American Board of Orthodontics (ABO) Practice Exam

Class II malocclusion, as described by Bishara, is characterized by a specific relationship between the first molars of the upper and lower jaws. A distal step occlusion, which indicates that the lower molar is positioned more than 1-7mm behind the upper molar, consistently leads to Class II malocclusion in patients. This positioning creates a scenario where the lower jaw is effectively positioned too far back relative to the upper jaw, resulting in an asymmetrical bite and the associated characteristics of Class II malocclusion.

The rationale for this strong correlation is rooted in the development of the dental arches and how the molars erupt and occlude. When the lower first molar is set back significantly (more than 1-7mm) compared to the upper molar, it sets a foundational anatomical relationship that predisposes the entire dental occlusion to a Class II classification.

Other types of molar relationships, like flush terminal plane occlusion or mesial step occlusion, do not inherently result in Class II malocclusion. A flush terminal plane may lead to a more neutral occlusal relationship, while mesial step occlusion is more likely to result in Class I, as it positions the lower molar ahead of the