A retrospective study of Angle Class I malocclusions treated orthodontically without extractions using two palatal expansion methods

The correction and relapse of mandibular anterior crowding was evaluated in a population of 58 patients with Angle Class I malocclusion who were treat ed orthodontically without extraction of permanent teeth. The subjects were retrospectively evaluated from records taken before treatment, posttreatme nt, and postretention. The postretention period averaged 8 years (minimum o f 4 and maximum of 20 years). All cases in Groups A and B were given orthop edic treatment to develop the maxillary apical base in the transverse and a nteroposterior planes. Group A was treated with expansion of the inner bow of the face bow appliance (Kloehn), and Group B was treated with the Haas p alatal expansion appliance. Both groups were then treated orthodontically w ith tandem mechanics. The response variables measured were: overbite, overj et, intercanine distance, intermolar distance, and irregularity index. Stud y groups A and B were not significantly different for subject age, retentio n, or postretention time. Moreover, the groups did not show significant dif ference for any of the response variables before treatment. However, there was a statistically significant difference in the treatment times (P = .013 3). A statistically significant treatment effect was observed for most resp onse variables in the groups. Overbite, overjet, and irregularity index wer e significantly reduced, intermolar distance was significantly increased, a nd intercanine distance showed no significant change in Groups A and B. In the postretention period, there was a tendency for variables to change slig htly toward their before treatment values but no compromise of orthodontic correction was noted. The irregularity index in Group A was corrected from 4.8 to 1.1 mm and remained at 1.1 mm in the postretention period. The irreg ularity index in Group B was corrected from 5.1 to 1.2 mm (P = .0001) and c hanged slightly from 1.2 to 1.7 mm (P = .0540) in the postretention period. We concluded that mandibular incisors tended to become more crowded postre tention. However, in contrast to previous reports, we calculate this relaps e to be small. Neither before treatment nor posttreatment variables were pr edictive of relapse.