained primary tooth/teeth *early loss of primary tooth/teeth (extraction or exfoliation)

Question 18

List four supernumary teeth

Answer 18

*conical *tuberculate *supplimental *odontome

Question 19

How can a crossbite be corrected?

Answer 19

A URA with a palatal midline screw

Question 20

how often should a palatal midline screw be activated?

Answer 20

one per month

Question 21

How can a URA be modified for a thumb sucker?

Answer 21

a deterant rake to stop the active habit and prevent relapse after treatment

Question 22

what does the acronym ARAB stand for?

Answer 22

*Active component; induces a force by introducing displacement forces *Retention; resistance to displacement forces *Anchorage; resistance to unwanted tooth movement. Newtons 3rd law (for every action there is an equal and opposite reaction) *Baseplate; to provide anchorage, connector for the retentive components, cohesion, adhesion and stability

Question 23

how would you write a prescription to correct a anterior crossbite?

Answer 23

Aim; please construct a URA to correct an anterior crossbite on tooth 12 A; z-spring on 12 0.5mm HSSW R; 16, 14, 24, 26 Adams clasps 0.7mm HSSW A; yes B; self cure PMMA, posterior bite plane

Question 24

how would you write a prescription to correct a posterior crossbite?

Answer 24

Aim; please construct a URA to expand the upper arch A; midline palatal screw R; 16, 14, 24, 26 Adams clasps 0.7mm HSSW A; reciprocal anchorage B; self cured PMMA, posterior bite plane (most incorporate all posterior teeth to prevent unwanted tooth eruption)

Question 25

list 6 things that can go wrong with the growth and development of teeth

Answer 25

\*increased over jet \*anterior/posterior cross bite \*retained deciduous teeth \*ectopic teeth \*crowding \*trauma \*anterior/lateral open bites \*ankylosis of deciduous teeth \*diastema \*dental asymmetries \*deep overbit \*early loss of deciduous teeth \*impacted first molars \*spacing \*habits \*cysts \*supernummaries

Question 26

Name five potential risks of orthodontic treatment

Answer 26

\*decalcification \*relapse \*root resorption \*pain/discomfort \*soft tissue trauma \*failure to complete treatment \*loss of tooth vitality \*inhale or swallow small components \*candidal infections

Question 27

When should an orthodontic exam be carried out?

Answer 27

\*brief exam at around aged 9 \*comprehensive exam when premolars and canines erupt (11-12 years) \*when older patients first present \*if a malocclusion develops later in life

Question 28

What are Andrews 6 keys?

Answer 28

i) Molar relationship; the distal surface of the disto-buccal cusp of the upper first permanent molar occludes with the mesial surface of the mesio-buccal cusp of the lower second permanent molar ii) crown angulation iii) crown inclination iv) no rotations v) no spaces vi) flat occlusal planes (no curve of spee)

Question 29

Describe FMPA

Answer 29

Frankfort mandibular plane angle; and angle created between teh frankfort horizontal plane and the lower border of the mandible. An increased FMPA if theres a premature meeting point A decreased FMPA if theres a delayed meeting point (should be at the back of the head)

Question 30

Give the Britisd standards institute classification of incisor relationships

Answer 30

\*Class I - the lower incisor edges occlude with or lie immediately below the cingulum plateau of the upper central incisors \*Class II - the lower incisor edges lie posterior to the cingulum plateau of the upper incisors - Division I; the upper incisors are proclined or are of average inclination and there is an INCREASE IN OVERJET - Division II; the UPPER CENTRAL INCISORS ARE RETROCLINED. The OJ is usually minimal or may be increased \*Class III - lower incisor edges lie anterior to the cingulum plateau of the upper incisors. The OJ is reduced or reversed

Question 31

What special investigations should be carried out as part of an orthodontic assessment?

Answer 31

\*radiographs (OPT, maxillary anterior occlusal, lateral cephalogram) \*vitality tests \*study models \*photographs

Question 32

When should you refer patient for orthodontic assessment?

Answer 32

deciduous dentition - CLP, craniofacial abnormalities (if not under MDT care) early mixed dentition - delayed eruption of perm incisors, impaction/FOE of 6s, poor prognosis of 6s, severe class 3, AXB, ectopic canines, pathology late mixed dentition - growth mod in class 2, hypodontia, other routine problems

Question 33

What is ideal occlusion?

