Longitudinal stability of rapid and slow maxillary expansion.

OBJECTIVE: The aim of this retrospective study was to compare the longitudinal stability of two types of posterior crossbite correction: rapid maxillary expansion (RME) and slow maxillary expansion (SME). METHODS: Study casts of 90 adolescent patients were assessed for interdental width changes at three different periods: pretreatment (T1), post-treatment (T2) and at least, five years post-retention (T3). Three groups of 30 patients were established according to the treatment received to correct posterior crossbite: Group A (RME), group B (SME) and group C (control- Edgewise therapy only). After crossbite correction, all patients received fixed edgewise orthodontic appliances. Paired t-tests and one-way ANOVA were used to identify significant intra and intergroup changes, respectively (P < 0.05). RESULTS: Except for intercanine distance, all widths increased in groups A and B from T(1) to T(2). In the long-term, the amount of relapse was not different for groups A and B, except for 3-3 widths which showed greater decrease in group A. However, the percentage of clinically relapsed cases of posterior crossbite was similar for rapid and slow maxillary expansion. CONCLUSION: Rapid and slow maxillary expansion showed similar stability in the long-term.