What defines a class II occlusion?

A class II occlusion is characterized by the positioning of the upper and lower molars, specifically regarding the relationship of the first molars. In this classification, the mesiobuccal cusp of the maxillary first molar occludes between the mandibular first and second molars. This positioning signifies that the maxillary molars are further back than the mandibular molars when the jaws are closed, resulting in a class II relationship. This type of occlusion is often referred to as a "retrognathic" or "overbite" situation, where the upper jaw is positioned more forward relative to the lower jaw.

The other choices do not accurately describe class II occlusion. For example, if the maxillary molar is positioned ahead of the mandibular molar, as described in one option, it would represent a class I occlusion or a class III relationship, depending on the specifics of the positioning. Similarly, having the mandibular molar ahead of the maxillary molar indicates a class III occlusion, which is the opposite of a class II. The mention of the mesiobuccal cusp occluding in the interdental space is also not applicable to class II and suggests a different type of occlusal relationship entirely