Transversal anomalies are very common in clinical practice. In 80% of cases, their interceptive treatment is essential and must be administered as soon as possible to avoid periodontal, joint, or functional problems. It is based on an orthopedic technique aimed at separating the two maxillae above the level of the intermaxillary palatal suture. In 1860 2 , Angell who first described rapid maxillary expansion, which was very quickly discredited; however, since the 1960s it has been most widely used treatment in our arsenal. Conventionally, rapid maxillary expansion is performed in children who are still growing (no suture synostosis; at approximately 12 years), using a disjunctor (described by Biederman) supported by the teeth (two or four rings) and using a median activator twice a day, or 0.5 mm per day. Many studies, including meta-analyses, have

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