Abstract
This study examined changes in angulation and anterior-posterior position of the first molar in crowding dentition. The subjects were divided into four groups depending on their dentition scores at Hellman's dental stage IV A: 1) normal males (n=5),2) males with crowding (n=5),3) normal females (n=5) and 4) females with crowding (n=5). Tooth position was determined by lateral cephalometric X rays taken longitudinally from III A to IV A, and the following results were obtained;
(1) ANS-PNS and Me-Go for both males and females with crowding were smaller than that for normal males and females at all of the dental stages.
(2) The forward displacement of the upper first molar from III A to NA for both males and females with crowding was significantly greater than that for normal males and females.
(3)∠U 6-Pal. Pl. at III A for both males and females with crowding was smaller than that for normal males and females. The increase in ∠U 6-Pal. Pl, from III A to IV A for both males and females with crowding was larger than that for normal males and females.
(4) The forward displacement of the lower first molar from III A to IV A for both males and females with crowding was not significantly different from that for normal males and females. One characteristic of developmental change of the first molar in crowding dentition is that the upper first molar erupts with distal tipping, and subsequently migrates mesially with mesial rotation.
