When the mesiobuccal cusp of the upper molar lies behind the buccal groove of the lower molar, which classification of malocclusion is present?

In dental occlusion, the positioning of the upper and lower molars relative to one another is crucial for determining the classification of malocclusion. When the mesiobuccal cusp of the upper molar is situated behind the buccal groove of the lower molar, this indicates a Class II malocclusion, specifically a Class II Division 1 or Division 2, depending on other factors such as the positioning of the incisors.

However, in the case of Class III malocclusion, the lower molars are positioned further forward than the upper molars. Thus, if the mesiobuccal cusp of the upper molar is behind, it suggests a more advanced positioning of the lower molars, which is characteristic of Class III malocclusion. This positioning can lead to a more pronounced overbite, where the lower teeth may also protrude relative to the upper teeth.

In summary, the correct classification of the malocclusion is indicated by the relationship and positional alignment of the molar cusps, and the alignment described corresponds to Class III, marking a significant deviation from normal occlusion.