Functional changes after early treatment of unilateral posterior cross-bite associated with mandibular shift: a systematic review.

The objective of this systematic review was to investigate whether oral functional asymmetry in children treated for unilateral functional posterior cross-bite disappears after orthodontic treatment with a resulting normalisation of oral functions. A literature search was carried out using PubMed, Web of Science and the Cochrane Library to locate longitudinal studies reporting on clinical oral functional changes, recorded by methods including masseter muscle thickness, bite force, masticatory/chewing cycle or electromyographic masticatory muscle activity, following the treatment of unilateral functional posterior cross-bite. All potential articles were initially screened according to their title and abstract, the full text of selected articles was evaluated, and the final study selection was made based on the pre-defined criteria. Data extraction was subsequently carried out. The initial literature search identified 736 articles, with 12 articles fulfilling pre-defined criteria. Although there was a lack of high-quality prospective studies, based on the available evidence, results suggest that the abnormal masticatory cycle associated with functional posterior unilateral cross-bite tends to normalise following early cross-bite treatment. Masticatory muscle activity shows an increase after early functional unilateral posterior cross-bite treatment, and this activity approaches normal levels. Insufficient evidence was available to conclude on maximal molar bite force or masticatory muscle thickness changes following early treatment of functional unilateral posterior cross-bite. Results should be interpreted with caution due to the lack of high-quality controlled studies. Well-designed prospective studies with large patient samples and long-term follow-up are necessary before making reliable conclusions concerning change in functional asymmetry following unilateral functional posterior cross-bite correction.