Answer 33

anatomically perfect arrangement of teeth

Question 34

what is normal occlusion?

Answer 34

acceptable variation from the ideal

Question 35

what are competent lips?

Answer 35

lips meet with minimal or no muscle activity

Question 36

what are incompetent lips?

Answer 36

evident muscle activity is needed to make lips meet

Question 37

Class I incisor relationship

Answer 37

lower incisors occlude with or lie immediately below cingulum of upper incisors

Question 38

Class II incisor relationship

Answer 38

lower incisor edges lie posterior to cingulum of upper incisors div 1 - max centrals are upright or proclined, OJ increased div 2 - max centrals retroclined, OJ usually decreased, may be increased

Question 39

Class III incisor relationship

Answer 39

lower incisors lie anterior to cingulum of upper incisors, OJ is decreased or reversed

Question 40

OJ and OB

Answer 40

OJ - distance between max and mand incisors in horizontal plane OB - overlap of incisors in vertical plane

Question 41

Complete vs incomplete OB

Answer 41

Complete - lower incisors contact upper incisors or palatal mucosa incomplete - they dont

Question 42

Anterior Open bite

Answer 42

no vertical overlap of incisors when the buccal segments are in contact

Question 43

Dento-alveolar compensation

Answer 43

inclination of the teeth to compensate for underlying skeletal abnormalities

Question 44

Why are study models taken?

Answer 44

clinical records, legal documents, show what could be achievable, show what has changed, show the final treatment position

Question 45

What indices are used for assessing orthodontic need

Answer 45

IOTN - grade 1 - minor malocclusions grade 2 - minimal need grade 3 - moderate need - use the aesthetic component grade 4 - great need grade 5 - very great grade 4/5 get NHS treatment grade 3 needs aesthetic component of 6+

Question 46

How do you assess the dental health component?

Answer 46

MOCDOO Missing teeth overjet crossbite displacement overbite other

Question 47

What are balancing extractions and compensating extractions?

Answer 47

balancing - extraction of same/adjacent tooth on the opposite side of the same arch - preserves symmetry compensating - extract of occluding tooth on the opposing arch. stops over eruption

Question 48

When do you extract FPM?

Answer 48

poor prognosis, need calcification of the furcation of the 7s as optimal. if late - little space closure and 7 tilts mesially if early - get crowding

Question 49

What is a median diastema, what causes it and how to treat

Answer 49

Diastema - gap between central incisors. 6yo = 98%, 12yo = 7% caused by small teeth, absent/peg laterals, midline discrepancy, proclination of ULS, physiological from pressure of developing teeth on roots, fraenum treatment - wait. before 3s erupt and \<3mm after 3s - ortho Tx and retention.

Question 50

Anchorage options for distal movement

Answer 50

temporary anchorage devices are preferred to headgear

Question 51

How to treat buccally displaced max 3s

Answer 51

if crowded - XLA 4s and fixed applicances ortho Tx - buccal canine retractor

Question 52

How to treat impacted canines

Answer 52

1. do nothing and monitor for pathology 2. XLA 3s, restorative to close space (possible trauma from XLA, fixed treatment) 3. open exposure of 3s, ortho Tx to pull down (only if in favourable position, takes a while, fixed Tx and requires good cooperation) 4. autotransplantation - not always successful, can cause ankylosis/necrosis

Question 53

Causes of increased OJ

Answer 53

Skeletal pattern, soft tissues, lip trap, habits, crowding

Question 54

management of increased OJ

Answer 54

fixed appliances for class I and II to retract ULA, +/- XLA. functional appliance in class II to tilt teeth/growth mod ortho camouflage surgical correction if severe

Question 55

Causes of increased OB

Answer 55

normal is 1/2-1/3 overlap. increased is associated with class II/2 only treat if traumatic. decreased LFH, high lower lip, retroclined incisors, increased inter incisal angle

Question 56

how to treat increased OB

Answer 56

FABP to allow molars to erupt procline lower incisors

Question 57

Cause of AOB

Answer 57

vertical growth \> horizontal growth habits, tongue thrust, iatrogenic, CLP

Question 58

Treatment of AOB

Answer 58

cease habit, FPBP

Question 59

Treatment of reverse OJ

Answer 59

1. Do nothing and accept 2. camouflage 3. surgery if ANB below -4 lower incisal angle to mand plan \<80

Question 60

How do you treat XB?

