Maxillary Anterior Crowding and Dentition Morphology During Growth: A Longitudinal Study of Japanese Elementary School Children

The morphological causes of crowding remain unclear. This study investigated the movement of the maxillary first molars as a possible morphological factor of crowding during child growth. Individual longitudinal data were gathered from 66 participating children(34 boys, 32 girls, grouped by dental age)every other year from 2012 to 2019. We measured the dental arch length and width, palatal depth, and aspect of first molar movement at T1(permanent incisors, first molar eruption completed, bilateral deciduous canines remaining)and T2(permanent dentition after complete canine eruption). In both the crowding and normal dentition groups, the width of the dental arch and the buccolingual inclination angle of the maxillary first molar(BLI)incremented significantly from T1 to T2. The maxillary first molar showed a greater mesial rotation in the crowding group, but a greater distal rotation in the normal dentition group. The width of the dental arch was greater in the normal group than in the crowding group at both T1 and T2, and the rotation angle(RA)was also greater in the normal group at T1. Spearman’s rank correlation analysis showed that incremented intercanine width(3AW) and BLI during child growth were positively correlated with crowding, while RA was negatively correlated. Multiple regression analysis indicated that changes in the AL, 3AW, BLI, and RA may reduce anterior crowding. Increments in dental arch width, buccal inclination, and distal rotation of the maxillary first molars may reduce anterior crowding at completion of the permanent dentition.