Maxillary expansion of unilateral cross-bite in preschool children.

The influence of a low force appliance on the maxilla in correction of unilateral cross-bite was studied clinically and radiographically in 29 preschool children following a standardized treatment schedule. Four weeks' expansion was followed by a 4-wk retention and a 12-wk postretention period. Inter- and intraobserver evaluations of the reliability of the measurements on radiographs were performed. In all children but one the cross-bites were corrected after 4 wk of expansion. The mean maxillary expansion was 3.3 mm in the second molar and 1.3 mm in the canine region, but decreased to 1.5 mm and 1.0 mm, respectively, at the end of the postretention period without relapse of the corrected malocclusion. No significant remaining orthopedic effects could be registered on radiographs by this low force appliance used. The modified quad helix appliance was found to be suitable for correction of unilateral cross-bite in the primary dentition and was well tolerated by the children.