Formation and development of maxillary first molars with delayed XXXX .

@entity1 @entity203 @entity74
Cases of congenitally missing and delayed @entity203 of the maxillary first molar are rare. However, in recent years, we have experienced cases of suspected delayed @entity203 of or congenitally missing first molars. The purpose of this study was to analyze the formation of delayed erupted maxillary first molars (M1) (>2 standard deviations), which play important roles in occlusion, and normal @entity203 of the maxillary first molars (U6). The frequency of M1 among @entity1 born between 1974 and 1994 in one institution with a clear total @entity1 number and personal oral histories was 1.55  % [80  % bilateral @entity203 in 8 of 806 male @entity1 (0.99  %) and 23 of 1195 female @entity1 (1.92  %)]. To evaluate the formation and @entity203 of M1 according to Moorrees's tooth formation stages, panoramic X-ray films were obtained every year for 73 @entity1 with M1 from 3 institutions (20 male and 53 female @entity1 , total 131 M1s) without systematic histories or @entity74 . The development/growth curve of M1 was fitted to both the logistic curve and U6 curve. The M1 development/growth curve was started behind with U6 curve; however, the straight part of the M1 curve exhibited steep inclination compared with the straight part of the U6 curve. The curve of the @entity203 pathway of M1 also exhibited a sigmoid S shape. These results indicate that the development and migration speed of M1 are faster than that of U6, excluding the delayed start point. These results may help orthodontists in treatment planning for @entity1 with M1.
