Summary: Handbook

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• 1 Occlusion and Malocclusion

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• 1.1 Ideal Occlusion

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• Andrews' six keys of occlusion?

  Molar relationship
  Correct crown angulations (tip)
  Correct crown inclinations (torque)
  No rotations
  No spaces
  Flat plane of occlusion
  
  120 "non-orthodontic normals"
  Andrews LF 1972 AJO

• Mutual protection is thought to be achieved in the presence of: (3)

  1. An immediate and permanent posterior disclusion in lateral and protrusive contact with no associated non-working side interferences (tooth contacts); canine guidance or group function in lateral excursion and incisal guidance in protrusion. Thus, the anterior teeth protect the posterior teeth.
  
  2. Multiple, simultaneous and bilateral contacts of the posterior teeth in MIP (or centric occlusion) with the incisor teeth slightly out of contact; thus the posterior teeth protect the anterior teeth
  
  3. MIP coincident with CMMR (or centric relation), but with some limited freedom for the mandible to move forwards in the sagittal and horizontal planes from MIP.

• What is Centric Maxillomandibular Relationship - CMMR/Centric Relation - CR/Retruded Contact Position - RCP?

  A term to describe the position of the mandible relative to the maxilla, with the condyles in the most stable and reproducible position.
  It is when the condyle-disc assembly is in the most anterior, superior position in the glenoid fossa. It is independent of tooth contact.

• What is Maximum Intercuspation - MIP/Intercuspal Position - ICP/ Centric Occlusion - CO?

  The complete intercuspation of opposing teeth independent of condylar position in the glenoid fossa. It is a tooth-determined position.

• What is canine guidance?

  A form of mutually protected occlusion in which the vertical and horizontal overlap of the canine teeth disengage the posterior teeth in excursive movements of the mandible.
  Contact is maintained on the working side canine teeth during lateral excursion.

• What is group function?

  Multiple contact relations between the maxillary and mandibular teeth in lateral movements on the working side whereby simultaneous contact on several teeth acts as a group to distribute occlusal forces.
  Contacts are maintained between several teeth on the working side during lateral excursion of the mandible.

• 1.2 Classification of Malocclusion

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• Andrews class I molar relationship?

  Distal surface of the distal marginal ridge of the upper first permanent molar occludes with the mesial surface of the mesial marginal ridge of the lower second molar.
  
  The mesiobuccal cusp of the upper first permanent molar falls within the groove between the mesial and middle cusps of the lower first permanent molar.

• Angle's Molar Classification (1899)

  Class I - mesiobuccal cusp of the upper first permanent molar occludes with the groove between the mesial and distal buccal cusps of the lower first permanent molar
  
  Class II - the mesiobuccal cusp of the lower first molar occludes distal to the Class I position
  
  Class III - the mesiobuccal cusp of the lower first molar occludes mesial to the Class I position

• Class II Intermediate (Williams and Stephens, 1992)

  The lower incisor edges lie posterior to the cingulum plateau of the upper central incisors. The upper incisors are upright or slightly retroclined and the overjet lies between 5 and 7mm.
  
  In reality this description falls into the category of a class II div 2 incisor relationship

• 1.3 Prevalence of Malocclusion

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• Prevalence of Malocclusion USA Data

  NHANES USA (1988-1991) - 7000 individuals examined, 57-59% had a need for orthodontic treatment (Proffit et al 1998).
  
  Most common problem was incisor irregularity. Only 34% had well-aligned mandibular incisors and 45% well-aligned maxillary incisors.
  
  20% had a marked AP skeletal discrepancy, 2% of these being disfiguring and requiring orthognathic surgery.