Answer 60

AXB - z spring and FPBP to disclude teeth PXB - quad helix, RME, midline palatal screw and FPBP

Question 61

what are indications for removable appliances?

Answer 61

Require movement of blocs of teeth (PXB) interceptive treatment in mixed dentition (AXB) overbite reduction elimination of occlusal interferences spacemaintainer when passive retention when passive habit deterrent

Question 62

What are the active components of removable appliances and what are they made out of

Answer 62

Z springs - 0.5mm HSSW buccal canine retractor roberts retractor midline palatal screw

Question 63

What are the retentive components of removable appliances and what are they made out of?

Answer 63

Adams cribs - 0.7mm HSSW (0.6mm on deciduous) southend clasp labial bow

Question 64

What are the components of fixed orthodontic appliances?

Answer 64

Bands - on molars Brackets - on each teeth, usually labial surfaces Archwire - active component. NiTi or steel. ligatures - elastic bands or wire to hold archwire in bracket can have class II or class III inter arch bands

Question 65

What is the mode of action of functional appliances? and give an example of one

Answer 65

25% skeletal change, 75% dental tooth tipping twin block appliance

Question 66

What information would you give a patient who has jsut been given their removable appliance?

Answer 66

1. non compliance with significantly increase your treatment time 2. it will feel big, you will salivate more and you will find it hard to talk. practice and these will aleviate 3. wear is 24/7 except contact sports and swimming. clean after meals with toothbrush over filled sink 4. if it breaks, come back 5. some discomfort initially is to be expected - it means it is working. this will reduce 6. emergency contact details

Question 67

How does a twin block appliance work?

Answer 67

retroclination of upper anteriors proclination of lower anteriors mid line palatal screw frequently incorportated to tip posterior teeth to correct PCB re-positions mandible forward reduces muscle action on jaws some skeletal grown from secondary growth centres correcting AOB with posterior bite planes and allows further eruption of anteriors

Question 68

What is dento-alveolar compensation?

Answer 68

a system which attempts to maintain normal inter arch relationships can maintain occlusal relationship even though there are variations in growth and facial pattern

Question 69

What is a supernumerary tooth?

Answer 69

a tooth that is in addition to the regular dentition

Question 70

list the steps involved in class III malocclusion treatment

Answer 70

tooth alignment, eliminating crowding/spaces and XB coordination of the arches decompensate incisors flatten occlusal plane surgical fixatoin port surgery ortho

Question 71

What are the risk/benefits you need to discuss with a patient who has carious 6s but wants ortho Tx?

Answer 71

- removal of 6s, tipping of 7s, loss of bone, spaces - long term prognosis of 6s - LA/GA for Xn, risk of death if GA - risks of ortho Tx

Question 72

What are some risks of orthodontic treatment?

Answer 72

- root resorption - relapse - failure to complete treatment - treatment failure - devitalising of tooth - pain - trauma from components - decalcification of tooth

Question 73

when would you treat an anterior over bite?

Answer 73

if mand displacement on closing if traumatic aesthetics

Question 74

What characteristics of a malocclusion would make it ideal for treatment with a URA

Answer 74

- palatally tipped teeth - 1 or 2 teeth needing movement - class 1 molar relationship - space

Question 75

What are causes of ectopic canines?

Answer 75

- ectopic crypt position - absent laterals - crowding - retention of deciduous canine - genetics

Question 76

How do you monitor the eruption of canines?

Answer 76

palpation from 9/10 look at inclination of 2s mobility of cs colour of cs

Question 77

What are the signs of impacted canines?

Answer 77

- delayed eruption - retained Cs - unable to palpate - distal tipping of 2s loss of vitality or mobility of 1s/2s

Question 78

What are functions of a URA other than tipping teeth?

Answer 78

- space maintainer - habit breaker - retainer - correct OB

Question 79

What warnings do you give someone on provision of a URA?

Answer 79

- big and bulky - non compliance increases duration - will feel uncomfortable, saliva, speech - will settle - beware of hot drinks

Question 80

What do you use in a URA to correct an ACB and a PCB?

