American Board of Orthodontics (ABO) Practice Exam

The percentage of Class I and Class II occlusions resulting from a mesial step of 1mm being reported as 76.2% Class I and 22.8% Class II is based on studies that link the molar relationships observed in these occlusions to specific dental developmental patterns. A mesial step of 1mm indicates that the first molar of the mandible is positioned slightly more forward relative to the first molar of the maxilla. This relationship tends to favor the establishment of a Class I occlusion, which is characterized by the normal interdigitation of the molars and proper alignment of the dental arches.

In contrast, the remaining percentage reflecting Class II occlusion suggests that while the majority of cases result in a Class I relationship, there is still a significant number that can develop into Class II due to various other factors, including dental compensations, direction of growth, and individual skeletal variations.

The distribution of these percentages illustrates the tendency for a mesial step of this magnitude to generally produce Class I outcomes, underlining the importance of identifying initial molar relationships in orthodontic diagnostics and treatment planning.