THE SEQUENCE OF CALCIFICATION OF THE MANDIBULAR MOLAR AND PREMOLAR TEETH

¹ Fels Research Institute, Antioch College, Yellow Springs, Ohio

1. The sequence of calcification of the mandibular molar and premolar teeth was investigated in serial oblique-jaw x-rays of 359 native-born white children from southwestern Ohio.

2. M₁ P₁ and M₃ invariably showed initial calcification first, second, and last, respectively. P₂ and M₂ calcification varied in the order of appearance, and in many cases these teeth began to calcify at the same time.

3. In the girls the tendency for P₂ to precede M₂ was more marked. The boys, however, tended to the (P₂ M₂) sequence, thus exhibiting "bunching" in tooth calcification as they are known to do in tooth emergence.

4. Among 191 boys and girls, the M₁ P₁ P₂ M₂ M₃ sequence was observed in 40.3 per cent, the M₁ P₁ (P₂ M₂) M₃ sequence in 37.7 per cent, and the M₁ P₁ M₂ P₂ M₃ sequence in 21.9 per cent.

5. Siblings of P₂ M₂ children tended to the P₂ M₂ sequence and siblings of M₂ P₂ children to the M₂ P₂ sequence more often than would be expected on a chance basis.

6. It was suggested that there has been a gradual evolutionary change from the M₂ P₂ sequence in the direction of the P₂ M₂ sequence, with a different rate of evolution in different hominid groups.