9 The aetiology of malocclusion: (ii) locals factors and habits


The aetiology of malocclusion
(ii) locals factors and habits

Table 9.1 The effects of early loss of deciduous teeth. Balancing extraction refers to the loss of teeth from the contralateral side of the arch to minimise a centreline shift.

Tooth lost Effects on permanent dentition Action required
Deciduous incisors
  • Minimal effect – some space loss if crowding. Spacing may affect aesthetics
  • None
Deciduous canines
  • Centreline shift if unilateral loss with some relief of incisor crowding
  • Space loss for permanent canines
  • If crowding, consider balancing extractions to protect the centreline
Deciduous first molars
  • Small centreline shift if crowding with minimal relief of labial segment crowding
  • Mesial molar movement with space loss
  • Consider balancing or space maintenance
Deciduous second molars
  • Often no effect on centrelines or incisor crowding
  • Mesial drift of molars with space loss for second premolars
  • Space maintenance except in spaced arches

Table 9.2 Consequences of infraocclusion of a deciduous molar.

Tooth Consequences
Infra-occluded deciduous molar
  • Delayed exfoliation
  • Progressive submergence with failure of alveolar development
  • Difficult extraction often requiring surgery
Permanent successor
  • Delayed and abnormal eruption
  • Disturbed root development
  • Centreline shift
Developing occlusion
  • Tipping of adjacent teeth
  • Localised posterior open bite
  • Higher frequency of canine impaction, hypodontia and ectopic first permanent molar eruption possibly due to a common aetiologic machanism

Figure 9.1 (A) Tension arises in the transseptal fibres (shown in red) as the infraoccluded molar moves below the occlusal plane. The direction of this force results in exaggerated tipping, reduced vertical development and a centreline shift of adjacent teeth. (B) Transposition of the right maxillary canine and first premolar. (C) Primary failure of eruption of the lower left first permanent molar. (D) (i) A low maxillary frenal attachment associated with a diastema. (ii) A positive blanch test. (iii) A small alveolar notch between the central incisors that results in disruption of the transseptal fibres. (iv) A high lower frenal attachment. (E) An asymmetrical anterior open bite is often associated with a digit sucking habit.

Local factors


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Jan 1, 2015 | Posted by in Orthodontics | Comments Off on 9 The aetiology of malocclusion: (ii) locals factors and habits
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