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Orthodontics (IODC) > Aetiology of malocclusion > Flashcards

Aetiology of malocclusion Flashcards

1
Q

Factors affecting tooth position

A

Skeletal pattern
Soft tissue
Dental factors
Local factors

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2
Q

Definition of skeletal classification

A

Relative positions of the jaws to one another due to the positions of the dental follicles when forming on the dental lamina. This in turn affects the relative positions of the teeth to one another.

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3
Q

Skeletal pattern planes of space considerations

A

Anterioposterior
Vertical
Transverse (looking from the front)

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4
Q

Anterioposterior (profile) assessment looks at

A

The relationship of top and bottom jaw
Can be class 1, 2, 3
Lower jaw should be slightly set back

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5
Q

Regions of the skull

A

1 and 2. skull

  1. Maxilla
  2. Mandible
  3. Dental bases
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6
Q

Class 2 aetiology

A

86% mandibular retrusion

14% other maxillary protrusion

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7
Q

Class 3 aetiology (more variation)

A

26% both
34% maxillary retrusion
40% mandibular protrusion

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8
Q

Vertical relationships splits head into 3rds

A

and mandibular plane ratio

Bottom of nose and bottom chin should be equal to nose to eyebrows (2&3 sections)

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9
Q

Frankfort mandibular plane definition

A

Angle formed by the intersection of the Frankfort horizontal plane and mandibular angle

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10
Q

Frankfort angle normal range

A

25 +/- 5 degrees

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11
Q

FMP clinical assessment

A

Palpate lower border of mandible and imagine ff plane

Where these 2 lines meet

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12
Q

Increased FMP =

A

Anterior open bite
Very steep mandibular plane angle
The lines meet anterior to the back of head
30 degrees or more

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13
Q

Decreased FMP angle =

A

Deep bite
Lines meet off back of the head
Reduced lower anterior face height
20 degrees or less

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14
Q

Crossbite comes from narrow upper or wide lower arch. It =

A

Upper molar buccal cusps meet in the groove of the lower molars

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15
Q

Asymmetry

A

Most patients have slight asymmetry

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16
Q

Asymmetry caused by

A

Enlargement of one side of face

Reduced size of one side of face

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17
Q

Teeth are in the neutral zone

A

Position of stability between tongue and lips

The forces balance each other

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18
Q

Tongue force increases during

A

Eating, speaking but is transient

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19
Q

Lip length problems

A

Short lips = incompetency
-can see upper gums
Gummy smile: vertical maxillary excess (when upper jaw is displaced lower than it should be)

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20
Q

Potentially competent lips

A

Lips would meet if overjet was reduced

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21
Q

Are digit and dummy sucking problems?

A

Dummy sucking not really a problem as decreases with age. 50% of babies start sucking dummy but by age 5 less than 5% still do (incisors erupt at 6&7)
Digit sucking: 1/3 of babies suck thumb. Around 20% sucking digits and 6/7 which will affect position of teeth (as this is when incisors will erupt)

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22
Q

Asymmetry can be caused by thumb sucking

A

Asymmetrical open bite

Don’t treat them until they’ve stopped sucking

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23
Q

Dental factors affecting tooth position

A

Tooth-tissue ratio
Number of teeth (missing teeth, extra teeth)
Relative position and path of eruption of teeth

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24
Q

Local factors influencing tooth position

A

Habits
Effect of labial fraenum
Pathological conditions

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25
Q

Skeletal class I

A

Basal bone of mandible is normal in relation to maxilla

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26
Q

Skeletal class II

A

Basal bone of mandible is post-normal to maxilla

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27
Q

Skeletal class III

A

Basal bone of mandible is pre-normal to maxilla

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28
Q

Possible causes of antero-posterior class II relationship

A 
Discrepancy of sizes of jaws (rare)
Protrusive maxilla (not common)
Retrusive mandible (most common)
-mandibular joint set further back on cranial base
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29
Q

Possible causes of antero-posterior class III relationship

A

Often a true size discrepancy

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30
Q

Skeletal pattern - vertical relation

A

Increased lower face height results in < OB or ANB
Decreased lower face height results in deep OB
-both difficult to treat without favourable growth

