Which cusp and tooth are typically involved in Angle Class I occlusion as described in standard references?

• A. Mesiobuccal cusp of the maxillary first molar occludes in the buccal groove of the mandibular first molar
• B. Mesiobuccal cusp of the mandibular first molar occludes in the embrasure area between the maxillary second premolar and first molar
• C. Distobuccal cusp of the maxillary second molar occludes with the mandibular first molar
• D. Mesiolingual cusp of the maxillary first molar occludes with the mandibular second molar

Answer: (A)

The main idea being tested is Angle’s Class I molar relationship. In this pattern, the mesiobuccal cusp of the upper first molar aligns with the buccal groove of the lower first molar. This cusp–groove alignment is the defining feature of Class I and is what standard references describe as the normal posterior relationship, even if the teeth elsewhere may be crowded or misaligned.

So the correct description is exactly that: the mesiobuccal cusp of the maxillary first molar occludes in the buccal groove of the mandibular first molar. The other cusp-tooth contacts described do not match the classic molar relationship used to define Class I, hence they describe different occlusal patterns.