Introduction: Aim of this study is an Evidence-based review on the existing literature about the treatment of unilateral crossbite via "quad helix", "transpalatal arch" and "rapid maxillary expansion". The relevant literature is analyzed and the evidence levels of the articles are determined.
Methods: Relevant articles were searched in five electronic databases by help of selected keywords. The results were divided into irrelevant, cumulatively relevant and actually relevant hits. All relevant literature was tabularly evaluated regarding to year of publication, chosen treatment equipment and evidence level.
Results: The Internet research yields 22144 total hits. 34 contributions turned out to be actually relevant hits. Most publications, namely 25, are concerned with the "quad helix". The classification into evidence levels yielded four publications with evidence level 1, three with evidence level 2, seven with evidence level 3 and 20 with the lowest evidence level 5.
Conclusions: The research reveals a great number of irrelevant and cumulatively relevant hits. The evaluation yields only four contributions with the highest evidence level, but none of these could be used for derivation of a treatment recommendation. Therefore there is demand for studies with high evidence, so that a clear choice can be made concerning the best therapy of unilateral crossbite.