Answer 80

ACB - Z spring PCB - midline palatal screw

Question 81

What are risks of bonded and pressure formed retainers?

Answer 81

bonded: can debond, caries, gingivitis, poor OH, fracture of wire pressure: lost/chewed by dog compliance and no longer fitting, keeping clean

Question 82

How would you assess vertical skeletal relationship?

Answer 82

LAFH vs TFH - should be 50% ish FMPA - should meet at the back of the head

Question 83

What are some causes of AOB?

Answer 83

digit sucking tongue thrust fracture of mandible skeletal discrepancy

Question 84

How would you monitor canine movement?

Answer 84

measure, can use a definite point to compare against

Question 85

A patient with fixed ortho presents with white areas around the brackets, what could be the cause?

Answer 85

- demineralisation - excess cements - plaque

Question 86

How does a URA affect the anterio-posterior skeletal relationship?

Answer 86

it doesnt

Question 87

How does a URA affect the vertical skeletal relationship?

Answer 87

FABP would decrease overbite and increased LAFH

Question 88

design a URA for proclining anterior teeth

Answer 88

• Active: Roberts retractor 0.5mm in tubing • Retention: Adams cribs 6/6 0.7mm HSSW • ?Anchorage: Stops mesial to 3/3? • Baseplate: Flat anterior biteplane

Question 89

What special tests are required for an orthodontic diagnosis?

Answer 89

\*study models \*Radiographs (OPT, lateral cephalogram) \*Photos \*Sensibility tests \*cone beam CT scan

Question 90

What are the three aims of orthodontic treatment?

Answer 90

To achieve; Stable occlusion Functional occlusion Aesthetic occlusion

Question 91

What are the three main risks of orthodontic treatment?

Answer 91

\*Decalcification \*Relapse \*Root resorption

Question 92

When should an orthodontic exam be carried out?

Answer 92

\*Brief exam at around age 9 \*Comprehensive exam when premolars and canines erupt \*When older patients first present \*if a malocclusion develops later in life

Question 93

What is ideal occlusion?

Answer 93

It is a hypothetical rarely found in nature. It is the gold standard by which occlusal irregularities and treatment may be judged

Question 94

Describe the AP class I relationship

Answer 94

maxilla 2-3mm in front of mandible

Question 95

Describe the AP class II relationship

Answer 95

maxilla \>3mm in front of mandible

Question 96

Describe the AP class III relationship

Answer 96

mandible in front of maxilla

Question 97

What is an increased FMPA?

Answer 97

Frankfort mandibular plane angle increased if premature meeting point

Question 98

What is a decreased FMPA?

Answer 98

Frankfort mandibular plane angle decreased if delayed meeting point

Question 99

Where is the ideal meeting point of the FMPA?

Answer 99

external occipital protuberance

Question 100

What are the occlusal features of a sucking habit?

Answer 100

\*Proclination of upper anteriors \*Retroclination of the lower anteriors \*Localised AOB or incomplete over bite \*Narrow upper arch

Question 101

What are the average values in class I cephalometrics?

Answer 101

\*SNA relates maxilla to anterior cranial base Average value 81o +/- 3o \*SNB relates mandible to anterior cranial base Average value 78o +/- 3o \*ANB relates mandible to maxilla Average value 3o +/- 2o

Question 102

Clinically speaking, what is the upper anterior face height and lower anterior face height?

Answer 102

Upper; glabella to base of nose \*Lower; base of nose to inferior aspect of chin \*Average ratio of LAFH to TAFH 50%

Question 103

What is the average value of FMPA

Answer 103

27o +/- 4o

Question 104

In terms of cephalometrics, what is the upper and lower anterior face height?

Answer 104

\*Upper; nasion to anterior nasal spine \*Lower; anterior nasal spine to menton \*average value of LAFH to TAFH 55%

Question 105

What is a dental cause of facial asymmetry?

Answer 105

displacement of normal mandible due to unilateral crossbite

Question 106

What is a true mandibular cause of facial asymmetry?

Answer 106

\*Hemi mandibular hypoplasia \*condylar hypoplasia

Question 107

What are the four aetiologies of malocclusion?

