Fig. 2.

The distribution of development stages within the three groups for tooth 37 for one observer’s assessment. According to Demirjian et al. [15], the tooth development could be rated on a scale from the beginning of calcification of crown to apical root apex completely closed (see Table 1 for description of stages A–H). In all three groups, tooth 37 were classified to be in development stages D, E, or F. In stage D, the crown formation is completed down to the cemento-enamel junction. In stage E, the root length is still less than the crown height and in stage F, the root length is equal to or greater than the crown height. When comparison between groups were made, it was found that tooth 37 was significant in more undeveloped stages in both the extremely preterm group (EPT) (p < 0.000) and in the very preterm group (VPT) (p = 0.016) compared to the full-term group (FT)