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BDS3 Orthodontics > Aetiology of Malocclusion > Flashcards

Aetiology of Malocclusion Flashcards

1
Q

What are the 3 general etiological factors of malocclusion?

A
  • skeletal
    • shape
    • size
    • relative position of upper and lower jaws
  • muscular
    • form and function of muscles
    • lips, cheek, tongue
  • dentoalveolar
    • size of teeth in relation to size of jaws
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2
Q

What is the cranial base angle measured from?

A
  • attachment of the maxillary complex to the anterior cranial base
  • articulation of the mandible with the posterior cranial base
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3
Q

What are possible aetiologies of skeletal variation?

A
  • genetic
    • strong hereditary component
    • especially class III
  • environmental
    • masticatory muscles
    • mouth breathing
    • head posture
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4
Q

How are lateral cephalograms analysed?

A
  • hand traced onto paper
  • digitised using a computer
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5
Q

What is SNA on a lateral cephalogram?

A
  • maxilla and anterior cranial base angle
    • average class I value = 81 degrees

S = sella turcica
N = nasion
A = maxilla

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6
Q

What is SNB on a lateral cephalogram?

A
  • mandible and anterior cranial base angle
    • average class I value = 78 degrees

S = sella turcica
N = nasion
B = mandible

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7
Q

What is ANB on a lateral cephalogram?

A
  • angle formed by the maxilla, anion and mandible
    • average class I value = 3 degrees
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8
Q

What are the possible aetiologies of a class II skeletal relationship?

A
  • mandibular deficiency
    • mandible too small
    • most common
  • posteriorly positioned mandible
    • set back due to obtuse cranial base
    • normal sized mandible
  • larger maxilla
  • maxillary protrusion
    • not common
  • teeth erupt into post normal occlusion
    • class II
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9
Q

How do the cephalometric values of a class II skeletal relationship compare to a class I?

A
  • SNA usually average
    • 81 degrees
    • increased if maxilla is prognathic
  • SNB usually decreased
    • <78 degrees
  • ANB increased
    • > 5 degrees
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10
Q

What are the possible aetiologies of a class III skeletal relationship?

A
  • mandible placed anterior relative to maxilla
    • sue to acute cranial base angle
  • maxillary deficiency
    • maxilla too small
    • most common
    • paranasal hollowing visible
  • larger mandible
  • teeth erupt into pre-normal occlusion
    • class III
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11
Q

How do the cephalometric values of a class III skeletal relationship compare to a class I?

A
  • SNA usually decreased
    • <81 degrees
    • if maxilla is deficient
  • SNB usually average
    • 78 degrees
    • increased if mandible prognathic
  • ANB decreased
    • <1 degree or negative
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12
Q

What planes are used to assess vertical jaw relationship?

A
  • Frankfort place
    • lower orbital rim to superior border of external auditor meatus
  • mandibular plane
    • lower border of mandible
  • should meet at external occipital protuberance
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13
Q

What clinical values are used to asses vertical jaw relationship?

A
  • upper anterior face height
    • brow ridge (labella) to base of nose
  • lower anterior face height
    • base of nose (sub nasal) to inferior aspect of chin (menton)
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14
Q

What is the average ratio of lower anterior face height to total anterior face height?

A
  • 50% clinically
  • 55% cephalometrically
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15
Q

What is the averrable value of the Frankfort mandibular plane angle?

A

27 degrees

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16
Q

What are the characteristic signs and measurements of a long facial type?

A
  • LAFH-TAFH >55%
  • FMPA >31 degrees
  • step inclined mandibular plane
  • backward mandibular growth rotation
  • anterior open bite tendency
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17
Q

Hat are the characteristic signs and measurements of a short facial type?

A
  • LAFH-TAFH <55%
  • FMPA <23 degrees
  • tendency to parallelism of jaws
  • forward mandibular growth rotation
  • deep overbite tendency
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18
Q

What are arch width discrepancies?

A
  • disproportion of maxillary and mandibular dental arches
  • causes unilateral or bilateral buccal segment cross-bites
  • often exaggerated by antero-posterior discrepancies
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19
Q

What is mandibular displacement?

A
  • mandible forced to deviate to one side to achieve intercuspation
  • occurs where interarch width discrepancies causes upper and lower posterior teeth to meet cusp to cusp
20
Q

What are the possible causes of facial asymmetries?

A
  • dental
    • displacement of normal mandible due to unilateral cross bite
  • true mandibular asymmetry
    • hemi-mandibular hyperplasia/elongation
    • condylar hyperplasia
  • hemi-facial microsomia
21
Q

What is dente-alveolar disproportion?

A
  • discrepancy between size of teeth and jaws
  • crowding
    • small jaws and normally sized teeth
    • large teeth (macrodontia)
  • spacing
    • large jaws and normally sized teeth
    • small teeth (microdontia)
      - more common
22
Q

What is the definition of a local cause of malocclusion?

A

localised problem or abnormality within either arch, usually confined to one, two or several teeth producing a malocclusion

  • tend to get worse over time
  • scope for interceptive treatment
23
Q

Provide examples of local causes of malocclusion

A
  • variation in tooth number
  • variation in tooth size of form
  • abnormalities of tooth position
  • local soft tissue abnormalities
  • local pathology
24
Q

In what ways can variation in tooth number present?

A
  • supernumerary teeth
  • hypodontia
  • retained primary teeth
  • early loss of primary teeth
  • unscheduled loss of permanent teeth
25
Q

Where are supernumerary teeth most commonly found

A
  • anterior maxilla
26
Q

What are the four types of supernumerary teeth?

