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這類是屬於MESIAL STEP型態

  1. 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%)
  2. 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)
  3.  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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