Answer 107

\*skeletal (ie class III) \*dental (missing teeth) \*soft tissue (lip trap) \*habit (thumb sucking)

Question 108

What are five local causes of malocclusion?

Answer 108

\*variation in tooth number \*variation in tooth size or form \*abnormalities of tooth position \*local abnormalities of soft tissues \*local pathology

Question 109

What are the four types of supernumerary teeth?

Answer 109

\*conical \*tuberculate \*supplemental \*odontome

Question 110

Describe balancing extraction

Answer 110

by extraction of a tooth from the opposite side of the same arch. Designed to minimise midline shift.

Question 111

Describe compensating extraction

Answer 111

by extraction of a tooth from the opposing arch of the same side. Designed to maintain occlusal relationship

Question 112

What methods are there of clinically assessing ectopic canines?

Answer 112

\*visualisation, palpation of any obvious bumps \*Inclination of 2(s) \*Mobility of c(s) or 2(s) \*colour of c(s) or 2(s) \*radiographic assessment (usually OPT and anterior occlusal (parallax technique)) \*3p's; presence, position, pathology

Question 113

What is the physiological basis of orthodontics?

Answer 113

If an external force is applied to a tooth, the tooth will move as the bone around it remodels. This bony remodelling is mediated by the PDL.

Question 114

What are the six types of tooth movement and their ideal force?

Answer 114

\*Tipping (35-60g) \*Bodily movement (150-200g) \*Intrusion (10-20g) \*extrusion (35-60g) \*rotation (35-60g) \*torgue (50-100g)

Question 115

What is interceptive orthodontics?

Answer 115

Any procedure that will reduce or eliminate the severity of developing malocclusion

Question 116

What are the eruption dates for the 6's 1's 2's

Answer 116

6's - 6 yo 1's - 7 yo 2's - 8 yo

Question 117

What are the eruption dates for 4's 3's + 5's 7's

Answer 117

4's - 10yo 3's + 5's - 11-12 yo 7's - 12-13 yo

Question 118

What are the causes of unerupted central incisors?

Answer 118

Supernumeraries preventing eruption. Trauma/dilaceration

Question 119

What are the treatement options for an unerupted central incisor due to a supernumerary?

Answer 119

Remove deciduous and supernumerary. Expose unerupted tooth (potentially bond gold chain). Create space. Monitor for up to 18 months

Question 120

what is the term given to a tooth that sits below the occlusal plane?

Answer 120

Infraoccluded

Question 121

According to Andrews six keys; what is the correct molar relationship?

Answer 121

The mesio-buccal cusp of the upper first molar occludes with the groove between the mesio-buccal and middle buccal cusp of the lower first molar. The disto-buccal cusp of the upper first molar contacts with mesio-buccal cusp of the lower second molar

Question 122

According to Andrews six keys, what is correct crown angulation?

Answer 122

All tooth crowns are angulated mesially

Question 123

According to Andrews six keys, what is correct crown inclination?

Answer 123

incisors are inclined towards the labial surfce. Buccal segment teeth are inclined lingually

Question 124

What are the stages of treatment planning in orthodontics?

Answer 124

- Plan around the lower arch (angularion of lower labial segment is stable) - Decide on treatment in lower (ext or no ext) - Build upper arch around lower. Aim for class i incisor and canine relationship - Decide on molar relationship. Class i or full unit class ii

Question 125

What is the overlap technique?

Answer 125

A method of measuring space available and space required. Measure how much the teeth overlap to guage how much space is required

Question 126

What are the general principles of space required in the lower arch?

Answer 126

- Mild (0-4mm) stripping or ext of 5s - Moderated 5-8mm - extract 5s or 4s - Severe \>8mm - extract 4s

Question 127

How should an orthodontic treatment plan be written?

Answer 127

- Diagnosis - Problem list - Treatment plan; \*list successive stages stating tooth movements to be carried out and appliances to be used \*Estimate length of treatment \*If it is not possible to give a detailed plan, indicate when it will be reviewed (ie following eruption of teeth)

Question 128

What are the six options of treatment in orthodontics?

Answer 128

1) Accept malocclusions 2) Extractions only 3) URA 4) Functional appliances 5) Fixed appliances 6) complex treatment involving orthodontics and restorative treatment or orthodontics and orthognatic surgery