Study of delayed development of the upper first molars.

The present study was undertaken to analyze the status of formation of the upper first molar in individuals suspected as having delayed eruption of the upper first molar. The subjects of this study were 51 patients presenting to orthodontic specialists with delayed eruption of the upper first molars. The 95 teeth of these 51 patients were observed. The investigation of the tooth development status included evaluation of the tooth development stage on panoramic radiographs according to the method of Moorrees et al. The upper first molars that showed delayed development were at the stage of initial cleft formation, reflecting a delay by 2.09 years in boys and 2.84 years in girls. In most cases, the delayed eruption was bilateral, and the development stage of the subject teeth did not differ between right and left sides. The plot of the developmental stage of the subject teeth (Y-axis) against the calendar age of the subjects (X-axis) showing delayed upper first molar development was fitted to the logistic curve. The tooth development was at the stage of initial cleft formation was delayed 2.5 years or more, according to these curves.