PRIMARY OCCLUSION AND DEVELOPMENT OF PERMANENT OCCLUSION

1. Generalized spacing - 40% of children
   
   
2. Primate spaces (distal of mandibular canine and mesial of maxillary canines) in most
   children = "Neutroclusion"
   
   
3. Shallow overbite is typical, edge-to-edge common
   
   
4. Classification of Primary Occlusion
   Mesial step, Distal step and Flush terminal plane, (primary molar terminal plane relationships). Distal step is least desirable -- will result in permanent Class II.
   
   
5. Classification of Permanent Malocclusion - Permanent first molar relationship is best measure to classify malocclusion in the mixed and permanent dentition.
   
   Class I - Crowding with normal permanent molar relationship
   Class II - Maxillary permanent molar (arch) anteriorly positioned
   Class III - Mandibular permanent molar (arch) anteriorly positioned
   
   
6. How does Class I permanent molar relationship develop?
   
   a) Primary molars in mesial step relationship OR
   b) Flush terminal plane with primate spaces--early mesial shift with closing of mandibular primate space when permanent first molars erupt.
   c) Flush terminal plane, followed by late mesial shift (after exfoliation of primary molars) using Leeway space
   
   
7. Causes of Malocclusion
   
   a) Hereditary lack of arch length -- small jaw or large jaw
   b) Hereditary - tooth size and arch length discrepancy
   c) premature loss of primary molars è premolars blocked out due to permanent first molar shift
   d) premature loss of primary canines
   e) Space loss due to proximal caries è premolars blocked out due to anterior component of force
   f) Habits: thumb or lip sucking, tongue thrust
   g) Ectopic Tooth Eruption
   
   1. idiopathic eruption of permanent first molars -- maxillary most common
   2. over-retention of primary molars due to trauma and/or ankylosis of cementum to alveolar bone
   3. supernumerary teeth