Introduction: Scientific studies with good methodological quality according to the Cochrane criteria suggest that the more efficient appliances in maxillary expansion are the fixed ones and that more randomized trials are needed with a control group to assess the relapse. Material and Methods: A randomized trial with a sample of 60 patients in mixed dentition and posterior crossbite in at least one permanent molar. The sample was reduced to 45 patients and was divided into three groups: 15 quad-helix (QH), 14 hyrax appliances (DY) and 16 controls (C). In the treated groups, T1 models (initial treatment) were taken, also in T2 six months later (after removing the device) and six months post-treatment (T3). In T1 and T3 frontal telerradiographies were also taken. The aim of the study was to assess the short-term changes produced in the maxilla comparing two types of expansion treatment. Results: The sample at T1 was homogeneous in the three groups on gender and age. All treated patients were able to resolve posterior crossbite with an average increase of intermolar expansion in the QH of 6.9 mm and 6.3 mm in the Hyrax group. In T3, the group treated with QH had more relapse than hyrax appliance, but there were no significant differences. Conclusions: (a) The effects in the arch form after maxillary expansion are significant in the transverse axis. (b) The QH allows further expansion and molar tipping but is less stable than the hyrax appliance at six months post-treatment. Both the QH and DY are equally effective at six months post-treatment, although the DY allows more predictable results. (c) Suffering of intermolar relapse in QH is 1/3 of the expansion achieved, while DY is 1/4. However, the intercanine relapse is 1/3 in both groups.
(Rev Esp Ortod. 2015;45(1):013-018)