Chronology of Deciduous and Permanent Dentition in Japanese Children II

<p>We performed a cross-sectional nationwide investigation of permanent tooth eruption timing and sequence in 30,825 children in Japan between the ages of 4 years and 18 years 11 months in order to assess changes in permanent tooth emergence. The following results were obtained :</p><p></p><p>1.Tooth emergence in boys occurred as follows. Tooth 1 emergence occurred between the ages of 5 Y 6 M and 7 Y 0 M, 6 between 5 Y 10 M and 7 Y 6 M, 1 between 6 Y 6 M and 7 Y 10 M, 2 between 6 Y 3 M and 8 Y 3 M, 6 between 5 Y 11 M and 8 Y 7 M, 2 between 7 Y 6 M and 9 Y 2 M, 3 between 9 Y 2 M and 11 Y 3 M, 4 between 9 Y 1 M and 11 Y 7 M, 4 between 9 Y 5 M and 11 Y 6 M, 3 between 9 Y 10 M and 12 Y 1 M, 5 between 10 Y 4 M and 13 Y 0 M, 5 between 10 Y 3 M and 13 Y 2 M, 7 between 11 Y 3 M and 13 Y 10 M,and 7 between 12 Y 1 M and 14 Y 5 M.</p><p></p><p>2.Tooth emergence in girls occurred as follows. Tooth 1 emergence occurred between the ages of 5 Y 5 M and 6 Y 7 M, 6 between 5 Y 6 M and 7 Y 0 M, 1 between 6 Y 3 M and 7 Y 7 M, 2 between 6 Y 3 M and 7 Y 8 M, 6 between 5 Y 10 M and 8 Y 4 M, 2 between 7 Y 2 M and 8 Y 8 M, 3 between 8 Y 8 M and 10 Y 5 M, 4 between 8 Y 11Mand11Y0M,4between9Y1M and11Y1M,3between9Y2M and11Y4M,5between 10 Y 1 M and 12 Y 11 M, 5 between 10 Y 2 M and 13 Y 1 M, 7 between 11 Y 2 M and 13 Y 10 M, and 7 between 11 Y 9 M and 14 Y 3 M.</p><p></p><p>3.The sequence of tooth eruption was not significantly different between boys and girls. The general eruption sequence was 6≒1 →2 →4 →3 →5 →7 for the maxilla and 1 →6 →2 →3 →4 →5 →7 for the mandible.</p><p></p><p>4.For boys, the eruption patterns of the first molar and central incisor were 77.2% for M type and 22.8% for I type in the maxilla, and 29.2% for M type and 70.8% for I type in the mandible. Those in girls were 73.4 % for M type and 26.6% for I type in the maxilla, and 36.7% for M type and 63.3% for I type in the mandible.</p><p></p><p>5.A comparison between boys and girls showed a significant difference regarding the eruption timing of 1, 1, 2, 2, 3, 3, 4, 4, and 6, as those erupted earlier in girls.</p><p></p><p>6.As compared to a previous report presented in Japan in 1988, eruption timing was significantly later for 4, 4, 5, 5, 6, and 6 in boys, and for 3, 4, 4, 5, 5, 6, and 7 in girls.</p>