A
  • conical
    • small peg shaped
    • slender and pointed
    • mostly in upper incisor region, close to midline
    • usually present individually or in pairs
    • often erupt, can extract
    • tend not to prevent eruption but can displace adjacent teeth
  • tuberculate
    • round, barrel shape
    • often paired
    • mostly in upper incisor region
    • tend not to erupt
    • usually extracted
    • can cause eruption failure in permanent incisors
      - develop in the cingulum area
  • supplemental
    • normal morphology
    • in addition to adjacent teeth
    • usually upper laterals or lower incisors
    • often extracted
      - decision based on form and position
  • odontome
    • collection of toothlike substances
    • disorganised form
    • compound
      - discreet denticles
    • complex
      - disorganised mass of dentine, pulp and enamel
27
Q

What is hypodontia?

A
  • developmental absence of one or more teeth
    • commonly upper laterals and second premolars
  • strong genetic component
  • can be accompanied by microdontia
28
Q

When should retained primary teeth be investigated?

A

when there is a difference of more than 6 months between the shedding of contra-lateral teeth

29
Q

Why may primary teeth be retained?

A
  • absent successor
  • ectopic sucessor
  • infra occluded primary molars
    • ankylosed
    • common in Es, even with permanent successor
    • may require extraction
  • dentally delayed development
  • pathology/supernumerary
30
Q

How should retained primary teeth be managed when there is no permanent successor?

A
  • maintain primary tooth as long as possible
    - if good prognosis
  • extract deciduous tooth early
    • encourages space closure in crowded cases
  • early orthodontic referral
31
Q

What are infraoccluded primary molars?

A
  • primary teeth retained and permanent teeth erupt past
    • tooth fails to achieve occlusal relation ship
  • temporary ankylosis
    • percussion sounds like clicking
  • extraction
    • difficult to keep clean so often become carious
32
Q

What can cause early loss of primary teeth?

A
  • trauma
  • periapical pathology
  • caries
  • resorption by successor
33
Q

What can occur as a result of early loss of primary teeth?

A
  • localisation of crowding
    • influenced by:
      - tooth extracted
      - when extracted
      - inherent crowding
34
Q

What is a balancing extraction?

A
  • extracting a tooth from opposite side of the same arch
    • minimise midline shift
35
Q

What is a compensating extraction?

A
  • extracting a tooth from opposing arch on same side
    • maintain occlusal relationship
36
Q

What extractions should be considered for early loss of different kinds of primary teeth?

A
  • incisors
    • little impact
    • no compensating or balancing extractions
  • canines
    • unilateral loss in crowded arch can shift centre line
    • mesial drift of buccal segments
    • consider balancing extraction
  • molars
    • increased space loss with Es compared to Ds
    • more space loss in upper than lower
    • 6s drift medially into space for 5s
37
Q

What factors can influence the impact of loss of 6s?

A
  • age at loss
    • important for lower
      - if late, often poor space closure
      - if early, distal drift of 5s
    • in lower arch should be at time of bifurcation development in 7s
  • crowding
    • rapid space loss possible in upper arch
    • good result in lower arch
  • malocclusion
38
Q

What are the consequences of unscheduled loss of a central incisor and how should it be managed?

A
  • depends on timing of loss
    • early results in drifting of adjacent teeth
    • late results in long term space
  • ideally maintain space
    • reimplant
    • simple denture
  • plan how to deal with space longer term
    • definitive prosthesis
  • if lateral incisor drifts to fill space
    • reopen space for prosthesis
    • build up lateral
39
Q

What is macrodontia?

A
  • larger than average tooth
    • localised or generalised
  • problems:
    • crowding
    • asymmetry
    • aesthetics
  • management:
    • can be slimmed down but limited by pulp chamber
    • extraction and replacement with prosthesis
40
Q

What is microdontia?

A
  • smaller than average tooth
    • localised or generalised
    • peg incisors
  • leads to spacing
  • strong genetic link
    • also link with hypodontia
41
Q

What abnormal forms of teeth can present?

A
  • peg laterals
  • dens in dente
  • germinated/fused teeth
  • talon cusps
  • dilaceration
  • accessory cysts and ridges
42
Q

What teeth are most commonly ectopic?

A
  • third molars
  • upper canines
    • check for palpable buccal canine bulge from 9 years
    • due to long path of eruption
    • associated with peg laterals
    • higher incidence in class II, div 2 incisor relationships
    • buccal placement associated with crowding
    • managed with extraction of 3, surgical exposure or extraction
  • first permanent molars
    • reversible before age of 8
    • caries risk
    • indicated by crowding, mesial path of eruption and abnormal E
    • managed with separator, extraction of E, distalisation of 6
  • upper centrals
    • possibly due to supernumerary or trauma to primary predecessor
      - tuberculate or odontome
      - ankylosis of primary tooth, displacement of tooth germ
43
Q

What are transpositions of teeth?

A
  • interchange in the position of two teeth
    • true
      - teeth swap place entirely
    • pseudo
      - apices in correct position
  • most common teeth:
    • upper canines and first premolar
    • lower canines and incisors
  • management:
    • accept
    • extract
    • correct
44
Q

What local soft tissue abnormalities can cause malocclusion?

A
  • digit sucking
    • proclined upper incisors
    • retroclined lower incisors
    • anterior open bite
  • fraenum
    • labial frenum can cause median diastema
  • tongue thrusting
    • anterior open bite
    • common cause of relapse after treatment
45
Q

What local pathology can cause malocclusion?

A
  • caries
  • cysts
    • displacement of teeth
    • cyst renucleated to manage
  • tumours

BDS3 Orthodontics (5 decks)

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