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31
Q

Skeletal pattern - lateral relation

A

Imbalance –> X-bite
-buccal
-lingual
X-bite may be result of antero-posterior discrepancy in class III skeletal pattern

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32
Q

Soft tissue factors - lips. Consider:

A
  1. Size and form
    - competent or incompetent
  2. Function
    - lip line
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33
Q

Incompetent lips

A

Apart at rest
-rest = minimal evidence of muscular or electro-muscular activity
Up to 80% of children may have incompetent lips at some time
-may gradually become competent in time due to differential growth rates of skeletal and soft tissue elements

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34
Q

Aetiology of incompetent lips

A

Size: i.e. short upper lip
Skeletal discrepancy: as muscles, lips are related to bones of facial skeleton
-skeletal pattern may determine whether lips may be brought together completely
-may be affected by antero-posterior or vertical discrepancy

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35
Q

Lip seal may be obtained by 3 factors

A

Muscular effort
Mandibular posture
Lip/ tongue contact (depends on lip line)

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36
Q

What is the lip line?

A

The relationship of lower lip to upper incisors

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37
Q

A high lip line

A 
Severe antero-posterior skeletal discrepancy and class II div 1 incisor relationship --> lower lip behind upper incisors on palate or teeth
High lip line + reduced lower face height --> class II div 2 incisor relationship since lower lip will be on labial side of upper incisors
38
Q

A low lip line

A

Lower lip contacts tongue thus dispersing upper incisors
STRAP LOWER LIP particular problem (rare)
-hyperactive lower lip
-any OJ must be fully reduced in order to be stable
-deep mantalis fold is a sign

39
Q

Soft tissue factors - tongue. Consider:

A
  1. Anatomy: extrisnic muscles of tongue are attached to hyoid, styloid and palatal bones
  2. Size
  3. Function: action usually secondary to lips but will have reinforcing effect. Adaptive in mastication, swallowing (important) and speech
40
Q

Effects due to size of tongue

A
  • apparently large tongue may improve as child matures due to > in lower face height with growth and tongue coming to rest lower in mouth
  • if upper jaw > lower jaw, tongue may rest between them and prevent vertical development of posterior teeth
  • large tongue may be factor in relapse after orthognathic surgery (class III cases)
41
Q

How many times do we swallow per day?

How much time does it take to swallow

A

~1000 times

~1s

42
Q

The infantile swallow

A

Mandible held in lower position
Tongue lower and further forward from pharyngeal wall
Infant takes in air through nose
Feeding by suckling milk
-milk ducts surrounded by smooth muscle and are stimulating by suckling
-milk directed into tongue, which is over lower lip
“Process by which babies swallow before weaning. Breathing occurs through the nose. Feeding is done by ‘suckling and not sucking. The tongue covers the lower lip during swallowing.”

43
Q

The normal adult swallow

A

Lips are closed
Teeth in light occlusal contact
Tongue elevated to palate
Teeth clenched tightly as food is pressed between palate and floor of mouth

44
Q

What age do humans change to the adult swallow

A

By age 6, 50% of children have adult swallow

Others are in period of transition

45
Q

Types of adaptive swallow

A 
Teeth apart (lip incompetence)
Teeth together (< OB, ANB)
Endogenous tongue thrust swallow
46
Q

Teeth apart adaptive swallow

A

If tongue does not move up into upper arch, there may be a narrowing of upper arch, a buccal X-bite and lack of full development of buccal segments
-responds to tx

47
Q

Teeth together adaptive swallow

A

Tongue is positioned forward

-responds to tx

48
Q

Endogenous tongue thrust swallow

A

Primary an atypical neuromuscular pattern
Not the same as an infantile swallow
Occurs in <3% of cases
Not treatable

49
Q

Amount of typical masticatory forces

A

15kg for 11min/day

50
Q

Amount of typical swallowing forces

A

200kg for 1s

51
Q

Amount of typical speech forces

A

100kg for 0.2s

52
Q

Amount of typical force for relaxed muscles

A

10g for 24hrs/day

53
Q

Is the amount of force or the intensity more important?

