Three-dimensional evaluation of dentoskeletal changes after posterior cross-bite correction by quad-helix or removable appliances.

The aim of the study was to evaluate in a three-dimensional manner the dentoskeletal changes after slow maxillary expansion. The sample consisted of 34 children with a unilateral, symmetrical posterior cross-bite. Half of the children were treated with a quad-helix and the rest with a removable appliance. Assessment of the changes was made with study casts, and frontal and lateral cephalograms, before treatment, at the end of the expansion, after a retention period of 3 months, and after a post-retention period of 3 months. The results showed that sufficient expansion of the dental arches took place in both groups. The expansion expressed in the molar region in the quad-helix group was mostly due to buccal translation of the teeth and in the removable appliance group due to buccal tipping. The quad-helix group showed somewhat greater basal expansion than the removable appliance group, though the basal expansion in both groups was rather small. A tendency towards an increase of the NL/ML angle characterized the removable appliance group, but the opposite pattern was present in the quad-helix group.