Which distal surface relationship of the second primary molars leads to a permanent first molar Class II relationship by Angle?

Which distal surface relationship of the second primary molars leads to a permanent first molar Class II relationship by Angle?

• A. In flush terminal plane
• B. Distal step
• C. Mesial step up to 2 mm
• D. Mesial step more than 2 mm

Answer: (B)

The position of the distal surfaces of the second primary molars is used to predict how the permanent first molars will bite together. When there is a distal step, the lower second primary molar sits farther back than the upper, and that posterior relationship tends to be carried forward as the permanent first molars erupt. As a result, the upper first molar ends up ahead of the lower, producing a Class II relationship by Angle. Other patterns are less predictive of Class II: a flush terminal plane can still become Class I with favorable jaw growth, and a mesial step can lead to Class I or III depending on the amount of mesial shift, not Class II.

The position of the distal surfaces of the second primary molars is used to predict how the permanent first molars will bite together. When there is a distal step, the lower second primary molar sits farther back than the upper, and that posterior relationship tends to be carried forward as the permanent first molars erupt. As a result, the upper first molar ends up ahead of the lower, producing a Class II relationship by Angle.

Other patterns are less predictive of Class II: a flush terminal plane can still become Class I with favorable jaw growth, and a mesial step can lead to Class I or III depending on the amount of mesial shift, not Class II.