A

Duration > intensity

Most significant factor is continuous resting force from soft tissues

54
Q

Mandibular positions

A

Non-occlusal
-rest
-adaptive postural
Occlusal
-RCP (condyles in most posterior position)
-ICP (ideally should be same as RCP)
-ligamentous (forced retruded position, amount limited by ligaments, usually 2mm posterior to ICP)

55
Q

Mandibular rest position

A

Endogenous postural position
Muscles relaxed, condyles retruded, mandible unstrained
Freeway space i.e. inter-occlusal clearance
Controlled by feedback mechanisms
Not fixed

56
Q

Mandibular rest position affected by

A

Head posture: when head is tilted back, FWS increases. When tilted forward, FWS decreases
Age
Loss of mandibular teeth brings mandible closer to maxilla

57
Q

Adaptive postural positions are adopted in order to

A

Maintain oral seal

Achieve oral respiration

58
Q

In which incisor relatioships are adaptive postural positions adopted

A

Class I div 1 when there is adequate lip length - mandible postured forwards
Class II div 2: lower jaw may be postured forwards for comfort and function
Class II incisors: forward posture if teeth would meet edge to edge in rest position

59
Q

Mandibular movements: control

A

Under both voluntary control and reflex activities governed by sensory and proprioceptive impulses

60
Q

Types of mandibular movements

A

Normal to occlusion: simple hinge from rest over 3mm
Deviation: closure from postured position
Displacement: starts from rest but may displace from normal due to premature contact

61
Q

Types of displacement

A

Lateral displacement (crossbite)
-usually due to narrow upper arch
-posterior teeth meet cusp to cusp or crossbite
-must shift jaw right or left to get teeth into ICP
Antero-posterior. e.g. with an instanding anterior tooth (commonly a
palatal upper lateral incisor) or in a mild Class III case where the patient
can achieve an edge-to-edge incisal occlusion but then postures forward
into a more comfortable bite
Posterior. Due to overclosure with loss of posterior teeth

62
Q

Tooth/ tissue ratio

A

Imbalance in ratio of tooth and jaw size will produce crowding or spacing of dentition

63
Q

Possible aetiological genetic factors in crowding

A

Independent genetic control of teeth and jaws
Evolution - jaws are shrinking over time
Outbreeding - intermixing of racial/ ethnic groups
Diet - less gritty so we don’t wear out teeth as much
-wearing teeth below contact point –> enough space for teeth

64
Q

Prevalence of crowding

A

60-70% of UK population
Depends on ethnic group
Crowding in deciduous dentition unusual
-more often expressed as lack of normal spacing
40% increase in severity of crowding over last 100,000 yrs

65
Q

Possible effects of crowding on the dentition

A

Overlapping and displacement
Impaction
Mesial movement of teeth

66
Q

Causes of generalised spacing

A 
Hypodontia
Small teeth (narrower)/ well developed arches
Unusual in UK population
(localised spacing = diastema)
67
Q

Missing teeth: terms used for congenital absence

A

Anodontia: all teeth missing
Oligodontia: several teeth missing
Hypodontia: a few teeth missing

68
Q

Aetiology of congenital absence of teeth

A

May be linked to hereditary syndrome e.g. ectodermal dysplasia
-sex-linked recessive condition
-lack of sweat glands, sebaceous glands and hair follicles
-some degrees of anodontia or malformed teeth
Cleft lip and palate: absence of teeth may be due to surgery carried out in region of developing tooth germs
Often family history of some missing teeth

69
Q

Most common missing teeth

A 
Lower 8s: 13.6%
Upper 8s: 11%
Lower 5s: 3%
Upper 2s: 1.8%
Upper 5s: 1.1%
Lower incisor: 0.3%
70
Q

Effects of developmental hypodontia

A
  1. Form of teeth: often other teeth may be smaller or malformed (e.g. peg shaped laterals)
  2. Position of teeth: may be affected but will be minimal if there are only one or two teeth missing
  3. Growth: severe hypodontia may affect alveolar bone and > FWS (but will not > rest position of mandible)
71
Q

Missing teeth can be due to

A

Congenital absence

Acquired loss of teeth

72
Q

Acquired loss of teeth refers to

A

Premature loss of deciduous teeth
Loss of permanent teeth
Retention of deciduous teeth (can lead to upper 2s palatal deflection)
Delayed eruption of permanent teeth (normal variation, missing teeth, impeded eruption, trauma)

