OBJECTIVES: The aim of this study is to analyze the electromyographic and electrognatographic exams of 55 patients before and after rapid palatal expansion, and to find out a relationship between the results. MATERIALS AND METHODS: The sample consisted of 55 children (28 females and 27 males; age ranging between 6 and10 years) with unilateral posterior crossbite, and subjected to an electromyographic and electrognatographic examination before and after a rapid palatal expansion. RESULTS: By analyzing the results, it is possible to observe an increased electrical activity of the masticatory muscles (right and left masseters and anterior temporalis) both in rest position and during activities after rapid palatal expansion. CONCLUSIONS: Rapid palatal expansion produces important changes in the muscular tone and it increases the muscular activity of the masticatory muscles
