Changes in perioral muscle pressures following rapid maxillary expansion

Objectives: To analyse the changes in perioral muscle pressures following rapid maxillary expansion (RME) treatment and retention. Methods: Eighteen patients with constricted maxillary arch were treated with RME. They were 9 boys and 9 girls aged 11.3 to 15.8. A new perioral muscle measuring system was invented to measure pressures acting on upper and lower first molars and first premolars buccally and lingually pretreatment, posttreatment and postretention. Results: Cheek pressures and tongue pressures after treatment in maxillary regions were higher than those before treatment and in mandibular regions were lower than those before treatment. After retention, cheek pressures were similar with those with normal posterior overjet. Tongue was located in the normal position so tongue pressures were stable. Conclusions: Changes in arch form could cause significant changes in perioral soft tissues. After retention, perioral soft tissues were adaptive to the changed arch form. Good retention measures after RME must be taken so that perioral soft tissues could have adaptive changes.