73
Q

Extra teeth can be either

A 
2% of pts
Supplemental
Midline (premaxillary) supernumeraries 
-conical (mesiodens)
-tuberculate
74
Q

Supplemental teeth

  • what are they
  • where do they occur
  • who gets them
  • what do they lead to
  • treatment
A

Normal form
Usually occur at end of series
Europeans may have extra upper or lower 2
Africans have > prevalence of 9s and extra premolars
May > crowding potential of dentition
Usually treated by removal of suitable tooth

75
Q

Conical midline supernumeraries (mesiodens) characteristics and treatment

A 
Develops early
Root formation coincides with upper central
May erupt
Usually displace other teeth
Does not delay eruption
May be inverted
Tx: extract supernumerary unless it is high, inverted or removal would damage other teeth
Usually between 1/1
76
Q

What do tuberculate teeth represent and why?

A

Third dentition

  • develops later than upper 1
  • does not usually erupt
  • delays eruption of 1
  • other teeth may move into space
  • barrel shaped
77
Q

Development of tuberculate teeth

A

On palatal aspect of upper central

May be unilateral, bilateral or not associated with other supernumerary teeth

78
Q

Treatment of tuberculate teeth

A

Extract ASAP but other teeth often remain high when erupted or require ortho
NB essential to carry out full ortho assessment before dealing with supernumeraries
-space must be created for permanent teeth to erupt into
-any associated malocclusion must be dealt with

79
Q

Position and form of teeth affected by

A
  1. Shape and size
    - germination
    - fusion
    - macrodontia (teeth fused together)
    - microdontia (e.g. peg shaped laterals)
  2. Transposition (teeth swap places) and displacement (especially upper 3s)
    - very difficult to correct
  3. Traumatic displacement e.g. primary tooth pushed up into gum –> damage to adult teeth
  4. Impaction
80
Q

Examples of habits

A

Thumb/ finger/ dummy sucking

81
Q

Force and habits

A

According to equilibrium theory, force duration more important than magnitude
To affect teeth significantly, force applied for min 6hrs/day

82
Q

Prevalence of habits

A

> 50% infants suck digits between 6m-2yrs

Usually stopped by 4 years

83
Q

Effects of habits

A

No long term effects in deciduous dentition
In permanent dentition
-flared, spaced upper incisors
-lingually inclined lower incisors (but dependent on method of sucking - may be proclined)
-< OB or AOB
-narrowed upper arch
Does not affect molar relationship

84
Q

Treatment for habits

A

If habit stops early, OJ may < within 1 yr

Tongue may have adapted to < OB and prevent closing

85
Q

Development of labial frenum

A

Remnant of tecto-labial bands
Precedes tooth development (and therefore transeptal fibres)
Attached to papilla at birth and migrates with eruption of deciduous and permanent molars
Usually attaches to muscosa over labial plate
-sometimes attaches to crest of alveolar bone before tooth eruption (determined by 7 weeks IUL when there is separation of lip and alveolus by invaginating lip furrow band, familial tendency)

86
Q

Histology of labial frenum

A

Not muscle
Consists of vascularised collagen fibres
Interrupts transeptal fibres

87
Q

Effects of labial frenum

A

Midline spacing often associated with large fleshy fraenum

Space closure will relapse in some cases unless fraenetomy performed

88
Q

Diagnosis of low labial frenum attachment

A

Blanching on palatal mucosa when fraenum put under tension

V-shaped notch on radiograph

89
Q

Treatment of low labial frenum attachment

A

Fraenectomy
-not until upper 2s and 3s present (since 90% diastemas close spontaneously)
Either close space before or after surgery: most people recommend space closing first
Bonded retainer???

90
Q

Local factors: pathology

A

Rare and usually self-evident

  • fracture
  • cyst
  • neoplasm
  • inflammatory condition
91
Q

Infraoccluded teeth

A

Due to missing permanent tooth OR ankylosed root to bone (primary tooth)
Can submerge too much and drop below gum line –> surgical extraction

92
Q

In which stage of dentition should the problem of a sucking habit be dealt with?

A

Late mixed dentition

Orthodontics (IODC) (17 decks)

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