牙醫學(六)（包括齒顎矯正學、兒童牙科學、牙科公共衛生學等科目及其相關臨床實例與醫學倫理）題庫下載題庫

Early mesial shift: Early mesial shift:In patients with a spaced primary dentition and a straight terminal plane relationship of the primary molars, the permanent mandibular first molars emerge at about 6 years, move the primary molars mesially, close the space distal to the primary canines, convert the straight terminal plane to a mesial step relationship, reduce arch length in the mandibular dentition, and allow the permanent maxillary molars to emerge into a Class I relationship. 故 early mesial shift 時間為在六歲恆齒第一大臼齒萌發後,(C)錯
Late mesial shift: In patients with a closed primar ...

Early mesial shift: Early mesial shift:In patients with a spaced primary dentition and a straight terminal plane relationship of the primary molars, the permanent mandibular first molars emerge at about 6 years, move the primary molars mesially, close the space distal to the primary canines, convert the straight terminal plane to a mesial step relationship, reduce arch length in the mandibular dentition, and allow the permanent maxillary molars to emerge into a Class I relationship. 故 early mesial shift 時間為在六歲恆齒第一大臼齒萌發後,(C)錯
Late mesial shift: In patients with a closed primar Late mesial shift: y dentition and a straight terminal plane, the permanent maxillary and mandibular first molars emerge into a cusp-to-cusp relationship simply because no spaces exist. At about 11 years, the primary mandibular second molars are exfoliated,and the permanent mandibular first molars migrate mesially into the excess leeway space provided by the differences in mesiodistal dimensions of the primary second molars and the permanent second premolar teeth. This reduces arch length, converts the straight terminal plane to a mesial step, and provides for a ClassI relationship of the permanent first molars.