Long-Term Changes in the Dental Occlusion of Subjects Treated Orthodontically

A major challenge in orthodontics is to provide a treatment result that remains stable after appliances are removed. Orthodontic treatment can move teeth from their neutral positions, which increases potential for future relapse. The literature from the University of Washington, Seattle, shows that relapse is pervasive and of considerable magnitude (Little RM. Stability and relapse of mandibular anterior alignment: University of Washington studies. Semin Orthod 1999;5:191-204). The intent of this study was to quantify the posttreatment dental changes that occurred over approximately a quarter-century in a cohort of women who had received comprehensive orthodontic treatment as teenagers. Dental casts of 52 individuals were made at the start of treatment, at the end of the active phase of treatment, and at the long-term recall examination. Subjects were treated comprehensively by a single experienced orthodontist using Tweed edgewise mechanics. The amount of in-treatment change is one of the few identifiable predictors of the vectors of posttreatment relapse. Arch length and width decreased with age, accompanied by a 1.1 mm “relapse” in Incisor Irregularity during the posttreatment period. Arch depth decreased 1.3 mm during the posttreatment interval. Intercanine width was increased (2.2 mm) during treatment, but decreased (1.2 mm) towards the initial dimension after treatment. About half (1.0 mm) of the in-treatment intercanine expansion persisted at the recall examination. Intermolar width did not change significantly after treatment. Overjet increased and overbite deepened after treatment. Half (0.6 mm) of the treatment correction in overbite was lost during the posttreatment period. Buccal segment and canine relationship both remained stable after treatment. This suggests that, once established, cusp-fossa relationships tend to persist with time. Correction of the maxillary Incisor Irregularity remained stable with age (1% relapse). 65% of the correction in mandibular Incisor Irregularity was maintained over the long-term period. The mandibular Incisor Irregularity at the recall examination was less than 3.5 mm in 77% of the cases, which is the upper limit suggested as being clinically acceptable. The University of Washington studies reported that less than 30% of their cases exhibited clinically acceptable long-term mandibular Incisor Irregularity (Little RM, Wallen TR, Riedel RA. Stability and relapse of mandibular anterior alignment-first premolar extraction cases treated by traditional edgewise orthodontics. Am J Orthod 1981;80:349-65). The present results exhibit less relapse than those reported in most long-term recall studies, which suggests that the extent of relapse may be less in other venues