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Orthodontics · single question

Which of the following correctly describes the cuspal relationship in an Angle's Class III malocclusion?

  1. The mesiobuccal cusp of the maxillary first permanent molar occludes with the mesiobuccal groove of the mandibular first permanent molar
  2. The mesiobuccal cusp of the maxillary first permanent molar occludes distally to the mesiobuccal groove of the mandibular first molar
  3. The mesiobuccal cusp of the maxillary first permanent molar occludes mesially to the mesiobuccal groove of the mandibular first molar
  4. The mesiobuccal groove of the mandibular first molar is distally positioned when in occlusion with the mesiobuccal cusp of the maxillary first molar
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Correct answer: B. The mesiobuccal cusp of the maxillary first permanent molar occludes distally to the mesiobuccal groove of the mandibular first molar

In Class I, the MB cusp of the maxillary first molar occludes IN the MB groove of the mandibular first molar. In Class II, the mandible is retrognathic, so the maxillary MB cusp occludes MESIALLY (anteriorly) to the MB groove (the whole maxillary arch is forward relative to the mandible). In Class III, the mandible is prognathic, so the maxillary MB cusp occludes DISTALLY (posteriorly) to the MB groove.
  • A. INCORRECT. This describes Class I occlusion (MB cusp in the MB groove).
  • B. CORRECT. In Class III malocclusion, the mandible is positioned anteriorly relative to the maxilla. Therefore, the mesiobuccal cusp of the upper first molar falls DISTALLY (posterior) to the mesiobuccal groove of the lower first molar.
  • C. INCORRECT. The MB cusp occlusing MESIALLY to the groove describes Class II malocclusion.
  • D. INCORRECT. This option is ambiguous and does not correctly describe the standard Angle classification terminology.

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