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

Which distal surface relationship of the second primary molars leads to a permanent first molar Class III 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: (D)

In primary dentition, how the distal surfaces of the second primary molars relate tells you what the first permanent molars will do by Angle’s classification. A mesial step means the lower second primary molar sits ahead of the upper one, so as the permanent first molars erupt, the mandible tends to be forward relative to the maxilla. When that forward shift is greater than about 2 mm, it strongly predisposes a permanent first molar relationship of Class III, where the mandibular molar is ahead of the maxillary molar. So, among the possible patterns, a mesial step more than 2 mm best explains a Class III outcome. The other patterns are less likely to yield Class III: a flush terminal plane is a neutral alignment that can become Class I with growth, a distal step tends toward Class II, and a small mesial step up to 2 mm often remains Class I rather than Class III.

In primary dentition, how the distal surfaces of the second primary molars relate tells you what the first permanent molars will do by Angle’s classification. A mesial step means the lower second primary molar sits ahead of the upper one, so as the permanent first molars erupt, the mandible tends to be forward relative to the maxilla. When that forward shift is greater than about 2 mm, it strongly predisposes a permanent first molar relationship of Class III, where the mandibular molar is ahead of the maxillary molar.

So, among the possible patterns, a mesial step more than 2 mm best explains a Class III outcome. The other patterns are less likely to yield Class III: a flush terminal plane is a neutral alignment that can become Class I with growth, a distal step tends toward Class II, and a small mesial step up to 2 mm often remains Class I rather than Class III.