Early versus late treatment of crowded first premolar extraction cases: postretention evaluation of stability and relapse.

The purpose of this study was to evaluate the differences in the long-term stability of orthodontically induced changes in arch form between patients who receive early orthodontic treatment (Hellman's dental age III B, mixed dentition, n = 36) and those who are treated later (Hellman's dental age III C or after, permanent dentition, n = 47). Dental casts were evaluated before treatment, after treatment, and at a minimum of 10 years after retention. All patients had received routine edgewise orthodontic treatment that included maxillary and mandibular first premolar extraction. There were no significant differences between these groups at pretreatment and posttreatment. In the majority of cases, some degree of mandibular crowding occurred during the postretention period. There was a significant difference in the mandibular irregularity index at postretention between these groups. Regarding the deviation of the midline of the central incisors, there were no significant differences between these groups at pretreatment and posttreatment, but there was a significant difference at postretention. At the postretention stage, the late treatment group had greater mandibular anterior irregularity and deviation of the midline.