The objectives of our study were to analyze factors associated to the presence of crowding and to find predictive features of its relapse. A longitudinal retrospective study was carried out with plasters of patients in three moments: before starting the treatment, at the end of it and some years after removing appliances. Molar class, overjet, overbite, upper and lower intercanine and intermolar widths, upper and lower incisives and canines mesiodistal diameter, upper and lower crowding and irregularity, and upper and lower incisives rotations were measured. 26.5% of the sample were males and 73.5% females. Statistical analyses comprised mean, standard deviation, minimum, maximum, standard error, frequency, percentage, Wilcoxon signe-rank test, Pearson and Spearman correlation coefficients, and simple and multiple linear regression. Initial variables that wholly explain initial upper crowding are overjet, 1.2 tooth mesiodistal diameter, upper intercanine width and 2.2 tooth rotation. In the lower arch, 3.1 and 4.2 teeth mesiodistal diameter, lower intermolar width and 4.2 tooth rotation are initial variables that wholly explain initial lower crowding. Upper crowding relapse is related to upper intercanine width relapse, and lower crowding relapse is related to overbite and lower intercanine width relapse. Crowding and irregularity are not the same, although they are closely related.
(Rev Esp Ortod. 2012;42(1):005-016)