- Flush terminal plane(垂直型): The distal surfaces of maxillary and mandibular primary second molars lie in the same vertical plane. (上下的E/E的遠心面呈一直線,佔60~70%)
- Distal step(遠心階梯型): The distal surface of the mandibular primary second molar is distal to that of the maxillary primary second molar.(下顎的乳E的遠心面在上顎乳E的遠心位置,這類將來恆牙第一大臼齒較易形成遠心關係)
- Mesial step(近心階梯型): The distal surface of the mandibular primary second molar is mesial to that of the maxillary primary second molar. (下顎的乳E的遠心面在上顎的E的近心位置,這類的情形有形成CL III 戽斗的錯咬傾向,輕度一點的可能形成一類錯咬關係)
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