Center or buccal groove of the mandibular molar aligns with the mesial buccal cusp of the maxillary molar.
Use a probe on the buccal groove of the mandibular molar to check its alignment with the maxillary first molar.
Class 3 Occlusion (Mesioclusion)
Identification:
Buccal groove of the mandibular molar is mesial to the mesial buccal cusp of the maxillary molar.
To confirm true Class 3, the distance from the mesial buccal cusp of the maxillary molar to the buccal groove of the mandibular molar should be at least the width of a premolar (e.g., 7 mm).
If less than the premolar width, it's a tendency towards Class 3.
Class 2 Occlusion (Distoclusion)
Identification:
Buccal groove of the mandibular molar is distal to the mesial buccal cusp of the maxillary molar.
Verify true Class 2 with a distance of at least the width of a premolar (e.g., 8 mm) between the buccal groove of the mandibular molar and the mesial buccal cusp of the maxillary molar.
If less than the premolar width, it's a tendency towards Class 2.
Key Points to Remember
Class 1: Buccal groove of the mandibular first molar should align with the mesial buccal cusp of the maxillary first molar.
Class 3 (Mesioclusion): Buccal groove is mesial to the cusp.
Class 2 (Distoclusion): Buccal groove is distal to the cusp.
True Occlusion vs. Tendency: Depends on whether the separation between occlusal surfaces is at least the width of a premolar.
For correct classification, always start from the buccal groove of the mandibular first molar and determine its relation to the mesial buccal cusp of the maxillary first molar.